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* Elisp: (elisp). The Emacs Lisp Reference Manual.
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This Info file contains edition 2.8 of the GNU Emacs Lisp Reference
Manual, corresponding to Emacs version 21.2.
Published by the Free Software Foundation 59 Temple Place, Suite 330
Boston, MA 02111-1307 USA
Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999,
2000, 2001, 2002 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Copying", with the Front-Cover texts being "A
GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of
the license is included in the section entitled "GNU Free Documentation
License".
(a) The FSF's Back-Cover Text is: "You have freedom to copy and
modify this GNU Manual, like GNU software. Copies published by the Free
Software Foundation raise funds for GNU development."
This Info file contains edition 2.8 of the GNU Emacs Lisp Reference
Manual, corresponding to GNU Emacs version 21.2.
Introduction
************
Most of the GNU Emacs text editor is written in the programming
language called Emacs Lisp. You can write new code in Emacs Lisp and
install it as an extension to the editor. However, Emacs Lisp is more
than a mere "extension language"; it is a full computer programming
language in its own right. You can use it as you would any other
programming language.
Because Emacs Lisp is designed for use in an editor, it has special
features for scanning and parsing text as well as features for handling
files, buffers, displays, subprocesses, and so on. Emacs Lisp is
closely integrated with the editing facilities; thus, editing commands
are functions that can also conveniently be called from Lisp programs,
and parameters for customization are ordinary Lisp variables.
This manual attempts to be a full description of Emacs Lisp. For a
beginner's introduction to Emacs Lisp, see `An Introduction to Emacs
Lisp Programming', by Bob Chassell, also published by the Free Software
Foundation. This manual presumes considerable familiarity with the use
of Emacs for editing; see `The GNU Emacs Manual' for this basic
information.
Generally speaking, the earlier chapters describe features of Emacs
Lisp that have counterparts in many programming languages, and later
chapters describe features that are peculiar to Emacs Lisp or relate
specifically to editing.
This is edition 2.8.
Caveats
=======
This manual has gone through numerous drafts. It is nearly complete
but not flawless. There are a few topics that are not covered, either
because we consider them secondary (such as most of the individual
modes) or because they are yet to be written. Because we are not able
to deal with them completely, we have left out several parts
intentionally. This includes most information about usage on VMS.
The manual should be fully correct in what it does cover, and it is
therefore open to criticism on anything it says--from specific examples
and descriptive text, to the ordering of chapters and sections. If
something is confusing, or you find that you have to look at the sources
or experiment to learn something not covered in the manual, then perhaps
the manual should be fixed. Please let us know.
As you use this manual, we ask that you send corrections as soon as
you find them. If you think of a simple, real life example for a
function or group of functions, please make an effort to write it up
and send it in. Please reference any comments to the node name and
function or variable name, as appropriate. Also state the number of
the edition you are criticizing.
Please mail comments and corrections to
bug-lisp-manual@gnu.org
We let mail to this list accumulate unread until someone decides to
apply the corrections. Months, and sometimes years, go by between
updates. So please attach no significance to the lack of a reply--your
mail _will_ be acted on in due time. If you want to contact the Emacs
maintainers more quickly, send mail to `bug-gnu-emacs@gnu.org'.
Lisp History
============
Lisp (LISt Processing language) was first developed in the late 1950s
at the Massachusetts Institute of Technology for research in artificial
intelligence. The great power of the Lisp language makes it ideal for
other purposes as well, such as writing editing commands.
Dozens of Lisp implementations have been built over the years, each
with its own idiosyncrasies. Many of them were inspired by Maclisp,
which was written in the 1960s at MIT's Project MAC. Eventually the
implementors of the descendants of Maclisp came together and developed a
standard for Lisp systems, called Common Lisp. In the meantime, Gerry
Sussman and Guy Steele at MIT developed a simplified but very powerful
dialect of Lisp, called Scheme.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common
Lisp. If you know Common Lisp, you will notice many similarities.
However, many features of Common Lisp have been omitted or simplified
in order to reduce the memory requirements of GNU Emacs. Sometimes the
simplifications are so drastic that a Common Lisp user might be very
confused. We will occasionally point out how GNU Emacs Lisp differs
from Common Lisp. If you don't know Common Lisp, don't worry about it;
this manual is self-contained.
A certain amount of Common Lisp emulation is available via the `cl'
library. *Note Common Lisp Extension: (cl)Top.
Emacs Lisp is not at all influenced by Scheme; but the GNU project
has an implementation of Scheme, called Guile. We use Guile in all new
GNU software that calls for extensibility.
Conventions
===========
This section explains the notational conventions that are used in
this manual. You may want to skip this section and refer back to it
later.
Some Terms
----------
Throughout this manual, the phrases "the Lisp reader" and "the Lisp
printer" refer to those routines in Lisp that convert textual
representations of Lisp objects into actual Lisp objects, and vice
versa. *Note Printed Representation::, for more details. You, the
person reading this manual, are thought of as "the programmer" and are
addressed as "you". "The user" is the person who uses Lisp programs,
including those you write.
Examples of Lisp code are formatted like this: `(list 1 2 3)'.
Names that represent metasyntactic variables, or arguments to a function
being described, are formatted like this: FIRST-NUMBER.
`nil' and `t'
-------------
In Lisp, the symbol `nil' has three separate meanings: it is a
symbol with the name `nil'; it is the logical truth value FALSE; and it
is the empty list--the list of zero elements. When used as a variable,
`nil' always has the value `nil'.
As far as the Lisp reader is concerned, `()' and `nil' are
identical: they stand for the same object, the symbol `nil'. The
different ways of writing the symbol are intended entirely for human
readers. After the Lisp reader has read either `()' or `nil', there is
no way to determine which representation was actually written by the
programmer.
In this manual, we use `()' when we wish to emphasize that it means
the empty list, and we use `nil' when we wish to emphasize that it
means the truth value FALSE. That is a good convention to use in Lisp
programs also.
(cons 'foo ()) ; Emphasize the empty list
(not nil) ; Emphasize the truth value FALSE
In contexts where a truth value is expected, any non-`nil' value is
considered to be TRUE. However, `t' is the preferred way to represent
the truth value TRUE. When you need to choose a value which represents
TRUE, and there is no other basis for choosing, use `t'. The symbol
`t' always has the value `t'.
In Emacs Lisp, `nil' and `t' are special symbols that always
evaluate to themselves. This is so that you do not need to quote them
to use them as constants in a program. An attempt to change their
values results in a `setting-constant' error. The same is true of any
symbol whose name starts with a colon (`:'). *Note Constant
Variables::.
Evaluation Notation
-------------------
A Lisp expression that you can evaluate is called a "form".
Evaluating a form always produces a result, which is a Lisp object. In
the examples in this manual, this is indicated with `=>':
(car '(1 2))
=> 1
You can read this as "`(car '(1 2))' evaluates to 1".
When a form is a macro call, it expands into a new form for Lisp to
evaluate. We show the result of the expansion with `==>'. We may or
may not show the result of the evaluation of the expanded form.
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
=> c
Sometimes to help describe one form we show another form that
produces identical results. The exact equivalence of two forms is
indicated with `=='.
(make-sparse-keymap) == (list 'keymap)
Printing Notation
-----------------
Many of the examples in this manual print text when they are
evaluated. If you execute example code in a Lisp Interaction buffer
(such as the buffer `*scratch*'), the printed text is inserted into the
buffer. If you execute the example by other means (such as by
evaluating the function `eval-region'), the printed text is displayed
in the echo area.
Examples in this manual indicate printed text with `-|',
irrespective of where that text goes. The value returned by evaluating
the form (here `bar') follows on a separate line.
(progn (print 'foo) (print 'bar))
-| foo
-| bar
=> bar
Error Messages
--------------
Some examples signal errors. This normally displays an error message
in the echo area. We show the error message on a line starting with
`error-->'. Note that `error-->' itself does not appear in the echo
area.
(+ 23 'x)
error--> Wrong type argument: number-or-marker-p, x
Buffer Text Notation
--------------------
Some examples describe modifications to the contents of a buffer, by
showing the "before" and "after" versions of the text. These examples
show the contents of the buffer in question between two lines of dashes
containing the buffer name. In addition, `-!-' indicates the location
of point. (The symbol for point, of course, is not part of the text in
the buffer; it indicates the place _between_ two characters where point
is currently located.)
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
=> nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
Format of Descriptions
----------------------
Functions, variables, macros, commands, user options, and special
forms are described in this manual in a uniform format. The first line
of a description contains the name of the item followed by its
arguments, if any. The category--function, variable, or
whatever--appears at the beginning of the line. The description
follows on succeeding lines, sometimes with examples.
A Sample Function Description
.............................
In a function description, the name of the function being described
appears first. It is followed on the same line by a list of argument
names. These names are also used in the body of the description, to
stand for the values of the arguments.
The appearance of the keyword `&optional' in the argument list
indicates that the subsequent arguments may be omitted (omitted
arguments default to `nil'). Do not write `&optional' when you call
the function.
The keyword `&rest' (which must be followed by a single argument
name) indicates that any number of arguments can follow. The single
following argument name will have a value, as a variable, which is a
list of all these remaining arguments. Do not write `&rest' when you
call the function.
Here is a description of an imaginary function `foo':
- Function: foo integer1 &optional integer2 &rest integers
The function `foo' subtracts INTEGER1 from INTEGER2, then adds all
the rest of the arguments to the result. If INTEGER2 is not
supplied, then the number 19 is used by default.
(foo 1 5 3 9)
=> 16
(foo 5)
=> 14
More generally,
(foo W X Y...)
==
(+ (- X W) Y...)
Any argument whose name contains the name of a type (e.g., INTEGER,
INTEGER1 or BUFFER) is expected to be of that type. A plural of a type
(such as BUFFERS) often means a list of objects of that type.
Arguments named OBJECT may be of any type. (*Note Lisp Data Types::,
for a list of Emacs object types.) Arguments with other sorts of names
(e.g., NEW-FILE) are discussed specifically in the description of the
function. In some sections, features common to the arguments of
several functions are described at the beginning.
*Note Lambda Expressions::, for a more complete description of
optional and rest arguments.
Command, macro, and special form descriptions have the same format,
but the word `Function' is replaced by `Command', `Macro', or `Special
Form', respectively. Commands are simply functions that may be called
interactively; macros process their arguments differently from functions
(the arguments are not evaluated), but are presented the same way.
Special form descriptions use a more complex notation to specify
optional and repeated arguments because they can break the argument
list down into separate arguments in more complicated ways.
`[OPTIONAL-ARG]' means that OPTIONAL-ARG is optional and
`REPEATED-ARGS...' stands for zero or more arguments. Parentheses are
used when several arguments are grouped into additional levels of list
structure. Here is an example:
- Special Form: count-loop (VAR [FROM TO [INC]]) BODY...
This imaginary special form implements a loop that executes the
BODY forms and then increments the variable VAR on each iteration.
On the first iteration, the variable has the value FROM; on
subsequent iterations, it is incremented by one (or by INC if that
is given). The loop exits before executing BODY if VAR equals TO.
Here is an example:
(count-loop (i 0 10)
(prin1 i) (princ " ")
(prin1 (aref vector i))
(terpri))
If FROM and TO are omitted, VAR is bound to `nil' before the loop
begins, and the loop exits if VAR is non-`nil' at the beginning of
an iteration. Here is an example:
(count-loop (done)
(if (pending)
(fixit)
(setq done t)))
In this special form, the arguments FROM and TO are optional, but
must both be present or both absent. If they are present, INC may
optionally be specified as well. These arguments are grouped with
the argument VAR into a list, to distinguish them from BODY, which
includes all remaining elements of the form.
A Sample Variable Description
.............................
A "variable" is a name that can hold a value. Although any variable
can be set by the user, certain variables that exist specifically so
that users can change them are called "user options". Ordinary
variables and user options are described using a format like that for
functions except that there are no arguments.
Here is a description of the imaginary `electric-future-map'
variable.
- Variable: electric-future-map
The value of this variable is a full keymap used by Electric
Command Future mode. The functions in this map allow you to edit
commands you have not yet thought about executing.
User option descriptions have the same format, but `Variable' is
replaced by `User Option'.
Version Information
===================
These facilities provide information about which version of Emacs is
in use.
- Command: emacs-version
This function returns a string describing the version of Emacs
that is running. It is useful to include this string in bug
reports.
(emacs-version)
=> "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit)
of Sat Feb 14 1998 on psilocin.gnu.org"
Called interactively, the function prints the same information in
the echo area.
- Variable: emacs-build-time
The value of this variable indicates the time at which Emacs was
built at the local site. It is a list of three integers, like the
value of `current-time' (*note Time of Day::).
emacs-build-time
=> (13623 62065 344633)
- Variable: emacs-version
The value of this variable is the version of Emacs being run. It
is a string such as `"20.3.1"'. The last number in this string is
not really part of the Emacs release version number; it is
incremented each time you build Emacs in any given directory. A
value with four numeric components, such as `"20.3.9.1"',
indicates an unreleased test version.
The following two variables have existed since Emacs version 19.23:
- Variable: emacs-major-version
The major version number of Emacs, as an integer. For Emacs
version 20.3, the value is 20.
- Variable: emacs-minor-version
The minor version number of Emacs, as an integer. For Emacs
version 20.3, the value is 3.
Acknowledgements
================
This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte,
Richard M. Stallman and Chris Welty, the volunteers of the GNU manual
group, in an effort extending over several years. Robert J. Chassell
helped to review and edit the manual, with the support of the Defense
Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren
A. Hunt, Jr. of Computational Logic, Inc.
Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom,
Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R.
Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher,
David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob
Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida,
Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens,
Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip
Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti,
Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starba"ck,
Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard
Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty
Wright, and David D. Zuhn.
Lisp Data Types
***************
A Lisp "object" is a piece of data used and manipulated by Lisp
programs. For our purposes, a "type" or "data type" is a set of
possible objects.
Every object belongs to at least one type. Objects of the same type
have similar structures and may usually be used in the same contexts.
Types can overlap, and objects can belong to two or more types.
Consequently, we can ask whether an object belongs to a particular type,
but not for "the" type of an object.
A few fundamental object types are built into Emacs. These, from
which all other types are constructed, are called "primitive types".
Each object belongs to one and only one primitive type. These types
include "integer", "float", "cons", "symbol", "string", "vector",
"hash-table", "subr", and "byte-code function", plus several special
types, such as "buffer", that are related to editing. (*Note Editing
Types::.)
Each primitive type has a corresponding Lisp function that checks
whether an object is a member of that type.
Note that Lisp is unlike many other languages in that Lisp objects
are "self-typing": the primitive type of the object is implicit in the
object itself. For example, if an object is a vector, nothing can treat
it as a number; Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each
variable, and the type is known by the compiler but not represented in
the data. Such type declarations do not exist in Emacs Lisp. A Lisp
variable can have any type of value, and it remembers whatever value
you store in it, type and all.
This chapter describes the purpose, printed representation, and read
syntax of each of the standard types in GNU Emacs Lisp. Details on how
to use these types can be found in later chapters.
Printed Representation and Read Syntax
======================================
The "printed representation" of an object is the format of the
output generated by the Lisp printer (the function `prin1') for that
object. The "read syntax" of an object is the format of the input
accepted by the Lisp reader (the function `read') for that object.
*Note Read and Print::.
Most objects have more than one possible read syntax. Some types of
object have no read syntax, since it may not make sense to enter objects
of these types directly in a Lisp program. Except for these cases, the
printed representation of an object is also a read syntax for it.
In other languages, an expression is text; it has no other form. In
Lisp, an expression is primarily a Lisp object and only secondarily the
text that is the object's read syntax. Often there is no need to
emphasize this distinction, but you must keep it in the back of your
mind, or you will occasionally be very confused.
Every type has a printed representation. Some types have no read
syntax--for example, the buffer type has none. Objects of these types
are printed in "hash notation": the characters `#<' followed by a
descriptive string (typically the type name followed by the name of the
object), and closed with a matching `>'. Hash notation cannot be read
at all, so the Lisp reader signals the error `invalid-read-syntax'
whenever it encounters `#<'.
(current-buffer)
=> #<buffer objects.texi>
When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (*note Evaluation::). However,
evaluation and reading are separate activities. Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later. *Note Input Functions::, for a description of
`read', the basic function for reading objects.
Comments
========
A "comment" is text that is written in a program only for the sake
of humans that read the program, and that has no effect on the meaning
of the program. In Lisp, a semicolon (`;') starts a comment if it is
not within a string or character constant. The comment continues to
the end of line. The Lisp reader discards comments; they do not become
part of the Lisp objects which represent the program within the Lisp
system.
The `#@COUNT' construct, which skips the next COUNT characters, is
useful for program-generated comments containing binary data. The
Emacs Lisp byte compiler uses this in its output files (*note Byte
Compilation::). It isn't meant for source files, however.
*Note Comment Tips::, for conventions for formatting comments.
Programming Types
=================
There are two general categories of types in Emacs Lisp: those having
to do with Lisp programming, and those having to do with editing. The
former exist in many Lisp implementations, in one form or another. The
latter are unique to Emacs Lisp.
Integer Type
------------
The range of values for integers in Emacs Lisp is -134217728 to
134217727 (28 bits; i.e., -2**27 to 2**27 - 1) on most machines. (Some
machines may provide a wider range.) It is important to note that the
Emacs Lisp arithmetic functions do not check for overflow. Thus `(1+
134217727)' is -134217728 on most machines.
The read syntax for integers is a sequence of (base ten) digits with
an optional sign at the beginning and an optional period at the end.
The printed representation produced by the Lisp interpreter never has a
leading `+' or a final `.'.
-1 ; The integer -1.
1 ; The integer 1.
1. ; Also the integer 1.
+1 ; Also the integer 1.
268435457 ; Also the integer 1 on a 28-bit implementation.
*Note Numbers::, for more information.
Floating Point Type
-------------------
Floating point numbers are the computer equivalent of scientific
notation. The precise number of significant figures and the range of
possible exponents is machine-specific; Emacs always uses the C data
type `double' to store the value.
The printed representation for floating point numbers requires either
a decimal point (with at least one digit following), an exponent, or
both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4'
are five ways of writing a floating point number whose value is 1500.
They are all equivalent.
*Note Numbers::, for more information.
Character Type
--------------
A "character" in Emacs Lisp is nothing more than an integer. In
other words, characters are represented by their character codes. For
example, the character `A' is represented as the integer 65.
Individual characters are not often used in programs. It is far more
common to work with _strings_, which are sequences composed of
characters. *Note String Type::.
Characters in strings, buffers, and files are currently limited to
the range of 0 to 524287--nineteen bits. But not all values in that
range are valid character codes. Codes 0 through 127 are ASCII codes;
the rest are non-ASCII (*note Non-ASCII Characters::). Characters that
represent keyboard input have a much wider range, to encode modifier
keys such as Control, Meta and Shift.
Since characters are really integers, the printed representation of a
character is a decimal number. This is also a possible read syntax for
a character, but writing characters that way in Lisp programs is a very
bad idea. You should _always_ use the special read syntax formats that
Emacs Lisp provides for characters. These syntax formats start with a
question mark.
The usual read syntax for alphanumeric characters is a question mark
followed by the character; thus, `?A' for the character `A', `?B' for
the character `B', and `?a' for the character `a'.
For example:
?Q => 81 ?q => 113
You can use the same syntax for punctuation characters, but it is
often a good idea to add a `\' so that the Emacs commands for editing
Lisp code don't get confused. For example, `?\ ' is the way to write
the space character. If the character is `\', you _must_ use a second
`\' to quote it: `?\\'.
You can express the characters Control-g, backspace, tab, newline,
vertical tab, formfeed, return, del, and escape as `?\a', `?\b', `?\t',
`?\n', `?\v', `?\f', `?\r', `?\d', and `?\e', respectively. Thus,
?\a => 7 ; `C-g'
?\b => 8 ; backspace, <BS>, `C-h'
?\t => 9 ; tab, <TAB>, `C-i'
?\n => 10 ; newline, `C-j'
?\v => 11 ; vertical tab, `C-k'
?\f => 12 ; formfeed character, `C-l'
?\r => 13 ; carriage return, <RET>, `C-m'
?\e => 27 ; escape character, <ESC>, `C-['
?\\ => 92 ; backslash character, `\'
?\d => 127 ; delete character, <DEL>
These sequences which start with backslash are also known as "escape
sequences", because backslash plays the role of an escape character;
this usage has nothing to do with the character <ESC>.
Control characters may be represented using yet another read syntax.
This consists of a question mark followed by a backslash, caret, and the
corresponding non-control character, in either upper or lower case. For
example, both `?\^I' and `?\^i' are valid read syntax for the character
`C-i', the character whose value is 9.
Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to
`?\^I' and to `?\^i':
?\^I => 9 ?\C-I => 9
In strings and buffers, the only control characters allowed are those
that exist in ASCII; but for keyboard input purposes, you can turn any
character into a control character with `C-'. The character codes for
these non-ASCII control characters include the 2**26 bit as well as the
code for the corresponding non-control character. Ordinary terminals
have no way of generating non-ASCII control characters, but you can
generate them straightforwardly using X and other window systems.
For historical reasons, Emacs treats the <DEL> character as the
control equivalent of `?':
?\^? => 127 ?\C-? => 127
As a result, it is currently not possible to represent the character
`Control-?', which is a meaningful input character under X, using
`\C-'. It is not easy to change this, as various Lisp files refer to
<DEL> in this way.
For representing control characters to be found in files or strings,
we recommend the `^' syntax; for control characters in keyboard input,
we prefer the `C-' syntax. Which one you use does not affect the
meaning of the program, but may guide the understanding of people who
read it.
A "meta character" is a character typed with the <META> modifier
key. The integer that represents such a character has the 2**27 bit
set (which on most machines makes it a negative number). We use high
bits for this and other modifiers to make possible a wide range of
basic character codes.
In a string, the 2**7 bit attached to an ASCII character indicates a
meta character; thus, the meta characters that can fit in a string have
codes in the range from 128 to 255, and are the meta versions of the
ordinary ASCII characters. (In Emacs versions 18 and older, this
convention was used for characters outside of strings as well.)
The read syntax for meta characters uses `\M-'. For example,
`?\M-A' stands for `M-A'. You can use `\M-' together with octal
character codes (see below), with `\C-', or with any other syntax for a
character. Thus, you can write `M-A' as `?\M-A', or as `?\M-\101'.
Likewise, you can write `C-M-b' as `?\M-\C-b', `?\C-\M-b', or
`?\M-\002'.
The case of a graphic character is indicated by its character code;
for example, ASCII distinguishes between the characters `a' and `A'.
But ASCII has no way to represent whether a control character is upper
case or lower case. Emacs uses the 2**25 bit to indicate that the
shift key was used in typing a control character. This distinction is
possible only when you use X terminals or other special terminals;
ordinary terminals do not report the distinction to the computer in any
way. The Lisp syntax for the shift bit is `\S-'; thus, `?\C-\S-o' or
`?\C-\S-O' represents the shifted-control-o character.
The X Window System defines three other modifier bits that can be set
in a character: "hyper", "super" and "alt". The syntaxes for these
bits are `\H-', `\s-' and `\A-'. (Case is significant in these
prefixes.) Thus, `?\H-\M-\A-x' represents `Alt-Hyper-Meta-x'.
Numerically, the bit values are 2**22 for alt, 2**23 for super and
2**24 for hyper.
Finally, the most general read syntax for a character represents the
character code in either octal or hex. To use octal, write a question
mark followed by a backslash and the octal character code (up to three
octal digits); thus, `?\101' for the character `A', `?\001' for the
character `C-a', and `?\002' for the character `C-b'. Although this
syntax can represent any ASCII character, it is preferred only when the
precise octal value is more important than the ASCII representation.
?\012 => 10 ?\n => 10 ?\C-j => 10
?\101 => 65 ?A => 65
To use hex, write a question mark followed by a backslash, `x', and
the hexadecimal character code. You can use any number of hex digits,
so you can represent any character code in this way. Thus, `?\x41' for
the character `A', `?\x1' for the character `C-a', and `?\x8e0' for the
Latin-1 character `a' with grave accent.
A backslash is allowed, and harmless, preceding any character without
a special escape meaning; thus, `?\+' is equivalent to `?+'. There is
no reason to add a backslash before most characters. However, you
should add a backslash before any of the characters `()\|;'`"#.,' to
avoid confusing the Emacs commands for editing Lisp code. Also add a
backslash before whitespace characters such as space, tab, newline and
formfeed. However, it is cleaner to use one of the easily readable
escape sequences, such as `\t', instead of an actual whitespace
character such as a tab.
Symbol Type
-----------
A "symbol" in GNU Emacs Lisp is an object with a name. The symbol
name serves as the printed representation of the symbol. In ordinary
use, the name is unique--no two symbols have the same name.
A symbol can serve as a variable, as a function name, or to hold a
property list. Or it may serve only to be distinct from all other Lisp
objects, so that its presence in a data structure may be recognized
reliably. In a given context, usually only one of these uses is
intended. But you can use one symbol in all of these ways,
independently.
A symbol whose name starts with a colon (`:') is called a "keyword
symbol". These symbols automatically act as constants, and are
normally used only by comparing an unknown symbol with a few specific
alternatives.
A symbol name can contain any characters whatever. Most symbol names
are written with letters, digits, and the punctuation characters
`-+=*/'. Such names require no special punctuation; the characters of
the name suffice as long as the name does not look like a number. (If
it does, write a `\' at the beginning of the name to force
interpretation as a symbol.) The characters `_~!@$%^&:<>{}?' are less
often used but also require no special punctuation. Any other
characters may be included in a symbol's name by escaping them with a
backslash. In contrast to its use in strings, however, a backslash in
the name of a symbol simply quotes the single character that follows the
backslash. For example, in a string, `\t' represents a tab character;
in the name of a symbol, however, `\t' merely quotes the letter `t'.
To have a symbol with a tab character in its name, you must actually
use a tab (preceded with a backslash). But it's rare to do such a
thing.
Common Lisp note: In Common Lisp, lower case letters are always
"folded" to upper case, unless they are explicitly escaped. In
Emacs Lisp, upper case and lower case letters are distinct.
Here are several examples of symbol names. Note that the `+' in the
fifth example is escaped to prevent it from being read as a number.
This is not necessary in the sixth example because the rest of the name
makes it invalid as a number.
foo ; A symbol named `foo'.
FOO ; A symbol named `FOO', different from `foo'.
char-to-string ; A symbol named `char-to-string'.
1+ ; A symbol named `1+'
; (not `+1', which is an integer).
\+1 ; A symbol named `+1'
; (not a very readable name).
\(*\ 1\ 2\) ; A symbol named `(* 1 2)' (a worse name).
+-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'.
; These characters need not be escaped.
Normally the Lisp reader interns all symbols (*note Creating
Symbols::). To prevent interning, you can write `#:' before the name
of the symbol.
Sequence Types
--------------
A "sequence" is a Lisp object that represents an ordered set of
elements. There are two kinds of sequence in Emacs Lisp, lists and
arrays. Thus, an object of type list or of type array is also
considered a sequence.
Arrays are further subdivided into strings, vectors, char-tables and
bool-vectors. Vectors can hold elements of any type, but string
elements must be characters, and bool-vector elements must be `t' or
`nil'. Char-tables are like vectors except that they are indexed by
any valid character code. The characters in a string can have text
properties like characters in a buffer (*note Text Properties::), but
vectors do not support text properties, even when their elements happen
to be characters.
Lists, strings and the other array types are different, but they have
important similarities. For example, all have a length L, and all have
elements which can be indexed from zero to L minus one. Several
functions, called sequence functions, accept any kind of sequence. For
example, the function `elt' can be used to extract an element of a
sequence, given its index. *Note Sequences Arrays Vectors::.
It is generally impossible to read the same sequence twice, since
sequences are always created anew upon reading. If you read the read
syntax for a sequence twice, you get two sequences with equal contents.
There is one exception: the empty list `()' always stands for the same
object, `nil'.
Cons Cell and List Types
------------------------
A "cons cell" is an object that consists of two slots, called the
CAR slot and the CDR slot. Each slot can "hold" or "refer to" any Lisp
object. We also say that "the CAR of this cons cell is" whatever
object its CAR slot currently holds, and likewise for the CDR.
A note to C programmers: in Lisp, we do not distinguish between
"holding" a value and "pointing to" the value, because pointers in
Lisp are implicit.
A "list" is a series of cons cells, linked together so that the CDR
slot of each cons cell holds either the next cons cell or the empty
list. *Note Lists::, for functions that work on lists. Because most
cons cells are used as part of lists, the phrase "list structure" has
come to refer to any structure made out of cons cells.
The names CAR and CDR derive from the history of Lisp. The original
Lisp implementation ran on an IBM 704 computer which divided words into
two parts, called the "address" part and the "decrement"; CAR was an
instruction to extract the contents of the address part of a register,
and CDR an instruction to extract the contents of the decrement. By
contrast, "cons cells" are named for the function `cons' that creates
them, which in turn was named for its purpose, the construction of
cells.
Because cons cells are so central to Lisp, we also have a word for
"an object which is not a cons cell". These objects are called "atoms".
The read syntax and printed representation for lists are identical,
and consist of a left parenthesis, an arbitrary number of elements, and
a right parenthesis.
Upon reading, each object inside the parentheses becomes an element
of the list. That is, a cons cell is made for each element. The CAR
slot of the cons cell holds the element, and its CDR slot refers to the
next cons cell of the list, which holds the next element in the list.
The CDR slot of the last cons cell is set to hold `nil'.
A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes, like dominoes. (The Lisp reader cannot read
such an illustration; unlike the textual notation, which can be
understood by both humans and computers, the box illustrations can be
understood only by humans.) This picture represents the three-element
list `(rose violet buttercup)':
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
In this diagram, each box represents a slot that can hold or refer to
any Lisp object. Each pair of boxes represents a cons cell. Each arrow
represents a reference to a Lisp object, either an atom or another cons
cell.
In this example, the first box, which holds the CAR of the first
cons cell, refers to or "holds" `rose' (a symbol). The second box,
holding the CDR of the first cons cell, refers to the next pair of
boxes, the second cons cell. The CAR of the second cons cell is
`violet', and its CDR is the third cons cell. The CDR of the third
(and last) cons cell is `nil'.
Here is another diagram of the same list, `(rose violet buttercup)',
sketched in a different manner:
--------------- ---------------- -------------------
| car | cdr | | car | cdr | | car | cdr |
| rose | o-------->| violet | o-------->| buttercup | nil |
| | | | | | | | |
--------------- ---------------- -------------------
A list with no elements in it is the "empty list"; it is identical
to the symbol `nil'. In other words, `nil' is both a symbol and a list.
Here are examples of lists written in Lisp syntax:
(A 2 "A") ; A list of three elements.
() ; A list of no elements (the empty list).
nil ; A list of no elements (the empty list).
("A ()") ; A list of one element: the string `"A ()"'.
(A ()) ; A list of two elements: `A' and the empty list.
(A nil) ; Equivalent to the previous.
((A B C)) ; A list of one element
; (which is a list of three elements).
Here is the list `(A ())', or equivalently `(A nil)', depicted with
boxes and arrows:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> A --> nil
Dotted Pair Notation
....................
"Dotted pair notation" is an alternative syntax for cons cells that
represents the CAR and CDR explicitly. In this syntax, `(A . B)'
stands for a cons cell whose CAR is the object A, and whose CDR is the
object B. Dotted pair notation is therefore more general than list
syntax. In the dotted pair notation, the list `(1 2 3)' is written as
`(1 . (2 . (3 . nil)))'. For `nil'-terminated lists, you can use either
notation, but list notation is usually clearer and more convenient.
When printing a list, the dotted pair notation is only used if the CDR
of a cons cell is not a list.
Here's an example using boxes to illustrate dotted pair notation.
This example shows the pair `(rose . violet)':
--- ---
| | |--> violet
--- ---
|
|
--> rose
You can combine dotted pair notation with list notation to represent
conveniently a chain of cons cells with a non-`nil' final CDR. You
write a dot after the last element of the list, followed by the CDR of
the final cons cell. For example, `(rose violet . buttercup)' is
equivalent to `(rose . (violet . buttercup))'. The object looks like
this:
--- --- --- ---
| | |--> | | |--> buttercup
--- --- --- ---
| |
| |
--> rose --> violet
The syntax `(rose . violet . buttercup)' is invalid because there is
nothing that it could mean. If anything, it would say to put
`buttercup' in the CDR of a cons cell whose CDR is already used for
`violet'.
The list `(rose violet)' is equivalent to `(rose . (violet))', and
looks like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> rose --> violet
Similarly, the three-element list `(rose violet buttercup)' is
equivalent to `(rose . (violet . (buttercup)))'. It looks like this:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
Association List Type
.....................
An "association list" or "alist" is a specially-constructed list
whose elements are cons cells. In each element, the CAR is considered
a "key", and the CDR is considered an "associated value". (In some
cases, the associated value is stored in the CAR of the CDR.)
Association lists are often used as stacks, since it is easy to add or
remove associations at the front of the list.
For example,
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable `alist-of-colors' to an alist of three elements. In
the first element, `rose' is the key and `red' is the value.
*Note Association Lists::, for a further explanation of alists and
for functions that work on alists. *Note Hash Tables::, for another
kind of lookup table, which is much faster for handling a large number
of keys.
Array Type
----------
An "array" is composed of an arbitrary number of slots for holding
or referring to other Lisp objects, arranged in a contiguous block of
memory. Accessing any element of an array takes approximately the same
amount of time. In contrast, accessing an element of a list requires
time proportional to the position of the element in the list. (Elements
at the end of a list take longer to access than elements at the
beginning of a list.)
Emacs defines four types of array: strings, vectors, bool-vectors,
and char-tables.
A string is an array of characters and a vector is an array of
arbitrary objects. A bool-vector can hold only `t' or `nil'. These
kinds of array may have any length up to the largest integer.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.
The first element of an array has index zero, the second element has
index 1, and so on. This is called "zero-origin" indexing. For
example, an array of four elements has indices 0, 1, 2, and 3. The
largest possible index value is one less than the length of the array.
Once an array is created, its length is fixed.
All Emacs Lisp arrays are one-dimensional. (Most other programming
languages support multidimensional arrays, but they are not essential;
you can get the same effect with an array of arrays.) Each type of
array has its own read syntax; see the following sections for details.
The array type is contained in the sequence type and contains the
string type, the vector type, the bool-vector type, and the char-table
type.
String Type
-----------
A "string" is an array of characters. Strings are used for many
purposes in Emacs, as can be expected in a text editor; for example, as
the names of Lisp symbols, as messages for the user, and to represent
text extracted from buffers. Strings in Lisp are constants: evaluation
of a string returns the same string.
*Note Strings and Characters::, for functions that operate on
strings.
Syntax for Strings
..................
The read syntax for strings is a double-quote, an arbitrary number of
characters, and another double-quote, `"like this"'. To include a
double-quote in a string, precede it with a backslash; thus, `"\""' is
a string containing just a single double-quote character. Likewise,
you can include a backslash by preceding it with another backslash, like
this: `"this \\ is a single embedded backslash"'.
The newline character is not special in the read syntax for strings;
if you write a new line between the double-quotes, it becomes a
character in the string. But an escaped newline--one that is preceded
by `\'--does not become part of the string; i.e., the Lisp reader
ignores an escaped newline while reading a string. An escaped space
`\ ' is likewise ignored.
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
=> "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
Non-ASCII Characters in Strings
...............................
You can include a non-ASCII international character in a string
constant by writing it literally. There are two text representations
for non-ASCII characters in Emacs strings (and in buffers): unibyte and
multibyte. If the string constant is read from a multibyte source,
such as a multibyte buffer or string, or a file that would be visited as
multibyte, then the character is read as a multibyte character, and that
makes the string multibyte. If the string constant is read from a
unibyte source, then the character is read as unibyte and that makes the
string unibyte.
You can also represent a multibyte non-ASCII character with its
character code: use a hex escape, `\xNNNNNNN', with as many digits as
necessary. (Multibyte non-ASCII character codes are all greater than
256.) Any character which is not a valid hex digit terminates this
construct. If the next character in the string could be interpreted as
a hex digit, write `\ ' (backslash and space) to terminate the hex
escape--for example, `\x8e0\ ' represents one character, `a' with grave
accent. `\ ' in a string constant is just like backslash-newline; it
does not contribute any character to the string, but it does terminate
the preceding hex escape.
Using a multibyte hex escape forces the string to multibyte. You can
represent a unibyte non-ASCII character with its character code, which
must be in the range from 128 (0200 octal) to 255 (0377 octal). This
forces a unibyte string.
*Note Text Representations::, for more information about the two
text representations.
Nonprinting Characters in Strings
.................................
You can use the same backslash escape-sequences in a string constant
as in character literals (but do not use the question mark that begins a
character constant). For example, you can write a string containing the
nonprinting characters tab and `C-a', with commas and spaces between
them, like this: `"\t, \C-a"'. *Note Character Type::, for a
description of the read syntax for characters.
However, not all of the characters you can write with backslash
escape-sequences are valid in strings. The only control characters that
a string can hold are the ASCII control characters. Strings do not
distinguish case in ASCII control characters.
Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
that provides a way to represent meta versions of ASCII characters in a
string. If you use the `\M-' syntax to indicate a meta character in a
string constant, this sets the 2**7 bit of the character in the string.
If the string is used in `define-key' or `lookup-key', this numeric
code is translated into the equivalent meta character. *Note Character
Type::.
Strings cannot hold characters that have the hyper, super, or alt
modifiers.
Text Properties in Strings
..........................
A string can hold properties for the characters it contains, in
addition to the characters themselves. This enables programs that copy
text between strings and buffers to copy the text's properties with no
special effort. *Note Text Properties::, for an explanation of what
text properties mean. Strings with text properties use a special read
and print syntax:
#("CHARACTERS" PROPERTY-DATA...)
where PROPERTY-DATA consists of zero or more elements, in groups of
three as follows:
BEG END PLIST
The elements BEG and END are integers, and together specify a range of
indices in the string; PLIST is the property list for that range. For
example,
#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
represents a string whose textual contents are `foo bar', in which the
first three characters have a `face' property with value `bold', and
the last three have a `face' property with value `italic'. (The fourth
character has no text properties, so its property list is `nil'. It is
not actually necessary to mention ranges with `nil' as the property
list, since any characters not mentioned in any range will default to
having no properties.)
Vector Type
-----------
A "vector" is a one-dimensional array of elements of any type. It
takes a constant amount of time to access any element of a vector. (In
a list, the access time of an element is proportional to the distance of
the element from the beginning of the list.)
The printed representation of a vector consists of a left square
bracket, the elements, and a right square bracket. This is also the
read syntax. Like numbers and strings, vectors are considered constants
for evaluation.
[1 "two" (three)] ; A vector of three elements.
=> [1 "two" (three)]
*Note Vectors::, for functions that work with vectors.
Char-Table Type
---------------
A "char-table" is a one-dimensional array of elements of any type,
indexed by character codes. Char-tables have certain extra features to
make them more useful for many jobs that involve assigning information
to character codes--for example, a char-table can have a parent to
inherit from, a default value, and a small number of extra slots to use
for special purposes. A char-table can also specify a single value for
a whole character set.
The printed representation of a char-table is like a vector except
that there is an extra `#^' at the beginning.
*Note Char-Tables::, for special functions to operate on char-tables.
Uses of char-tables include:
* Case tables (*note Case Tables::).
* Character category tables (*note Categories::).
* Display tables (*note Display Tables::).
* Syntax tables (*note Syntax Tables::).
Bool-Vector Type
----------------
A "bool-vector" is a one-dimensional array of elements that must be
`t' or `nil'.
The printed representation of a bool-vector is like a string, except
that it begins with `#&' followed by the length. The string constant
that follows actually specifies the contents of the bool-vector as a
bitmap--each "character" in the string contains 8 bits, which specify
the next 8 elements of the bool-vector (1 stands for `t', and 0 for
`nil'). The least significant bits of the character correspond to the
lowest indices in the bool-vector. If the length is not a multiple of
8, the printed representation shows extra elements, but these extras
really make no difference.
(make-bool-vector 3 t)
=> #&3"\007"
(make-bool-vector 3 nil)
=> #&3"\0"
;; These are equal since only the first 3 bits are used.
(equal #&3"\377" #&3"\007")
=> t
Hash Table Type
---------------
A hash table is a very fast kind of lookup table, somewhat like an
alist in that it maps keys to corresponding values, but much faster.
Hash tables are a new feature in Emacs 21; they have no read syntax, and
print using hash notation. *Note Hash Tables::.
(make-hash-table)
=> #<hash-table 'eql nil 0/65 0x83af980>
Function Type
-------------
Just as functions in other programming languages are executable,
"Lisp function" objects are pieces of executable code. However,
functions in Lisp are primarily Lisp objects, and only secondarily the
text which represents them. These Lisp objects are lambda expressions:
lists whose first element is the symbol `lambda' (*note Lambda
Expressions::).
In most programming languages, it is impossible to have a function
without a name. In Lisp, a function has no intrinsic name. A lambda
expression is also called an "anonymous function" (*note Anonymous
Functions::). A named function in Lisp is actually a symbol with a
valid function in its function cell (*note Defining Functions::).
Most of the time, functions are called when their names are written
in Lisp expressions in Lisp programs. However, you can construct or
obtain a function object at run time and then call it with the primitive
functions `funcall' and `apply'. *Note Calling Functions::.
Macro Type
----------
A "Lisp macro" is a user-defined construct that extends the Lisp
language. It is represented as an object much like a function, but with
different argument-passing semantics. A Lisp macro has the form of a
list whose first element is the symbol `macro' and whose CDR is a Lisp
function object, including the `lambda' symbol.
Lisp macro objects are usually defined with the built-in `defmacro'
function, but any list that begins with `macro' is a macro as far as
Emacs is concerned. *Note Macros::, for an explanation of how to write
a macro.
*Warning*: Lisp macros and keyboard macros (*note Keyboard Macros::)
are entirely different things. When we use the word "macro" without
qualification, we mean a Lisp macro, not a keyboard macro.
Primitive Function Type
-----------------------
A "primitive function" is a function callable from Lisp but written
in the C programming language. Primitive functions are also called
"subrs" or "built-in functions". (The word "subr" is derived from
"subroutine".) Most primitive functions evaluate all their arguments
when they are called. A primitive function that does not evaluate all
its arguments is called a "special form" (*note Special Forms::).
It does not matter to the caller of a function whether the function
is primitive. However, this does matter if you try to redefine a
primitive with a function written in Lisp. The reason is that the
primitive function may be called directly from C code. Calls to the
redefined function from Lisp will use the new definition, but calls
from C code may still use the built-in definition. Therefore, *we
discourage redefinition of primitive functions*.
The term "function" refers to all Emacs functions, whether written
in Lisp or C. *Note Function Type::, for information about the
functions written in Lisp.
Primitive functions have no read syntax and print in hash notation
with the name of the subroutine.
(symbol-function 'car) ; Access the function cell
; of the symbol.
=> #<subr car>
(subrp (symbol-function 'car)) ; Is this a primitive function?
=> t ; Yes.
Byte-Code Function Type
-----------------------
The byte compiler produces "byte-code function objects".
Internally, a byte-code function object is much like a vector; however,
the evaluator handles this data type specially when it appears as a
function to be called. *Note Byte Compilation::, for information about
the byte compiler.
The printed representation and read syntax for a byte-code function
object is like that for a vector, with an additional `#' before the
opening `['.
Autoload Type
-------------
An "autoload object" is a list whose first element is the symbol
`autoload'. It is stored as the function definition of a symbol, where
it serves as a placeholder for the real definition. The autoload
object says that the real definition is found in a file of Lisp code
that should be loaded when necessary. It contains the name of the file,
plus some other information about the real definition.
After the file has been loaded, the symbol should have a new function
definition that is not an autoload object. The new definition is then
called as if it had been there to begin with. From the user's point of
view, the function call works as expected, using the function definition
in the loaded file.
An autoload object is usually created with the function `autoload',
which stores the object in the function cell of a symbol. *Note
Autoload::, for more details.
Editing Types
=============
The types in the previous section are used for general programming
purposes, and most of them are common to most Lisp dialects. Emacs Lisp
provides several additional data types for purposes connected with
editing.
Buffer Type
-----------
A "buffer" is an object that holds text that can be edited (*note
Buffers::). Most buffers hold the contents of a disk file (*note
Files::) so they can be edited, but some are used for other purposes.
Most buffers are also meant to be seen by the user, and therefore
displayed, at some time, in a window (*note Windows::). But a buffer
need not be displayed in any window.
The contents of a buffer are much like a string, but buffers are not
used like strings in Emacs Lisp, and the available operations are
different. For example, you can insert text efficiently into an
existing buffer, altering the buffer's contents, whereas "inserting"
text into a string requires concatenating substrings, and the result is
an entirely new string object.
Each buffer has a designated position called "point" (*note
Positions::). At any time, one buffer is the "current buffer". Most
editing commands act on the contents of the current buffer in the
neighborhood of point. Many of the standard Emacs functions manipulate
or test the characters in the current buffer; a whole chapter in this
manual is devoted to describing these functions (*note Text::).
Several other data structures are associated with each buffer:
* a local syntax table (*note Syntax Tables::);
* a local keymap (*note Keymaps::); and,
* a list of buffer-local variable bindings (*note Buffer-Local
Variables::).
* overlays (*note Overlays::).
* text properties for the text in the buffer (*note Text
Properties::).
The local keymap and variable list contain entries that individually
override global bindings or values. These are used to customize the
behavior of programs in different buffers, without actually changing the
programs.
A buffer may be "indirect", which means it shares the text of
another buffer, but presents it differently. *Note Indirect Buffers::.
Buffers have no read syntax. They print in hash notation, showing
the buffer name.
(current-buffer)
=> #<buffer objects.texi>
Marker Type
-----------
A "marker" denotes a position in a specific buffer. Markers
therefore have two components: one for the buffer, and one for the
position. Changes in the buffer's text automatically relocate the
position value as necessary to ensure that the marker always points
between the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the
current character position and the name of the buffer.
(point-marker)
=> #<marker at 10779 in objects.texi>
*Note Markers::, for information on how to test, create, copy, and
move markers.
Window Type
-----------
A "window" describes the portion of the terminal screen that Emacs
uses to display a buffer. Every window has one associated buffer, whose
contents appear in the window. By contrast, a given buffer may appear
in one window, no window, or several windows.
Though many windows may exist simultaneously, at any time one window
is designated the "selected window". This is the window where the
cursor is (usually) displayed when Emacs is ready for a command. The
selected window usually displays the current buffer, but this is not
necessarily the case.
Windows are grouped on the screen into frames; each window belongs to
one and only one frame. *Note Frame Type::.
Windows have no read syntax. They print in hash notation, giving the
window number and the name of the buffer being displayed. The window
numbers exist to identify windows uniquely, since the buffer displayed
in any given window can change frequently.
(selected-window)
=> #<window 1 on objects.texi>
*Note Windows::, for a description of the functions that work on
windows.
Frame Type
----------
A "frame" is a rectangle on the screen that contains one or more
Emacs windows. A frame initially contains a single main window (plus
perhaps a minibuffer window) which you can subdivide vertically or
horizontally into smaller windows.
Frames have no read syntax. They print in hash notation, giving the
frame's title, plus its address in core (useful to identify the frame
uniquely).
(selected-frame)
=> #<frame emacs@psilocin.gnu.org 0xdac80>
*Note Frames::, for a description of the functions that work on
frames.
Window Configuration Type
-------------------------
A "window configuration" stores information about the positions,
sizes, and contents of the windows in a frame, so you can recreate the
same arrangement of windows later.
Window configurations do not have a read syntax; their print syntax
looks like `#<window-configuration>'. *Note Window Configurations::,
for a description of several functions related to window configurations.
Frame Configuration Type
------------------------
A "frame configuration" stores information about the positions,
sizes, and contents of the windows in all frames. It is actually a
list whose CAR is `frame-configuration' and whose CDR is an alist.
Each alist element describes one frame, which appears as the CAR of
that element.
*Note Frame Configurations::, for a description of several functions
related to frame configurations.
Process Type
------------
The word "process" usually means a running program. Emacs itself
runs in a process of this sort. However, in Emacs Lisp, a process is a
Lisp object that designates a subprocess created by the Emacs process.
Programs such as shells, GDB, ftp, and compilers, running in
subprocesses of Emacs, extend the capabilities of Emacs.
An Emacs subprocess takes textual input from Emacs and returns
textual output to Emacs for further manipulation. Emacs can also send
signals to the subprocess.
Process objects have no read syntax. They print in hash notation,
giving the name of the process:
(process-list)
=> (#<process shell>)
*Note Processes::, for information about functions that create,
delete, return information about, send input or signals to, and receive
output from processes.
Stream Type
-----------
A "stream" is an object that can be used as a source or sink for
characters--either to supply characters for input or to accept them as
output. Many different types can be used this way: markers, buffers,
strings, and functions. Most often, input streams (character sources)
obtain characters from the keyboard, a buffer, or a file, and output
streams (character sinks) send characters to a buffer, such as a
`*Help*' buffer, or to the echo area.
The object `nil', in addition to its other meanings, may be used as
a stream. It stands for the value of the variable `standard-input' or
`standard-output'. Also, the object `t' as a stream specifies input
using the minibuffer (*note Minibuffers::) or output in the echo area
(*note The Echo Area::).
Streams have no special printed representation or read syntax, and
print as whatever primitive type they are.
*Note Read and Print::, for a description of functions related to
streams, including parsing and printing functions.
Keymap Type
-----------
A "keymap" maps keys typed by the user to commands. This mapping
controls how the user's command input is executed. A keymap is actually
a list whose CAR is the symbol `keymap'.
*Note Keymaps::, for information about creating keymaps, handling
prefix keys, local as well as global keymaps, and changing key bindings.
Overlay Type
------------
An "overlay" specifies properties that apply to a part of a buffer.
Each overlay applies to a specified range of the buffer, and contains a
property list (a list whose elements are alternating property names and
values). Overlay properties are used to present parts of the buffer
temporarily in a different display style. Overlays have no read
syntax, and print in hash notation, giving the buffer name and range of
positions.
*Note Overlays::, for how to create and use overlays.
Read Syntax for Circular Objects
================================
In Emacs 21, to represent shared or circular structure within a
complex of Lisp objects, you can use the reader constructs `#N=' and
`#N#'.
Use `#N=' before an object to label it for later reference;
subsequently, you can use `#N#' to refer the same object in another
place. Here, N is some integer. For example, here is how to make a
list in which the first element recurs as the third element:
(#1=(a) b #1#)
This differs from ordinary syntax such as this
((a) b (a))
which would result in a list whose first and third elements look alike
but are not the same Lisp object. This shows the difference:
(prog1 nil
(setq x '(#1=(a) b #1#)))
(eq (nth 0 x) (nth 2 x))
=> t
(setq x '((a) b (a)))
(eq (nth 0 x) (nth 2 x))
=> nil
You can also use the same syntax to make a circular structure, which
appears as an "element" within itself. Here is an example:
#1=(a #1#)
This makes a list whose second element is the list itself. Here's how
you can see that it really works:
(prog1 nil
(setq x '#1=(a #1#)))
(eq x (cadr x))
=> t
The Lisp printer can produce this syntax to record circular and
shared structure in a Lisp object, if you bind the variable
`print-circle' to a non-`nil' value. *Note Output Variables::.
Type Predicates
===============
The Emacs Lisp interpreter itself does not perform type checking on
the actual arguments passed to functions when they are called. It could
not do so, since function arguments in Lisp do not have declared data
types, as they do in other programming languages. It is therefore up to
the individual function to test whether each actual argument belongs to
a type that the function can use.
All built-in functions do check the types of their actual arguments
when appropriate, and signal a `wrong-type-argument' error if an
argument is of the wrong type. For example, here is what happens if you
pass an argument to `+' that it cannot handle:
(+ 2 'a)
error--> Wrong type argument: number-or-marker-p, a
If you want your program to handle different types differently, you
must do explicit type checking. The most common way to check the type
of an object is to call a "type predicate" function. Emacs has a type
predicate for each type, as well as some predicates for combinations of
types.
A type predicate function takes one argument; it returns `t' if the
argument belongs to the appropriate type, and `nil' otherwise.
Following a general Lisp convention for predicate functions, most type
predicates' names end with `p'.
Here is an example which uses the predicates `listp' to check for a
list and `symbolp' to check for a symbol.
(defun add-on (x)
(cond ((symbolp x)
;; If X is a symbol, put it on LIST.
(setq list (cons x list)))
((listp x)
;; If X is a list, add its elements to LIST.
(setq list (append x list)))
(t
;; We handle only symbols and lists.
(error "Invalid argument %s in add-on" x))))
Here is a table of predefined type predicates, in alphabetical order,
with references to further information.
`atom'
*Note atom: List-related Predicates.
`arrayp'
*Note arrayp: Array Functions.
`bool-vector-p'
*Note bool-vector-p: Bool-Vectors.
`bufferp'
*Note bufferp: Buffer Basics.
`byte-code-function-p'
*Note byte-code-function-p: Byte-Code Type.
`case-table-p'
*Note case-table-p: Case Tables.
`char-or-string-p'
*Note char-or-string-p: Predicates for Strings.
`char-table-p'
*Note char-table-p: Char-Tables.
`commandp'
*Note commandp: Interactive Call.
`consp'
*Note consp: List-related Predicates.
`display-table-p'
*Note display-table-p: Display Tables.
`floatp'
*Note floatp: Predicates on Numbers.
`frame-configuration-p'
*Note frame-configuration-p: Frame Configurations.
`frame-live-p'
*Note frame-live-p: Deleting Frames.
`framep'
*Note framep: Frames.
`functionp'
*Note functionp: Functions.
`integer-or-marker-p'
*Note integer-or-marker-p: Predicates on Markers.
`integerp'
*Note integerp: Predicates on Numbers.
`keymapp'
*Note keymapp: Creating Keymaps.
`keywordp'
*Note Constant Variables::.
`listp'
*Note listp: List-related Predicates.
`markerp'
*Note markerp: Predicates on Markers.
`wholenump'
*Note wholenump: Predicates on Numbers.
`nlistp'
*Note nlistp: List-related Predicates.
`numberp'
*Note numberp: Predicates on Numbers.
`number-or-marker-p'
*Note number-or-marker-p: Predicates on Markers.
`overlayp'
*Note overlayp: Overlays.
`processp'
*Note processp: Processes.
`sequencep'
*Note sequencep: Sequence Functions.
`stringp'
*Note stringp: Predicates for Strings.
`subrp'
*Note subrp: Function Cells.
`symbolp'
*Note symbolp: Symbols.
`syntax-table-p'
*Note syntax-table-p: Syntax Tables.
`user-variable-p'
*Note user-variable-p: Defining Variables.
`vectorp'
*Note vectorp: Vectors.
`window-configuration-p'
*Note window-configuration-p: Window Configurations.
`window-live-p'
*Note window-live-p: Deleting Windows.
`windowp'
*Note windowp: Basic Windows.
The most general way to check the type of an object is to call the
function `type-of'. Recall that each object belongs to one and only
one primitive type; `type-of' tells you which one (*note Lisp Data
Types::). But `type-of' knows nothing about non-primitive types. In
most cases, it is more convenient to use type predicates than `type-of'.
- Function: type-of object
This function returns a symbol naming the primitive type of
OBJECT. The value is one of the symbols `symbol', `integer',
`float', `string', `cons', `vector', `char-table', `bool-vector',
`hash-table', `subr', `compiled-function', `marker', `overlay',
`window', `buffer', `frame', `process', or `window-configuration'.
(type-of 1)
=> integer
(type-of 'nil)
=> symbol
(type-of '()) ; `()' is `nil'.
=> symbol
(type-of '(x))
=> cons
Equality Predicates
===================
Here we describe two functions that test for equality between any two
objects. Other functions test equality between objects of specific
types, e.g., strings. For these predicates, see the appropriate chapter
describing the data type.
- Function: eq object1 object2
This function returns `t' if OBJECT1 and OBJECT2 are the same
object, `nil' otherwise. The "same object" means that a change in
one will be reflected by the same change in the other.
`eq' returns `t' if OBJECT1 and OBJECT2 are integers with the same
value. Also, since symbol names are normally unique, if the
arguments are symbols with the same name, they are `eq'. For
other types (e.g., lists, vectors, strings), two arguments with
the same contents or elements are not necessarily `eq' to each
other: they are `eq' only if they are the same object.
(eq 'foo 'foo)
=> t
(eq 456 456)
=> t
(eq "asdf" "asdf")
=> nil
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(setq foo '(1 (2 (3))))
=> (1 (2 (3)))
(eq foo foo)
=> t
(eq foo '(1 (2 (3))))
=> nil
(eq [(1 2) 3] [(1 2) 3])
=> nil
(eq (point-marker) (point-marker))
=> nil
The `make-symbol' function returns an uninterned symbol, distinct
from the symbol that is used if you write the name in a Lisp
expression. Distinct symbols with the same name are not `eq'.
*Note Creating Symbols::.
(eq (make-symbol "foo") 'foo)
=> nil
- Function: equal object1 object2
This function returns `t' if OBJECT1 and OBJECT2 have equal
components, `nil' otherwise. Whereas `eq' tests if its arguments
are the same object, `equal' looks inside nonidentical arguments
to see if their elements or contents are the same. So, if two
objects are `eq', they are `equal', but the converse is not always
true.
(equal 'foo 'foo)
=> t
(equal 456 456)
=> t
(equal "asdf" "asdf")
=> t
(eq "asdf" "asdf")
=> nil
(equal '(1 (2 (3))) '(1 (2 (3))))
=> t
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(equal [(1 2) 3] [(1 2) 3])
=> t
(eq [(1 2) 3] [(1 2) 3])
=> nil
(equal (point-marker) (point-marker))
=> t
(eq (point-marker) (point-marker))
=> nil
Comparison of strings is case-sensitive, but does not take account
of text properties--it compares only the characters in the strings.
A unibyte string never equals a multibyte string unless the
contents are entirely ASCII (*note Text Representations::).
(equal "asdf" "ASDF")
=> nil
However, two distinct buffers are never considered `equal', even if
their textual contents are the same.
The test for equality is implemented recursively; for example, given
two cons cells X and Y, `(equal X Y)' returns `t' if and only if both
the expressions below return `t':
(equal (car X) (car Y))
(equal (cdr X) (cdr Y))
Because of this recursive method, circular lists may therefore cause
infinite recursion (leading to an error).
Numbers
*******
GNU Emacs supports two numeric data types: "integers" and "floating
point numbers". Integers are whole numbers such as -3, 0, 7, 13, and
511. Their values are exact. Floating point numbers are numbers with
fractional parts, such as -4.5, 0.0, or 2.71828. They can also be
expressed in exponential notation: 1.5e2 equals 150; in this example,
`e2' stands for ten to the second power, and that is multiplied by 1.5.
Floating point values are not exact; they have a fixed, limited amount
of precision.
Integer Basics
==============
The range of values for an integer depends on the machine. The
minimum range is -134217728 to 134217727 (28 bits; i.e., -2**27 to
2**27 - 1), but some machines may provide a wider range. Many examples
in this chapter assume an integer has 28 bits.
The Lisp reader reads an integer as a sequence of digits with
optional initial sign and optional final period.
1 ; The integer 1.
1. ; The integer 1.
+1 ; Also the integer 1.
-1 ; The integer -1.
268435457 ; Also the integer 1, due to overflow.
0 ; The integer 0.
-0 ; The integer 0.
In addition, the Lisp reader recognizes a syntax for integers in
bases other than 10: `#BINTEGER' reads INTEGER in binary (radix 2),
`#OINTEGER' reads INTEGER in octal (radix 8), `#XINTEGER' reads INTEGER
in hexadecimal (radix 16), and `#RADIXrINTEGER' reads INTEGER in radix
RADIX (where RADIX is between 2 and 36, inclusivley). Case is not
significant for the letter after `#' (`B', `O', etc.) that denotes the
radix.
To understand how various functions work on integers, especially the
bitwise operators (*note Bitwise Operations::), it is often helpful to
view the numbers in their binary form.
In 28-bit binary, the decimal integer 5 looks like this:
0000 0000 0000 0000 0000 0000 0101
(We have inserted spaces between groups of 4 bits, and two spaces
between groups of 8 bits, to make the binary integer easier to read.)
The integer -1 looks like this:
1111 1111 1111 1111 1111 1111 1111
-1 is represented as 28 ones. (This is called "two's complement"
notation.)
The negative integer, -5, is creating by subtracting 4 from -1. In
binary, the decimal integer 4 is 100. Consequently, -5 looks like this:
1111 1111 1111 1111 1111 1111 1011
In this implementation, the largest 28-bit binary integer value is
134,217,727 in decimal. In binary, it looks like this:
0111 1111 1111 1111 1111 1111 1111
Since the arithmetic functions do not check whether integers go
outside their range, when you add 1 to 134,217,727, the value is the
negative integer -134,217,728:
(+ 1 134217727)
=> -134217728
=> 1000 0000 0000 0000 0000 0000 0000
Many of the functions described in this chapter accept markers for
arguments in place of numbers. (*Note Markers::.) Since the actual
arguments to such functions may be either numbers or markers, we often
give these arguments the name NUMBER-OR-MARKER. When the argument
value is a marker, its position value is used and its buffer is ignored.
Floating Point Basics
=====================
Floating point numbers are useful for representing numbers that are
not integral. The precise range of floating point numbers is
machine-specific; it is the same as the range of the C data type
`double' on the machine you are using.
The read-syntax for floating point numbers requires either a decimal
point (with at least one digit following), an exponent, or both. For
example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways
of writing a floating point number whose value is 1500. They are all
equivalent. You can also use a minus sign to write negative floating
point numbers, as in `-1.0'.
Most modern computers support the IEEE floating point standard, which
provides for positive infinity and negative infinity as floating point
values. It also provides for a class of values called NaN or
"not-a-number"; numerical functions return such values in cases where
there is no correct answer. For example, `(sqrt -1.0)' returns a NaN.
For practical purposes, there's no significant difference between
different NaN values in Emacs Lisp, and there's no rule for precisely
which NaN value should be used in a particular case, so Emacs Lisp
doesn't try to distinguish them. Here are the read syntaxes for these
special floating point values:
positive infinity
`1.0e+INF'
negative infinity
`-1.0e+INF'
Not-a-number
`0.0e+NaN'.
In addition, the value `-0.0' is distinguishable from ordinary zero
in IEEE floating point (although `equal' and `=' consider them equal
values).
You can use `logb' to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):
- Function: logb number
This function returns the binary exponent of NUMBER. More
precisely, the value is the logarithm of NUMBER base 2, rounded
down to an integer.
(logb 10)
=> 3
(logb 10.0e20)
=> 69
Type Predicates for Numbers
===========================
The functions in this section test whether the argument is a number
or whether it is a certain sort of number. The functions `integerp'
and `floatp' can take any type of Lisp object as argument (the
predicates would not be of much use otherwise); but the `zerop'
predicate requires a number as its argument. See also
`integer-or-marker-p' and `number-or-marker-p', in *Note Predicates on
Markers::.
- Function: floatp object
This predicate tests whether its argument is a floating point
number and returns `t' if so, `nil' otherwise.
`floatp' does not exist in Emacs versions 18 and earlier.
- Function: integerp object
This predicate tests whether its argument is an integer, and
returns `t' if so, `nil' otherwise.
- Function: numberp object
This predicate tests whether its argument is a number (either
integer or floating point), and returns `t' if so, `nil' otherwise.
- Function: wholenump object
The `wholenump' predicate (whose name comes from the phrase
"whole-number-p") tests to see whether its argument is a
nonnegative integer, and returns `t' if so, `nil' otherwise. 0 is
considered non-negative.
`natnump' is an obsolete synonym for `wholenump'.
- Function: zerop number
This predicate tests whether its argument is zero, and returns `t'
if so, `nil' otherwise. The argument must be a number.
These two forms are equivalent: `(zerop x)' == `(= x 0)'.
Comparison of Numbers
=====================
To test numbers for numerical equality, you should normally use `=',
not `eq'. There can be many distinct floating point number objects
with the same numeric value. If you use `eq' to compare them, then you
test whether two values are the same _object_. By contrast, `='
compares only the numeric values of the objects.
At present, each integer value has a unique Lisp object in Emacs
Lisp. Therefore, `eq' is equivalent to `=' where integers are
concerned. It is sometimes convenient to use `eq' for comparing an
unknown value with an integer, because `eq' does not report an error if
the unknown value is not a number--it accepts arguments of any type.
By contrast, `=' signals an error if the arguments are not numbers or
markers. However, it is a good idea to use `=' if you can, even for
comparing integers, just in case we change the representation of
integers in a future Emacs version.
Sometimes it is useful to compare numbers with `equal'; it treats
two numbers as equal if they have the same data type (both integers, or
both floating point) and the same value. By contrast, `=' can treat an
integer and a floating point number as equal.
There is another wrinkle: because floating point arithmetic is not
exact, it is often a bad idea to check for equality of two floating
point values. Usually it is better to test for approximate equality.
Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (and (= x 0) (= y 0))
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
Common Lisp note: Comparing numbers in Common Lisp always requires
`=' because Common Lisp implements multi-word integers, and two
distinct integer objects can have the same numeric value. Emacs
Lisp can have just one integer object for any given value because
it has a limited range of integer values.
- Function: = number-or-marker1 number-or-marker2
This function tests whether its arguments are numerically equal,
and returns `t' if so, `nil' otherwise.
- Function: /= number-or-marker1 number-or-marker2
This function tests whether its arguments are numerically equal,
and returns `t' if they are not, and `nil' if they are.
- Function: < number-or-marker1 number-or-marker2
This function tests whether its first argument is strictly less
than its second argument. It returns `t' if so, `nil' otherwise.
- Function: <= number-or-marker1 number-or-marker2
This function tests whether its first argument is less than or
equal to its second argument. It returns `t' if so, `nil'
otherwise.
- Function: > number-or-marker1 number-or-marker2
This function tests whether its first argument is strictly greater
than its second argument. It returns `t' if so, `nil' otherwise.
- Function: >= number-or-marker1 number-or-marker2
This function tests whether its first argument is greater than or
equal to its second argument. It returns `t' if so, `nil'
otherwise.
- Function: max number-or-marker &rest numbers-or-markers
This function returns the largest of its arguments. If any of the
argument is floating-point, the value is returned as floating
point, even if it was given as an integer.
(max 20)
=> 20
(max 1 2.5)
=> 2.5
(max 1 3 2.5)
=> 3.0
- Function: min number-or-marker &rest numbers-or-markers
This function returns the smallest of its arguments. If any of
the argument is floating-point, the value is returned as floating
point, even if it was given as an integer.
(min -4 1)
=> -4
- Function: abs number
This function returns the absolute value of NUMBER.
Numeric Conversions
===================
To convert an integer to floating point, use the function `float'.
- Function: float number
This returns NUMBER converted to floating point. If NUMBER is
already a floating point number, `float' returns it unchanged.
There are four functions to convert floating point numbers to
integers; they differ in how they round. These functions accept
integer arguments also, and return such arguments unchanged.
- Function: truncate number
This returns NUMBER, converted to an integer by rounding towards
zero.
(truncate 1.2)
=> 1
(truncate 1.7)
=> 1
(truncate -1.2)
=> -1
(truncate -1.7)
=> -1
- Function: floor number &optional divisor
This returns NUMBER, converted to an integer by rounding downward
(towards negative infinity).
If DIVISOR is specified, `floor' divides NUMBER by DIVISOR and
then converts to an integer; this uses the kind of division
operation that corresponds to `mod', rounding downward. An
`arith-error' results if DIVISOR is 0.
(floor 1.2)
=> 1
(floor 1.7)
=> 1
(floor -1.2)
=> -2
(floor -1.7)
=> -2
(floor 5.99 3)
=> 1
- Function: ceiling number
This returns NUMBER, converted to an integer by rounding upward
(towards positive infinity).
(ceiling 1.2)
=> 2
(ceiling 1.7)
=> 2
(ceiling -1.2)
=> -1
(ceiling -1.7)
=> -1
- Function: round number
This returns NUMBER, converted to an integer by rounding towards
the nearest integer. Rounding a value equidistant between two
integers may choose the integer closer to zero, or it may prefer
an even integer, depending on your machine.
(round 1.2)
=> 1
(round 1.7)
=> 2
(round -1.2)
=> -1
(round -1.7)
=> -2
Arithmetic Operations
=====================
Emacs Lisp provides the traditional four arithmetic operations:
addition, subtraction, multiplication, and division. Remainder and
modulus functions supplement the division functions. The functions to
add or subtract 1 are provided because they are traditional in Lisp and
commonly used.
All of these functions except `%' return a floating point value if
any argument is floating.
It is important to note that in Emacs Lisp, arithmetic functions do
not check for overflow. Thus `(1+ 134217727)' may evaluate to
-134217728, depending on your hardware.
- Function: 1+ number-or-marker
This function returns NUMBER-OR-MARKER plus 1. For example,
(setq foo 4)
=> 4
(1+ foo)
=> 5
This function is not analogous to the C operator `++'--it does not
increment a variable. It just computes a sum. Thus, if we
continue,
foo
=> 4
If you want to increment the variable, you must use `setq', like
this:
(setq foo (1+ foo))
=> 5
- Function: 1- number-or-marker
This function returns NUMBER-OR-MARKER minus 1.
- Function: + &rest numbers-or-markers
This function adds its arguments together. When given no
arguments, `+' returns 0.
(+)
=> 0
(+ 1)
=> 1
(+ 1 2 3 4)
=> 10
- Function: - &optional number-or-marker &rest more-numbers-or-markers
The `-' function serves two purposes: negation and subtraction.
When `-' has a single argument, the value is the negative of the
argument. When there are multiple arguments, `-' subtracts each of
the MORE-NUMBERS-OR-MARKERS from NUMBER-OR-MARKER, cumulatively.
If there are no arguments, the result is 0.
(- 10 1 2 3 4)
=> 0
(- 10)
=> -10
(-)
=> 0
- Function: * &rest numbers-or-markers
This function multiplies its arguments together, and returns the
product. When given no arguments, `*' returns 1.
(*)
=> 1
(* 1)
=> 1
(* 1 2 3 4)
=> 24
- Function: / dividend divisor &rest divisors
This function divides DIVIDEND by DIVISOR and returns the
quotient. If there are additional arguments DIVISORS, then it
divides DIVIDEND by each divisor in turn. Each argument may be a
number or a marker.
If all the arguments are integers, then the result is an integer
too. This means the result has to be rounded. On most machines,
the result is rounded towards zero after each division, but some
machines may round differently with negative arguments. This is
because the Lisp function `/' is implemented using the C division
operator, which also permits machine-dependent rounding. As a
practical matter, all known machines round in the standard fashion.
If you divide an integer by 0, an `arith-error' error is signaled.
(*Note Errors::.) Floating point division by zero returns either
infinity or a NaN if your machine supports IEEE floating point;
otherwise, it signals an `arith-error' error.
(/ 6 2)
=> 3
(/ 5 2)
=> 2
(/ 5.0 2)
=> 2.5
(/ 5 2.0)
=> 2.5
(/ 5.0 2.0)
=> 2.5
(/ 25 3 2)
=> 4
(/ -17 6)
=> -2
The result of `(/ -17 6)' could in principle be -3 on some
machines.
- Function: % dividend divisor
This function returns the integer remainder after division of
DIVIDEND by DIVISOR. The arguments must be integers or markers.
For negative arguments, the remainder is in principle
machine-dependent since the quotient is; but in practice, all
known machines behave alike.
An `arith-error' results if DIVISOR is 0.
(% 9 4)
=> 1
(% -9 4)
=> -1
(% 9 -4)
=> 1
(% -9 -4)
=> -1
For any two integers DIVIDEND and DIVISOR,
(+ (% DIVIDEND DIVISOR)
(* (/ DIVIDEND DIVISOR) DIVISOR))
always equals DIVIDEND.
- Function: mod dividend divisor
This function returns the value of DIVIDEND modulo DIVISOR; in
other words, the remainder after division of DIVIDEND by DIVISOR,
but with the same sign as DIVISOR. The arguments must be numbers
or markers.
Unlike `%', `mod' returns a well-defined result for negative
arguments. It also permits floating point arguments; it rounds the
quotient downward (towards minus infinity) to an integer, and uses
that quotient to compute the remainder.
An `arith-error' results if DIVISOR is 0.
(mod 9 4)
=> 1
(mod -9 4)
=> 3
(mod 9 -4)
=> -3
(mod -9 -4)
=> -1
(mod 5.5 2.5)
=> .5
For any two numbers DIVIDEND and DIVISOR,
(+ (mod DIVIDEND DIVISOR)
(* (floor DIVIDEND DIVISOR) DIVISOR))
always equals DIVIDEND, subject to rounding error if either
argument is floating point. For `floor', see *Note Numeric
Conversions::.
Rounding Operations
===================
The functions `ffloor', `fceiling', `fround', and `ftruncate' take a
floating point argument and return a floating point result whose value
is a nearby integer. `ffloor' returns the nearest integer below;
`fceiling', the nearest integer above; `ftruncate', the nearest integer
in the direction towards zero; `fround', the nearest integer.
- Function: ffloor float
This function rounds FLOAT to the next lower integral value, and
returns that value as a floating point number.
- Function: fceiling float
This function rounds FLOAT to the next higher integral value, and
returns that value as a floating point number.
- Function: ftruncate float
This function rounds FLOAT towards zero to an integral value, and
returns that value as a floating point number.
- Function: fround float
This function rounds FLOAT to the nearest integral value, and
returns that value as a floating point number.
Bitwise Operations on Integers
==============================
In a computer, an integer is represented as a binary number, a
sequence of "bits" (digits which are either zero or one). A bitwise
operation acts on the individual bits of such a sequence. For example,
"shifting" moves the whole sequence left or right one or more places,
reproducing the same pattern "moved over".
The bitwise operations in Emacs Lisp apply only to integers.
- Function: lsh integer1 count
`lsh', which is an abbreviation for "logical shift", shifts the
bits in INTEGER1 to the left COUNT places, or to the right if
COUNT is negative, bringing zeros into the vacated bits. If COUNT
is negative, `lsh' shifts zeros into the leftmost
(most-significant) bit, producing a positive result even if
INTEGER1 is negative. Contrast this with `ash', below.
Here are two examples of `lsh', shifting a pattern of bits one
place to the left. We show only the low-order eight bits of the
binary pattern; the rest are all zero.
(lsh 5 1)
=> 10
;; Decimal 5 becomes decimal 10.
00000101 => 00001010
(lsh 7 1)
=> 14
;; Decimal 7 becomes decimal 14.
00000111 => 00001110
As the examples illustrate, shifting the pattern of bits one place
to the left produces a number that is twice the value of the
previous number.
Shifting a pattern of bits two places to the left produces results
like this (with 8-bit binary numbers):
(lsh 3 2)
=> 12
;; Decimal 3 becomes decimal 12.
00000011 => 00001100
On the other hand, shifting one place to the right looks like this:
(lsh 6 -1)
=> 3
;; Decimal 6 becomes decimal 3.
00000110 => 00000011
(lsh 5 -1)
=> 2
;; Decimal 5 becomes decimal 2.
00000101 => 00000010
As the example illustrates, shifting one place to the right
divides the value of a positive integer by two, rounding downward.
The function `lsh', like all Emacs Lisp arithmetic functions, does
not check for overflow, so shifting left can discard significant
bits and change the sign of the number. For example, left shifting
134,217,727 produces -2 on a 28-bit machine:
(lsh 134217727 1) ; left shift
=> -2
In binary, in the 28-bit implementation, the argument looks like
this:
;; Decimal 134,217,727
0111 1111 1111 1111 1111 1111 1111
which becomes the following when left shifted:
;; Decimal -2
1111 1111 1111 1111 1111 1111 1110
- Function: ash integer1 count
`ash' ("arithmetic shift") shifts the bits in INTEGER1 to the left
COUNT places, or to the right if COUNT is negative.
`ash' gives the same results as `lsh' except when INTEGER1 and
COUNT are both negative. In that case, `ash' puts ones in the
empty bit positions on the left, while `lsh' puts zeros in those
bit positions.
Thus, with `ash', shifting the pattern of bits one place to the
right looks like this:
(ash -6 -1) => -3
;; Decimal -6 becomes decimal -3.
1111 1111 1111 1111 1111 1111 1010
=>
1111 1111 1111 1111 1111 1111 1101
In contrast, shifting the pattern of bits one place to the right
with `lsh' looks like this:
(lsh -6 -1) => 134217725
;; Decimal -6 becomes decimal 134,217,725.
1111 1111 1111 1111 1111 1111 1010
=>
0111 1111 1111 1111 1111 1111 1101
Here are other examples:
; 28-bit binary values
(lsh 5 2) ; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 20 ; = 0000 0000 0000 0000 0000 0001 0100
(ash 5 2)
=> 20
(lsh -5 2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> -20 ; = 1111 1111 1111 1111 1111 1110 1100
(ash -5 2)
=> -20
(lsh 5 -2) ; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 1 ; = 0000 0000 0000 0000 0000 0000 0001
(ash 5 -2)
=> 1
(lsh -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> 4194302 ; = 0011 1111 1111 1111 1111 1111 1110
(ash -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> -2 ; = 1111 1111 1111 1111 1111 1111 1110
- Function: logand &rest ints-or-markers
This function returns the "logical and" of the arguments: the Nth
bit is set in the result if, and only if, the Nth bit is set in
all the arguments. ("Set" means that the value of the bit is 1
rather than 0.)
For example, using 4-bit binary numbers, the "logical and" of 13
and 12 is 12: 1101 combined with 1100 produces 1100. In both the
binary numbers, the leftmost two bits are set (i.e., they are
1's), so the leftmost two bits of the returned value are set.
However, for the rightmost two bits, each is zero in at least one
of the arguments, so the rightmost two bits of the returned value
are 0's.
Therefore,
(logand 13 12)
=> 12
If `logand' is not passed any argument, it returns a value of -1.
This number is an identity element for `logand' because its binary
representation consists entirely of ones. If `logand' is passed
just one argument, it returns that argument.
; 28-bit binary values
(logand 14 13) ; 14 = 0000 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 0000 1101
=> 12 ; 12 = 0000 0000 0000 0000 0000 0000 1100
(logand 14 13 4) ; 14 = 0000 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 0000 1101
; 4 = 0000 0000 0000 0000 0000 0000 0100
=> 4 ; 4 = 0000 0000 0000 0000 0000 0000 0100
(logand)
=> -1 ; -1 = 1111 1111 1111 1111 1111 1111 1111
- Function: logior &rest ints-or-markers
This function returns the "inclusive or" of its arguments: the Nth
bit is set in the result if, and only if, the Nth bit is set in at
least one of the arguments. If there are no arguments, the result
is zero, which is an identity element for this operation. If
`logior' is passed just one argument, it returns that argument.
; 28-bit binary values
(logior 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 13 ; 13 = 0000 0000 0000 0000 0000 0000 1101
(logior 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0000 0111
=> 15 ; 15 = 0000 0000 0000 0000 0000 0000 1111
- Function: logxor &rest ints-or-markers
This function returns the "exclusive or" of its arguments: the Nth
bit is set in the result if, and only if, the Nth bit is set in an
odd number of the arguments. If there are no arguments, the
result is 0, which is an identity element for this operation. If
`logxor' is passed just one argument, it returns that argument.
; 28-bit binary values
(logxor 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 9 ; 9 = 0000 0000 0000 0000 0000 0000 1001
(logxor 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0000 0111
=> 14 ; 14 = 0000 0000 0000 0000 0000 0000 1110
- Function: lognot integer
This function returns the logical complement of its argument: the
Nth bit is one in the result if, and only if, the Nth bit is zero
in INTEGER, and vice-versa.
(lognot 5)
=> -6
;; 5 = 0000 0000 0000 0000 0000 0000 0101
;; becomes
;; -6 = 1111 1111 1111 1111 1111 1111 1010
Standard Mathematical Functions
===============================
These mathematical functions allow integers as well as floating point
numbers as arguments.
- Function: sin arg
- Function: cos arg
- Function: tan arg
These are the ordinary trigonometric functions, with argument
measured in radians.
- Function: asin arg
The value of `(asin ARG)' is a number between -pi/2 and pi/2
(inclusive) whose sine is ARG; if, however, ARG is out of range
(outside [-1, 1]), then the result is a NaN.
- Function: acos arg
The value of `(acos ARG)' is a number between 0 and pi (inclusive)
whose cosine is ARG; if, however, ARG is out of range (outside
[-1, 1]), then the result is a NaN.
- Function: atan arg
The value of `(atan ARG)' is a number between -pi/2 and pi/2
(exclusive) whose tangent is ARG.
- Function: exp arg
This is the exponential function; it returns e to the power ARG. e
is a fundamental mathematical constant also called the base of
natural logarithms.
- Function: log arg &optional base
This function returns the logarithm of ARG, with base BASE. If
you don't specify BASE, the base e is used. If ARG is negative,
the result is a NaN.
- Function: log10 arg
This function returns the logarithm of ARG, with base 10. If ARG
is negative, the result is a NaN. `(log10 X)' == `(log X 10)', at
least approximately.
- Function: expt x y
This function returns X raised to power Y. If both arguments are
integers and Y is positive, the result is an integer; in this
case, it is truncated to fit the range of possible integer values.
- Function: sqrt arg
This returns the square root of ARG. If ARG is negative, the
value is a NaN.
Random Numbers
==============
A deterministic computer program cannot generate true random numbers.
For most purposes, "pseudo-random numbers" suffice. A series of
pseudo-random numbers is generated in a deterministic fashion. The
numbers are not truly random, but they have certain properties that
mimic a random series. For example, all possible values occur equally
often in a pseudo-random series.
In Emacs, pseudo-random numbers are generated from a "seed" number.
Starting from any given seed, the `random' function always generates
the same sequence of numbers. Emacs always starts with the same seed
value, so the sequence of values of `random' is actually the same in
each Emacs run! For example, in one operating system, the first call
to `(random)' after you start Emacs always returns -1457731, and the
second one always returns -7692030. This repeatability is helpful for
debugging.
If you want random numbers that don't always come out the same,
execute `(random t)'. This chooses a new seed based on the current
time of day and on Emacs's process ID number.
- Function: random &optional limit
This function returns a pseudo-random integer. Repeated calls
return a series of pseudo-random integers.
If LIMIT is a positive integer, the value is chosen to be
nonnegative and less than LIMIT.
If LIMIT is `t', it means to choose a new seed based on the
current time of day and on Emacs's process ID number.
On some machines, any integer representable in Lisp may be the
result of `random'. On other machines, the result can never be
larger than a certain maximum or less than a certain (negative)
minimum.
Strings and Characters
**********************
A string in Emacs Lisp is an array that contains an ordered sequence
of characters. Strings are used as names of symbols, buffers, and
files; to send messages to users; to hold text being copied between
buffers; and for many other purposes. Because strings are so important,
Emacs Lisp has many functions expressly for manipulating them. Emacs
Lisp programs use strings more often than individual characters.
*Note Strings of Events::, for special considerations for strings of
keyboard character events.
String and Character Basics
===========================
Characters are represented in Emacs Lisp as integers; whether an
integer is a character or not is determined only by how it is used.
Thus, strings really contain integers.
The length of a string (like any array) is fixed, and cannot be
altered once the string exists. Strings in Lisp are _not_ terminated
by a distinguished character code. (By contrast, strings in C are
terminated by a character with ASCII code 0.)
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions. (*Note
Sequences Arrays Vectors::.) For example, you can access or change
individual characters in a string using the functions `aref' and `aset'
(*note Array Functions::).
There are two text representations for non-ASCII characters in Emacs
strings (and in buffers): unibyte and multibyte (*note Text
Representations::). An ASCII character always occupies one byte in a
string; in fact, when a string is all ASCII, there is no real
difference between the unibyte and multibyte representations. For most
Lisp programming, you don't need to be concerned with these two
representations.
Sometimes key sequences are represented as strings. When a string is
a key sequence, string elements in the range 128 to 255 represent meta
characters (which are large integers) rather than character codes in
the range 128 to 255.
Strings cannot hold characters that have the hyper, super or alt
modifiers; they can hold ASCII control characters, but no other control
characters. They do not distinguish case in ASCII control characters.
If you want to store such characters in a sequence, such as a key
sequence, you must use a vector instead of a string. *Note Character
Type::, for more information about the representation of meta and other
modifiers for keyboard input characters.
Strings are useful for holding regular expressions. You can also
match regular expressions against strings (*note Regexp Search::). The
functions `match-string' (*note Simple Match Data::) and
`replace-match' (*note Replacing Match::) are useful for decomposing
and modifying strings based on regular expression matching.
Like a buffer, a string can contain text properties for the
characters in it, as well as the characters themselves. *Note Text
Properties::. All the Lisp primitives that copy text from strings to
buffers or other strings also copy the properties of the characters
being copied.
*Note Text::, for information about functions that display strings or
copy them into buffers. *Note Character Type::, and *Note String
Type::, for information about the syntax of characters and strings.
*Note Non-ASCII Characters::, for functions to convert between text
representations and to encode and decode character codes.
The Predicates for Strings
==========================
For more information about general sequence and array predicates,
see *Note Sequences Arrays Vectors::, and *Note Arrays::.
- Function: stringp object
This function returns `t' if OBJECT is a string, `nil' otherwise.
- Function: char-or-string-p object
This function returns `t' if OBJECT is a string or a character
(i.e., an integer), `nil' otherwise.
Creating Strings
================
The following functions create strings, either from scratch, or by
putting strings together, or by taking them apart.
- Function: make-string count character
This function returns a string made up of COUNT repetitions of
CHARACTER. If COUNT is negative, an error is signaled.
(make-string 5 ?x)
=> "xxxxx"
(make-string 0 ?x)
=> ""
Other functions to compare with this one include `char-to-string'
(*note String Conversion::), `make-vector' (*note Vectors::), and
`make-list' (*note Building Lists::).
- Function: string &rest characters
This returns a string containing the characters CHARACTERS.
(string ?a ?b ?c)
=> "abc"
- Function: substring string start &optional end
This function returns a new string which consists of those
characters from STRING in the range from (and including) the
character at the index START up to (but excluding) the character
at the index END. The first character is at index zero.
(substring "abcdefg" 0 3)
=> "abc"
Here the index for `a' is 0, the index for `b' is 1, and the index
for `c' is 2. Thus, three letters, `abc', are copied from the
string `"abcdefg"'. The index 3 marks the character position up
to which the substring is copied. The character whose index is 3
is actually the fourth character in the string.
A negative number counts from the end of the string, so that -1
signifies the index of the last character of the string. For
example:
(substring "abcdefg" -3 -1)
=> "ef"
In this example, the index for `e' is -3, the index for `f' is -2,
and the index for `g' is -1. Therefore, `e' and `f' are included,
and `g' is excluded.
When `nil' is used as an index, it stands for the length of the
string. Thus,
(substring "abcdefg" -3 nil)
=> "efg"
Omitting the argument END is equivalent to specifying `nil'. It
follows that `(substring STRING 0)' returns a copy of all of
STRING.
(substring "abcdefg" 0)
=> "abcdefg"
But we recommend `copy-sequence' for this purpose (*note Sequence
Functions::).
If the characters copied from STRING have text properties, the
properties are copied into the new string also. *Note Text
Properties::.
`substring' also accepts a vector for the first argument. For
example:
(substring [a b (c) "d"] 1 3)
=> [b (c)]
A `wrong-type-argument' error is signaled if either START or END
is not an integer or `nil'. An `args-out-of-range' error is
signaled if START indicates a character following END, or if
either integer is out of range for STRING.
Contrast this function with `buffer-substring' (*note Buffer
Contents::), which returns a string containing a portion of the
text in the current buffer. The beginning of a string is at index
0, but the beginning of a buffer is at index 1.
- Function: concat &rest sequences
This function returns a new string consisting of the characters in
the arguments passed to it (along with their text properties, if
any). The arguments may be strings, lists of numbers, or vectors
of numbers; they are not themselves changed. If `concat' receives
no arguments, it returns an empty string.
(concat "abc" "-def")
=> "abc-def"
(concat "abc" (list 120 121) [122])
=> "abcxyz"
;; `nil' is an empty sequence.
(concat "abc" nil "-def")
=> "abc-def"
(concat "The " "quick brown " "fox.")
=> "The quick brown fox."
(concat)
=> ""
The `concat' function always constructs a new string that is not
`eq' to any existing string.
In Emacs versions before 21, when an argument was an integer (not a
sequence of integers), it was converted to a string of digits
making up the decimal printed representation of the integer. This
obsolete usage no longer works. The proper way to convert an
integer to its decimal printed form is with `format' (*note
Formatting Strings::) or `number-to-string' (*note String
Conversion::).
For information about other concatenation functions, see the
description of `mapconcat' in *Note Mapping Functions::, `vconcat'
in *Note Vectors::, and `append' in *Note Building Lists::.
- Function: split-string string separators
This function splits STRING into substrings at matches for the
regular expression SEPARATORS. Each match for SEPARATORS defines a
splitting point; the substrings between the splitting points are
made into a list, which is the value returned by `split-string'.
If SEPARATORS is `nil' (or omitted), the default is `"[
\f\t\n\r\v]+"'.
For example,
(split-string "Soup is good food" "o")
=> ("S" "up is g" "" "d f" "" "d")
(split-string "Soup is good food" "o+")
=> ("S" "up is g" "d f" "d")
When there is a match adjacent to the beginning or end of the
string, this does not cause a null string to appear at the
beginning or end of the list:
(split-string "out to moo" "o+")
=> ("ut t" " m")
Empty matches do count, when not adjacent to another match:
(split-string "Soup is good food" "o*")
=>("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
(split-string "Nice doggy!" "")
=>("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
Modifying Strings
=================
The most basic way to alter the contents of an existing string is
with `aset' (*note Array Functions::). `(aset STRING IDX CHAR)' stores
CHAR into STRING at index IDX. Each character occupies one or more
bytes, and if CHAR needs a different number of bytes from the character
already present at that index, `aset' signals an error.
A more powerful function is `store-substring':
- Function: store-substring string idx obj
This function alters part of the contents of the string STRING, by
storing OBJ starting at index IDX. The argument OBJ may be either
a character or a (smaller) string.
Since it is impossible to change the length of an existing string,
it is an error if OBJ doesn't fit within STRING's actual length,
or if any new character requires a different number of bytes from
the character currently present at that point in STRING.
Comparison of Characters and Strings
====================================
- Function: char-equal character1 character2
This function returns `t' if the arguments represent the same
character, `nil' otherwise. This function ignores differences in
case if `case-fold-search' is non-`nil'.
(char-equal ?x ?x)
=> t
(let ((case-fold-search nil))
(char-equal ?x ?X))
=> nil
- Function: string= string1 string2
This function returns `t' if the characters of the two strings
match exactly. Case is always significant, regardless of
`case-fold-search'.
(string= "abc" "abc")
=> t
(string= "abc" "ABC")
=> nil
(string= "ab" "ABC")
=> nil
The function `string=' ignores the text properties of the two
strings. When `equal' (*note Equality Predicates::) compares two
strings, it uses `string='.
If the strings contain non-ASCII characters, and one is unibyte
while the other is multibyte, then they cannot be equal. *Note
Text Representations::.
- Function: string-equal string1 string2
`string-equal' is another name for `string='.
- Function: string< string1 string2
This function compares two strings a character at a time. It
scans both the strings at the same time to find the first pair of
corresponding characters that do not match. If the lesser
character of these two is the character from STRING1, then STRING1
is less, and this function returns `t'. If the lesser character
is the one from STRING2, then STRING1 is greater, and this
function returns `nil'. If the two strings match entirely, the
value is `nil'.
Pairs of characters are compared according to their character
codes. Keep in mind that lower case letters have higher numeric
values in the ASCII character set than their upper case
counterparts; digits and many punctuation characters have a lower
numeric value than upper case letters. An ASCII character is less
than any non-ASCII character; a unibyte non-ASCII character is
always less than any multibyte non-ASCII character (*note Text
Representations::).
(string< "abc" "abd")
=> t
(string< "abd" "abc")
=> nil
(string< "123" "abc")
=> t
When the strings have different lengths, and they match up to the
length of STRING1, then the result is `t'. If they match up to
the length of STRING2, the result is `nil'. A string of no
characters is less than any other string.
(string< "" "abc")
=> t
(string< "ab" "abc")
=> t
(string< "abc" "")
=> nil
(string< "abc" "ab")
=> nil
(string< "" "")
=> nil
- Function: string-lessp string1 string2
`string-lessp' is another name for `string<'.
- Function: compare-strings string1 start1 end1 string2 start2 end2
&optional ignore-case
This function compares the specified part of STRING1 with the
specified part of STRING2. The specified part of STRING1 runs
from index START1 up to index END1 (`nil' means the end of the
string). The specified part of STRING2 runs from index START2 up
to index END2 (`nil' means the end of the string).
The strings are both converted to multibyte for the comparison
(*note Text Representations::) so that a unibyte string can be
equal to a multibyte string. If IGNORE-CASE is non-`nil', then
case is ignored, so that upper case letters can be equal to lower
case letters.
If the specified portions of the two strings match, the value is
`t'. Otherwise, the value is an integer which indicates how many
leading characters agree, and which string is less. Its absolute
value is one plus the number of characters that agree at the
beginning of the two strings. The sign is negative if STRING1 (or
its specified portion) is less.
- Function: assoc-ignore-case key alist
This function works like `assoc', except that KEY must be a
string, and comparison is done using `compare-strings', ignoring
case differences. *Note Association Lists::.
- Function: assoc-ignore-representation key alist
This function works like `assoc', except that KEY must be a
string, and comparison is done using `compare-strings'. Case
differences are significant.
See also `compare-buffer-substrings' in *Note Comparing Text::, for
a way to compare text in buffers. The function `string-match', which
matches a regular expression against a string, can be used for a kind
of string comparison; see *Note Regexp Search::.
Conversion of Characters and Strings
====================================
This section describes functions for conversions between characters,
strings and integers. `format' and `prin1-to-string' (*note Output
Functions::) can also convert Lisp objects into strings.
`read-from-string' (*note Input Functions::) can "convert" a string
representation of a Lisp object into an object. The functions
`string-make-multibyte' and `string-make-unibyte' convert the text
representation of a string (*note Converting Representations::).
*Note Documentation::, for functions that produce textual
descriptions of text characters and general input events
(`single-key-description' and `text-char-description'). These
functions are used primarily for making help messages.
- Function: char-to-string character
This function returns a new string containing one character,
CHARACTER. This function is semi-obsolete because the function
`string' is more general. *Note Creating Strings::.
- Function: string-to-char string
This function returns the first character in STRING. If the
string is empty, the function returns 0. The value is also 0 when
the first character of STRING is the null character, ASCII code 0.
(string-to-char "ABC")
=> 65
(string-to-char "xyz")
=> 120
(string-to-char "")
=> 0
(string-to-char "\000")
=> 0
This function may be eliminated in the future if it does not seem
useful enough to retain.
- Function: number-to-string number
This function returns a string consisting of the printed base-ten
representation of NUMBER, which may be an integer or a floating
point number. The returned value starts with a minus sign if the
argument is negative.
(number-to-string 256)
=> "256"
(number-to-string -23)
=> "-23"
(number-to-string -23.5)
=> "-23.5"
`int-to-string' is a semi-obsolete alias for this function.
See also the function `format' in *Note Formatting Strings::.
- Function: string-to-number string &optional base
This function returns the numeric value of the characters in
STRING. If BASE is non-`nil', integers are converted in that
base. If BASE is `nil', then base ten is used. Floating point
conversion always uses base ten; we have not implemented other
radices for floating point numbers, because that would be much
more work and does not seem useful. If STRING looks like an
integer but its value is too large to fit into a Lisp integer,
`string-to-number' returns a floating point result.
The parsing skips spaces and tabs at the beginning of STRING, then
reads as much of STRING as it can interpret as a number. (On some
systems it ignores other whitespace at the beginning, not just
spaces and tabs.) If the first character after the ignored
whitespace is neither a digit, nor a plus or minus sign, nor the
leading dot of a floating point number, this function returns 0.
(string-to-number "256")
=> 256
(string-to-number "25 is a perfect square.")
=> 25
(string-to-number "X256")
=> 0
(string-to-number "-4.5")
=> -4.5
(string-to-number "1e5")
=> 100000.0
`string-to-int' is an obsolete alias for this function.
Here are some other functions that can convert to or from a string:
`concat'
`concat' can convert a vector or a list into a string. *Note
Creating Strings::.
`vconcat'
`vconcat' can convert a string into a vector. *Note Vector
Functions::.
`append'
`append' can convert a string into a list. *Note Building Lists::.
Formatting Strings
==================
"Formatting" means constructing a string by substitution of computed
values at various places in a constant string. This constant string
controls how the other values are printed, as well as where they appear;
it is called a "format string".
Formatting is often useful for computing messages to be displayed.
In fact, the functions `message' and `error' provide the same
formatting feature described here; they differ from `format' only in
how they use the result of formatting.
- Function: format string &rest objects
This function returns a new string that is made by copying STRING
and then replacing any format specification in the copy with
encodings of the corresponding OBJECTS. The arguments OBJECTS are
the computed values to be formatted.
The characters in STRING, other than the format specifications,
are copied directly into the output; starting in Emacs 21, if they
have text properties, these are copied into the output also.
A format specification is a sequence of characters beginning with a
`%'. Thus, if there is a `%d' in STRING, the `format' function
replaces it with the printed representation of one of the values to be
formatted (one of the arguments OBJECTS). For example:
(format "The value of fill-column is %d." fill-column)
=> "The value of fill-column is 72."
If STRING contains more than one format specification, the format
specifications correspond to successive values from OBJECTS. Thus, the
first format specification in STRING uses the first such value, the
second format specification uses the second such value, and so on. Any
extra format specifications (those for which there are no corresponding
values) cause unpredictable behavior. Any extra values to be formatted
are ignored.
Certain format specifications require values of particular types. If
you supply a value that doesn't fit the requirements, an error is
signaled.
Here is a table of valid format specifications:
`%s'
Replace the specification with the printed representation of the
object, made without quoting (that is, using `princ', not
`prin1'--*note Output Functions::). Thus, strings are represented
by their contents alone, with no `"' characters, and symbols appear
without `\' characters.
Starting in Emacs 21, if the object is a string, its text
properties are copied into the output. The text properties of the
`%s' itself are also copied, but those of the object take priority.
If there is no corresponding object, the empty string is used.
`%S'
Replace the specification with the printed representation of the
object, made with quoting (that is, using `prin1'--*note Output
Functions::). Thus, strings are enclosed in `"' characters, and
`\' characters appear where necessary before special characters.
If there is no corresponding object, the empty string is used.
`%o'
Replace the specification with the base-eight representation of an
integer.
`%d'
Replace the specification with the base-ten representation of an
integer.
`%x'
`%X'
Replace the specification with the base-sixteen representation of
an integer. `%x' uses lower case and `%X' uses upper case.
`%c'
Replace the specification with the character which is the value
given.
`%e'
Replace the specification with the exponential notation for a
floating point number.
`%f'
Replace the specification with the decimal-point notation for a
floating point number.
`%g'
Replace the specification with notation for a floating point
number, using either exponential notation or decimal-point
notation, whichever is shorter.
`%%'
Replace the specification with a single `%'. This format
specification is unusual in that it does not use a value. For
example, `(format "%% %d" 30)' returns `"% 30"'.
Any other format character results in an `Invalid format operation'
error.
Here are several examples:
(format "The name of this buffer is %s." (buffer-name))
=> "The name of this buffer is strings.texi."
(format "The buffer object prints as %s." (current-buffer))
=> "The buffer object prints as strings.texi."
(format "The octal value of %d is %o,
and the hex value is %x." 18 18 18)
=> "The octal value of 18 is 22,
and the hex value is 12."
All the specification characters allow an optional numeric prefix
between the `%' and the character. The optional numeric prefix defines
the minimum width for the object. If the printed representation of the
object contains fewer characters than this, then it is padded. The
padding is on the left if the prefix is positive (or starts with zero)
and on the right if the prefix is negative. The padding character is
normally a space, but if the numeric prefix starts with a zero, zeros
are used for padding. Here are some examples of padding:
(format "%06d is padded on the left with zeros" 123)
=> "000123 is padded on the left with zeros"
(format "%-6d is padded on the right" 123)
=> "123 is padded on the right"
`format' never truncates an object's printed representation, no
matter what width you specify. Thus, you can use a numeric prefix to
specify a minimum spacing between columns with no risk of losing
information.
In the following three examples, `%7s' specifies a minimum width of
7. In the first case, the string inserted in place of `%7s' has only 3
letters, so 4 blank spaces are inserted for padding. In the second
case, the string `"specification"' is 13 letters wide but is not
truncated. In the third case, the padding is on the right.
(format "The word `%7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word ` foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
"specification" (length "specification"))
=> "The word `specification' actually has 13 letters in it."
(format "The word `%-7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word `foo ' actually has 3 letters in it."
Case Conversion in Lisp
=======================
The character case functions change the case of single characters or
of the contents of strings. The functions normally convert only
alphabetic characters (the letters `A' through `Z' and `a' through `z',
as well as non-ASCII letters); other characters are not altered. You
can specify a different case conversion mapping by specifying a case
table (*note Case Tables::).
These functions do not modify the strings that are passed to them as
arguments.
The examples below use the characters `X' and `x' which have ASCII
codes 88 and 120 respectively.
- Function: downcase string-or-char
This function converts a character or a string to lower case.
When the argument to `downcase' is a string, the function creates
and returns a new string in which each letter in the argument that
is upper case is converted to lower case. When the argument to
`downcase' is a character, `downcase' returns the corresponding
lower case character. This value is an integer. If the original
character is lower case, or is not a letter, then the value equals
the original character.
(downcase "The cat in the hat")
=> "the cat in the hat"
(downcase ?X)
=> 120
- Function: upcase string-or-char
This function converts a character or a string to upper case.
When the argument to `upcase' is a string, the function creates
and returns a new string in which each letter in the argument that
is lower case is converted to upper case.
When the argument to `upcase' is a character, `upcase' returns the
corresponding upper case character. This value is an integer. If
the original character is upper case, or is not a letter, then the
value returned equals the original character.
(upcase "The cat in the hat")
=> "THE CAT IN THE HAT"
(upcase ?x)
=> 88
- Function: capitalize string-or-char
This function capitalizes strings or characters. If
STRING-OR-CHAR is a string, the function creates and returns a new
string, whose contents are a copy of STRING-OR-CHAR in which each
word has been capitalized. This means that the first character of
each word is converted to upper case, and the rest are converted
to lower case.
The definition of a word is any sequence of consecutive characters
that are assigned to the word constituent syntax class in the
current syntax table (*note Syntax Class Table::).
When the argument to `capitalize' is a character, `capitalize' has
the same result as `upcase'.
(capitalize "The cat in the hat")
=> "The Cat In The Hat"
(capitalize "THE 77TH-HATTED CAT")
=> "The 77th-Hatted Cat"
(capitalize ?x)
=> 88
- Function: upcase-initials string
This function capitalizes the initials of the words in STRING,
without altering any letters other than the initials. It returns
a new string whose contents are a copy of STRING, in which each
word has had its initial letter converted to upper case.
The definition of a word is any sequence of consecutive characters
that are assigned to the word constituent syntax class in the
current syntax table (*note Syntax Class Table::).
(upcase-initials "The CAT in the hAt")
=> "The CAT In The HAt"
*Note Text Comparison::, for functions that compare strings; some of
them ignore case differences, or can optionally ignore case differences.
The Case Table
==============
You can customize case conversion by installing a special "case
table". A case table specifies the mapping between upper case and lower
case letters. It affects both the case conversion functions for Lisp
objects (see the previous section) and those that apply to text in the
buffer (*note Case Changes::). Each buffer has a case table; there is
also a standard case table which is used to initialize the case table
of new buffers.
A case table is a char-table (*note Char-Tables::) whose subtype is
`case-table'. This char-table maps each character into the
corresponding lower case character. It has three extra slots, which
hold related tables:
UPCASE
The upcase table maps each character into the corresponding upper
case character.
CANONICALIZE
The canonicalize table maps all of a set of case-related characters
into a particular member of that set.
EQUIVALENCES
The equivalences table maps each one of a set of case-related
characters into the next character in that set.
In simple cases, all you need to specify is the mapping to
lower-case; the three related tables will be calculated automatically
from that one.
For some languages, upper and lower case letters are not in
one-to-one correspondence. There may be two different lower case
letters with the same upper case equivalent. In these cases, you need
to specify the maps for both lower case and upper case.
The extra table CANONICALIZE maps each character to a canonical
equivalent; any two characters that are related by case-conversion have
the same canonical equivalent character. For example, since `a' and
`A' are related by case-conversion, they should have the same canonical
equivalent character (which should be either `a' for both of them, or
`A' for both of them).
The extra table EQUIVALENCES is a map that cyclicly permutes each
equivalence class (of characters with the same canonical equivalent).
(For ordinary ASCII, this would map `a' into `A' and `A' into `a', and
likewise for each set of equivalent characters.)
When you construct a case table, you can provide `nil' for
CANONICALIZE; then Emacs fills in this slot from the lower case and
upper case mappings. You can also provide `nil' for EQUIVALENCES; then
Emacs fills in this slot from CANONICALIZE. In a case table that is
actually in use, those components are non-`nil'. Do not try to specify
EQUIVALENCES without also specifying CANONICALIZE.
Here are the functions for working with case tables:
- Function: case-table-p object
This predicate returns non-`nil' if OBJECT is a valid case table.
- Function: set-standard-case-table table
This function makes TABLE the standard case table, so that it will
be used in any buffers created subsequently.
- Function: standard-case-table
This returns the standard case table.
- Function: current-case-table
This function returns the current buffer's case table.
- Function: set-case-table table
This sets the current buffer's case table to TABLE.
The following three functions are convenient subroutines for packages
that define non-ASCII character sets. They modify the specified case
table CASE-TABLE; they also modify the standard syntax table. *Note
Syntax Tables::. Normally you would use these functions to change the
standard case table.
- Function: set-case-syntax-pair uc lc case-table
This function specifies a pair of corresponding letters, one upper
case and one lower case.
- Function: set-case-syntax-delims l r case-table
This function makes characters L and R a matching pair of
case-invariant delimiters.
- Function: set-case-syntax char syntax case-table
This function makes CHAR case-invariant, with syntax SYNTAX.
- Command: describe-buffer-case-table
This command displays a description of the contents of the current
buffer's case table.
Lists
*****
A "list" represents a sequence of zero or more elements (which may
be any Lisp objects). The important difference between lists and
vectors is that two or more lists can share part of their structure; in
addition, you can insert or delete elements in a list without copying
the whole list.
Lists and Cons Cells
====================
Lists in Lisp are not a primitive data type; they are built up from
"cons cells". A cons cell is a data object that represents an ordered
pair. That is, it has two slots, and each slot "holds", or "refers
to", some Lisp object. One slot is known as the CAR, and the other is
known as the CDR. (These names are traditional; see *Note Cons Cell
Type::.) CDR is pronounced "could-er."
We say that "the CAR of this cons cell is" whatever object its CAR
slot currently holds, and likewise for the CDR.
A list is a series of cons cells "chained together," so that each
cell refers to the next one. There is one cons cell for each element of
the list. By convention, the CARs of the cons cells hold the elements
of the list, and the CDRs are used to chain the list: the CDR slot of
each cons cell refers to the following cons cell. The CDR of the last
cons cell is `nil'. This asymmetry between the CAR and the CDR is
entirely a matter of convention; at the level of cons cells, the CAR
and CDR slots have the same characteristics.
Because most cons cells are used as part of lists, the phrase "list
structure" has come to mean any structure made out of cons cells.
The symbol `nil' is considered a list as well as a symbol; it is the
list with no elements. For convenience, the symbol `nil' is considered
to have `nil' as its CDR (and also as its CAR).
The CDR of any nonempty list L is a list containing all the elements
of L except the first.
Lists as Linked Pairs of Boxes
==============================
A cons cell can be illustrated as a pair of boxes. The first box
represents the CAR and the second box represents the CDR. Here is an
illustration of the two-element list, `(tulip lily)', made from two
cons cells:
--------------- ---------------
| car | cdr | | car | cdr |
| tulip | o---------->| lily | nil |
| | | | | |
--------------- ---------------
Each pair of boxes represents a cons cell. Each box "refers to",
"points to" or "holds" a Lisp object. (These terms are synonymous.)
The first box, which describes the CAR of the first cons cell, contains
the symbol `tulip'. The arrow from the CDR box of the first cons cell
to the second cons cell indicates that the CDR of the first cons cell
is the second cons cell.
The same list can be illustrated in a different sort of box notation
like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> tulip --> lily
Here is a more complex illustration, showing the three-element list,
`((pine needles) oak maple)', the first element of which is a
two-element list:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| --> oak --> maple
|
| --- --- --- ---
--> | | |--> | | |--> nil
--- --- --- ---
| |
| |
--> pine --> needles
The same list represented in the first box notation looks like this:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
*Note Cons Cell Type::, for the read and print syntax of cons cells
and lists, and for more "box and arrow" illustrations of lists.
Predicates on Lists
===================
The following predicates test whether a Lisp object is an atom, is a
cons cell or is a list, or whether it is the distinguished object
`nil'. (Many of these predicates can be defined in terms of the
others, but they are used so often that it is worth having all of them.)
- Function: consp object
This function returns `t' if OBJECT is a cons cell, `nil'
otherwise. `nil' is not a cons cell, although it _is_ a list.
- Function: atom object
This function returns `t' if OBJECT is an atom, `nil' otherwise.
All objects except cons cells are atoms. The symbol `nil' is an
atom and is also a list; it is the only Lisp object that is both.
(atom OBJECT) == (not (consp OBJECT))
- Function: listp object
This function returns `t' if OBJECT is a cons cell or `nil'.
Otherwise, it returns `nil'.
(listp '(1))
=> t
(listp '())
=> t
- Function: nlistp object
This function is the opposite of `listp': it returns `t' if OBJECT
is not a list. Otherwise, it returns `nil'.
(listp OBJECT) == (not (nlistp OBJECT))
- Function: null object
This function returns `t' if OBJECT is `nil', and returns `nil'
otherwise. This function is identical to `not', but as a matter
of clarity we use `null' when OBJECT is considered a list and
`not' when it is considered a truth value (see `not' in *Note
Combining Conditions::).
(null '(1))
=> nil
(null '())
=> t
Accessing Elements of Lists
===========================
- Function: car cons-cell
This function returns the value referred to by the first slot of
the cons cell CONS-CELL. Expressed another way, this function
returns the CAR of CONS-CELL.
As a special case, if CONS-CELL is `nil', then `car' is defined to
return `nil'; therefore, any list is a valid argument for `car'.
An error is signaled if the argument is not a cons cell or `nil'.
(car '(a b c))
=> a
(car '())
=> nil
- Function: cdr cons-cell
This function returns the value referred to by the second slot of
the cons cell CONS-CELL. Expressed another way, this function
returns the CDR of CONS-CELL.
As a special case, if CONS-CELL is `nil', then `cdr' is defined to
return `nil'; therefore, any list is a valid argument for `cdr'.
An error is signaled if the argument is not a cons cell or `nil'.
(cdr '(a b c))
=> (b c)
(cdr '())
=> nil
- Function: car-safe object
This function lets you take the CAR of a cons cell while avoiding
errors for other data types. It returns the CAR of OBJECT if
OBJECT is a cons cell, `nil' otherwise. This is in contrast to
`car', which signals an error if OBJECT is not a list.
(car-safe OBJECT)
==
(let ((x OBJECT))
(if (consp x)
(car x)
nil))
- Function: cdr-safe object
This function lets you take the CDR of a cons cell while avoiding
errors for other data types. It returns the CDR of OBJECT if
OBJECT is a cons cell, `nil' otherwise. This is in contrast to
`cdr', which signals an error if OBJECT is not a list.
(cdr-safe OBJECT)
==
(let ((x OBJECT))
(if (consp x)
(cdr x)
nil))
- Macro: pop listname
This macro is a way of examining the CAR of a list, and taking it
off the list, all at once. It is new in Emacs 21.
It operates on the list which is stored in the symbol LISTNAME.
It removes this element from the list by setting LISTNAME to the
CDR of its old value--but it also returns the CAR of that list,
which is the element being removed.
x
=> (a b c)
(pop x)
=> a
x
=> (b c)
- Function: nth n list
This function returns the Nth element of LIST. Elements are
numbered starting with zero, so the CAR of LIST is element number
zero. If the length of LIST is N or less, the value is `nil'.
If N is negative, `nth' returns the first element of LIST.
(nth 2 '(1 2 3 4))
=> 3
(nth 10 '(1 2 3 4))
=> nil
(nth -3 '(1 2 3 4))
=> 1
(nth n x) == (car (nthcdr n x))
The function `elt' is similar, but applies to any kind of sequence.
For historical reasons, it takes its arguments in the opposite
order. *Note Sequence Functions::.
- Function: nthcdr n list
This function returns the Nth CDR of LIST. In other words, it
skips past the first N links of LIST and returns what follows.
If N is zero or negative, `nthcdr' returns all of LIST. If the
length of LIST is N or less, `nthcdr' returns `nil'.
(nthcdr 1 '(1 2 3 4))
=> (2 3 4)
(nthcdr 10 '(1 2 3 4))
=> nil
(nthcdr -3 '(1 2 3 4))
=> (1 2 3 4)
- Function: last list &optional n
This function returns the last link of LIST. The `car' of this
link is the list's last element. If LIST is null, `nil' is
returned. If N is non-nil the N-th-to-last link is returned
instead, or the whole LIST if N is bigger than LIST's length.
- Function: safe-length list
This function returns the length of LIST, with no risk of either
an error or an infinite loop.
If LIST is not really a list, `safe-length' returns 0. If LIST is
circular, it returns a finite value which is at least the number
of distinct elements.
The most common way to compute the length of a list, when you are not
worried that it may be circular, is with `length'. *Note Sequence
Functions::.
- Function: caar cons-cell
This is the same as `(car (car CONS-CELL))'.
- Function: cadr cons-cell
This is the same as `(car (cdr CONS-CELL))' or `(nth 1 CONS-CELL)'.
- Function: cdar cons-cell
This is the same as `(cdr (car CONS-CELL))'.
- Function: cddr cons-cell
This is the same as `(cdr (cdr CONS-CELL))' or `(nthcdr 2
CONS-CELL)'.
- Function: butlast x &optional n
This function returns the list X with the last element, or the
last N elements, removed. If N is greater than zero it makes a
copy of the list so as not to damage the original list. In
general, `(append (butlast X N) (last X N))' will return a list
equal to X.
- Function: nbutlast x &optional n
This is a version of `butlast' that works by destructively
modifying the `cdr' of the appropriate element, rather than making
a copy of the list.
Building Cons Cells and Lists
=============================
Many functions build lists, as lists reside at the very heart of
Lisp. `cons' is the fundamental list-building function; however, it is
interesting to note that `list' is used more times in the source code
for Emacs than `cons'.
- Function: cons object1 object2
This function is the fundamental function used to build new list
structure. It creates a new cons cell, making OBJECT1 the CAR,
and OBJECT2 the CDR. It then returns the new cons cell. The
arguments OBJECT1 and OBJECT2 may be any Lisp objects, but most
often OBJECT2 is a list.
(cons 1 '(2))
=> (1 2)
(cons 1 '())
=> (1)
(cons 1 2)
=> (1 . 2)
`cons' is often used to add a single element to the front of a
list. This is called "consing the element onto the list". (1)
For example:
(setq list (cons newelt list))
Note that there is no conflict between the variable named `list'
used in this example and the function named `list' described below;
any symbol can serve both purposes.
- Macro: push newelt listname
This macro provides an alternative way to write `(setq LISTNAME
(cons NEWELT LISTNAME))'. It is new in Emacs 21.
(setq l '(a b))
=> (a b)
(push 'c l)
=> (c a b)
l
=> (c a b)
- Function: list &rest objects
This function creates a list with OBJECTS as its elements. The
resulting list is always `nil'-terminated. If no OBJECTS are
given, the empty list is returned.
(list 1 2 3 4 5)
=> (1 2 3 4 5)
(list 1 2 '(3 4 5) 'foo)
=> (1 2 (3 4 5) foo)
(list)
=> nil
- Function: make-list length object
This function creates a list of LENGTH elements, in which each
element is OBJECT. Compare `make-list' with `make-string' (*note
Creating Strings::).
(make-list 3 'pigs)
=> (pigs pigs pigs)
(make-list 0 'pigs)
=> nil
(setq l (make-list 3 '(a b))
=> ((a b) (a b) (a b))
(eq (car l) (cadr l))
=> t
- Function: append &rest sequences
This function returns a list containing all the elements of
SEQUENCES. The SEQUENCES may be lists, vectors, bool-vectors, or
strings, but the last one should usually be a list. All arguments
except the last one are copied, so none of the arguments is
altered. (See `nconc' in *Note Rearrangement::, for a way to join
lists with no copying.)
More generally, the final argument to `append' may be any Lisp
object. The final argument is not copied or converted; it becomes
the CDR of the last cons cell in the new list. If the final
argument is itself a list, then its elements become in effect
elements of the result list. If the final element is not a list,
the result is a "dotted list" since its final CDR is not `nil' as
required in a true list.
The `append' function also allows integers as arguments. It
converts them to strings of digits, making up the decimal print
representation of the integer, and then uses the strings instead
of the original integers. *Don't use this feature; we plan to
eliminate it. If you already use this feature, change your
programs now!* The proper way to convert an integer to a decimal
number in this way is with `format' (*note Formatting Strings::)
or `number-to-string' (*note String Conversion::).
Here is an example of using `append':
(setq trees '(pine oak))
=> (pine oak)
(setq more-trees (append '(maple birch) trees))
=> (maple birch pine oak)
trees
=> (pine oak)
more-trees
=> (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
=> t
You can see how `append' works by looking at a box diagram. The
variable `trees' is set to the list `(pine oak)' and then the variable
`more-trees' is set to the list `(maple birch pine oak)'. However, the
variable `trees' continues to refer to the original list:
more-trees trees
| |
| --- --- --- --- -> --- --- --- ---
--> | | |--> | | |--> | | |--> | | |--> nil
--- --- --- --- --- --- --- ---
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
`append'. As a consequence of this, a final `nil' argument forces a
copy of the previous argument:
trees
=> (pine oak)
(setq wood (append trees nil))
=> (pine oak)
wood
=> (pine oak)
(eq wood trees)
=> nil
This once was the usual way to copy a list, before the function
`copy-sequence' was invented. *Note Sequences Arrays Vectors::.
Here we show the use of vectors and strings as arguments to `append':
(append [a b] "cd" nil)
=> (a b 99 100)
With the help of `apply' (*note Calling Functions::), we can append
all the lists in a list of lists:
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
If no SEQUENCES are given, `nil' is returned:
(append)
=> nil
Here are some examples where the final argument is not a list:
(append '(x y) 'z)
=> (x y . z)
(append '(x y) [z])
=> (x y . [z])
The second example shows that when the final argument is a sequence but
not a list, the sequence's elements do not become elements of the
resulting list. Instead, the sequence becomes the final CDR, like any
other non-list final argument.
- Function: reverse list
This function creates a new list whose elements are the elements of
LIST, but in reverse order. The original argument LIST is _not_
altered.
(setq x '(1 2 3 4))
=> (1 2 3 4)
(reverse x)
=> (4 3 2 1)
x
=> (1 2 3 4)
- Function: remq object list
This function returns a copy of LIST, with all elements removed
which are `eq' to OBJECT. The letter `q' in `remq' says that it
uses `eq' to compare OBJECT against the elements of `list'.
(setq sample-list '(a b c a b c))
=> (a b c a b c)
(remq 'a sample-list)
=> (b c b c)
sample-list
=> (a b c a b c)
The function `delq' offers a way to perform this operation
destructively. See *Note Sets And Lists::.
---------- Footnotes ----------
(1) There is no strictly equivalent way to add an element to the end
of a list. You can use `(append LISTNAME (list NEWELT))', which
creates a whole new list by copying LISTNAME and adding NEWELT to its
end. Or you can use `(nconc LISTNAME (list NEWELT))', which modifies
LISTNAME by following all the CDRs and then replacing the terminating
`nil'. Compare this to adding an element to the beginning of a list
with `cons', which neither copies nor modifies the list.
Modifying Existing List Structure
=================================
You can modify the CAR and CDR contents of a cons cell with the
primitives `setcar' and `setcdr'. We call these "destructive"
operations because they change existing list structure.
Common Lisp note: Common Lisp uses functions `rplaca' and `rplacd'
to alter list structure; they change structure the same way as
`setcar' and `setcdr', but the Common Lisp functions return the
cons cell while `setcar' and `setcdr' return the new CAR or CDR.
Altering List Elements with `setcar'
------------------------------------
Changing the CAR of a cons cell is done with `setcar'. When used on
a list, `setcar' replaces one element of a list with a different
element.
- Function: setcar cons object
This function stores OBJECT as the new CAR of CONS, replacing its
previous CAR. In other words, it changes the CAR slot of CONS to
refer to OBJECT. It returns the value OBJECT. For example:
(setq x '(1 2))
=> (1 2)
(setcar x 4)
=> 4
x
=> (4 2)
When a cons cell is part of the shared structure of several lists,
storing a new CAR into the cons changes one element of each of these
lists. Here is an example:
;; Create two lists that are partly shared.
(setq x1 '(a b c))
=> (a b c)
(setq x2 (cons 'z (cdr x1)))
=> (z b c)
;; Replace the CAR of a shared link.
(setcar (cdr x1) 'foo)
=> foo
x1 ; Both lists are changed.
=> (a foo c)
x2
=> (z foo c)
;; Replace the CAR of a link that is not shared.
(setcar x1 'baz)
=> baz
x1 ; Only one list is changed.
=> (baz foo c)
x2
=> (z foo c)
Here is a graphical depiction of the shared structure of the two
lists in the variables `x1' and `x2', showing why replacing `b' changes
them both:
--- --- --- --- --- ---
x1---> | | |----> | | |--> | | |--> nil
--- --- --- --- --- ---
| --> | |
| | | |
--> a | --> b --> c
|
--- --- |
x2--> | | |--
--- ---
|
|
--> z
Here is an alternative form of box diagram, showing the same
relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
Altering the CDR of a List
--------------------------
The lowest-level primitive for modifying a CDR is `setcdr':
- Function: setcdr cons object
This function stores OBJECT as the new CDR of CONS, replacing its
previous CDR. In other words, it changes the CDR slot of CONS to
refer to OBJECT. It returns the value OBJECT.
Here is an example of replacing the CDR of a list with a different
list. All but the first element of the list are removed in favor of a
different sequence of elements. The first element is unchanged,
because it resides in the CAR of the list, and is not reached via the
CDR.
(setq x '(1 2 3))
=> (1 2 3)
(setcdr x '(4))
=> (4)
x
=> (1 4)
You can delete elements from the middle of a list by altering the
CDRs of the cons cells in the list. For example, here we delete the
second element, `b', from the list `(a b c)', by changing the CDR of
the first cons cell:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cdr (cdr x1)))
=> (c)
x1
=> (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element `b', still
exists and its CAR is still `b', but it no longer forms part of this
list.
It is equally easy to insert a new element by changing CDRs:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cons 'd (cdr x1)))
=> (d b c)
x1
=> (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Functions that Rearrange Lists
------------------------------
Here are some functions that rearrange lists "destructively" by
modifying the CDRs of their component cons cells. We call these
functions "destructive" because they chew up the original lists passed
to them as arguments, relinking their cons cells to form a new list that
is the returned value.
See `delq', in *Note Sets And Lists::, for another function that
modifies cons cells.
- Function: nconc &rest lists
This function returns a list containing all the elements of LISTS.
Unlike `append' (*note Building Lists::), the LISTS are _not_
copied. Instead, the last CDR of each of the LISTS is changed to
refer to the following list. The last of the LISTS is not
altered. For example:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x '(4 5))
=> (1 2 3 4 5)
x
=> (1 2 3 4 5)
Since the last argument of `nconc' is not itself modified, it is
reasonable to use a constant list, such as `'(4 5)', as in the
above example. For the same reason, the last argument need not be
a list:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x 'z)
=> (1 2 3 . z)
x
=> (1 2 3 . z)
However, the other arguments (all but the last) must be lists.
A common pitfall is to use a quoted constant list as a non-last
argument to `nconc'. If you do this, your program will change
each time you run it! Here is what happens:
(defun add-foo (x) ; We want this function to add
(nconc '(foo) x)) ; `foo' to the front of its arg.
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo)) x))
(setq xx (add-foo '(1 2))) ; It seems to work.
=> (foo 1 2)
(setq xy (add-foo '(3 4))) ; What happened?
=> (foo 1 2 3 4)
(eq xx xy)
=> t
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
- Function: nreverse list
This function reverses the order of the elements of LIST. Unlike
`reverse', `nreverse' alters its argument by reversing the CDRs in
the cons cells forming the list. The cons cell that used to be
the last one in LIST becomes the first cons cell of the value.
For example:
(setq x '(a b c))
=> (a b c)
x
=> (a b c)
(nreverse x)
=> (c b a)
;; The cons cell that was first is now last.
x
=> (a)
To avoid confusion, we usually store the result of `nreverse' back
in the same variable which held the original list:
(setq x (nreverse x))
Here is the `nreverse' of our favorite example, `(a b c)',
presented graphically:
Original list head: Reversed list:
------------- ------------- ------------
| car | cdr | | car | cdr | | car | cdr |
| a | nil |<-- | b | o |<-- | c | o |
| | | | | | | | | | | | |
------------- | --------- | - | -------- | -
| | | |
------------- ------------
- Function: sort list predicate
This function sorts LIST stably, though destructively, and returns
the sorted list. It compares elements using PREDICATE. A stable
sort is one in which elements with equal sort keys maintain their
relative order before and after the sort. Stability is important
when successive sorts are used to order elements according to
different criteria.
The argument PREDICATE must be a function that accepts two
arguments. It is called with two elements of LIST. To get an
increasing order sort, the PREDICATE should return `t' if the
first element is "less than" the second, or `nil' if not.
The comparison function PREDICATE must give reliable results for
any given pair of arguments, at least within a single call to
`sort'. It must be "antisymmetric"; that is, if A is less than B,
B must not be less than A. It must be "transitive"--that is, if A
is less than B, and B is less than C, then A must be less than C.
If you use a comparison function which does not meet these
requirements, the result of `sort' is unpredictable.
The destructive aspect of `sort' is that it rearranges the cons
cells forming LIST by changing CDRs. A nondestructive sort
function would create new cons cells to store the elements in their
sorted order. If you wish to make a sorted copy without
destroying the original, copy it first with `copy-sequence' and
then sort.
Sorting does not change the CARs of the cons cells in LIST; the
cons cell that originally contained the element `a' in LIST still
has `a' in its CAR after sorting, but it now appears in a
different position in the list due to the change of CDRs. For
example:
(setq nums '(1 3 2 6 5 4 0))
=> (1 3 2 6 5 4 0)
(sort nums '<)
=> (0 1 2 3 4 5 6)
nums
=> (1 2 3 4 5 6)
*Warning*: Note that the list in `nums' no longer contains 0; this
is the same cons cell that it was before, but it is no longer the
first one in the list. Don't assume a variable that formerly held
the argument now holds the entire sorted list! Instead, save the
result of `sort' and use that. Most often we store the result
back into the variable that held the original list:
(setq nums (sort nums '<))
*Note Sorting::, for more functions that perform sorting. See
`documentation' in *Note Accessing Documentation::, for a useful
example of `sort'.
Using Lists as Sets
===================
A list can represent an unordered mathematical set--simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use `append' (as
long as you don't mind having duplicate elements). Other useful
functions for sets include `memq' and `delq', and their `equal'
versions, `member' and `delete'.
Common Lisp note: Common Lisp has functions `union' (which avoids
duplicate elements) and `intersection' for set operations, but GNU
Emacs Lisp does not have them. You can write them in Lisp if you
wish.
- Function: memq object list
This function tests to see whether OBJECT is a member of LIST. If
it is, `memq' returns a list starting with the first occurrence of
OBJECT. Otherwise, it returns `nil'. The letter `q' in `memq'
says that it uses `eq' to compare OBJECT against the elements of
the list. For example:
(memq 'b '(a b c b a))
=> (b c b a)
(memq '(2) '((1) (2))) ; `(2)' and `(2)' are not `eq'.
=> nil
- Function: member-ignore-case object list
This function is like `member', except that it ignores differences
in letter-case and text representation: upper-case and lower-case
letters are treated as equal, and unibyte strings are converted to
multibyte prior to comparison.
- Function: delq object list
This function destructively removes all elements `eq' to OBJECT
from LIST. The letter `q' in `delq' says that it uses `eq' to
compare OBJECT against the elements of the list, like `memq' and
`remq'.
When `delq' deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list,
removing it involves changing the CDRs (*note Setcdr::).
(setq sample-list '(a b c (4)))
=> (a b c (4))
(delq 'a sample-list)
=> (b c (4))
sample-list
=> (a b c (4))
(delq 'c sample-list)
=> (a b (4))
sample-list
=> (a b (4))
Note that `(delq 'c sample-list)' modifies `sample-list' to splice
out the third element, but `(delq 'a sample-list)' does not splice
anything--it just returns a shorter list. Don't assume that a variable
which formerly held the argument LIST now has fewer elements, or that
it still holds the original list! Instead, save the result of `delq'
and use that. Most often we store the result back into the variable
that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the `(4)' that `delq' attempts to match
and the `(4)' in the `sample-list' are not `eq':
(delq '(4) sample-list)
=> (a c (4))
The following two functions are like `memq' and `delq' but use
`equal' rather than `eq' to compare elements. *Note Equality
Predicates::.
- Function: member object list
The function `member' tests to see whether OBJECT is a member of
LIST, comparing members with OBJECT using `equal'. If OBJECT is a
member, `member' returns a list starting with its first occurrence
in LIST. Otherwise, it returns `nil'.
Compare this with `memq':
(member '(2) '((1) (2))) ; `(2)' and `(2)' are `equal'.
=> ((2))
(memq '(2) '((1) (2))) ; `(2)' and `(2)' are not `eq'.
=> nil
;; Two strings with the same contents are `equal'.
(member "foo" '("foo" "bar"))
=> ("foo" "bar")
- Function: delete object sequence
If `sequence' is a list, this function destructively removes all
elements `equal' to OBJECT from SEQUENCE. For lists, `delete' is
to `delq' as `member' is to `memq': it uses `equal' to compare
elements with OBJECT, like `member'; when it finds an element that
matches, it removes the element just as `delq' would.
If `sequence' is a vector or string, `delete' returns a copy of
`sequence' with all elements `equal' to `object' removed.
For example:
(delete '(2) '((2) (1) (2)))
=> ((1))
(delete '(2) [(2) (1) (2)])
=> [(1)]
- Function: remove object sequence
This function is the non-destructive counterpart of `delete'. If
returns a copy of `sequence', a list, vector, or string, with
elements `equal' to `object' removed. For example:
(remove '(2) '((2) (1) (2)))
=> ((1))
(remove '(2) [(2) (1) (2)])
=> [(1)]
Common Lisp note: The functions `member', `delete' and `remove' in
GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The
Common Lisp versions do not use `equal' to compare elements.
See also the function `add-to-list', in *Note Setting Variables::,
for another way to add an element to a list stored in a variable.
Association Lists
=================
An "association list", or "alist" for short, records a mapping from
keys to values. It is a list of cons cells called "associations": the
CAR of each cons cell is the "key", and the CDR is the "associated
value".(1)
Here is an example of an alist. The key `pine' is associated with
the value `cones'; the key `oak' is associated with `acorns'; and the
key `maple' is associated with `seeds'.
((pine . cones)
(oak . acorns)
(maple . seeds))
The associated values in an alist may be any Lisp objects; so may the
keys. For example, in the following alist, the symbol `a' is
associated with the number `1', and the string `"b"' is associated with
the _list_ `(2 3)', which is the CDR of the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated
value in the CAR of the CDR of the element. Here is an example of such
an alist:
((rose red) (lily white) (buttercup yellow))
Here we regard `red' as the value associated with `rose'. One
advantage of this kind of alist is that you can store other related
information--even a list of other items--in the CDR of the CDR. One
disadvantage is that you cannot use `rassq' (see below) to find the
element containing a given value. When neither of these considerations
is important, the choice is a matter of taste, as long as you are
consistent about it for any given alist.
Note that the same alist shown above could be regarded as having the
associated value in the CDR of the element; the value associated with
`rose' would be the list `(red)'.
Association lists are often used to record information that you might
otherwise keep on a stack, since new associations may be added easily to
the front of the list. When searching an association list for an
association with a given key, the first one found is returned, if there
is more than one.
In Emacs Lisp, it is _not_ an error if an element of an association
list is not a cons cell. The alist search functions simply ignore such
elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several
respects. A property list behaves like an association list in which
each key can occur only once. *Note Property Lists::, for a comparison
of property lists and association lists.
- Function: assoc key alist
This function returns the first association for KEY in ALIST. It
compares KEY against the alist elements using `equal' (*note
Equality Predicates::). It returns `nil' if no association in
ALIST has a CAR `equal' to KEY. For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
=> ((pine . cones) (oak . acorns) (maple . seeds))
(assoc 'oak trees)
=> (oak . acorns)
(cdr (assoc 'oak trees))
=> acorns
(assoc 'birch trees)
=> nil
Here is another example, in which the keys and values are not
symbols:
(setq needles-per-cluster
'((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine")))
(cdr (assoc 3 needles-per-cluster))
=> ("Pitch Pine")
(cdr (assoc 2 needles-per-cluster))
=> ("Austrian Pine" "Red Pine")
The functions `assoc-ignore-representation' and `assoc-ignore-case'
are much like `assoc' except using `compare-strings' to do the
comparison. *Note Text Comparison::.
- Function: rassoc value alist
This function returns the first association with value VALUE in
ALIST. It returns `nil' if no association in ALIST has a CDR
`equal' to VALUE.
`rassoc' is like `assoc' except that it compares the CDR of each
ALIST association instead of the CAR. You can think of this as
"reverse `assoc'", finding the key for a given value.
- Function: assq key alist
This function is like `assoc' in that it returns the first
association for KEY in ALIST, but it makes the comparison using
`eq' instead of `equal'. `assq' returns `nil' if no association
in ALIST has a CAR `eq' to KEY. This function is used more often
than `assoc', since `eq' is faster than `equal' and most alists
use symbols as keys. *Note Equality Predicates::.
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
=> ((pine . cones) (oak . acorns) (maple . seeds))
(assq 'pine trees)
=> (pine . cones)
On the other hand, `assq' is not usually useful in alists where the
keys may not be symbols:
(setq leaves
'(("simple leaves" . oak)
("compound leaves" . horsechestnut)))
(assq "simple leaves" leaves)
=> nil
(assoc "simple leaves" leaves)
=> ("simple leaves" . oak)
- Function: rassq value alist
This function returns the first association with value VALUE in
ALIST. It returns `nil' if no association in ALIST has a CDR `eq'
to VALUE.
`rassq' is like `assq' except that it compares the CDR of each
ALIST association instead of the CAR. You can think of this as
"reverse `assq'", finding the key for a given value.
For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
(rassq 'acorns trees)
=> (oak . acorns)
(rassq 'spores trees)
=> nil
Note that `rassq' cannot search for a value stored in the CAR of
the CDR of an element:
(setq colors '((rose red) (lily white) (buttercup yellow)))
(rassq 'white colors)
=> nil
In this case, the CDR of the association `(lily white)' is not the
symbol `white', but rather the list `(white)'. This becomes
clearer if the association is written in dotted pair notation:
(lily white) == (lily . (white))
- Function: assoc-default key alist &optional test default
This function searches ALIST for a match for KEY. For each
element of ALIST, it compares the element (if it is an atom) or
the element's CAR (if it is a cons) against KEY, by calling TEST
with two arguments: the element or its CAR, and KEY. The
arguments are passed in that order so that you can get useful
results using `string-match' with an alist that contains regular
expressions (*note Regexp Search::). If TEST is omitted or `nil',
`equal' is used for comparison.
If an alist element matches KEY by this criterion, then
`assoc-default' returns a value based on this element. If the
element is a cons, then the value is the element's CDR.
Otherwise, the return value is DEFAULT.
If no alist element matches KEY, `assoc-default' returns `nil'.
- Function: copy-alist alist
This function returns a two-level deep copy of ALIST: it creates a
new copy of each association, so that you can alter the
associations of the new alist without changing the old one.
(setq needles-per-cluster
'((2 . ("Austrian Pine" "Red Pine"))
(3 . ("Pitch Pine"))
(5 . ("White Pine"))))
=>
((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine"))
(setq copy (copy-alist needles-per-cluster))
=>
((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine"))
(eq needles-per-cluster copy)
=> nil
(equal needles-per-cluster copy)
=> t
(eq (car needles-per-cluster) (car copy))
=> nil
(cdr (car (cdr needles-per-cluster)))
=> ("Pitch Pine")
(eq (cdr (car (cdr needles-per-cluster)))
(cdr (car (cdr copy))))
=> t
This example shows how `copy-alist' makes it possible to change
the associations of one copy without affecting the other:
(setcdr (assq 3 copy) '("Martian Vacuum Pine"))
(cdr (assq 3 needles-per-cluster))
=> ("Pitch Pine")
- Function: assq-delete-all key alist
This function deletes from ALIST all the elements whose CAR is
`eq' to KEY. It returns ALIST, modified in this way. Note that
it modifies the original list structure of ALIST.
(assq-delete-all 'foo
'((foo 1) (bar 2) (foo 3) (lose 4)))
=> ((bar 2) (lose 4))
---------- Footnotes ----------
(1) This usage of "key" is not related to the term "key sequence";
it means a value used to look up an item in a table. In this case, the
table is the alist, and the alist associations are the items.
Sequences, Arrays, and Vectors
******************************
Recall that the "sequence" type is the union of two other Lisp
types: lists and arrays. In other words, any list is a sequence, and
any array is a sequence. The common property that all sequences have is
that each is an ordered collection of elements.
An "array" is a single primitive object that has a slot for each of
its elements. All the elements are accessible in constant time, but
the length of an existing array cannot be changed. Strings, vectors,
char-tables and bool-vectors are the four types of arrays.
A list is a sequence of elements, but it is not a single primitive
object; it is made of cons cells, one cell per element. Finding the
Nth element requires looking through N cons cells, so elements farther
from the beginning of the list take longer to access. But it is
possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
The elements of vectors and lists may be any Lisp objects. The
elements of strings are all characters.
Sequences
=========
In Emacs Lisp, a "sequence" is either a list or an array. The
common property of all sequences is that they are ordered collections of
elements. This section describes functions that accept any kind of
sequence.
- Function: sequencep object
Returns `t' if OBJECT is a list, vector, or string, `nil'
otherwise.
- Function: length sequence
This function returns the number of elements in SEQUENCE. If
SEQUENCE is a cons cell that is not a list (because the final CDR
is not `nil'), a `wrong-type-argument' error is signaled.
*Note List Elements::, for the related function `safe-length'.
(length '(1 2 3))
=> 3
(length ())
=> 0
(length "foobar")
=> 6
(length [1 2 3])
=> 3
(length (make-bool-vector 5 nil))
=> 5
- Function: elt sequence index
This function returns the element of SEQUENCE indexed by INDEX.
Legitimate values of INDEX are integers ranging from 0 up to one
less than the length of SEQUENCE. If SEQUENCE is a list, then
out-of-range values of INDEX return `nil'; otherwise, they trigger
an `args-out-of-range' error.
(elt [1 2 3 4] 2)
=> 3
(elt '(1 2 3 4) 2)
=> 3
;; We use `string' to show clearly which character `elt' returns.
(string (elt "1234" 2))
=> "3"
(elt [1 2 3 4] 4)
error--> Args out of range: [1 2 3 4], 4
(elt [1 2 3 4] -1)
error--> Args out of range: [1 2 3 4], -1
This function generalizes `aref' (*note Array Functions::) and
`nth' (*note List Elements::).
- Function: copy-sequence sequence
Returns a copy of SEQUENCE. The copy is the same type of object
as the original sequence, and it has the same elements in the same
order.
Storing a new element into the copy does not affect the original
SEQUENCE, and vice versa. However, the elements of the new
sequence are not copies; they are identical (`eq') to the elements
of the original. Therefore, changes made within these elements, as
found via the copied sequence, are also visible in the original
sequence.
If the sequence is a string with text properties, the property
list in the copy is itself a copy, not shared with the original's
property list. However, the actual values of the properties are
shared. *Note Text Properties::.
See also `append' in *Note Building Lists::, `concat' in *Note
Creating Strings::, and `vconcat' in *Note Vectors::, for other
ways to copy sequences.
(setq bar '(1 2))
=> (1 2)
(setq x (vector 'foo bar))
=> [foo (1 2)]
(setq y (copy-sequence x))
=> [foo (1 2)]
(eq x y)
=> nil
(equal x y)
=> t
(eq (elt x 1) (elt y 1))
=> t
;; Replacing an element of one sequence.
(aset x 0 'quux)
x => [quux (1 2)]
y => [foo (1 2)]
;; Modifying the inside of a shared element.
(setcar (aref x 1) 69)
x => [quux (69 2)]
y => [foo (69 2)]
Arrays
======
An "array" object has slots that hold a number of other Lisp
objects, called the elements of the array. Any element of an array may
be accessed in constant time. In contrast, an element of a list
requires access time that is proportional to the position of the element
in the list.
Emacs defines four types of array, all one-dimensional: "strings",
"vectors", "bool-vectors" and "char-tables". A vector is a general
array; its elements can be any Lisp objects. A string is a specialized
array; its elements must be characters. Each type of array has its own
read syntax. *Note String Type::, and *Note Vector Type::.
All four kinds of array share these characteristics:
* The first element of an array has index zero, the second element
has index 1, and so on. This is called "zero-origin" indexing.
For example, an array of four elements has indices 0, 1, 2, and 3.
* The length of the array is fixed once you create it; you cannot
change the length of an existing array.
* The array is a constant, for evaluation--in other words, it
evaluates to itself.
* The elements of an array may be referenced or changed with the
functions `aref' and `aset', respectively (*note Array
Functions::).
When you create an array, other than a char-table, you must specify
its length. You cannot specify the length of a char-table, because that
is determined by the range of character codes.
In principle, if you want an array of text characters, you could use
either a string or a vector. In practice, we always choose strings for
such applications, for four reasons:
* They occupy one-fourth the space of a vector of the same elements.
* Strings are printed in a way that shows the contents more clearly
as text.
* Strings can hold text properties. *Note Text Properties::.
* Many of the specialized editing and I/O facilities of Emacs accept
only strings. For example, you cannot insert a vector of
characters into a buffer the way you can insert a string. *Note
Strings and Characters::.
By contrast, for an array of keyboard input characters (such as a key
sequence), a vector may be necessary, because many keyboard input
characters are outside the range that will fit in a string. *Note Key
Sequence Input::.
Functions that Operate on Arrays
================================
In this section, we describe the functions that accept all types of
arrays.
- Function: arrayp object
This function returns `t' if OBJECT is an array (i.e., a vector, a
string, a bool-vector or a char-table).
(arrayp [a])
=> t
(arrayp "asdf")
=> t
(arrayp (syntax-table)) ;; A char-table.
=> t
- Function: aref array index
This function returns the INDEXth element of ARRAY. The first
element is at index zero.
(setq primes [2 3 5 7 11 13])
=> [2 3 5 7 11 13]
(aref primes 4)
=> 11
(aref "abcdefg" 1)
=> 98 ; `b' is ASCII code 98.
See also the function `elt', in *Note Sequence Functions::.
- Function: aset array index object
This function sets the INDEXth element of ARRAY to be OBJECT. It
returns OBJECT.
(setq w [foo bar baz])
=> [foo bar baz]
(aset w 0 'fu)
=> fu
w
=> [fu bar baz]
(setq x "asdfasfd")
=> "asdfasfd"
(aset x 3 ?Z)
=> 90
x
=> "asdZasfd"
If ARRAY is a string and OBJECT is not a character, a
`wrong-type-argument' error results. The function converts a
unibyte string to multibyte if necessary to insert a character.
- Function: fillarray array object
This function fills the array ARRAY with OBJECT, so that each
element of ARRAY is OBJECT. It returns ARRAY.
(setq a [a b c d e f g])
=> [a b c d e f g]
(fillarray a 0)
=> [0 0 0 0 0 0 0]
a
=> [0 0 0 0 0 0 0]
(setq s "When in the course")
=> "When in the course"
(fillarray s ?-)
=> "------------------"
If ARRAY is a string and OBJECT is not a character, a
`wrong-type-argument' error results.
The general sequence functions `copy-sequence' and `length' are
often useful for objects known to be arrays. *Note Sequence
Functions::.
Vectors
=======
Arrays in Lisp, like arrays in most languages, are blocks of memory
whose elements can be accessed in constant time. A "vector" is a
general-purpose array of specified length; its elements can be any Lisp
objects. (By contrast, a string can hold only characters as elements.)
Vectors in Emacs are used for obarrays (vectors of symbols), and as part
of keymaps (vectors of commands). They are also used internally as part
of the representation of a byte-compiled function; if you print such a
function, you will see a vector in it.
In Emacs Lisp, the indices of the elements of a vector start from
zero and count up from there.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols `a', `b' and `a' is
printed as `[a b a]'. You can write vectors in the same way in Lisp
input.
A vector, like a string or a number, is considered a constant for
evaluation: the result of evaluating it is the same vector. This does
not evaluate or even examine the elements of the vector. *Note
Self-Evaluating Forms::.
Here are examples illustrating these principles:
(setq avector [1 two '(three) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(eval avector)
=> [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
=> t
Functions for Vectors
=====================
Here are some functions that relate to vectors:
- Function: vectorp object
This function returns `t' if OBJECT is a vector.
(vectorp [a])
=> t
(vectorp "asdf")
=> nil
- Function: vector &rest objects
This function creates and returns a vector whose elements are the
arguments, OBJECTS.
(vector 'foo 23 [bar baz] "rats")
=> [foo 23 [bar baz] "rats"]
(vector)
=> []
- Function: make-vector length object
This function returns a new vector consisting of LENGTH elements,
each initialized to OBJECT.
(setq sleepy (make-vector 9 'Z))
=> [Z Z Z Z Z Z Z Z Z]
- Function: vconcat &rest sequences
This function returns a new vector containing all the elements of
the SEQUENCES. The arguments SEQUENCES may be any kind of arrays,
including lists, vectors, or strings. If no SEQUENCES are given,
an empty vector is returned.
The value is a newly constructed vector that is not `eq' to any
existing vector.
(setq a (vconcat '(A B C) '(D E F)))
=> [A B C D E F]
(eq a (vconcat a))
=> nil
(vconcat)
=> []
(vconcat [A B C] "aa" '(foo (6 7)))
=> [A B C 97 97 foo (6 7)]
The `vconcat' function also allows byte-code function objects as
arguments. This is a special feature to make it easy to access
the entire contents of a byte-code function object. *Note
Byte-Code Objects::.
The `vconcat' function also allows integers as arguments. It
converts them to strings of digits, making up the decimal print
representation of the integer, and then uses the strings instead
of the original integers. *Don't use this feature; we plan to
eliminate it. If you already use this feature, change your
programs now!* The proper way to convert an integer to a decimal
number in this way is with `format' (*note Formatting Strings::)
or `number-to-string' (*note String Conversion::).
For other concatenation functions, see `mapconcat' in *Note
Mapping Functions::, `concat' in *Note Creating Strings::, and
`append' in *Note Building Lists::.
The `append' function provides a way to convert a vector into a list
with the same elements (*note Building Lists::):
(setq avector [1 two (quote (three)) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(append avector nil)
=> (1 two (quote (three)) "four" [five])
Char-Tables
===========
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with `aref' and `aset', as with any array. In addition, a
char-table can have "extra slots" to hold additional data not
associated with particular character codes. Char-tables are constants
when evaluated.
Each char-table has a "subtype" which is a symbol. The subtype has
two purposes: to distinguish char-tables meant for different uses, and
to control the number of extra slots. For example, display tables are
char-tables with `display-table' as the subtype, and syntax tables are
char-tables with `syntax-table' as the subtype. A valid subtype must
have a `char-table-extra-slots' property which is an integer between 0
and 10. This integer specifies the number of "extra slots" in the
char-table.
A char-table can have a "parent", which is another char-table. If
it does, then whenever the char-table specifies `nil' for a particular
character C, it inherits the value specified in the parent. In other
words, `(aref CHAR-TABLE C)' returns the value from the parent of
CHAR-TABLE if CHAR-TABLE itself specifies `nil'.
A char-table can also have a "default value". If so, then `(aref
CHAR-TABLE C)' returns the default value whenever the char-table does
not specify any other non-`nil' value.
- Function: make-char-table subtype &optional init
Return a newly created char-table, with subtype SUBTYPE. Each
element is initialized to INIT, which defaults to `nil'. You
cannot alter the subtype of a char-table after the char-table is
created.
There is no argument to specify the length of the char-table,
because all char-tables have room for any valid character code as
an index.
- Function: char-table-p object
This function returns `t' if OBJECT is a char-table, otherwise
`nil'.
- Function: char-table-subtype char-table
This function returns the subtype symbol of CHAR-TABLE.
- Function: set-char-table-default char-table new-default
This function sets the default value of CHAR-TABLE to NEW-DEFAULT.
There is no special function to access the default value of a
char-table. To do that, use `(char-table-range CHAR-TABLE nil)'.
- Function: char-table-parent char-table
This function returns the parent of CHAR-TABLE. The parent is
always either `nil' or another char-table.
- Function: set-char-table-parent char-table new-parent
This function sets the parent of CHAR-TABLE to NEW-PARENT.
- Function: char-table-extra-slot char-table n
This function returns the contents of extra slot N of CHAR-TABLE.
The number of extra slots in a char-table is determined by its
subtype.
- Function: set-char-table-extra-slot char-table n value
This function stores VALUE in extra slot N of CHAR-TABLE.
A char-table can specify an element value for a single character
code; it can also specify a value for an entire character set.
- Function: char-table-range char-table range
This returns the value specified in CHAR-TABLE for a range of
characters RANGE. Here are the possibilities for RANGE:
`nil'
Refers to the default value.
CHAR
Refers to the element for character CHAR (supposing CHAR is a
valid character code).
CHARSET
Refers to the value specified for the whole character set
CHARSET (*note Character Sets::).
GENERIC-CHAR
A generic character stands for a character set; specifying
the generic character as argument is equivalent to specifying
the character set name. *Note Splitting Characters::, for a
description of generic characters.
- Function: set-char-table-range char-table range value
This function sets the value in CHAR-TABLE for a range of
characters RANGE. Here are the possibilities for RANGE:
`nil'
Refers to the default value.
`t'
Refers to the whole range of character codes.
CHAR
Refers to the element for character CHAR (supposing CHAR is a
valid character code).
CHARSET
Refers to the value specified for the whole character set
CHARSET (*note Character Sets::).
GENERIC-CHAR
A generic character stands for a character set; specifying
the generic character as argument is equivalent to specifying
the character set name. *Note Splitting Characters::, for a
description of generic characters.
- Function: map-char-table function char-table
This function calls FUNCTION for each element of CHAR-TABLE.
FUNCTION is called with two arguments, a key and a value. The key
is a possible RANGE argument for `char-table-range'--either a
valid character or a generic character--and the value is
`(char-table-range CHAR-TABLE KEY)'.
Overall, the key-value pairs passed to FUNCTION describe all the
values stored in CHAR-TABLE.
The return value is always `nil'; to make this function useful,
FUNCTION should have side effects. For example, here is how to
examine each element of the syntax table:
(let (accumulator)
(map-char-table
#'(lambda (key value)
(setq accumulator
(cons (list key value) accumulator)))
(syntax-table))
accumulator)
=>
((475008 nil) (474880 nil) (474752 nil) (474624 nil)
... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3)))
Bool-vectors
============
A bool-vector is much like a vector, except that it stores only the
values `t' and `nil'. If you try to store any non-`nil' value into an
element of the bool-vector, the effect is to store `t' there. As with
all arrays, bool-vector indices start from 0, and the length cannot be
changed once the bool-vector is created. Bool-vectors are constants
when evaluated.
There are two special functions for working with bool-vectors; aside
from that, you manipulate them with same functions used for other kinds
of arrays.
- Function: make-bool-vector length initial
Return a new bool-vector of LENGTH elements, each one initialized
to INITIAL.
- Function: bool-vector-p object
This returns `t' if OBJECT is a bool-vector, and `nil' otherwise.
Here is an example of creating, examining, and updating a
bool-vector. Note that the printed form represents up to 8 boolean
values as a single character.
(setq bv (make-bool-vector 5 t))
=> #&5"^_"
(aref bv 1)
=> t
(aset bv 3 nil)
=> nil
bv
=> #&5"^W"
These results make sense because the binary codes for control-_ and
control-W are 11111 and 10111, respectively.
Hash Tables
***********
A hash table is a very fast kind of lookup table, somewhat like an
alist in that it maps keys to corresponding values. It differs from an
alist in these ways:
* Lookup in a hash table is extremely fast for large tables--in
fact, the time required is essentially _independent_ of how many
elements are stored in the table. For smaller tables (a few tens
of elements) alists may still be faster because hash tables have a
more-or-less constant overhead.
* The correspondences in a hash table are in no particular order.
* There is no way to share structure between two hash tables, the
way two alists can share a common tail.
Emacs Lisp (starting with Emacs 21) provides a general-purpose hash
table data type, along with a series of functions for operating on them.
Hash tables have no read syntax, and print in hash notation, like this:
(make-hash-table)
=> #<hash-table 'eql nil 0/65 0x83af980>
(The term "hash notation" refers to the initial `#' character--*note
Printed Representation::--and has nothing to do with the term "hash
table.")
Obarrays are also a kind of hash table, but they are a different type
of object and are used only for recording interned symbols (*note
Creating Symbols::).
Creating Hash Tables
====================
The principal function for creating a hash table is
`make-hash-table'.
- Function: make-hash-table &rest keyword-args
This function creates a new hash table according to the specified
arguments. The arguments should consist of alternating keywords
(particular symbols recognized specially) and values corresponding
to them.
Several keywords make sense in `make-hash-table', but the only two
that you really need to know about are `:test' and `:weakness'.
`:test TEST'
This specifies the method of key lookup for this hash table.
The default is `eql'; `eq' and `equal' are other alternatives:
`eql'
Keys which are numbers are "the same" if they are equal
in value; otherwise, two distinct objects are never "the
same".
`eq'
Any two distinct Lisp objects are "different" as keys.
`equal'
Two Lisp objects are "the same", as keys, if they are
equal according to `equal'.
You can use `define-hash-table-test' (*note Defining Hash::)
to define additional possibilities for TEST.
`:weakness WEAK'
The weakness of a hash table specifies whether the presence
of a key or value in the hash table preserves it from garbage
collection.
The value, WEAK, must be one of `nil', `key', `value',
`key-or-value', `key-and-value', or `t' which is an alias for
`key-and-value'. If WEAK is `key' then the hash table does
not prevent its keys from being collected as garbage (if they
are not referenced anywhere else); if a particular key does
get collected, the corresponding association is removed from
the hash table.
If WEAK is `value', then the hash table does not prevent
values from being collected as garbage (if they are not
referenced anywhere else); if a particular value does get
collected, the corresponding association is removed from the
hash table.
If WEAK is `key-or-value' or `t', the hash table does not
protect either keys or values from garbage collection; if
either one is collected as garbage, the association is
removed.
If WEAK is `key-and-value', associations are removed from the
hash table when both their key and value would be collected as
garbage, again not considering references to the key and
value from weak hash tables.
The default for WEAK is `nil', so that all keys and values
referenced in the hash table are preserved from garbage
collection. If WEAK is `t', neither keys nor values are
protected (that is, both are weak).
`:size SIZE'
This specifies a hint for how many associations you plan to
store in the hash table. If you know the approximate number,
you can make things a little more efficient by specifying it
this way. If you specify too small a size, the hash table
will grow automatically when necessary, but doing that takes
some extra time.
The default size is 65.
`:rehash-size REHASH-SIZE'
When you add an association to a hash table and the table is
"full," it grows automatically. This value specifies how to
make the hash table larger, at that time.
If REHASH-SIZE is an integer, it should be positive, and the
hash table grows by adding that much to the nominal size. If
REHASH-SIZE is a floating point number, it had better be
greater than 1, and the hash table grows by multiplying the
old size by that number.
The default value is 1.5.
`:rehash-threshold THRESHOLD'
This specifies the criterion for when the hash table is
"full." The value, THRESHOLD, should be a positive floating
point number, no greater than 1. The hash table is "full"
whenever the actual number of entries exceeds this fraction
of the nominal size. The default for THRESHOLD is 0.8.
- Function: makehash &optional test
This is equivalent to `make-hash-table', but with a different style
argument list. The argument TEST specifies the method of key
lookup.
If you want to specify other parameters, you should use
`make-hash-table'.
Hash Table Access
=================
This section describes the functions for accessing and storing
associations in a hash table.
- Function: gethash key table &optional default
This function looks up KEY in TABLE, and returns its associated
VALUE--or DEFAULT, if KEY has no association in TABLE.
- Function: puthash key value table
This function enters an association for KEY in TABLE, with value
VALUE. If KEY already has an association in TABLE, VALUE replaces
the old associated value.
- Function: remhash key table
This function removes the association for KEY from TABLE, if there
is one. If KEY has no association, `remhash' does nothing.
- Function: clrhash table
This function removes all the associations from hash table TABLE,
so that it becomes empty. This is also called "clearing" the hash
table.
- Function: maphash function table
This function calls FUNCTION once for each of the associations in
TABLE. The function FUNCTION should accept two arguments--a KEY
listed in TABLE, and its associated VALUE.
Defining Hash Comparisons
=========================
You can define new methods of key lookup by means of
`define-hash-table-test'. In order to use this feature, you need to
understand how hash tables work, and what a "hash code" means.
You can think of a hash table conceptually as a large array of many
slots, each capable of holding one association. To look up a key,
`gethash' first computes an integer, the hash code, from the key. It
reduces this integer modulo the length of the array, to produce an
index in the array. Then it looks in that slot, and if necessary in
other nearby slots, to see if it has found the key being sought.
Thus, to define a new method of key lookup, you need to specify both
a function to compute the hash code from a key, and a function to
compare two keys directly.
- Function: define-hash-table-test name test-fn hash-fn
This function defines a new hash table test, named NAME.
After defining NAME in this way, you can use it as the TEST
argument in `make-hash-table'. When you do that, the hash table
will use TEST-FN to compare key values, and HASH-FN to compute a
"hash code" from a key value.
The function TEST-FN should accept two arguments, two keys, and
return non-`nil' if they are considered "the same."
The function HASH-FN should accept one argument, a key, and return
an integer that is the "hash code" of that key. For good results,
the function should use the whole range of integer values for hash
codes, including negative integers.
The specified functions are stored in the property list of NAME
under the property `hash-table-test'; the property value's form is
`(TEST-FN HASH-FN)'.
- Function: sxhash obj
This function returns a hash code for Lisp object OBJ. This is an
integer which reflects the contents of OBJ and the other Lisp
objects it points to.
If two objects OBJ1 and OBJ2 are equal, then `(sxhash OBJ1)' and
`(sxhash OBJ2)' are the same integer.
If the two objects are not equal, the values returned by `sxhash'
are usually different, but not always; but once in a rare while, by
luck, you will encounter two distinct-looking objects that give
the same result from `sxhash'.
This example creates a hash table whose keys are strings that are
compared case-insensitively.
(defun case-fold-string= (a b)
(compare-strings a nil nil b nil nil t))
(defun case-fold-string-hash (a)
(sxhash (upcase a)))
(define-hash-table-test 'case-fold 'case-fold-string=
'case-fold-string-hash))
(make-hash-table :test 'case-fold)
Here is how you could define a hash table test equivalent to the
predefined test value `equal'. The keys can be any Lisp object, and
equal-looking objects are considered the same key.
(define-hash-table-test 'contents-hash 'equal 'sxhash)
(make-hash-table :test 'contents-hash)
Other Hash Table Functions
==========================
Here are some other functions for working with hash tables.
- Function: hash-table-p table
This returns non-`nil' if TABLE is a hash table object.
- Function: copy-hash-table table
This function creates and returns a copy of TABLE. Only the table
itself is copied--the keys and values are shared.
- Function: hash-table-count table
This function returns the actual number of entries in TABLE.
- Function: hash-table-test table
This returns the TEST value that was given when TABLE was created,
to specify how to hash and compare keys. See `make-hash-table'
(*note Creating Hash::).
- Function: hash-table-weakness table
This function returns the WEAK value that was specified for hash
table TABLE.
- Function: hash-table-rehash-size table
This returns the rehash size of TABLE.
- Function: hash-table-rehash-threshold table
This returns the rehash threshold of TABLE.
- Function: hash-table-size table
This returns the current nominal size of TABLE.
Symbols
*******
A "symbol" is an object with a unique name. This chapter describes
symbols, their components, their property lists, and how they are
created and interned. Separate chapters describe the use of symbols as
variables and as function names; see *Note Variables::, and *Note
Functions::. For the precise read syntax for symbols, see *Note Symbol
Type::.
You can test whether an arbitrary Lisp object is a symbol with
`symbolp':
- Function: symbolp object
This function returns `t' if OBJECT is a symbol, `nil' otherwise.
Symbol Components
=================
Each symbol has four components (or "cells"), each of which
references another object:
Print name
The "print name cell" holds a string that names the symbol for
reading and printing. See `symbol-name' in *Note Creating
Symbols::.
Value
The "value cell" holds the current value of the symbol as a
variable. When a symbol is used as a form, the value of the form
is the contents of the symbol's value cell. See `symbol-value' in
*Note Accessing Variables::.
Function
The "function cell" holds the function definition of the symbol.
When a symbol is used as a function, its function definition is
used in its place. This cell is also used to make a symbol stand
for a keymap or a keyboard macro, for editor command execution.
Because each symbol has separate value and function cells,
variables names and function names do not conflict. See
`symbol-function' in *Note Function Cells::.
Property list
The "property list cell" holds the property list of the symbol.
See `symbol-plist' in *Note Property Lists::.
The print name cell always holds a string, and cannot be changed.
The other three cells can be set individually to any specified Lisp
object.
The print name cell holds the string that is the name of the symbol.
Since symbols are represented textually by their names, it is important
not to have two symbols with the same name. The Lisp reader ensures
this: every time it reads a symbol, it looks for an existing symbol with
the specified name before it creates a new one. (In GNU Emacs Lisp,
this lookup uses a hashing algorithm and an obarray; see *Note Creating
Symbols::.)
The value cell holds the symbol's value as a variable (*note
Variables::). That is what you get if you evaluate the symbol as a
Lisp expression (*note Evaluation::). Any Lisp object is a legitimate
value. Certain symbols have values that cannot be changed; these
include `nil' and `t', and any symbol whose name starts with `:' (those
are called "keywords"). *Note Constant Variables::.
We often refer to "the function `foo'" when we really mean the
function stored in the function cell of the symbol `foo'. We make the
distinction explicit only when necessary. In normal usage, the
function cell usually contains a function (*note Functions::) or a
macro (*note Macros::), as that is what the Lisp interpreter expects to
see there (*note Evaluation::). Keyboard macros (*note Keyboard
Macros::), keymaps (*note Keymaps::) and autoload objects (*note
Autoloading::) are also sometimes stored in the function cells of
symbols.
The property list cell normally should hold a correctly formatted
property list (*note Property Lists::), as a number of functions expect
to see a property list there.
The function cell or the value cell may be "void", which means that
the cell does not reference any object. (This is not the same thing as
holding the symbol `void', nor the same as holding the symbol `nil'.)
Examining a function or value cell that is void results in an error,
such as `Symbol's value as variable is void'.
The four functions `symbol-name', `symbol-value', `symbol-plist',
and `symbol-function' return the contents of the four cells of a
symbol. Here as an example we show the contents of the four cells of
the symbol `buffer-file-name':
(symbol-name 'buffer-file-name)
=> "buffer-file-name"
(symbol-value 'buffer-file-name)
=> "/gnu/elisp/symbols.texi"
(symbol-plist 'buffer-file-name)
=> (variable-documentation 29529)
(symbol-function 'buffer-file-name)
=> #<subr buffer-file-name>
Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list `(variable-documentation
29529)' which tells the documentation functions where to find the
documentation string for the variable `buffer-file-name' in the
`DOC-VERSION' file. (29529 is the offset from the beginning of the
`DOC-VERSION' file to where that documentation string begins--see *Note
Documentation Basics::.) The function cell contains the function for
returning the name of the file. `buffer-file-name' names a primitive
function, which has no read syntax and prints in hash notation (*note
Primitive Function Type::). A symbol naming a function written in Lisp
would have a lambda expression (or a byte-code object) in this cell.
Defining Symbols
================
A "definition" in Lisp is a special form that announces your
intention to use a certain symbol in a particular way. In Emacs Lisp,
you can define a symbol as a variable, or define it as a function (or
macro), or both independently.
A definition construct typically specifies a value or meaning for the
symbol for one kind of use, plus documentation for its meaning when used
in this way. Thus, when you define a symbol as a variable, you can
supply an initial value for the variable, plus documentation for the
variable.
`defvar' and `defconst' are special forms that define a symbol as a
global variable. They are documented in detail in *Note Defining
Variables::. For defining user option variables that can be
customized, use `defcustom' (*note Customization::).
`defun' defines a symbol as a function, creating a lambda expression
and storing it in the function cell of the symbol. This lambda
expression thus becomes the function definition of the symbol. (The
term "function definition", meaning the contents of the function cell,
is derived from the idea that `defun' gives the symbol its definition
as a function.) `defsubst' and `defalias' are two other ways of
defining a function. *Note Functions::.
`defmacro' defines a symbol as a macro. It creates a macro object
and stores it in the function cell of the symbol. Note that a given
symbol can be a macro or a function, but not both at once, because both
macro and function definitions are kept in the function cell, and that
cell can hold only one Lisp object at any given time. *Note Macros::.
In Emacs Lisp, a definition is not required in order to use a symbol
as a variable or function. Thus, you can make a symbol a global
variable with `setq', whether you define it first or not. The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
_intended_ to be used as variables, or as functions. In addition,
utilities such as `etags' and `make-docfile' recognize definitions, and
add appropriate information to tag tables and the `DOC-VERSION' file.
*Note Accessing Documentation::.
Creating and Interning Symbols
==============================
To understand how symbols are created in GNU Emacs Lisp, you must
know how Lisp reads them. Lisp must ensure that it finds the same
symbol every time it reads the same set of characters. Failure to do
so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters
of the name. Then it "hashes" those characters to find an index in a
table called an "obarray". Hashing is an efficient method of looking
something up. For example, instead of searching a telephone book cover
to cover when looking up Jan Jones, you start with the J's and go from
there. That is a simple version of hashing. Each element of the
obarray is a "bucket" which holds all the symbols with a given hash
code; to look for a given name, it is sufficient to look through all
the symbols in the bucket for that name's hash code. (The same idea is
used for general Emacs hash tables, but they are a different data type;
see *Note Hash Tables::.)
If a symbol with the desired name is found, the reader uses that
symbol. If the obarray does not contain a symbol with that name, the
reader makes a new symbol and adds it to the obarray. Finding or adding
a symbol with a certain name is called "interning" it, and the symbol
is then called an "interned symbol".
Interning ensures that each obarray has just one symbol with any
particular name. Other like-named symbols may exist, but not in the
same obarray. Thus, the reader gets the same symbols for the same
names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes
other programs need to do it. For example, after the `M-x' command
obtains the command name as a string using the minibuffer, it then
interns the string, to get the interned symbol with that name.
No obarray contains all symbols; in fact, some symbols are not in any
obarray. They are called "uninterned symbols". An uninterned symbol
has the same four cells as other symbols; however, the only way to gain
access to it is by finding it in some other object or as the value of a
variable.
Creating an uninterned symbol is useful in generating Lisp code,
because an uninterned symbol used as a variable in the code you generate
cannot clash with any variables used in other Lisp programs.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
find all the symbols in an obarray except using `mapatoms' (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, so you can create an obarray
with `(make-vector LENGTH 0)'. *This is the only valid way to create
an obarray.* Prime numbers as lengths tend to result in good hashing;
lengths one less than a power of two are also good.
*Do not try to put symbols in an obarray yourself.* This does not
work--only `intern' can enter a symbol in an obarray properly.
Common Lisp note: In Common Lisp, a single symbol may be interned
in several obarrays.
Most of the functions below take a name and sometimes an obarray as
arguments. A `wrong-type-argument' error is signaled if the name is
not a string, or if the obarray is not a vector.
- Function: symbol-name symbol
This function returns the string that is SYMBOL's name. For
example:
(symbol-name 'foo)
=> "foo"
*Warning:* Changing the string by substituting characters does
change the name of the symbol, but fails to update the obarray, so
don't do it!
- Function: make-symbol name
This function returns a newly-allocated, uninterned symbol whose
name is NAME (which must be a string). Its value and function
definition are void, and its property list is `nil'. In the
example below, the value of `sym' is not `eq' to `foo' because it
is a distinct uninterned symbol whose name is also `foo'.
(setq sym (make-symbol "foo"))
=> foo
(eq sym 'foo)
=> nil
- Function: intern name &optional obarray
This function returns the interned symbol whose name is NAME. If
there is no such symbol in the obarray OBARRAY, `intern' creates a
new one, adds it to the obarray, and returns it. If OBARRAY is
omitted, the value of the global variable `obarray' is used.
(setq sym (intern "foo"))
=> foo
(eq sym 'foo)
=> t
(setq sym1 (intern "foo" other-obarray))
=> foo
(eq sym1 'foo)
=> nil
Common Lisp note: In Common Lisp, you can intern an existing symbol
in an obarray. In Emacs Lisp, you cannot do this, because the
argument to `intern' must be a string, not a symbol.
- Function: intern-soft name &optional obarray
This function returns the symbol in OBARRAY whose name is NAME, or
`nil' if OBARRAY has no symbol with that name. Therefore, you can
use `intern-soft' to test whether a symbol with a given name is
already interned. If OBARRAY is omitted, the value of the global
variable `obarray' is used.
The argument NAME may also be a symbol; in that case, the function
returns NAME if NAME is interned in the specified obarray, and
otherwise `nil'.
(intern-soft "frazzle") ; No such symbol exists.
=> nil
(make-symbol "frazzle") ; Create an uninterned one.
=> frazzle
(intern-soft "frazzle") ; That one cannot be found.
=> nil
(setq sym (intern "frazzle")) ; Create an interned one.
=> frazzle
(intern-soft "frazzle") ; That one can be found!
=> frazzle
(eq sym 'frazzle) ; And it is the same one.
=> t
- Variable: obarray
This variable is the standard obarray for use by `intern' and
`read'.
- Function: mapatoms function &optional obarray
This function calls FUNCTION once with each symbol in the obarray
OBARRAY. Then it returns `nil'. If OBARRAY is omitted, it
defaults to the value of `obarray', the standard obarray for
ordinary symbols.
(setq count 0)
=> 0
(defun count-syms (s)
(setq count (1+ count)))
=> count-syms
(mapatoms 'count-syms)
=> nil
count
=> 1871
See `documentation' in *Note Accessing Documentation::, for another
example using `mapatoms'.
- Function: unintern symbol &optional obarray
This function deletes SYMBOL from the obarray OBARRAY. If
`symbol' is not actually in the obarray, `unintern' does nothing.
If OBARRAY is `nil', the current obarray is used.
If you provide a string instead of a symbol as SYMBOL, it stands
for a symbol name. Then `unintern' deletes the symbol (if any) in
the obarray which has that name. If there is no such symbol,
`unintern' does nothing.
If `unintern' does delete a symbol, it returns `t'. Otherwise it
returns `nil'.
Property Lists
==============
A "property list" ("plist" for short) is a list of paired elements
stored in the property list cell of a symbol. Each of the pairs
associates a property name (usually a symbol) with a property or value.
Property lists are generally used to record information about a
symbol, such as its documentation as a variable, the name of the file
where it was defined, or perhaps even the grammatical class of the
symbol (representing a word) in a language-understanding system.
Character positions in a string or buffer can also have property
lists. *Note Text Properties::.
The property names and values in a property list can be any Lisp
objects, but the names are usually symbols. Property list functions
compare the property names using `eq'. Here is an example of a
property list, found on the symbol `progn' when the compiler is loaded:
(lisp-indent-function 0 byte-compile byte-compile-progn)
Here `lisp-indent-function' and `byte-compile' are property names, and
the other two elements are the corresponding values.
Property Lists and Association Lists
------------------------------------
Association lists (*note Association Lists::) are very similar to
property lists. In contrast to association lists, the order of the
pairs in the property list is not significant since the property names
must be distinct.
Property lists are better than association lists for attaching
information to various Lisp function names or variables. If your
program keeps all of its associations in one association list, it will
typically need to search that entire list each time it checks for an
association. This could be slow. By contrast, if you keep the same
information in the property lists of the function names or variables
themselves, each search will scan only the length of one property list,
which is usually short. This is why the documentation for a variable is
recorded in a property named `variable-documentation'. The byte
compiler likewise uses properties to record those functions needing
special treatment.
However, association lists have their own advantages. Depending on
your application, it may be faster to add an association to the front of
an association list than to update a property. All properties for a
symbol are stored in the same property list, so there is a possibility
of a conflict between different uses of a property name. (For this
reason, it is a good idea to choose property names that are probably
unique, such as by beginning the property name with the program's usual
name-prefix for variables and functions.) An association list may be
used like a stack where associations are pushed on the front of the list
and later discarded; this is not possible with a property list.
Property List Functions for Symbols
-----------------------------------
- Function: symbol-plist symbol
This function returns the property list of SYMBOL.
- Function: setplist symbol plist
This function sets SYMBOL's property list to PLIST. Normally,
PLIST should be a well-formed property list, but this is not
enforced.
(setplist 'foo '(a 1 b (2 3) c nil))
=> (a 1 b (2 3) c nil)
(symbol-plist 'foo)
=> (a 1 b (2 3) c nil)
For symbols in special obarrays, which are not used for ordinary
purposes, it may make sense to use the property list cell in a
nonstandard fashion; in fact, the abbrev mechanism does so (*note
Abbrevs::).
- Function: get symbol property
This function finds the value of the property named PROPERTY in
SYMBOL's property list. If there is no such property, `nil' is
returned. Thus, there is no distinction between a value of `nil'
and the absence of the property.
The name PROPERTY is compared with the existing property names
using `eq', so any object is a legitimate property.
See `put' for an example.
- Function: put symbol property value
This function puts VALUE onto SYMBOL's property list under the
property name PROPERTY, replacing any previous property value.
The `put' function returns VALUE.
(put 'fly 'verb 'transitive)
=>'transitive
(put 'fly 'noun '(a buzzing little bug))
=> (a buzzing little bug)
(get 'fly 'verb)
=> transitive
(symbol-plist 'fly)
=> (verb transitive noun (a buzzing little bug))
Property Lists Outside Symbols
------------------------------
These functions are useful for manipulating property lists that are
stored in places other than symbols:
- Function: plist-get plist property
This returns the value of the PROPERTY property stored in the
property list PLIST. For example,
(plist-get '(foo 4) 'foo)
=> 4
- Function: plist-put plist property value
This stores VALUE as the value of the PROPERTY property in the
property list PLIST. It may modify PLIST destructively, or it may
construct a new list structure without altering the old. The
function returns the modified property list, so you can store that
back in the place where you got PLIST. For example,
(setq my-plist '(bar t foo 4))
=> (bar t foo 4)
(setq my-plist (plist-put my-plist 'foo 69))
=> (bar t foo 69)
(setq my-plist (plist-put my-plist 'quux '(a)))
=> (bar t foo 69 quux (a))
You could define `put' in terms of `plist-put' as follows:
(defun put (symbol prop value)
(setplist symbol
(plist-put (symbol-plist symbol) prop value)))
- Function: plist-member plist property
This returns non-`nil' if PLIST contains the given PROPERTY.
Unlike `plist-get', this allows you to distinguish between a
missing property and a property with the value `nil'. The value
is actually the tail of PLIST whose `car' is PROPERTY.
Evaluation
**********
The "evaluation" of expressions in Emacs Lisp is performed by the
"Lisp interpreter"--a program that receives a Lisp object as input and
computes its "value as an expression". How it does this depends on the
data type of the object, according to rules described in this chapter.
The interpreter runs automatically to evaluate portions of your
program, but can also be called explicitly via the Lisp primitive
function `eval'.
Introduction to Evaluation
==========================
The Lisp interpreter, or evaluator, is the program that computes the
value of an expression that is given to it. When a function written in
Lisp is called, the evaluator computes the value of the function by
evaluating the expressions in the function body. Thus, running any
Lisp program really means running the Lisp interpreter.
How the evaluator handles an object depends primarily on the data
type of the object.
A Lisp object that is intended for evaluation is called an
"expression" or a "form". The fact that expressions are data objects
and not merely text is one of the fundamental differences between
Lisp-like languages and typical programming languages. Any object can
be evaluated, but in practice only numbers, symbols, lists and strings
are evaluated very often.
It is very common to read a Lisp expression and then evaluate the
expression, but reading and evaluation are separate activities, and
either can be performed alone. Reading per se does not evaluate
anything; it converts the printed representation of a Lisp object to the
object itself. It is up to the caller of `read' whether this object is
a form to be evaluated, or serves some entirely different purpose.
*Note Input Functions::.
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses `call-interactively' to invoke the command. The execution of the
command itself involves evaluation if the command is written in Lisp,
but that is not a part of command key interpretation itself. *Note
Command Loop::.
Evaluation is a recursive process. That is, evaluation of a form may
call `eval' to evaluate parts of the form. For example, evaluation of
a function call first evaluates each argument of the function call, and
then evaluates each form in the function body. Consider evaluation of
the form `(car x)': the subform `x' must first be evaluated
recursively, so that its value can be passed as an argument to the
function `car'.
Evaluation of a function call ultimately calls the function specified
in it. *Note Functions::. The execution of the function may itself
work by evaluating the function definition; or the function may be a
Lisp primitive implemented in C, or it may be a byte-compiled function
(*note Byte Compilation::).
The evaluation of forms takes place in a context called the
"environment", which consists of the current values and bindings of all
Lisp variables.(1) Whenever a form refers to a variable without
creating a new binding for it, the value of the variable's binding in
the current environment is used. *Note Variables::.
Evaluation of a form may create new environments for recursive
evaluation by binding variables (*note Local Variables::). These
environments are temporary and vanish by the time evaluation of the form
is complete. The form may also make changes that persist; these changes
are called "side effects". An example of a form that produces side
effects is `(setq foo 1)'.
The details of what evaluation means for each kind of form are
described below (*note Forms::).
---------- Footnotes ----------
(1) This definition of "environment" is specifically not intended to
include all the data that can affect the result of a program.
Kinds of Forms
==============
A Lisp object that is intended to be evaluated is called a "form".
How Emacs evaluates a form depends on its data type. Emacs has three
different kinds of form that are evaluated differently: symbols, lists,
and "all other types". This section describes all three kinds, one by
one, starting with the "all other types" which are self-evaluating
forms.
Self-Evaluating Forms
---------------------
A "self-evaluating form" is any form that is not a list or symbol.
Self-evaluating forms evaluate to themselves: the result of evaluation
is the same object that was evaluated. Thus, the number 25 evaluates to
25, and the string `"foo"' evaluates to the string `"foo"'. Likewise,
evaluation of a vector does not cause evaluation of the elements of the
vector--it returns the same vector with its contents unchanged.
'123 ; A number, shown without evaluation.
=> 123
123 ; Evaluated as usual--result is the same.
=> 123
(eval '123) ; Evaluated "by hand"--result is the same.
=> 123
(eval (eval '123)) ; Evaluating twice changes nothing.
=> 123
It is common to write numbers, characters, strings, and even vectors
in Lisp code, taking advantage of the fact that they self-evaluate.
However, it is quite unusual to do this for types that lack a read
syntax, because there's no way to write them textually. It is possible
to construct Lisp expressions containing these types by means of a Lisp
program. Here is an example:
;; Build an expression containing a buffer object.
(setq print-exp (list 'print (current-buffer)))
=> (print #<buffer eval.texi>)
;; Evaluate it.
(eval print-exp)
-| #<buffer eval.texi>
=> #<buffer eval.texi>
Symbol Forms
------------
When a symbol is evaluated, it is treated as a variable. The result
is the variable's value, if it has one. If it has none (if its value
cell is void), an error is signaled. For more information on the use of
variables, see *Note Variables::.
In the following example, we set the value of a symbol with `setq'.
Then we evaluate the symbol, and get back the value that `setq' stored.
(setq a 123)
=> 123
(eval 'a)
=> 123
a
=> 123
The symbols `nil' and `t' are treated specially, so that the value
of `nil' is always `nil', and the value of `t' is always `t'; you
cannot set or bind them to any other values. Thus, these two symbols
act like self-evaluating forms, even though `eval' treats them like any
other symbol. A symbol whose name starts with `:' also self-evaluates
in the same way; likewise, its value ordinarily cannot be changed.
*Note Constant Variables::.
Classification of List Forms
----------------------------
A form that is a nonempty list is either a function call, a macro
call, or a special form, according to its first element. These three
kinds of forms are evaluated in different ways, described below. The
remaining list elements constitute the "arguments" for the function,
macro, or special form.
The first step in evaluating a nonempty list is to examine its first
element. This element alone determines what kind of form the list is
and how the rest of the list is to be processed. The first element is
_not_ evaluated, as it would be in some Lisp dialects such as Scheme.
Symbol Function Indirection
---------------------------
If the first element of the list is a symbol then evaluation examines
the symbol's function cell, and uses its contents instead of the
original symbol. If the contents are another symbol, this process,
called "symbol function indirection", is repeated until it obtains a
non-symbol. *Note Function Names::, for more information about using a
symbol as a name for a function stored in the function cell of the
symbol.
One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol. Or a
symbol may have a void function cell, in which case the subroutine
`symbol-function' signals a `void-function' error. But if neither of
these things happens, we eventually obtain a non-symbol, which ought to
be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro, a
special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one of
these types, the error `invalid-function' is signaled.
The following example illustrates the symbol indirection process. We
use `fset' to set the function cell of a symbol and `symbol-function'
to get the function cell contents (*note Function Cells::).
Specifically, we store the symbol `car' into the function cell of
`first', and the symbol `first' into the function cell of `erste'.
;; Build this function cell linkage:
;; ------------- ----- ------- -------
;; | #<subr car> | <-- | car | <-- | first | <-- | erste |
;; ------------- ----- ------- -------
(symbol-function 'car)
=> #<subr car>
(fset 'first 'car)
=> car
(fset 'erste 'first)
=> first
(erste '(1 2 3)) ; Call the function referenced by `erste'.
=> 1
By contrast, the following example calls a function without any
symbol function indirection, because the first element is an anonymous
Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
=> 1
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling `erste'.
The built-in function `indirect-function' provides an easy way to
perform symbol function indirection explicitly.
- Function: indirect-function function
This function returns the meaning of FUNCTION as a function. If
FUNCTION is a symbol, then it finds FUNCTION's function definition
and starts over with that value. If FUNCTION is not a symbol,
then it returns FUNCTION itself.
Here is how you could define `indirect-function' in Lisp:
(defun indirect-function (function)
(if (symbolp function)
(indirect-function (symbol-function function))
function))
Evaluation of Function Forms
----------------------------
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a "function call". For example, here is a call to the function `+':
(+ 1 x)
The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right. The results are the
actual argument values, one value for each list element. The next step
is to call the function with this list of arguments, effectively using
the function `apply' (*note Calling Functions::). If the function is
written in Lisp, the arguments are used to bind the argument variables
of the function (*note Lambda Expressions::); then the forms in the
function body are evaluated in order, and the value of the last body
form becomes the value of the function call.
Lisp Macro Evaluation
---------------------
If the first element of a list being evaluated is a macro object,
then the list is a "macro call". When a macro call is evaluated, the
elements of the rest of the list are _not_ initially evaluated.
Instead, these elements themselves are used as the arguments of the
macro. The macro definition computes a replacement form, called the
"expansion" of the macro, to be evaluated in place of the original
form. The expansion may be any sort of form: a self-evaluating
constant, a symbol, or a list. If the expansion is itself a macro call,
this process of expansion repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the
expansion. However, the macro expansion is not necessarily evaluated
right away, or at all, because other programs also expand macro calls,
and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of
computing the macro expansion, but instead appear as part of the
expansion, so they are computed when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x)
(list 'car (list 'cdr x)))
an expression such as `(cadr (assq 'handler list))' is a macro call,
and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument `(assq 'handler list)' appears in the expansion.
*Note Macros::, for a complete description of Emacs Lisp macros.
Special Forms
-------------
A "special form" is a primitive function specially marked so that
its arguments are not all evaluated. Most special forms define control
structures or perform variable bindings--things which functions cannot
do.
Each special form has its own rules for which arguments are evaluated
and which are used without evaluation. Whether a particular argument is
evaluated may depend on the results of evaluating other arguments.
Here is a list, in alphabetical order, of all of the special forms in
Emacs Lisp with a reference to where each is described.
`and'
*note Combining Conditions::
`catch'
*note Catch and Throw::
`cond'
*note Conditionals::
`condition-case'
*note Handling Errors::
`defconst'
*note Defining Variables::
`defmacro'
*note Defining Macros::
`defun'
*note Defining Functions::
`defvar'
*note Defining Variables::
`function'
*note Anonymous Functions::
`if'
*note Conditionals::
`interactive'
*note Interactive Call::
`let'
`let*'
*note Local Variables::
`or'
*note Combining Conditions::
`prog1'
`prog2'
`progn'
*note Sequencing::
`quote'
*note Quoting::
`save-current-buffer'
*note Current Buffer::
`save-excursion'
*note Excursions::
`save-restriction'
*note Narrowing::
`save-window-excursion'
*note Window Configurations::
`setq'
*note Setting Variables::
`setq-default'
*note Creating Buffer-Local::
`track-mouse'
*note Mouse Tracking::
`unwind-protect'
*note Nonlocal Exits::
`while'
*note Iteration::
`with-output-to-temp-buffer'
*note Temporary Displays::
Common Lisp note: Here are some comparisons of special forms in
GNU Emacs Lisp and Common Lisp. `setq', `if', and `catch' are
special forms in both Emacs Lisp and Common Lisp. `defun' is a
special form in Emacs Lisp, but a macro in Common Lisp.
`save-excursion' is a special form in Emacs Lisp, but doesn't
exist in Common Lisp. `throw' is a special form in Common Lisp
(because it must be able to throw multiple values), but it is a
function in Emacs Lisp (which doesn't have multiple values).
Autoloading
-----------
The "autoload" feature allows you to call a function or macro whose
function definition has not yet been loaded into Emacs. It specifies
which file contains the definition. When an autoload object appears as
a symbol's function definition, calling that symbol as a function
automatically loads the specified file; then it calls the real
definition loaded from that file. *Note Autoload::.
Quoting
=======
The special form `quote' returns its single argument, as written,
without evaluating it. This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program. (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)
- Special Form: quote object
This special form returns OBJECT, without evaluating it.
Because `quote' is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (`'') followed
by a Lisp object (in read syntax) expands to a list whose first element
is `quote', and whose second element is the object. Thus, the read
syntax `'x' is an abbreviation for `(quote x)'.
Here are some examples of expressions that use `quote':
(quote (+ 1 2))
=> (+ 1 2)
(quote foo)
=> foo
'foo
=> foo
''foo
=> (quote foo)
'(quote foo)
=> (quote foo)
['foo]
=> [(quote foo)]
Other quoting constructs include `function' (*note Anonymous
Functions::), which causes an anonymous lambda expression written in
Lisp to be compiled, and ``' (*note Backquote::), which is used to quote
only part of a list, while computing and substituting other parts.
Eval
====
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the `eval' function.
The functions and variables described in this section evaluate forms,
specify limits to the evaluation process, or record recently returned
values. Loading a file also does evaluation (*note Loading::).
*Note:* it is generally cleaner and more flexible to store a
function in a data structure, and call it with `funcall' or `apply',
than to store an expression in the data structure and evaluate it.
Using functions provides the ability to pass information to them as
arguments.
- Function: eval form
This is the basic function evaluating an expression. It evaluates
FORM in the current environment and returns the result. How the
evaluation proceeds depends on the type of the object (*note
Forms::).
Since `eval' is a function, the argument expression that appears
in a call to `eval' is evaluated twice: once as preparation before
`eval' is called, and again by the `eval' function itself. Here
is an example:
(setq foo 'bar)
=> bar
(setq bar 'baz)
=> baz
;; Here `eval' receives argument `foo'
(eval 'foo)
=> bar
;; Here `eval' receives argument `bar', which is the value of `foo'
(eval foo)
=> baz
The number of currently active calls to `eval' is limited to
`max-lisp-eval-depth' (see below).
- Command: eval-region start end &optional stream read-function
This function evaluates the forms in the current buffer in the
region defined by the positions START and END. It reads forms from
the region and calls `eval' on them until the end of the region is
reached, or until an error is signaled and not handled.
If STREAM is non-`nil', the values that result from evaluating the
expressions in the region are printed using STREAM. *Note Output
Streams::.
If READ-FUNCTION is non-`nil', it should be a function, which is
used instead of `read' to read expressions one by one. This
function is called with one argument, the stream for reading
input. You can also use the variable `load-read-function' (*note
How Programs Do Loading::) to specify this function, but it is
more robust to use the READ-FUNCTION argument.
`eval-region' always returns `nil'.
- Command: eval-current-buffer &optional stream
This is like `eval-region' except that it operates on the whole
buffer.
- Variable: max-lisp-eval-depth
This variable defines the maximum depth allowed in calls to `eval',
`apply', and `funcall' before an error is signaled (with error
message `"Lisp nesting exceeds max-lisp-eval-depth"'). This limit,
with the associated error when it is exceeded, is one way that Lisp
avoids infinite recursion on an ill-defined function.
The depth limit counts internal uses of `eval', `apply', and
`funcall', such as for calling the functions mentioned in Lisp
expressions, and recursive evaluation of function call arguments
and function body forms, as well as explicit calls in Lisp code.
The default value of this variable is 300. If you set it to a
value less than 100, Lisp will reset it to 100 if the given value
is reached. Entry to the Lisp debugger increases the value, if
there is little room left, to make sure the debugger itself has
room to execute.
`max-specpdl-size' provides another limit on nesting. *Note Local
Variables::.
- Variable: values
The value of this variable is a list of the values returned by all
the expressions that were read, evaluated, and printed from buffers
(including the minibuffer) by the standard Emacs commands which do
this. The elements are ordered most recent first.
(setq x 1)
=> 1
(list 'A (1+ 2) auto-save-default)
=> (A 3 t)
values
=> ((A 3 t) 1 ...)
This variable is useful for referring back to values of forms
recently evaluated. It is generally a bad idea to print the value
of `values' itself, since this may be very long. Instead, examine
particular elements, like this:
;; Refer to the most recent evaluation result.
(nth 0 values)
=> (A 3 t)
;; That put a new element on,
;; so all elements move back one.
(nth 1 values)
=> (A 3 t)
;; This gets the element that was next-to-most-recent
;; before this example.
(nth 3 values)
=> 1
Control Structures
******************
A Lisp program consists of expressions or "forms" (*note Forms::).
We control the order of execution of these forms by enclosing them in
"control structures". Control structures are special forms which
control when, whether, or how many times to execute the forms they
contain.
The simplest order of execution is sequential execution: first form
A, then form B, and so on. This is what happens when you write several
forms in succession in the body of a function, or at top level in a
file of Lisp code--the forms are executed in the order written. We
call this "textual order". For example, if a function body consists of
two forms A and B, evaluation of the function evaluates first A and
then B. The result of evaluating B becomes the value of the function.
Explicit control structures make possible an order of execution other
than sequential.
Emacs Lisp provides several kinds of control structure, including
other varieties of sequencing, conditionals, iteration, and (controlled)
jumps--all discussed below. The built-in control structures are
special forms since their subforms are not necessarily evaluated or not
evaluated sequentially. You can use macros to define your own control
structure constructs (*note Macros::).
Sequencing
==========
Evaluating forms in the order they appear is the most common way
control passes from one form to another. In some contexts, such as in a
function body, this happens automatically. Elsewhere you must use a
control structure construct to do this: `progn', the simplest control
construct of Lisp.
A `progn' special form looks like this:
(progn A B C ...)
and it says to execute the forms A, B, C, and so on, in that order.
These forms are called the "body" of the `progn' form. The value of
the last form in the body becomes the value of the entire `progn'.
`(progn)' returns `nil'.
In the early days of Lisp, `progn' was the only way to execute two
or more forms in succession and use the value of the last of them. But
programmers found they often needed to use a `progn' in the body of a
function, where (at that time) only one form was allowed. So the body
of a function was made into an "implicit `progn'": several forms are
allowed just as in the body of an actual `progn'. Many other control
structures likewise contain an implicit `progn'. As a result, `progn'
is not used as much as it was many years ago. It is needed now most
often inside an `unwind-protect', `and', `or', or in the THEN-part of
an `if'.
- Special Form: progn forms...
This special form evaluates all of the FORMS, in textual order,
returning the result of the final form.
(progn (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The third form"
Two other control constructs likewise evaluate a series of forms but
return a different value:
- Special Form: prog1 form1 forms...
This special form evaluates FORM1 and all of the FORMS, in textual
order, returning the result of FORM1.
(prog1 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The first form"
Here is a way to remove the first element from a list in the
variable `x', then return the value of that former element:
(prog1 (car x) (setq x (cdr x)))
- Special Form: prog2 form1 form2 forms...
This special form evaluates FORM1, FORM2, and all of the following
FORMS, in textual order, returning the result of FORM2.
(prog2 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The second form"
Conditionals
============
Conditional control structures choose among alternatives. Emacs Lisp
has four conditional forms: `if', which is much the same as in other
languages; `when' and `unless', which are variants of `if'; and `cond',
which is a generalized case statement.
- Special Form: if condition then-form else-forms...
`if' chooses between the THEN-FORM and the ELSE-FORMS based on the
value of CONDITION. If the evaluated CONDITION is non-`nil',
THEN-FORM is evaluated and the result returned. Otherwise, the
ELSE-FORMS are evaluated in textual order, and the value of the
last one is returned. (The ELSE part of `if' is an example of an
implicit `progn'. *Note Sequencing::.)
If CONDITION has the value `nil', and no ELSE-FORMS are given,
`if' returns `nil'.
`if' is a special form because the branch that is not selected is
never evaluated--it is ignored. Thus, in the example below,
`true' is not printed because `print' is never called.
(if nil
(print 'true)
'very-false)
=> very-false
- Macro: when condition then-forms...
This is a variant of `if' where there are no ELSE-FORMS, and
possibly several THEN-FORMS. In particular,
(when CONDITION A B C)
is entirely equivalent to
(if CONDITION (progn A B C) nil)
- Macro: unless condition forms...
This is a variant of `if' where there is no THEN-FORM:
(unless CONDITION A B C)
is entirely equivalent to
(if CONDITION nil
A B C)
- Special Form: cond clause...
`cond' chooses among an arbitrary number of alternatives. Each
CLAUSE in the `cond' must be a list. The CAR of this list is the
CONDITION; the remaining elements, if any, the BODY-FORMS. Thus,
a clause looks like this:
(CONDITION BODY-FORMS...)
`cond' tries the clauses in textual order, by evaluating the
CONDITION of each clause. If the value of CONDITION is non-`nil',
the clause "succeeds"; then `cond' evaluates its BODY-FORMS, and
the value of the last of BODY-FORMS becomes the value of the
`cond'. The remaining clauses are ignored.
If the value of CONDITION is `nil', the clause "fails", so the
`cond' moves on to the following clause, trying its CONDITION.
If every CONDITION evaluates to `nil', so that every clause fails,
`cond' returns `nil'.
A clause may also look like this:
(CONDITION)
Then, if CONDITION is non-`nil' when tested, the value of
CONDITION becomes the value of the `cond' form.
The following example has four clauses, which test for the cases
where the value of `x' is a number, string, buffer and symbol,
respectively:
(cond ((numberp x) x)
((stringp x) x)
((bufferp x)
(setq temporary-hack x) ; multiple body-forms
(buffer-name x)) ; in one clause
((symbolp x) (symbol-value x)))
Often we want to execute the last clause whenever none of the
previous clauses was successful. To do this, we use `t' as the
CONDITION of the last clause, like this: `(t BODY-FORMS)'. The
form `t' evaluates to `t', which is never `nil', so this clause
never fails, provided the `cond' gets to it at all.
For example,
(setq a 5)
(cond ((eq a 'hack) 'foo)
(t "default"))
=> "default"
This `cond' expression returns `foo' if the value of `a' is
`hack', and returns the string `"default"' otherwise.
Any conditional construct can be expressed with `cond' or with `if'.
Therefore, the choice between them is a matter of style. For example:
(if A B C)
==
(cond (A B) (t C))
Constructs for Combining Conditions
===================================
This section describes three constructs that are often used together
with `if' and `cond' to express complicated conditions. The constructs
`and' and `or' can also be used individually as kinds of multiple
conditional constructs.
- Function: not condition
This function tests for the falsehood of CONDITION. It returns
`t' if CONDITION is `nil', and `nil' otherwise. The function
`not' is identical to `null', and we recommend using the name
`null' if you are testing for an empty list.
- Special Form: and conditions...
The `and' special form tests whether all the CONDITIONS are true.
It works by evaluating the CONDITIONS one by one in the order
written.
If any of the CONDITIONS evaluates to `nil', then the result of
the `and' must be `nil' regardless of the remaining CONDITIONS; so
`and' returns `nil' right away, ignoring the remaining CONDITIONS.
If all the CONDITIONS turn out non-`nil', then the value of the
last of them becomes the value of the `and' form. Just `(and)',
with no CONDITIONS, returns `t', appropriate because all the
CONDITIONS turned out non-`nil'. (Think about it; which one did
not?)
Here is an example. The first condition returns the integer 1,
which is not `nil'. Similarly, the second condition returns the
integer 2, which is not `nil'. The third condition is `nil', so
the remaining condition is never evaluated.
(and (print 1) (print 2) nil (print 3))
-| 1
-| 2
=> nil
Here is a more realistic example of using `and':
(if (and (consp foo) (eq (car foo) 'x))
(message "foo is a list starting with x"))
Note that `(car foo)' is not executed if `(consp foo)' returns
`nil', thus avoiding an error.
`and' can be expressed in terms of either `if' or `cond'. For
example:
(and ARG1 ARG2 ARG3)
==
(if ARG1 (if ARG2 ARG3))
==
(cond (ARG1 (cond (ARG2 ARG3))))
- Special Form: or conditions...
The `or' special form tests whether at least one of the CONDITIONS
is true. It works by evaluating all the CONDITIONS one by one in
the order written.
If any of the CONDITIONS evaluates to a non-`nil' value, then the
result of the `or' must be non-`nil'; so `or' returns right away,
ignoring the remaining CONDITIONS. The value it returns is the
non-`nil' value of the condition just evaluated.
If all the CONDITIONS turn out `nil', then the `or' expression
returns `nil'. Just `(or)', with no CONDITIONS, returns `nil',
appropriate because all the CONDITIONS turned out `nil'. (Think
about it; which one did not?)
For example, this expression tests whether `x' is either `nil' or
the integer zero:
(or (eq x nil) (eq x 0))
Like the `and' construct, `or' can be written in terms of `cond'.
For example:
(or ARG1 ARG2 ARG3)
==
(cond (ARG1)
(ARG2)
(ARG3))
You could almost write `or' in terms of `if', but not quite:
(if ARG1 ARG1
(if ARG2 ARG2
ARG3))
This is not completely equivalent because it can evaluate ARG1 or
ARG2 twice. By contrast, `(or ARG1 ARG2 ARG3)' never evaluates
any argument more than once.
Iteration
=========
Iteration means executing part of a program repetitively. For
example, you might want to repeat some computation once for each element
of a list, or once for each integer from 0 to N. You can do this in
Emacs Lisp with the special form `while':
- Special Form: while condition forms...
`while' first evaluates CONDITION. If the result is non-`nil', it
evaluates FORMS in textual order. Then it reevaluates CONDITION,
and if the result is non-`nil', it evaluates FORMS again. This
process repeats until CONDITION evaluates to `nil'.
There is no limit on the number of iterations that may occur. The
loop will continue until either CONDITION evaluates to `nil' or
until an error or `throw' jumps out of it (*note Nonlocal Exits::).
The value of a `while' form is always `nil'.
(setq num 0)
=> 0
(while (< num 4)
(princ (format "Iteration %d." num))
(setq num (1+ num)))
-| Iteration 0.
-| Iteration 1.
-| Iteration 2.
-| Iteration 3.
=> nil
To write a "repeat...until" loop, which will execute something on
each iteration and then do the end-test, put the body followed by
the end-test in a `progn' as the first argument of `while', as
shown here:
(while (progn
(forward-line 1)
(not (looking-at "^$"))))
This moves forward one line and continues moving by lines until it
reaches an empty line. It is peculiar in that the `while' has no
body, just the end test (which also does the real work of moving
point).
The `dolist' and `dotimes' macros provide convenient ways to write
two common kinds of loops.
- Macro: dolist (var list [result]) body...
This construct executes BODY once for each element of LIST, using
the variable VAR to hold the current element. Then it returns the
value of evaluating RESULT, or `nil' if RESULT is omitted. For
example, here is how you could use `dolist' to define the
`reverse' function:
(defun reverse (list)
(let (value)
(dolist (elt list value)
(setq value (cons elt value)))))
- Macro: dotimes (var count [result]) body...
This construct executes BODY once for each integer from 0
(inclusive) to COUNT (exclusive), using the variable VAR to hold
the integer for the current iteration. Then it returns the value
of evaluating RESULT, or `nil' if RESULT is omitted. Here is an
example of using `dotimes' do something 100 times:
(dotimes (i 100)
(insert "I will not obey absurd orders\n"))
Nonlocal Exits
==============
A "nonlocal exit" is a transfer of control from one point in a
program to another remote point. Nonlocal exits can occur in Emacs Lisp
as a result of errors; you can also use them under explicit control.
Nonlocal exits unbind all variable bindings made by the constructs being
exited.
Explicit Nonlocal Exits: `catch' and `throw'
--------------------------------------------
Most control constructs affect only the flow of control within the
construct itself. The function `throw' is the exception to this rule
of normal program execution: it performs a nonlocal exit on request.
(There are other exceptions, but they are for error handling only.)
`throw' is used inside a `catch', and jumps back to that `catch'. For
example:
(defun foo-outer ()
(catch 'foo
(foo-inner)))
(defun foo-inner ()
...
(if x
(throw 'foo t))
...)
The `throw' form, if executed, transfers control straight back to the
corresponding `catch', which returns immediately. The code following
the `throw' is not executed. The second argument of `throw' is used as
the return value of the `catch'.
The function `throw' finds the matching `catch' based on the first
argument: it searches for a `catch' whose first argument is `eq' to the
one specified in the `throw'. If there is more than one applicable
`catch', the innermost one takes precedence. Thus, in the above
example, the `throw' specifies `foo', and the `catch' in `foo-outer'
specifies the same symbol, so that `catch' is the applicable one
(assuming there is no other matching `catch' in between).
Executing `throw' exits all Lisp constructs up to the matching
`catch', including function calls. When binding constructs such as
`let' or function calls are exited in this way, the bindings are
unbound, just as they are when these constructs exit normally (*note
Local Variables::). Likewise, `throw' restores the buffer and position
saved by `save-excursion' (*note Excursions::), and the narrowing
status saved by `save-restriction' and the window selection saved by
`save-window-excursion' (*note Window Configurations::). It also runs
any cleanups established with the `unwind-protect' special form when it
exits that form (*note Cleanups::).
The `throw' need not appear lexically within the `catch' that it
jumps to. It can equally well be called from another function called
within the `catch'. As long as the `throw' takes place chronologically
after entry to the `catch', and chronologically before exit from it, it
has access to that `catch'. This is why `throw' can be used in
commands such as `exit-recursive-edit' that throw back to the editor
command loop (*note Recursive Editing::).
Common Lisp note: Most other versions of Lisp, including Common
Lisp, have several ways of transferring control nonsequentially:
`return', `return-from', and `go', for example. Emacs Lisp has
only `throw'.
- Special Form: catch tag body...
`catch' establishes a return point for the `throw' function. The
return point is distinguished from other such return points by
TAG, which may be any Lisp object except `nil'. The argument TAG
is evaluated normally before the return point is established.
With the return point in effect, `catch' evaluates the forms of the
BODY in textual order. If the forms execute normally (without
error or nonlocal exit) the value of the last body form is
returned from the `catch'.
If a `throw' is executed during the execution of BODY, specifying
the same value TAG, the `catch' form exits immediately; the value
it returns is whatever was specified as the second argument of
`throw'.
- Function: throw tag value
The purpose of `throw' is to return from a return point previously
established with `catch'. The argument TAG is used to choose
among the various existing return points; it must be `eq' to the
value specified in the `catch'. If multiple return points match
TAG, the innermost one is used.
The argument VALUE is used as the value to return from that
`catch'.
If no return point is in effect with tag TAG, then a `no-catch'
error is signaled with data `(TAG VALUE)'.
Examples of `catch' and `throw'
-------------------------------
One way to use `catch' and `throw' is to exit from a doubly nested
loop. (In most languages, this would be done with a "go to".) Here we
compute `(foo I J)' for I and J varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If `foo' ever returns non-`nil', we stop immediately and return a list
of I and J. If `foo' always returns `nil', the `catch' returns
normally, and the value is `nil', since that is the result of the
`while'.
Here are two tricky examples, slightly different, showing two return
points at once. First, two return points with the same tag, `hack':
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
=> no
Since both return points have tags that match the `throw', it goes to
the inner one, the one established in `catch2'. Therefore, `catch2'
returns normally with value `yes', and this value is printed. Finally
the second body form in the outer `catch', which is `'no', is evaluated
and returned from the outer `catch'.
Now let's change the argument given to `catch2':
(catch 'hack
(print (catch2 'quux))
'no)
=> yes
We still have two return points, but this time only the outer one has
the tag `hack'; the inner one has the tag `quux' instead. Therefore,
`throw' makes the outer `catch' return the value `yes'. The function
`print' is never called, and the body-form `'no' is never evaluated.
Errors
------
When Emacs Lisp attempts to evaluate a form that, for some reason,
cannot be evaluated, it "signals" an "error".
When an error is signaled, Emacs's default reaction is to print an
error message and terminate execution of the current command. This is
the right thing to do in most cases, such as if you type `C-f' at the
end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished. In such cases, you would use `unwind-protect'
to establish "cleanup expressions" to be evaluated in case of error.
(*Note Cleanups::.) Occasionally, you may wish the program to continue
execution despite an error in a subroutine. In these cases, you would
use `condition-case' to establish "error handlers" to recover control
in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use `catch' and `throw' instead.
*Note Catch and Throw::.
How to Signal an Error
......................
Most errors are signaled "automatically" within Lisp primitives
which you call for other purposes, such as if you try to take the CAR
of an integer or move forward a character at the end of the buffer.
You can also signal errors explicitly with the functions `error' and
`signal'.
Quitting, which happens when the user types `C-g', is not considered
an error, but it is handled almost like an error. *Note Quitting::.
The error message should state what is wrong ("File does not
exist"), not how things ought to be ("File must exist"). The
convention in Emacs Lisp is that error messages should start with a
capital letter, but should not end with any sort of punctuation.
- Function: error format-string &rest args
This function signals an error with an error message constructed by
applying `format' (*note String Conversion::) to FORMAT-STRING and
ARGS.
These examples show typical uses of `error':
(error "That is an error -- try something else")
error--> That is an error -- try something else
(error "You have committed %d errors" 10)
error--> You have committed 10 errors
`error' works by calling `signal' with two arguments: the error
symbol `error', and a list containing the string returned by
`format'.
*Warning:* If you want to use your own string as an error message
verbatim, don't just write `(error STRING)'. If STRING contains
`%', it will be interpreted as a format specifier, with
undesirable results. Instead, use `(error "%s" STRING)'.
- Function: signal error-symbol data
This function signals an error named by ERROR-SYMBOL. The
argument DATA is a list of additional Lisp objects relevant to the
circumstances of the error.
The argument ERROR-SYMBOL must be an "error symbol"--a symbol
bearing a property `error-conditions' whose value is a list of
condition names. This is how Emacs Lisp classifies different
sorts of errors.
The number and significance of the objects in DATA depends on
ERROR-SYMBOL. For example, with a `wrong-type-arg' error, there
should be two objects in the list: a predicate that describes the
type that was expected, and the object that failed to fit that
type. *Note Error Symbols::, for a description of error symbols.
Both ERROR-SYMBOL and DATA are available to any error handlers
that handle the error: `condition-case' binds a local variable to
a list of the form `(ERROR-SYMBOL . DATA)' (*note Handling
Errors::). If the error is not handled, these two values are used
in printing the error message.
The function `signal' never returns (though in older Emacs versions
it could sometimes return).
(signal 'wrong-number-of-arguments '(x y))
error--> Wrong number of arguments: x, y
(signal 'no-such-error '("My unknown error condition"))
error--> peculiar error: "My unknown error condition"
Common Lisp note: Emacs Lisp has nothing like the Common Lisp
concept of continuable errors.
How Emacs Processes Errors
..........................
When an error is signaled, `signal' searches for an active "handler"
for the error. A handler is a sequence of Lisp expressions designated
to be executed if an error happens in part of the Lisp program. If the
error has an applicable handler, the handler is executed, and control
resumes following the handler. The handler executes in the environment
of the `condition-case' that established it; all functions called
within that `condition-case' have already been exited, and the handler
cannot return to them.
If there is no applicable handler for the error, the current command
is terminated and control returns to the editor command loop, because
the command loop has an implicit handler for all kinds of errors. The
command loop's handler uses the error symbol and associated data to
print an error message.
An error that has no explicit handler may call the Lisp debugger.
The debugger is enabled if the variable `debug-on-error' (*note Error
Debugging::) is non-`nil'. Unlike error handlers, the debugger runs in
the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.
Writing Code to Handle Errors
.............................
The usual effect of signaling an error is to terminate the command
that is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form `condition-case'.
A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named FILENAME, catching any error and returning
`nil' if an error occurs.
The second argument of `condition-case' is called the "protected
form". (In the example above, the protected form is a call to
`delete-file'.) The error handlers go into effect when this form
begins execution and are deactivated when this form returns. They
remain in effect for all the intervening time. In particular, they are
in effect during the execution of functions called by this form, in
their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
`signal' and `error') called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more "condition names" (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
`error', which covers all errors.
The search for an applicable handler checks all the established
handlers starting with the most recently established one. Thus, if two
nested `condition-case' forms offer to handle the same error, the inner
of the two gets to handle it.
If an error is handled by some `condition-case' form, this
ordinarily prevents the debugger from being run, even if
`debug-on-error' says this error should invoke the debugger. *Note
Error Debugging::. If you want to be able to debug errors that are
caught by a `condition-case', set the variable `debug-on-signal' to a
non-`nil' value.
When an error is handled, control returns to the handler. Before
this happens, Emacs unbinds all variable bindings made by binding
constructs that are being exited and executes the cleanups of all
`unwind-protect' forms that are exited. Once control arrives at the
handler, the body of the handler is executed.
After execution of the handler body, execution returns from the
`condition-case' form. Because the protected form is exited completely
before execution of the handler, the handler cannot resume execution at
the point of the error, nor can it examine variable bindings that were
made within the protected form. All it can do is clean up and proceed.
The `condition-case' construct is often used to trap errors that are
predictable, such as failure to open a file in a call to
`insert-file-contents'. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
Error signaling and handling have some resemblance to `throw' and
`catch' (*note Catch and Throw::), but they are entirely separate
facilities. An error cannot be caught by a `catch', and a `throw'
cannot be handled by an error handler (though using `throw' when there
is no suitable `catch' signals an error that can be handled).
- Special Form: condition-case var protected-form handlers...
This special form establishes the error handlers HANDLERS around
the execution of PROTECTED-FORM. If PROTECTED-FORM executes
without error, the value it returns becomes the value of the
`condition-case' form; in this case, the `condition-case' has no
effect. The `condition-case' form makes a difference when an
error occurs during PROTECTED-FORM.
Each of the HANDLERS is a list of the form `(CONDITIONS BODY...)'.
Here CONDITIONS is an error condition name to be handled, or a
list of condition names; BODY is one or more Lisp expressions to
be executed when this handler handles an error. Here are examples
of handlers:
(error nil)
(arith-error (message "Division by zero"))
((arith-error file-error)
(message
"Either division by zero or failure to open a file"))
Each error that occurs has an "error symbol" that describes what
kind of error it is. The `error-conditions' property of this
symbol is a list of condition names (*note Error Symbols::). Emacs
searches all the active `condition-case' forms for a handler that
specifies one or more of these condition names; the innermost
matching `condition-case' handles the error. Within this
`condition-case', the first applicable handler handles the error.
After executing the body of the handler, the `condition-case'
returns normally, using the value of the last form in the handler
body as the overall value.
The argument VAR is a variable. `condition-case' does not bind
this variable when executing the PROTECTED-FORM, only when it
handles an error. At that time, it binds VAR locally to an "error
description", which is a list giving the particulars of the error.
The error description has the form `(ERROR-SYMBOL . DATA)'. The
handler can refer to this list to decide what to do. For example,
if the error is for failure opening a file, the file name is the
second element of DATA--the third element of the error description.
If VAR is `nil', that means no variable is bound. Then the error
symbol and associated data are not available to the handler.
- Function: error-message-string error-description
This function returns the error message string for a given error
descriptor. It is useful if you want to handle an error by
printing the usual error message for that error.
Here is an example of using `condition-case' to handle the error
that results from dividing by zero. The handler displays the error
message (but without a beep), then returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))
=> safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
=> 1000000
The handler specifies condition name `arith-error' so that it will
handle only division-by-zero errors. Other kinds of errors will not be
handled, at least not by this `condition-case'. Thus,
(safe-divide nil 3)
error--> Wrong type argument: number-or-marker-p, nil
Here is a `condition-case' that catches all kinds of errors,
including those signaled with `error':
(setq baz 34)
=> 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function `error'.
(error "Rats! The variable %s was %s, not 35" 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35")
=> 2
Error Symbols and Condition Names
.................................
When you signal an error, you specify an "error symbol" to specify
the kind of error you have in mind. Each error has one and only one
error symbol to categorize it. This is the finest classification of
errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called "error conditions", identified by "condition names".
The narrowest such classes belong to the error symbols themselves: each
error symbol is also a condition name. There are also condition names
for more extensive classes, up to the condition name `error' which
takes in all kinds of errors. Thus, each error has one or more
condition names: `error', the error symbol if that is distinct from
`error', and perhaps some intermediate classifications.
In order for a symbol to be an error symbol, it must have an
`error-conditions' property which gives a list of condition names.
This list defines the conditions that this kind of error belongs to.
(The error symbol itself, and the symbol `error', should always be
members of this list.) Thus, the hierarchy of condition names is
defined by the `error-conditions' properties of the error symbols.
In addition to the `error-conditions' list, the error symbol should
have an `error-message' property whose value is a string to be printed
when that error is signaled but not handled. If the `error-message'
property exists, but is not a string, the error message `peculiar
error' is used.
Here is how we define a new error symbol, `new-error':
(put 'new-error
'error-conditions
'(error my-own-errors new-error))
=> (error my-own-errors new-error)
(put 'new-error 'error-message "A new error")
=> "A new error"
This error has three condition names: `new-error', the narrowest
classification; `my-own-errors', which we imagine is a wider
classification; and `error', which is the widest of all.
The error string should start with a capital letter but it should
not end with a period. This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal `new-error' on its own; only an
explicit call to `signal' (*note Signaling Errors::) in your code can
do this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of the three condition names.
This example handles `new-error' and any other errors in the class
`my-own-errors':
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names--the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. It would be cumbersome to give `signal' a
list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would
seriously decrease the power of `condition-case'. Condition names make
it possible to categorize errors at various levels of generality when
you write an error handler. Using error symbols alone would eliminate
all but the narrowest level of classification.
*Note Standard Errors::, for a list of all the standard error symbols
and their conditions.
Cleaning Up from Nonlocal Exits
-------------------------------
The `unwind-protect' construct is essential whenever you temporarily
put a data structure in an inconsistent state; it permits you to make
the data consistent again in the event of an error or throw.
- Special Form: unwind-protect body cleanup-forms...
`unwind-protect' executes the BODY with a guarantee that the
CLEANUP-FORMS will be evaluated if control leaves BODY, no matter
how that happens. The BODY may complete normally, or execute a
`throw' out of the `unwind-protect', or cause an error; in all
cases, the CLEANUP-FORMS will be evaluated.
If the BODY forms finish normally, `unwind-protect' returns the
value of the last BODY form, after it evaluates the CLEANUP-FORMS.
If the BODY forms do not finish, `unwind-protect' does not return
any value in the normal sense.
Only the BODY is protected by the `unwind-protect'. If any of the
CLEANUP-FORMS themselves exits nonlocally (via a `throw' or an
error), `unwind-protect' is _not_ guaranteed to evaluate the rest
of them. If the failure of one of the CLEANUP-FORMS has the
potential to cause trouble, then protect it with another
`unwind-protect' around that form.
The number of currently active `unwind-protect' forms counts,
together with the number of local variable bindings, against the
limit `max-specpdl-size' (*note Local Variables::).
For example, here we make an invisible buffer for temporary use, and
make sure to kill it before finishing:
(save-excursion
(let ((buffer (get-buffer-create " *temp*")))
(set-buffer buffer)
(unwind-protect
BODY
(kill-buffer buffer))))
You might think that we could just as well write `(kill-buffer
(current-buffer))' and dispense with the variable `buffer'. However,
the way shown above is safer, if BODY happens to get an error after
switching to a different buffer! (Alternatively, you could write
another `save-excursion' around the body, to ensure that the temporary
buffer becomes current again in time to kill it.)
Emacs includes a standard macro called `with-temp-buffer' which
expands into more or less the code shown above (*note Current Buffer::).
Several of the macros defined in this manual use `unwind-protect' in
this way.
Here is an actual example derived from an FTP package. It creates a
process (*note Processes::) to try to establish a connection to a remote
machine. As the function `ftp-login' is highly susceptible to numerous
problems that the writer of the function cannot anticipate, it is
protected with a form that guarantees deletion of the process in the
event of failure. Otherwise, Emacs might fill up with useless
subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example has a small bug: if the user types `C-g' to quit, and
the quit happens immediately after the function `ftp-setup-buffer'
returns but before the variable `process' is set, the process will not
be killed. There is no easy way to fix this bug, but at least it is
very unlikely.
Variables
*********
A "variable" is a name used in a program to stand for a value.
Nearly all programming languages have variables of some sort. In the
text of a Lisp program, variables are written using the syntax for
symbols.
In Lisp, unlike most programming languages, programs are represented
primarily as Lisp objects and only secondarily as text. The Lisp
objects used for variables are symbols: the symbol name is the variable
name, and the variable's value is stored in the value cell of the
symbol. The use of a symbol as a variable is independent of its use as
a function name. *Note Symbol Components::.
The Lisp objects that constitute a Lisp program determine the textual
form of the program--it is simply the read syntax for those Lisp
objects. This is why, for example, a variable in a textual Lisp program
is written using the read syntax for the symbol that represents the
variable.
Global Variables
================
The simplest way to use a variable is "globally". This means that
the variable has just one value at a time, and this value is in effect
(at least for the moment) throughout the Lisp system. The value remains
in effect until you specify a new one. When a new value replaces the
old one, no trace of the old value remains in the variable.
You specify a value for a symbol with `setq'. For example,
(setq x '(a b))
gives the variable `x' the value `(a b)'. Note that `setq' does not
evaluate its first argument, the name of the variable, but it does
evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the
symbol by itself as an expression. Thus,
x => (a b)
assuming the `setq' form shown above has already been executed.
If you do set the same variable again, the new value replaces the old
one:
x
=> (a b)
(setq x 4)
=> 4
x
=> 4
Variables that Never Change
===========================
In Emacs Lisp, certain symbols normally evaluate to themselves.
These include `nil' and `t', as well as any symbol whose name starts
with `:' (these are called "keywords"). These symbols cannot be
rebound, nor can their values be changed. Any attempt to set or bind
`nil' or `t' signals a `setting-constant' error. The same is true for
a keyword (a symbol whose name starts with `:'), if it is interned in
the standard obarray, except that setting such a symbol to itself is
not an error.
nil == 'nil
=> nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
- Function: keywordp object
function returns `t' if OBJECT is a symbol whose name starts with
`:', interned in the standard obarray, and returns `nil' otherwise.
Local Variables
===============
Global variables have values that last until explicitly superseded
with new values. Sometimes it is useful to create variable values that
exist temporarily--only until a certain part of the program finishes.
These values are called "local", and the variables so used are called
"local variables".
For example, when a function is called, its argument variables
receive new local values that last until the function exits. The `let'
special form explicitly establishes new local values for specified
variables; these last until exit from the `let' form.
Establishing a local value saves away the previous value (or lack of
one) of the variable. When the life span of the local value is over,
the previous value is restored. In the mean time, we say that the
previous value is "shadowed" and "not visible". Both global and local
values may be shadowed (*note Scope::).
If you set a variable (such as with `setq') while it is local, this
replaces the local value; it does not alter the global value, or
previous local values, that are shadowed. To model this behavior, we
speak of a "local binding" of the variable as well as a local value.
The local binding is a conceptual place that holds a local value.
Entry to a function, or a special form such as `let', creates the local
binding; exit from the function or from the `let' removes the local
binding. As long as the local binding lasts, the variable's value is
stored within it. Use of `setq' or `set' while there is a local
binding stores a different value into the local binding; it does not
create a new binding.
We also speak of the "global binding", which is where (conceptually)
the global value is kept.
A variable can have more than one local binding at a time (for
example, if there are nested `let' forms that bind it). In such a
case, the most recently created local binding that still exists is the
"current binding" of the variable. (This rule is called "dynamic
scoping"; see *Note Variable Scoping::.) If there are no local
bindings, the variable's global binding is its current binding. We
sometimes call the current binding the "most-local existing binding",
for emphasis. Ordinary evaluation of a symbol always returns the value
of its current binding.
The special forms `let' and `let*' exist to create local bindings.
- Special Form: let (bindings...) forms...
This special form binds variables according to BINDINGS and then
evaluates all of the FORMS in textual order. The `let'-form
returns the value of the last form in FORMS.
Each of the BINDINGS is either (i) a symbol, in which case that
symbol is bound to `nil'; or (ii) a list of the form `(SYMBOL
VALUE-FORM)', in which case SYMBOL is bound to the result of
evaluating VALUE-FORM. If VALUE-FORM is omitted, `nil' is used.
All of the VALUE-FORMs in BINDINGS are evaluated in the order they
appear and _before_ binding any of the symbols to them. Here is
an example of this: `Z' is bound to the old value of `Y', which is
2, not the new value of `Y', which is 1.
(setq Y 2)
=> 2
(let ((Y 1)
(Z Y))
(list Y Z))
=> (1 2)
- Special Form: let* (bindings...) forms...
This special form is like `let', but it binds each variable right
after computing its local value, before computing the local value
for the next variable. Therefore, an expression in BINDINGS can
reasonably refer to the preceding symbols bound in this `let*'
form. Compare the following example with the example above for
`let'.
(setq Y 2)
=> 2
(let* ((Y 1)
(Z Y)) ; Use the just-established value of `Y'.
(list Y Z))
=> (1 1)
Here is a complete list of the other facilities that create local
bindings:
* Function calls (*note Functions::).
* Macro calls (*note Macros::).
* `condition-case' (*note Errors::).
Variables can also have buffer-local bindings (*note Buffer-Local
Variables::) and frame-local bindings (*note Frame-Local Variables::); a
few variables have terminal-local bindings (*note Multiple Displays::).
These kinds of bindings work somewhat like ordinary local bindings, but
they are localized depending on "where" you are in Emacs, rather than
localized in time.
- Variable: max-specpdl-size
This variable defines the limit on the total number of local
variable bindings and `unwind-protect' cleanups (*note Nonlocal
Exits::) that are allowed before signaling an error (with data
`"Variable binding depth exceeds max-specpdl-size"').
This limit, with the associated error when it is exceeded, is one
way that Lisp avoids infinite recursion on an ill-defined function.
`max-lisp-eval-depth' provides another limit on depth of nesting.
*Note Eval::.
The default value is 600. Entry to the Lisp debugger increases the
value, if there is little room left, to make sure the debugger
itself has room to execute.
When a Variable is "Void"
=========================
If you have never given a symbol any value as a global variable, we
say that that symbol's global value is "void". In other words, the
symbol's value cell does not have any Lisp object in it. If you try to
evaluate the symbol, you get a `void-variable' error rather than a
value.
Note that a value of `nil' is not the same as void. The symbol
`nil' is a Lisp object and can be the value of a variable just as any
other object can be; but it is _a value_. A void variable does not
have any value.
After you have given a variable a value, you can make it void once
more using `makunbound'.
- Function: makunbound symbol
This function makes the current variable binding of SYMBOL void.
Subsequent attempts to use this symbol's value as a variable will
signal the error `void-variable', unless and until you set it
again.
`makunbound' returns SYMBOL.
(makunbound 'x) ; Make the global value of `x' void.
=> x
x
error--> Symbol's value as variable is void: x
If SYMBOL is locally bound, `makunbound' affects the most local
existing binding. This is the only way a symbol can have a void
local binding, since all the constructs that create local bindings
create them with values. In this case, the voidness lasts at most
as long as the binding does; when the binding is removed due to
exit from the construct that made it, the previous local or global
binding is reexposed as usual, and the variable is no longer void
unless the newly reexposed binding was void all along.
(setq x 1) ; Put a value in the global binding.
=> 1
(let ((x 2)) ; Locally bind it.
(makunbound 'x) ; Void the local binding.
x)
error--> Symbol's value as variable is void: x
x ; The global binding is unchanged.
=> 1
(let ((x 2)) ; Locally bind it.
(let ((x 3)) ; And again.
(makunbound 'x) ; Void the innermost-local binding.
x)) ; And refer: it's void.
error--> Symbol's value as variable is void: x
(let ((x 2))
(let ((x 3))
(makunbound 'x)) ; Void inner binding, then remove it.
x) ; Now outer `let' binding is visible.
=> 2
A variable that has been made void with `makunbound' is
indistinguishable from one that has never received a value and has
always been void.
You can use the function `boundp' to test whether a variable is
currently void.
- Function: boundp variable
`boundp' returns `t' if VARIABLE (a symbol) is not void; more
precisely, if its current binding is not void. It returns `nil'
otherwise.
(boundp 'abracadabra) ; Starts out void.
=> nil
(let ((abracadabra 5)) ; Locally bind it.
(boundp 'abracadabra))
=> t
(boundp 'abracadabra) ; Still globally void.
=> nil
(setq abracadabra 5) ; Make it globally nonvoid.
=> 5
(boundp 'abracadabra)
=> t
Defining Global Variables
=========================
You may announce your intention to use a symbol as a global variable
with a "variable definition": a special form, either `defconst' or
`defvar'.
In Emacs Lisp, definitions serve three purposes. First, they inform
people who read the code that certain symbols are _intended_ to be used
a certain way (as variables). Second, they inform the Lisp system of
these things, supplying a value and documentation. Third, they provide
information to utilities such as `etags' and `make-docfile', which
create data bases of the functions and variables in a program.
The difference between `defconst' and `defvar' is primarily a matter
of intent, serving to inform human readers of whether the value should
ever change. Emacs Lisp does not restrict the ways in which a variable
can be used based on `defconst' or `defvar' declarations. However, it
does make a difference for initialization: `defconst' unconditionally
initializes the variable, while `defvar' initializes it only if it is
void.
- Special Form: defvar symbol [value [doc-string]]
This special form defines SYMBOL as a variable and can also
initialize and document it. The definition informs a person
reading your code that SYMBOL is used as a variable that might be
set or changed. Note that SYMBOL is not evaluated; the symbol to
be defined must appear explicitly in the `defvar'.
If SYMBOL is void and VALUE is specified, `defvar' evaluates it
and sets SYMBOL to the result. But if SYMBOL already has a value
(i.e., it is not void), VALUE is not even evaluated, and SYMBOL's
value remains unchanged. If VALUE is omitted, the value of SYMBOL
is not changed in any case.
If SYMBOL has a buffer-local binding in the current buffer,
`defvar' operates on the default value, which is
buffer-independent, not the current (buffer-local) binding. It
sets the default value if the default value is void. *Note
Buffer-Local Variables::.
When you evaluate a top-level `defvar' form with `C-M-x' in Emacs
Lisp mode (`eval-defun'), a special feature of `eval-defun'
arranges to set the variable unconditionally, without testing
whether its value is void.
If the DOC-STRING argument appears, it specifies the documentation
for the variable. (This opportunity to specify documentation is
one of the main benefits of defining the variable.) The
documentation is stored in the symbol's `variable-documentation'
property. The Emacs help functions (*note Documentation::) look
for this property.
If the variable is a user option that users would want to set
interactively, you should use `*' as the first character of
DOC-STRING. This lets users set the variable conveniently using
the `set-variable' command. Note that you should nearly always
use `defcustom' instead of `defvar' to define these variables, so
that users can use `M-x customize' and related commands to set
them. *Note Customization::.
Here are some examples. This form defines `foo' but does not
initialize it:
(defvar foo)
=> foo
This example initializes the value of `bar' to `23', and gives it
a documentation string:
(defvar bar 23
"The normal weight of a bar.")
=> bar
The following form changes the documentation string for `bar',
making it a user option, but does not change the value, since `bar'
already has a value. (The addition `(1+ nil)' would get an error
if it were evaluated, but since it is not evaluated, there is no
error.)
(defvar bar (1+ nil)
"*The normal weight of a bar.")
=> bar
bar
=> 23
Here is an equivalent expression for the `defvar' special form:
(defvar SYMBOL VALUE DOC-STRING)
==
(progn
(if (not (boundp 'SYMBOL))
(setq SYMBOL VALUE))
(if 'DOC-STRING
(put 'SYMBOL 'variable-documentation 'DOC-STRING))
'SYMBOL)
The `defvar' form returns SYMBOL, but it is normally used at top
level in a file where its value does not matter.
- Special Form: defconst symbol [value [doc-string]]
This special form defines SYMBOL as a value and initializes it.
It informs a person reading your code that SYMBOL has a standard
global value, established here, that should not be changed by the
user or by other programs. Note that SYMBOL is not evaluated; the
symbol to be defined must appear explicitly in the `defconst'.
`defconst' always evaluates VALUE, and sets the value of SYMBOL to
the result if VALUE is given. If SYMBOL does have a buffer-local
binding in the current buffer, `defconst' sets the default value,
not the buffer-local value. (But you should not be making
buffer-local bindings for a symbol that is defined with
`defconst'.)
Here, `pi' is a constant that presumably ought not to be changed
by anyone (attempts by the Indiana State Legislature
notwithstanding). As the second form illustrates, however, this
is only advisory.
(defconst pi 3.1415 "Pi to five places.")
=> pi
(setq pi 3)
=> pi
pi
=> 3
- Function: user-variable-p variable
This function returns `t' if VARIABLE is a user option--a variable
intended to be set by the user for customization--and `nil'
otherwise. (Variables other than user options exist for the
internal purposes of Lisp programs, and users need not know about
them.)
User option variables are distinguished from other variables either
though being declared using `defcustom'(1) or by the first
character of their `variable-documentation' property. If the
property exists and is a string, and its first character is `*',
then the variable is a user option.
If a user option variable has a `variable-interactive' property, the
`set-variable' command uses that value to control reading the new value
for the variable. The property's value is used as if it were specified
in `interactive' (*note Using Interactive::). However, this feature is
largely obsoleted by `defcustom' (*note Customization::).
*Warning:* If the `defconst' and `defvar' special forms are used
while the variable has a local binding, they set the local binding's
value; the global binding is not changed. This is not what you usually
want. To prevent it, use these special forms at top level in a file,
where normally no local binding is in effect, and make sure to load the
file before making a local binding for the variable.
---------- Footnotes ----------
(1) They may also be declared equivalently in `cus-start.el'.
Tips for Defining Variables Robustly
====================================
When you define a variable whose value is a function, or a list of
functions, use a name that ends in `-function' or `-functions',
respectively.
There are several other variable name conventions; here is a
complete list:
`...-hook'
The variable is a normal hook (*note Hooks::).
`...-function'
The value is a function.
`...-functions'
The value is a list of functions.
`...-form'
The value is a form (an expression).
`...-forms'
The value is a list of forms (expressions).
`...-predicate'
The value is a predicate--a function of one argument that returns
non-`nil' for "good" arguments and `nil' for "bad" arguments.
`...-flag'
The value is significant only as to whether it is `nil' or not.
`...-program'
The value is a program name.
`...-command'
The value is a whole shell command.
``'-switches'
The value specifies options for a command.
When you define a variable, always consider whether you should mark
it as "risky"; see *Note File Local Variables::.
When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the `defvar', like this:
(defvar my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
map)
DOCSTRING)
This method has several benefits. First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents (such
as, to rebind keys). Third, evaluating the `defvar' form with `C-M-x'
_will_ reinitialize the map completely.
Putting so much code in the `defvar' form has one disadvantage: it
puts the documentation string far away from the line which names the
variable. Here's a safe way to avoid that:
(defvar my-mode-map nil
DOCSTRING)
(unless my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
(setq my-mode-map map)))
This has all the same advantages as putting the initialization inside
the `defvar', except that you must type `C-M-x' twice, once on each
form, if you do want to reinitialize the variable.
But be careful not to write the code like this:
(defvar my-mode-map nil
DOCSTRING)
(unless my-mode-map
(setq my-mode-map (make-sparse-keymap))
(define-key my-mode-map "\C-c\C-a" 'my-command)
...)
This code sets the variable, then alters it, but it does so in more than
one step. If the user quits just after the `setq', that leaves the
variable neither correctly initialized nor void nor `nil'. Once that
happens, reloading the file will not initialize the variable; it will
remain incomplete.
Accessing Variable Values
=========================
The usual way to reference a variable is to write the symbol which
names it (*note Symbol Forms::). This requires you to specify the
variable name when you write the program. Usually that is exactly what
you want to do. Occasionally you need to choose at run time which
variable to reference; then you can use `symbol-value'.
- Function: symbol-value symbol
This function returns the value of SYMBOL. This is the value in
the innermost local binding of the symbol, or its global value if
it has no local bindings.
(setq abracadabra 5)
=> 5
(setq foo 9)
=> 9
;; Here the symbol `abracadabra'
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value 'abracadabra))
=> foo
;; Here the value of `abracadabra',
;; which is `foo',
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value abracadabra))
=> 9
(symbol-value 'abracadabra)
=> 5
A `void-variable' error is signaled if the current binding of
SYMBOL is void.
How to Alter a Variable Value
=============================
The usual way to change the value of a variable is with the special
form `setq'. When you need to compute the choice of variable at run
time, use the function `set'.
- Special Form: setq [symbol form]...
This special form is the most common method of changing a
variable's value. Each SYMBOL is given a new value, which is the
result of evaluating the corresponding FORM. The most-local
existing binding of the symbol is changed.
`setq' does not evaluate SYMBOL; it sets the symbol that you
write. We say that this argument is "automatically quoted". The
`q' in `setq' stands for "quoted."
The value of the `setq' form is the value of the last FORM.
(setq x (1+ 2))
=> 3
x ; `x' now has a global value.
=> 3
(let ((x 5))
(setq x 6) ; The local binding of `x' is set.
x)
=> 6
x ; The global value is unchanged.
=> 3
Note that the first FORM is evaluated, then the first SYMBOL is
set, then the second FORM is evaluated, then the second SYMBOL is
set, and so on:
(setq x 10 ; Notice that `x' is set before
y (1+ x)) ; the value of `y' is computed.
=> 11
- Function: set symbol value
This function sets SYMBOL's value to VALUE, then returns VALUE.
Since `set' is a function, the expression written for SYMBOL is
evaluated to obtain the symbol to set.
The most-local existing binding of the variable is the binding
that is set; shadowed bindings are not affected.
(set one 1)
error--> Symbol's value as variable is void: one
(set 'one 1)
=> 1
(set 'two 'one)
=> one
(set two 2) ; `two' evaluates to symbol `one'.
=> 2
one ; So it is `one' that was set.
=> 2
(let ((one 1)) ; This binding of `one' is set,
(set 'one 3) ; not the global value.
one)
=> 3
one
=> 2
If SYMBOL is not actually a symbol, a `wrong-type-argument' error
is signaled.
(set '(x y) 'z)
error--> Wrong type argument: symbolp, (x y)
Logically speaking, `set' is a more fundamental primitive than
`setq'. Any use of `setq' can be trivially rewritten to use
`set'; `setq' could even be defined as a macro, given the
availability of `set'. However, `set' itself is rarely used;
beginners hardly need to know about it. It is useful only for
choosing at run time which variable to set. For example, the
command `set-variable', which reads a variable name from the user
and then sets the variable, needs to use `set'.
Common Lisp note: In Common Lisp, `set' always changes the
symbol's "special" or dynamic value, ignoring any lexical
bindings. In Emacs Lisp, all variables and all bindings are
dynamic, so `set' always affects the most local existing
binding.
One other function for setting a variable is designed to add an
element to a list if it is not already present in the list.
- Function: add-to-list symbol element
This function sets the variable SYMBOL by consing ELEMENT onto the
old value, if ELEMENT is not already a member of that value. It
returns the resulting list, whether updated or not. The value of
SYMBOL had better be a list already before the call.
The argument SYMBOL is not implicitly quoted; `add-to-list' is an
ordinary function, like `set' and unlike `setq'. Quote the
argument yourself if that is what you want.
Here's a scenario showing how to use `add-to-list':
(setq foo '(a b))
=> (a b)
(add-to-list 'foo 'c) ;; Add `c'.
=> (c a b)
(add-to-list 'foo 'b) ;; No effect.
=> (c a b)
foo ;; `foo' was changed.
=> (c a b)
An equivalent expression for `(add-to-list 'VAR VALUE)' is this:
(or (member VALUE VAR)
(setq VAR (cons VALUE VAR)))
Scoping Rules for Variable Bindings
===================================
A given symbol `foo' can have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding. The most recently established binding takes precedence over
the others.
Local bindings in Emacs Lisp have "indefinite scope" and "dynamic
extent". "Scope" refers to _where_ textually in the source code the
binding can be accessed. "Indefinite scope" means that any part of the
program can potentially access the variable binding. "Extent" refers
to _when_, as the program is executing, the binding exists. "Dynamic
extent" means that the binding lasts as long as the activation of the
construct that established it.
The combination of dynamic extent and indefinite scope is called
"dynamic scoping". By contrast, most programming languages use
"lexical scoping", in which references to a local variable must be
located textually within the function or block that binds the variable.
Common Lisp note: Variables declared "special" in Common Lisp are
dynamically scoped, like all variables in Emacs Lisp.
Scope
-----
Emacs Lisp uses "indefinite scope" for local variable bindings.
This means that any function anywhere in the program text might access a
given binding of a variable. Consider the following function
definitions:
(defun binder (x) ; `x' is bound in `binder'.
(foo 5)) ; `foo' is some other function.
(defun user () ; `x' is used "free" in `user'.
(list x))
In a lexically scoped language, the binding of `x' in `binder' would
never be accessible in `user', because `user' is not textually
contained within the function `binder'. However, in dynamically-scoped
Emacs Lisp, `user' may or may not refer to the binding of `x'
established in `binder', depending on the circumstances:
* If we call `user' directly without calling `binder' at all, then
whatever binding of `x' is found, it cannot come from `binder'.
* If we define `foo' as follows and then call `binder', then the
binding made in `binder' will be seen in `user':
(defun foo (lose)
(user))
* However, if we define `foo' as follows and then call `binder',
then the binding made in `binder' _will not_ be seen in `user':
(defun foo (x)
(user))
Here, when `foo' is called by `binder', it binds `x'. (The
binding in `foo' is said to "shadow" the one made in `binder'.)
Therefore, `user' will access the `x' bound by `foo' instead of
the one bound by `binder'.
Emacs Lisp uses dynamic scoping because simple implementations of
lexical scoping are slow. In addition, every Lisp system needs to offer
dynamic scoping at least as an option; if lexical scoping is the norm,
there must be a way to specify dynamic scoping instead for a particular
variable. It might not be a bad thing for Emacs to offer both, but
implementing it with dynamic scoping only was much easier.
Extent
------
"Extent" refers to the time during program execution that a variable
name is valid. In Emacs Lisp, a variable is valid only while the form
that bound it is executing. This is called "dynamic extent". "Local"
or "automatic" variables in most languages, including C and Pascal,
have dynamic extent.
One alternative to dynamic extent is "indefinite extent". This
means that a variable binding can live on past the exit from the form
that made the binding. Common Lisp and Scheme, for example, support
this, but Emacs Lisp does not.
To illustrate this, the function below, `make-add', returns a
function that purports to add N to its own argument M. This would work
in Common Lisp, but it does not do the job in Emacs Lisp, because after
the call to `make-add' exits, the variable `n' is no longer bound to
the actual argument 2.
(defun make-add (n)
(function (lambda (m) (+ n m)))) ; Return a function.
=> make-add
(fset 'add2 (make-add 2)) ; Define function `add2'
; with `(make-add 2)'.
=> (lambda (m) (+ n m))
(add2 4) ; Try to add 2 to 4.
error--> Symbol's value as variable is void: n
Some Lisp dialects have "closures", objects that are like functions
but record additional variable bindings. Emacs Lisp does not have
closures.
Implementation of Dynamic Scoping
---------------------------------
A simple sample implementation (which is not how Emacs Lisp actually
works) may help you understand dynamic binding. This technique is
called "deep binding" and was used in early Lisp systems.
Suppose there is a stack of bindings, which are variable-value pairs.
At entry to a function or to a `let' form, we can push bindings onto
the stack for the arguments or local variables created there. We can
pop those bindings from the stack at exit from the binding construct.
We can find the value of a variable by searching the stack from top
to bottom for a binding for that variable; the value from that binding
is the value of the variable. To set the variable, we search for the
current binding, then store the new value into that binding.
As you can see, a function's bindings remain in effect as long as it
continues execution, even during its calls to other functions. That is
why we say the extent of the binding is dynamic. And any other function
can refer to the bindings, if it uses the same variables while the
bindings are in effect. That is why we say the scope is indefinite.
The actual implementation of variable scoping in GNU Emacs Lisp uses
a technique called "shallow binding". Each variable has a standard
place in which its current value is always found--the value cell of the
symbol.
In shallow binding, setting the variable works by storing a value in
the value cell. Creating a new binding works by pushing the old value
(belonging to a previous binding) onto a stack, and storing the new
local value in the value cell. Eliminating a binding works by popping
the old value off the stack, into the value cell.
We use shallow binding because it has the same results as deep
binding, but runs faster, since there is never a need to search for a
binding.
Proper Use of Dynamic Scoping
-----------------------------
Binding a variable in one function and using it in another is a
powerful technique, but if used without restraint, it can make programs
hard to understand. There are two clean ways to use this technique:
* Use or bind the variable only in a few related functions, written
close together in one file. Such a variable is used for
communication within one program.
You should write comments to inform other programmers that they
can see all uses of the variable before them, and to advise them
not to add uses elsewhere.
* Give the variable a well-defined, documented meaning, and make all
appropriate functions refer to it (but not bind it or set it)
wherever that meaning is relevant. For example, the variable
`case-fold-search' is defined as "non-`nil' means ignore case when
searching"; various search and replace functions refer to it
directly or through their subroutines, but do not bind or set it.
Then you can bind the variable in other programs, knowing reliably
what the effect will be.
In either case, you should define the variable with `defvar'. This
helps other people understand your program by telling them to look for
inter-function usage. It also avoids a warning from the byte compiler.
Choose the variable's name to avoid name conflicts--don't use short
names like `x'.
Buffer-Local Variables
======================
Global and local variable bindings are found in most programming
languages in one form or another. Emacs, however, also supports
additional, unusual kinds of variable binding: "buffer-local" bindings,
which apply only in one buffer, and "frame-local" bindings, which apply
only in one frame. Having different values for a variable in different
buffers and/or frames is an important customization method.
This section describes buffer-local bindings; for frame-local
bindings, see the following section, *Note Frame-Local Variables::. (A
few variables have bindings that are local to each terminal; see *Note
Multiple Displays::.)
Introduction to Buffer-Local Variables
--------------------------------------
A buffer-local variable has a buffer-local binding associated with a
particular buffer. The binding is in effect when that buffer is
current; otherwise, it is not in effect. If you set the variable while
a buffer-local binding is in effect, the new value goes in that binding,
so its other bindings are unchanged. This means that the change is
visible only in the buffer where you made it.
The variable's ordinary binding, which is not associated with any
specific buffer, is called the "default binding". In most cases, this
is the global binding.
A variable can have buffer-local bindings in some buffers but not in
other buffers. The default binding is shared by all the buffers that
don't have their own bindings for the variable. (This includes all
newly-created buffers.) If you set the variable in a buffer that does
not have a buffer-local binding for it, this sets the default binding
(assuming there are no frame-local bindings to complicate the matter),
so the new value is visible in all the buffers that see the default
binding.
The most common use of buffer-local bindings is for major modes to
change variables that control the behavior of commands. For example, C
mode and Lisp mode both set the variable `paragraph-start' to specify
that only blank lines separate paragraphs. They do this by making the
variable buffer-local in the buffer that is being put into C mode or
Lisp mode, and then setting it to the new value for that mode. *Note
Major Modes::.
The usual way to make a buffer-local binding is with
`make-local-variable', which is what major mode commands typically use.
This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as "automatically
buffer-local" by calling `make-variable-buffer-local'. You can think
of this as making the variable local in all buffers, even those yet to
be created. More precisely, the effect is that setting the variable
automatically makes the variable local to the current buffer if it is
not already so. All buffers start out by sharing the default value of
the variable as usual, but setting the variable creates a buffer-local
binding for the current buffer. The new value is stored in the
buffer-local binding, leaving the default binding untouched. This
means that the default value cannot be changed with `setq' in any
buffer; the only way to change it is with `setq-default'.
*Warning:* When a variable has buffer-local values in one or more
buffers, you can get Emacs very confused by binding the variable with
`let', changing to a different current buffer in which a different
binding is in effect, and then exiting the `let'. This can scramble
the values of the buffer-local and default bindings.
To preserve your sanity, avoid using a variable in that way. If you
use `save-excursion' around each piece of code that changes to a
different current buffer, you will not have this problem (*note
Excursions::). Here is an example of what to avoid:
(setq foo 'b)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
(set-buffer "b")
BODY...)
foo => 'a ; The old buffer-local value from buffer `a'
; is now the default value.
(set-buffer "a")
foo => 'temp ; The local `let' value that should be gone
; is now the buffer-local value in buffer `a'.
But `save-excursion' as shown here avoids the problem:
(let ((foo 'temp))
(save-excursion
(set-buffer "b")
BODY...))
Note that references to `foo' in BODY access the buffer-local
binding of buffer `b'.
When a file specifies local variable values, these become
buffer-local values when you visit the file. *Note File Variables:
(emacs)File Variables.
Creating and Deleting Buffer-Local Bindings
-------------------------------------------
- Command: make-local-variable variable
This function creates a buffer-local binding in the current buffer
for VARIABLE (a symbol). Other buffers are not affected. The
value returned is VARIABLE.
The buffer-local value of VARIABLE starts out as the same value
VARIABLE previously had. If VARIABLE was void, it remains void.
;; In buffer `b1':
(setq foo 5) ; Affects all buffers.
=> 5
(make-local-variable 'foo) ; Now it is local in `b1'.
=> foo
foo ; That did not change
=> 5 ; the value.
(setq foo 6) ; Change the value
=> 6 ; in `b1'.
foo
=> 6
;; In buffer `b2', the value hasn't changed.
(save-excursion
(set-buffer "b2")
foo)
=> 5
Making a variable buffer-local within a `let'-binding for that
variable does not work reliably, unless the buffer in which you do
this is not current either on entry to or exit from the `let'.
This is because `let' does not distinguish between different kinds
of bindings; it knows only which variable the binding was made for.
If the variable is terminal-local, this function signals an error.
Such variables cannot have buffer-local bindings as well. *Note
Multiple Displays::.
*Note:* Do not use `make-local-variable' for a hook variable.
Instead, use `make-local-hook'. *Note Hooks::.
- Command: make-variable-buffer-local variable
This function marks VARIABLE (a symbol) automatically
buffer-local, so that any subsequent attempt to set it will make it
local to the current buffer at the time.
A peculiar wrinkle of this feature is that binding the variable
(with `let' or other binding constructs) does not create a
buffer-local binding for it. Only setting the variable (with
`set' or `setq') does so.
The value returned is VARIABLE.
*Warning:* Don't assume that you should use
`make-variable-buffer-local' for user-option variables, simply
because users _might_ want to customize them differently in
different buffers. Users can make any variable local, when they
wish to. It is better to leave the choice to them.
The time to use `make-variable-buffer-local' is when it is crucial
that no two buffers ever share the same binding. For example,
when a variable is used for internal purposes in a Lisp program
which depends on having separate values in separate buffers, then
using `make-variable-buffer-local' can be the best solution.
- Function: local-variable-p variable &optional buffer
This returns `t' if VARIABLE is buffer-local in buffer BUFFER
(which defaults to the current buffer); otherwise, `nil'.
- Function: buffer-local-variables &optional buffer
This function returns a list describing the buffer-local variables
in buffer BUFFER. (If BUFFER is omitted, the current buffer is
used.) It returns an association list (*note Association Lists::)
in which each element contains one buffer-local variable and its
value. However, when a variable's buffer-local binding in BUFFER
is void, then the variable appears directly in the resulting list.
(make-local-variable 'foobar)
(makunbound 'foobar)
(make-local-variable 'bind-me)
(setq bind-me 69)
(setq lcl (buffer-local-variables))
;; First, built-in variables local in all buffers:
=> ((mark-active . nil)
(buffer-undo-list . nil)
(mode-name . "Fundamental")
...
;; Next, non-built-in buffer-local variables.
;; This one is buffer-local and void:
foobar
;; This one is buffer-local and nonvoid:
(bind-me . 69))
Note that storing new values into the CDRs of cons cells in this
list does _not_ change the buffer-local values of the variables.
- Command: kill-local-variable variable
This function deletes the buffer-local binding (if any) for
VARIABLE (a symbol) in the current buffer. As a result, the
default binding of VARIABLE becomes visible in this buffer. This
typically results in a change in the value of VARIABLE, since the
default value is usually different from the buffer-local value just
eliminated.
If you kill the buffer-local binding of a variable that
automatically becomes buffer-local when set, this makes the
default value visible in the current buffer. However, if you set
the variable again, that will once again create a buffer-local
binding for it.
`kill-local-variable' returns VARIABLE.
This function is a command because it is sometimes useful to kill
one buffer-local variable interactively, just as it is useful to
create buffer-local variables interactively.
- Function: kill-all-local-variables
This function eliminates all the buffer-local variable bindings of
the current buffer except for variables marked as "permanent". As
a result, the buffer will see the default values of most variables.
This function also resets certain other information pertaining to
the buffer: it sets the local keymap to `nil', the syntax table to
the value of `(standard-syntax-table)', the case table to
`(standard-case-table)', and the abbrev table to the value of
`fundamental-mode-abbrev-table'.
The very first thing this function does is run the normal hook
`change-major-mode-hook' (see below).
Every major mode command begins by calling this function, which
has the effect of switching to Fundamental mode and erasing most
of the effects of the previous major mode. To ensure that this
does its job, the variables that major modes set should not be
marked permanent.
`kill-all-local-variables' returns `nil'.
- Variable: change-major-mode-hook
The function `kill-all-local-variables' runs this normal hook
before it does anything else. This gives major modes a way to
arrange for something special to be done if the user switches to a
different major mode. For best results, make this variable
buffer-local, so that it will disappear after doing its job and
will not interfere with the subsequent major mode. *Note Hooks::.
A buffer-local variable is "permanent" if the variable name (a
symbol) has a `permanent-local' property that is non-`nil'. Permanent
locals are appropriate for data pertaining to where the file came from
or how to save it, rather than with how to edit the contents.
The Default Value of a Buffer-Local Variable
--------------------------------------------
The global value of a variable with buffer-local bindings is also
called the "default" value, because it is the value that is in effect
whenever neither the current buffer nor the selected frame has its own
binding for the variable.
The functions `default-value' and `setq-default' access and change a
variable's default value regardless of whether the current buffer has a
buffer-local binding. For example, you could use `setq-default' to
change the default setting of `paragraph-start' for most buffers; and
this would work even when you are in a C or Lisp mode buffer that has a
buffer-local value for this variable.
The special forms `defvar' and `defconst' also set the default value
(if they set the variable at all), rather than any buffer-local or
frame-local value.
- Function: default-value symbol
This function returns SYMBOL's default value. This is the value
that is seen in buffers and frames that do not have their own
values for this variable. If SYMBOL is not buffer-local, this is
equivalent to `symbol-value' (*note Accessing Variables::).
- Function: default-boundp symbol
The function `default-boundp' tells you whether SYMBOL's default
value is nonvoid. If `(default-boundp 'foo)' returns `nil', then
`(default-value 'foo)' would get an error.
`default-boundp' is to `default-value' as `boundp' is to
`symbol-value'.
- Special Form: setq-default [symbol form]...
This special form gives each SYMBOL a new default value, which is
the result of evaluating the corresponding FORM. It does not
evaluate SYMBOL, but does evaluate FORM. The value of the
`setq-default' form is the value of the last FORM.
If a SYMBOL is not buffer-local for the current buffer, and is not
marked automatically buffer-local, `setq-default' has the same
effect as `setq'. If SYMBOL is buffer-local for the current
buffer, then this changes the value that other buffers will see
(as long as they don't have a buffer-local value), but not the
value that the current buffer sees.
;; In buffer `foo':
(make-local-variable 'buffer-local)
=> buffer-local
(setq buffer-local 'value-in-foo)
=> value-in-foo
(setq-default buffer-local 'new-default)
=> new-default
buffer-local
=> value-in-foo
(default-value 'buffer-local)
=> new-default
;; In (the new) buffer `bar':
buffer-local
=> new-default
(default-value 'buffer-local)
=> new-default
(setq buffer-local 'another-default)
=> another-default
(default-value 'buffer-local)
=> another-default
;; Back in buffer `foo':
buffer-local
=> value-in-foo
(default-value 'buffer-local)
=> another-default
- Function: set-default symbol value
This function is like `setq-default', except that SYMBOL is an
ordinary evaluated argument.
(set-default (car '(a b c)) 23)
=> 23
(default-value 'a)
=> 23
Frame-Local Variables
=====================
Just as variables can have buffer-local bindings, they can also have
frame-local bindings. These bindings belong to one frame, and are in
effect when that frame is selected. Frame-local bindings are actually
frame parameters: you create a frame-local binding in a specific frame
by calling `modify-frame-parameters' and specifying the variable name
as the parameter name.
To enable frame-local bindings for a certain variable, call the
function `make-variable-frame-local'.
- Command: make-variable-frame-local variable
Enable the use of frame-local bindings for VARIABLE. This does
not in itself create any frame-local bindings for the variable;
however, if some frame already has a value for VARIABLE as a frame
parameter, that value automatically becomes a frame-local binding.
If the variable is terminal-local, this function signals an error,
because such variables cannot have frame-local bindings as well.
*Note Multiple Displays::. A few variables that are implemented
specially in Emacs can be (and usually are) buffer-local, but can
never be frame-local.
Buffer-local bindings take precedence over frame-local bindings.
Thus, consider a variable `foo': if the current buffer has a
buffer-local binding for `foo', that binding is active; otherwise, if
the selected frame has a frame-local binding for `foo', that binding is
active; otherwise, the default binding of `foo' is active.
Here is an example. First we prepare a few bindings for `foo':
(setq f1 (selected-frame))
(make-variable-frame-local 'foo)
;; Make a buffer-local binding for `foo' in `b1'.
(set-buffer (get-buffer-create "b1"))
(make-local-variable 'foo)
(setq foo '(b 1))
;; Make a frame-local binding for `foo' in a new frame.
;; Store that frame in `f2'.
(setq f2 (make-frame))
(modify-frame-parameters f2 '((foo . (f 2))))
Now we examine `foo' in various contexts. Whenever the buffer `b1'
is current, its buffer-local binding is in effect, regardless of the
selected frame:
(select-frame f1)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
(select-frame f2)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
Otherwise, the frame gets a chance to provide the binding; when frame
`f2' is selected, its frame-local binding is in effect:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
foo
=> (f 2)
When neither the current buffer nor the selected frame provides a
binding, the default binding is used:
(select-frame f1)
(set-buffer (get-buffer "*scratch*"))
foo
=> nil
When the active binding of a variable is a frame-local binding, setting
the variable changes that binding. You can observe the result with
`frame-parameters':
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
(setq foo 'nobody)
(assq 'foo (frame-parameters f2))
=> (foo . nobody)
Possible Future Local Variables
===============================
We have considered the idea of bindings that are local to a category
of frames--for example, all color frames, or all frames with dark
backgrounds. We have not implemented them because it is not clear that
this feature is really useful. You can get more or less the same
results by adding a function to `after-make-frame-functions', set up to
define a particular frame parameter according to the appropriate
conditions for each frame.
It would also be possible to implement window-local bindings. We
don't know of many situations where they would be useful, and it seems
that indirect buffers (*note Indirect Buffers::) with buffer-local
bindings offer a way to handle these situations more robustly.
If sufficient application is found for either of these two kinds of
local bindings, we will provide it in a subsequent Emacs version.
File Local Variables
====================
This section describes the functions and variables that affect
processing of local variables lists in files.
- User Option: enable-local-variables
This variable controls whether to process file local variables
lists. A value of `t' means process the local variables lists
unconditionally; `nil' means ignore them; anything else means ask
the user what to do for each file. The default value is `t'.
- Function: hack-local-variables &optional force
This function parses, and binds or evaluates as appropriate, any
local variables specified by the contents of the current buffer.
The variable `enable-local-variables' has its effect here.
The argument FORCE usually comes from the argument FIND-FILE given
to `normal-mode'.
If a file local variable list could specify the a function that will
be called later, or an expression that will be executed later, simply
visiting a file could take over your Emacs. To prevent this, Emacs
takes care not to allow local variable lists to set such variables.
For one thing, any variable whose name ends in `-function',
`-functions', `-hook', `-hooks', `-form', `-forms', `-program',
`-command' or `-predicate' cannot be set in a local variable list. In
general, you should use such a name whenever it is appropriate for the
variable's meaning.
In addition, any variable whose name has a non-`nil'
`risky-local-variable' property is also ignored. So are all variables
listed in `ignored-local-variables':
- Variable: ignored-local-variables
This variable holds a list of variables that should not be set by
a file's local variables list. Any value specified for one of
these variables is ignored.
The `Eval:' "variable" is also a potential loophole, so Emacs
normally asks for confirmation before handling it.
- User Option: enable-local-eval
This variable controls processing of `Eval:' in local variables
lists in files being visited. A value of `t' means process them
unconditionally; `nil' means ignore them; anything else means ask
the user what to do for each file. The default value is `maybe'.
Functions
*********
A Lisp program is composed mainly of Lisp functions. This chapter
explains what functions are, how they accept arguments, and how to
define them.
What Is a Function?
===================
In a general sense, a function is a rule for carrying on a
computation given several values called "arguments". The result of the
computation is called the value of the function. The computation can
also have side effects: lasting changes in the values of variables or
the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other
function-like objects.
"function"
In Emacs Lisp, a "function" is anything that can be applied to
arguments in a Lisp program. In some cases, we use it more
specifically to mean a function written in Lisp. Special forms and
macros are not functions.
"primitive"
A "primitive" is a function callable from Lisp that is written in
C, such as `car' or `append'. These functions are also called
"built-in" functions or "subrs". (Special forms are also
considered primitives.)
Usually the reason we implement a function as a primitive is either
because it is fundamental, because it provides a low-level
interface to operating system services, or because it needs to run
fast. Primitives can be modified or added only by changing the C
sources and recompiling the editor. See *Note Writing Emacs
Primitives::.
"lambda expression"
A "lambda expression" is a function written in Lisp. These are
described in the following section. *Note Lambda Expressions::.
"special form"
A "special form" is a primitive that is like a function but does
not evaluate all of its arguments in the usual way. It may
evaluate only some of the arguments, or may evaluate them in an
unusual order, or several times. Many special forms are described
in *Note Control Structures::.
"macro"
A "macro" is a construct defined in Lisp by the programmer. It
differs from a function in that it translates a Lisp expression
that you write into an equivalent expression to be evaluated
instead of the original expression. Macros enable Lisp
programmers to do the sorts of things that special forms can do.
*Note Macros::, for how to define and use macros.
"command"
A "command" is an object that `command-execute' can invoke; it is
a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
interactive declaration (*note Defining Commands::). Such a
function can be called from Lisp expressions like other functions;
in this case, the fact that the function is a command makes no
difference.
Keyboard macros (strings and vectors) are commands also, even
though they are not functions. A symbol is a command if its
function definition is a command; such symbols can be invoked with
`M-x'. The symbol is a function as well if the definition is a
function. *Note Command Overview::.
"keystroke command"
A "keystroke command" is a command that is bound to a key sequence
(typically one to three keystrokes). The distinction is made here
merely to avoid confusion with the meaning of "command" in
non-Emacs editors; for Lisp programs, the distinction is normally
unimportant.
"byte-code function"
A "byte-code function" is a function that has been compiled by the
byte compiler. *Note Byte-Code Type::.
- Function: functionp object
This function returns `t' if OBJECT is any kind of function, or a
special form or macro.
- Function: subrp object
This function returns `t' if OBJECT is a built-in function (i.e.,
a Lisp primitive).
(subrp 'message) ; `message' is a symbol,
=> nil ; not a subr object.
(subrp (symbol-function 'message))
=> t
- Function: byte-code-function-p object
This function returns `t' if OBJECT is a byte-code function. For
example:
(byte-code-function-p (symbol-function 'next-line))
=> t
- Function: subr-arity subr
This function provides information about the argument list of a
primitive, SUBR. The returned value is a pair `(MIN . MAX)'. MIN
is the minimum number of args. MAX is the maximum number or the
symbol `many', for a function with `&rest' arguments, or the
symbol `unevalled' if SUBR is a special form.
Lambda Expressions
==================
A function written in Lisp is a list that looks like this:
(lambda (ARG-VARIABLES...)
[DOCUMENTATION-STRING]
[INTERACTIVE-DECLARATION]
BODY-FORMS...)
Such a list is called a "lambda expression". In Emacs Lisp, it
actually is valid as an expression--it evaluates to itself. In some
other Lisp dialects, a lambda expression is not a valid expression at
all. In either case, its main use is not to be evaluated as an
expression, but to be called as a function.
Components of a Lambda Expression
---------------------------------
A function written in Lisp (a "lambda expression") is a list that
looks like this:
(lambda (ARG-VARIABLES...)
[DOCUMENTATION-STRING]
[INTERACTIVE-DECLARATION]
BODY-FORMS...)
The first element of a lambda expression is always the symbol
`lambda'. This indicates that the list represents a function. The
reason functions are defined to start with `lambda' is so that other
lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of symbols--the argument variable names.
This is called the "lambda list". When a Lisp function is called, the
argument values are matched up against the variables in the lambda
list, which are given local bindings with the values provided. *Note
Local Variables::.
The documentation string is a Lisp string object placed within the
function definition to describe the function for the Emacs help
facilities. *Note Function Documentation::.
The interactive declaration is a list of the form `(interactive
CODE-STRING)'. This declares how to provide arguments if the function
is used interactively. Functions with this declaration are called
"commands"; they can be called using `M-x' or bound to a key.
Functions not intended to be called in this way should not have
interactive declarations. *Note Defining Commands::, for how to write
an interactive declaration.
The rest of the elements are the "body" of the function: the Lisp
code to do the work of the function (or, as a Lisp programmer would say,
"a list of Lisp forms to evaluate"). The value returned by the
function is the value returned by the last element of the body.
A Simple Lambda-Expression Example
----------------------------------
Consider for example the following function:
(lambda (a b c) (+ a b c))
We can call this function by writing it as the CAR of an expression,
like this:
((lambda (a b c) (+ a b c))
1 2 3)
This call evaluates the body of the lambda expression with the variable
`a' bound to 1, `b' bound to 2, and `c' bound to 3. Evaluation of the
body adds these three numbers, producing the result 6; therefore, this
call to the function returns the value 6.
Note that the arguments can be the results of other function calls,
as in this example:
((lambda (a b c) (+ a b c))
1 (* 2 3) (- 5 4))
This evaluates the arguments `1', `(* 2 3)', and `(- 5 4)' from left to
right. Then it applies the lambda expression to the argument values 1,
6 and 1 to produce the value 8.
It is not often useful to write a lambda expression as the CAR of a
form in this way. You can get the same result, of making local
variables and giving them values, using the special form `let' (*note
Local Variables::). And `let' is clearer and easier to use. In
practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (*note Anonymous Functions::).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form `let' was invented. At that
time, they were the only way to bind and initialize local variables.
Other Features of Argument Lists
--------------------------------
Our simple sample function, `(lambda (a b c) (+ a b c))', specifies
three argument variables, so it must be called with three arguments: if
you try to call it with only two arguments or four arguments, you get a
`wrong-number-of-arguments' error.
It is often convenient to write a function that allows certain
arguments to be omitted. For example, the function `substring' accepts
three arguments--a string, the start index and the end index--but the
third argument defaults to the LENGTH of the string if you omit it. It
is also convenient for certain functions to accept an indefinite number
of arguments, as the functions `list' and `+' do.
To specify optional arguments that may be omitted when a function is
called, simply include the keyword `&optional' before the optional
arguments. To specify a list of zero or more extra arguments, include
the keyword `&rest' before one final argument.
Thus, the complete syntax for an argument list is as follows:
(REQUIRED-VARS...
[&optional OPTIONAL-VARS...]
[&rest REST-VAR])
The square brackets indicate that the `&optional' and `&rest' clauses,
and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
REQUIRED-VARS. There may be actual arguments for zero or more of the
OPTIONAL-VARS, and there cannot be any actual arguments beyond that
unless the lambda list uses `&rest'. In that case, there may be any
number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to `nil'. There is no way for the function to
distinguish between an explicit argument of `nil' and an omitted
argument. However, the body of the function is free to consider `nil'
an abbreviation for some other meaningful value. This is what
`substring' does; `nil' as the third argument to `substring' means to
use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what
default value to use when an optional argument is omitted; Emacs
Lisp always uses `nil'. Emacs Lisp does not support "supplied-p"
variables that tell you whether an argument was explicitly passed.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds `a' and `b' to the first two actual arguments, which are
required. If one or two more arguments are provided, `c' and `d' are
bound to them respectively; any arguments after the first four are
collected into a list and `e' is bound to that list. If there are only
two arguments, `c' is `nil'; if two or three arguments, `d' is `nil';
if four arguments or fewer, `e' is `nil'.
There is no way to have required arguments following optional
ones--it would not make sense. To see why this must be so, suppose
that `c' in the example were optional and `d' were required. Suppose
three actual arguments are given; which variable would the third
argument be for? Would it be used for the C, or for D? One can argue
for both possibilities. Similarly, it makes no sense to have any more
arguments (either required or optional) after a `&rest' argument.
Here are some examples of argument lists and proper calls:
((lambda (n) (1+ n)) ; One required:
1) ; requires exactly one argument.
=> 2
((lambda (n &optional n1) ; One required and one optional:
(if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments.
1 2)
=> 3
((lambda (n &rest ns) ; One required and one rest:
(+ n (apply '+ ns))) ; 1 or more arguments.
1 2 3 4 5)
=> 15
Documentation Strings of Functions
----------------------------------
A lambda expression may optionally have a "documentation string" just
after the lambda list. This string does not affect execution of the
function; it is a kind of comment, but a systematized comment which
actually appears inside the Lisp world and can be used by the Emacs help
facilities. *Note Documentation::, for how the DOCUMENTATION-STRING is
accessed.
It is a good idea to provide documentation strings for all the
functions in your program, even those that are called only from within
your program. Documentation strings are like comments, except that they
are easier to access.
The first line of the documentation string should stand on its own,
because `apropos' displays just this first line. It should consist of
one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented in the
source file, but since these spaces come before the starting
double-quote, they are not part of the string. Some people make a
practice of indenting any additional lines of the string so that the
text lines up in the program source. _This is a mistake._ The
indentation of the following lines is inside the string; what looks
nice in the source code will look ugly when displayed by the help
commands.
You may wonder how the documentation string could be optional, since
there are required components of the function that follow it (the body).
Since evaluation of a string returns that string, without any side
effects, it has no effect if it is not the last form in the body.
Thus, in practice, there is no confusion between the first form of the
body and the documentation string; if the only body form is a string
then it serves both as the return value and as the documentation.
Naming a Function
=================
In most computer languages, every function has a name; the idea of a
function without a name is nonsensical. In Lisp, a function in the
strictest sense has no name. It is simply a list whose first element is
`lambda', a byte-code function object, or a primitive subr-object.
However, a symbol can serve as the name of a function. This happens
when you put the function in the symbol's "function cell" (*note Symbol
Components::). Then the symbol itself becomes a valid, callable
function, equivalent to the list or subr-object that its function cell
refers to. The contents of the function cell are also called the
symbol's "function definition". The procedure of using a symbol's
function definition in place of the symbol is called "symbol function
indirection"; see *Note Function Indirection::.
In practice, nearly all functions are given names in this way and
referred to through their names. For example, the symbol `car' works
as a function and does what it does because the primitive subr-object
`#<subr car>' is stored in its function cell.
We give functions names because it is convenient to refer to them by
their names in Lisp expressions. For primitive subr-objects such as
`#<subr car>', names are the only way you can refer to them: there is
no read syntax for such objects. For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression. Also, a function with a name can refer to itself--it can
be recursive. Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).
We often identify functions with the symbols used to name them. For
example, we often speak of "the function `car'", not distinguishing
between the symbol `car' and the primitive subr-object that is its
function definition. For most purposes, there is no need to
distinguish.
Even so, keep in mind that a function need not have a unique name.
While a given function object _usually_ appears in the function cell of
only one symbol, this is just a matter of convenience. It is easy to
store it in several symbols using `fset'; then each of the symbols is
equally well a name for the same function.
A symbol used as a function name may also be used as a variable;
these two uses of a symbol are independent and do not conflict. (Some
Lisp dialects, such as Scheme, do not distinguish between a symbol's
value and its function definition; a symbol's value as a variable is
also its function definition.) If you have not given a symbol a
function definition, you cannot use it as a function; whether the
symbol has a value as a variable makes no difference to this.
Defining Functions
==================
We usually give a name to a function when it is first created. This
is called "defining a function", and it is done with the `defun'
special form.
- Special Form: defun name argument-list body-forms
`defun' is the usual way to define new Lisp functions. It defines
the symbol NAME as a function that looks like this:
(lambda ARGUMENT-LIST . BODY-FORMS)
`defun' stores this lambda expression in the function cell of
NAME. It returns the value NAME, but usually we ignore this value.
As described previously (*note Lambda Expressions::),
ARGUMENT-LIST is a list of argument names and may include the
keywords `&optional' and `&rest'. Also, the first two of the
BODY-FORMS may be a documentation string and an interactive
declaration.
There is no conflict if the same symbol NAME is also used as a
variable, since the symbol's value cell is independent of the
function cell. *Note Symbol Components::.
Here are some examples:
(defun foo () 5)
=> foo
(foo)
=> 5
(defun bar (a &optional b &rest c)
(list a b c))
=> bar
(bar 1 2 3 4 5)
=> (1 2 (3 4 5))
(bar 1)
=> (1 nil nil)
(bar)
error--> Wrong number of arguments.
(defun capitalize-backwards ()
"Upcase the last letter of a word."
(interactive)
(backward-word 1)
(forward-word 1)
(backward-char 1)
(capitalize-word 1))
=> capitalize-backwards
Be careful not to redefine existing functions unintentionally.
`defun' redefines even primitive functions such as `car' without
any hesitation or notification. Redefining a function already
defined is often done deliberately, and there is no way to
distinguish deliberate redefinition from unintentional
redefinition.
- Function: defalias name definition
This special form defines the symbol NAME as a function, with
definition DEFINITION (which can be any valid Lisp function).
The proper place to use `defalias' is where a specific function
name is being defined--especially where that name appears
explicitly in the source file being loaded. This is because
`defalias' records which file defined the function, just like
`defun' (*note Unloading::).
By contrast, in programs that manipulate function definitions for
other purposes, it is better to use `fset', which does not keep
such records.
See also `defsubst', which defines a function like `defun' and tells
the Lisp compiler to open-code it. *Note Inline Functions::.
Calling Functions
=================
Defining functions is only half the battle. Functions don't do
anything until you "call" them, i.e., tell them to run. Calling a
function is also known as "invocation".
The most common way of invoking a function is by evaluating a list.
For example, evaluating the list `(concat "a" "b")' calls the function
`concat' with arguments `"a"' and `"b"'. *Note Evaluation::, for a
description of evaluation.
When you write a list as an expression in your program, the function
name it calls is written in your program. This means that you choose
which function to call, and how many arguments to give it, when you
write the program. Usually that's just what you want. Occasionally you
need to compute at run time which function to call. To do that, use the
function `funcall'. When you also need to determine at run time how
many arguments to pass, use `apply'.
- Function: funcall function &rest arguments
`funcall' calls FUNCTION with ARGUMENTS, and returns whatever
FUNCTION returns.
Since `funcall' is a function, all of its arguments, including
FUNCTION, are evaluated before `funcall' is called. This means
that you can use any expression to obtain the function to be
called. It also means that `funcall' does not see the expressions
you write for the ARGUMENTS, only their values. These values are
_not_ evaluated a second time in the act of calling FUNCTION;
`funcall' enters the normal procedure for calling a function at the
place where the arguments have already been evaluated.
The argument FUNCTION must be either a Lisp function or a
primitive function. Special forms and macros are not allowed,
because they make sense only when given the "unevaluated" argument
expressions. `funcall' cannot provide these because, as we saw
above, it never knows them in the first place.
(setq f 'list)
=> list
(funcall f 'x 'y 'z)
=> (x y z)
(funcall f 'x 'y '(z))
=> (x y (z))
(funcall 'and t nil)
error--> Invalid function: #<subr and>
Compare these examples with the examples of `apply'.
- Function: apply function &rest arguments
`apply' calls FUNCTION with ARGUMENTS, just like `funcall' but
with one difference: the last of ARGUMENTS is a list of objects,
which are passed to FUNCTION as separate arguments, rather than a
single list. We say that `apply' "spreads" this list so that each
individual element becomes an argument.
`apply' returns the result of calling FUNCTION. As with
`funcall', FUNCTION must either be a Lisp function or a primitive
function; special forms and macros do not make sense in `apply'.
(setq f 'list)
=> list
(apply f 'x 'y 'z)
error--> Wrong type argument: listp, z
(apply '+ 1 2 '(3 4))
=> 10
(apply '+ '(1 2 3 4))
=> 10
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
For an interesting example of using `apply', see the description of
`mapcar', in *Note Mapping Functions::.
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using `funcall' or `apply'. Functions that accept
function arguments are often called "functionals".
Sometimes, when you call a functional, it is useful to supply a no-op
function as the argument. Here are two different kinds of no-op
function:
- Function: identity arg
This function returns ARG and has no side effects.
- Function: ignore &rest args
This function ignores any arguments and returns `nil'.
Mapping Functions
=================
A "mapping function" applies a given function to each element of a
list or other collection. Emacs Lisp has several such functions;
`mapcar' and `mapconcat', which scan a list, are described here. *Note
Creating Symbols::, for the function `mapatoms' which maps over the
symbols in an obarray. *Note Hash Access::, for the function `maphash'
which maps over key/value associations in a hash table.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function `map-char-table' (*note Char-Tables::).
- Function: mapcar function sequence
`mapcar' applies FUNCTION to each element of SEQUENCE in turn, and
returns a list of the results.
The argument SEQUENCE can be any kind of sequence except a
char-table; that is, a list, a vector, a bool-vector, or a string.
The result is always a list. The length of the result is the
same as the length of SEQUENCE.
For example:
(mapcar 'car '((a b) (c d) (e f)))
=> (a c e)
(mapcar '1+ [1 2 3])
=> (2 3 4)
(mapcar 'char-to-string "abc")
=> ("a" "b" "c")
;; Call each function in `my-hooks'.
(mapcar 'funcall my-hooks)
(defun mapcar* (function &rest args)
"Apply FUNCTION to successive cars of all ARGS.
Return the list of results."
;; If no list is exhausted,
(if (not (memq 'nil args))
;; apply function to CARs.
(cons (apply function (mapcar 'car args))
(apply 'mapcar* function
;; Recurse for rest of elements.
(mapcar 'cdr args)))))
(mapcar* 'cons '(a b c) '(1 2 3 4))
=> ((a . 1) (b . 2) (c . 3))
- Function: mapc function sequence
`mapc' is like `mapcar' except that FUNCTION is used for
side-effects only--the values it returns are ignored, not collected
into a list. `mapc' always returns SEQUENCE.
- Function: mapconcat function sequence separator
`mapconcat' applies FUNCTION to each element of SEQUENCE: the
results, which must be strings, are concatenated. Between each
pair of result strings, `mapconcat' inserts the string SEPARATOR.
Usually SEPARATOR contains a space or comma or other suitable
punctuation.
The argument FUNCTION must be a function that can take one
argument and return a string. The argument SEQUENCE can be any
kind of sequence except a char-table; that is, a list, a vector, a
bool-vector, or a string.
(mapconcat 'symbol-name
'(The cat in the hat)
" ")
=> "The cat in the hat"
(mapconcat (function (lambda (x) (format "%c" (1+ x))))
"HAL-8000"
"")
=> "IBM.9111"
Anonymous Functions
===================
In Lisp, a function is a list that starts with `lambda', a byte-code
function compiled from such a list, or alternatively a primitive
subr-object; names are "extra". Although usually functions are defined
with `defun' and given names at the same time, it is occasionally more
concise to use an explicit lambda expression--an anonymous function.
Such a list is valid wherever a function name is.
Any method of creating such a list makes a valid function. Even
this:
(setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
=> (lambda (x) (+ 12 x))
This computes a list that looks like `(lambda (x) (+ 12 x))' and makes
it the value (_not_ the function definition!) of `silly'.
Here is how we might call this function:
(funcall silly 1)
=> 13
(It does _not_ work to write `(silly 1)', because this function is not
the _function definition_ of `silly'. We have not given `silly' any
function definition, just a value as a variable.)
Most of the time, anonymous functions are constants that appear in
your program. For example, you might want to pass one as an argument to
the function `mapcar', which applies any given function to each element
of a list.
Here we define a function `change-property' which uses a function as
its third argument:
(defun change-property (symbol prop function)
(let ((value (get symbol prop)))
(put symbol prop (funcall function value))))
Here we define a function that uses `change-property', passing it a
function to double a number:
(defun double-property (symbol prop)
(change-property symbol prop '(lambda (x) (* 2 x))))
In such cases, we usually use the special form `function' instead of
simple quotation to quote the anonymous function, like this:
(defun double-property (symbol prop)
(change-property symbol prop
(function (lambda (x) (* 2 x)))))
Using `function' instead of `quote' makes a difference if you
compile the function `double-property'. For example, if you compile
the second definition of `double-property', the anonymous function is
compiled as well. By contrast, if you compile the first definition
which uses ordinary `quote', the argument passed to `change-property'
is the precise list shown:
(lambda (x) (* x 2))
The Lisp compiler cannot assume this list is a function, even though it
looks like one, since it does not know what `change-property' will do
with the list. Perhaps it will check whether the CAR of the third
element is the symbol `*'! Using `function' tells the compiler it is
safe to go ahead and compile the constant function.
Nowadays it is possible to omit `function' entirely, like this:
(defun double-property (symbol prop)
(change-property symbol prop (lambda (x) (* 2 x))))
This is because `lambda' itself implies `function'.
We sometimes write `function' instead of `quote' when quoting the
name of a function, but this usage is just a sort of comment:
(function SYMBOL) == (quote SYMBOL) == 'SYMBOL
The read syntax `#'' is a short-hand for using `function'. For
example,
#'(lambda (x) (* x x))
is equivalent to
(function (lambda (x) (* x x)))
- Special Form: function function-object
This special form returns FUNCTION-OBJECT without evaluating it.
In this, it is equivalent to `quote'. However, it serves as a
note to the Emacs Lisp compiler that FUNCTION-OBJECT is intended
to be used only as a function, and therefore can safely be
compiled. Contrast this with `quote', in *Note Quoting::.
See `documentation' in *Note Accessing Documentation::, for a
realistic example using `function' and an anonymous function.
Accessing Function Cell Contents
================================
The "function definition" of a symbol is the object stored in the
function cell of the symbol. The functions described here access, test,
and set the function cell of symbols.
See also the function `indirect-function' in *Note Function
Indirection::.
- Function: symbol-function symbol
This returns the object in the function cell of SYMBOL. If the
symbol's function cell is void, a `void-function' error is
signaled.
This function does not check that the returned object is a
legitimate function.
(defun bar (n) (+ n 2))
=> bar
(symbol-function 'bar)
=> (lambda (n) (+ n 2))
(fset 'baz 'bar)
=> bar
(symbol-function 'baz)
=> bar
If you have never given a symbol any function definition, we say that
that symbol's function cell is "void". In other words, the function
cell does not have any Lisp object in it. If you try to call such a
symbol as a function, it signals a `void-function' error.
Note that void is not the same as `nil' or the symbol `void'. The
symbols `nil' and `void' are Lisp objects, and can be stored into a
function cell just as any other object can be (and they can be valid
functions if you define them in turn with `defun'). A void function
cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
`fboundp'. After you have given a symbol a function definition, you
can make it void once more using `fmakunbound'.
- Function: fboundp symbol
This function returns `t' if the symbol has an object in its
function cell, `nil' otherwise. It does not check that the object
is a legitimate function.
- Function: fmakunbound symbol
This function makes SYMBOL's function cell void, so that a
subsequent attempt to access this cell will cause a `void-function'
error. (See also `makunbound', in *Note Void Variables::.)
(defun foo (x) x)
=> foo
(foo 1)
=>1
(fmakunbound 'foo)
=> foo
(foo 1)
error--> Symbol's function definition is void: foo
- Function: fset symbol definition
This function stores DEFINITION in the function cell of SYMBOL.
The result is DEFINITION. Normally DEFINITION should be a
function or the name of a function, but this is not checked. The
argument SYMBOL is an ordinary evaluated argument.
There are three normal uses of this function:
* Copying one symbol's function definition to another--in other
words, making an alternate name for a function. (If you
think of this as the definition of the new name, you should
use `defalias' instead of `fset'; see *Note Defining
Functions::.)
* Giving a symbol a function definition that is not a list and
therefore cannot be made with `defun'. For example, you can
use `fset' to give a symbol `s1' a function definition which
is another symbol `s2'; then `s1' serves as an alias for
whatever definition `s2' presently has. (Once again use
`defalias' instead of `fset' if you think of this as the
definition of `s1'.)
* In constructs for defining or altering functions. If `defun'
were not a primitive, it could be written in Lisp (as a
macro) using `fset'.
Here are examples of these uses:
;; Save `foo''s definition in `old-foo'.
(fset 'old-foo (symbol-function 'foo))
;; Make the symbol `car' the function definition of `xfirst'.
;; (Most likely, `defalias' would be better than `fset' here.)
(fset 'xfirst 'car)
=> car
(xfirst '(1 2 3))
=> 1
(symbol-function 'xfirst)
=> car
(symbol-function (symbol-function 'xfirst))
=> #<subr car>
;; Define a named keyboard macro.
(fset 'kill-two-lines "\^u2\^k")
=> "\^u2\^k"
;; Here is a function that alters other functions.
(defun copy-function-definition (new old)
"Define NEW with the same function definition as OLD."
(fset new (symbol-function old)))
When writing a function that extends a previously defined function,
the following idiom is sometimes used:
(fset 'old-foo (symbol-function 'foo))
(defun foo ()
"Just like old-foo, except more so."
(old-foo)
(more-so))
This does not work properly if `foo' has been defined to autoload. In
such a case, when `foo' calls `old-foo', Lisp attempts to define
`old-foo' by loading a file. Since this presumably defines `foo'
rather than `old-foo', it does not produce the proper results. The
only way to avoid this problem is to make sure the file is loaded
before moving aside the old definition of `foo'.
But it is unmodular and unclean, in any case, for a Lisp file to
redefine a function defined elsewhere. It is cleaner to use the advice
facility (*note Advising Functions::).
Inline Functions
================
You can define an "inline function" by using `defsubst' instead of
`defun'. An inline function works just like an ordinary function
except for one thing: when you compile a call to the function, the
function's definition is open-coded into the caller.
Making a function inline makes explicit calls run faster. But it
also has disadvantages. For one thing, it reduces flexibility; if you
change the definition of the function, calls already inlined still use
the old definition until you recompile them. Since the flexibility of
redefining functions is an important feature of Emacs, you should not
make a function inline unless its speed is really crucial.
Another disadvantage is that making a large function inline can
increase the size of compiled code both in files and in memory. Since
the speed advantage of inline functions is greatest for small
functions, you generally should not make large functions inline.
It's possible to define a macro to expand into the same code that an
inline function would execute. (*Note Macros::.) But the macro would
be limited to direct use in expressions--a macro cannot be called with
`apply', `mapcar' and so on. Also, it takes some work to convert an
ordinary function into a macro. To convert it into an inline function
is very easy; simply replace `defun' with `defsubst'. Since each
argument of an inline function is evaluated exactly once, you needn't
worry about how many times the body uses the arguments, as you do for
macros. (*Note Argument Evaluation::.)
Inline functions can be used and open-coded later on in the same
file, following the definition, just like macros.
Other Topics Related to Functions
=================================
Here is a table of several functions that do things related to
function calling and function definitions. They are documented
elsewhere, but we provide cross references here.
`apply'
See *Note Calling Functions::.
`autoload'
See *Note Autoload::.
`call-interactively'
See *Note Interactive Call::.
`commandp'
See *Note Interactive Call::.
`documentation'
See *Note Accessing Documentation::.
`eval'
See *Note Eval::.
`funcall'
See *Note Calling Functions::.
`function'
See *Note Anonymous Functions::.
`ignore'
See *Note Calling Functions::.
`indirect-function'
See *Note Function Indirection::.
`interactive'
See *Note Using Interactive::.
`interactive-p'
See *Note Interactive Call::.
`mapatoms'
See *Note Creating Symbols::.
`mapcar'
See *Note Mapping Functions::.
`map-char-table'
See *Note Char-Tables::.
`mapconcat'
See *Note Mapping Functions::.
`undefined'
See *Note Key Lookup::.
Macros
******
"Macros" enable you to define new control constructs and other
language features. A macro is defined much like a function, but instead
of telling how to compute a value, it tells how to compute another Lisp
expression which will in turn compute the value. We call this
expression the "expansion" of the macro.
Macros can do this because they operate on the unevaluated
expressions for the arguments, not on the argument values as functions
do. They can therefore construct an expansion containing these
argument expressions or parts of them.
If you are using a macro to do something an ordinary function could
do, just for the sake of speed, consider using an inline function
instead. *Note Inline Functions::.
A Simple Example of a Macro
===========================
Suppose we would like to define a Lisp construct to increment a
variable value, much like the `++' operator in C. We would like to
write `(inc x)' and have the effect of `(setq x (1+ x))'. Here's a
macro definition that does the job:
(defmacro inc (var)
(list 'setq var (list '1+ var)))
When this is called with `(inc x)', the argument VAR is the symbol
`x'--_not_ the _value_ of `x', as it would be in a function. The body
of the macro uses this to construct the expansion, which is `(setq x
(1+ x))'. Once the macro definition returns this expansion, Lisp
proceeds to evaluate it, thus incrementing `x'.
Expansion of a Macro Call
=========================
A macro call looks just like a function call in that it is a list
which starts with the name of the macro. The rest of the elements of
the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function
call except for one crucial difference: the macro arguments are the
actual expressions appearing in the macro call. They are not evaluated
before they are given to the macro definition. By contrast, the
arguments of a function are results of evaluating the elements of the
function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a `&rest' argument. And the macro body executes and returns
its value just as a function body does.
The second crucial difference between macros and functions is that
the value returned by the macro body is not the value of the macro call.
Instead, it is an alternate expression for computing that value, also
known as the "expansion" of the macro. The Lisp interpreter proceeds
to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain
calls to other macros. It may even be a call to the same macro, though
this is unusual.
You can see the expansion of a given macro call by calling
`macroexpand'.
- Function: macroexpand form &optional environment
This function expands FORM, if it is a macro call. If the result
is another macro call, it is expanded in turn, until something
which is not a macro call results. That is the value returned by
`macroexpand'. If FORM is not a macro call to begin with, it is
returned as given.
Note that `macroexpand' does not look at the subexpressions of
FORM (although some macro definitions may do so). Even if they
are macro calls themselves, `macroexpand' does not expand them.
The function `macroexpand' does not expand calls to inline
functions. Normally there is no need for that, since a call to an
inline function is no harder to understand than a call to an
ordinary function.
If ENVIRONMENT is provided, it specifies an alist of macro
definitions that shadow the currently defined macros. Byte
compilation uses this feature.
(defmacro inc (var)
(list 'setq var (list '1+ var)))
=> inc
(macroexpand '(inc r))
=> (setq r (1+ r))
(defmacro inc2 (var1 var2)
(list 'progn (list 'inc var1) (list 'inc var2)))
=> inc2
(macroexpand '(inc2 r s))
=> (progn (inc r) (inc s)) ; `inc' not expanded here.
Macros and Byte Compilation
===========================
You might ask why we take the trouble to compute an expansion for a
macro and then evaluate the expansion. Why not have the macro body
produce the desired results directly? The reason has to do with
compilation.
When a macro call appears in a Lisp program being compiled, the Lisp
compiler calls the macro definition just as the interpreter would, and
receives an expansion. But instead of evaluating this expansion, it
compiles the expansion as if it had appeared directly in the program.
As a result, the compiled code produces the value and side effects
intended for the macro, but executes at full compiled speed. This would
not work if the macro body computed the value and side effects
itself--they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled. The
compiler has a special feature to help you do this: if a file being
compiled contains a `defmacro' form, the macro is defined temporarily
for the rest of the compilation of that file. To make this feature
work, you must put the `defmacro' in the same file where it is used,
and before its first use.
Byte-compiling a file executes any `require' calls at top-level in
the file. This is in case the file needs the required packages for
proper compilation. One way to ensure that necessary macro definitions
are available during compilation is to require the files that define
them (*note Named Features::). To avoid loading the macro definition
files when someone _runs_ the compiled program, write
`eval-when-compile' around the `require' calls (*note Eval During
Compile::).
Defining Macros
===============
A Lisp macro is a list whose CAR is `macro'. Its CDR should be a
function; expansion of the macro works by applying the function (with
`apply') to the list of unevaluated argument-expressions from the macro
call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to functionals such as `mapcar'. In practice, all
Lisp macros have names, and they are usually defined with the special
form `defmacro'.
- Special Form: defmacro name argument-list body-forms...
`defmacro' defines the symbol NAME as a macro that looks like this:
(macro lambda ARGUMENT-LIST . BODY-FORMS)
(Note that the CDR of this list is a function--a lambda
expression.) This macro object is stored in the function cell of
NAME. The value returned by evaluating the `defmacro' form is
NAME, but usually we ignore this value.
The shape and meaning of ARGUMENT-LIST is the same as in a
function, and the keywords `&rest' and `&optional' may be used
(*note Argument List::). Macros may have a documentation string,
but any `interactive' declaration is ignored since macros cannot be
called interactively.
Backquote
=========
Macros often need to construct large list structures from a mixture
of constants and nonconstant parts. To make this easier, use the ``'
syntax (usually called "backquote").
Backquote allows you to quote a list, but selectively evaluate
elements of that list. In the simplest case, it is identical to the
special form `quote' (*note Quoting::). For example, these two forms
yield identical results:
`(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
'(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
The special marker `,' inside of the argument to backquote indicates
a value that isn't constant. Backquote evaluates the argument of `,'
and puts the value in the list structure:
(list 'a 'list 'of (+ 2 3) 'elements)
=> (a list of 5 elements)
`(a list of ,(+ 2 3) elements)
=> (a list of 5 elements)
Substitution with `,' is allowed at deeper levels of the list
structure also. For example:
(defmacro t-becomes-nil (variable)
`(if (eq ,variable t)
(setq ,variable nil)))
(t-becomes-nil foo)
== (if (eq foo t) (setq foo nil))
You can also "splice" an evaluated value into the resulting list,
using the special marker `,@'. The elements of the spliced list become
elements at the same level as the other elements of the resulting list.
The equivalent code without using ``' is often unreadable. Here are
some examples:
(setq some-list '(2 3))
=> (2 3)
(cons 1 (append some-list '(4) some-list))
=> (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
=> (1 2 3 4 2 3)
(setq list '(hack foo bar))
=> (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
=> (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
=> (use the words foo bar as elements)
In old Emacs versions, before version 19.29, ``' used a different
syntax which required an extra level of parentheses around the entire
backquote construct. Likewise, each `,' or `,@' substitution required
an extra level of parentheses surrounding both the `,' or `,@' and the
following expression. The old syntax required whitespace between the
``', `,' or `,@' and the following expression.
This syntax is still accepted, for compatibility with old Emacs
versions, but we recommend not using it in new programs.
Common Problems Using Macros
============================
The basic facts of macro expansion have counterintuitive
consequences. This section describes some important consequences that
can lead to trouble, and rules to follow to avoid trouble.
Wrong Time
----------
The most common problem in writing macros is doing too some of the
real work prematurely--while expanding the macro, rather than in the
expansion itself. For instance, one real package had this nmacro
definition:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled. This macro definition called
`set-buffer-multibyte' during compilation, which was wrong, and then
did nothing when the compiled package was run. The definition that the
programmer really wanted was this:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to
`set-buffer-multibyte' that will be executed when the compiled program
is actually run.
Evaluating Macro Arguments Repeatedly
-------------------------------------
When defining a macro you must pay attention to the number of times
the arguments will be evaluated when the expansion is executed. The
following macro (used to facilitate iteration) illustrates the problem.
This macro allows us to write a simple "for" loop such as one might
find in Pascal.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while (cons (list '<= var final)
(append body (list (list 'inc var)))))))
=> for
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
=> nil
The arguments `from', `to', and `do' in this macro are "syntactic
sugar"; they are entirely ignored. The idea is that you will write
noise words (such as `from', `to', and `do') in those positions in the
macro call.
Here's an equivalent definition simplified through use of backquote:
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
`(let ((,var ,init))
(while (<= ,var ,final)
,@body
(inc ,var))))
Both forms of this definition (with backquote and without) suffer
from the defect that FINAL is evaluated on every iteration. If FINAL
is a constant, this is not a problem. If it is a more complex form,
say `(long-complex-calculation x)', this can slow down the execution
significantly. If FINAL has side effects, executing it more than once
is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the `for' macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
Unfortunately, this fix introduces another problem, described in the
following section.
Local Variables in Macro Expansions
-----------------------------------
In the previous section, the definition of `for' was fixed as
follows to make the expansion evaluate the macro arguments the proper
number of times:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
The new definition of `for' has a new problem: it introduces a local
variable named `max' which the user does not expect. This causes
trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to `max' inside the body of the `for', which are
supposed to refer to the user's binding of `max', really access the
binding made by `for'.
The way to correct this is to use an uninterned symbol instead of
`max' (*note Creating Symbols::). The uninterned symbol can be bound
and referred to just like any other symbol, but since it is created by
`for', we know that it cannot already appear in the user's program.
Since it is not interned, there is no way the user can put it into the
program later. It will never appear anywhere except where put by
`for'. Here is a definition of `for' that works this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
`(let ((,var ,init)
(,tempvar ,final))
(while (<= ,var ,tempvar)
,@body
(inc ,var)))))
This creates an uninterned symbol named `max' and puts it in the
expansion instead of the usual interned symbol `max' that appears in
expressions ordinarily.
Evaluating Macro Arguments in Expansion
---------------------------------------
Another problem can happen if the macro definition itself evaluates
any of the macro argument expressions, such as by calling `eval' (*note
Eval::). If the argument is supposed to refer to the user's variables,
you may have trouble if the user happens to use a variable with the
same name as one of the macro arguments. Inside the macro body, the
macro argument binding is the most local binding of this variable, so
any references inside the form being evaluated do refer to it. Here is
an example:
(defmacro foo (a)
(list 'setq (eval a) t))
=> foo
(setq x 'b)
(foo x) ==> (setq b t)
=> t ; and `b' has been set.
;; but
(setq a 'c)
(foo a) ==> (setq a t)
=> t ; but this set `a', not `c'.
It makes a difference whether the user's variable is named `a' or
`x', because `a' conflicts with the macro argument variable `a'.
Another problem with calling `eval' in a macro definition is that it
probably won't do what you intend in a compiled program. The
byte-compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with `eval') don't occur and its local variable bindings don't exist.
To avoid these problems, *don't evaluate an argument expression
while computing the macro expansion*. Instead, substitute the
expression into the macro expansion, so that its value will be computed
as part of executing the expansion. This is how the other examples in
this chapter work.
How Many Times is the Macro Expanded?
-------------------------------------
Occasionally problems result from the fact that a macro call is
expanded each time it is evaluated in an interpreted function, but is
expanded only once (during compilation) for a compiled function. If the
macro definition has side effects, they will work differently depending
on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro
expansion, unless you really know what you are doing.
One special kind of side effect can't be avoided: constructing Lisp
objects. Almost all macro expansions include constructed lists; that is
the whole point of most macros. This is usually safe; there is just one
case where you must be careful: when the object you construct is part
of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object
is constructed just once, during compilation. But in interpreted
execution, the macro is expanded each time the macro call runs, and this
means a new object is constructed each time.
In most clean Lisp code, this difference won't matter. It can matter
only if you perform side-effects on the objects constructed by the macro
definition. Thus, to avoid trouble, *avoid side effects on objects
constructed by macro definitions*. Here is an example of how such side
effects can get you into trouble:
(defmacro empty-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (empty-object)))
(if condition
(setcar object condition))
object))
If `initialize' is interpreted, a new list `(nil)' is constructed each
time `initialize' is called. Thus, no side effect survives between
calls. If `initialize' is compiled, then the macro `empty-object' is
expanded during compilation, producing a single "constant" `(nil)' that
is reused and altered each time `initialize' is called.
One way to avoid pathological cases like this is to think of
`empty-object' as a funny kind of constant, not as a memory allocation
construct. You wouldn't use `setcar' on a constant such as `'(nil)',
so naturally you won't use it on `(empty-object)' either.
Writing Customization Definitions
*********************************
This chapter describes how to declare user options for customization,
and also customization groups for classifying them. We use the term
"customization item" to include both kinds of customization
definitions--as well as face definitions (*note Defining Faces::).
Common Item Keywords
====================
All kinds of customization declarations (for variables and groups,
and for faces) accept keyword arguments for specifying various
information. This section describes some keywords that apply to all
kinds.
All of these keywords, except `:tag', can be used more than once in
a given item. Each use of the keyword has an independent effect. The
keyword `:tag' is an exception because any given item can only display
one name.
`:tag LABEL'
Use LABEL, a string, instead of the item's name, to label the item
in customization menus and buffers.
`:group GROUP'
Put this customization item in group GROUP. When you use `:group'
in a `defgroup', it makes the new group a subgroup of GROUP.
If you use this keyword more than once, you can put a single item
into more than one group. Displaying any of those groups will
show this item. Please don't overdo this, since the result would
be annoying.
`:link LINK-DATA'
Include an external link after the documentation string for this
item. This is a sentence containing an active field which
references some other documentation.
There are three alternatives you can use for LINK-DATA:
`(custom-manual INFO-NODE)'
Link to an Info node; INFO-NODE is a string which specifies
the node name, as in `"(emacs)Top"'. The link appears as
`[manual]' in the customization buffer.
`(info-link INFO-NODE)'
Like `custom-manual' except that the link appears in the
customization buffer with the Info node name.
`(url-link URL)'
Link to a web page; URL is a string which specifies the URL.
The link appears in the customization buffer as URL.
`(emacs-commentary-link LIBRARY)'
Link to the commentary section of a library; LIBRARY is a
string which specifies the library name.
You can specify the text to use in the customization buffer by
adding `:tag NAME' after the first element of the LINK-DATA; for
example, `(info-link :tag "foo" "(emacs)Top")' makes a link to the
Emacs manual which appears in the buffer as `foo'.
An item can have more than one external link; however, most items
have none at all.
`:load FILE'
Load file FILE (a string) before displaying this customization
item. Loading is done with `load-library', and only if the file is
not already loaded.
`:require FEATURE'
Require feature FEATURE (a symbol) when installing a value for
this item (an option or a face) that was saved using the
customization feature. This is done by calling `require'.
The most common reason to use `:require' is when a variable enables
a feature such as a minor mode, and just setting the variable
won't have any effect unless the code which implements the mode is
loaded.
Defining Custom Groups
======================
Each Emacs Lisp package should have one main customization group
which contains all the options, faces and other groups in the package.
If the package has a small number of options and faces, use just one
group and put everything in it. When there are more than twelve or so
options and faces, then you should structure them into subgroups, and
put the subgroups under the package's main customization group. It is
OK to put some of the options and faces in the package's main group
alongside the subgroups.
The package's main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use `M-x customize'.) Choose one or more of them (but not too many),
and add your group to each of them using the `:group' keyword.
The way to declare new customization groups is with `defgroup'.
- Macro: defgroup group members doc [keyword value]...
Declare GROUP as a customization group containing MEMBERS. Do not
quote the symbol GROUP. The argument DOC specifies the
documentation string for the group. It should not start with a
`*' as in `defcustom'; that convention is for variables only.
The argument MEMBERS is a list specifying an initial set of
customization items to be members of the group. However, most
often MEMBERS is `nil', and you specify the group's members by
using the `:group' keyword when defining those members.
If you want to specify group members through MEMBERS, each element
should have the form `(NAME WIDGET)'. Here NAME is a symbol, and
WIDGET is a widget type for editing that symbol. Useful widgets
are `custom-variable' for a variable, `custom-face' for a face,
and `custom-group' for a group.
When a new group is introduced into Emacs, use this keyword in
`defgroup':
`:version VERSION'
This option specifies that the group was first introduced in
Emacs version VERSION. The value VERSION must be a string.
Tag the group with a version like this when it is introduced,
rather than the individual members (*note Variable Definitions::).
In addition to the common keywords (*note Common Keywords::), you
can also use this keyword in `defgroup':
`:prefix PREFIX'
If the name of an item in the group starts with PREFIX, then
the tag for that item is constructed (by default) by omitting
PREFIX.
One group can have any number of prefixes.
The prefix-discarding feature is currently turned off, which means
that `:prefix' currently has no effect. We did this because we found
that discarding the specified prefixes often led to confusing names for
options. This happened because the people who wrote the `defgroup'
definitions for various groups added `:prefix' keywords whenever they
make logical sense--that is, whenever the variables in the library have
a common prefix.
In order to obtain good results with `:prefix', it would be
necessary to check the specific effects of discarding a particular
prefix, given the specific items in a group and their names and
documentation. If the resulting text is not clear, then `:prefix'
should not be used in that case.
It should be possible to recheck all the customization groups, delete
the `:prefix' specifications which give unclear results, and then turn
this feature back on, if someone would like to do the work.
Defining Customization Variables
================================
Use `defcustom' to declare user-editable variables.
- Macro: defcustom option default doc [keyword value]...
Declare OPTION as a customizable user option variable. Do not
quote OPTION. The argument DOC specifies the documentation string
for the variable. It should often start with a `*' to mark it as
a "user option" (*note Defining Variables::). Do not start the
documentation string with `*' for options which cannot or normally
should not be set with `set-variable'; examples of the former are
global minor mode options such as `global-font-lock-mode' and
examples of the latter are hooks.
If OPTION is void, `defcustom' initializes it to DEFAULT. DEFAULT
should be an expression to compute the value; be careful in
writing it, because it can be evaluated on more than one occasion.
You should normally avoid using backquotes in DEFAULT because
they are not expanded when editing the value, causing list values
to appear to have the wrong structure.
When you evaluate a `defcustom' form with `C-M-x' in Emacs Lisp
mode (`eval-defun'), a special feature of `eval-defun' arranges to
set the variable unconditionally, without testing whether its
value is void. (The same feature applies to `defvar'.) *Note
Defining Variables::.
`defcustom' accepts the following additional keywords:
`:type TYPE'
Use TYPE as the data type for this option. It specifies which
values are legitimate, and how to display the value. *Note
Customization Types::, for more information.
`:options LIST'
Specify LIST as the list of reasonable values for use in this
option. The user is not restricted to using only these values,
but they are offered as convenient alternatives.
This is meaningful only for certain types, currently including
`hook', `plist' and `alist'. See the definition of the individual
types for a description of how to use `:options'.
`:version VERSION'
This option specifies that the variable was first introduced, or
its default value was changed, in Emacs version VERSION. The value
VERSION must be a string. For example,
(defcustom foo-max 34
"*Maximum number of foo's allowed."
:type 'integer
:group 'foo
:version "20.3")
`:set SETFUNCTION'
Specify SETFUNCTION as the way to change the value of this option.
The function SETFUNCTION should take two arguments, a symbol and
the new value, and should do whatever is necessary to update the
value properly for this option (which may not mean simply setting
the option as a Lisp variable). The default for SETFUNCTION is
`set-default'.
`:get GETFUNCTION'
Specify GETFUNCTION as the way to extract the value of this
option. The function GETFUNCTION should take one argument, a
symbol, and should return the "current value" for that symbol
(which need not be the symbol's Lisp value). The default is
`default-value'.
`:initialize FUNCTION'
FUNCTION should be a function used to initialize the variable when
the `defcustom' is evaluated. It should take two arguments, the
symbol and value. Here are some predefined functions meant for
use in this way:
`custom-initialize-set'
Use the variable's `:set' function to initialize the
variable, but do not reinitialize it if it is already
non-void. This is the default `:initialize' function.
`custom-initialize-default'
Like `custom-initialize-set', but use the function
`set-default' to set the variable, instead of the variable's
`:set' function. This is the usual choice for a variable
whose `:set' function enables or disables a minor mode; with
this choice, defining the variable will not call the minor
mode function, but customizing the variable will do so.
`custom-initialize-reset'
Always use the `:set' function to initialize the variable.
If the variable is already non-void, reset it by calling the
`:set' function using the current value (returned by the
`:get' method).
`custom-initialize-changed'
Use the `:set' function to initialize the variable, if it is
already set or has been customized; otherwise, just use
`set-default'.
`:set-after VARIABLES'
When setting variables according to saved customizations, make
sure to set the variables VARIABLES before this one; in other
words, delay setting this variable until after those others have
been handled. Use `:set-after' if setting this variable won't
work properly unless those other variables already have their
intended values.
The `:require' option is useful for an option that turns on the
operation of a certain feature. Assuming that the package is coded to
check the value of the option, you still need to arrange for the package
to be loaded. You can do that with `:require'. *Note Common
Keywords::. Here is an example, from the library `paren.el':
(defcustom show-paren-mode nil
"Toggle Show Paren mode..."
:set (lambda (symbol value)
(show-paren-mode (or value 0)))
:initialize 'custom-initialize-default
:type 'boolean
:group 'paren-showing
:require 'paren)
If a customization item has a type such as `hook' or `alist', which
supports `:options', you can add additional options to the item,
outside the `defcustom' declaration, by calling `custom-add-option'.
For example, if you define a function `my-lisp-mode-initialization'
intended to be called from `emacs-lisp-mode-hook', you might want to
add that to the list of options for `emacs-lisp-mode-hook', but not by
editing its definition. You can do it thus:
(custom-add-option 'emacs-lisp-mode-hook
'my-lisp-mode-initialization)
- Function: custom-add-option symbol option
To the customization SYMBOL, add OPTION.
The precise effect of adding OPTION depends on the customization
type of SYMBOL.
Internally, `defcustom' uses the symbol property `standard-value' to
record the expression for the default value, and `saved-value' to
record the value saved by the user with the customization buffer. The
`saved-value' property is actually a list whose car is an expression
which evaluates to the value.
Customization Types
===================
When you define a user option with `defcustom', you must specify its
"customization type". That is a Lisp object which describes (1) which
values are legitimate and (2) how to display the value in the
customization buffer for editing.
You specify the customization type in `defcustom' with the `:type'
keyword. The argument of `:type' is evaluated; since types that vary
at run time are rarely useful, normally you use a quoted constant. For
example:
(defcustom diff-command "diff"
"*The command to use to run diff."
:type '(string)
:group 'diff)
In general, a customization type is a list whose first element is a
symbol, one of the customization type names defined in the following
sections. After this symbol come a number of arguments, depending on
the symbol. Between the type symbol and its arguments, you can
optionally write keyword-value pairs (*note Type Keywords::).
Some of the type symbols do not use any arguments; those are called
"simple types". For a simple type, if you do not use any keyword-value
pairs, you can omit the parentheses around the type symbol. For
example just `string' as a customization type is equivalent to
`(string)'.
Simple Types
------------
This section describes all the simple customization types.
`sexp'
The value may be any Lisp object that can be printed and read
back. You can use `sexp' as a fall-back for any option, if you
don't want to take the time to work out a more specific type to
use.
`integer'
The value must be an integer, and is represented textually in the
customization buffer.
`number'
The value must be a number, and is represented textually in the
customization buffer.
`string'
The value must be a string, and the customization buffer shows
just the contents, with no delimiting `"' characters and no
quoting with `\'.
`regexp'
Like `string' except that the string must be a valid regular
expression.
`character'
The value must be a character code. A character code is actually
an integer, but this type shows the value by inserting the
character in the buffer, rather than by showing the number.
`file'
The value must be a file name, and you can do completion with
`M-<TAB>'.
`(file :must-match t)'
The value must be a file name for an existing file, and you can do
completion with `M-<TAB>'.
`directory'
The value must be a directory name, and you can do completion with
`M-<TAB>'.
`hook'
The value must be a list of functions (or a single function, but
that is obsolete usage). This customization type is used for hook
variables. You can use the `:options' keyword in a hook variable's
`defcustom' to specify a list of functions recommended for use in
the hook; see *Note Variable Definitions::.
`alist'
The value must be a list of cons-cells, the CAR of each cell
representing a key, and the CDR of the same cell representing an
associated value. The user can add and delete key/value pairs, and
edit both the key and the value of each pair.
You can specify the key and value types like this:
(alist :key-type KEY-TYPE :value-type VALUE-TYPE)
where KEY-TYPE and VALUE-TYPE are customization type
specifications. The default key type is `sexp', and the default
value type is `sexp'.
The user can add any key matching the specified key type, but you
can give some keys a preferential treatment by specifying them
with the `:options' (see *Note Variable Definitions::). The
specified keys will always be shown in the customize buffer
(together with a suitable value), with a checkbox to include or
exclude or disable the key/value pair from the alist. The user
will not be able to edit the keys specified by the `:options'
keyword argument.
The argument to the `:options' keywords should be a list of option
specifications. Ordinarily, the options are simply atoms, which
are the specified keys. For example:
:options '("foo" "bar" "baz")
specifies that there are three "known" keys, namely `"foo"',
`"bar"' and `"baz"', which will always be shown first.
You may want to restrict the value type for specific keys, for
example, the value associated with the `"bar"' key can only be an
integer. You can specify this by using a list instead of an atom
in the option specification. The first element will specify the
key, like before, while the second element will specify the value
type.
:options '("foo" ("bar" integer) "baz")
Finally, you may want to change how the key is presented. By
default, the key is simply shown as a `const', since the user
cannot change the special keys specified with the `:options'
keyword. However, you may want to use a more specialized type for
presenting the key, like `function-item' if you know it is a
symbol with a function binding. This is done by using a
customization type specification instead of a symbol for the key.
:options '("foo" ((function-item some-function) integer) "baz")
Many alists use lists with two elements, instead of cons cells.
For example,
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE).")
instead of
(defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3))
"Each element is a cons-cell (KEY . VALUE).")
Because of the way lists are implemented on top of cons cells, you
can treat `list-alist' in the example above as a cons cell alist,
where the value type is a list with a single element containing
the real value.
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE)."
:type '(alist :value-type (group integer)))
The `group' widget is used here instead of `list' only because the
formatting is better suited for the purpose.
Similarily, you can have alists with more values associated with
each key, using variations of this trick:
(defcustom person-data '(("brian" 50 t)
("dorith" 55 nil)
("ken" 52 t))
"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG)."
:type '(alist :value-type (group age boolean)))
(defcustom pets '(("brian")
("dorith" "dog" "guppy")
("ken" "cat"))
"Alist of people's pets.
In an element (KEY . VALUE), KEY is the person's name,
and the VALUE is a list of that person's pets."
:type '(alist :value-type (repeat string)))
`plist'
The `plist' custom type is similar to the `alist' (see above),
except that the information is stored as a property list, i.e. a
list of this form:
(KEY VALUE KEY VALUE KEY VALUE ...)
The default `:key-type' for `plist' is `symbol', rather than
`sexp'.
`symbol'
The value must be a symbol. It appears in the customization
buffer as the name of the symbol.
`function'
The value must be either a lambda expression or a function name.
When it is a function name, you can do completion with `M-<TAB>'.
`variable'
The value must be a variable name, and you can do completion with
`M-<TAB>'.
`face'
The value must be a symbol which is a face name, and you can do
completion with `M-<TAB>'.
`boolean'
The value is boolean--either `nil' or `t'. Note that by using
`choice' and `const' together (see the next section), you can
specify that the value must be `nil' or `t', but also specify the
text to describe each value in a way that fits the specific
meaning of the alternative.
`coding-system'
The value must be a coding-system name, and you can do completion
with `M-<TAB>'.
`color'
The value must be a valid color name, and you can do completion
with `M-<TAB>'. A sample is provided,
Composite Types
---------------
When none of the simple types is appropriate, you can use composite
types, which build new types from other types. Here are several ways of
doing that:
`(restricted-sexp :match-alternatives CRITERIA)'
The value may be any Lisp object that satisfies one of CRITERIA.
CRITERIA should be a list, and each element should be one of these
possibilities:
* A predicate--that is, a function of one argument that has no
side effects, and returns either `nil' or non-`nil' according
to the argument. Using a predicate in the list says that
objects for which the predicate returns non-`nil' are
acceptable.
* A quoted constant--that is, `'OBJECT'. This sort of element
in the list says that OBJECT itself is an acceptable value.
For example,
(restricted-sexp :match-alternatives
(integerp 't 'nil))
allows integers, `t' and `nil' as legitimate values.
The customization buffer shows all legitimate values using their
read syntax, and the user edits them textually.
`(cons CAR-TYPE CDR-TYPE)'
The value must be a cons cell, its CAR must fit CAR-TYPE, and its
CDR must fit CDR-TYPE. For example, `(cons string symbol)' is a
customization type which matches values such as `("foo" . foo)'.
In the customization buffer, the CAR and the CDR are displayed and
edited separately, each according to the type that you specify for
it.
`(list ELEMENT-TYPES...)'
The value must be a list with exactly as many elements as the
ELEMENT-TYPES you have specified; and each element must fit the
corresponding ELEMENT-TYPE.
For example, `(list integer string function)' describes a list of
three elements; the first element must be an integer, the second a
string, and the third a function.
In the customization buffer, each element is displayed and edited
separately, according to the type specified for it.
`(vector ELEMENT-TYPES...)'
Like `list' except that the value must be a vector instead of a
list. The elements work the same as in `list'.
`(choice ALTERNATIVE-TYPES...)'
The value must fit at least one of ALTERNATIVE-TYPES. For
example, `(choice integer string)' allows either an integer or a
string.
In the customization buffer, the user selects one of the
alternatives using a menu, and can then edit the value in the
usual way for that alternative.
Normally the strings in this menu are determined automatically
from the choices; however, you can specify different strings for
the menu by including the `:tag' keyword in the alternatives. For
example, if an integer stands for a number of spaces, while a
string is text to use verbatim, you might write the customization
type this way,
(choice (integer :tag "Number of spaces")
(string :tag "Literal text"))
so that the menu offers `Number of spaces' and `Literal Text'.
In any alternative for which `nil' is not a valid value, other than
a `const', you should specify a valid default for that alternative
using the `:value' keyword. *Note Type Keywords::.
`(radio ELEMENT-TYPES...)'
This is similar to `choice', except that the choices are displayed
using `radio buttons' rather than a menu. This has the advantage
of displaying documentation for the choices when applicable and so
is often a good choice for a choice between constant functions
(`function-item' customization types).
`(const VALUE)'
The value must be VALUE--nothing else is allowed.
The main use of `const' is inside of `choice'. For example,
`(choice integer (const nil))' allows either an integer or `nil'.
`:tag' is often used with `const', inside of `choice'. For
example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(const :tag "Ask" foo))
describes a variable for which `t' means yes, `nil' means no, and
`foo' means "ask."
`(other VALUE)'
This alternative can match any Lisp value, but if the user chooses
this alternative, that selects the value VALUE.
The main use of `other' is as the last element of `choice'. For
example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(other :tag "Ask" foo))
describes a variable for which `t' means yes, `nil' means no, and
anything else means "ask." If the user chooses `Ask' from the
menu of alternatives, that specifies the value `foo'; but any
other value (not `t', `nil' or `foo') displays as `Ask', just like
`foo'.
`(function-item FUNCTION)'
Like `const', but used for values which are functions. This
displays the documentation string as well as the function name.
The documentation string is either the one you specify with
`:doc', or FUNCTION's own documentation string.
`(variable-item VARIABLE)'
Like `const', but used for values which are variable names. This
displays the documentation string as well as the variable name.
The documentation string is either the one you specify with
`:doc', or VARIABLE's own documentation string.
`(set TYPES...)'
The value must be a list, and each element of the list must match
one of the TYPES specified.
This appears in the customization buffer as a checklist, so that
each of TYPES may have either one corresponding element or none.
It is not possible to specify two different elements that match
the same one of TYPES. For example, `(set integer symbol)' allows
one integer and/or one symbol in the list; it does not allow
multiple integers or multiple symbols. As a result, it is rare to
use nonspecific types such as `integer' in a `set'.
Most often, the TYPES in a `set' are `const' types, as shown here:
(set (const :bold) (const :italic))
Sometimes they describe possible elements in an alist:
(set (cons :tag "Height" (const height) integer)
(cons :tag "Width" (const width) integer))
That lets the user specify a height value optionally and a width
value optionally.
`(repeat ELEMENT-TYPE)'
The value must be a list and each element of the list must fit the
type ELEMENT-TYPE. This appears in the customization buffer as a
list of elements, with `[INS]' and `[DEL]' buttons for adding more
elements or removing elements.
Splicing into Lists
-------------------
The `:inline' feature lets you splice a variable number of elements
into the middle of a list or vector. You use it in a `set', `choice'
or `repeat' type which appears among the element-types of a `list' or
`vector'.
Normally, each of the element-types in a `list' or `vector'
describes one and only one element of the list or vector. Thus, if an
element-type is a `repeat', that specifies a list of unspecified length
which appears as one element.
But when the element-type uses `:inline', the value it matches is
merged directly into the containing sequence. For example, if it
matches a list with three elements, those become three elements of the
overall sequence. This is analogous to using `,@' in the backquote
construct.
For example, to specify a list whose first element must be `t' and
whose remaining arguments should be zero or more of `foo' and `bar',
use this customization type:
(list (const t) (set :inline t foo bar))
This matches values such as `(t)', `(t foo)', `(t bar)' and `(t foo
bar)'.
When the element-type is a `choice', you use `:inline' not in the
`choice' itself, but in (some of) the alternatives of the `choice'.
For example, to match a list which must start with a file name,
followed either by the symbol `t' or two strings, use this
customization type:
(list file
(choice (const t)
(list :inline t string string)))
If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is `t'. If the
user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
Type Keywords
-------------
You can specify keyword-argument pairs in a customization type after
the type name symbol. Here are the keywords you can use, and their
meanings:
`:value DEFAULT'
This is used for a type that appears as an alternative inside of
`choice'; it specifies the default value to use, at first, if and
when the user selects this alternative with the menu in the
customization buffer.
Of course, if the actual value of the option fits this
alternative, it will appear showing the actual value, not DEFAULT.
If `nil' is not a valid value for the alternative, then it is
essential to specify a valid default with `:value'.
`:format FORMAT-STRING'
This string will be inserted in the buffer to represent the value
corresponding to the type. The following `%' escapes are available
for use in FORMAT-STRING:
`%[BUTTON%]'
Display the text BUTTON marked as a button. The `:action'
attribute specifies what the button will do if the user
invokes it; its value is a function which takes two
arguments--the widget which the button appears in, and the
event.
There is no way to specify two different buttons with
different actions.
`%{SAMPLE%}'
Show SAMPLE in a special face specified by `:sample-face'.
`%v'
Substitute the item's value. How the value is represented
depends on the kind of item, and (for variables) on the
customization type.
`%d'
Substitute the item's documentation string.
`%h'
Like `%d', but if the documentation string is more than one
line, add an active field to control whether to show all of
it or just the first line.
`%t'
Substitute the tag here. You specify the tag with the `:tag'
keyword.
`%%'
Display a literal `%'.
`:action ACTION'
Perform ACTION if the user clicks on a button.
`:button-face FACE'
Use the face FACE (a face name or a list of face names) for button
text displayed with `%[...%]'.
`:button-prefix PREFIX'
`:button-suffix SUFFIX'
These specify the text to display before and after a button. Each
can be:
`nil'
No text is inserted.
a string
The string is inserted literally.
a symbol
The symbol's value is used.
`:tag TAG'
Use TAG (a string) as the tag for the value (or part of the value)
that corresponds to this type.
`:doc DOC'
Use DOC as the documentation string for this value (or part of the
value) that corresponds to this type. In order for this to work,
you must specify a value for `:format', and use `%d' or `%h' in
that value.
The usual reason to specify a documentation string for a type is to
provide more information about the meanings of alternatives inside
a `:choice' type or the parts of some other composite type.
`:help-echo MOTION-DOC'
When you move to this item with `widget-forward' or
`widget-backward', it will display the string MOTION-DOC in the
echo area. In addition, MOTION-DOC is used as the mouse
`help-echo' string and may actually be a function or form evaluated
to yield a help string as for `help-echo' text properties.
`:match FUNCTION'
Specify how to decide whether a value matches the type. The
corresponding value, FUNCTION, should be a function that accepts
two arguments, a widget and a value; it should return non-`nil' if
the value is acceptable.
Loading
*******
Loading a file of Lisp code means bringing its contents into the Lisp
environment in the form of Lisp objects. Emacs finds and opens the
file, reads the text, evaluates each form, and then closes the file.
The load functions evaluate all the expressions in a file just as
the `eval-current-buffer' function evaluates all the expressions in a
buffer. The difference is that the load functions read and evaluate
the text in the file as found on disk, not the text in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code
or as byte-compiled code. Each form in the file is called a "top-level
form". There is no special format for the forms in a loadable file;
any form in a file may equally well be typed directly into a buffer and
evaluated there. (Indeed, most code is tested this way.) Most often,
the forms are function definitions and variable definitions.
A file containing Lisp code is often called a "library". Thus, the
"Rmail library" is a file containing code for Rmail mode. Similarly, a
"Lisp library directory" is a directory of files containing Lisp code.
How Programs Do Loading
=======================
Emacs Lisp has several interfaces for loading. For example,
`autoload' creates a placeholder object for a function defined in a
file; trying to call the autoloading function loads the file to get the
function's real definition (*note Autoload::). `require' loads a file
if it isn't already loaded (*note Named Features::). Ultimately, all
these facilities call the `load' function to do the work.
- Function: load filename &optional missing-ok nomessage nosuffix
must-suffix
This function finds and opens a file of Lisp code, evaluates all
the forms in it, and closes the file.
To find the file, `load' first looks for a file named
`FILENAME.elc', that is, for a file whose name is FILENAME with
`.elc' appended. If such a file exists, it is loaded. If there
is no file by that name, then `load' looks for a file named
`FILENAME.el'. If that file exists, it is loaded. Finally, if
neither of those names is found, `load' looks for a file named
FILENAME with nothing appended, and loads it if it exists. (The
`load' function is not clever about looking at FILENAME. In the
perverse case of a file named `foo.el.el', evaluation of `(load
"foo.el")' will indeed find it.)
If the optional argument NOSUFFIX is non-`nil', then the suffixes
`.elc' and `.el' are not tried. In this case, you must specify
the precise file name you want. By specifying the precise file
name and using `t' for NOSUFFIX, you can prevent perverse file
names such as `foo.el.el' from being tried.
If the optional argument MUST-SUFFIX is non-`nil', then `load'
insists that the file name used must end in either `.el' or
`.elc', unless it contains an explicit directory name. If
FILENAME does not contain an explicit directory name, and does not
end in a suffix, then `load' insists on adding one.
If FILENAME is a relative file name, such as `foo' or
`baz/foo.bar', `load' searches for the file using the variable
`load-path'. It appends FILENAME to each of the directories
listed in `load-path', and loads the first file it finds whose name
matches. The current default directory is tried only if it is
specified in `load-path', where `nil' stands for the default
directory. `load' tries all three possible suffixes in the first
directory in `load-path', then all three suffixes in the second
directory, and so on. *Note Library Search::.
If you get a warning that `foo.elc' is older than `foo.el', it
means you should consider recompiling `foo.el'. *Note Byte
Compilation::.
When loading a source file (not compiled), `load' performs
character set translation just as Emacs would do when visiting the
file. *Note Coding Systems::.
Messages like `Loading foo...' and `Loading foo...done' appear in
the echo area during loading unless NOMESSAGE is non-`nil'.
Any unhandled errors while loading a file terminate loading. If
the load was done for the sake of `autoload', any function
definitions made during the loading are undone.
If `load' can't find the file to load, then normally it signals the
error `file-error' (with `Cannot open load file FILENAME'). But
if MISSING-OK is non-`nil', then `load' just returns `nil'.
You can use the variable `load-read-function' to specify a function
for `load' to use instead of `read' for reading expressions. See
below.
`load' returns `t' if the file loads successfully.
- Command: load-file filename
This command loads the file FILENAME. If FILENAME is a relative
file name, then the current default directory is assumed.
`load-path' is not used, and suffixes are not appended. Use this
command if you wish to specify precisely the file name to load.
- Command: load-library library
This command loads the library named LIBRARY. It is equivalent to
`load', except in how it reads its argument interactively.
- Variable: load-in-progress
This variable is non-`nil' if Emacs is in the process of loading a
file, and it is `nil' otherwise.
- Variable: load-read-function
This variable specifies an alternate expression-reading function
for `load' and `eval-region' to use instead of `read'. The
function should accept one argument, just as `read' does.
Normally, the variable's value is `nil', which means those
functions should use `read'.
*Note:* Instead of using this variable, it is cleaner to use
another, newer feature: to pass the function as the READ-FUNCTION
argument to `eval-region'. *Note Eval::.
For information about how `load' is used in building Emacs, see
*Note Building Emacs::.
Library Search
==============
When Emacs loads a Lisp library, it searches for the library in a
list of directories specified by the variable `load-path'.
- User Option: load-path
The value of this variable is a list of directories to search when
loading files with `load'. Each element is a string (which must be
a directory name) or `nil' (which stands for the current working
directory).
The value of `load-path' is initialized from the environment
variable `EMACSLOADPATH', if that exists; otherwise its default value
is specified in `emacs/src/paths.h' when Emacs is built. Then the list
is expanded by adding subdirectories of the directories in the list.
The syntax of `EMACSLOADPATH' is the same as used for `PATH'; `:'
(or `;', according to the operating system) separates directory names,
and `.' is used for the current default directory. Here is an example
of how to set your `EMACSLOADPATH' variable from a `csh' `.login' file:
setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is how to set it using `sh':
export EMACSLOADPATH
EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is an example of code you can place in your init file (*note
Init File::) to add several directories to the front of your default
`load-path':
(setq load-path
(append (list nil "/user/bil/emacs"
"/usr/local/lisplib"
"~/emacs")
load-path))
In this example, the path searches the current working directory first,
followed then by the `/user/bil/emacs' directory, the
`/usr/local/lisplib' directory, and the `~/emacs' directory, which are
then followed by the standard directories for Lisp code.
Dumping Emacs uses a special value of `load-path'. If the value of
`load-path' at the end of dumping is unchanged (that is, still the same
special value), the dumped Emacs switches to the ordinary `load-path'
value when it starts up, as described above. But if `load-path' has
any other value at the end of dumping, that value is used for execution
of the dumped Emacs also.
Therefore, if you want to change `load-path' temporarily for loading
a few libraries in `site-init.el' or `site-load.el', you should bind
`load-path' locally with `let' around the calls to `load'.
The default value of `load-path', when running an Emacs which has
been installed on the system, includes two special directories (and
their subdirectories as well):
"/usr/local/share/emacs/VERSION/site-lisp"
and
"/usr/local/share/emacs/site-lisp"
The first one is for locally installed packages for a particular Emacs
version; the second is for locally installed packages meant for use with
all installed Emacs versions.
There are several reasons why a Lisp package that works well in one
Emacs version can cause trouble in another. Sometimes packages need
updating for incompatible changes in Emacs; sometimes they depend on
undocumented internal Emacs data that can change without notice;
sometimes a newer Emacs version incorporates a version of the package,
and should be used only with that version.
Emacs finds these directories' subdirectories and adds them to
`load-path' when it starts up. Both immediate subdirectories and
subdirectories multiple levels down are added to `load-path'.
Not all subdirectories are included, though. Subdirectories whose
names do not start with a letter or digit are excluded. Subdirectories
named `RCS' or `CVS' are excluded. Also, a subdirectory which contains
a file named `.nosearch' is excluded. You can use these methods to
prevent certain subdirectories of the `site-lisp' directories from
being searched.
If you run Emacs from the directory where it was built--that is, an
executable that has not been formally installed--then `load-path'
normally contains two additional directories. These are the `lisp' and
`site-lisp' subdirectories of the main build directory. (Both are
represented as absolute file names.)
- Command: locate-library library &optional nosuffix path
interactive-call
This command finds the precise file name for library LIBRARY. It
searches for the library in the same way `load' does, and the
argument NOSUFFIX has the same meaning as in `load': don't add
suffixes `.elc' or `.el' to the specified name LIBRARY.
If the PATH is non-`nil', that list of directories is used instead
of `load-path'.
When `locate-library' is called from a program, it returns the file
name as a string. When the user runs `locate-library'
interactively, the argument INTERACTIVE-CALL is `t', and this
tells `locate-library' to display the file name in the echo area.
Loading Non-ASCII Characters
============================
When Emacs Lisp programs contain string constants with non-ASCII
characters, these can be represented within Emacs either as unibyte
strings or as multibyte strings (*note Text Representations::). Which
representation is used depends on how the file is read into Emacs. If
it is read with decoding into multibyte representation, the text of the
Lisp program will be multibyte text, and its string constants will be
multibyte strings. If a file containing Latin-1 characters (for
example) is read without decoding, the text of the program will be
unibyte text, and its string constants will be unibyte strings. *Note
Coding Systems::.
To make the results more predictable, Emacs always performs decoding
into the multibyte representation when loading Lisp files, even if it
was started with the `--unibyte' option. This means that string
constants with non-ASCII characters translate into multibyte strings.
The only exception is when a particular file specifies no decoding.
The reason Emacs is designed this way is so that Lisp programs give
predictable results, regardless of how Emacs was started. In addition,
this enables programs that depend on using multibyte text to work even
in a unibyte Emacs. Of course, such programs should be designed to
notice whether the user prefers unibyte or multibyte text, by checking
`default-enable-multibyte-characters', and convert representations
appropriately.
In most Emacs Lisp programs, the fact that non-ASCII strings are
multibyte strings should not be noticeable, since inserting them in
unibyte buffers converts them to unibyte automatically. However, if
this does make a difference, you can force a particular Lisp file to be
interpreted as unibyte by writing `-*-unibyte: t;-*-' in a comment on
the file's first line. With that designator, the file will
unconditionally be interpreted as unibyte, even in an ordinary
multibyte Emacs session. This can matter when making keybindings to
non-ASCII characters written as `?vLITERAL'.
Autoload
========
The "autoload" facility allows you to make a function or macro known
in Lisp, but put off loading the file that defines it. The first call
to the function automatically reads the proper file to install the real
definition and other associated code, then runs the real definition as
if it had been loaded all along.
There are two ways to set up an autoloaded function: by calling
`autoload', and by writing a special "magic" comment in the source
before the real definition. `autoload' is the low-level primitive for
autoloading; any Lisp program can call `autoload' at any time. Magic
comments are the most convenient way to make a function autoload, for
packages installed along with Emacs. These comments do nothing on
their own, but they serve as a guide for the command
`update-file-autoloads', which constructs calls to `autoload' and
arranges to execute them when Emacs is built.
- Function: autoload function filename &optional docstring interactive
type
This function defines the function (or macro) named FUNCTION so as
to load automatically from FILENAME. The string FILENAME
specifies the file to load to get the real definition of FUNCTION.
If FILENAME does not contain either a directory name, or the
suffix `.el' or `.elc', then `autoload' insists on adding one of
these suffixes, and it will not load from a file whose name is
just FILENAME with no added suffix.
The argument DOCSTRING is the documentation string for the
function. Normally, this should be identical to the documentation
string in the function definition itself. Specifying the
documentation string in the call to `autoload' makes it possible
to look at the documentation without loading the function's real
definition.
If INTERACTIVE is non-`nil', that says FUNCTION can be called
interactively. This lets completion in `M-x' work without loading
FUNCTION's real definition. The complete interactive
specification is not given here; it's not needed unless the user
actually calls FUNCTION, and when that happens, it's time to load
the real definition.
You can autoload macros and keymaps as well as ordinary functions.
Specify TYPE as `macro' if FUNCTION is really a macro. Specify
TYPE as `keymap' if FUNCTION is really a keymap. Various parts of
Emacs need to know this information without loading the real
definition.
An autoloaded keymap loads automatically during key lookup when a
prefix key's binding is the symbol FUNCTION. Autoloading does not
occur for other kinds of access to the keymap. In particular, it
does not happen when a Lisp program gets the keymap from the value
of a variable and calls `define-key'; not even if the variable
name is the same symbol FUNCTION.
If FUNCTION already has a non-void function definition that is not
an autoload object, `autoload' does nothing and returns `nil'. If
the function cell of FUNCTION is void, or is already an autoload
object, then it is defined as an autoload object like this:
(autoload FILENAME DOCSTRING INTERACTIVE TYPE)
For example,
(symbol-function 'run-prolog)
=> (autoload "prolog" 169681 t nil)
In this case, `"prolog"' is the name of the file to load, 169681
refers to the documentation string in the `emacs/etc/DOC-VERSION'
file (*note Documentation Basics::), `t' means the function is
interactive, and `nil' that it is not a macro or a keymap.
The autoloaded file usually contains other definitions and may
require or provide one or more features. If the file is not completely
loaded (due to an error in the evaluation of its contents), any function
definitions or `provide' calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data `"Autoloading failed to
define function FUNCTION-NAME"'.
A magic autoload comment consists of `;;;###autoload', on a line by
itself, just before the real definition of the function in its
autoloadable source file. The command `M-x update-file-autoloads'
writes a corresponding `autoload' call into `loaddefs.el'. Building
Emacs loads `loaddefs.el' and thus calls `autoload'. `M-x
update-directory-autoloads' is even more powerful; it updates autoloads
for all files in the current directory.
The same magic comment can copy any kind of form into `loaddefs.el'.
If the form following the magic comment is not a function-defining
form or a `defcustom' form, it is copied verbatim. "Function-defining
forms" include `define-skeleton', `define-derived-mode',
`define-generic-mode' and `define-minor-mode' as well as `defun' and
`defmacro'. To save space, a `defcustom' form is converted to a
`defvar' in `loaddefs.el', with some additional information if it uses
`:require'.
You can also use a magic comment to execute a form at build time
_without_ executing it when the file itself is loaded. To do this,
write the form _on the same line_ as the magic comment. Since it is in
a comment, it does nothing when you load the source file; but `M-x
update-file-autoloads' copies it to `loaddefs.el', where it is executed
while building Emacs.
The following example shows how `doctor' is prepared for autoloading
with a magic comment:
;;;###autoload
(defun doctor ()
"Switch to *doctor* buffer and start giving psychotherapy."
(interactive)
(switch-to-buffer "*doctor*")
(doctor-mode))
Here's what that produces in `loaddefs.el':
(autoload 'doctor "doctor" "\
Switch to *doctor* buffer and start giving psychotherapy."
t)
The backslash and newline immediately following the double-quote are a
convention used only in the preloaded uncompiled Lisp files such as
`loaddefs.el'; they tell `make-docfile' to put the documentation string
in the `etc/DOC' file. *Note Building Emacs::. See also the
commentary in `lib-src/make-docfile.c'.
Repeated Loading
================
You can load a given file more than once in an Emacs session. For
example, after you have rewritten and reinstalled a function definition
by editing it in a buffer, you may wish to return to the original
version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the `load' and
`load-library' functions automatically load a byte-compiled file rather
than a non-compiled file of similar name. If you rewrite a file that
you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file! If that happens, the message
displayed when loading the file includes, `(compiled; note, source is
newer)', to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once. For example, think about whether
each variable should be reinitialized when you reload the library;
`defvar' does not change the value if the variable is already
initialized. (*Note Defining Variables::.)
The simplest way to add an element to an alist is like this:
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist))
But this would add multiple elements if the library is reloaded. To
avoid the problem, write this:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
To add an element to a list just once, you can also use `add-to-list'
(*note Setting Variables::).
Occasionally you will want to test explicitly whether a library has
already been loaded. Here's one way to test, in a library, whether it
has been loaded before:
(defvar foo-was-loaded nil)
(unless foo-was-loaded
EXECUTE-FIRST-TIME-ONLY
(setq foo-was-loaded t))
If the library uses `provide' to provide a named feature, you can use
`featurep' earlier in the file to test whether the `provide' call has
been executed before. *Note Named Features::.
Features
========
`provide' and `require' are an alternative to `autoload' for loading
files automatically. They work in terms of named "features".
Autoloading is triggered by calling a specific function, but a feature
is loaded the first time another program asks for it by name.
A feature name is a symbol that stands for a collection of functions,
variables, etc. The file that defines them should "provide" the
feature. Another program that uses them may ensure they are defined by
"requiring" the feature. This loads the file of definitions if it
hasn't been loaded already.
To require the presence of a feature, call `require' with the
feature name as argument. `require' looks in the global variable
`features' to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call `provide' at the top level to add the feature to
`features'; if it fails to do so, `require' signals an error.
For example, in `emacs/lisp/prolog.el', the definition for
`run-prolog' includes the following code:
(defun run-prolog ()
"Run an inferior Prolog process, with I/O via buffer *prolog*."
(interactive)
(require 'comint)
(switch-to-buffer (make-comint "prolog" prolog-program-name))
(inferior-prolog-mode))
The expression `(require 'comint)' loads the file `comint.el' if it has
not yet been loaded. This ensures that `make-comint' is defined.
Features are normally named after the files that provide them, so that
`require' need not be given the file name.
The `comint.el' file contains the following top-level expression:
(provide 'comint)
This adds `comint' to the global `features' list, so that `(require
'comint)' will henceforth know that nothing needs to be done.
When `require' is used at top level in a file, it takes effect when
you byte-compile that file (*note Byte Compilation::) as well as when
you load it. This is in case the required package contains macros that
the byte compiler must know about. It also avoids byte-compiler
warnings for functions and variables defined in the file loaded with
`require'.
Although top-level calls to `require' are evaluated during byte
compilation, `provide' calls are not. Therefore, you can ensure that a
file of definitions is loaded before it is byte-compiled by including a
`provide' followed by a `require' for the same feature, as in the
following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by `load'.
(require 'my-feature) ; Evaluated by byte compiler.
The compiler ignores the `provide', then processes the `require' by
loading the file in question. Loading the file does execute the
`provide' call, so the subsequent `require' call does nothing when the
file is loaded.
- Function: provide feature
This function announces that FEATURE is now loaded, or being
loaded, into the current Emacs session. This means that the
facilities associated with FEATURE are or will be available for
other Lisp programs.
The direct effect of calling `provide' is to add FEATURE to the
front of the list `features' if it is not already in the list.
The argument FEATURE must be a symbol. `provide' returns FEATURE.
features
=> (bar bish)
(provide 'foo)
=> foo
features
=> (foo bar bish)
When a file is loaded to satisfy an autoload, and it stops due to
an error in the evaluating its contents, any function definitions
or `provide' calls that occurred during the load are undone.
*Note Autoload::.
- Function: require feature &optional filename noerror
This function checks whether FEATURE is present in the current
Emacs session (using `(featurep FEATURE)'; see below). The
argument FEATURE must be a symbol.
If the feature is not present, then `require' loads FILENAME with
`load'. If FILENAME is not supplied, then the name of the symbol
FEATURE is used as the base file name to load. However, in this
case, `require' insists on finding FEATURE with an added suffix; a
file whose name is just FEATURE won't be used.
If loading the file fails to provide FEATURE, `require' signals an
error, `Required feature FEATURE was not provided', unless NOERROR
is non-`nil'.
- Function: featurep feature
This function returns `t' if FEATURE has been provided in the
current Emacs session (i.e., if FEATURE is a member of `features'.)
- Variable: features
The value of this variable is a list of symbols that are the
features loaded in the current Emacs session. Each symbol was put
in this list with a call to `provide'. The order of the elements
in the `features' list is not significant.
Unloading
=========
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
`unload-feature':
- Command: unload-feature feature &optional force
This command unloads the library that provided feature FEATURE.
It undefines all functions, macros, and variables defined in that
library with `defun', `defalias', `defsubst', `defmacro',
`defconst', `defvar', and `defcustom'. It then restores any
autoloads formerly associated with those symbols. (Loading saves
these in the `autoload' property of the symbol.)
Before restoring the previous definitions, `unload-feature' runs
`remove-hook' to remove functions in the library from certain
hooks. These hooks include variables whose names end in `hook' or
`-hooks', plus those listed in `loadhist-special-hooks'. This is
to prevent Emacs from ceasing to function because important hooks
refer to functions that are no longer defined.
If these measures are not sufficient to prevent malfunction, a
library can define an explicit unload hook. If
`FEATURE-unload-hook' is defined, it is run as a normal hook
before restoring the previous definitions, _instead of_ the usual
hook-removing actions. The unload hook ought to undo all the
global state changes made by the library that might cease to work
once the library is unloaded. `unload-feature' can cause problems
with libraries that fail to do this, so it should be used with
caution.
Ordinarily, `unload-feature' refuses to unload a library on which
other loaded libraries depend. (A library A depends on library B
if A contains a `require' for B.) If the optional argument FORCE
is non-`nil', dependencies are ignored and you can unload any
library.
The `unload-feature' function is written in Lisp; its actions are
based on the variable `load-history'.
- Variable: load-history
This variable's value is an alist connecting library names with the
names of functions and variables they define, the features they
provide, and the features they require.
Each element is a list and describes one library. The CAR of the
list is the name of the library, as a string. The rest of the
list is composed of these kinds of objects:
* Symbols that were defined by this library.
* Cons cells of the form `(require . FEATURE)' indicating
features that were required.
* Cons cells of the form `(provide . FEATURE)' indicating
features that were provided.
The value of `load-history' may have one element whose CAR is
`nil'. This element describes definitions made with `eval-buffer'
on a buffer that is not visiting a file.
The command `eval-region' updates `load-history', but does so by
adding the symbols defined to the element for the file being visited,
rather than replacing that element. *Note Eval::.
Preloaded libraries don't contribute initially to `load-history'.
Instead, preloading writes information about preloaded libraries into a
file, which can be loaded later on to add information to `load-history'
describing the preloaded files. This file is installed in
`exec-directory' and has a name of the form `fns-EMACSVERSION.el'.
See the source for the function `symbol-file', for an example of
code that loads this file to find functions in preloaded libraries.
- Variable: loadhist-special-hooks
This variable holds a list of hooks to be scanned before unloading
a library, to remove functions defined in the library.
Hooks for Loading
=================
You can ask for code to be executed if and when a particular library
is loaded, by calling `eval-after-load'.
- Function: eval-after-load library form
This function arranges to evaluate FORM at the end of loading the
library LIBRARY, if and when LIBRARY is loaded. If LIBRARY is
already loaded, it evaluates FORM right away.
The library name LIBRARY must exactly match the argument of
`load'. To get the proper results when an installed library is
found by searching `load-path', you should not include any
directory names in LIBRARY.
An error in FORM does not undo the load, but does prevent
execution of the rest of FORM.
In general, well-designed Lisp programs should not use this feature.
The clean and modular ways to interact with a Lisp library are (1)
examine and set the library's variables (those which are meant for
outside use), and (2) call the library's functions. If you wish to do
(1), you can do it immediately--there is no need to wait for when the
library is loaded. To do (2), you must load the library (preferably
with `require').
But it is OK to use `eval-after-load' in your personal
customizations if you don't feel they must meet the design standards for
programs meant for wider use.
- Variable: after-load-alist
This variable holds an alist of expressions to evaluate if and when
particular libraries are loaded. Each element looks like this:
(FILENAME FORMS...)
The function `load' checks `after-load-alist' in order to
implement `eval-after-load'.
Byte Compilation
****************
Emacs Lisp has a "compiler" that translates functions written in
Lisp into a special representation called "byte-code" that can be
executed more efficiently. The compiler replaces Lisp function
definitions with byte-code. When a byte-code function is called, its
definition is evaluated by the "byte-code interpreter".
Because the byte-compiled code is evaluated by the byte-code
interpreter, instead of being executed directly by the machine's
hardware (as true compiled code is), byte-code is completely
transportable from machine to machine without recompilation. It is not,
however, as fast as true compiled code.
Compiling a Lisp file with the Emacs byte compiler always reads the
file as multibyte text, even if Emacs was started with `--unibyte',
unless the file specifies otherwise. This is so that compilation gives
results compatible with running the same file without compilation.
*Note Loading Non-ASCII::.
In general, any version of Emacs can run byte-compiled code produced
by recent earlier versions of Emacs, but the reverse is not true. A
major incompatible change was introduced in Emacs version 19.29, and
files compiled with versions since that one will definitely not run in
earlier versions unless you specify a special option. In addition, the
modifier bits in keyboard characters were renumbered in Emacs 19.29; as
a result, files compiled in versions before 19.29 will not work in
subsequent versions if they contain character constants with modifier
bits.
*Note Compilation Errors::, for how to investigate errors occurring
in byte compilation.
Performance of Byte-Compiled Code
=================================
A byte-compiled function is not as efficient as a primitive function
written in C, but runs much faster than the version written in Lisp.
Here is an example:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(silly-loop 100000)
=> ("Fri Mar 18 17:25:57 1994"
"Fri Mar 18 17:26:28 1994") ; 31 seconds
(byte-compile 'silly-loop)
=> [Compiled code not shown]
(silly-loop 100000)
=> ("Fri Mar 18 17:26:52 1994"
"Fri Mar 18 17:26:58 1994") ; 6 seconds
In this example, the interpreted code required 31 seconds to run,
whereas the byte-compiled code required 6 seconds. These results are
representative, but actual results will vary greatly.
The Compilation Functions
=========================
You can byte-compile an individual function or macro definition with
the `byte-compile' function. You can compile a whole file with
`byte-compile-file', or several files with `byte-recompile-directory'
or `batch-byte-compile'.
The byte compiler produces error messages and warnings about each
file in a buffer called `*Compile-Log*'. These report things in your
program that suggest a problem but are not necessarily erroneous.
Be careful when writing macro calls in files that you may someday
byte-compile. Macro calls are expanded when they are compiled, so the
macros must already be defined for proper compilation. For more
details, see *Note Compiling Macros::. If a program does not work the
same way when compiled as it does when interpreted, erroneous macro
definitions are one likely cause (*note Problems with Macros::).
Normally, compiling a file does not evaluate the file's contents or
load the file. But it does execute any `require' calls at top level in
the file. One way to ensure that necessary macro definitions are
available during compilation is to require the file that defines them
(*note Named Features::). To avoid loading the macro definition files
when someone _runs_ the compiled program, write `eval-when-compile'
around the `require' calls (*note Eval During Compile::).
- Function: byte-compile symbol
This function byte-compiles the function definition of SYMBOL,
replacing the previous definition with the compiled one. The
function definition of SYMBOL must be the actual code for the
function; i.e., the compiler does not follow indirection to
another symbol. `byte-compile' returns the new, compiled
definition of SYMBOL.
If SYMBOL's definition is a byte-code function object,
`byte-compile' does nothing and returns `nil'. Lisp records only
one function definition for any symbol, and if that is already
compiled, non-compiled code is not available anywhere. So there
is no way to "compile the same definition again."
(defun factorial (integer)
"Compute factorial of INTEGER."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(byte-compile 'factorial)
=>
#[(integer)
"^H\301U\203^H^@\301\207\302^H\303^HS!\"\207"
[integer 1 * factorial]
4 "Compute factorial of INTEGER."]
The result is a byte-code function object. The string it contains
is the actual byte-code; each character in it is an instruction or
an operand of an instruction. The vector contains all the
constants, variable names and function names used by the function,
except for certain primitives that are coded as special
instructions.
- Command: compile-defun
This command reads the defun containing point, compiles it, and
evaluates the result. If you use this on a defun that is actually
a function definition, the effect is to install a compiled version
of that function.
- Command: byte-compile-file filename
This function compiles a file of Lisp code named FILENAME into a
file of byte-code. The output file's name is made by changing the
`.el' suffix into `.elc'; if FILENAME does not end in `.el', it
adds `.elc' to the end of FILENAME.
Compilation works by reading the input file one form at a time.
If it is a definition of a function or macro, the compiled
function or macro definition is written out. Other forms are
batched together, then each batch is compiled, and written so that
its compiled code will be executed when the file is read. All
comments are discarded when the input file is read.
This command returns `t'. When called interactively, it prompts
for the file name.
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
(byte-compile-file "~/emacs/push.el")
=> t
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
-rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
- Command: byte-recompile-directory directory flag
This function recompiles every `.el' file in DIRECTORY that needs
recompilation. A file needs recompilation if a `.elc' file exists
but is older than the `.el' file.
When a `.el' file has no corresponding `.elc' file, FLAG says what
to do. If it is `nil', these files are ignored. If it is
non-`nil', the user is asked whether to compile each such file.
The returned value of this command is unpredictable.
- Function: batch-byte-compile
This function runs `byte-compile-file' on files specified on the
command line. This function must be used only in a batch
execution of Emacs, as it kills Emacs on completion. An error in
one file does not prevent processing of subsequent files, but no
output file will be generated for it, and the Emacs process will
terminate with a nonzero status code.
% emacs -batch -f batch-byte-compile *.el
- Function: byte-code code-string data-vector max-stack
This function actually interprets byte-code. A byte-compiled
function is actually defined with a body that calls `byte-code'.
Don't call this function yourself--only the byte compiler knows
how to generate valid calls to this function.
In Emacs version 18, byte-code was always executed by way of a
call to the function `byte-code'. Nowadays, byte-code is usually
executed as part of a byte-code function object, and only rarely
through an explicit call to `byte-code'.
Documentation Strings and Compilation
=====================================
Functions and variables loaded from a byte-compiled file access their
documentation strings dynamically from the file whenever needed. This
saves space within Emacs, and makes loading faster because the
documentation strings themselves need not be processed while loading the
file. Actual access to the documentation strings becomes slower as a
result, but this normally is not enough to bother users.
Dynamic access to documentation strings does have drawbacks:
* If you delete or move the compiled file after loading it, Emacs
can no longer access the documentation strings for the functions
and variables in the file.
* If you alter the compiled file (such as by compiling a new
version), then further access to documentation strings in this
file will give nonsense results.
If your site installs Emacs following the usual procedures, these
problems will never normally occur. Installing a new version uses a new
directory with a different name; as long as the old version remains
installed, its files will remain unmodified in the places where they are
expected to be.
However, if you have built Emacs yourself and use it from the
directory where you built it, you will experience this problem
occasionally if you edit and recompile Lisp files. When it happens, you
can cure the problem by reloading the file after recompiling it.
Byte-compiled files made with recent versions of Emacs (since 19.29)
will not load into older versions because the older versions don't
support this feature. You can turn off this feature at compile time by
setting `byte-compile-dynamic-docstrings' to `nil'; then you can
compile files that will load into older Emacs versions. You can do
this globally, or for one source file by specifying a file-local binding
for the variable. One way to do that is by adding this string to the
file's first line:
-*-byte-compile-dynamic-docstrings: nil;-*-
- Variable: byte-compile-dynamic-docstrings
If this is non-`nil', the byte compiler generates compiled files
that are set up for dynamic loading of documentation strings.
The dynamic documentation string feature writes compiled files that
use a special Lisp reader construct, `#@COUNT'. This construct skips
the next COUNT characters. It also uses the `#$' construct, which
stands for "the name of this file, as a string." It is usually best
not to use these constructs in Lisp source files, since they are not
designed to be clear to humans reading the file.
Dynamic Loading of Individual Functions
=======================================
When you compile a file, you can optionally enable the "dynamic
function loading" feature (also known as "lazy loading"). With dynamic
function loading, loading the file doesn't fully read the function
definitions in the file. Instead, each function definition contains a
place-holder which refers to the file. The first time each function is
called, it reads the full definition from the file, to replace the
place-holder.
The advantage of dynamic function loading is that loading the file
becomes much faster. This is a good thing for a file which contains
many separate user-callable functions, if using one of them does not
imply you will probably also use the rest. A specialized mode which
provides many keyboard commands often has that usage pattern: a user may
invoke the mode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:
* If you delete or move the compiled file after loading it, Emacs
can no longer load the remaining function definitions not already
loaded.
* If you alter the compiled file (such as by compiling a new
version), then trying to load any function not already loaded will
yield nonsense results.
These problems will never happen in normal circumstances with
installed Emacs files. But they are quite likely to happen with Lisp
files that you are changing. The easiest way to prevent these problems
is to reload the new compiled file immediately after each recompilation.
The byte compiler uses the dynamic function loading feature if the
variable `byte-compile-dynamic' is non-`nil' at compilation time. Do
not set this variable globally, since dynamic loading is desirable only
for certain files. Instead, enable the feature for specific source
files with file-local variable bindings. For example, you could do it
by writing this text in the source file's first line:
-*-byte-compile-dynamic: t;-*-
- Variable: byte-compile-dynamic
If this is non-`nil', the byte compiler generates compiled files
that are set up for dynamic function loading.
- Function: fetch-bytecode function
This immediately finishes loading the definition of FUNCTION from
its byte-compiled file, if it is not fully loaded already. The
argument FUNCTION may be a byte-code function object or a function
name.
Evaluation During Compilation
=============================
These features permit you to write code to be evaluated during
compilation of a program.
- Special Form: eval-and-compile body
This form marks BODY to be evaluated both when you compile the
containing code and when you run it (whether compiled or not).
You can get a similar result by putting BODY in a separate file
and referring to that file with `require'. That method is
preferable when BODY is large.
- Special Form: eval-when-compile body
This form marks BODY to be evaluated at compile time but not when
the compiled program is loaded. The result of evaluation by the
compiler becomes a constant which appears in the compiled program.
If you load the source file, rather than compiling it, BODY is
evaluated normally.
*Common Lisp Note:* At top level, this is analogous to the Common
Lisp idiom `(eval-when (compile eval) ...)'. Elsewhere, the
Common Lisp `#.' reader macro (but not when interpreting) is closer
to what `eval-when-compile' does.
Byte-Code Function Objects
==========================
Byte-compiled functions have a special data type: they are
"byte-code function objects".
Internally, a byte-code function object is much like a vector;
however, the evaluator handles this data type specially when it appears
as a function to be called. The printed representation for a byte-code
function object is like that for a vector, with an additional `#'
before the opening `['.
A byte-code function object must have at least four elements; there
is no maximum number, but only the first six elements have any normal
use. They are:
ARGLIST
The list of argument symbols.
BYTE-CODE
The string containing the byte-code instructions.
CONSTANTS
The vector of Lisp objects referenced by the byte code. These
include symbols used as function names and variable names.
STACKSIZE
The maximum stack size this function needs.
DOCSTRING
The documentation string (if any); otherwise, `nil'. The value may
be a number or a list, in case the documentation string is stored
in a file. Use the function `documentation' to get the real
documentation string (*note Accessing Documentation::).
INTERACTIVE
The interactive spec (if any). This can be a string or a Lisp
expression. It is `nil' for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command `backward-sexp'.
#[(&optional arg)
"^H\204^F^@\301^P\302^H[!\207"
[arg 1 forward-sexp]
2
254435
"p"]
The primitive way to create a byte-code object is with
`make-byte-code':
- Function: make-byte-code &rest elements
This function constructs and returns a byte-code function object
with ELEMENTS as its elements.
You should not try to come up with the elements for a byte-code
function yourself, because if they are inconsistent, Emacs may crash
when you call the function. Always leave it to the byte compiler to
create these objects; it makes the elements consistent (we hope).
You can access the elements of a byte-code object using `aref'; you
can also use `vconcat' to create a vector with the same elements.
Disassembled Byte-Code
======================
People do not write byte-code; that job is left to the byte compiler.
But we provide a disassembler to satisfy a cat-like curiosity. The
disassembler converts the byte-compiled code into humanly readable form.
The byte-code interpreter is implemented as a simple stack machine.
It pushes values onto a stack of its own, then pops them off to use them
in calculations whose results are themselves pushed back on the stack.
When a byte-code function returns, it pops a value off the stack and
returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set
ordinary Lisp variables, by transferring values between variables and
the stack.
- Command: disassemble object &optional stream
This function prints the disassembled code for OBJECT. If STREAM
is supplied, then output goes there. Otherwise, the disassembled
code is printed to the stream `standard-output'. The argument
OBJECT can be a function name or a lambda expression.
As a special exception, if this function is used interactively, it
outputs to a buffer named `*Disassemble*'.
Here are two examples of using the `disassemble' function. We have
added explanatory comments to help you relate the byte-code to the Lisp
source; these do not appear in the output of `disassemble'. These
examples show unoptimized byte-code. Nowadays byte-code is usually
optimized, but we did not want to rewrite these examples, since they
still serve their purpose.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(factorial 4)
=> 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 constant 1 ; Push 1 onto stack.
1 varref integer ; Get value of `integer'
; from the environment
; and push the value
; onto the stack.
2 eqlsign ; Pop top two values off stack,
; compare them,
; and push result onto stack.
3 goto-if-nil 10 ; Pop and test top of stack;
; if `nil', go to 10,
; else continue.
6 constant 1 ; Push 1 onto top of stack.
7 goto 17 ; Go to 17 (in this case, 1 will be
; returned by the function).
10 constant * ; Push symbol `*' onto stack.
11 varref integer ; Push value of `integer' onto stack.
12 constant factorial ; Push `factorial' onto stack.
13 varref integer ; Push value of `integer' onto stack.
14 sub1 ; Pop `integer', decrement value,
; push new value onto stack.
; Stack now contains:
; - decremented value of `integer'
; - `factorial'
; - value of `integer'
; - `*'
15 call 1 ; Call function `factorial' using
; the first (i.e., the top) element
; of the stack as the argument;
; push returned value onto stack.
; Stack now contains:
; - result of recursive
; call to `factorial'
; - value of `integer'
; - `*'
16 call 2 ; Using the first two
; (i.e., the top two)
; elements of the stack
; as arguments,
; call the function `*',
; pushing the result onto the stack.
17 return ; Return the top element
; of the stack.
=> nil
The `silly-loop' function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push
; `current-time-string'
; onto top of stack.
1 call 0 ; Call `current-time-string'
; with no argument,
; pushing result onto stack.
2 varbind t1 ; Pop stack and bind `t1'
; to popped value.
3 varref n ; Get value of `n' from
; the environment and push
; the value onto the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate the top of the stack;
; i.e., copy the top of
; the stack and push the
; copy onto the stack.
6 varset n ; Pop the top of the stack,
; and bind `n' to the value.
; In effect, the sequence `dup varset'
; copies the top of the stack
; into the value of `n'
; without popping it.
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if N is greater than 0
; and push result onto stack.
9 goto-if-nil-else-pop 17 ; Goto 17 if `n' <= 0
; (this exits the while loop).
; else pop top of stack
; and continue
12 constant nil ; Push `nil' onto stack
; (this is the body of the loop).
13 discard ; Discard result of the body
; of the loop (a while loop
; is always evaluated for
; its side effects).
14 goto 3 ; Jump back to beginning
; of while loop.
17 discard ; Discard result of while loop
; by popping top of stack.
; This result is the value `nil' that
; was not popped by the goto at 9.
18 varref t1 ; Push value of `t1' onto stack.
19 constant current-time-string ; Push
; `current-time-string'
; onto top of stack.
20 call 0 ; Call `current-time-string' again.
21 list2 ; Pop top two elements off stack,
; create a list of them,
; and push list onto stack.
22 unbind 1 ; Unbind `t1' in local environment.
23 return ; Return value of the top of stack.
=> nil
Advising Emacs Lisp Functions
*****************************
The "advice" feature lets you add to the existing definition of a
function, by "advising the function". This is a clean method for a
library to customize functions defined by other parts of Emacs--cleaner
than redefining the whole function.
Each function can have multiple "pieces of advice", separately
defined. Each defined piece of advice can be "enabled" or disabled
explicitly. All the enabled pieces of advice for any given function
actually take effect when you "activate" advice for that function, or
when you define or redefine the function. Note that enabling a piece
of advice and activating advice for a function are not the same thing.
*Usage Note:* Advice is useful for altering the behavior of existing
calls to an existing function. If you want the new behavior for new
calls, or for key bindings, it is cleaner to define a new function (or
a new command) which uses the existing function.
A Simple Advice Example
=======================
The command `next-line' moves point down vertically one or more
lines; it is the standard binding of `C-n'. When used on the last line
of the buffer, this command inserts a newline to create a line to move
to if `next-line-add-newlines' is non-`nil' (its default is `nil'.)
Suppose you wanted to add a similar feature to `previous-line',
which would insert a new line at the beginning of the buffer for the
command to move to. How could you do this?
You could do it by redefining the whole function, but that is not
modular. The advice feature provides a cleaner alternative: you can
effectively add your code to the existing function definition, without
actually changing or even seeing that definition. Here is how to do
this:
(defadvice previous-line (before next-line-at-end (arg))
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
This expression defines a "piece of advice" for the function
`previous-line'. This piece of advice is named `next-line-at-end', and
the symbol `before' says that it is "before-advice" which should run
before the regular definition of `previous-line'. `(arg)' specifies
how the advice code can refer to the function's arguments.
When this piece of advice runs, it creates an additional line, in the
situation where that is appropriate, but does not move point to that
line. This is the correct way to write the advice, because the normal
definition will run afterward and will move back to the newly inserted
line.
Defining the advice doesn't immediately change the function
`previous-line'. That happens when you "activate" the advice, like
this:
(ad-activate 'previous-line)
This is what actually begins to use the advice that has been defined so
far for the function `previous-line'. Henceforth, whenever that
function is run, whether invoked by the user with `C-p' or `M-x', or
called from Lisp, it runs the advice first, and its regular definition
second.
This example illustrates before-advice, which is one "class" of
advice: it runs before the function's base definition. There are two
other advice classes: "after-advice", which runs after the base
definition, and "around-advice", which lets you specify an expression
to wrap around the invocation of the base definition.
Defining Advice
===============
To define a piece of advice, use the macro `defadvice'. A call to
`defadvice' has the following syntax, which is based on the syntax of
`defun' and `defmacro', but adds more:
(defadvice FUNCTION (CLASS NAME
[POSITION] [ARGLIST]
FLAGS...)
[DOCUMENTATION-STRING]
[INTERACTIVE-FORM]
BODY-FORMS...)
Here, FUNCTION is the name of the function (or macro or special form)
to be advised. From now on, we will write just "function" when
describing the entity being advised, but this always includes macros and
special forms.
CLASS specifies the "class" of the advice--one of `before', `after',
or `around'. Before-advice runs before the function itself;
after-advice runs after the function itself; around-advice is wrapped
around the execution of the function itself. After-advice and
around-advice can override the return value by setting
`ad-return-value'.
- Variable: ad-return-value
While advice is executing, after the function's original
definition has been executed, this variable holds its return
value, which will ultimately be returned to the caller after
finishing all the advice. After-advice and around-advice can
arrange to return some other value by storing it in this variable.
The argument NAME is the name of the advice, a non-`nil' symbol.
The advice name uniquely identifies one piece of advice, within all the
pieces of advice in a particular class for a particular FUNCTION. The
name allows you to refer to the piece of advice--to redefine it, or to
enable or disable it.
In place of the argument list in an ordinary definition, an advice
definition calls for several different pieces of information.
The optional POSITION specifies where, in the current list of advice
of the specified CLASS, this new advice should be placed. It should be
either `first', `last' or a number that specifies a zero-based position
(`first' is equivalent to 0). If no position is specified, the default
is `first'. Position values outside the range of existing positions in
this class are mapped to the beginning or the end of the range,
whichever is closer. The POSITION value is ignored when redefining an
existing piece of advice.
The optional ARGLIST can be used to define the argument list for the
sake of advice. This becomes the argument list of the combined
definition that is generated in order to run the advice (*note Combined
Definition::). Therefore, the advice expressions can use the argument
variables in this list to access argument values.
The argument list used in advice need not be the same as the argument
list used in the original function, but must be compatible with it, so
that it can handle the ways the function is actually called. If two
pieces of advice for a function both specify an argument list, they must
specify the same argument list.
*Note Argument Access in Advice::, for more information about
argument lists and advice, and a more flexible way for advice to access
the arguments.
The remaining elements, FLAGS, are symbols that specify further
information about how to use this piece of advice. Here are the valid
symbols and their meanings:
`activate'
Activate the advice for FUNCTION now. Changes in a function's
advice always take effect the next time you activate advice for the
function; this flag says to do so, for FUNCTION, immediately after
defining this piece of advice.
This flag has no immediate effect if FUNCTION itself is not
defined yet (a situation known as "forward advice"), because it is
impossible to activate an undefined function's advice. However,
defining FUNCTION will automatically activate its advice.
`protect'
Protect this piece of advice against non-local exits and errors in
preceding code and advice. Protecting advice places it as a
cleanup in an `unwind-protect' form, so that it will execute even
if the previous code gets an error or uses `throw'. *Note
Cleanups::.
`compile'
Compile the combined definition that is used to run the advice.
This flag is ignored unless `activate' is also specified. *Note
Combined Definition::.
`disable'
Initially disable this piece of advice, so that it will not be used
unless subsequently explicitly enabled. *Note Enabling Advice::.
`preactivate'
Activate advice for FUNCTION when this `defadvice' is compiled or
macroexpanded. This generates a compiled advised definition
according to the current advice state, which will be used during
activation if appropriate. *Note Preactivation::.
This is useful only if this `defadvice' is byte-compiled.
The optional DOCUMENTATION-STRING serves to document this piece of
advice. When advice is active for FUNCTION, the documentation for
FUNCTION (as returned by `documentation') combines the documentation
strings of all the advice for FUNCTION with the documentation string of
its original function definition.
The optional INTERACTIVE-FORM form can be supplied to change the
interactive behavior of the original function. If more than one piece
of advice has an INTERACTIVE-FORM, then the first one (the one with the
smallest position) found among all the advice takes precedence.
The possibly empty list of BODY-FORMS specifies the body of the
advice. The body of an advice can access or change the arguments, the
return value, the binding environment, and perform any other kind of
side effect.
*Warning:* When you advise a macro, keep in mind that macros are
expanded when a program is compiled, not when a compiled program is run.
All subroutines used by the advice need to be available when the byte
compiler expands the macro.
- Command: ad-unadvise function
This command deletes the advice from FUNCTION.
- Command: ad-unadvise-all
This command deletes all pieces of advice from all functions.
Around-Advice
=============
Around-advice lets you "wrap" a Lisp expression "around" the
original function definition. You specify where the original function
definition should go by means of the special symbol `ad-do-it'. Where
this symbol occurs inside the around-advice body, it is replaced with a
`progn' containing the forms of the surrounded code. Here is an
example:
(defadvice foo (around foo-around)
"Ignore case in `foo'."
(let ((case-fold-search t))
ad-do-it))
Its effect is to make sure that case is ignored in searches when the
original definition of `foo' is run.
- Variable: ad-do-it
This is not really a variable, but it is somewhat used like one in
around-advice. It specifies the place to run the function's
original definition and other "earlier" around-advice.
If the around-advice does not use `ad-do-it', then it does not run
the original function definition. This provides a way to override the
original definition completely. (It also overrides lower-positioned
pieces of around-advice).
If the around-advice uses `ad-do-it' more than once, the original
definition is run at each place. In this way, around-advice can execute
the original definition (and lower-positioned pieces of around-advice)
several times. Another way to do that is by using `ad-do-it' inside of
a loop.
Computed Advice
===============
The macro `defadvice' resembles `defun' in that the code for the
advice, and all other information about it, are explicitly stated in
the source code. You can also create advice whose details are computed,
using the function `ad-add-advice'.
- Function: ad-add-advice function advice class position
Calling `ad-add-advice' adds ADVICE as a piece of advice to
FUNCTION in class CLASS. The argument ADVICE has this form:
(NAME PROTECTED ENABLED DEFINITION)
Here PROTECTED and ENABLED are flags, and DEFINITION is the
expression that says what the advice should do. If ENABLED is
`nil', this piece of advice is initially disabled (*note Enabling
Advice::).
If FUNCTION already has one or more pieces of advice in the
specified CLASS, then POSITION specifies where in the list to put
the new piece of advice. The value of POSITION can either be
`first', `last', or a number (counting from 0 at the beginning of
the list). Numbers outside the range are mapped to the beginning
or the end of the range, whichever is closer. The POSITION value
is ignored when redefining an existing piece of advice.
If FUNCTION already has a piece of ADVICE with the same name, then
the position argument is ignored and the old advice is replaced
with the new one.
Activation of Advice
====================
By default, advice does not take effect when you define it--only when
you "activate" advice for the function that was advised. You can
request the activation of advice for a function when you define the
advice, by specifying the `activate' flag in the `defadvice'. But
normally you activate the advice for a function by calling the function
`ad-activate' or one of the other activation commands listed below.
Separating the activation of advice from the act of defining it
permits you to add several pieces of advice to one function
efficiently, without redefining the function over and over as each
advice is added. More importantly, it permits defining advice for a
function before that function is actually defined.
When a function's advice is first activated, the function's original
definition is saved, and all enabled pieces of advice for that function
are combined with the original definition to make a new definition.
(Pieces of advice that are currently disabled are not used; see *Note
Enabling Advice::.) This definition is installed, and optionally
byte-compiled as well, depending on conditions described below.
In all of the commands to activate advice, if COMPILE is `t', the
command also compiles the combined definition which implements the
advice.
- Command: ad-activate function &optional compile
This command activates all the advice defined for FUNCTION.
To activate advice for a function whose advice is already active is
not a no-op. It is a useful operation which puts into effect any
changes in that function's advice since the previous activation of
advice for that function.
- Command: ad-deactivate function
This command deactivates the advice for FUNCTION.
- Command: ad-update function &optional compile
This command activates the advice for FUNCTION if its advice is
already activated. This is useful if you change the advice.
- Command: ad-activate-all &optional compile
This command activates the advice for all functions.
- Command: ad-deactivate-all
This command deactivates the advice for all functions.
- Command: ad-update-all &optional compile
This command activates the advice for all functions whose advice
is already activated. This is useful if you change the advice of
some functions.
- Command: ad-activate-regexp regexp &optional compile
This command activates all pieces of advice whose names match
REGEXP. More precisely, it activates all advice for any function
which has at least one piece of advice that matches REGEXP.
- Command: ad-deactivate-regexp regexp
This command deactivates all pieces of advice whose names match
REGEXP. More precisely, it deactivates all advice for any
function which has at least one piece of advice that matches
REGEXP.
- Command: ad-update-regexp regexp &optional compile
This command activates pieces of advice whose names match REGEXP,
but only those for functions whose advice is already activated.
Reactivating a function's advice is useful for putting into effect
all the changes that have been made in its advice (including
enabling and disabling specific pieces of advice; *note Enabling
Advice::) since the last time it was activated.
- Command: ad-start-advice
Turn on automatic advice activation when a function is defined or
redefined. If you turn on this mode, then advice takes effect
immediately when defined.
- Command: ad-stop-advice
Turn off automatic advice activation when a function is defined or
redefined.
- User Option: ad-default-compilation-action
This variable controls whether to compile the combined definition
that results from activating advice for a function.
A value of `always' specifies to compile unconditionally. A value
of `nil' specifies never compile the advice.
A value of `maybe' specifies to compile if the byte-compiler is
already loaded. A value of `like-original' specifies to compile
the advice if the original definition of the advised function is
compiled or a built-in function.
This variable takes effect only if the COMPILE argument of
`ad-activate' (or any of the above functions) was supplied as
`nil'. If that argument is non-`nil', that means to compile the
advice regardless.
If the advised definition was constructed during "preactivation"
(*note Preactivation::), then that definition must already be compiled,
because it was constructed during byte-compilation of the file that
contained the `defadvice' with the `preactivate' flag.
Enabling and Disabling Advice
=============================
Each piece of advice has a flag that says whether it is enabled or
not. By enabling or disabling a piece of advice, you can turn it on
and off without having to undefine and redefine it. For example, here
is how to disable a particular piece of advice named `my-advice' for
the function `foo':
(ad-disable-advice 'foo 'before 'my-advice)
This function by itself only changes the enable flag for a piece of
advice. To make the change take effect in the advised definition, you
must activate the advice for `foo' again:
(ad-activate 'foo)
- Command: ad-disable-advice function class name
This command disables the piece of advice named NAME in class
CLASS on FUNCTION.
- Command: ad-enable-advice function class name
This command enables the piece of advice named NAME in class CLASS
on FUNCTION.
You can also disable many pieces of advice at once, for various
functions, using a regular expression. As always, the changes take real
effect only when you next reactivate advice for the functions in
question.
- Command: ad-disable-regexp regexp
This command disables all pieces of advice whose names match
REGEXP, in all classes, on all functions.
- Command: ad-enable-regexp regexp
This command enables all pieces of advice whose names match
REGEXP, in all classes, on all functions.
Preactivation
=============
Constructing a combined definition to execute advice is moderately
expensive. When a library advises many functions, this can make loading
the library slow. In that case, you can use "preactivation" to
construct suitable combined definitions in advance.
To use preactivation, specify the `preactivate' flag when you define
the advice with `defadvice'. This `defadvice' call creates a combined
definition which embodies this piece of advice (whether enabled or not)
plus any other currently enabled advice for the same function, and the
function's own definition. If the `defadvice' is compiled, that
compiles the combined definition also.
When the function's advice is subsequently activated, if the enabled
advice for the function matches what was used to make this combined
definition, then the existing combined definition is used, thus avoiding
the need to construct one. Thus, preactivation never causes wrong
results--but it may fail to do any good, if the enabled advice at the
time of activation doesn't match what was used for preactivation.
Here are some symptoms that can indicate that a preactivation did not
work properly, because of a mismatch.
* Activation of the advised function takes longer than usual.
* The byte-compiler gets loaded while an advised function gets
activated.
* `byte-compile' is included in the value of `features' even though
you did not ever explicitly use the byte-compiler.
Compiled preactivated advice works properly even if the function
itself is not defined until later; however, the function needs to be
defined when you _compile_ the preactivated advice.
There is no elegant way to find out why preactivated advice is not
being used. What you can do is to trace the function
`ad-cache-id-verification-code' (with the function
`trace-function-background') before the advised function's advice is
activated. After activation, check the value returned by
`ad-cache-id-verification-code' for that function: `verified' means
that the preactivated advice was used, while other values give some
information about why they were considered inappropriate.
*Warning:* There is one known case that can make preactivation fail,
in that a preconstructed combined definition is used even though it
fails to match the current state of advice. This can happen when two
packages define different pieces of advice with the same name, in the
same class, for the same function. But you should avoid that anyway.
Argument Access in Advice
=========================
The simplest way to access the arguments of an advised function in
the body of a piece of advice is to use the same names that the function
definition uses. To do this, you need to know the names of the argument
variables of the original function.
While this simple method is sufficient in many cases, it has a
disadvantage: it is not robust, because it hard-codes the argument names
into the advice. If the definition of the original function changes,
the advice might break.
Another method is to specify an argument list in the advice itself.
This avoids the need to know the original function definition's argument
names, but it has a limitation: all the advice on any particular
function must use the same argument list, because the argument list
actually used for all the advice comes from the first piece of advice
for that function.
A more robust method is to use macros that are translated into the
proper access forms at activation time, i.e., when constructing the
advised definition. Access macros access actual arguments by position
regardless of how these actual arguments get distributed onto the
argument variables of a function. This is robust because in Emacs Lisp
the meaning of an argument is strictly determined by its position in the
argument list.
- Macro: ad-get-arg position
This returns the actual argument that was supplied at POSITION.
- Macro: ad-get-args position
This returns the list of actual arguments supplied starting at
POSITION.
- Macro: ad-set-arg position value
This sets the value of the actual argument at POSITION to VALUE
- Macro: ad-set-args position value-list
This sets the list of actual arguments starting at POSITION to
VALUE-LIST.
Now an example. Suppose the function `foo' is defined as
(defun foo (x y &optional z &rest r) ...)
and is then called with
(foo 0 1 2 3 4 5 6)
which means that X is 0, Y is 1, Z is 2 and R is `(3 4 5 6)' within the
body of `foo'. Here is what `ad-get-arg' and `ad-get-args' return in
this case:
(ad-get-arg 0) => 0
(ad-get-arg 1) => 1
(ad-get-arg 2) => 2
(ad-get-arg 3) => 3
(ad-get-args 2) => (2 3 4 5 6)
(ad-get-args 4) => (4 5 6)
Setting arguments also makes sense in this example:
(ad-set-arg 5 "five")
has the effect of changing the sixth argument to `"five"'. If this
happens in advice executed before the body of `foo' is run, then R will
be `(3 4 "five" 6)' within that body.
Here is an example of setting a tail of the argument list:
(ad-set-args 0 '(5 4 3 2 1 0))
If this happens in advice executed before the body of `foo' is run,
then within that body, X will be 5, Y will be 4, Z will be 3, and R
will be `(2 1 0)' inside the body of `foo'.
These argument constructs are not really implemented as Lisp macros.
Instead they are implemented specially by the advice mechanism.
Definition of Subr Argument Lists
=================================
When the advice facility constructs the combined definition, it needs
to know the argument list of the original function. This is not always
possible for primitive functions. When advice cannot determine the
argument list, it uses `(&rest ad-subr-args)', which always works but
is inefficient because it constructs a list of the argument values.
You can use `ad-define-subr-args' to declare the proper argument names
for a primitive function:
- Function: ad-define-subr-args function arglist
This function specifies that ARGLIST should be used as the
argument list for function FUNCTION.
For example,
(ad-define-subr-args 'fset '(sym newdef))
specifies the argument list for the function `fset'.
The Combined Definition
=======================
Suppose that a function has N pieces of before-advice (numbered from
0 through N-1), M pieces of around-advice and K pieces of after-advice.
Assuming no piece of advice is protected, the combined definition
produced to implement the advice for a function looks like this:
(lambda ARGLIST
[ [ADVISED-DOCSTRING] [(interactive ...)] ]
(let (ad-return-value)
before-0-body-form...
....
before-N-1-body-form...
around-0-body-form...
around-1-body-form...
....
around-M-1-body-form...
(setq ad-return-value
apply original definition to ARGLIST)
end-of-around-M-1-body-form...
....
end-of-around-1-body-form...
end-of-around-0-body-form...
after-0-body-form...
....
after-K-1-body-form...
ad-return-value))
Macros are redefined as macros, which means adding `macro' to the
beginning of the combined definition.
The interactive form is present if the original function or some
piece of advice specifies one. When an interactive primitive function
is advised, advice uses a special method: it calls the primitive with
`call-interactively' so that it will read its own arguments. In this
case, the advice cannot access the arguments.
The body forms of the various advice in each class are assembled
according to their specified order. The forms of around-advice L are
included in one of the forms of around-advice L - 1.
The innermost part of the around advice onion is
apply original definition to ARGLIST
whose form depends on the type of the original function. The variable
`ad-return-value' is set to whatever this returns. The variable is
visible to all pieces of advice, which can access and modify it before
it is actually returned from the advised function.
The semantic structure of advised functions that contain protected
pieces of advice is the same. The only difference is that
`unwind-protect' forms ensure that the protected advice gets executed
even if some previous piece of advice had an error or a non-local exit.
If any around-advice is protected, then the whole around-advice onion
is protected as a result.
Debugging Lisp Programs
***********************
There are three ways to investigate a problem in an Emacs Lisp
program, depending on what you are doing with the program when the
problem appears.
* If the problem occurs when you run the program, you can use a Lisp
debugger to investigate what is happening during execution. In
addition to the ordinary debugger, Emacs comes with a source level
debugger, Edebug. This chapter describes both of them.
* If the problem is syntactic, so that Lisp cannot even read the
program, you can use the Emacs facilities for editing Lisp to
localize it.
* If the problem occurs when trying to compile the program with the
byte compiler, you need to know how to examine the compiler's
input buffer.
Another useful debugging tool is the dribble file. When a dribble
file is open, Emacs copies all keyboard input characters to that file.
Afterward, you can examine the file to find out what input was used.
*Note Terminal Input::.
For debugging problems in terminal descriptions, the
`open-termscript' function can be useful. *Note Terminal Output::.
The Lisp Debugger
=================
The ordinary "Lisp debugger" provides the ability to suspend
evaluation of a form. While evaluation is suspended (a state that is
commonly known as a "break"), you may examine the run time stack,
examine the values of local or global variables, or change those values.
Since a break is a recursive edit, all the usual editing facilities of
Emacs are available; you can even run programs that will enter the
debugger recursively. *Note Recursive Editing::.
Entering the Debugger on an Error
---------------------------------
The most important time to enter the debugger is when a Lisp error
happens. This allows you to investigate the immediate causes of the
error.
However, entry to the debugger is not a normal consequence of an
error. Many commands frequently cause Lisp errors when invoked
inappropriately (such as `C-f' at the end of the buffer), and during
ordinary editing it would be very inconvenient to enter the debugger
each time this happens. So if you want errors to enter the debugger,
set the variable `debug-on-error' to non-`nil'. (The command
`toggle-debug-on-error' provides an easy way to do this.)
- User Option: debug-on-error
This variable determines whether the debugger is called when an
error is signaled and not handled. If `debug-on-error' is `t', all
kinds of errors call the debugger (except those listed in
`debug-ignored-errors'). If it is `nil', none call the debugger.
The value can also be a list of error conditions that should call
the debugger. For example, if you set it to the list
`(void-variable)', then only errors about a variable that has no
value invoke the debugger.
When this variable is non-`nil', Emacs does not create an error
handler around process filter functions and sentinels. Therefore,
errors in these functions also invoke the debugger. *Note
Processes::.
- User Option: debug-ignored-errors
This variable specifies certain kinds of errors that should not
enter the debugger. Its value is a list of error condition
symbols and/or regular expressions. If the error has any of those
condition symbols, or if the error message matches any of the
regular expressions, then that error does not enter the debugger,
regardless of the value of `debug-on-error'.
The normal value of this variable lists several errors that happen
often during editing but rarely result from bugs in Lisp programs.
However, "rarely" is not "never"; if your program fails with an
error that matches this list, you will need to change this list in
order to debug the error. The easiest way is usually to set
`debug-ignored-errors' to `nil'.
- User Option: debug-on-signal
Normally, errors that are caught by `condition-case' never run the
debugger, even if `debug-on-error' is non-`nil'. In other words,
`condition-case' gets a chance to handle the error before the
debugger gets a chance.
If you set `debug-on-signal' to a non-`nil' value, then the
debugger gets the first chance at every error; an error will
invoke the debugger regardless of any `condition-case', if it fits
the criteria specified by the values of `debug-on-error' and
`debug-ignored-errors'.
*Warning:* This variable is strong medicine! Various parts of
Emacs handle errors in the normal course of affairs, and you may
not even realize that errors happen there. If you set
`debug-on-signal' to a non-`nil' value, those errors will enter
the debugger.
*Warning:* `debug-on-signal' has no effect when `debug-on-error'
is `nil'.
To debug an error that happens during loading of the init file, use
the option `--debug-init'. This binds `debug-on-error' to `t' while
loading the init file, and bypasses the `condition-case' which normally
catches errors in the init file.
If your init file sets `debug-on-error', the effect may not last
past the end of loading the init file. (This is an undesirable
byproduct of the code that implements the `--debug-init' command line
option.) The best way to make the init file set `debug-on-error'
permanently is with `after-init-hook', like this:
(add-hook 'after-init-hook
(lambda () (setq debug-on-error t)))
Debugging Infinite Loops
------------------------
When a program loops infinitely and fails to return, your first
problem is to stop the loop. On most operating systems, you can do this
with `C-g', which causes a "quit".
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
`debug-on-quit' to non-`nil'. Quitting with `C-g' is not considered an
error, and `debug-on-error' has no effect on the handling of `C-g'.
Likewise, `debug-on-quit' has no effect on errors.
Once you have the debugger running in the middle of the infinite
loop, you can proceed from the debugger using the stepping commands.
If you step through the entire loop, you will probably get enough
information to solve the problem.
- User Option: debug-on-quit
This variable determines whether the debugger is called when `quit'
is signaled and not handled. If `debug-on-quit' is non-`nil',
then the debugger is called whenever you quit (that is, type
`C-g'). If `debug-on-quit' is `nil', then the debugger is not
called when you quit. *Note Quitting::.
Entering the Debugger on a Function Call
----------------------------------------
To investigate a problem that happens in the middle of a program, one
useful technique is to enter the debugger whenever a certain function is
called. You can do this to the function in which the problem occurs,
and then step through the function, or you can do this to a function
called shortly before the problem, step quickly over the call to that
function, and then step through its caller.
- Command: debug-on-entry function-name
This function requests FUNCTION-NAME to invoke the debugger each
time it is called. It works by inserting the form `(debug
'debug)' into the function definition as the first form.
Any function defined as Lisp code may be set to break on entry,
regardless of whether it is interpreted code or compiled code. If
the function is a command, it will enter the debugger when called
from Lisp and when called interactively (after the reading of the
arguments). You can't debug primitive functions (i.e., those
written in C) this way.
When `debug-on-entry' is called interactively, it prompts for
FUNCTION-NAME in the minibuffer. If the function is already set
up to invoke the debugger on entry, `debug-on-entry' does nothing.
`debug-on-entry' always returns FUNCTION-NAME.
*Note:* if you redefine a function after using `debug-on-entry' on
it, the code to enter the debugger is discarded by the
redefinition. In effect, redefining the function cancels the
break-on-entry feature for that function.
(defun fact (n)
(if (zerop n) 1
(* n (fact (1- n)))))
=> fact
(debug-on-entry 'fact)
=> fact
(fact 3)
------ Buffer: *Backtrace* ------
Entering:
* fact(3)
eval-region(4870 4878 t)
byte-code("...")
eval-last-sexp(nil)
(let ...)
eval-insert-last-sexp(nil)
* call-interactively(eval-insert-last-sexp)
------ Buffer: *Backtrace* ------
(symbol-function 'fact)
=> (lambda (n)
(debug (quote debug))
(if (zerop n) 1 (* n (fact (1- n)))))
- Command: cancel-debug-on-entry function-name
This function undoes the effect of `debug-on-entry' on
FUNCTION-NAME. When called interactively, it prompts for
FUNCTION-NAME in the minibuffer. If FUNCTION-NAME is `nil' or the
empty string, it cancels break-on-entry for all functions.
Calling `cancel-debug-on-entry' does nothing to a function which is
not currently set up to break on entry. It always returns
FUNCTION-NAME.
Explicit Entry to the Debugger
------------------------------
You can cause the debugger to be called at a certain point in your
program by writing the expression `(debug)' at that point. To do this,
visit the source file, insert the text `(debug)' at the proper place,
and type `C-M-x'. *Warning:* if you do this for temporary debugging
purposes, be sure to undo this insertion before you save the file!
The place where you insert `(debug)' must be a place where an
additional form can be evaluated and its value ignored. (If the value
of `(debug)' isn't ignored, it will alter the execution of the
program!) The most common suitable places are inside a `progn' or an
implicit `progn' (*note Sequencing::).
Using the Debugger
------------------
When the debugger is entered, it displays the previously selected
buffer in one window and a buffer named `*Backtrace*' in another
window. The backtrace buffer contains one line for each level of Lisp
function execution currently going on. At the beginning of this buffer
is a message describing the reason that the debugger was invoked (such
as the error message and associated data, if it was invoked due to an
error).
The backtrace buffer is read-only and uses a special major mode,
Debugger mode, in which letters are defined as debugger commands. The
usual Emacs editing commands are available; thus, you can switch windows
to examine the buffer that was being edited at the time of the error,
switch buffers, visit files, or do any other sort of editing. However,
the debugger is a recursive editing level (*note Recursive Editing::)
and it is wise to go back to the backtrace buffer and exit the debugger
(with the `q' command) when you are finished with it. Exiting the
debugger gets out of the recursive edit and kills the backtrace buffer.
The backtrace buffer shows you the functions that are executing and
their argument values. It also allows you to specify a stack frame by
moving point to the line describing that frame. (A stack frame is the
place where the Lisp interpreter records information about a particular
invocation of a function.) The frame whose line point is on is
considered the "current frame". Some of the debugger commands operate
on the current frame.
The debugger itself must be run byte-compiled, since it makes
assumptions about how many stack frames are used for the debugger
itself. These assumptions are false if the debugger is running
interpreted.
Debugger Commands
-----------------
Inside the debugger (in Debugger mode), these special commands are
available in addition to the usual cursor motion commands. (Keep in
mind that all the usual facilities of Emacs, such as switching windows
or buffers, are still available.)
The most important use of debugger commands is for stepping through
code, so that you can see how control flows. The debugger can step
through the control structures of an interpreted function, but cannot do
so in a byte-compiled function. If you would like to step through a
byte-compiled function, replace it with an interpreted definition of the
same function. (To do this, visit the source for the function and type
`C-M-x' on its definition.)
Here is a list of Debugger mode commands:
`c'
Exit the debugger and continue execution. When continuing is
possible, it resumes execution of the program as if the debugger
had never been entered (aside from any side-effects that you
caused by changing variable values or data structures while inside
the debugger).
Continuing is possible after entry to the debugger due to function
entry or exit, explicit invocation, or quitting. You cannot
continue if the debugger was entered because of an error.
`d'
Continue execution, but enter the debugger the next time any Lisp
function is called. This allows you to step through the
subexpressions of an expression, seeing what values the
subexpressions compute, and what else they do.
The stack frame made for the function call which enters the
debugger in this way will be flagged automatically so that the
debugger will be called again when the frame is exited. You can
use the `u' command to cancel this flag.
`b'
Flag the current frame so that the debugger will be entered when
the frame is exited. Frames flagged in this way are marked with
stars in the backtrace buffer.
`u'
Don't enter the debugger when the current frame is exited. This
cancels a `b' command on that frame. The visible effect is to
remove the star from the line in the backtrace buffer.
`e'
Read a Lisp expression in the minibuffer, evaluate it, and print
the value in the echo area. The debugger alters certain important
variables, and the current buffer, as part of its operation; `e'
temporarily restores their values from outside the debugger, so
you can examine and change them. This makes the debugger more
transparent. By contrast, `M-:' does nothing special in the
debugger; it shows you the variable values within the debugger.
`R'
Like `e', but also save the result of evaluation in the buffer
`*Debugger-record*'.
`q'
Terminate the program being debugged; return to top-level Emacs
command execution.
If the debugger was entered due to a `C-g' but you really want to
quit, and not debug, use the `q' command.
`r'
Return a value from the debugger. The value is computed by
reading an expression with the minibuffer and evaluating it.
The `r' command is useful when the debugger was invoked due to exit
from a Lisp call frame (as requested with `b' or by entering the
frame with `d'); then the value specified in the `r' command is
used as the value of that frame. It is also useful if you call
`debug' and use its return value. Otherwise, `r' has the same
effect as `c', and the specified return value does not matter.
You can't use `r' when the debugger was entered due to an error.
Invoking the Debugger
---------------------
Here we describe in full detail the function `debug' that is used to
invoke the debugger.
- Function: debug &rest debugger-args
This function enters the debugger. It switches buffers to a buffer
named `*Backtrace*' (or `*Backtrace*<2>' if it is the second
recursive entry to the debugger, etc.), and fills it with
information about the stack of Lisp function calls. It then
enters a recursive edit, showing the backtrace buffer in Debugger
mode.
The Debugger mode `c' and `r' commands exit the recursive edit;
then `debug' switches back to the previous buffer and returns to
whatever called `debug'. This is the only way the function
`debug' can return to its caller.
The use of the DEBUGGER-ARGS is that `debug' displays the rest of
its arguments at the top of the `*Backtrace*' buffer, so that the
user can see them. Except as described below, this is the _only_
way these arguments are used.
However, certain values for first argument to `debug' have a
special significance. (Normally, these values are used only by the
internals of Emacs, and not by programmers calling `debug'.) Here
is a table of these special values:
`lambda'
A first argument of `lambda' means `debug' was called because
of entry to a function when `debug-on-next-call' was
non-`nil'. The debugger displays `Entering:' as a line of
text at the top of the buffer.
`debug'
`debug' as first argument indicates a call to `debug' because
of entry to a function that was set to debug on entry. The
debugger displays `Entering:', just as in the `lambda' case.
It also marks the stack frame for that function so that it
will invoke the debugger when exited.
`t'
When the first argument is `t', this indicates a call to
`debug' due to evaluation of a list form when
`debug-on-next-call' is non-`nil'. The debugger displays the
following as the top line in the buffer:
Beginning evaluation of function call form:
`exit'
When the first argument is `exit', it indicates the exit of a
stack frame previously marked to invoke the debugger on exit.
The second argument given to `debug' in this case is the
value being returned from the frame. The debugger displays
`Return value:' in the top line of the buffer, followed by
the value being returned.
`error'
When the first argument is `error', the debugger indicates
that it is being entered because an error or `quit' was
signaled and not handled, by displaying `Signaling:' followed
by the error signaled and any arguments to `signal'. For
example,
(let ((debug-on-error t))
(/ 1 0))
------ Buffer: *Backtrace* ------
Signaling: (arith-error)
/(1 0)
...
------ Buffer: *Backtrace* ------
If an error was signaled, presumably the variable
`debug-on-error' is non-`nil'. If `quit' was signaled, then
presumably the variable `debug-on-quit' is non-`nil'.
`nil'
Use `nil' as the first of the DEBUGGER-ARGS when you want to
enter the debugger explicitly. The rest of the DEBUGGER-ARGS
are printed on the top line of the buffer. You can use this
feature to display messages--for example, to remind yourself
of the conditions under which `debug' is called.
Internals of the Debugger
-------------------------
This section describes functions and variables used internally by the
debugger.
- Variable: debugger
The value of this variable is the function to call to invoke the
debugger. Its value must be a function of any number of
arguments, or, more typically, the name of a function. This
function should invoke some kind of debugger. The default value
of the variable is `debug'.
The first argument that Lisp hands to the function indicates why it
was called. The convention for arguments is detailed in the
description of `debug'.
- Command: backtrace
This function prints a trace of Lisp function calls currently
active. This is the function used by `debug' to fill up the
`*Backtrace*' buffer. It is written in C, since it must have
access to the stack to determine which function calls are active.
The return value is always `nil'.
In the following example, a Lisp expression calls `backtrace'
explicitly. This prints the backtrace to the stream
`standard-output', which, in this case, is the buffer
`backtrace-output'.
Each line of the backtrace represents one function call. The line
shows the values of the function's arguments if they are all
known; if they are still being computed, the line says so. The
arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output"
(let ((var 1))
(save-excursion
(setq var (eval '(progn
(1+ var)
(list 'testing (backtrace))))))))
=> nil
----------- Buffer: backtrace-output ------------
backtrace()
(list ...computing arguments...)
(progn ...)
eval((progn (1+ var) (list (quote testing) (backtrace))))
(setq ...)
(save-excursion ...)
(let ...)
(with-output-to-temp-buffer ...)
eval-region(1973 2142 #<buffer *scratch*>)
byte-code("... for eval-print-last-sexp ...")
eval-print-last-sexp(nil)
* call-interactively(eval-print-last-sexp)
----------- Buffer: backtrace-output ------------
The character `*' indicates a frame whose debug-on-exit flag is
set.
- Variable: debug-on-next-call
If this variable is non-`nil', it says to call the debugger before
the next `eval', `apply' or `funcall'. Entering the debugger sets
`debug-on-next-call' to `nil'.
The `d' command in the debugger works by setting this variable.
- Function: backtrace-debug level flag
This function sets the debug-on-exit flag of the stack frame LEVEL
levels down the stack, giving it the value FLAG. If FLAG is
non-`nil', this will cause the debugger to be entered when that
frame later exits. Even a nonlocal exit through that frame will
enter the debugger.
This function is used only by the debugger.
- Variable: command-debug-status
This variable records the debugging status of the current
interactive command. Each time a command is called interactively,
this variable is bound to `nil'. The debugger can set this
variable to leave information for future debugger invocations
during the same command invocation.
The advantage of using this variable rather than an ordinary global
variable is that the data will never carry over to a subsequent
command invocation.
- Function: backtrace-frame frame-number
The function `backtrace-frame' is intended for use in Lisp
debuggers. It returns information about what computation is
happening in the stack frame FRAME-NUMBER levels down.
If that frame has not evaluated the arguments yet, or is a special
form, the value is `(nil FUNCTION ARG-FORMS...)'.
If that frame has evaluated its arguments and called its function
already, the return value is `(t FUNCTION ARG-VALUES...)'.
In the return value, FUNCTION is whatever was supplied as the CAR
of the evaluated list, or a `lambda' expression in the case of a
macro call. If the function has a `&rest' argument, that is
represented as the tail of the list ARG-VALUES.
If FRAME-NUMBER is out of range, `backtrace-frame' returns `nil'.
Edebug
======
Edebug is a source-level debugger for Emacs Lisp programs with which
you can:
* Step through evaluation, stopping before and after each expression.
* Set conditional or unconditional breakpoints.
* Stop when a specified condition is true (the global break event).
* Trace slow or fast, stopping briefly at each stop point, or at
each breakpoint.
* Display expression results and evaluate expressions as if outside
of Edebug.
* Automatically re-evaluate a list of expressions and display their
results each time Edebug updates the display.
* Output trace info on function enter and exit.
* Stop when an error occurs.
* Display a backtrace, omitting Edebug's own frames.
* Specify argument evaluation for macros and defining forms.
* Obtain rudimentary coverage testing and frequency counts.
The first three sections below should tell you enough about Edebug to
enable you to use it.
Using Edebug
------------
To debug a Lisp program with Edebug, you must first "instrument" the
Lisp code that you want to debug. A simple way to do this is to first
move point into the definition of a function or macro and then do `C-u
C-M-x' (`eval-defun' with a prefix argument). See *Note
Instrumenting::, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates
Edebug. Depending on which Edebug execution mode you have selected,
activating Edebug may stop execution and let you step through the
function, or it may update the display and continue execution while
checking for debugging commands. The default execution mode is step,
which stops execution. *Note Edebug Execution Modes::.
Within Edebug, you normally view an Emacs buffer showing the source
of the Lisp code you are debugging. This is referred to as the "source
code buffer", and it is temporarily read-only.
An arrow at the left margin indicates the line where the function is
executing. Point initially shows where within the line the function is
executing, but this ceases to be true if you move point yourself.
If you instrument the definition of `fac' (shown below) and then
execute `(fac 3)', here is what you would normally see. Point is at
the open-parenthesis before `if'.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are
called "stop points". These occur both before and after each
subexpression that is a list, and also after each variable reference.
Here we use periods to show the stop points in the function `fac':
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac (1- n.).).).
1).)
The special commands of Edebug are available in the source code
buffer in addition to the commands of Emacs Lisp mode. For example,
you can type the Edebug command <SPC> to execute until the next stop
point. If you type <SPC> once after entry to `fac', here is the
display you will see:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the
expression's value in the echo area.
Other frequently used commands are `b' to set a breakpoint at a stop
point, `g' to execute until a breakpoint is reached, and `q' to exit
Edebug and return to the top-level command loop. Type `?' to display a
list of all Edebug commands.
Instrumenting for Edebug
------------------------
In order to use Edebug to debug Lisp code, you must first
"instrument" the code. Instrumenting code inserts additional code into
it, to invoke Edebug at the proper places.
Once you have loaded Edebug, the command `C-M-x' (`eval-defun') is
redefined so that when invoked with a prefix argument on a definition,
it instruments the definition before evaluating it. (The source code
itself is not modified.) If the variable `edebug-all-defs' is
non-`nil', that inverts the meaning of the prefix argument: in this
case, `C-M-x' instruments the definition _unless_ it has a prefix
argument. The default value of `edebug-all-defs' is `nil'. The
command `M-x edebug-all-defs' toggles the value of the variable
`edebug-all-defs'.
If `edebug-all-defs' is non-`nil', then the commands `eval-region',
`eval-current-buffer', and `eval-buffer' also instrument any
definitions they evaluate. Similarly, `edebug-all-forms' controls
whether `eval-region' should instrument _any_ form, even non-defining
forms. This doesn't apply to loading or evaluations in the minibuffer.
The command `M-x edebug-all-forms' toggles this option.
Another command, `M-x edebug-eval-top-level-form', is available to
instrument any top-level form regardless of the values of
`edebug-all-defs' and `edebug-all-forms'.
While Edebug is active, the command `I' (`edebug-instrument-callee')
instruments the definition of the function or macro called by the list
form after point, if is not already instrumented. This is possible
only if Edebug knows where to find the source for that function; for
this reading, after loading Edebug, `eval-region' records the position
of every definition it evaluates, even if not instrumenting it. See
also the `i' command (*note Jumping::), which steps into the call after
instrumenting the function.
Edebug knows how to instrument all the standard special forms,
`interactive' forms with an expression argument, anonymous lambda
expressions, and other defining forms. However, Edebug cannot determine
on its own what a user-defined macro will do with the arguments of a
macro call, so you must provide that information; see *Note
Instrumenting Macro Calls::, for details.
When Edebug is about to instrument code for the first time in a
session, it runs the hook `edebug-setup-hook', then sets it to `nil'.
You can use this to load Edebug specifications (*note Instrumenting
Macro Calls::) associated with a package you are using, but only when
you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with `load',
and from the minibuffer with `eval-expression' (`M-:').
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an `invalid-read-syntax' error.
*Note Edebug Eval::, for other evaluation functions available inside
of Edebug.
Edebug Execution Modes
----------------------
Edebug supports several execution modes for running the program you
are debugging. We call these alternatives "Edebug execution modes"; do
not confuse them with major or minor modes. The current Edebug
execution mode determines how far Edebug continues execution before
stopping--whether it stops at each stop point, or continues to the next
breakpoint, for example--and how much Edebug displays the progress of
the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command
to continue the program in a certain mode. Here is a table of these
commands; all except for `S' resume execution of the program, at least
for a certain distance.
`S'
Stop: don't execute any more of the program, but wait for more
Edebug commands (`edebug-stop').
`<SPC>'
Step: stop at the next stop point encountered (`edebug-step-mode').
`n'
Next: stop at the next stop point encountered after an expression
(`edebug-next-mode'). Also see `edebug-forward-sexp' in *Note
Edebug Misc::.
`t'
Trace: pause one second at each Edebug stop point
(`edebug-trace-mode').
`T'
Rapid trace: update the display at each stop point, but don't
actually pause (`edebug-Trace-fast-mode').
`g'
Go: run until the next breakpoint (`edebug-go-mode'). *Note
Breakpoints::.
`c'
Continue: pause one second at each breakpoint, and then continue
(`edebug-continue-mode').
`C'
Rapid continue: move point to each breakpoint, but don't pause
(`edebug-Continue-fast-mode').
`G'
Go non-stop: ignore breakpoints (`edebug-Go-nonstop-mode'). You
can still stop the program by typing `S', or any editing command.
In general, the execution modes earlier in the above list run the
program more slowly or stop sooner than the modes later in the list.
While executing or tracing, you can interrupt the execution by typing
any Edebug command. Edebug stops the program at the next stop point and
then executes the command you typed. For example, typing `t' during
execution switches to trace mode at the next stop point. You can use
`S' to stop execution without doing anything else.
If your function happens to read input, a character you type
intending to interrupt execution may be read by the function instead.
You can avoid such unintended results by paying attention to when your
program wants input.
Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro. This is not easy to fix. Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug. This is usually an advantage. See also the
`edebug-continue-kbd-macro' option (*note Edebug Options::).
When you enter a new Edebug level, the initial execution mode comes
from the value of the variable `edebug-initial-mode'. By default, this
specifies step mode. Note that you may reenter the same Edebug level
several times if, for example, an instrumented function is called
several times from one command.
Jumping
-------
The commands described in this section execute until they reach a
specified location. All except `i' make a temporary breakpoint to
establish the place to stop, then switch to go mode. Any other
breakpoint reached before the intended stop point will also stop
execution. *Note Breakpoints::, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit,
as that can bypass the temporary breakpoint where you expected the
program to stop.
`h'
Proceed to the stop point near where point is (`edebug-goto-here').
`f'
Run the program forward over one expression
(`edebug-forward-sexp').
`o'
Run the program until the end of the containing sexp.
`i'
Step into the function or macro called by the form after point.
The `h' command proceeds to the stop point near the current location
of point, using a temporary breakpoint. See *Note Breakpoints::, for
more information about breakpoints.
The `f' command runs the program forward over one expression. More
precisely, it sets a temporary breakpoint at the position that `C-M-f'
would reach, then executes in go mode so that the program will stop at
breakpoints.
With a prefix argument N, the temporary breakpoint is placed N sexps
beyond point. If the containing list ends before N more elements, then
the place to stop is after the containing expression.
You must check that the position `C-M-f' finds is a place that the
program will really get to. In `cond', for example, this may not be
true.
For flexibility, the `f' command does `forward-sexp' starting at
point, rather than at the stop point. If you want to execute one
expression _from the current stop point_, first type `w', to move point
there, and then type `f'.
The `o' command continues "out of" an expression. It places a
temporary breakpoint at the end of the sexp containing point. If the
containing sexp is a function definition itself, `o' continues until
just before the last sexp in the definition. If that is where you are
now, it returns from the function and then stops. In other words, this
command does not exit the currently executing function unless you are
positioned after the last sexp.
The `i' command steps into the function or macro called by the list
form after point, and stops at its first stop point. Note that the form
need not be the one about to be evaluated. But if the form is a
function call about to be evaluated, remember to use this command before
any of the arguments are evaluated, since otherwise it will be too late.
The `i' command instruments the function or macro it's supposed to
step into, if it isn't instrumented already. This is convenient, but
keep in mind that the function or macro remains instrumented unless you
explicitly arrange to deinstrument it.
Miscellaneous Edebug Commands
-----------------------------
Some miscellaneous Edebug commands are described here.
`?'
Display the help message for Edebug (`edebug-help').
`C-]'
Abort one level back to the previous command level
(`abort-recursive-edit').
`q'
Return to the top level editor command loop (`top-level'). This
exits all recursive editing levels, including all levels of Edebug
activity. However, instrumented code protected with
`unwind-protect' or `condition-case' forms may resume debugging.
`Q'
Like `q', but don't stop even for protected code
(`top-level-nonstop').
`r'
Redisplay the most recently known expression result in the echo
area (`edebug-previous-result').
`d'
Display a backtrace, excluding Edebug's own functions for clarity
(`edebug-backtrace').
You cannot use debugger commands in the backtrace buffer in Edebug
as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue
execution.
You can invoke commands from Edebug that activate Edebug again
recursively. Whenever Edebug is active, you can quit to the top level
with `q' or abort one recursive edit level with `C-]'. You can display
a backtrace of all the pending evaluations with `d'.
Breakpoints
-----------
Edebug's step mode stops execution when the next stop point is
reached. There are three other ways to stop Edebug execution once it
has started: breakpoints, the global break condition, and source
breakpoints.
While using Edebug, you can specify "breakpoints" in the program you
are testing: these are places where execution should stop. You can set
a breakpoint at any stop point, as defined in *Note Using Edebug::. For
setting and unsetting breakpoints, the stop point that is affected is
the first one at or after point in the source code buffer. Here are the
Edebug commands for breakpoints:
`b'
Set a breakpoint at the stop point at or after point
(`edebug-set-breakpoint'). If you use a prefix argument, the
breakpoint is temporary--it turns off the first time it stops the
program.
`u'
Unset the breakpoint (if any) at the stop point at or after point
(`edebug-unset-breakpoint').
`x CONDITION <RET>'
Set a conditional breakpoint which stops the program only if
CONDITION evaluates to a non-`nil' value
(`edebug-set-conditional-breakpoint'). With a prefix argument, the
breakpoint is temporary.
`B'
Move point to the next breakpoint in the current definition
(`edebug-next-breakpoint').
While in Edebug, you can set a breakpoint with `b' and unset one
with `u'. First move point to the Edebug stop point of your choice,
then type `b' or `u' to set or unset a breakpoint there. Unsetting a
breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition removes all of its
previous breakpoints.
A "conditional breakpoint" tests a condition each time the program
gets there. Any errors that occur as a result of evaluating the
condition are ignored, as if the result were `nil'. To set a
conditional breakpoint, use `x', and specify the condition expression
in the minibuffer. Setting a conditional breakpoint at a stop point
that has a previously established conditional breakpoint puts the
previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint "temporary"
by using a prefix argument with the command to set the breakpoint.
When a temporary breakpoint stops the program, it is automatically
unset.
Edebug always stops or pauses at a breakpoint, except when the Edebug
mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the `B' command, which
moves point to the next breakpoint following point, within the same
function, or to the first breakpoint if there are no following
breakpoints. This command does not continue execution--it just moves
point in the buffer.
Global Break Condition
......................
A "global break condition" stops execution when a specified
condition is satisfied, no matter where that may occur. Edebug
evaluates the global break condition at every stop point; if it
evaluates to a non-`nil' value, then execution stops or pauses
depending on the execution mode, as if a breakpoint had been hit. If
evaluating the condition gets an error, execution does not stop.
The condition expression is stored in
`edebug-global-break-condition'. You can specify a new expression
using the `X' command (`edebug-set-global-break-condition').
The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly. So you
should reset the condition to `nil' when not using it.
Source Breakpoints
..................
All breakpoints in a definition are forgotten each time you
reinstrument it. If you wish to make a breakpoint that won't be
forgotten, you can write a "source breakpoint", which is simply a call
to the function `edebug' in your source code. You can, of course, make
such a call conditional. For example, in the `fac' function, you can
insert the first line as shown below, to stop when the argument reaches
zero:
(defun fac (n)
(if (= n 0) (edebug))
(if (< 0 n)
(* n (fac (1- n)))
1))
When the `fac' definition is instrumented and the function is
called, the call to `edebug' acts as a breakpoint. Depending on the
execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when `edebug' is called,
that function calls `debug'.
Trapping Errors
---------------
Emacs normally displays an error message when an error is signaled
and not handled with `condition-case'. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options `edebug-on-error' and
`edebug-on-quit'; see *Note Edebug Options::.
When Edebug responds to an error, it shows the last stop point
encountered before the error. This may be the location of a call to a
function which was not instrumented, and within which the error actually
occurred. For an unbound variable error, the last known stop point
might be quite distant from the offending variable reference. In that
case, you might want to display a full backtrace (*note Edebug Misc::).
If you change `debug-on-error' or `debug-on-quit' while Edebug is
active, these changes will be forgotten when Edebug becomes inactive.
Furthermore, during Edebug's recursive edit, these variables are bound
to the values they had outside of Edebug.
Edebug Views
------------
These Edebug commands let you view aspects of the buffer and window
status as they were before entry to Edebug. The outside window
configuration is the collection of windows and contents that were in
effect outside of Edebug.
`v'
Temporarily view the outside window configuration
(`edebug-view-outside').
`p'
Temporarily display the outside current buffer with point at its
outside position (`edebug-bounce-point'). With a prefix argument
N, pause for N seconds instead.
`w'
Move point back to the current stop point in the source code buffer
(`edebug-where').
If you use this command in a different window displaying the same
buffer, that window will be used instead to display the current
definition in the future.
`W'
Toggle whether Edebug saves and restores the outside window
configuration (`edebug-toggle-save-windows').
With a prefix argument, `W' only toggles saving and restoring of
the selected window. To specify a window that is not displaying
the source code buffer, you must use `C-x X W' from the global
keymap.
You can view the outside window configuration with `v' or just
bounce to the point in the current buffer with `p', even if it is not
normally displayed. After moving point, you may wish to jump back to
the stop point with `w' from a source code buffer.
Each time you use `W' to turn saving _off_, Edebug forgets the saved
outside window configuration--so that even if you turn saving back
_on_, the current window configuration remains unchanged when you next
exit Edebug (by continuing the program). However, the automatic
redisplay of `*edebug*' and `*edebug-trace*' may conflict with the
buffers you wish to see unless you have enough windows open.
Evaluation
----------
While within Edebug, you can evaluate expressions "as if" Edebug
were not running. Edebug tries to be invisible to the expression's
evaluation and printing. Evaluation of expressions that cause side
effects will work as expected, except for changes to data that Edebug
explicitly saves and restores. *Note The Outside Context::, for details
on this process.
`e EXP <RET>'
Evaluate expression EXP in the context outside of Edebug
(`edebug-eval-expression'). That is, Edebug tries to minimize its
interference with the evaluation.
`M-: EXP <RET>'
Evaluate expression EXP in the context of Edebug itself.
`C-x C-e'
Evaluate the expression before point, in the context outside of
Edebug (`edebug-eval-last-sexp').
Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in `cl.el'
(version 2.03 or later): `lexical-let', `macrolet', and
`symbol-macrolet'.
Evaluation List Buffer
----------------------
You can use the "evaluation list buffer", called `*edebug*', to
evaluate expressions interactively. You can also set up the
"evaluation list" of expressions to be evaluated automatically each
time Edebug updates the display.
`E'
Switch to the evaluation list buffer `*edebug*'
(`edebug-visit-eval-list').
In the `*edebug*' buffer you can use the commands of Lisp
Interaction mode (*note Lisp Interaction: (emacs)Lisp Interaction.) as
well as these special commands:
`C-j'
Evaluate the expression before point, in the outside context, and
insert the value in the buffer (`edebug-eval-print-last-sexp').
`C-x C-e'
Evaluate the expression before point, in the context outside of
Edebug (`edebug-eval-last-sexp').
`C-c C-u'
Build a new evaluation list from the contents of the buffer
(`edebug-update-eval-list').
`C-c C-d'
Delete the evaluation list group that point is in
(`edebug-delete-eval-item').
`C-c C-w'
Switch back to the source code buffer at the current stop point
(`edebug-where').
You can evaluate expressions in the evaluation list window with
`C-j' or `C-x C-e', just as you would in `*scratch*'; but they are
evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost
when you continue execution; but you can set up an "evaluation list"
consisting of expressions to be evaluated each time execution stops.
To do this, write one or more "evaluation list groups" in the
evaluation list buffer. An evaluation list group consists of one or
more Lisp expressions. Groups are separated by comment lines.
The command `C-c C-u' (`edebug-update-eval-list') rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group. (The idea is that the second expression of the group is the
value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each
expression in the buffer, followed by its current value. It also
inserts comment lines so that each expression becomes its own group.
Thus, if you type `C-c C-u' again without changing the buffer text, the
evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the
error message is displayed in a string as if it were the result.
Therefore, expressions that use variables not currently valid do not
interrupt your debugging.
Here is an example of what the evaluation list window looks like
after several expressions have been added to it:
(current-buffer)
#<buffer *scratch*>
;---------------------------------------------------------------
(selected-window)
#<window 16 on *scratch*>
;---------------------------------------------------------------
(point)
196
;---------------------------------------------------------------
bad-var
"Symbol's value as variable is void: bad-var"
;---------------------------------------------------------------
(recursion-depth)
0
;---------------------------------------------------------------
this-command
eval-last-sexp
;---------------------------------------------------------------
To delete a group, move point into it and type `C-c C-d', or simply
delete the text for the group and update the evaluation list with `C-c
C-u'. To add a new expression to the evaluation list, insert the
expression at a suitable place, insert a new comment line, then type
`C-c C-u'. You need not insert dashes in the comment line--its
contents don't matter.
After selecting `*edebug*', you can return to the source code buffer
with `C-c C-w'. The `*edebug*' buffer is killed when you continue
execution, and recreated next time it is needed.
Printing in Edebug
------------------
If an expression in your program produces a value containing circular
list structure, you may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set `print-length' or
`print-level' to truncate the printing. Edebug does this for you; it
binds `print-length' and `print-level' to 50 if they were `nil'.
(Actually, the variables `edebug-print-length' and `edebug-print-level'
specify the values to use within Edebug.) *Note Output Variables::.
- User Option: edebug-print-length
If non-`nil', Edebug binds `print-length' to this value while
printing results. The default value is `50'.
- User Option: edebug-print-level
If non-`nil', Edebug binds `print-level' to this value while
printing results. The default value is `50'.
You can also print circular structures and structures that share
elements more informatively by binding `print-circle' to a non-`nil'
value.
Here is an example of code that creates a circular structure:
(setq a '(x y))
(setcar a a)
Custom printing prints this as `Result: #1=(#1# y)'. The `#1='
notation labels the structure that follows it with the label `1', and
the `#1#' notation references the previously labeled structure. This
notation is used for any shared elements of lists or vectors.
- User Option: edebug-print-circle
If non-`nil', Edebug binds `print-circle' to this value while
printing results. The default value is `nil'.
Other programs can also use custom printing; see `cust-print.el' for
details.
Trace Buffer
------------
Edebug can record an execution trace, storing it in a buffer named
`*edebug-trace*'. This is a log of function calls and returns, showing
the function names and their arguments and values. To enable trace
recording, set `edebug-trace' to a non-`nil' value.
Making a trace buffer is not the same thing as using trace execution
mode (*note Edebug Execution Modes::).
When trace recording is enabled, each function entry and exit adds
lines to the trace buffer. A function entry record consists of
`::::{', followed by the function name and argument values. A function
exit record consists of `::::}', followed by the function name and
result of the function.
The number of `:'s in an entry shows its recursion depth. You can
use the braces in the trace buffer to find the matching beginning or
end of function calls.
You can customize trace recording for function entry and exit by
redefining the functions `edebug-print-trace-before' and
`edebug-print-trace-after'.
- Macro: edebug-tracing string body...
This macro requests additional trace information around the
execution of the BODY forms. The argument STRING specifies text
to put in the trace buffer. All the arguments are evaluated, and
`edebug-tracing' returns the value of the last form in BODY.
- Function: edebug-trace format-string &rest format-args
This function inserts text in the trace buffer. It computes the
text with `(apply 'format FORMAT-STRING FORMAT-ARGS)'. It also
appends a newline to separate entries.
`edebug-tracing' and `edebug-trace' insert lines in the trace buffer
whenever they are called, even if Edebug is not active. Adding text to
the trace buffer also scrolls its window to show the last lines
inserted.
Coverage Testing
----------------
Edebug provides rudimentary coverage testing and display of execution
frequency.
Coverage testing works by comparing the result of each expression
with the previous result; each form in the program is considered
"covered" if it has returned two different values since you began
testing coverage in the current Emacs session. Thus, to do coverage
testing on your program, execute it under various conditions and note
whether it behaves correctly; Edebug will tell you when you have tried
enough different conditions that each form has returned two different
values.
Coverage testing makes execution slower, so it is only done if
`edebug-test-coverage' is non-`nil'. Frequency counting is performed
for all execution of an instrumented function, even if the execution
mode is Go-nonstop, and regardless of whether coverage testing is
enabled.
Use `M-x edebug-display-freq-count' to display both the coverage
information and the frequency counts for a definition.
- Command: edebug-display-freq-count
This command displays the frequency count data for each line of the
current definition.
The frequency counts appear as comment lines after each line of
code, and you can undo all insertions with one `undo' command. The
counts appear under the `(' before an expression or the `)' after
an expression, or on the last character of a variable. To
simplify the display, a count is not shown if it is equal to the
count of an earlier expression on the same line.
The character `=' following the count for an expression says that
the expression has returned the same value each time it was
evaluated. In other words, it is not yet "covered" for coverage
testing purposes.
To clear the frequency count and coverage data for a definition,
simply reinstrument it with `eval-defun'.
For example, after evaluating `(fac 5)' with a source breakpoint,
and setting `edebug-test-coverage' to `t', when the breakpoint is
reached, the frequency data looks like this:
(defun fac (n)
(if (= n 0) (edebug))
;#6 1 0 =5
(if (< 0 n)
;#5 =
(* n (fac (1- n)))
;# 5 0
1))
;# 0
The comment lines show that `fac' was called 6 times. The first
`if' statement returned 5 times with the same result each time; the
same is true of the condition on the second `if'. The recursive call
of `fac' did not return at all.
The Outside Context
-------------------
Edebug tries to be transparent to the program you are debugging, but
it does not succeed completely. Edebug also tries to be transparent
when you evaluate expressions with `e' or with the evaluation list
buffer, by temporarily restoring the outside context. This section
explains precisely what context Edebug restores, and how Edebug fails to
be completely transparent.
Checking Whether to Stop
........................
Whenever Edebug is entered, it needs to save and restore certain data
before even deciding whether to make trace information or stop the
program.
* `max-lisp-eval-depth' and `max-specpdl-size' are both incremented
once to reduce Edebug's impact on the stack. You could, however,
still run out of stack space when using Edebug.
* The state of keyboard macro execution is saved and restored. While
Edebug is active, `executing-macro' is bound to
`edebug-continue-kbd-macro'.
Edebug Display Update
.....................
When Edebug needs to display something (e.g., in trace mode), it
saves the current window configuration from "outside" Edebug (*note
Window Configurations::). When you exit Edebug (by continuing the
program), it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue
execution, the program re-enters Edebug at a breakpoint or after
stepping, without pausing or reading input in between. In such cases,
Emacs never gets a chance to redisplay the "outside" configuration.
Consequently, what you see is the same window configuration as the last
time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the
following data (though some of them are deliberately not restored if an
error or quit signal occurs).
* Which buffer is current, and the positions of point and the mark
in the current buffer, are saved and restored.
* The outside window configuration is saved and restored if
`edebug-save-windows' is non-`nil' (*note Edebug Display Update::).
The window configuration is not restored on error or quit, but the
outside selected window _is_ reselected even on error or quit in
case a `save-excursion' is active. If the value of
`edebug-save-windows' is a list, only the listed windows are saved
and restored.
The window start and horizontal scrolling of the source code
buffer are not restored, however, so that the display remains
coherent within Edebug.
* The value of point in each displayed buffer is saved and restored
if `edebug-save-displayed-buffer-points' is non-`nil'.
* The variables `overlay-arrow-position' and `overlay-arrow-string'
are saved and restored. So you can safely invoke Edebug from the
recursive edit elsewhere in the same buffer.
* `cursor-in-echo-area' is locally bound to `nil' so that the cursor
shows up in the window.
Edebug Recursive Edit
.....................
When Edebug is entered and actually reads commands from the user, it
saves (and later restores) these additional data:
* The current match data. *Note Match Data::.
* `last-command', `this-command', `last-command-char',
`last-input-char', `last-input-event', `last-command-event',
`last-event-frame', `last-nonmenu-event', and `track-mouse'.
Commands used within Edebug do not affect these variables outside
of Edebug.
The key sequence returned by `this-command-keys' is changed by
executing commands within Edebug and there is no way to reset the
key sequence from Lisp.
Edebug cannot save and restore the value of
`unread-command-events'. Entering Edebug while this variable has a
nontrivial value can interfere with execution of the program you
are debugging.
* Complex commands executed while in Edebug are added to the variable
`command-history'. In rare cases this can alter execution.
* Within Edebug, the recursion depth appears one deeper than the
recursion depth outside Edebug. This is not true of the
automatically updated evaluation list window.
* `standard-output' and `standard-input' are bound to `nil' by the
`recursive-edit', but Edebug temporarily restores them during
evaluations.
* The state of keyboard macro definition is saved and restored.
While Edebug is active, `defining-kbd-macro' is bound to
`edebug-continue-kbd-macro'.
Instrumenting Macro Calls
-------------------------
When Edebug instruments an expression that calls a Lisp macro, it
needs additional information about the macro to do the job properly.
This is because there is no a-priori way to tell which subexpressions
of the macro call are forms to be evaluated. (Evaluation may occur
explicitly in the macro body, or when the resulting expansion is
evaluated, or any time later.)
Therefore, you must define an Edebug specification for each macro
that Edebug will encounter, to explain the format of calls to that
macro. To do this, use `def-edebug-spec'.
- Macro: def-edebug-spec macro specification
Specify which expressions of a call to macro MACRO are forms to be
evaluated. For simple macros, the SPECIFICATION often looks very
similar to the formal argument list of the macro definition, but
specifications are much more general than macro arguments.
The MACRO argument can actually be any symbol, not just a macro
name.
Here is a simple example that defines the specification for the
`for' example macro (*note Argument Evaluation::), followed by an
alternative, equivalent specification.
(def-edebug-spec for
(symbolp "from" form "to" form "do" &rest form))
(def-edebug-spec for
(symbolp ['from form] ['to form] ['do body]))
Here is a table of the possibilities for SPECIFICATION and how each
directs processing of arguments.
`t'
All arguments are instrumented for evaluation.
`0'
None of the arguments is instrumented.
a symbol
The symbol must have an Edebug specification which is used instead.
This indirection is repeated until another kind of specification is
found. This allows you to inherit the specification from another
macro.
a list
The elements of the list describe the types of the arguments of a
calling form. The possible elements of a specification list are
described in the following sections.
Specification List
..................
A "specification list" is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
"specification keywords", are symbols beginning with `&' (such as
`&optional').
A specification list may contain sublists which match arguments that
are themselves lists, or it may contain vectors used for grouping.
Sublists and groups thus subdivide the specification list into a
hierarchy of levels. Specification keywords apply only to the
remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition,
matching it against an actual macro call may require backtracking.
*Note Backtracking::, for more details.
Edebug specifications provide the power of regular expression
matching, plus some context-free grammar constructs: the matching of
sublists with balanced parentheses, recursive processing of forms, and
recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with
their meanings:
`sexp'
A single unevaluated Lisp object, which is not instrumented.
`form'
A single evaluated expression, which is instrumented.
`place'
A place to store a value, as in the Common Lisp `setf' construct.
`body'
Short for `&rest form'. See `&rest' below.
`function-form'
A function form: either a quoted function symbol, a quoted lambda
expression, or a form (that should evaluate to a function symbol or
lambda expression). This is useful when an argument that's a
lambda expression might be quoted with `quote' rather than
`function', since it instruments the body of the lambda expression
either way.
`lambda-expr'
A lambda expression with no quoting.
`&optional'
All following elements in the specification list are optional; as
soon as one does not match, Edebug stops matching at this level.
To make just a few elements optional followed by non-optional
elements, use `[&optional SPECS...]'. To specify that several
elements must all match or none, use `&optional [SPECS...]'. See
the `defun' example below.
`&rest'
All following elements in the specification list are repeated zero
or more times. In the last repetition, however, it is not a
problem if the expression runs out before matching all of the
elements of the specification list.
To repeat only a few elements, use `[&rest SPECS...]'. To specify
several elements that must all match on every repetition, use
`&rest [SPECS...]'.
`&or'
Each of the following elements in the specification list is an
alternative. One of the alternatives must match, or the `&or'
specification fails.
Each list element following `&or' is a single alternative. To
group two or more list elements as a single alternative, enclose
them in `[...]'.
`¬'
Each of the following elements is matched as alternatives as if by
using `&or', but if any of them match, the specification fails.
If none of them match, nothing is matched, but the `¬'
specification succeeds.
`&define'
Indicates that the specification is for a defining form. The
defining form itself is not instrumented (that is, Edebug does not
stop before and after the defining form), but forms inside it
typically will be instrumented. The `&define' keyword should be
the first element in a list specification.
`nil'
This is successful when there are no more arguments to match at the
current argument list level; otherwise it fails. See sublist
specifications and the backquote example below.
`gate'
No argument is matched but backtracking through the gate is
disabled while matching the remainder of the specifications at
this level. This is primarily used to generate more specific
syntax error messages. See *Note Backtracking::, for more
details. Also see the `let' example below.
`OTHER-SYMBOL'
Any other symbol in a specification list may be a predicate or an
indirect specification.
If the symbol has an Edebug specification, this "indirect
specification" should be either a list specification that is used
in place of the symbol, or a function that is called to process the
arguments. The specification may be defined with `def-edebug-spec'
just as for macros. See the `defun' example below.
Otherwise, the symbol should be a predicate. The predicate is
called with the argument and the specification fails if the
predicate returns `nil'. In either case, that argument is not
instrumented.
Some suitable predicates include `symbolp', `integerp', `stringp',
`vectorp', and `atom'.
`[ELEMENTS...]'
A vector of elements groups the elements into a single "group
specification". Its meaning has nothing to do with vectors.
`"STRING"'
The argument should be a symbol named STRING. This specification
is equivalent to the quoted symbol, `'SYMBOL', where the name of
SYMBOL is the STRING, but the string form is preferred.
`(vector ELEMENTS...)'
The argument should be a vector whose elements must match the
ELEMENTS in the specification. See the backquote example below.
`(ELEMENTS...)'
Any other list is a "sublist specification" and the argument must
be a list whose elements match the specification ELEMENTS.
A sublist specification may be a dotted list and the corresponding
list argument may then be a dotted list. Alternatively, the last
CDR of a dotted list specification may be another sublist
specification (via a grouping or an indirect specification, e.g.,
`(spec . [(more specs...)])') whose elements match the non-dotted
list arguments. This is useful in recursive specifications such
as in the backquote example below. Also see the description of a
`nil' specification above for terminating such recursion.
Note that a sublist specification written as `(specs . nil)' is
equivalent to `(specs)', and `(specs . (sublist-elements...))' is
equivalent to `(specs sublist-elements...)'.
Here is a list of additional specifications that may appear only
after `&define'. See the `defun' example below.
`name'
The argument, a symbol, is the name of the defining form.
A defining form is not required to have a name field; and it may
have multiple name fields.
`:name'
This construct does not actually match an argument. The element
following `:name' should be a symbol; it is used as an additional
name component for the definition. You can use this to add a
unique, static component to the name of the definition. It may be
used more than once.
`arg'
The argument, a symbol, is the name of an argument of the defining
form. However, lambda-list keywords (symbols starting with `&')
are not allowed.
`lambda-list'
This matches a lambda list--the argument list of a lambda
expression.
`def-body'
The argument is the body of code in a definition. This is like
`body', described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated
with the definition. Use `def-body' for the highest level list of
forms within the definition.
`def-form'
The argument is a single, highest-level form in a definition.
This is like `def-body', except use this to match a single form
rather than a list of forms. As a special case, `def-form' also
means that tracing information is not output when the form is
executed. See the `interactive' example below.
Backtracking in Specifications
..............................
If a specification fails to match at some point, this does not
necessarily mean a syntax error will be signaled; instead,
"backtracking" will take place until all alternatives have been
exhausted. Eventually every element of the argument list must be
matched by some element in the specification, and every required element
in the specification must match some argument.
When a syntax error is detected, it might not be reported until much
later after higher-level alternatives have been exhausted, and with the
point positioned further from the real error. But if backtracking is
disabled when an error occurs, it can be reported immediately. Note
that backtracking is also reenabled automatically in several situations;
it is reenabled when a new alternative is established by `&optional',
`&rest', or `&or', or at the start of processing a sublist, group, or
indirect specification. The effect of enabling or disabling
backtracking is limited to the remainder of the level currently being
processed and lower levels.
Backtracking is disabled while matching any of the form
specifications (that is, `form', `body', `def-form', and `def-body').
These specifications will match any form so any error must be in the
form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. But if you have a set of alternative constructs
that all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
`["foo" &or [first case] [second case] ...]'.
Most needs are satisfied by these two ways that bactracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the `gate' specification. This is useful
when you know that no higher alternatives could apply. See the example
of the `let' specification.
Specification Examples
......................
It may be easier to understand Edebug specifications by studying the
examples provided here.
A `let' special form has a sequence of bindings and a body. Each of
the bindings is either a symbol or a sublist with a symbol and optional
expression. In the specification below, notice the `gate' inside of
the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for `defun' and `defmacro'
and the associated argument list and `interactive' specifications. It
is necessary to handle interactive forms specially since an expression
argument it is actually evaluated outside of the function body.
(def-edebug-spec defmacro defun) ; Indirect ref to `defun' spec.
(def-edebug-spec defun
(&define name lambda-list
[&optional stringp] ; Match the doc string, if present.
[&optional ("interactive" interactive)]
def-body))
(def-edebug-spec lambda-list
(([&rest arg]
[&optional ["&optional" arg &rest arg]]
&optional ["&rest" arg]
)))
(def-edebug-spec interactive
(&optional &or stringp def-form)) ; Notice: `def-form'
The specification for backquote below illustrates how to match
dotted lists and use `nil' to terminate recursion. It also illustrates
how components of a vector may be matched. (The actual specification
defined by Edebug does not support dotted lists because doing so causes
very deep recursion that could fail.)
(def-edebug-spec ` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
Edebug Options
--------------
These options affect the behavior of Edebug:
- User Option: edebug-setup-hook
Functions to call before Edebug is used. Each time it is set to a
new value, Edebug will call those functions once and then
`edebug-setup-hook' is reset to `nil'. You could use this to load
up Edebug specifications associated with a package you are using
but only when you also use Edebug. *Note Instrumenting::.
- User Option: edebug-all-defs
If this is non-`nil', normal evaluation of defining forms such as
`defun' and `defmacro' instruments them for Edebug. This applies
to `eval-defun', `eval-region', `eval-buffer', and
`eval-current-buffer'.
Use the command `M-x edebug-all-defs' to toggle the value of this
option. *Note Instrumenting::.
- User Option: edebug-all-forms
If this is non-`nil', the commands `eval-defun', `eval-region',
`eval-buffer', and `eval-current-buffer' instrument all forms,
even those that don't define anything. This doesn't apply to
loading or evaluations in the minibuffer.
Use the command `M-x edebug-all-forms' to toggle the value of this
option. *Note Instrumenting::.
- User Option: edebug-save-windows
If this is non-`nil', Edebug saves and restores the window
configuration. That takes some time, so if your program does not
care what happens to the window configurations, it is better to
set this variable to `nil'.
If the value is a list, only the listed windows are saved and
restored.
You can use the `W' command in Edebug to change this variable
interactively. *Note Edebug Display Update::.
- User Option: edebug-save-displayed-buffer-points
If this is non-`nil', Edebug saves and restores point in all
displayed buffers.
Saving and restoring point in other buffers is necessary if you are
debugging code that changes the point of a buffer which is
displayed in a non-selected window. If Edebug or the user then
selects the window, point in that buffer will move to the window's
value of point.
Saving and restoring point in all buffers is expensive, since it
requires selecting each window twice, so enable this only if you
need it. *Note Edebug Display Update::.
- User Option: edebug-initial-mode
If this variable is non-`nil', it specifies the initial execution
mode for Edebug when it is first activated. Possible values are
`step', `next', `go', `Go-nonstop', `trace', `Trace-fast',
`continue', and `Continue-fast'.
The default value is `step'. *Note Edebug Execution Modes::.
- User Option: edebug-trace
Non-`nil' means display a trace of function entry and exit.
Tracing output is displayed in a buffer named `*edebug-trace*', one
function entry or exit per line, indented by the recursion level.
The default value is `nil'.
Also see `edebug-tracing', in *Note Trace Buffer::.
- User Option: edebug-test-coverage
If non-`nil', Edebug tests coverage of all expressions debugged.
*Note Coverage Testing::.
- User Option: edebug-continue-kbd-macro
If non-`nil', continue defining or executing any keyboard macro
that is executing outside of Edebug. Use this with caution since
it is not debugged. *Note Edebug Execution Modes::.
- User Option: edebug-on-error
Edebug binds `debug-on-error' to this value, if `debug-on-error'
was previously `nil'. *Note Trapping Errors::.
- User Option: edebug-on-quit
Edebug binds `debug-on-quit' to this value, if `debug-on-quit' was
previously `nil'. *Note Trapping Errors::.
If you change the values of `edebug-on-error' or `edebug-on-quit'
while Edebug is active, their values won't be used until the _next_
time Edebug is invoked via a new command.
- User Option: edebug-global-break-condition
If non-`nil', an expression to test for at every stop point. If
the result is non-nil, then break. Errors are ignored. *Note
Global Break Condition::.
Debugging Invalid Lisp Syntax
=============================
The Lisp reader reports invalid syntax, but cannot say where the real
problem is. For example, the error "End of file during parsing" in
evaluating an expression indicates an excess of open parentheses (or
square brackets). The reader detects this imbalance at the end of the
file, but it cannot figure out where the close parenthesis should have
been. Likewise, "Invalid read syntax: ")"" indicates an excess close
parenthesis or missing open parenthesis, but does not say where the
missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful
technique is to try `C-M-e' at the beginning of each defun, and see if
it goes to the place where that defun appears to end. If it does not,
there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in
Lisp, and we can give further advice for those cases. (In addition,
just moving point through the code with Show Paren mode enabled might
find the mismatch.)
Excess Open Parentheses
-----------------------
The first step is to find the defun that is unbalanced. If there is
an excess open parenthesis, the way to do this is to go to the end of
the file and type `C-u C-M-u'. This will move you to the beginning of
the defun that is unbalanced.
The next step is to determine precisely what is wrong. There is no
way to be sure of this except by studying the program, but often the
existing indentation is a clue to where the parentheses should have
been. The easiest way to use this clue is to reindent with `C-M-q' and
see what moves. *But don't do this yet!* Keep reading, first.
Before you do this, make sure the defun has enough close parentheses.
Otherwise, `C-M-q' will get an error, or will reindent all the rest of
the file until the end. So move to the end of the defun and insert a
close parenthesis there. Don't use `C-M-e' to move there, since that
too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type `C-M-q'.
Usually all the lines from a certain point to the end of the function
will shift to the right. There is probably a missing close parenthesis,
or a superfluous open parenthesis, near that point. (However, don't
assume this is true; study the code to make sure.) Once you have found
the discrepancy, undo the `C-M-q' with `C-_', since the old indentation
is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use `C-M-q' again. If
the old indentation actually fit the intended nesting of parentheses,
and you have put back those parentheses, `C-M-q' should not change
anything.
Excess Close Parentheses
------------------------
To deal with an excess close parenthesis, first go to the beginning
of the file, then type `C-u -1 C-M-u' to find the end of the unbalanced
defun.
Then find the actual matching close parenthesis by typing `C-M-f' at
the beginning of that defun. This will leave you somewhere short of
the place where the defun ought to end. It is possible that you will
find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to
type `C-M-q' at the beginning of the defun. A range of lines will
probably shift left; if so, the missing open parenthesis or spurious
close parenthesis is probably near the first of those lines. (However,
don't assume this is true; study the code to make sure.) Once you have
found the discrepancy, undo the `C-M-q' with `C-_', since the old
indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use `C-M-q' again. If
the old indentation actually fits the intended nesting of parentheses,
and you have put back those parentheses, `C-M-q' should not change
anything.
Debugging Problems in Compilation
=================================
When an error happens during byte compilation, it is normally due to
invalid syntax in the program you are compiling. The compiler prints a
suitable error message in the `*Compile-Log*' buffer, and then stops.
The message may state a function name in which the error was found, or
it may not. Either way, here is how to find out where in the file the
error occurred.
What you should do is switch to the buffer ` *Compiler Input*'.
(Note that the buffer name starts with a space, so it does not show up
in `M-x list-buffers'.) This buffer contains the program being
compiled, and point shows how far the byte compiler was able to read.
If the error was due to invalid Lisp syntax, point shows exactly
where the invalid syntax was _detected_. The cause of the error is not
necessarily near by! Use the techniques in the previous section to find
the error.
If the error was detected while compiling a form that had been read
successfully, then point is located at the end of the form. In this
case, this technique can't localize the error precisely, but can still
show you which function to check.
Reading and Printing Lisp Objects
*********************************
"Printing" and "reading" are the operations of converting Lisp
objects to textual form and vice versa. They use the printed
representations and read syntax described in *Note Lisp Data Types::.
This chapter describes the Lisp functions for reading and printing.
It also describes "streams", which specify where to get the text (if
reading) or where to put it (if printing).
Introduction to Reading and Printing
====================================
"Reading" a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
"read syntax" of the object. For example, the text `(a . 5)' is the
read syntax for a cons cell whose CAR is `a' and whose CDR is the
number 5.
"Printing" a Lisp object means producing text that represents that
object--converting the object to its "printed representation" (*note
Printed Representation::). Printing the cons cell described above
produces the text `(a . 5)'.
Reading and printing are more or less inverse operations: printing
the object that results from reading a given piece of text often
produces the same text, and reading the text that results from printing
an object usually produces a similar-looking object. For example,
printing the symbol `foo' produces the text `foo', and reading that text
returns the symbol `foo'. Printing a list whose elements are `a' and
`b' produces the text `(a b)', and reading that text produces a list
(but not the same list) with elements `a' and `b'.
However, these two operations are not precisely inverse to each
other. There are three kinds of exceptions:
* Printing can produce text that cannot be read. For example,
buffers, windows, frames, subprocesses and markers print as text
that starts with `#'; if you try to read this text, you get an
error. There is no way to read those data types.
* One object can have multiple textual representations. For example,
`1' and `01' represent the same integer, and `(a b)' and `(a .
(b))' represent the same list. Reading will accept any of the
alternatives, but printing must choose one of them.
* Comments can appear at certain points in the middle of an object's
read sequence without affecting the result of reading it.
Input Streams
=============
Most of the Lisp functions for reading text take an "input stream"
as an argument. The input stream specifies where or how to get the
characters of the text to be read. Here are the possible types of input
stream:
BUFFER
The input characters are read from BUFFER, starting with the
character directly after point. Point advances as characters are
read.
MARKER
The input characters are read from the buffer that MARKER is in,
starting with the character directly after the marker. The marker
position advances as characters are read. The value of point in
the buffer has no effect when the stream is a marker.
STRING
The input characters are taken from STRING, starting at the first
character in the string and using as many characters as required.
FUNCTION
The input characters are generated by FUNCTION, which must support
two kinds of calls:
* When it is called with no arguments, it should return the
next character.
* When it is called with one argument (always a character),
FUNCTION should save the argument and arrange to return it on
the next call. This is called "unreading" the character; it
happens when the Lisp reader reads one character too many and
wants to "put it back where it came from". In this case, it
makes no difference what value FUNCTION returns.
`t'
`t' used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream. If Emacs is running in batch mode, standard input
is used instead of the minibuffer. For example,
(message "%s" (read t))
will read a Lisp expression from standard input and print the
result to standard output.
`nil'
`nil' supplied as an input stream means to use the value of
`standard-input' instead; that value is the "default input
stream", and must be a non-`nil' input stream.
SYMBOL
A symbol as input stream is equivalent to the symbol's function
definition (if any).
Here is an example of reading from a stream that is a buffer, showing
where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
=> is
(read (get-buffer "foo"))
=> the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space. Reading skips any amount of
whitespace preceding the significant text.
Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown. The value
read is the symbol `This'.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
=> #<marker at 1 in foo>
(read m)
=> This
m
=> #<marker at 5 in foo> ;; Before the first space.
Here we read from the contents of a string:
(read "(When in) the course")
=> (When in)
The following example reads from the minibuffer. The prompt is:
`Lisp expression: '. (That is always the prompt used when you read
from the stream `t'.) The user's input is shown following the prompt.
(read t)
=> 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 <RET>
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
`useless-stream'. Before we use the stream, we initialize the variable
`useless-list' to a list of characters. Then each call to the function
`useless-stream' obtains the next character in the list or unreads a
character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
=> (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
=> useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
=> XY
useless-list
=> (40 41)
Note that the open and close parentheses remain in the list. The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it. Another attempt to read from the stream at this
point would read `()' and return `nil'.
- Function: get-file-char
This function is used internally as an input stream to read from
the input file opened by the function `load'. Don't use this
function yourself.
Input Functions
===============
This section describes the Lisp functions and variables that pertain
to reading.
In the functions below, STREAM stands for an input stream (see the
previous section). If STREAM is `nil' or omitted, it defaults to the
value of `standard-input'.
An `end-of-file' error is signaled if reading encounters an
unterminated list, vector, or string.
- Function: read &optional stream
This function reads one textual Lisp expression from STREAM,
returning it as a Lisp object. This is the basic Lisp input
function.
- Function: read-from-string string &optional start end
This function reads the first textual Lisp expression from the
text in STRING. It returns a cons cell whose CAR is that
expression, and whose CDR is an integer giving the position of the
next remaining character in the string (i.e., the first one not
read).
If START is supplied, then reading begins at index START in the
string (where the first character is at index 0). If you specify
END, then reading is forced to stop just before that index, as if
the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)")
=> ((setq x 55) . 11)
(read-from-string "\"A short string\"")
=> ("A short string" . 16)
;; Read starting at the first character.
(read-from-string "(list 112)" 0)
=> ((list 112) . 10)
;; Read starting at the second character.
(read-from-string "(list 112)" 1)
=> (list . 5)
;; Read starting at the seventh character,
;; and stopping at the ninth.
(read-from-string "(list 112)" 6 8)
=> (11 . 8)
- Variable: standard-input
This variable holds the default input stream--the stream that
`read' uses when the STREAM argument is `nil'.
Output Streams
==============
An output stream specifies what to do with the characters produced
by printing. Most print functions accept an output stream as an
optional argument. Here are the possible types of output stream:
BUFFER
The output characters are inserted into BUFFER at point. Point
advances as characters are inserted.
MARKER
The output characters are inserted into the buffer that MARKER
points into, at the marker position. The marker position advances
as characters are inserted. The value of point in the buffer has
no effect on printing when the stream is a marker, and this kind
of printing does not move point.
FUNCTION
The output characters are passed to FUNCTION, which is responsible
for storing them away. It is called with a single character as
argument, as many times as there are characters to be output, and
is responsible for storing the characters wherever you want to put
them.
`t'
The output characters are displayed in the echo area.
`nil'
`nil' specified as an output stream means to use the value of
`standard-output' instead; that value is the "default output
stream", and must not be `nil'.
SYMBOL
A symbol as output stream is equivalent to the symbol's function
definition (if any).
Many of the valid output streams are also valid as input streams.
The difference between input and output streams is therefore more a
matter of how you use a Lisp object, than of different types of object.
Here is an example of a buffer used as an output stream. Point is
initially located as shown immediately before the `h' in `the'. At the
end, point is located directly before that same `h'.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker is in buffer `foo', between the `t' and the `h' in the word
`the'. At the end, the marker has advanced over the inserted text so
that it remains positioned before the same `h'. Note that the location
of point, shown in the usual fashion, has no effect.
---------- Buffer: foo ----------
This is the -!-output
---------- Buffer: foo ----------
(setq m (copy-marker 10))
=> #<marker at 10 in foo>
(print "More output for foo." m)
=> "More output for foo."
---------- Buffer: foo ----------
This is t
"More output for foo."
he -!-output
---------- Buffer: foo ----------
m
=> #<marker at 34 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
=> "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show the use of a function as an output stream. The
function `eat-output' takes each character that it is given and conses
it onto the front of the list `last-output' (*note Building Lists::).
At the end, the list contains all the characters output, but in reverse
order.
(setq last-output nil)
=> nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
=> eat-output
(print "This is the output" 'eat-output)
=> "This is the output"
last-output
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
=> "
\"This is the output\"
"
Calling `concat' converts the list to a string so you can see its
contents more clearly.
Output Functions
================
This section describes the Lisp functions for printing Lisp
objects--converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the
output when necessary so that it can be read properly. The quoting
characters used are `"' and `\'; they distinguish strings from symbols,
and prevent punctuation characters in strings and symbols from being
taken as delimiters when reading. *Note Printed Representation::, for
full details. You specify quoting or no quoting by the choice of
printing function.
If the text is to be read back into Lisp, then you should print with
quoting characters to avoid ambiguity. Likewise, if the purpose is to
describe a Lisp object clearly for a Lisp programmer. However, if the
purpose of the output is to look nice for humans, then it is usually
better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential
object in the normal way would require an infinite amount of text, and
the attempt could cause infinite recursion. Emacs detects such
recursion and prints `#LEVEL' instead of recursively printing an object
already being printed. For example, here `#0' indicates a recursive
reference to the object at level 0 of the current print operation:
(setq foo (list nil))
=> (nil)
(setcar foo foo)
=> (#0)
In the functions below, STREAM stands for an output stream. (See
the previous section for a description of output streams.) If STREAM
is `nil' or omitted, it defaults to the value of `standard-output'.
- Function: print object &optional stream
The `print' function is a convenient way of printing. It outputs
the printed representation of OBJECT to STREAM, printing in
addition one newline before OBJECT and another after it. Quoting
characters are used. `print' returns OBJECT. For example:
(progn (print 'The\ cat\ in)
(print "the hat")
(print " came back"))
-|
-| The\ cat\ in
-|
-| "the hat"
-|
-| " came back"
-|
=> " came back"
- Function: prin1 object &optional stream
This function outputs the printed representation of OBJECT to
STREAM. It does not print newlines to separate output as `print'
does, but it does use quoting characters just like `print'. It
returns OBJECT.
(progn (prin1 'The\ cat\ in)
(prin1 "the hat")
(prin1 " came back"))
-| The\ cat\ in"the hat"" came back"
=> " came back"
- Function: princ object &optional stream
This function outputs the printed representation of OBJECT to
STREAM. It returns OBJECT.
This function is intended to produce output that is readable by
people, not by `read', so it doesn't insert quoting characters and
doesn't put double-quotes around the contents of strings. It does
not add any spacing between calls.
(progn
(princ 'The\ cat)
(princ " in the \"hat\""))
-| The cat in the "hat"
=> " in the \"hat\""
- Function: terpri &optional stream
This function outputs a newline to STREAM. The name stands for
"terminate print".
- Function: write-char character &optional stream
This function outputs CHARACTER to STREAM. It returns CHARACTER.
- Function: prin1-to-string object &optional noescape
This function returns a string containing the text that `prin1'
would have printed for the same argument.
(prin1-to-string 'foo)
=> "foo"
(prin1-to-string (mark-marker))
=> "#<marker at 2773 in strings.texi>"
If NOESCAPE is non-`nil', that inhibits use of quoting characters
in the output. (This argument is supported in Emacs versions 19
and later.)
(prin1-to-string "foo")
=> "\"foo\""
(prin1-to-string "foo" t)
=> "foo"
See `format', in *Note String Conversion::, for other ways to
obtain the printed representation of a Lisp object as a string.
- Macro: with-output-to-string body...
This macro executes the BODY forms with `standard-output' set up
to feed output into a string. Then it returns that string.
For example, if the current buffer name is `foo',
(with-output-to-string
(princ "The buffer is ")
(princ (buffer-name)))
returns `"The buffer is foo"'.
Variables Affecting Output
==========================
- Variable: standard-output
The value of this variable is the default output stream--the stream
that print functions use when the STREAM argument is `nil'.
- Variable: print-escape-newlines
If this variable is non-`nil', then newline characters in strings
are printed as `\n' and formfeeds are printed as `\f'. Normally
these characters are printed as actual newlines and formfeeds.
This variable affects the print functions `prin1' and `print' that
print with quoting. It does not affect `princ'. Here is an
example using `prin1':
(prin1 "a\nb")
-| "a
-| b"
=> "a
b"
(let ((print-escape-newlines t))
(prin1 "a\nb"))
-| "a\nb"
=> "a
b"
In the second expression, the local binding of
`print-escape-newlines' is in effect during the call to `prin1',
but not during the printing of the result.
- Variable: print-escape-nonascii
If this variable is non-`nil', then unibyte non-ASCII characters
in strings are unconditionally printed as backslash sequences by
the print functions `prin1' and `print' that print with quoting.
Those functions also use backslash sequences for unibyte non-ASCII
characters, regardless of the value of this variable, when the
output stream is a multibyte buffer or a marker pointing into one.
- Variable: print-escape-multibyte
If this variable is non-`nil', then multibyte non-ASCII characters
in strings are unconditionally printed as backslash sequences by
the print functions `prin1' and `print' that print with quoting.
Those functions also use backslash sequences for multibyte
non-ASCII characters, regardless of the value of this variable,
when the output stream is a unibyte buffer or a marker pointing
into one.
- Variable: print-length
The value of this variable is the maximum number of elements to
print in any list, vector or bool-vector. If an object being
printed has more than this many elements, it is abbreviated with
an ellipsis.
If the value is `nil' (the default), then there is no limit.
(setq print-length 2)
=> 2
(print '(1 2 3 4 5))
-| (1 2 ...)
=> (1 2 ...)
- Variable: print-level
The value of this variable is the maximum depth of nesting of
parentheses and brackets when printed. Any list or vector at a
depth exceeding this limit is abbreviated with an ellipsis. A
value of `nil' (which is the default) means no limit.
These variables are used for detecting and reporting circular and
shared structure--but they are only defined in Emacs 21.
- Variable: print-circle
If non-`nil', this variable enables detection of circular and
shared structure in printing.
- Variable: print-gensym
If non-`nil', this variable enables detection of uninterned symbols
(*note Creating Symbols::) in printing. When this is enabled,
uninterned symbols print with the prefix `#:', which tells the Lisp
reader to produce an uninterned symbol.
Minibuffers
***********
A "minibuffer" is a special buffer that Emacs commands use to read
arguments more complicated than the single numeric prefix argument.
These arguments include file names, buffer names, and command names (as
in `M-x'). The minibuffer is displayed on the bottom line of the
frame, in the same place as the echo area, but only while it is in use
for reading an argument.
Introduction to Minibuffers
===========================
In most ways, a minibuffer is a normal Emacs buffer. Most operations
_within_ a buffer, such as editing commands, work normally in a
minibuffer. However, many operations for managing buffers do not apply
to minibuffers. The name of a minibuffer always has the form
` *Minibuf-NUMBER', and it cannot be changed. Minibuffers are
displayed only in special windows used only for minibuffers; these
windows always appear at the bottom of a frame. (Sometimes frames have
no minibuffer window, and sometimes a special kind of frame contains
nothing but a minibuffer window; see *Note Minibuffers and Frames::.)
The text in the minibuffer always starts with the "prompt string",
the text that was specified by the program that is using the minibuffer
to tell the user what sort of input to type. This text is marked
read-only so you won't accidentally delete or change it. It is also
marked as a field (*note Fields::), so that certain motion functions,
including `beginning-of-line', `forward-word', `forward-sentence', and
`forward-paragraph', stop at the boundary between the prompt and the
actual text. (In older Emacs versions, the prompt was displayed using
a special mechanism and was not part of the buffer contents.)
The minibuffer's window is normally a single line; it grows
automatically if necessary if the contents require more space. You can
explicitly resize it temporarily with the window sizing commands; it
reverts to its normal size when the minibuffer is exited. You can
resize it permanently by using the window sizing commands in the frame's
other window, when the minibuffer is not active. If the frame contains
just a minibuffer, you can change the minibuffer's size by changing the
frame's size.
If a command uses a minibuffer while there is an active minibuffer,
this is called a "recursive minibuffer". The first minibuffer is named
` *Minibuf-0*'. Recursive minibuffers are named by incrementing the
number at the end of the name. (The names begin with a space so that
they won't show up in normal buffer lists.) Of several recursive
minibuffers, the innermost (or most recently entered) is the active
minibuffer. We usually call this "the" minibuffer. You can permit or
forbid recursive minibuffers by setting the variable
`enable-recursive-minibuffers' or by putting properties of that name on
command symbols (*note Minibuffer Misc::).
Like other buffers, a minibuffer may use any of several local keymaps
(*note Keymaps::); these contain various exit commands and in some cases
completion commands (*note Completion::).
* `minibuffer-local-map' is for ordinary input (no completion).
* `minibuffer-local-ns-map' is similar, except that <SPC> exits just
like <RET>. This is used mainly for Mocklisp compatibility.
* `minibuffer-local-completion-map' is for permissive completion.
* `minibuffer-local-must-match-map' is for strict completion and for
cautious completion.
When Emacs is running in batch mode, any request to read from the
minibuffer actually reads a line from the standard input descriptor that
was supplied when Emacs was started.
Reading Text Strings with the Minibuffer
========================================
Most often, the minibuffer is used to read text as a string. It can
also be used to read a Lisp object in textual form. The most basic
primitive for minibuffer input is `read-from-minibuffer'; it can do
either one.
In most cases, you should not call minibuffer input functions in the
middle of a Lisp function. Instead, do all minibuffer input as part of
reading the arguments for a command, in the `interactive'
specification. *Note Defining Commands::.
- Function: read-from-minibuffer prompt-string &optional
initial-contents keymap read hist default inherit-input-method
This function is the most general way to get input through the
minibuffer. By default, it accepts arbitrary text and returns it
as a string; however, if READ is non-`nil', then it uses `read' to
convert the text into a Lisp object (*note Input Functions::).
The first thing this function does is to activate a minibuffer and
display it with PROMPT-STRING as the prompt. This value must be a
string. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer,
`read-from-minibuffer' constructs the return value from the text in
the minibuffer. Normally it returns a string containing that text.
However, if READ is non-`nil', `read-from-minibuffer' reads the
text and returns the resulting Lisp object, unevaluated. (*Note
Input Functions::, for information about reading.)
The argument DEFAULT specifies a default value to make available
through the history commands. It should be a string, or `nil'. If
READ is non-`nil', then DEFAULT is also used as the input to
`read', if the user enters empty input. However, in the usual
case (where READ is `nil'), `read-from-minibuffer' does not return
DEFAULT when the user enters empty input; it returns an empty
string, `""'. In this respect, it is different from all the other
minibuffer input functions in this chapter.
If KEYMAP is non-`nil', that keymap is the local keymap to use in
the minibuffer. If KEYMAP is omitted or `nil', the value of
`minibuffer-local-map' is used as the keymap. Specifying a keymap
is the most important way to customize the minibuffer for various
applications such as completion.
The argument HIST specifies which history list variable to use for
saving the input and for history commands used in the minibuffer.
It defaults to `minibuffer-history'. *Note Minibuffer History::.
If the variable `minibuffer-allow-text-properties' is non-`nil',
then the string which is returned includes whatever text
properties were present in the minibuffer. Otherwise all the text
properties are stripped when the value is returned.
If the argument INHERIT-INPUT-METHOD is non-`nil', then the
minibuffer inherits the current input method (*note Input
Methods::) and the setting of `enable-multibyte-characters' (*note
Text Representations::) from whichever buffer was current before
entering the minibuffer.
If INITIAL-CONTENTS is a string, `read-from-minibuffer' inserts it
into the minibuffer, leaving point at the end, before the user
starts to edit the text. The minibuffer appears with this text as
its initial contents.
Alternatively, INITIAL-CONTENTS can be a cons cell of the form
`(STRING . POSITION)'. This means to insert STRING in the
minibuffer but put point POSITION characters from the beginning,
rather than at the end.
*Usage note:* The INITIAL-CONTENTS argument and the DEFAULT
argument are two alternative features for more or less the same
job. It does not make sense to use both features in a single call
to `read-from-minibuffer'. In general, we recommend using
DEFAULT, since this permits the user to insert the default value
when it is wanted, but does not burden the user with deleting it
from the minibuffer on other occasions.
- Function: read-string prompt &optional initial history default
inherit-input-method
This function reads a string from the minibuffer and returns it.
The arguments PROMPT and INITIAL are used as in
`read-from-minibuffer'. The keymap used is `minibuffer-local-map'.
The optional argument HISTORY, if non-nil, specifies a history
list and optionally the initial position in the list. The optional
argument DEFAULT specifies a default value to return if the user
enters null input; it should be a string. The optional argument
INHERIT-INPUT-METHOD specifies whether to inherit the current
buffer's input method.
This function is a simplified interface to the
`read-from-minibuffer' function:
(read-string PROMPT INITIAL HISTORY DEFAULT INHERIT)
==
(let ((value
(read-from-minibuffer PROMPT INITIAL nil nil
HISTORY DEFAULT INHERIT)))
(if (equal value "")
DEFAULT
value))
- Variable: minibuffer-allow-text-properties
If this variable is `nil', then `read-from-minibuffer' strips all
text properties from the minibuffer input before returning it.
Since all minibuffer input uses `read-from-minibuffer', this
variable applies to all minibuffer input.
Note that the completion functions discard text properties
unconditionally, regardless of the value of this variable.
- Variable: minibuffer-local-map
This is the default local keymap for reading from the minibuffer.
By default, it makes the following bindings:
`C-j'
`exit-minibuffer'
<RET>
`exit-minibuffer'
`C-g'
`abort-recursive-edit'
`M-n'
`next-history-element'
`M-p'
`previous-history-element'
`M-r'
`next-matching-history-element'
`M-s'
`previous-matching-history-element'
- Function: read-no-blanks-input prompt &optional initial
inherit-input-method
This function reads a string from the minibuffer, but does not
allow whitespace characters as part of the input: instead, those
characters terminate the input. The arguments PROMPT, INITIAL, and
INHERIT-INPUT-METHOD are used as in `read-from-minibuffer'.
This is a simplified interface to the `read-from-minibuffer'
function, and passes the value of the `minibuffer-local-ns-map'
keymap as the KEYMAP argument for that function. Since the keymap
`minibuffer-local-ns-map' does not rebind `C-q', it _is_ possible
to put a space into the string, by quoting it.
(read-no-blanks-input PROMPT INITIAL)
==
(read-from-minibuffer PROMPT INITIAL minibuffer-local-ns-map)
- Variable: minibuffer-local-ns-map
This built-in variable is the keymap used as the minibuffer local
keymap in the function `read-no-blanks-input'. By default, it
makes the following bindings, in addition to those of
`minibuffer-local-map':
<SPC>
`exit-minibuffer'
<TAB>
`exit-minibuffer'
`?'
`self-insert-and-exit'
Reading Lisp Objects with the Minibuffer
========================================
This section describes functions for reading Lisp objects with the
minibuffer.
- Function: read-minibuffer prompt &optional initial
This function reads a Lisp object using the minibuffer, and
returns it without evaluating it. The arguments PROMPT and
INITIAL are used as in `read-from-minibuffer'.
This is a simplified interface to the `read-from-minibuffer'
function:
(read-minibuffer PROMPT INITIAL)
==
(read-from-minibuffer PROMPT INITIAL nil t)
Here is an example in which we supply the string `"(testing)"' as
initial input:
(read-minibuffer
"Enter an expression: " (format "%s" '(testing)))
;; Here is how the minibuffer is displayed:
---------- Buffer: Minibuffer ----------
Enter an expression: (testing)-!-
---------- Buffer: Minibuffer ----------
The user can type <RET> immediately to use the initial input as a
default, or can edit the input.
- Function: eval-minibuffer prompt &optional initial
This function reads a Lisp expression using the minibuffer,
evaluates it, then returns the result. The arguments PROMPT and
INITIAL are used as in `read-from-minibuffer'.
This function simply evaluates the result of a call to
`read-minibuffer':
(eval-minibuffer PROMPT INITIAL)
==
(eval (read-minibuffer PROMPT INITIAL))
- Function: edit-and-eval-command prompt form
This function reads a Lisp expression in the minibuffer, and then
evaluates it. The difference between this command and
`eval-minibuffer' is that here the initial FORM is not optional
and it is treated as a Lisp object to be converted to printed
representation rather than as a string of text. It is printed with
`prin1', so if it is a string, double-quote characters (`"')
appear in the initial text. *Note Output Functions::.
The first thing `edit-and-eval-command' does is to activate the
minibuffer with PROMPT as the prompt. Then it inserts the printed
representation of FORM in the minibuffer, and lets the user edit
it. When the user exits the minibuffer, the edited text is read
with `read' and then evaluated. The resulting value becomes the
value of `edit-and-eval-command'.
In the following example, we offer the user an expression with
initial text which is a valid form already:
(edit-and-eval-command "Please edit: " '(forward-word 1))
;; After evaluation of the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
Please edit: (forward-word 1)-!-
---------- Buffer: Minibuffer ----------
Typing <RET> right away would exit the minibuffer and evaluate the
expression, thus moving point forward one word.
`edit-and-eval-command' returns `nil' in this example.
Minibuffer History
==================
A "minibuffer history list" records previous minibuffer inputs so
the user can reuse them conveniently. A history list is actually a
symbol, not a list; it is a variable whose value is a list of strings
(previous inputs), most recent first.
There are many separate history lists, used for different kinds of
inputs. It's the Lisp programmer's job to specify the right history
list for each use of the minibuffer.
The basic minibuffer input functions `read-from-minibuffer' and
`completing-read' both accept an optional argument named HIST which is
how you specify the history list. Here are the possible values:
VARIABLE
Use VARIABLE (a symbol) as the history list.
(VARIABLE . STARTPOS)
Use VARIABLE (a symbol) as the history list, and assume that the
initial history position is STARTPOS (an integer, counting from
zero which specifies the most recent element of the history).
If you specify STARTPOS, then you should also specify that element
of the history as the initial minibuffer contents, for consistency.
If you don't specify HIST, then the default history list
`minibuffer-history' is used. For other standard history lists, see
below. You can also create your own history list variable; just
initialize it to `nil' before the first use.
Both `read-from-minibuffer' and `completing-read' add new elements
to the history list automatically, and provide commands to allow the
user to reuse items on the list. The only thing your program needs to
do to use a history list is to initialize it and to pass its name to
the input functions when you wish. But it is safe to modify the list
by hand when the minibuffer input functions are not using it.
Here are some of the standard minibuffer history list variables:
- Variable: minibuffer-history
The default history list for minibuffer history input.
- Variable: query-replace-history
A history list for arguments to `query-replace' (and similar
arguments to other commands).
- Variable: file-name-history
A history list for file-name arguments.
- Variable: buffer-name-history
A history list for buffer-name arguments.
- Variable: regexp-history
A history list for regular expression arguments.
- Variable: extended-command-history
A history list for arguments that are names of extended commands.
- Variable: shell-command-history
A history list for arguments that are shell commands.
- Variable: read-expression-history
A history list for arguments that are Lisp expressions to evaluate.
Completion
==========
"Completion" is a feature that fills in the rest of a name starting
from an abbreviation for it. Completion works by comparing the user's
input against a list of valid names and determining how much of the
name is determined uniquely by what the user has typed. For example,
when you type `C-x b' (`switch-to-buffer') and then type the first few
letters of the name of the buffer to which you wish to switch, and then
type <TAB> (`minibuffer-complete'), Emacs extends the name as far as it
can.
Standard Emacs commands offer completion for names of symbols, files,
buffers, and processes; with the functions in this section, you can
implement completion for other kinds of names.
The `try-completion' function is the basic primitive for completion:
it returns the longest determined completion of a given initial string,
with a given set of strings to match against.
The function `completing-read' provides a higher-level interface for
completion. A call to `completing-read' specifies how to determine the
list of valid names. The function then activates the minibuffer with a
local keymap that binds a few keys to commands useful for completion.
Other functions provide convenient simple interfaces for reading
certain kinds of names with completion.
Basic Completion Functions
--------------------------
The two functions `try-completion' and `all-completions' have
nothing in themselves to do with minibuffers. We describe them in this
chapter so as to keep them near the higher-level completion features
that do use the minibuffer.
- Function: try-completion string collection &optional predicate
This function returns the longest common substring of all possible
completions of STRING in COLLECTION. The value of COLLECTION must
be an alist, an obarray, or a function that implements a virtual
set of strings (see below).
Completion compares STRING against each of the permissible
completions specified by COLLECTION; if the beginning of the
permissible completion equals STRING, it matches. If no
permissible completions match, `try-completion' returns `nil'. If
only one permissible completion matches, and the match is exact,
then `try-completion' returns `t'. Otherwise, the value is the
longest initial sequence common to all the permissible completions
that match.
If COLLECTION is an alist (*note Association Lists::), the CARs of
the alist elements form the set of permissible completions.
If COLLECTION is an obarray (*note Creating Symbols::), the names
of all symbols in the obarray form the set of permissible
completions. The global variable `obarray' holds an obarray
containing the names of all interned Lisp symbols.
Note that the only valid way to make a new obarray is to create it
empty and then add symbols to it one by one using `intern'. Also,
you cannot intern a given symbol in more than one obarray.
If the argument PREDICATE is non-`nil', then it must be a function
of one argument. It is used to test each possible match, and the
match is accepted only if PREDICATE returns non-`nil'. The
argument given to PREDICATE is either a cons cell from the alist
(the CAR of which is a string) or else it is a symbol (_not_ a
symbol name) from the obarray.
You can also use a symbol that is a function as COLLECTION. Then
the function is solely responsible for performing completion;
`try-completion' returns whatever this function returns. The
function is called with three arguments: STRING, PREDICATE and
`nil'. (The reason for the third argument is so that the same
function can be used in `all-completions' and do the appropriate
thing in either case.) *Note Programmed Completion::.
In the first of the following examples, the string `foo' is
matched by three of the alist CARs. All of the matches begin with
the characters `fooba', so that is the result. In the second
example, there is only one possible match, and it is exact, so the
value is `t'.
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
=> "fooba"
(try-completion "foo" '(("barfoo" 2) ("foo" 3)))
=> t
In the following example, numerous symbols begin with the
characters `forw', and all of them begin with the word `forward'.
In most of the symbols, this is followed with a `-', but not in
all, so no more than `forward' can be completed.
(try-completion "forw" obarray)
=> "forward"
Finally, in the following example, only two of the three possible
matches pass the predicate `test' (the string `foobaz' is too
short). Both of those begin with the string `foobar'.
(defun test (s)
(> (length (car s)) 6))
=> test
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> "foobar"
- Function: all-completions string collection &optional predicate
nospace
This function returns a list of all possible completions of
STRING. The arguments to this function (aside from NOSPACE) are
the same as those of `try-completion'. If NOSPACE is non-`nil',
completions that start with a space are ignored unless STRING also
starts with a space.
If COLLECTION is a function, it is called with three arguments:
STRING, PREDICATE and `t'; then `all-completions' returns whatever
the function returns. *Note Programmed Completion::.
Here is an example, using the function `test' shown in the example
for `try-completion':
(defun test (s)
(> (length (car s)) 6))
=> test
(all-completions
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> ("foobar1" "foobar2")
- Variable: completion-ignore-case
If the value of this variable is non-`nil', Emacs does not
consider case significant in completion.
Completion and the Minibuffer
-----------------------------
This section describes the basic interface for reading from the
minibuffer with completion.
- Function: completing-read prompt collection &optional predicate
require-match initial hist default inherit-input-method
This function reads a string in the minibuffer, assisting the user
by providing completion. It activates the minibuffer with prompt
PROMPT, which must be a string.
The actual completion is done by passing COLLECTION and PREDICATE
to the function `try-completion'. This happens in certain
commands bound in the local keymaps used for completion.
If REQUIRE-MATCH is `nil', the exit commands work regardless of
the input in the minibuffer. If REQUIRE-MATCH is `t', the usual
minibuffer exit commands won't exit unless the input completes to
an element of COLLECTION. If REQUIRE-MATCH is neither `nil' nor
`t', then the exit commands won't exit unless the input already in
the buffer matches an element of COLLECTION.
However, empty input is always permitted, regardless of the value
of REQUIRE-MATCH; in that case, `completing-read' returns DEFAULT.
The value of DEFAULT (if non-`nil') is also available to the user
through the history commands.
The user can exit with null input by typing <RET> with an empty
minibuffer. Then `completing-read' returns `""'. This is how the
user requests whatever default the command uses for the value being
read. The user can return using <RET> in this way regardless of
the value of REQUIRE-MATCH, and regardless of whether the empty
string is included in COLLECTION.
The function `completing-read' works by calling `read-minibuffer'.
It uses `minibuffer-local-completion-map' as the keymap if
REQUIRE-MATCH is `nil', and uses `minibuffer-local-must-match-map'
if REQUIRE-MATCH is non-`nil'. *Note Completion Commands::.
The argument HIST specifies which history list variable to use for
saving the input and for minibuffer history commands. It defaults
to `minibuffer-history'. *Note Minibuffer History::.
If INITIAL is non-`nil', `completing-read' inserts it into the
minibuffer as part of the input. Then it allows the user to edit
the input, providing several commands to attempt completion. In
most cases, we recommend using DEFAULT, and not INITIAL.
*We discourage use of a non-`nil' value for INITIAL*, because it
is an intrusive interface. The history list feature (which did
not exist when we introduced INITIAL) offers a far more convenient
and general way for the user to get the default and edit it, and
it is always available.
If the argument INHERIT-INPUT-METHOD is non-`nil', then the
minibuffer inherits the current input method (*note Input
Methods::) and the setting of `enable-multibyte-characters' (*note
Text Representations::) from whichever buffer was current before
entering the minibuffer.
Completion ignores case when comparing the input against the
possible matches, if the built-in variable
`completion-ignore-case' is non-`nil'. *Note Basic Completion::.
Here's an example of using `completing-read':
(completing-read
"Complete a foo: "
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
nil t "fo")
;; After evaluation of the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
Complete a foo: fo-!-
---------- Buffer: Minibuffer ----------
If the user then types `<DEL> <DEL> b <RET>', `completing-read'
returns `barfoo'.
The `completing-read' function binds three variables to pass
information to the commands that actually do completion. These
variables are `minibuffer-completion-table',
`minibuffer-completion-predicate' and
`minibuffer-completion-confirm'. For more information about them,
see *Note Completion Commands::.
Minibuffer Commands that Do Completion
--------------------------------------
This section describes the keymaps, commands and user options used in
the minibuffer to do completion.
- Variable: minibuffer-local-completion-map
`completing-read' uses this value as the local keymap when an
exact match of one of the completions is not required. By
default, this keymap makes the following bindings:
`?'
`minibuffer-completion-help'
<SPC>
`minibuffer-complete-word'
<TAB>
`minibuffer-complete'
with other characters bound as in `minibuffer-local-map' (*note
Text from Minibuffer::).
- Variable: minibuffer-local-must-match-map
`completing-read' uses this value as the local keymap when an
exact match of one of the completions is required. Therefore, no
keys are bound to `exit-minibuffer', the command that exits the
minibuffer unconditionally. By default, this keymap makes the
following bindings:
`?'
`minibuffer-completion-help'
<SPC>
`minibuffer-complete-word'
<TAB>
`minibuffer-complete'
`C-j'
`minibuffer-complete-and-exit'
<RET>
`minibuffer-complete-and-exit'
with other characters bound as in `minibuffer-local-map'.
- Variable: minibuffer-completion-table
The value of this variable is the alist or obarray used for
completion in the minibuffer. This is the global variable that
contains what `completing-read' passes to `try-completion'. It is
used by minibuffer completion commands such as
`minibuffer-complete-word'.
- Variable: minibuffer-completion-predicate
This variable's value is the predicate that `completing-read'
passes to `try-completion'. The variable is also used by the other
minibuffer completion functions.
- Command: minibuffer-complete-word
This function completes the minibuffer contents by at most a single
word. Even if the minibuffer contents have only one completion,
`minibuffer-complete-word' does not add any characters beyond the
first character that is not a word constituent. *Note Syntax
Tables::.
- Command: minibuffer-complete
This function completes the minibuffer contents as far as possible.
- Command: minibuffer-complete-and-exit
This function completes the minibuffer contents, and exits if
confirmation is not required, i.e., if
`minibuffer-completion-confirm' is `nil'. If confirmation _is_
required, it is given by repeating this command immediately--the
command is programmed to work without confirmation when run twice
in succession.
- Variable: minibuffer-completion-confirm
When the value of this variable is non-`nil', Emacs asks for
confirmation of a completion before exiting the minibuffer. The
function `minibuffer-complete-and-exit' checks the value of this
variable before it exits.
- Command: minibuffer-completion-help
This function creates a list of the possible completions of the
current minibuffer contents. It works by calling `all-completions'
using the value of the variable `minibuffer-completion-table' as
the COLLECTION argument, and the value of
`minibuffer-completion-predicate' as the PREDICATE argument. The
list of completions is displayed as text in a buffer named
`*Completions*'.
- Function: display-completion-list completions
This function displays COMPLETIONS to the stream in
`standard-output', usually a buffer. (*Note Read and Print::, for
more information about streams.) The argument COMPLETIONS is
normally a list of completions just returned by `all-completions',
but it does not have to be. Each element may be a symbol or a
string, either of which is simply printed, or a list of two
strings, which is printed as if the strings were concatenated.
This function is called by `minibuffer-completion-help'. The most
common way to use it is together with
`with-output-to-temp-buffer', like this:
(with-output-to-temp-buffer "*Completions*"
(display-completion-list
(all-completions (buffer-string) my-alist)))
- User Option: completion-auto-help
If this variable is non-`nil', the completion commands
automatically display a list of possible completions whenever
nothing can be completed because the next character is not
uniquely determined.
High-Level Completion Functions
--------------------------------
This section describes the higher-level convenient functions for
reading certain sorts of names with completion.
In most cases, you should not call these functions in the middle of a
Lisp function. When possible, do all minibuffer input as part of
reading the arguments for a command, in the `interactive'
specification. *Note Defining Commands::.
- Function: read-buffer prompt &optional default existing
This function reads the name of a buffer and returns it as a
string. The argument DEFAULT is the default name to use, the
value to return if the user exits with an empty minibuffer. If
non-`nil', it should be a string or a buffer. It is mentioned in
the prompt, but is not inserted in the minibuffer as initial input.
If EXISTING is non-`nil', then the name specified must be that of
an existing buffer. The usual commands to exit the minibuffer do
not exit if the text is not valid, and <RET> does completion to
attempt to find a valid name. (However, DEFAULT is not checked
for validity; it is returned, whatever it is, if the user exits
with the minibuffer empty.)
In the following example, the user enters `minibuffer.t', and then
types <RET>. The argument EXISTING is `t', and the only buffer
name starting with the given input is `minibuffer.texi', so that
name is the value.
(read-buffer "Buffer name? " "foo" t)
;; After evaluation of the preceding expression,
;; the following prompt appears,
;; with an empty minibuffer:
---------- Buffer: Minibuffer ----------
Buffer name? (default foo) -!-
---------- Buffer: Minibuffer ----------
;; The user types `minibuffer.t <RET>'.
=> "minibuffer.texi"
- Variable: read-buffer-function
This variable specifies how to read buffer names. For example, if
you set this variable to `iswitchb-read-buffer', all Emacs commands
that call `read-buffer' to read a buffer name will actually use the
`iswitchb' package to read it.
- Function: read-command prompt &optional default
This function reads the name of a command and returns it as a Lisp
symbol. The argument PROMPT is used as in `read-from-minibuffer'.
Recall that a command is anything for which `commandp' returns
`t', and a command name is a symbol for which `commandp' returns
`t'. *Note Interactive Call::.
The argument DEFAULT specifies what to return if the user enters
null input. It can be a symbol or a string; if it is a string,
`read-command' interns it before returning it. If DEFAULT is
`nil', that means no default has been specified; then if the user
enters null input, the return value is `nil'.
(read-command "Command name? ")
;; After evaluation of the preceding expression,
;; the following prompt appears with an empty minibuffer:
---------- Buffer: Minibuffer ----------
Command name?
---------- Buffer: Minibuffer ----------
If the user types `forward-c <RET>', then this function returns
`forward-char'.
The `read-command' function is a simplified interface to
`completing-read'. It uses the variable `obarray' so as to
complete in the set of extant Lisp symbols, and it uses the
`commandp' predicate so as to accept only command names:
(read-command PROMPT)
==
(intern (completing-read PROMPT obarray
'commandp t nil))
- Function: read-variable prompt &optional default
This function reads the name of a user variable and returns it as a
symbol.
The argument DEFAULT specifies what to return if the user enters
null input. It can be a symbol or a string; if it is a string,
`read-variable' interns it before returning it. If DEFAULT is
`nil', that means no default has been specified; then if the user
enters null input, the return value is `nil'.
(read-variable "Variable name? ")
;; After evaluation of the preceding expression,
;; the following prompt appears,
;; with an empty minibuffer:
---------- Buffer: Minibuffer ----------
Variable name? -!-
---------- Buffer: Minibuffer ----------
If the user then types `fill-p <RET>', `read-variable' returns
`fill-prefix'.
This function is similar to `read-command', but uses the predicate
`user-variable-p' instead of `commandp':
(read-variable PROMPT)
==
(intern
(completing-read PROMPT obarray
'user-variable-p t nil))
See also the functions `read-coding-system' and
`read-non-nil-coding-system', in *Note User-Chosen Coding Systems::.
Reading File Names
------------------
Here is another high-level completion function, designed for reading
a file name. It provides special features including automatic insertion
of the default directory.
- Function: read-file-name prompt &optional directory default existing
initial
This function reads a file name in the minibuffer, prompting with
PROMPT and providing completion. If DEFAULT is non-`nil', then
the function returns DEFAULT if the user just types <RET>.
DEFAULT is not checked for validity; it is returned, whatever it
is, if the user exits with the minibuffer empty.
If EXISTING is non-`nil', then the user must specify the name of
an existing file; <RET> performs completion to make the name valid
if possible, and then refuses to exit if it is not valid. If the
value of EXISTING is neither `nil' nor `t', then <RET> also
requires confirmation after completion. If EXISTING is `nil',
then the name of a nonexistent file is acceptable.
The argument DIRECTORY specifies the directory to use for
completion of relative file names. If `insert-default-directory'
is non-`nil', DIRECTORY is also inserted in the minibuffer as
initial input. It defaults to the current buffer's value of
`default-directory'.
If you specify INITIAL, that is an initial file name to insert in
the buffer (after DIRECTORY, if that is inserted). In this case,
point goes at the beginning of INITIAL. The default for INITIAL
is `nil'--don't insert any file name. To see what INITIAL does,
try the command `C-x C-v'. *Note:* we recommend using DEFAULT
rather than INITIAL in most cases.
Here is an example:
(read-file-name "The file is ")
;; After evaluation of the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
The file is /gp/gnu/elisp/-!-
---------- Buffer: Minibuffer ----------
Typing `manual <TAB>' results in the following:
---------- Buffer: Minibuffer ----------
The file is /gp/gnu/elisp/manual.texi-!-
---------- Buffer: Minibuffer ----------
If the user types <RET>, `read-file-name' returns the file name as
the string `"/gp/gnu/elisp/manual.texi"'.
- User Option: insert-default-directory
This variable is used by `read-file-name'. Its value controls
whether `read-file-name' starts by placing the name of the default
directory in the minibuffer, plus the initial file name if any.
If the value of this variable is `nil', then `read-file-name' does
not place any initial input in the minibuffer (unless you specify
initial input with the INITIAL argument). In that case, the
default directory is still used for completion of relative file
names, but is not displayed.
For example:
;; Here the minibuffer starts out with the default directory.
(let ((insert-default-directory t))
(read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is ~lewis/manual/-!-
---------- Buffer: Minibuffer ----------
;; Here the minibuffer is empty and only the prompt
;; appears on its line.
(let ((insert-default-directory nil))
(read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is -!-
---------- Buffer: Minibuffer ----------
Programmed Completion
---------------------
Sometimes it is not possible to create an alist or an obarray
containing all the intended possible completions. In such a case, you
can supply your own function to compute the completion of a given
string. This is called "programmed completion".
To use this feature, pass a symbol with a function definition as the
COLLECTION argument to `completing-read'. The function
`completing-read' arranges to pass your completion function along to
`try-completion' and `all-completions', which will then let your
function do all the work.
The completion function should accept three arguments:
* The string to be completed.
* The predicate function to filter possible matches, or `nil' if
none. Your function should call the predicate for each possible
match, and ignore the possible match if the predicate returns
`nil'.
* A flag specifying the type of operation.
There are three flag values for three operations:
* `nil' specifies `try-completion'. The completion function should
return the completion of the specified string, or `t' if the
string is a unique and exact match already, or `nil' if the string
matches no possibility.
If the string is an exact match for one possibility, but also
matches other longer possibilities, the function should return the
string, not `t'.
* `t' specifies `all-completions'. The completion function should
return a list of all possible completions of the specified string.
* `lambda' specifies a test for an exact match. The completion
function should return `t' if the specified string is an exact
match for some possibility; `nil' otherwise.
It would be consistent and clean for completion functions to allow
lambda expressions (lists that are functions) as well as function
symbols as COLLECTION, but this is impossible. Lists as completion
tables are already assigned another meaning--as alists. It would be
unreliable to fail to handle an alist normally because it is also a
possible function. So you must arrange for any function you wish to
use for completion to be encapsulated in a symbol.
Emacs uses programmed completion when completing file names. *Note
File Name Completion::.
Yes-or-No Queries
=================
This section describes functions used to ask the user a yes-or-no
question. The function `y-or-n-p' can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. `yes-or-no-p' is suitable for more
momentous questions, since it requires three or four characters to
answer.
If either of these functions is called in a command that was invoked
using the mouse--more precisely, if `last-nonmenu-event' (*note Command
Loop Info::) is either `nil' or a list--then it uses a dialog box or
pop-up menu to ask the question. Otherwise, it uses keyboard input.
You can force use of the mouse or use of keyboard input by binding
`last-nonmenu-event' to a suitable value around the call.
Strictly speaking, `yes-or-no-p' uses the minibuffer and `y-or-n-p'
does not; but it seems best to describe them together.
- Function: y-or-n-p prompt
This function asks the user a question, expecting input in the echo
area. It returns `t' if the user types `y', `nil' if the user
types `n'. This function also accepts <SPC> to mean yes and <DEL>
to mean no. It accepts `C-]' to mean "quit", like `C-g', because
the question might look like a minibuffer and for that reason the
user might try to use `C-]' to get out. The answer is a single
character, with no <RET> needed to terminate it. Upper and lower
case are equivalent.
"Asking the question" means printing PROMPT in the echo area,
followed by the string `(y or n) '. If the input is not one of
the expected answers (`y', `n', `<SPC>', `<DEL>', or something
that quits), the function responds `Please answer y or n.', and
repeats the request.
This function does not actually use the minibuffer, since it does
not allow editing of the answer. It actually uses the echo area
(*note The Echo Area::), which uses the same screen space as the
minibuffer. The cursor moves to the echo area while the question
is being asked.
The answers and their meanings, even `y' and `n', are not
hardwired. The keymap `query-replace-map' specifies them. *Note
Search and Replace::.
In the following example, the user first types `q', which is
invalid. At the next prompt the user types `y'.
(y-or-n-p "Do you need a lift? ")
;; After evaluation of the preceding expression,
;; the following prompt appears in the echo area:
---------- Echo area ----------
Do you need a lift? (y or n)
---------- Echo area ----------
;; If the user then types `q', the following appears:
---------- Echo area ----------
Please answer y or n. Do you need a lift? (y or n)
---------- Echo area ----------
;; When the user types a valid answer,
;; it is displayed after the question:
---------- Echo area ----------
Do you need a lift? (y or n) y
---------- Echo area ----------
We show successive lines of echo area messages, but only one
actually appears on the screen at a time.
- Function: y-or-n-p-with-timeout prompt seconds default-value
Like `y-or-n-p', except that if the user fails to answer within
SECONDS seconds, this function stops waiting and returns
DEFAULT-VALUE. It works by setting up a timer; see *Note Timers::.
The argument SECONDS may be an integer or a floating point number.
- Function: yes-or-no-p prompt
This function asks the user a question, expecting input in the
minibuffer. It returns `t' if the user enters `yes', `nil' if the
user types `no'. The user must type <RET> to finalize the
response. Upper and lower case are equivalent.
`yes-or-no-p' starts by displaying PROMPT in the echo area,
followed by `(yes or no) '. The user must type one of the
expected responses; otherwise, the function responds `Please answer
yes or no.', waits about two seconds and repeats the request.
`yes-or-no-p' requires more work from the user than `y-or-n-p' and
is appropriate for more crucial decisions.
Here is an example:
(yes-or-no-p "Do you really want to remove everything? ")
;; After evaluation of the preceding expression,
;; the following prompt appears,
;; with an empty minibuffer:
---------- Buffer: minibuffer ----------
Do you really want to remove everything? (yes or no)
---------- Buffer: minibuffer ----------
If the user first types `y <RET>', which is invalid because this
function demands the entire word `yes', it responds by displaying
these prompts, with a brief pause between them:
---------- Buffer: minibuffer ----------
Please answer yes or no.
Do you really want to remove everything? (yes or no)
---------- Buffer: minibuffer ----------
Asking Multiple Y-or-N Questions
================================
When you have a series of similar questions to ask, such as "Do you
want to save this buffer" for each buffer in turn, you should use
`map-y-or-n-p' to ask the collection of questions, rather than asking
each question individually. This gives the user certain convenient
facilities such as the ability to answer the whole series at once.
- Function: map-y-or-n-p prompter actor list &optional help
action-alist no-cursor-in-echo-area
This function asks the user a series of questions, reading a
single-character answer in the echo area for each one.
The value of LIST specifies the objects to ask questions about.
It should be either a list of objects or a generator function. If
it is a function, it should expect no arguments, and should return
either the next object to ask about, or `nil' meaning stop asking
questions.
The argument PROMPTER specifies how to ask each question. If
PROMPTER is a string, the question text is computed like this:
(format PROMPTER OBJECT)
where OBJECT is the next object to ask about (as obtained from
LIST).
If not a string, PROMPTER should be a function of one argument
(the next object to ask about) and should return the question
text. If the value is a string, that is the question to ask the
user. The function can also return `t' meaning do act on this
object (and don't ask the user), or `nil' meaning ignore this
object (and don't ask the user).
The argument ACTOR says how to act on the answers that the user
gives. It should be a function of one argument, and it is called
with each object that the user says yes for. Its argument is
always an object obtained from LIST.
If the argument HELP is given, it should be a list of this form:
(SINGULAR PLURAL ACTION)
where SINGULAR is a string containing a singular noun that
describes the objects conceptually being acted on, PLURAL is the
corresponding plural noun, and ACTION is a transitive verb
describing what ACTOR does.
If you don't specify HELP, the default is `("object" "objects"
"act on")'.
Each time a question is asked, the user may enter `y', `Y', or
<SPC> to act on that object; `n', `N', or <DEL> to skip that
object; `!' to act on all following objects; <ESC> or `q' to exit
(skip all following objects); `.' (period) to act on the current
object and then exit; or `C-h' to get help. These are the same
answers that `query-replace' accepts. The keymap
`query-replace-map' defines their meaning for `map-y-or-n-p' as
well as for `query-replace'; see *Note Search and Replace::.
You can use ACTION-ALIST to specify additional possible answers
and what they mean. It is an alist of elements of the form `(CHAR
FUNCTION HELP)', each of which defines one additional answer. In
this element, CHAR is a character (the answer); FUNCTION is a
function of one argument (an object from LIST); HELP is a string.
When the user responds with CHAR, `map-y-or-n-p' calls FUNCTION.
If it returns non-`nil', the object is considered "acted upon",
and `map-y-or-n-p' advances to the next object in LIST. If it
returns `nil', the prompt is repeated for the same object.
Normally, `map-y-or-n-p' binds `cursor-in-echo-area' while
prompting. But if NO-CURSOR-IN-ECHO-AREA is non-`nil', it does
not do that.
If `map-y-or-n-p' is called in a command that was invoked using the
mouse--more precisely, if `last-nonmenu-event' (*note Command Loop
Info::) is either `nil' or a list--then it uses a dialog box or
pop-up menu to ask the question. In this case, it does not use
keyboard input or the echo area. You can force use of the mouse
or use of keyboard input by binding `last-nonmenu-event' to a
suitable value around the call.
The return value of `map-y-or-n-p' is the number of objects acted
on.
Reading a Password
==================
To read a password to pass to another program, you can use the
function `read-passwd'.
- Function: read-passwd prompt &optional confirm default
This function reads a password, prompting with PROMPT. It does
not echo the password as the user types it; instead, it echoes `.'
for each character in the password.
The optional argument CONFIRM, if non-`nil', says to read the
password twice and insist it must be the same both times. If it
isn't the same, the user has to type it over and over until the
last two times match.
The optional argument DEFAULT specifies the default password to
return if the user enters empty input. If DEFAULT is `nil', then
`read-passwd' returns the null string in that case.
Minibuffer Miscellany
=====================
This section describes some basic functions and variables related to
minibuffers.
- Command: exit-minibuffer
This command exits the active minibuffer. It is normally bound to
keys in minibuffer local keymaps.
- Command: self-insert-and-exit
This command exits the active minibuffer after inserting the last
character typed on the keyboard (found in `last-command-char';
*note Command Loop Info::).
- Command: previous-history-element n
This command replaces the minibuffer contents with the value of the
Nth previous (older) history element.
- Command: next-history-element n
This command replaces the minibuffer contents with the value of the
Nth more recent history element.
- Command: previous-matching-history-element pattern n
This command replaces the minibuffer contents with the value of the
Nth previous (older) history element that matches PATTERN (a
regular expression).
- Command: next-matching-history-element pattern n
This command replaces the minibuffer contents with the value of the
Nth next (newer) history element that matches PATTERN (a regular
expression).
- Function: minibuffer-prompt
This function returns the prompt string of the currently active
minibuffer. If no minibuffer is active, it returns `nil'.
- Function: minibuffer-prompt-end
This function, available starting in Emacs 21, returns the current
position of the end of the minibuffer prompt, if a minibuffer is
current. Otherwise, it returns the minimum valid buffer position.
- Function: minibuffer-contents
This function, available starting in Emacs 21, returns the editable
contents of the minibuffer (that is, everything except the prompt)
as a string, if a minibuffer is current. Otherwise, it returns the
entire contents of the current buffer.
- Function: minibuffer-contents-no-properties
This is like `minibuffer-contents', except that it does not copy
text properties, just the characters themselves. *Note Text
Properties::.
- Function: delete-minibuffer-contents
This function, available starting in Emacs 21, erases the editable
contents of the minibuffer (that is, everything except the
prompt), if a minibuffer is current. Otherwise, it erases the
entire buffer.
- Function: minubuffer-prompt-width
This function returns the current display-width of the minibuffer
prompt, if a minibuffer is current. Otherwise, it returns zero.
- Variable: minibuffer-setup-hook
This is a normal hook that is run whenever the minibuffer is
entered. *Note Hooks::.
- Variable: minibuffer-exit-hook
This is a normal hook that is run whenever the minibuffer is
exited. *Note Hooks::.
- Variable: minibuffer-help-form
The current value of this variable is used to rebind `help-form'
locally inside the minibuffer (*note Help Functions::).
- Function: active-minibuffer-window
This function returns the currently active minibuffer window, or
`nil' if none is currently active.
- Function: minibuffer-window &optional frame
This function returns the minibuffer window used for frame FRAME.
If FRAME is `nil', that stands for the current frame. Note that
the minibuffer window used by a frame need not be part of that
frame--a frame that has no minibuffer of its own necessarily uses
some other frame's minibuffer window.
- Function: window-minibuffer-p window
This function returns non-`nil' if WINDOW is a minibuffer window.
It is not correct to determine whether a given window is a
minibuffer by comparing it with the result of `(minibuffer-window)',
because there can be more than one minibuffer window if there is more
than one frame.
- Function: minibuffer-window-active-p window
This function returns non-`nil' if WINDOW, assumed to be a
minibuffer window, is currently active.
- Variable: minibuffer-scroll-window
If the value of this variable is non-`nil', it should be a window
object. When the function `scroll-other-window' is called in the
minibuffer, it scrolls this window.
Finally, some functions and variables deal with recursive minibuffers
(*note Recursive Editing::):
- Function: minibuffer-depth
This function returns the current depth of activations of the
minibuffer, a nonnegative integer. If no minibuffers are active,
it returns zero.
- User Option: enable-recursive-minibuffers
If this variable is non-`nil', you can invoke commands (such as
`find-file') that use minibuffers even while the minibuffer window
is active. Such invocation produces a recursive editing level for
a new minibuffer. The outer-level minibuffer is invisible while
you are editing the inner one.
If this variable is `nil', you cannot invoke minibuffer commands
when the minibuffer window is active, not even if you switch to
another window to do it.
If a command name has a property `enable-recursive-minibuffers' that
is non-`nil', then the command can use the minibuffer to read arguments
even if it is invoked from the minibuffer. The minibuffer command
`next-matching-history-element' (normally `M-s' in the minibuffer) uses
this feature.
Command Loop
************
When you run Emacs, it enters the "editor command loop" almost
immediately. This loop reads key sequences, executes their definitions,
and displays the results. In this chapter, we describe how these things
are done, and the subroutines that allow Lisp programs to do them.
Command Loop Overview
=====================
The first thing the command loop must do is read a key sequence,
which is a sequence of events that translates into a command. It does
this by calling the function `read-key-sequence'. Your Lisp code can
also call this function (*note Key Sequence Input::). Lisp programs
can also do input at a lower level with `read-event' (*note Reading One
Event::) or discard pending input with `discard-input' (*note Event
Input Misc::).
The key sequence is translated into a command through the currently
active keymaps. *Note Key Lookup::, for information on how this is
done. The result should be a keyboard macro or an interactively
callable function. If the key is `M-x', then it reads the name of
another command, which it then calls. This is done by the command
`execute-extended-command' (*note Interactive Call::).
To execute a command requires first reading the arguments for it.
This is done by calling `command-execute' (*note Interactive Call::).
For commands written in Lisp, the `interactive' specification says how
to read the arguments. This may use the prefix argument (*note Prefix
Command Arguments::) or may read with prompting in the minibuffer
(*note Minibuffers::). For example, the command `find-file' has an
`interactive' specification which says to read a file name using the
minibuffer. The command's function body does not use the minibuffer;
if you call this command from Lisp code as a function, you must supply
the file name string as an ordinary Lisp function argument.
If the command is a string or vector (i.e., a keyboard macro) then
`execute-kbd-macro' is used to execute it. You can call this function
yourself (*note Keyboard Macros::).
To terminate the execution of a running command, type `C-g'. This
character causes "quitting" (*note Quitting::).
- Variable: pre-command-hook
The editor command loop runs this normal hook before each command.
At that time, `this-command' contains the command that is about to
run, and `last-command' describes the previous command. *Note
Hooks::.
- Variable: post-command-hook
The editor command loop runs this normal hook after each command
(including commands terminated prematurely by quitting or by
errors), and also when the command loop is first entered. At that
time, `this-command' describes the command that just ran, and
`last-command' describes the command before that. *Note Hooks::.
Quitting is suppressed while running `pre-command-hook' and
`post-command-hook'. If an error happens while executing one of these
hooks, it terminates execution of the hook, and clears the hook
variable to `nil' so as to prevent an infinite loop of errors.
Defining Commands
=================
A Lisp function becomes a command when its body contains, at top
level, a form that calls the special form `interactive'. This form
does nothing when actually executed, but its presence serves as a flag
to indicate that interactive calling is permitted. Its argument
controls the reading of arguments for an interactive call.
Using `interactive'
-------------------
This section describes how to write the `interactive' form that
makes a Lisp function an interactively-callable command, and how to
examine a commands's `interactive' form.
- Special Form: interactive arg-descriptor
This special form declares that the function in which it appears
is a command, and that it may therefore be called interactively
(via `M-x' or by entering a key sequence bound to it). The
argument ARG-DESCRIPTOR declares how to compute the arguments to
the command when the command is called interactively.
A command may be called from Lisp programs like any other
function, but then the caller supplies the arguments and
ARG-DESCRIPTOR has no effect.
The `interactive' form has its effect because the command loop
(actually, its subroutine `call-interactively') scans through the
function definition looking for it, before calling the function.
Once the function is called, all its body forms including the
`interactive' form are executed, but at this time `interactive'
simply returns `nil' without even evaluating its argument.
There are three possibilities for the argument ARG-DESCRIPTOR:
* It may be omitted or `nil'; then the command is called with no
arguments. This leads quickly to an error if the command requires
one or more arguments.
* It may be a Lisp expression that is not a string; then it should
be a form that is evaluated to get a list of arguments to pass to
the command.
If this expression reads keyboard input (this includes using the
minibuffer), keep in mind that the integer value of point or the
mark before reading input may be incorrect after reading input.
This is because the current buffer may be receiving subprocess
output; if subprocess output arrives while the command is waiting
for input, it could relocate point and the mark.
Here's an example of what _not_ to do:
(interactive
(list (region-beginning) (region-end)
(read-string "Foo: " nil 'my-history)))
Here's how to avoid the problem, by examining point and the mark
only after reading the keyboard input:
(interactive
(let ((string (read-string "Foo: " nil 'my-history)))
(list (region-beginning) (region-end) string)))
* It may be a string; then its contents should consist of a code
character followed by a prompt (which some code characters use and
some ignore). The prompt ends either with the end of the string
or with a newline. Here is a simple example:
(interactive "bFrobnicate buffer: ")
The code letter `b' says to read the name of an existing buffer,
with completion. The buffer name is the sole argument passed to
the command. The rest of the string is a prompt.
If there is a newline character in the string, it terminates the
prompt. If the string does not end there, then the rest of the
string should contain another code character and prompt,
specifying another argument. You can specify any number of
arguments in this way.
The prompt string can use `%' to include previous argument values
(starting with the first argument) in the prompt. This is done
using `format' (*note Formatting Strings::). For example, here is
how you could read the name of an existing buffer followed by a
new name to give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If the first character in the string is `*', then an error is
signaled if the buffer is read-only.
If the first character in the string is `@', and if the key
sequence used to invoke the command includes any mouse events, then
the window associated with the first of those events is selected
before the command is run.
You can use `*' and `@' together; the order does not matter.
Actual reading of arguments is controlled by the rest of the prompt
string (starting with the first character that is not `*' or `@').
- Function: interactive-form function
This function returns the `interactive' form of FUNCTION. If
FUNCTION is a command (*note Interactive Call::), the value is a
list of the form `(interactive SPEC)', where SPEC is the
descriptor specification used by the command's `interactive' form
to compute the function's arguments (*note Using Interactive::).
If FUNCTION is not a command, `interactive-form' returns `nil'.
Code Characters for `interactive'
---------------------------------
The code character descriptions below contain a number of key words,
defined here as follows:
Completion
Provide completion. <TAB>, <SPC>, and <RET> perform name
completion because the argument is read using `completing-read'
(*note Completion::). `?' displays a list of possible completions.
Existing
Require the name of an existing object. An invalid name is not
accepted; the commands to exit the minibuffer do not exit if the
current input is not valid.
Default
A default value of some sort is used if the user enters no text in
the minibuffer. The default depends on the code character.
No I/O
This code letter computes an argument without reading any input.
Therefore, it does not use a prompt string, and any prompt string
you supply is ignored.
Even though the code letter doesn't use a prompt string, you must
follow it with a newline if it is not the last code character in
the string.
Prompt
A prompt immediately follows the code character. The prompt ends
either with the end of the string or with a newline.
Special
This code character is meaningful only at the beginning of the
interactive string, and it does not look for a prompt or a newline.
It is a single, isolated character.
Here are the code character descriptions for use with `interactive':
`*'
Signal an error if the current buffer is read-only. Special.
`@'
Select the window mentioned in the first mouse event in the key
sequence that invoked this command. Special.
`a'
A function name (i.e., a symbol satisfying `fboundp'). Existing,
Completion, Prompt.
`b'
The name of an existing buffer. By default, uses the name of the
current buffer (*note Buffers::). Existing, Completion, Default,
Prompt.
`B'
A buffer name. The buffer need not exist. By default, uses the
name of a recently used buffer other than the current buffer.
Completion, Default, Prompt.
`c'
A character. The cursor does not move into the echo area. Prompt.
`C'
A command name (i.e., a symbol satisfying `commandp'). Existing,
Completion, Prompt.
`d'
The position of point, as an integer (*note Point::). No I/O.
`D'
A directory name. The default is the current default directory of
the current buffer, `default-directory' (*note System
Environment::). Existing, Completion, Default, Prompt.
`e'
The first or next mouse event in the key sequence that invoked the
command. More precisely, `e' gets events that are lists, so you
can look at the data in the lists. *Note Input Events::. No I/O.
You can use `e' more than once in a single command's interactive
specification. If the key sequence that invoked the command has N
events that are lists, the Nth `e' provides the Nth such event.
Events that are not lists, such as function keys and ASCII
characters, do not count where `e' is concerned.
`f'
A file name of an existing file (*note File Names::). The default
directory is `default-directory'. Existing, Completion, Default,
Prompt.
`F'
A file name. The file need not exist. Completion, Default,
Prompt.
`i'
An irrelevant argument. This code always supplies `nil' as the
argument's value. No I/O.
`k'
A key sequence (*note Keymap Terminology::). This keeps reading
events until a command (or undefined command) is found in the
current key maps. The key sequence argument is represented as a
string or vector. The cursor does not move into the echo area.
Prompt.
This kind of input is used by commands such as `describe-key' and
`global-set-key'.
`K'
A key sequence, whose definition you intend to change. This works
like `k', except that it suppresses, for the last input event in
the key sequence, the conversions that are normally used (when
necessary) to convert an undefined key into a defined one.
`m'
The position of the mark, as an integer. No I/O.
`M'
Arbitrary text, read in the minibuffer using the current buffer's
input method, and returned as a string (*note Input Methods:
(emacs)Input Methods.). Prompt.
`n'
A number read with the minibuffer. If the input is not a number,
the user is asked to try again. The prefix argument, if any, is
not used. Prompt.
`N'
The numeric prefix argument; but if there is no prefix argument,
read a number as with `n'. Requires a number. *Note Prefix
Command Arguments::. Prompt.
`p'
The numeric prefix argument. (Note that this `p' is lower case.)
No I/O.
`P'
The raw prefix argument. (Note that this `P' is upper case.) No
I/O.
`r'
Point and the mark, as two numeric arguments, smallest first.
This is the only code letter that specifies two successive
arguments rather than one. No I/O.
`s'
Arbitrary text, read in the minibuffer and returned as a string
(*note Text from Minibuffer::). Terminate the input with either
`C-j' or <RET>. (`C-q' may be used to include either of these
characters in the input.) Prompt.
`S'
An interned symbol whose name is read in the minibuffer. Any
whitespace character terminates the input. (Use `C-q' to include
whitespace in the string.) Other characters that normally
terminate a symbol (e.g., parentheses and brackets) do not do so
here. Prompt.
`v'
A variable declared to be a user option (i.e., satisfying the
predicate `user-variable-p'). *Note High-Level Completion::.
Existing, Completion, Prompt.
`x'
A Lisp object, specified with its read syntax, terminated with a
`C-j' or <RET>. The object is not evaluated. *Note Object from
Minibuffer::. Prompt.
`X'
A Lisp form is read as with `x', but then evaluated so that its
value becomes the argument for the command. Prompt.
`z'
A coding system name (a symbol). If the user enters null input,
the argument value is `nil'. *Note Coding Systems::. Completion,
Existing, Prompt.
`Z'
A coding system name (a symbol)--but only if this command has a
prefix argument. With no prefix argument, `Z' provides `nil' as
the argument value. Completion, Existing, Prompt.
Examples of Using `interactive'
-------------------------------
Here are some examples of `interactive':
(defun foo1 () ; `foo1' takes no arguments,
(interactive) ; just moves forward two words.
(forward-word 2))
=> foo1
(defun foo2 (n) ; `foo2' takes one argument,
(interactive "p") ; which is the numeric prefix.
(forward-word (* 2 n)))
=> foo2
(defun foo3 (n) ; `foo3' takes one argument,
(interactive "nCount:") ; which is read with the Minibuffer.
(forward-word (* 2 n)))
=> foo3
(defun three-b (b1 b2 b3)
"Select three existing buffers.
Put them into three windows, selecting the last one."
(interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")
(delete-other-windows)
(split-window (selected-window) 8)
(switch-to-buffer b1)
(other-window 1)
(split-window (selected-window) 8)
(switch-to-buffer b2)
(other-window 1)
(switch-to-buffer b3))
=> three-b
(three-b "*scratch*" "declarations.texi" "*mail*")
=> nil
Interactive Call
================
After the command loop has translated a key sequence into a command
it invokes that command using the function `command-execute'. If the
command is a function, `command-execute' calls `call-interactively',
which reads the arguments and calls the command. You can also call
these functions yourself.
- Function: commandp object
Returns `t' if OBJECT is suitable for calling interactively; that
is, if OBJECT is a command. Otherwise, returns `nil'.
The interactively callable objects include strings and vectors
(treated as keyboard macros), lambda expressions that contain a
top-level call to `interactive', byte-code function objects made
from such lambda expressions, autoload objects that are declared
as interactive (non-`nil' fourth argument to `autoload'), and some
of the primitive functions.
A symbol satisfies `commandp' if its function definition satisfies
`commandp'.
Keys and keymaps are not commands. Rather, they are used to look
up commands (*note Keymaps::).
See `documentation' in *Note Accessing Documentation::, for a
realistic example of using `commandp'.
- Function: call-interactively command &optional record-flag keys
This function calls the interactively callable function COMMAND,
reading arguments according to its interactive calling
specifications. An error is signaled if COMMAND is not a function
or if it cannot be called interactively (i.e., is not a command).
Note that keyboard macros (strings and vectors) are not accepted,
even though they are considered commands, because they are not
functions.
If RECORD-FLAG is non-`nil', then this command and its arguments
are unconditionally added to the list `command-history'.
Otherwise, the command is added only if it uses the minibuffer to
read an argument. *Note Command History::.
The argument KEYS, if given, specifies the sequence of events to
supply if the command inquires which events were used to invoke it.
- Function: command-execute command &optional record-flag keys special
This function executes COMMAND. The argument COMMAND must satisfy
the `commandp' predicate; i.e., it must be an interactively
callable function or a keyboard macro.
A string or vector as COMMAND is executed with
`execute-kbd-macro'. A function is passed to
`call-interactively', along with the optional RECORD-FLAG.
A symbol is handled by using its function definition in its place.
A symbol with an `autoload' definition counts as a command if it
was declared to stand for an interactively callable function.
Such a definition is handled by loading the specified library and
then rechecking the definition of the symbol.
The argument KEYS, if given, specifies the sequence of events to
supply if the command inquires which events were used to invoke it.
The argument SPECIAL, if given, means to ignore the prefix
argument and not clear it. This is used for executing special
events (*note Special Events::).
- Command: execute-extended-command prefix-argument
This function reads a command name from the minibuffer using
`completing-read' (*note Completion::). Then it uses
`command-execute' to call the specified command. Whatever that
command returns becomes the value of `execute-extended-command'.
If the command asks for a prefix argument, it receives the value
PREFIX-ARGUMENT. If `execute-extended-command' is called
interactively, the current raw prefix argument is used for
PREFIX-ARGUMENT, and thus passed on to whatever command is run.
`execute-extended-command' is the normal definition of `M-x', so
it uses the string `M-x ' as a prompt. (It would be better to
take the prompt from the events used to invoke
`execute-extended-command', but that is painful to implement.) A
description of the value of the prefix argument, if any, also
becomes part of the prompt.
(execute-extended-command 1)
---------- Buffer: Minibuffer ----------
1 M-x forward-word RET
---------- Buffer: Minibuffer ----------
=> t
- Function: interactive-p
This function returns `t' if the containing function (the one whose
code includes the call to `interactive-p') was called
interactively, with the function `call-interactively'. (It makes
no difference whether `call-interactively' was called from Lisp or
directly from the editor command loop.) If the containing
function was called by Lisp evaluation (or with `apply' or
`funcall'), then it was not called interactively.
The most common use of `interactive-p' is for deciding whether to
print an informative message. As a special exception, `interactive-p'
returns `nil' whenever a keyboard macro is being run. This is to
suppress the informative messages and speed execution of the macro.
For example:
(defun foo ()
(interactive)
(when (interactive-p)
(message "foo")))
=> foo
(defun bar ()
(interactive)
(setq foobar (list (foo) (interactive-p))))
=> bar
;; Type `M-x foo'.
-| foo
;; Type `M-x bar'.
;; This does not print anything.
foobar
=> (nil t)
The other way to do this sort of job is to make the command take an
argument `print-message' which should be non-`nil' in an interactive
call, and use the `interactive' spec to make sure it is non-`nil'.
Here's how:
(defun foo (&optional print-message)
(interactive "p")
(when print-message
(message "foo")))
The numeric prefix argument, provided by `p', is never `nil'.
Information from the Command Loop
=================================
The editor command loop sets several Lisp variables to keep status
records for itself and for commands that are run.
- Variable: last-command
This variable records the name of the previous command executed by
the command loop (the one before the current command). Normally
the value is a symbol with a function definition, but this is not
guaranteed.
The value is copied from `this-command' when a command returns to
the command loop, except when the command has specified a prefix
argument for the following command.
This variable is always local to the current terminal and cannot be
buffer-local. *Note Multiple Displays::.
- Variable: real-last-command
This variable is set up by Emacs just like `last-command', but
never altered by Lisp programs.
- Variable: this-command
This variable records the name of the command now being executed by
the editor command loop. Like `last-command', it is normally a
symbol with a function definition.
The command loop sets this variable just before running a command,
and copies its value into `last-command' when the command finishes
(unless the command specified a prefix argument for the following
command).
Some commands set this variable during their execution, as a flag
for whatever command runs next. In particular, the functions for
killing text set `this-command' to `kill-region' so that any kill
commands immediately following will know to append the killed text
to the previous kill.
If you do not want a particular command to be recognized as the
previous command in the case where it got an error, you must code that
command to prevent this. One way is to set `this-command' to `t' at the
beginning of the command, and set `this-command' back to its proper
value at the end, like this:
(defun foo (args...)
(interactive ...)
(let ((old-this-command this-command))
(setq this-command t)
...do the work...
(setq this-command old-this-command)))
We do not bind `this-command' with `let' because that would restore the
old value in case of error--a feature of `let' which in this case does
precisely what we want to avoid.
- Function: this-command-keys
This function returns a string or vector containing the key
sequence that invoked the present command, plus any previous
commands that generated the prefix argument for this command. The
value is a string if all those events were characters. *Note
Input Events::.
(this-command-keys)
;; Now use `C-u C-x C-e' to evaluate that.
=> "^U^X^E"
- Function: this-command-keys-vector
Like `this-command-keys', except that it always returns the events
in a vector, so you don't need to deal with the complexities of
storing input events in a string (*note Strings of Events::).
- Function: clear-this-command-keys
This function empties out the table of events for
`this-command-keys' to return, and also empties the records that
the function `recent-keys' (*note Recording Input::) will
subsequently return. This is useful after reading a password, to
prevent the password from echoing inadvertently as part of the next
command in certain cases.
- Variable: last-nonmenu-event
This variable holds the last input event read as part of a key
sequence, not counting events resulting from mouse menus.
One use of this variable is for telling `x-popup-menu' where to pop
up a menu. It is also used internally by `y-or-n-p' (*note
Yes-or-No Queries::).
- Variable: last-command-event
- Variable: last-command-char
This variable is set to the last input event that was read by the
command loop as part of a command. The principal use of this
variable is in `self-insert-command', which uses it to decide which
character to insert.
last-command-event
;; Now use `C-u C-x C-e' to evaluate that.
=> 5
The value is 5 because that is the ASCII code for `C-e'.
The alias `last-command-char' exists for compatibility with Emacs
version 18.
- Variable: last-event-frame
This variable records which frame the last input event was
directed to. Usually this is the frame that was selected when the
event was generated, but if that frame has redirected input focus
to another frame, the value is the frame to which the event was
redirected. *Note Input Focus::.
Adjusting Point After Commands
==============================
It is not easy to display a value of point in the middle of a
sequence of text that has the `display' or `composition' property. So
after a command finishes and returns to the command loop, if point is
within such a sequence, the command loop normally moves point to the
edge of the sequence.
A command can inhibit this feature by setting the variable
`disable-point-adjustment':
- Variable: disable-point-adjustment
If this variable is non-`nil' when a command returns to the command
loop, then the command loop does not check for text properties
such as `display' and `composition', and does not move point out of
sequences that have these properties.
The command loop sets this variable to `nil' before each command,
so if a command sets it, the effect applies only to that command.
- Variable: global-disable-point-adjustment
If you set this variable to a non-`nil' value, the feature of
moving point out of these sequences is completely turned off.
Input Events
============
The Emacs command loop reads a sequence of "input events" that
represent keyboard or mouse activity. The events for keyboard activity
are characters or symbols; mouse events are always lists. This section
describes the representation and meaning of input events in detail.
- Function: eventp object
This function returns non-`nil' if OBJECT is an input event or
event type.
Note that any symbol might be used as an event or an event type.
`eventp' cannot distinguish whether a symbol is intended by Lisp
code to be used as an event. Instead, it distinguishes whether the
symbol has actually been used in an event that has been read as
input in the current Emacs session. If a symbol has not yet been
so used, `eventp' returns `nil'.
Keyboard Events
---------------
There are two kinds of input you can get from the keyboard: ordinary
keys, and function keys. Ordinary keys correspond to characters; the
events they generate are represented in Lisp as characters. The event
type of a character event is the character itself (an integer); see
*Note Classifying Events::.
An input character event consists of a "basic code" between 0 and
524287, plus any or all of these "modifier bits":
meta
The 2**27 bit in the character code indicates a character typed
with the meta key held down.
control
The 2**26 bit in the character code indicates a non-ASCII control
character.
ASCII control characters such as `C-a' have special basic codes of
their own, so Emacs needs no special bit to indicate them. Thus,
the code for `C-a' is just 1.
But if you type a control combination not in ASCII, such as `%'
with the control key, the numeric value you get is the code for
`%' plus 2**26 (assuming the terminal supports non-ASCII control
characters).
shift
The 2**25 bit in the character code indicates an ASCII control
character typed with the shift key held down.
For letters, the basic code itself indicates upper versus lower
case; for digits and punctuation, the shift key selects an
entirely different character with a different basic code. In
order to keep within the ASCII character set whenever possible,
Emacs avoids using the 2**25 bit for those characters.
However, ASCII provides no way to distinguish `C-A' from `C-a', so
Emacs uses the 2**25 bit in `C-A' and not in `C-a'.
hyper
The 2**24 bit in the character code indicates a character typed
with the hyper key held down.
super
The 2**23 bit in the character code indicates a character typed
with the super key held down.
alt
The 2**22 bit in the character code indicates a character typed
with the alt key held down. (On some terminals, the key labeled
<ALT> is actually the meta key.)
It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
`event-modifiers' (*note Classifying Events::). When making key
bindings, you can use the read syntax for characters with modifier bits
(`\C-', `\M-', and so on). For making key bindings with `define-key',
you can use lists such as `(control hyper ?x)' to specify the
characters (*note Changing Key Bindings::). The function
`event-convert-list' converts such a list into an event type (*note
Classifying Events::).
Function Keys
-------------
Most keyboards also have "function keys"--keys that have names or
symbols that are not characters. Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
case. For example, pressing a key labeled <F1> places the symbol `f1'
in the input stream.
The event type of a function key event is the event symbol itself.
*Note Classifying Events::.
Here are a few special cases in the symbol-naming convention for
function keys:
`backspace', `tab', `newline', `return', `delete'
These keys correspond to common ASCII control characters that have
special keys on most keyboards.
In ASCII, `C-i' and <TAB> are the same character. If the terminal
can distinguish between them, Emacs conveys the distinction to
Lisp programs by representing the former as the integer 9, and the
latter as the symbol `tab'.
Most of the time, it's not useful to distinguish the two. So
normally `function-key-map' (*note Translating Input::) is set up
to map `tab' into 9. Thus, a key binding for character code 9 (the
character `C-i') also applies to `tab'. Likewise for the other
symbols in this group. The function `read-char' likewise converts
these events into characters.
In ASCII, <BS> is really `C-h'. But `backspace' converts into the
character code 127 (<DEL>), not into code 8 (<BS>). This is what
most users prefer.
`left', `up', `right', `down'
Cursor arrow keys
`kp-add', `kp-decimal', `kp-divide', ...
Keypad keys (to the right of the regular keyboard).
`kp-0', `kp-1', ...
Keypad keys with digits.
`kp-f1', `kp-f2', `kp-f3', `kp-f4'
Keypad PF keys.
`kp-home', `kp-left', `kp-up', `kp-right', `kp-down'
Keypad arrow keys. Emacs normally translates these into the
corresponding non-keypad keys `home', `left', ...
`kp-prior', `kp-next', `kp-end', `kp-begin', `kp-insert', `kp-delete'
Additional keypad duplicates of keys ordinarily found elsewhere.
Emacs normally translates these into the like-named non-keypad
keys.
You can use the modifier keys <ALT>, <CTRL>, <HYPER>, <META>,
<SHIFT>, and <SUPER> with function keys. The way to represent them is
with prefixes in the symbol name:
`A-'
The alt modifier.
`C-'
The control modifier.
`H-'
The hyper modifier.
`M-'
The meta modifier.
`S-'
The shift modifier.
`s-'
The super modifier.
Thus, the symbol for the key <F3> with <META> held down is `M-f3'.
When you use more than one prefix, we recommend you write them in
alphabetical order; but the order does not matter in arguments to the
key-binding lookup and modification functions.
Mouse Events
------------
Emacs supports four kinds of mouse events: click events, drag events,
button-down events, and motion events. All mouse events are represented
as lists. The CAR of the list is the event type; this says which mouse
button was involved, and which modifier keys were used with it. The
event type can also distinguish double or triple button presses (*note
Repeat Events::). The rest of the list elements give position and time
information.
For key lookup, only the event type matters: two events of the same
type necessarily run the same command. The command can access the full
values of these events using the `e' interactive code. *Note
Interactive Codes::.
A key sequence that starts with a mouse event is read using the
keymaps of the buffer in the window that the mouse was in, not the
current buffer. This does not imply that clicking in a window selects
that window or its buffer--that is entirely under the control of the
command binding of the key sequence.
Click Events
------------
When the user presses a mouse button and releases it at the same
location, that generates a "click" event. Mouse click events have this
form:
(EVENT-TYPE
(WINDOW BUFFER-POS (X . Y) TIMESTAMP)
CLICK-COUNT)
Here is what the elements normally mean:
EVENT-TYPE
This is a symbol that indicates which mouse button was used. It is
one of the symbols `mouse-1', `mouse-2', ..., where the buttons
are numbered left to right.
You can also use prefixes `A-', `C-', `H-', `M-', `S-' and `s-'
for modifiers alt, control, hyper, meta, shift and super, just as
you would with function keys.
This symbol also serves as the event type of the event. Key
bindings describe events by their types; thus, if there is a key
binding for `mouse-1', that binding would apply to all events whose
EVENT-TYPE is `mouse-1'.
WINDOW
This is the window in which the click occurred.
X, Y
These are the pixel-denominated coordinates of the click, relative
to the top left corner of WINDOW, which is `(0 . 0)'.
BUFFER-POS
This is the buffer position of the character clicked on.
TIMESTAMP
This is the time at which the event occurred, in milliseconds.
(Since this value wraps around the entire range of Emacs Lisp
integers in about five hours, it is useful only for relating the
times of nearby events.)
CLICK-COUNT
This is the number of rapid repeated presses so far of the same
mouse button. *Note Repeat Events::.
The meanings of BUFFER-POS, X and Y are somewhat different when the
event location is in a special part of the screen, such as the mode
line or a scroll bar.
If the location is in a scroll bar, then BUFFER-POS is the symbol
`vertical-scroll-bar' or `horizontal-scroll-bar', and the pair `(X .
Y)' is replaced with a pair `(PORTION . WHOLE)', where PORTION is the
distance of the click from the top or left end of the scroll bar, and
WHOLE is the length of the entire scroll bar.
If the position is on a mode line or the vertical line separating
WINDOW from its neighbor to the right, then BUFFER-POS is the symbol
`mode-line', `header-line', or `vertical-line'. For the mode line, Y
does not have meaningful data. For the vertical line, X does not have
meaningful data.
In one special case, BUFFER-POS is a list containing a symbol (one
of the symbols listed above) instead of just the symbol. This happens
after the imaginary prefix keys for the event are inserted into the
input stream. *Note Key Sequence Input::.
Drag Events
-----------
With Emacs, you can have a drag event without even changing your
clothes. A "drag event" happens every time the user presses a mouse
button and then moves the mouse to a different character position before
releasing the button. Like all mouse events, drag events are
represented in Lisp as lists. The lists record both the starting mouse
position and the final position, like this:
(EVENT-TYPE
(WINDOW1 BUFFER-POS1 (X1 . Y1) TIMESTAMP1)
(WINDOW2 BUFFER-POS2 (X2 . Y2) TIMESTAMP2)
CLICK-COUNT)
For a drag event, the name of the symbol EVENT-TYPE contains the
prefix `drag-'. For example, dragging the mouse with button 2 held
down generates a `drag-mouse-2' event. The second and third elements
of the event give the starting and ending position of the drag. Aside
from that, the data have the same meanings as in a click event (*note
Click Events::). You can access the second element of any mouse event
in the same way, with no need to distinguish drag events from others.
The `drag-' prefix follows the modifier key prefixes such as `C-'
and `M-'.
If `read-key-sequence' receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Button-Down Events
------------------
Click and drag events happen when the user releases a mouse button.
They cannot happen earlier, because there is no way to distinguish a
click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need
to handle "button-down" events.(1) These occur as soon as a button is
pressed. They are represented by lists that look exactly like click
events (*note Click Events::), except that the EVENT-TYPE symbol name
contains the prefix `down-'. The `down-' prefix follows modifier key
prefixes such as `C-' and `M-'.
The function `read-key-sequence' ignores any button-down events that
don't have command bindings; therefore, the Emacs command loop ignores
them too. This means that you need not worry about defining
button-down events unless you want them to do something. The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released. *Note
Motion Events::.
---------- Footnotes ----------
(1) Button-down is the conservative antithesis of drag.
Repeat Events
-------------
If you press the same mouse button more than once in quick succession
without moving the mouse, Emacs generates special "repeat" mouse events
for the second and subsequent presses.
The most common repeat events are "double-click" events. Emacs
generates a double-click event when you click a button twice; the event
happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
`double-'. Thus, a double click on the second mouse button with <meta>
held down comes to the Lisp program as `M-double-mouse-2'. If a
double-click event has no binding, the binding of the corresponding
ordinary click event is used to execute it. Thus, you need not pay
attention to the double click feature unless you really want to.
When the user performs a double click, Emacs generates first an
ordinary click event, and then a double-click event. Therefore, you
must design the command binding of the double click event to assume
that the single-click command has already run. It must produce the
desired results of a double click, starting from the results of a
single click.
This is convenient, if the meaning of a double click somehow "builds
on" the meaning of a single click--which is recommended user interface
design practice for double clicks.
If you click a button, then press it down again and start moving the
mouse with the button held down, then you get a "double-drag" event
when you ultimately release the button. Its event type contains
`double-drag' instead of just `drag'. If a double-drag event has no
binding, Emacs looks for an alternate binding as if the event were an
ordinary drag.
Before the double-click or double-drag event, Emacs generates a
"double-down" event when the user presses the button down for the
second time. Its event type contains `double-down' instead of just
`down'. If a double-down event has no binding, Emacs looks for an
alternate binding as if the event were an ordinary button-down event.
If it finds no binding that way either, the double-down event is
ignored.
To summarize, when you click a button and then press it again right
away, Emacs generates a down event and a click event for the first
click, a double-down event when you press the button again, and finally
either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick
succession, Emacs generates a "triple-down" event, followed by either a
"triple-click" or a "triple-drag". The event types of these events
contain `triple' instead of `double'. If any triple event has no
binding, Emacs uses the binding that it would use for the corresponding
double event.
If you click a button three or more times and then press it again,
the events for the presses beyond the third are all triple events.
Emacs does not have separate event types for quadruple, quintuple, etc.
events. However, you can look at the event list to find out precisely
how many times the button was pressed.
- Function: event-click-count event
This function returns the number of consecutive button presses
that led up to EVENT. If EVENT is a double-down, double-click or
double-drag event, the value is 2. If EVENT is a triple event,
the value is 3 or greater. If EVENT is an ordinary mouse event
(not a repeat event), the value is 1.
- Variable: double-click-fuzz
To generate repeat events, successive mouse button presses must be
at approximately the same screen position. The value of
`double-click-fuzz' specifies the maximum number of pixels the
mouse may be moved between two successive clicks to make a
double-click.
- Variable: double-click-time
To generate repeat events, the number of milliseconds between
successive button presses must be less than the value of
`double-click-time'. Setting `double-click-time' to `nil'
disables multi-click detection entirely. Setting it to `t'
removes the time limit; Emacs then detects multi-clicks by
position only.
Motion Events
-------------
Emacs sometimes generates "mouse motion" events to describe motion
of the mouse without any button activity. Mouse motion events are
represented by lists that look like this:
(mouse-movement (WINDOW BUFFER-POS (X . Y) TIMESTAMP))
The second element of the list describes the current position of the
mouse, just as in a click event (*note Click Events::).
The special form `track-mouse' enables generation of motion events
within its body. Outside of `track-mouse' forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear. *Note Mouse Tracking::.
Focus Events
------------
Window systems provide general ways for the user to control which
window gets keyboard input. This choice of window is called the
"focus". When the user does something to switch between Emacs frames,
that generates a "focus event". The normal definition of a focus event,
in the global keymap, is to select a new frame within Emacs, as the user
would expect. *Note Input Focus::.
Focus events are represented in Lisp as lists that look like this:
(switch-frame NEW-FRAME)
where NEW-FRAME is the frame switched to.
Most X window managers are set up so that just moving the mouse into
a window is enough to set the focus there. Emacs appears to do this,
because it changes the cursor to solid in the new frame. However, there
is no need for the Lisp program to know about the focus change until
some other kind of input arrives. So Emacs generates a focus event only
when the user actually types a keyboard key or presses a mouse button in
the new frame; just moving the mouse between frames does not generate a
focus event.
A focus event in the middle of a key sequence would garble the
sequence. So Emacs never generates a focus event in the middle of a key
sequence. If the user changes focus in the middle of a key
sequence--that is, after a prefix key--then Emacs reorders the events
so that the focus event comes either before or after the multi-event key
sequence, and not within it.
Miscellaneous Window System Events
----------------------------------
A few other event types represent occurrences within the window
system.
`(delete-frame (FRAME))'
This kind of event indicates that the user gave the window manager
a command to delete a particular window, which happens to be an
Emacs frame.
The standard definition of the `delete-frame' event is to delete
FRAME.
`(iconify-frame (FRAME))'
This kind of event indicates that the user iconified FRAME using
the window manager. Its standard definition is `ignore'; since the
frame has already been iconified, Emacs has no work to do. The
purpose of this event type is so that you can keep track of such
events if you want to.
`(make-frame-visible (FRAME))'
This kind of event indicates that the user deiconified FRAME using
the window manager. Its standard definition is `ignore'; since the
frame has already been made visible, Emacs has no work to do.
`(mouse-wheel POSITION DELTA)'
This kind of event is generated by moving a wheel on a mouse (such
as the MS Intellimouse). Its effect is typically a kind of scroll
or zoom.
The element DELTA describes the amount and direction of the wheel
rotation. Its absolute value is the number of increments by which
the wheel was rotated. A negative DELTA indicates that the wheel
was rotated backwards, towards the user, and a positive DELTA
indicates that the wheel was rotated forward, away from the user.
The element POSITION is a list describing the position of the
event, in the same format as used in a mouse-click event.
This kind of event is generated only on some kinds of systems.
`(drag-n-drop POSITION FILES)'
This kind of event is generated when a group of files is selected
in an application outside of Emacs, and then dragged and dropped
onto an Emacs frame.
The element POSITION is a list describing the position of the
event, in the same format as used in a mouse-click event, and
FILES is the list of file names that were dragged and dropped.
The usual way to handle this event is by visiting these files.
This kind of event is generated, at present, only on some kinds of
systems.
If one of these events arrives in the middle of a key sequence--that
is, after a prefix key--then Emacs reorders the events so that this
event comes either before or after the multi-event key sequence, not
within it.
Event Examples
--------------
If the user presses and releases the left mouse button over the same
location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
While holding the control key down, the user might hold down the
second mouse button, and drag the mouse from one line to the next.
That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
While holding down the meta and shift keys, the user might press the
second mouse button on the window's mode line, and then drag the mouse
into another window. That produces a pair of events like these:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
Classifying Events
------------------
Every event has an "event type", which classifies the event for key
binding purposes. For a keyboard event, the event type equals the
event value; thus, the event type for a character is the character, and
the event type for a function key symbol is the symbol itself. For
events that are lists, the event type is the symbol in the CAR of the
list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are
concerned; thus, they always run the same command. That does not
necessarily mean they do the same things, however, as some commands look
at the whole event to decide what to do. For example, some commands use
the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example,
you might want to ask whether an event involved the <META> key,
regardless of which other key or mouse button was used.
The functions `event-modifiers' and `event-basic-type' are provided
to get such information conveniently.
- Function: event-modifiers event
This function returns a list of the modifiers that EVENT has. The
modifiers are symbols; they include `shift', `control', `meta',
`alt', `hyper' and `super'. In addition, the modifiers list of a
mouse event symbol always contains one of `click', `drag', and
`down'.
The argument EVENT may be an entire event object, or just an event
type.
Here are some examples:
(event-modifiers ?a)
=> nil
(event-modifiers ?\C-a)
=> (control)
(event-modifiers ?\C-%)
=> (control)
(event-modifiers ?\C-\S-a)
=> (control shift)
(event-modifiers 'f5)
=> nil
(event-modifiers 's-f5)
=> (super)
(event-modifiers 'M-S-f5)
=> (meta shift)
(event-modifiers 'mouse-1)
=> (click)
(event-modifiers 'down-mouse-1)
=> (down)
The modifiers list for a click event explicitly contains `click',
but the event symbol name itself does not contain `click'.
- Function: event-basic-type event
This function returns the key or mouse button that EVENT
describes, with all modifiers removed. For example:
(event-basic-type ?a)
=> 97
(event-basic-type ?A)
=> 97
(event-basic-type ?\C-a)
=> 97
(event-basic-type ?\C-\S-a)
=> 97
(event-basic-type 'f5)
=> f5
(event-basic-type 's-f5)
=> f5
(event-basic-type 'M-S-f5)
=> f5
(event-basic-type 'down-mouse-1)
=> mouse-1
- Function: mouse-movement-p object
This function returns non-`nil' if OBJECT is a mouse movement
event.
- Function: event-convert-list list
This function converts a list of modifier names and a basic event
type to an event type which specifies all of them. For example,
(event-convert-list '(control ?a))
=> 1
(event-convert-list '(control meta ?a))
=> -134217727
(event-convert-list '(control super f1))
=> C-s-f1
Accessing Events
----------------
This section describes convenient functions for accessing the data in
a mouse button or motion event.
These two functions return the starting or ending position of a
mouse-button event, as a list of this form:
(WINDOW BUFFER-POSITION (X . Y) TIMESTAMP)
- Function: event-start event
This returns the starting position of EVENT.
If EVENT is a click or button-down event, this returns the
location of the event. If EVENT is a drag event, this returns the
drag's starting position.
- Function: event-end event
This returns the ending position of EVENT.
If EVENT is a drag event, this returns the position where the user
released the mouse button. If EVENT is a click or button-down
event, the value is actually the starting position, which is the
only position such events have.
These five functions take a position list as described above, and
return various parts of it.
- Function: posn-window position
Return the window that POSITION is in.
- Function: posn-point position
Return the buffer position in POSITION. This is an integer.
- Function: posn-x-y position
Return the pixel-based x and y coordinates in POSITION, as a cons
cell `(X . Y)'.
- Function: posn-col-row position
Return the row and column (in units of characters) of POSITION, as
a cons cell `(COL . ROW)'. These are computed from the X and Y
values actually found in POSITION.
- Function: posn-timestamp position
Return the timestamp in POSITION.
These functions are useful for decoding scroll bar events.
- Function: scroll-bar-event-ratio event
This function returns the fractional vertical position of a scroll
bar event within the scroll bar. The value is a cons cell
`(PORTION . WHOLE)' containing two integers whose ratio is the
fractional position.
- Function: scroll-bar-scale ratio total
This function multiplies (in effect) RATIO by TOTAL, rounding the
result to an integer. The argument RATIO is not a number, but
rather a pair `(NUM . DENOM)'--typically a value returned by
`scroll-bar-event-ratio'.
This function is handy for scaling a position on a scroll bar into
a buffer position. Here's how to do that:
(+ (point-min)
(scroll-bar-scale
(posn-x-y (event-start event))
(- (point-max) (point-min))))
Recall that scroll bar events have two integers forming a ratio,
in place of a pair of x and y coordinates.
Putting Keyboard Events in Strings
----------------------------------
In most of the places where strings are used, we conceptualize the
string as containing text characters--the same kind of characters found
in buffers or files. Occasionally Lisp programs use strings that
conceptually contain keyboard characters; for example, they may be key
sequences or keyboard macro definitions. However, storing keyboard
characters in a string is a complex matter, for reasons of historical
compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities
by not storing keyboard events in strings. Here is how to do that:
* Use vectors instead of strings for key sequences, when you plan to
use them for anything other than as arguments to `lookup-key' and
`define-key'. For example, you can use `read-key-sequence-vector'
instead of `read-key-sequence', and `this-command-keys-vector'
instead of `this-command-keys'.
* Use vectors to write key sequence constants containing meta
characters, even when passing them directly to `define-key'.
* When you have to look at the contents of a key sequence that might
be a string, use `listify-key-sequence' (*note Event Input Misc::)
first, to convert it to a list.
The complexities stem from the modifier bits that keyboard input
characters can include. Aside from the Meta modifier, none of these
modifier bits can be included in a string, and the Meta modifier is
allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255. At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string. Many Lisp programs used `\M-' in string constants to stand for
meta characters, especially in arguments to `define-key' and similar
functions, and key sequences and sequences of events were always
represented as strings.
When we added support for larger basic character codes beyond 127,
and additional modifier bits, we had to change the representation of
meta characters. Now the flag that represents the Meta modifier in a
character is 2**27 and such numbers cannot be included in a string.
To support programs with `\M-' in string constants, there are
special rules for including certain meta characters in a string. Here
are the rules for interpreting a string as a sequence of input
characters:
* If the keyboard character value is in the range of 0 to 127, it
can go in the string unchanged.
* The meta variants of those characters, with codes in the range of
2**27 to 2**27+127, can also go in the string, but you must change
their numeric values. You must set the 2**7 bit instead of the
2**27 bit, resulting in a value between 128 and 255. Only a
unibyte string can include these codes.
* Non-ASCII characters above 256 can be included in a multibyte
string.
* Other keyboard character events cannot fit in a string. This
includes keyboard events in the range of 128 to 255.
Functions such as `read-key-sequence' that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.
When you use the read syntax `\M-' in a string, it produces a code
in the range of 128 to 255--the same code that you get if you modify
the corresponding keyboard event to put it in the string. Thus, meta
events in strings work consistently regardless of how they get into the
strings.
However, most programs would do well to avoid these issues by
following the recommendations at the beginning of this section.
Reading Input
=============
The editor command loop reads key sequences using the function
`read-key-sequence', which uses `read-event'. These and other
functions for event input are also available for use in Lisp programs.
See also `momentary-string-display' in *Note Temporary Displays::, and
`sit-for' in *Note Waiting::. *Note Terminal Input::, for functions
and variables for controlling terminal input modes and debugging
terminal input. *Note Translating Input::, for features you can use
for translating or modifying input events while reading them.
For higher-level input facilities, see *Note Minibuffers::.
Key Sequence Input
------------------
The command loop reads input a key sequence at a time, by calling
`read-key-sequence'. Lisp programs can also call this function; for
example, `describe-key' uses it to read the key to describe.
- Function: read-key-sequence prompt
This function reads a key sequence and returns it as a string or
vector. It keeps reading events until it has accumulated a
complete key sequence; that is, enough to specify a non-prefix
command using the currently active keymaps.
If the events are all characters and all can fit in a string, then
`read-key-sequence' returns a string (*note Strings of Events::).
Otherwise, it returns a vector, since a vector can hold all kinds
of events--characters, symbols, and lists. The elements of the
string or vector are the events in the key sequence.
The argument PROMPT is either a string to be displayed in the echo
area as a prompt, or `nil', meaning not to display a prompt.
In the example below, the prompt `?' is displayed in the echo area,
and the user types `C-x C-f'.
(read-key-sequence "?")
---------- Echo Area ----------
?C-x C-f
---------- Echo Area ----------
=> "^X^F"
The function `read-key-sequence' suppresses quitting: `C-g' typed
while reading with this function works like any other character,
and does not set `quit-flag'. *Note Quitting::.
- Function: read-key-sequence-vector prompt
This is like `read-key-sequence' except that it always returns the
key sequence as a vector, never as a string. *Note Strings of
Events::.
If an input character is an upper-case letter and has no key binding,
but its lower-case equivalent has one, then `read-key-sequence'
converts the character to lower case. Note that `lookup-key' does not
perform case conversion in this way.
The function `read-key-sequence' also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special--it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event--in the coordinates. But `read-key-sequence'
translates this information into imaginary "prefix keys", all of which
are symbols: `header-line', `horizontal-scroll-bar', `menu-bar',
`mode-line', `vertical-line', and `vertical-scroll-bar'. You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.
For example, if you call `read-key-sequence' and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ")
=> [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
- Variable: num-input-keys
This variable's value is the number of key sequences processed so
far in this Emacs session. This includes key sequences read from
the terminal and key sequences read from keyboard macros being
executed.
- Variable: num-nonmacro-input-events
This variable holds the total number of input events received so
far from the terminal--not counting those generated by keyboard
macros.
Reading One Event
-----------------
The lowest level functions for command input are those that read a
single event.
- Function: read-event &optional prompt inherit-input-method
This function reads and returns the next event of command input,
waiting if necessary until an event is available. Events can come
directly from the user or from a keyboard macro.
If the optional argument PROMPT is non-`nil', it should be a
string to display in the echo area as a prompt. Otherwise,
`read-event' does not display any message to indicate it is waiting
for input; instead, it prompts by echoing: it displays
descriptions of the events that led to or were read by the current
command. *Note The Echo Area::.
If INHERIT-INPUT-METHOD is non-`nil', then the current input
method (if any) is employed to make it possible to enter a
non-ASCII character. Otherwise, input method handling is disabled
for reading this event.
If `cursor-in-echo-area' is non-`nil', then `read-event' moves the
cursor temporarily to the echo area, to the end of any message
displayed there. Otherwise `read-event' does not move the cursor.
If `read-event' gets an event that is defined as a help character,
in some cases `read-event' processes the event directly without
returning. *Note Help Functions::. Certain other events, called
"special events", are also processed directly within `read-event'
(*note Special Events::).
Here is what happens if you call `read-event' and then press the
right-arrow function key:
(read-event)
=> right
- Function: read-char &optional prompt inherit-input-method
This function reads and returns a character of command input. If
the user generates an event which is not a character (i.e. a mouse
click or function key event), `read-char' signals an error. The
arguments work as in `read-event'.
In the first example, the user types the character `1' (ASCII code
49). The second example shows a keyboard macro definition that
calls `read-char' from the minibuffer using `eval-expression'.
`read-char' reads the keyboard macro's very next character, which
is `1'. Then `eval-expression' displays its return value in the
echo area.
(read-char)
=> 49
;; We assume here you use `M-:' to evaluate this.
(symbol-function 'foo)
=> "^[:(read-char)^M1"
(execute-kbd-macro 'foo)
-| 49
=> nil
- Function: read-char-exclusive &optional prompt inherit-input-method
This function reads and returns a character of command input. If
the user generates an event which is not a character,
`read-char-exclusive' ignores it and reads another event, until it
gets a character. The arguments work as in `read-event'.
Invoking the Input Method
-------------------------
The event-reading functions invoke the current input method, if any
(*note Input Methods::). If the value of `input-method-function' is
non-`nil', it should be a function; when `read-event' reads a printing
character (including <SPC>) with no modifier bits, it calls that
function, passing the character as an argument.
- Variable: input-method-function
If this is non-`nil', its value specifies the current input method
function.
*Note:* Don't bind this variable with `let'. It is often
buffer-local, and if you bind it around reading input (which is
exactly when you _would_ bind it), switching buffers
asynchronously while Emacs is waiting will cause the value to be
restored in the wrong buffer.
The input method function should return a list of events which should
be used as input. (If the list is `nil', that means there is no input,
so `read-event' waits for another event.) These events are processed
before the events in `unread-command-events' (*note Event Input
Misc::). Events returned by the input method function are not passed
to the input method function again, even if they are printing
characters with no modifier bits.
If the input method function calls `read-event' or
`read-key-sequence', it should bind `input-method-function' to `nil'
first, to prevent recursion.
The input method function is not called when reading the second and
subsequent events of a key sequence. Thus, these characters are not
subject to input method processing. The input method function should
test the values of `overriding-local-map' and
`overriding-terminal-local-map'; if either of these variables is
non-`nil', the input method should put its argument into a list and
return that list with no further processing.
Quoted Character Input
----------------------
You can use the function `read-quoted-char' to ask the user to
specify a character, and allow the user to specify a control or meta
character conveniently, either literally or as an octal character code.
The command `quoted-insert' uses this function.
- Function: read-quoted-char &optional prompt
This function is like `read-char', except that if the first
character read is an octal digit (0-7), it reads any number of
octal digits (but stopping if a non-octal digit is found), and
returns the character represented by that numeric character code.
Quitting is suppressed when the first character is read, so that
the user can enter a `C-g'. *Note Quitting::.
If PROMPT is supplied, it specifies a string for prompting the
user. The prompt string is always displayed in the echo area,
followed by a single `-'.
In the following example, the user types in the octal number 177
(which is 127 in decimal).
(read-quoted-char "What character")
---------- Echo Area ----------
What character-177
---------- Echo Area ----------
=> 127
Miscellaneous Event Input Features
----------------------------------
This section describes how to "peek ahead" at events without using
them up, how to check for pending input, and how to discard pending
input. See also the function `read-passwd' (*note Reading a
Password::).
- Variable: unread-command-events
This variable holds a list of events waiting to be read as command
input. The events are used in the order they appear in the list,
and removed one by one as they are used.
The variable is needed because in some cases a function reads an
event and then decides not to use it. Storing the event in this
variable causes it to be processed normally, by the command loop
or by the functions to read command input.
For example, the function that implements numeric prefix arguments
reads any number of digits. When it finds a non-digit event, it
must unread the event so that it can be read normally by the
command loop. Likewise, incremental search uses this feature to
unread events with no special meaning in a search, because these
events should exit the search and then execute normally.
The reliable and easy way to extract events from a key sequence so
as to put them in `unread-command-events' is to use
`listify-key-sequence' (*note Strings of Events::).
Normally you add events to the front of this list, so that the
events most recently unread will be reread first.
- Function: listify-key-sequence key
This function converts the string or vector KEY to a list of
individual events, which you can put in `unread-command-events'.
- Variable: unread-command-char
This variable holds a character to be read as command input. A
value of -1 means "empty".
This variable is mostly obsolete now that you can use
`unread-command-events' instead; it exists only to support programs
written for Emacs versions 18 and earlier.
- Function: input-pending-p
This function determines whether any command input is currently
available to be read. It returns immediately, with value `t' if
there is available input, `nil' otherwise. On rare occasions it
may return `t' when no input is available.
- Variable: last-input-event
- Variable: last-input-char
This variable records the last terminal input event read, whether
as part of a command or explicitly by a Lisp program.
In the example below, the Lisp program reads the character `1',
ASCII code 49. It becomes the value of `last-input-event', while
`C-e' (we assume `C-x C-e' command is used to evaluate this
expression) remains the value of `last-command-event'.
(progn (print (read-char))
(print last-command-event)
last-input-event)
-| 49
-| 5
=> 49
The alias `last-input-char' exists for compatibility with Emacs
version 18.
- Function: discard-input
This function discards the contents of the terminal input buffer
and cancels any keyboard macro that might be in the process of
definition. It returns `nil'.
In the following example, the user may type a number of characters
right after starting the evaluation of the form. After the
`sleep-for' finishes sleeping, `discard-input' discards any
characters typed during the sleep.
(progn (sleep-for 2)
(discard-input))
=> nil
Special Events
==============
Special events are handled at a very low level--as soon as they are
read. The `read-event' function processes these events itself, and
never returns them.
Events that are handled in this way do not echo, they are never
grouped into key sequences, and they never appear in the value of
`last-command-event' or `(this-command-keys)'. They do not discard a
numeric argument, they cannot be unread with `unread-command-events',
they may not appear in a keyboard macro, and they are not recorded in a
keyboard macro while you are defining one.
These events do, however, appear in `last-input-event' immediately
after they are read, and this is the way for the event's definition to
find the actual event.
The events types `iconify-frame', `make-frame-visible' and
`delete-frame' are normally handled in this way. The keymap which
defines how to handle special events--and which events are special--is
in the variable `special-event-map' (*note Active Keymaps::).
Waiting for Elapsed Time or Input
=================================
The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
`sit-for' pauses and updates the screen, and returns immediately if
input comes in, while `sleep-for' pauses without updating the screen.
- Function: sit-for seconds &optional millisec nodisp
This function performs redisplay (provided there is no pending
input from the user), then waits SECONDS seconds, or until input is
available. The value is `t' if `sit-for' waited the full time
with no input arriving (see `input-pending-p' in *Note Event Input
Misc::). Otherwise, the value is `nil'.
The argument SECONDS need not be an integer. If it is a floating
point number, `sit-for' waits for a fractional number of seconds.
Some systems support only a whole number of seconds; on these
systems, SECONDS is rounded down.
The optional argument MILLISEC specifies an additional waiting
period measured in milliseconds. This adds to the period
specified by SECONDS. If the system doesn't support waiting
fractions of a second, you get an error if you specify nonzero
MILLISEC.
The expression `(sit-for 0)' is a convenient way to request a
redisplay, without any delay. *Note Forcing Redisplay::.
If NODISP is non-`nil', then `sit-for' does not redisplay, but it
still returns as soon as input is available (or when the timeout
elapses).
Iconifying or deiconifying a frame makes `sit-for' return, because
that generates an event. *Note Misc Events::.
The usual purpose of `sit-for' is to give the user time to read
text that you display.
- Function: sleep-for seconds &optional millisec
This function simply pauses for SECONDS seconds without updating
the display. It pays no attention to available input. It returns
`nil'.
The argument SECONDS need not be an integer. If it is a floating
point number, `sleep-for' waits for a fractional number of seconds.
Some systems support only a whole number of seconds; on these
systems, SECONDS is rounded down.
The optional argument MILLISEC specifies an additional waiting
period measured in milliseconds. This adds to the period
specified by SECONDS. If the system doesn't support waiting
fractions of a second, you get an error if you specify nonzero
MILLISEC.
Use `sleep-for' when you wish to guarantee a delay.
*Note Time of Day::, for functions to get the current time.
Quitting
========
Typing `C-g' while a Lisp function is running causes Emacs to "quit"
whatever it is doing. This means that control returns to the innermost
active command loop.
Typing `C-g' while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because `C-g' normally
runs the command `keyboard-quit', whose effect is to quit. However,
when `C-g' follows a prefix key, they combine to form an undefined key.
The effect is to cancel the prefix key as well as any prefix argument.
In the minibuffer, `C-g' has a different definition: it aborts out
of the minibuffer. This means, in effect, that it exits the minibuffer
and then quits. (Simply quitting would return to the command loop
_within_ the minibuffer.) The reason why `C-g' does not quit directly
when the command reader is reading input is so that its meaning can be
redefined in the minibuffer in this way. `C-g' following a prefix key
is not redefined in the minibuffer, and it has its normal effect of
canceling the prefix key and prefix argument. This too would not be
possible if `C-g' always quit directly.
When `C-g' does directly quit, it does so by setting the variable
`quit-flag' to `t'. Emacs checks this variable at appropriate times
and quits if it is not `nil'. Setting `quit-flag' non-`nil' in any way
thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only
at the special places that check `quit-flag'. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place,
quitting cannot make Emacs crash.
Certain functions such as `read-key-sequence' or `read-quoted-char'
prevent quitting entirely even though they wait for input. Instead of
quitting, `C-g' serves as the requested input. In the case of
`read-key-sequence', this serves to bring about the special behavior of
`C-g' in the command loop. In the case of `read-quoted-char', this is
so that `C-q' can be used to quote a `C-g'.
You can prevent quitting for a portion of a Lisp function by binding
the variable `inhibit-quit' to a non-`nil' value. Then, although `C-g'
still sets `quit-flag' to `t' as usual, the usual result of this--a
quit--is prevented. Eventually, `inhibit-quit' will become `nil'
again, such as when its binding is unwound at the end of a `let' form.
At that time, if `quit-flag' is still non-`nil', the requested quit
happens immediately. This behavior is ideal when you wish to make sure
that quitting does not happen within a "critical section" of the
program.
In some functions (such as `read-quoted-char'), `C-g' is handled in
a special way that does not involve quitting. This is done by reading
the input with `inhibit-quit' bound to `t', and setting `quit-flag' to
`nil' before `inhibit-quit' becomes `nil' again. This excerpt from the
definition of `read-quoted-char' shows how this is done; it also shows
that normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...DOCUMENTATION..."
(let ((message-log-max nil) done (first t) (code 0) char)
(while (not done)
(let ((inhibit-quit first)
...)
(and prompt (message "%s-" prompt))
(setq char (read-event))
(if inhibit-quit (setq quit-flag nil)))
...set the variable `code'...)
code))
- Variable: quit-flag
If this variable is non-`nil', then Emacs quits immediately, unless
`inhibit-quit' is non-`nil'. Typing `C-g' ordinarily sets
`quit-flag' non-`nil', regardless of `inhibit-quit'.
- Variable: inhibit-quit
This variable determines whether Emacs should quit when `quit-flag'
is set to a value other than `nil'. If `inhibit-quit' is
non-`nil', then `quit-flag' has no special effect.
- Command: keyboard-quit
This function signals the `quit' condition with `(signal 'quit
nil)'. This is the same thing that quitting does. (See `signal'
in *Note Errors::.)
You can specify a character other than `C-g' to use for quitting.
See the function `set-input-mode' in *Note Terminal Input::.
Prefix Command Arguments
========================
Most Emacs commands can use a "prefix argument", a number specified
before the command itself. (Don't confuse prefix arguments with prefix
keys.) The prefix argument is at all times represented by a value,
which may be `nil', meaning there is currently no prefix argument.
Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: "raw" and
"numeric". The editor command loop uses the raw representation
internally, and so do the Lisp variables that store the information, but
commands can request either representation.
Here are the possible values of a raw prefix argument:
* `nil', meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between `nil' and the
integer 1.
* An integer, which stands for itself.
* A list of one element, which is an integer. This form of prefix
argument results from one or a succession of `C-u''s with no
digits. The numeric value is the integer in the list, but some
commands make a distinction between such a list and an integer
alone.
* The symbol `-'. This indicates that `M--' or `C-u -' was typed,
without following digits. The equivalent numeric value is -1, but
some commands make a distinction between the integer -1 and the
symbol `-'.
We illustrate these possibilities by calling the following function
with various prefixes:
(defun display-prefix (arg)
"Display the value of the raw prefix arg."
(interactive "P")
(message "%s" arg))
Here are the results of calling `display-prefix' with various raw
prefix arguments:
M-x display-prefix -| nil
C-u M-x display-prefix -| (4)
C-u C-u M-x display-prefix -| (16)
C-u 3 M-x display-prefix -| 3
M-3 M-x display-prefix -| 3 ; (Same as `C-u 3'.)
C-u - M-x display-prefix -| -
M-- M-x display-prefix -| - ; (Same as `C-u -'.)
C-u - 7 M-x display-prefix -| -7
M-- 7 M-x display-prefix -| -7 ; (Same as `C-u -7'.)
Emacs uses two variables to store the prefix argument: `prefix-arg'
and `current-prefix-arg'. Commands such as `universal-argument' that
set up prefix arguments for other commands store them in `prefix-arg'.
In contrast, `current-prefix-arg' conveys the prefix argument to the
current command, so setting it has no effect on the prefix arguments
for future commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the `interactive' declaration.
(*Note Using Interactive::.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
`current-prefix-arg', but this is less clean.
- Function: prefix-numeric-value arg
This function returns the numeric meaning of a valid raw prefix
argument value, ARG. The argument may be a symbol, a number, or a
list. If it is `nil', the value 1 is returned; if it is `-', the
value -1 is returned; if it is a number, that number is returned;
if it is a list, the CAR of that list (which should be a number) is
returned.
- Variable: current-prefix-arg
This variable holds the raw prefix argument for the _current_
command. Commands may examine it directly, but the usual method
for accessing it is with `(interactive "P")'.
- Variable: prefix-arg
The value of this variable is the raw prefix argument for the
_next_ editing command. Commands such as `universal-argument'
that specify prefix arguments for the following command work by
setting this variable.
- Variable: last-prefix-arg
The raw prefix argument value used by the previous command.
The following commands exist to set up prefix arguments for the
following command. Do not call them for any other reason.
- Command: universal-argument
This command reads input and specifies a prefix argument for the
following command. Don't call this command yourself unless you
know what you are doing.
- Command: digit-argument arg
This command adds to the prefix argument for the following
command. The argument ARG is the raw prefix argument as it was
before this command; it is used to compute the updated prefix
argument. Don't call this command yourself unless you know what
you are doing.
- Command: negative-argument arg
This command adds to the numeric argument for the next command.
The argument ARG is the raw prefix argument as it was before this
command; its value is negated to form the new prefix argument.
Don't call this command yourself unless you know what you are
doing.
Recursive Editing
=================
The Emacs command loop is entered automatically when Emacs starts up.
This top-level invocation of the command loop never exits; it keeps
running as long as Emacs does. Lisp programs can also invoke the
command loop. Since this makes more than one activation of the command
loop, we call it "recursive editing". A recursive editing level has
the effect of suspending whatever command invoked it and permitting the
user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones
available in the top-level editing loop and defined in the keymaps.
Only a few special commands exit the recursive editing level; the others
return to the recursive editing level when they finish. (The special
commands for exiting are always available, but they do nothing when
recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error
handlers so that an error in a command run from the command loop will
not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a
few special wrinkles, such as enabling display of the minibuffer and the
minibuffer window, but fewer than you might suppose. Certain keys
behave differently in the minibuffer, but that is only because of the
minibuffer's local map; if you switch windows, you get the usual Emacs
commands.
To invoke a recursive editing level, call the function
`recursive-edit'. This function contains the command loop; it also
contains a call to `catch' with tag `exit', which makes it possible to
exit the recursive editing level by throwing to `exit' (*note Catch and
Throw::). If you throw a value other than `t', then `recursive-edit'
returns normally to the function that called it. The command `C-M-c'
(`exit-recursive-edit') does this. Throwing a `t' value causes
`recursive-edit' to quit, so that control returns to the command loop
one level up. This is called "aborting", and is done by `C-]'
(`abort-recursive-edit').
Most applications should not use recursive editing, except as part of
using the minibuffer. Usually it is more convenient for the user if you
change the major mode of the current buffer temporarily to a special
major mode, which should have a command to go back to the previous mode.
(The `e' command in Rmail uses this technique.) Or, if you wish to
give the user different text to edit "recursively", create and select a
new buffer in a special mode. In this mode, define a command to
complete the processing and go back to the previous buffer. (The `m'
command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
`debug' into a function definition as a sort of breakpoint, so that you
can look around when the function gets there. `debug' invokes a
recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type `C-r' in
`query-replace' or use `C-x q' (`kbd-macro-query').
- Function: recursive-edit
This function invokes the editor command loop. It is called
automatically by the initialization of Emacs, to let the user begin
editing. When called from a Lisp program, it enters a recursive
editing level.
In the following example, the function `simple-rec' first advances
point one word, then enters a recursive edit, printing out a
message in the echo area. The user can then do any editing
desired, and then type `C-M-c' to exit and continue executing
`simple-rec'.
(defun simple-rec ()
(forward-word 1)
(message "Recursive edit in progress")
(recursive-edit)
(forward-word 1))
=> simple-rec
(simple-rec)
=> nil
- Command: exit-recursive-edit
This function exits from the innermost recursive edit (including
minibuffer input). Its definition is effectively `(throw 'exit
nil)'.
- Command: abort-recursive-edit
This function aborts the command that requested the innermost
recursive edit (including minibuffer input), by signaling `quit'
after exiting the recursive edit. Its definition is effectively
`(throw 'exit t)'. *Note Quitting::.
- Command: top-level
This function exits all recursive editing levels; it does not
return a value, as it jumps completely out of any computation
directly back to the main command loop.
- Function: recursion-depth
This function returns the current depth of recursive edits. When
no recursive edit is active, it returns 0.
Disabling Commands
==================
"Disabling a command" marks the command as requiring user
confirmation before it can be executed. Disabling is used for commands
which might be confusing to beginning users, to prevent them from using
the commands by accident.
The low-level mechanism for disabling a command is to put a
non-`nil' `disabled' property on the Lisp symbol for the command.
These properties are normally set up by the user's init file (*note
Init File::) with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default (you can
remove them in your init file if you wish).
If the value of the `disabled' property is a string, the message
saying the command is disabled includes that string. For example:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
*Note Disabling: (emacs)Disabling, for the details on what happens
when a disabled command is invoked interactively. Disabling a command
has no effect on calling it as a function from Lisp programs.
- Command: enable-command command
Allow COMMAND to be executed without special confirmation from now
on, and (if the user confirms) alter the user's init file (*note
Init File::) so that this will apply to future sessions.
- Command: disable-command command
Require special confirmation to execute COMMAND from now on, and
(if the user confirms) alter the user's init file so that this
will apply to future sessions.
- Variable: disabled-command-hook
When the user invokes a disabled command interactively, this
normal hook is run instead of the disabled command. The hook
functions can use `this-command-keys' to determine what the user
typed to run the command, and thus find the command itself. *Note
Hooks::.
By default, `disabled-command-hook' contains a function that asks
the user whether to proceed.
Command History
===============
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
"complex command" is one for which the interactive argument reading
uses the minibuffer. This includes any `M-x' command, any `M-:'
command, and any command whose `interactive' specification reads an
argument from the minibuffer. Explicit use of the minibuffer during
the execution of the command itself does not cause the command to be
considered complex.
- Variable: command-history
This variable's value is a list of recent complex commands, each
represented as a form to evaluate. It continues to accumulate all
complex commands for the duration of the editing session, but when
it reaches the maximum size (specified by the variable
`history-length'), the oldest elements are deleted as new ones are
added.
command-history
=> ((switch-to-buffer "chistory.texi")
(describe-key "^X^[")
(visit-tags-table "~/emacs/src/")
(find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history
(*note Minibuffer History::), with one special twist: the elements are
expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands `repeat-complex-command', and
`list-command-history' are described in the user manual (*note
Repetition: (emacs)Repetition.). Within the minibuffer, the usual
minibuffer history commands are available.
Keyboard Macros
===============
A "keyboard macro" is a canned sequence of input events that can be
considered a command and made the definition of a key. The Lisp
representation of a keyboard macro is a string or vector containing the
events. Don't confuse keyboard macros with Lisp macros (*note
Macros::).
- Function: execute-kbd-macro kbdmacro &optional count
This function executes KBDMACRO as a sequence of events. If
KBDMACRO is a string or vector, then the events in it are executed
exactly as if they had been input by the user. The sequence is
_not_ expected to be a single key sequence; normally a keyboard
macro definition consists of several key sequences concatenated.
If KBDMACRO is a symbol, then its function definition is used in
place of KBDMACRO. If that is another symbol, this process
repeats. Eventually the result should be a string or vector. If
the result is not a symbol, string, or vector, an error is
signaled.
The argument COUNT is a repeat count; KBDMACRO is executed that
many times. If COUNT is omitted or `nil', KBDMACRO is executed
once. If it is 0, KBDMACRO is executed over and over until it
encounters an error or a failing search.
*Note Reading One Event::, for an example of using
`execute-kbd-macro'.
- Variable: executing-macro
This variable contains the string or vector that defines the
keyboard macro that is currently executing. It is `nil' if no
macro is currently executing. A command can test this variable so
as to behave differently when run from an executing macro. Do not
set this variable yourself.
- Variable: defining-kbd-macro
This variable indicates whether a keyboard macro is being defined.
A command can test this variable so as to behave differently
while a macro is being defined. The commands `start-kbd-macro' and
`end-kbd-macro' set this variable--do not set it yourself.
The variable is always local to the current terminal and cannot be
buffer-local. *Note Multiple Displays::.
- Variable: last-kbd-macro
This variable is the definition of the most recently defined
keyboard macro. Its value is a string or vector, or `nil'.
The variable is always local to the current terminal and cannot be
buffer-local. *Note Multiple Displays::.
- Variable: kbd-macro-termination-hook
This normal hook (*note Standard Hooks::) is run when a keyboard
macro terminates, regardless of what caused it to terminate
(reaching the macro end or an error which ended the macro
prematurely).
Keymaps
*******
The bindings between input events and commands are recorded in data
structures called "keymaps". Each binding in a keymap associates (or
"binds") an individual event type either to another keymap or to a
command. When an event type is bound to a keymap, that keymap is used
to look up the next input event; this continues until a command is
found. The whole process is called "key lookup".
Keymap Terminology
==================
A "keymap" is a table mapping event types to definitions (which can
be any Lisp objects, though only certain types are meaningful for
execution by the command loop). Given an event (or an event type) and a
keymap, Emacs can get the event's definition. Events include
characters, function keys, and mouse actions (*note Input Events::).
A sequence of input events that form a unit is called a "key
sequence", or "key" for short. A sequence of one event is always a key
sequence, and so are some multi-event sequences.
A keymap determines a binding or definition for any key sequence. If
the key sequence is a single event, its binding is the definition of the
event in the keymap. The binding of a key sequence of more than one
event is found by an iterative process: the binding of the first event
is found, and must be a keymap; then the second event's binding is found
in that keymap, and so on until all the events in the key sequence are
used up.
If the binding of a key sequence is a keymap, we call the key
sequence a "prefix key". Otherwise, we call it a "complete key"
(because no more events can be added to it). If the binding is `nil',
we call the key "undefined". Examples of prefix keys are `C-c', `C-x',
and `C-x 4'. Examples of defined complete keys are `X', <RET>, and
`C-x 4 C-f'. Examples of undefined complete keys are `C-x C-g', and
`C-c 3'. *Note Prefix Keys::, for more details.
The rule for finding the binding of a key sequence assumes that the
intermediate bindings (found for the events before the last) are all
keymaps; if this is not so, the sequence of events does not form a
unit--it is not really one key sequence. In other words, removing one
or more events from the end of any valid key sequence must always yield
a prefix key. For example, `C-f C-n' is not a key sequence; `C-f' is
not a prefix key, so a longer sequence starting with `C-f' cannot be a
key sequence.
The set of possible multi-event key sequences depends on the bindings
for prefix keys; therefore, it can be different for different keymaps,
and can change when bindings are changed. However, a one-event sequence
is always a key sequence, because it does not depend on any prefix keys
for its well-formedness.
At any time, several primary keymaps are "active"--that is, in use
for finding key bindings. These are the "global map", which is shared
by all buffers; the "local keymap", which is usually associated with a
specific major mode; and zero or more "minor mode keymaps", which
belong to currently enabled minor modes. (Not all minor modes have
keymaps.) The local keymap bindings shadow (i.e., take precedence
over) the corresponding global bindings. The minor mode keymaps shadow
both local and global keymaps. *Note Active Keymaps::, for details.
Format of Keymaps
=================
A keymap is a list whose CAR is the symbol `keymap'. The remaining
elements of the list define the key bindings of the keymap. Use the
function `keymapp' (see below) to test whether an object is a keymap.
Several kinds of elements may appear in a keymap, after the symbol
`keymap' that begins it:
`(TYPE . BINDING)'
This specifies one binding, for events of type TYPE. Each
ordinary binding applies to events of a particular "event type",
which is always a character or a symbol. *Note Classifying
Events::.
`(t . BINDING)'
This specifies a "default key binding"; any event not bound by
other elements of the keymap is given BINDING as its binding.
Default bindings allow a keymap to bind all possible event types
without having to enumerate all of them. A keymap that has a
default binding completely masks any lower-precedence keymap.
`VECTOR'
If an element of a keymap is a vector, the vector counts as
bindings for all the ASCII characters, codes 0 through 127; vector
element N is the binding for the character with code N. This is a
compact way to record lots of bindings. A keymap with such a
vector is called a "full keymap". Other keymaps are called "sparse
keymaps".
When a keymap contains a vector, it always defines a binding for
each ASCII character, even if the vector contains `nil' for that
character. Such a binding of `nil' overrides any default key
binding in the keymap, for ASCII characters. However, default
bindings are still meaningful for events other than ASCII
characters. A binding of `nil' does _not_ override
lower-precedence keymaps; thus, if the local map gives a binding of
`nil', Emacs uses the binding from the global map.
`STRING'
Aside from bindings, a keymap can also have a string as an element.
This is called the "overall prompt string" and makes it possible to
use the keymap as a menu. *Note Defining Menus::.
Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for purposes of key lookup as
sequences of two characters, the first of which is <ESC> (or whatever
is currently the value of `meta-prefix-char'). Thus, the key `M-a' is
internally represented as `<ESC> a', and its global binding is found at
the slot for `a' in `esc-map' (*note Prefix Keys::).
This conversion applies only to characters, not to function keys or
other input events; thus, `M-<end>' has nothing to do with `<ESC>
<end>'.
Here as an example is the local keymap for Lisp mode, a sparse
keymap. It defines bindings for <DEL> and <TAB>, plus `C-c C-l',
`M-C-q', and `M-C-x'.
lisp-mode-map
=>
(keymap
;; <TAB>
(9 . lisp-indent-line)
;; <DEL>
(127 . backward-delete-char-untabify)
(3 keymap
;; C-c C-l
(12 . run-lisp))
(27 keymap
;; `M-C-q', treated as `<ESC> C-q'
(17 . indent-sexp)
;; `M-C-x', treated as `<ESC> C-x'
(24 . lisp-send-defun)))
- Function: keymapp object
This function returns `t' if OBJECT is a keymap, `nil' otherwise.
More precisely, this function tests for a list whose CAR is
`keymap'.
(keymapp '(keymap))
=> t
(keymapp (current-global-map))
=> t
Creating Keymaps
================
Here we describe the functions for creating keymaps.
- Function: make-keymap &optional prompt
This function creates and returns a new full keymap. That keymap
contains a char-table (*note Char-Tables::) with 384 slots: the
first 128 slots are for defining all the ASCII characters, the
next 128 slots are for 8-bit European characters, and each one of
the final 128 slots is for one character set of non-ASCII
characters supported by Emacs. The new keymap initially binds all
these characters to `nil', and does not bind any other kind of
event.
(make-keymap)
=> (keymap [nil nil nil ... nil nil])
If you specify PROMPT, that becomes the overall prompt string for
the keymap. The prompt string should be provided for menu keymaps
(*note Defining Menus::).
- Function: make-sparse-keymap &optional prompt
This function creates and returns a new sparse keymap with no
entries. The new keymap does not contain a char-table, unlike
`make-keymap', and does not bind any events. The argument PROMPT
specifies a prompt string, as in `make-keymap'.
(make-sparse-keymap)
=> (keymap)
- Function: copy-keymap keymap
This function returns a copy of KEYMAP. Any keymaps that appear
directly as bindings in KEYMAP are also copied recursively, and so
on to any number of levels. However, recursive copying does not
take place when the definition of a character is a symbol whose
function definition is a keymap; the same symbol appears in the
new copy.
(setq map (copy-keymap (current-local-map)))
=> (keymap
;; (This implements meta characters.)
(27 keymap
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
(eq map (current-local-map))
=> nil
(equal map (current-local-map))
=> t
Inheritance and Keymaps
=======================
A keymap can inherit the bindings of another keymap, which we call
the "parent keymap". Such a keymap looks like this:
(keymap BINDINGS... . PARENT-KEYMAP)
The effect is that this keymap inherits all the bindings of
PARENT-KEYMAP, whatever they may be at the time a key is looked up, but
can add to them or override them with BINDINGS.
If you change the bindings in PARENT-KEYMAP using `define-key' or
other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by BINDINGS. The converse is not
true: if you use `define-key' to change the inheriting keymap, that
affects BINDINGS, but has no effect on PARENT-KEYMAP.
The proper way to construct a keymap with a parent is to use
`set-keymap-parent'; if you have code that directly constructs a keymap
with a parent, please convert the program to use `set-keymap-parent'
instead.
- Function: keymap-parent keymap
This returns the parent keymap of KEYMAP. If KEYMAP has no
parent, `keymap-parent' returns `nil'.
- Function: set-keymap-parent keymap parent
This sets the parent keymap of KEYMAP to PARENT, and returns
PARENT. If PARENT is `nil', this function gives KEYMAP no parent
at all.
If KEYMAP has submaps (bindings for prefix keys), they too receive
new parent keymaps that reflect what PARENT specifies for those
prefix keys.
Here is an example showing how to make a keymap that inherits from
`text-mode-map':
(let ((map (make-sparse-keymap)))
(set-keymap-parent map text-mode-map)
map)
Prefix Keys
===========
A "prefix key" is a key sequence whose binding is a keymap. The
keymap defines what to do with key sequences that extend the prefix key.
For example, `C-x' is a prefix key, and it uses a keymap that is also
stored in the variable `ctl-x-map'. This keymap defines bindings for
key sequences starting with `C-x'.
Some of the standard Emacs prefix keys use keymaps that are also
found in Lisp variables:
* `esc-map' is the global keymap for the <ESC> prefix key. Thus,
the global definitions of all meta characters are actually found
here. This map is also the function definition of `ESC-prefix'.
* `help-map' is the global keymap for the `C-h' prefix key.
* `mode-specific-map' is the global keymap for the prefix key `C-c'.
This map is actually global, not mode-specific, but its name
provides useful information about `C-c' in the output of `C-h b'
(`display-bindings'), since the main use of this prefix key is for
mode-specific bindings.
* `ctl-x-map' is the global keymap used for the `C-x' prefix key.
This map is found via the function cell of the symbol
`Control-X-prefix'.
* `mule-keymap' is the global keymap used for the `C-x <RET>' prefix
key.
* `ctl-x-4-map' is the global keymap used for the `C-x 4' prefix key.
* `ctl-x-5-map' is the global keymap used for the `C-x 5' prefix key.
* `2C-mode-map' is the global keymap used for the `C-x 6' prefix key.
* `vc-prefix-map' is the global keymap used for the `C-x v' prefix
key.
* `facemenu-keymap' is the global keymap used for the `M-g' prefix
key.
* The other Emacs prefix keys are `C-x @', `C-x a i', `C-x <ESC>'
and `<ESC> <ESC>'. They use keymaps that have no special names.
The keymap binding of a prefix key is used for looking up the event
that follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves
as a name for the prefix key.) Thus, the binding of `C-x' is the
symbol `Control-X-prefix', whose function cell holds the keymap for
`C-x' commands. (The same keymap is also the value of `ctl-x-map'.)
Prefix key definitions can appear in any active keymap. The
definitions of `C-c', `C-x', `C-h' and <ESC> as prefix keys appear in
the global map, so these prefix keys are always available. Major and
minor modes can redefine a key as a prefix by putting a prefix key
definition for it in the local map or the minor mode's map. *Note
Active Keymaps::.
If a key is defined as a prefix in more than one active map, then its
various definitions are in effect merged: the commands defined in the
minor mode keymaps come first, followed by those in the local map's
prefix definition, and then by those from the global map.
In the following example, we make `C-p' a prefix key in the local
keymap, in such a way that `C-p' is identical to `C-x'. Then the
binding for `C-p C-f' is the function `find-file', just like `C-x C-f'.
The key sequence `C-p 6' is not found in any active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
- Function: define-prefix-command symbol &optional mapvar prompt
This function prepares SYMBOL for use as a prefix key's binding:
it creates a sparse keymap and stores it as SYMBOL's function
definition. Subsequently binding a key sequence to SYMBOL will
make that key sequence into a prefix key. The return value is
`symbol'.
This function also sets SYMBOL as a variable, with the keymap as
its value. But if MAPVAR is non-`nil', it sets MAPVAR as a
variable instead.
If PROMPT is non-`nil', that becomes the overall prompt string for
the keymap. The prompt string should be given for menu keymaps
(*note Defining Menus::).
Active Keymaps
==============
Emacs normally contains many keymaps; at any given time, just a few
of them are "active" in that they participate in the interpretation of
user input. These are the global keymap, the current buffer's local
keymap, and the keymaps of any enabled minor modes.
The "global keymap" holds the bindings of keys that are defined
regardless of the current buffer, such as `C-f'. The variable
`global-map' holds this keymap, which is always active.
Each buffer may have another keymap, its "local keymap", which may
contain new or overriding definitions for keys. The current buffer's
local keymap is always active except when `overriding-local-map'
overrides it. Text properties can specify an alternative local map for
certain parts of the buffer; see *Note Special Properties::.
Each minor mode can have a keymap; if it does, the keymap is active
when the minor mode is enabled.
The variable `overriding-local-map', if non-`nil', specifies another
local keymap that overrides the buffer's local map and all the minor
mode keymaps.
All the active keymaps are used together to determine what command to
execute when a key is entered. Emacs searches these maps one by one, in
order of decreasing precedence, until it finds a binding in one of the
maps. The procedure for searching a single keymap is called "key
lookup"; see *Note Key Lookup::.
Normally, Emacs first searches for the key in the minor mode maps, in
the order specified by `minor-mode-map-alist'; if they do not supply a
binding for the key, Emacs searches the local map; if that too has no
binding, Emacs then searches the global map. However, if
`overriding-local-map' is non-`nil', Emacs searches that map first,
before the global map.
Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode. A
change to the local keymap of a buffer (using `local-set-key', for
example) is seen also in the other buffers that share that keymap.
The local keymaps that are used for Lisp mode and some other major
modes exist even if they have not yet been used. These local maps are
the values of variables such as `lisp-mode-map'. For most major modes,
which are less frequently used, the local keymap is constructed only
when the mode is used for the first time in a session.
The minibuffer has local keymaps, too; they contain various
completion and exit commands. *Note Intro to Minibuffers::.
Emacs has other keymaps that are used in a different way--translating
events within `read-key-sequence'. *Note Translating Input::.
*Note Standard Keymaps::, for a list of standard keymaps.
- Variable: global-map
This variable contains the default global keymap that maps Emacs
keyboard input to commands. The global keymap is normally this
keymap. The default global keymap is a full keymap that binds
`self-insert-command' to all of the printing characters.
It is normal practice to change the bindings in the global map,
but you should not assign this variable any value other than the
keymap it starts out with.
- Function: current-global-map
This function returns the current global keymap. This is the same
as the value of `global-map' unless you change one or the other.
(current-global-map)
=> (keymap [set-mark-command beginning-of-line ...
delete-backward-char])
- Function: current-local-map
This function returns the current buffer's local keymap, or `nil'
if it has none. In the following example, the keymap for the
`*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap
in which the entry for <ESC>, ASCII code 27, is another sparse
keymap.
(current-local-map)
=> (keymap
(10 . eval-print-last-sexp)
(9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap
(24 . eval-defun)
(17 . indent-sexp)))
- Function: current-minor-mode-maps
This function returns a list of the keymaps of currently enabled
minor modes.
- Function: use-global-map keymap
This function makes KEYMAP the new current global keymap. It
returns `nil'.
It is very unusual to change the global keymap.
- Function: use-local-map keymap
This function makes KEYMAP the new local keymap of the current
buffer. If KEYMAP is `nil', then the buffer has no local keymap.
`use-local-map' returns `nil'. Most major mode commands use this
function.
- Variable: minor-mode-map-alist
This variable is an alist describing keymaps that may or may not be
active according to the values of certain variables. Its elements
look like this:
(VARIABLE . KEYMAP)
The keymap KEYMAP is active whenever VARIABLE has a non-`nil'
value. Typically VARIABLE is the variable that enables or
disables a minor mode. *Note Keymaps and Minor Modes::.
Note that elements of `minor-mode-map-alist' do not have the same
structure as elements of `minor-mode-alist'. The map must be the
CDR of the element; a list with the map as the second element will
not do. The CDR can be either a keymap (a list) or a symbol whose
function definition is a keymap.
When more than one minor mode keymap is active, their order of
priority is the order of `minor-mode-map-alist'. But you should
design minor modes so that they don't interfere with each other.
If you do this properly, the order will not matter.
See *Note Keymaps and Minor Modes::, for more information about
minor modes. See also `minor-mode-key-binding' (*note Functions
for Key Lookup::).
- Variable: minor-mode-overriding-map-alist
This variable allows major modes to override the key bindings for
particular minor modes. The elements of this alist look like the
elements of `minor-mode-map-alist': `(VARIABLE . KEYMAP)'.
If a variable appears as an element of
`minor-mode-overriding-map-alist', the map specified by that
element totally replaces any map specified for the same variable in
`minor-mode-map-alist'.
`minor-mode-overriding-map-alist' is automatically buffer-local in
all buffers.
- Variable: overriding-local-map
If non-`nil', this variable holds a keymap to use instead of the
buffer's local keymap and instead of all the minor mode keymaps.
This keymap, if any, overrides all other maps that would have been
active, except for the current global map.
- Variable: overriding-terminal-local-map
If non-`nil', this variable holds a keymap to use instead of
`overriding-local-map', the buffer's local keymap and all the minor
mode keymaps.
This variable is always local to the current terminal and cannot be
buffer-local. *Note Multiple Displays::. It is used to implement
incremental search mode.
- Variable: overriding-local-map-menu-flag
If this variable is non-`nil', the value of `overriding-local-map'
or `overriding-terminal-local-map' can affect the display of the
menu bar. The default value is `nil', so those map variables have
no effect on the menu bar.
Note that these two map variables do affect the execution of key
sequences entered using the menu bar, even if they do not affect
the menu bar display. So if a menu bar key sequence comes in, you
should clear the variables before looking up and executing that
key sequence. Modes that use the variables would typically do
this anyway; normally they respond to events that they do not
handle by "unreading" them and exiting.
- Variable: special-event-map
This variable holds a keymap for special events. If an event type
has a binding in this keymap, then it is special, and the binding
for the event is run directly by `read-event'. *Note Special
Events::.
Key Lookup
==========
"Key lookup" is the process of finding the binding of a key sequence
from a given keymap. Actual execution of the binding is not part of
key lookup.
Key lookup uses just the event type of each event in the key
sequence; the rest of the event is ignored. In fact, a key sequence
used for key lookup may designate mouse events with just their types
(symbols) instead of with entire mouse events (lists). *Note Input
Events::. Such a "key-sequence" is insufficient for `command-execute'
to run, but it is sufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup
processes the events sequentially: the binding of the first event is
found, and must be a keymap; then the second event's binding is found in
that keymap, and so on until all the events in the key sequence are used
up. (The binding thus found for the last event may or may not be a
keymap.) Thus, the process of key lookup is defined in terms of a
simpler process for looking up a single event in a keymap. How that is
done depends on the type of object associated with the event in that
keymap.
Let's use the term "keymap entry" to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in menu key bindings, because
`lookup-key' and other key lookup functions don't include them in the
returned value.) While any Lisp object may be stored in a keymap as a
keymap entry, not all make sense for key lookup. Here is a table of
the meaningful kinds of keymap entries:
`nil'
`nil' means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at
all, and has no default binding, that is equivalent to a binding
of `nil' for that event type.
COMMAND
The events used so far in the lookup form a complete key, and
COMMAND is its binding. *Note What Is a Function::.
ARRAY
The array (either a string or a vector) is a keyboard macro. The
events used so far in the lookup form a complete key, and the
array is its binding. See *Note Keyboard Macros::, for more
information.
KEYMAP
The events used so far in the lookup form a prefix key. The next
event of the key sequence is looked up in KEYMAP.
LIST
The meaning of a list depends on the types of the elements of the
list.
* If the CAR of LIST is the symbol `keymap', then the list is a
keymap, and is treated as a keymap (see above).
* If the CAR of LIST is `lambda', then the list is a lambda
expression. This is presumed to be a command, and is treated
as such (see above).
* If the CAR of LIST is a keymap and the CDR is an event type,
then this is an "indirect entry":
(OTHERMAP . OTHERTYPE)
When key lookup encounters an indirect entry, it looks up
instead the binding of OTHERTYPE in OTHERMAP and uses that.
This feature permits you to define one key as an alias for
another key. For example, an entry whose CAR is the keymap
called `esc-map' and whose CDR is 32 (the code for <SPC>)
means, "Use the global binding of `Meta-<SPC>', whatever that
may be."
SYMBOL
The function definition of SYMBOL is used in place of SYMBOL. If
that too is a symbol, then this process is repeated, any number of
times. Ultimately this should lead to an object that is a keymap,
a command, or a keyboard macro. A list is allowed if it is a
keymap or a command, but indirect entries are not understood when
found via symbols.
Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string, or vector as
its function definition is invalid as a function. It is, however,
valid as a key binding. If the definition is a keyboard macro,
then the symbol is also valid as an argument to `command-execute'
(*note Interactive Call::).
The symbol `undefined' is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and
its binding is the command `undefined'; but that command does the
same thing that is done automatically for an undefined key: it
rings the bell (by calling `ding') but does not signal an error.
`undefined' is used in local keymaps to override a global key
binding and make the key "undefined" locally. A local binding of
`nil' would fail to do this because it would not override the
global binding.
ANYTHING ELSE
If any other type of object is found, the events used so far in the
lookup form a complete key, and the object is its binding, but the
binding is not executable as a command.
In short, a keymap entry may be a keymap, a command, a keyboard
macro, a symbol that leads to one of them, or an indirection or `nil'.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of `emacs-lisp-mode-map'. Note that 9 is the code for <TAB>, 127 for
<DEL>, 27 for <ESC>, 17 for `C-q' and 24 for `C-x'.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Functions for Key Lookup
========================
Here are the functions and variables pertaining to key lookup.
- Function: lookup-key keymap key &optional accept-defaults
This function returns the definition of KEY in KEYMAP. All the
other functions described in this chapter that look up keys use
`lookup-key'. Here are examples:
(lookup-key (current-global-map) "\C-x\C-f")
=> find-file
(lookup-key (current-global-map) "\C-x\C-f12345")
=> 2
If the string or vector KEY is not a valid key sequence according
to the prefix keys specified in KEYMAP, it must be "too long" and
have extra events at the end that do not fit into a single key
sequence. Then the value is a number, the number of events at the
front of KEY that compose a complete key.
If ACCEPT-DEFAULTS is non-`nil', then `lookup-key' considers
default bindings as well as bindings for the specific events in
KEY. Otherwise, `lookup-key' reports only bindings for the
specific sequence KEY, ignoring default bindings except when you
explicitly ask about them. (To do this, supply `t' as an element
of KEY; see *Note Format of Keymaps::.)
If KEY contains a meta character (not a function key), that
character is implicitly replaced by a two-character sequence: the
value of `meta-prefix-char', followed by the corresponding non-meta
character. Thus, the first example below is handled by conversion
into the second example.
(lookup-key (current-global-map) "\M-f")
=> forward-word
(lookup-key (current-global-map) "\ef")
=> forward-word
Unlike `read-key-sequence', this function does not modify the
specified events in ways that discard information (*note Key
Sequence Input::). In particular, it does not convert letters to
lower case and it does not change drag events to clicks.
- Command: undefined
Used in keymaps to undefine keys. It calls `ding', but does not
cause an error.
- Function: key-binding key &optional accept-defaults
This function returns the binding for KEY in the current keymaps,
trying all the active keymaps. The result is `nil' if KEY is
undefined in the keymaps.
The argument ACCEPT-DEFAULTS controls checking for default
bindings, as in `lookup-key' (above).
An error is signaled if KEY is not a string or a vector.
(key-binding "\C-x\C-f")
=> find-file
- Function: local-key-binding key &optional accept-defaults
This function returns the binding for KEY in the current local
keymap, or `nil' if it is undefined there.
The argument ACCEPT-DEFAULTS controls checking for default
bindings, as in `lookup-key' (above).
- Function: global-key-binding key &optional accept-defaults
This function returns the binding for command KEY in the current
global keymap, or `nil' if it is undefined there.
The argument ACCEPT-DEFAULTS controls checking for default
bindings, as in `lookup-key' (above).
- Function: minor-mode-key-binding key &optional accept-defaults
This function returns a list of all the active minor mode bindings
of KEY. More precisely, it returns an alist of pairs `(MODENAME .
BINDING)', where MODENAME is the variable that enables the minor
mode, and BINDING is KEY's binding in that mode. If KEY has no
minor-mode bindings, the value is `nil'.
If the first binding found is not a prefix definition (a keymap or
a symbol defined as a keymap), all subsequent bindings from other
minor modes are omitted, since they would be completely shadowed.
Similarly, the list omits non-prefix bindings that follow prefix
bindings.
The argument ACCEPT-DEFAULTS controls checking for default
bindings, as in `lookup-key' (above).
- Variable: meta-prefix-char
This variable is the meta-prefix character code. It is used when
translating a meta character to a two-character sequence so it can
be looked up in a keymap. For useful results, the value should be
a prefix event (*note Prefix Keys::). The default value is 27,
which is the ASCII code for <ESC>.
As long as the value of `meta-prefix-char' remains 27, key lookup
translates `M-b' into `<ESC> b', which is normally defined as the
`backward-word' command. However, if you were to set
`meta-prefix-char' to 24, the code for `C-x', then Emacs will
translate `M-b' into `C-x b', whose standard binding is the
`switch-to-buffer' command. (Don't actually do this!) Here is an
illustration of what would happen:
meta-prefix-char ; The default value.
=> 27
(key-binding "\M-b")
=> backward-word
?\C-x ; The print representation
=> 24 ; of a character.
(setq meta-prefix-char 24)
=> 24
(key-binding "\M-b")
=> switch-to-buffer ; Now, typing `M-b' is
; like typing `C-x b'.
(setq meta-prefix-char 27) ; Avoid confusion!
=> 27 ; Restore the default value!
This translation of one event into two happens only for
characters, not for other kinds of input events. Thus, `M-<F1>',
a function key, is not converted into `<ESC> <F1>'.
Changing Key Bindings
=====================
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The `global-set-key' and `local-set-key' functions are convenient
interfaces for these operations (*note Key Binding Commands::). You
can also use `define-key', a more general function; then you must
specify explicitly the map to change.
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (*note String Type::).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character. Thus, the string `"\M-x"' is read as containing a single
`M-x', `"\C-f"' is read as containing a single `C-f', and `"\M-\C-x"'
and `"\C-\M-x"' are both read as containing a single `C-M-x'. You can
also use this escape syntax in vectors, as well as others that aren't
allowed in strings; one example is `[?\C-\H-x home]'. *Note Character
Type::.
The key definition and lookup functions accept an alternate syntax
for event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name). For example, `(control ?a)' is equivalent to `?\C-a' and
`(hyper control left)' is equivalent to `C-H-left'. One advantage of
such lists is that the precise numeric codes for the modifier bits
don't appear in compiled files.
For the functions below, an error is signaled if KEYMAP is not a
keymap or if KEY is not a string or vector representing a key sequence.
You can use event types (symbols) as shorthand for events that are
lists.
- Function: define-key keymap key binding
This function sets the binding for KEY in KEYMAP. (If KEY is more
than one event long, the change is actually made in another keymap
reached from KEYMAP.) The argument BINDING can be any Lisp
object, but only certain types are meaningful. (For a list of
meaningful types, see *Note Key Lookup::.) The value returned by
`define-key' is BINDING.
Every prefix of KEY must be a prefix key (i.e., bound to a keymap)
or undefined; otherwise an error is signaled. If some prefix of
KEY is undefined, then `define-key' defines it as a prefix key so
that the rest of KEY can be defined as specified.
If there was previously no binding for KEY in KEYMAP, the new
binding is added at the beginning of KEYMAP. The order of
bindings in a keymap makes no difference in most cases, but it does
matter for menu keymaps (*note Menu Keymaps::).
Here is an example that creates a sparse keymap and makes a number of
bindings in it:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for `C-x' and bind `f' in that.
(define-key map "\C-xf" 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind `C-p' to the `ctl-x-map'.
(define-key map "\C-p" ctl-x-map)
;; `ctl-x-map'
=> [nil ... find-file ... backward-kill-sentence]
;; Bind `C-f' to `foo' in the `ctl-x-map'.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
map
=> (keymap ; Note `foo' in `ctl-x-map'.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for `C-p C-f' actually works by
changing an entry in `ctl-x-map', and this has the effect of changing
the bindings of both `C-p C-f' and `C-x C-f' in the default global map.
- Function: substitute-key-definition olddef newdef keymap &optional
oldmap
This function replaces OLDDEF with NEWDEF for any keys in KEYMAP
that were bound to OLDDEF. In other words, OLDDEF is replaced
with NEWDEF wherever it appears. The function returns `nil'.
For example, this redefines `C-x C-f', if you do it in an Emacs
with standard bindings:
(substitute-key-definition
'find-file 'find-file-read-only (current-global-map))
If OLDMAP is non-`nil', that changes the behavior of
`substitute-key-definition': the bindings in OLDMAP determine
which keys to rebind. The rebindings still happen in KEYMAP, not
in OLDMAP. Thus, you can change one map under the control of the
bindings in another. For example,
(substitute-key-definition
'delete-backward-char 'my-funny-delete
my-map global-map)
puts the special deletion command in `my-map' for whichever keys
are globally bound to the standard deletion command.
Here is an example showing a keymap before and after substitution:
(setq map '(keymap
(?1 . olddef-1)
(?2 . olddef-2)
(?3 . olddef-1)))
=> (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
(substitute-key-definition 'olddef-1 'newdef map)
=> nil
map
=> (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
- Function: suppress-keymap keymap &optional nodigits
This function changes the contents of the full keymap KEYMAP by
making all the printing characters undefined. More precisely, it
binds them to the command `undefined'. This makes ordinary
insertion of text impossible. `suppress-keymap' returns `nil'.
If NODIGITS is `nil', then `suppress-keymap' defines digits to run
`digit-argument', and `-' to run `negative-argument'. Otherwise
it makes them undefined like the rest of the printing characters.
The `suppress-keymap' function does not make it impossible to
modify a buffer, as it does not suppress commands such as `yank'
and `quoted-insert'. To prevent any modification of a buffer, make
it read-only (*note Read Only Buffers::).
Since this function modifies KEYMAP, you would normally use it on
a newly created keymap. Operating on an existing keymap that is
used for some other purpose is likely to cause trouble; for
example, suppressing `global-map' would make it impossible to use
most of Emacs.
Most often, `suppress-keymap' is used to initialize local keymaps
of modes such as Rmail and Dired where insertion of text is not
desirable and the buffer is read-only. Here is an example taken
from the file `emacs/lisp/dired.el', showing how the local keymap
for Dired mode is set up:
(setq dired-mode-map (make-keymap))
(suppress-keymap dired-mode-map)
(define-key dired-mode-map "r" 'dired-rename-file)
(define-key dired-mode-map "\C-d" 'dired-flag-file-deleted)
(define-key dired-mode-map "d" 'dired-flag-file-deleted)
(define-key dired-mode-map "v" 'dired-view-file)
(define-key dired-mode-map "e" 'dired-find-file)
(define-key dired-mode-map "f" 'dired-find-file)
...
Commands for Binding Keys
=========================
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling `define-key'.
People often use `global-set-key' in their init files (*note Init
File::) for simple customization. For example,
(global-set-key "\C-x\C-\\" 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
or
(global-set-key [(control ?x) (control ?\\)] 'next-line)
redefines `C-x C-\' to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, typed with the Meta key, to
set point where you click.
Be careful when using non-ASCII text characters in Lisp
specifications of keys to bind. If these are read as multibyte text, as
they usually will be in a Lisp file (*note Loading Non-ASCII::), you
must type the keys as multibyte too. For instance, if you use this:
(global-set-key "o"" 'my-function) ; bind o-umlaut
or
(global-set-key ?o" 'my-function) ; bind o-umlaut
and your language environment is multibyte Latin-1, these commands
actually bind the multibyte character with code 2294, not the unibyte
Latin-1 character with code 246 (`M-v'). In order to use this binding,
you need to enter the multibyte Latin-1 character as keyboard input.
One way to do this is by using an appropriate input method (*note Input
Methods: (emacs)Input Methods.).
If you want to use a unibyte character in the key binding, you can
construct the key sequence string using `multibyte-char-to-unibyte' or
`string-make-unibyte' (*note Converting Representations::).
- Command: global-set-key key definition
This function sets the binding of KEY in the current global map to
DEFINITION.
(global-set-key KEY DEFINITION)
==
(define-key (current-global-map) KEY DEFINITION)
- Command: global-unset-key key
This function removes the binding of KEY from the current global
map.
One use of this function is in preparation for defining a longer
key that uses KEY as a prefix--which would not be allowed if KEY
has a non-prefix binding. For example:
(global-unset-key "\C-l")
=> nil
(global-set-key "\C-l\C-l" 'redraw-display)
=> nil
This function is implemented simply using `define-key':
(global-unset-key KEY)
==
(define-key (current-global-map) KEY nil)
- Command: local-set-key key definition
This function sets the binding of KEY in the current local keymap
to DEFINITION.
(local-set-key KEY DEFINITION)
==
(define-key (current-local-map) KEY DEFINITION)
- Command: local-unset-key key
This function removes the binding of KEY from the current local
map.
(local-unset-key KEY)
==
(define-key (current-local-map) KEY nil)
Scanning Keymaps
================
This section describes functions used to scan all the current keymaps
for the sake of printing help information.
- Function: accessible-keymaps keymap &optional prefix
This function returns a list of all the keymaps that can be
reached (via zero or more prefix keys) from KEYMAP. The value is
an association list with elements of the form `(KEY . MAP)',
where KEY is a prefix key whose definition in KEYMAP is MAP.
The elements of the alist are ordered so that the KEY increases in
length. The first element is always `("" . KEYMAP)', because the
specified keymap is accessible from itself with a prefix of no
events.
If PREFIX is given, it should be a prefix key sequence; then
`accessible-keymaps' includes only the submaps whose prefixes start
with PREFIX. These elements look just as they do in the value of
`(accessible-keymaps)'; the only difference is that some elements
are omitted.
In the example below, the returned alist indicates that the key
<ESC>, which is displayed as `^[', is a prefix key whose
definition is the sparse keymap `(keymap (83 . center-paragraph)
(115 . foo))'.
(accessible-keymaps (current-local-map))
=>(("" keymap
(27 keymap ; Note this keymap for <ESC> is repeated below.
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
("^[" keymap
(83 . center-paragraph)
(115 . foo)))
In the following example, `C-h' is a prefix key that uses a sparse
keymap starting with `(keymap (118 . describe-variable)...)'.
Another prefix, `C-x 4', uses a keymap which is also the value of
the variable `ctl-x-4-map'. The event `mode-line' is one of
several dummy events used as prefixes for mouse actions in special
parts of a window.
(accessible-keymaps (current-global-map))
=> (("" keymap [set-mark-command beginning-of-line ...
delete-backward-char])
("^H" keymap (118 . describe-variable) ...
(8 . help-for-help))
("^X" keymap [x-flush-mouse-queue ...
backward-kill-sentence])
("^[" keymap [mark-sexp backward-sexp ...
backward-kill-word])
("^X4" keymap (15 . display-buffer) ...)
([mode-line] keymap
(S-mouse-2 . mouse-split-window-horizontally) ...))
These are not all the keymaps you would see in actuality.
- Function: where-is-internal command &optional keymap firstonly
noindirect
This function is a subroutine used by the `where-is' command
(*note Help: (emacs)Help.). It returns a list of key sequences
(of any length) that are bound to COMMAND in a set of keymaps.
The argument COMMAND can be any object; it is compared with all
keymap entries using `eq'.
If KEYMAP is `nil', then the maps used are the current active
keymaps, disregarding `overriding-local-map' (that is, pretending
its value is `nil'). If KEYMAP is non-`nil', then the maps
searched are KEYMAP and the global keymap. If KEYMAP is a list of
keymaps, only those keymaps are searched.
Usually it's best to use `overriding-local-map' as the expression
for KEYMAP. Then `where-is-internal' searches precisely the
keymaps that are active. To search only the global map, pass
`(keymap)' (an empty keymap) as KEYMAP.
If FIRSTONLY is `non-ascii', then the value is a single string
representing the first key sequence found, rather than a list of
all possible key sequences. If FIRSTONLY is `t', then the value
is the first key sequence, except that key sequences consisting
entirely of ASCII characters (or meta variants of ASCII
characters) are preferred to all other key sequences.
If NOINDIRECT is non-`nil', `where-is-internal' doesn't follow
indirect keymap bindings. This makes it possible to search for an
indirect definition itself.
(where-is-internal 'describe-function)
=> ("\^hf" "\^hd")
- Command: describe-bindings &optional prefix
This function creates a listing of all current key bindings, and
displays it in a buffer named `*Help*'. The text is grouped by
modes--minor modes first, then the major mode, then global
bindings.
If PREFIX is non-`nil', it should be a prefix key; then the
listing includes only keys that start with PREFIX.
The listing describes meta characters as <ESC> followed by the
corresponding non-meta character.
When several characters with consecutive ASCII codes have the same
definition, they are shown together, as `FIRSTCHAR..LASTCHAR'. In
this instance, you need to know the ASCII codes to understand
which characters this means. For example, in the default global
map, the characters `<SPC> .. ~' are described by a single line.
<SPC> is ASCII 32, `~' is ASCII 126, and the characters between
them include all the normal printing characters, (e.g., letters,
digits, punctuation, etc.); all these characters are bound to
`self-insert-command'.
Menu Keymaps
============
A keymap can define a menu as well as bindings for keyboard keys and
mouse button. Menus are usually actuated with the mouse, but they can
work with the keyboard also.
Defining Menus
--------------
A keymap is suitable for menu use if it has an "overall prompt
string", which is a string that appears as an element of the keymap.
(*Note Format of Keymaps::.) The string should describe the purpose of
the menu's commands. Emacs displays the overall prompt string as the
menu title in some cases, depending on the toolkit (if any) used for
displaying menus.(1) Keyboard menus also display the overall prompt
string.
The easiest way to construct a keymap with a prompt string is to
specify the string as an argument when you call `make-keymap',
`make-sparse-keymap' or `define-prefix-command' (*note Creating
Keymaps::).
The order of items in the menu is the same as the order of bindings
in the keymap. Since `define-key' puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
`define-key-after' (*note Modifying Menus::).
---------- Footnotes ----------
(1) It is required for menus which do not use a toolkit, e.g. under
MS-DOS.
Simple Menu Items
.................
The simpler and older way to define a menu keymap binding looks like
this:
(ITEM-STRING . REAL-BINDING)
The CAR, ITEM-STRING, is the string to be displayed in the menu. It
should be short--preferably one to three words. It should describe the
action of the command it corresponds to.
You can also supply a second string, called the help string, as
follows:
(ITEM-STRING HELP . REAL-BINDING)
HELP specifies a "help-echo" string to display while the mouse is on
that item in the same way as `help-echo' text properties (*note Help
display::).
As far as `define-key' is concerned, ITEM-STRING and HELP-STRING are
part of the event's binding. However, `lookup-key' returns just
REAL-BINDING, and only REAL-BINDING is used for executing the key.
If REAL-BINDING is `nil', then ITEM-STRING appears in the menu but
cannot be selected.
If REAL-BINDING is a symbol and has a non-`nil' `menu-enable'
property, that property is an expression that controls whether the menu
item is enabled. Every time the keymap is used to display a menu,
Emacs evaluates the expression, and it enables the menu item only if
the expression's value is non-`nil'. When a menu item is disabled, it
is displayed in a "fuzzy" fashion, and cannot be selected.
The menu bar does not recalculate which items are enabled every time
you look at a menu. This is because the X toolkit requires the whole
tree of menus in advance. To force recalculation of the menu bar, call
`force-mode-line-update' (*note Mode Line Format::).
You've probably noticed that menu items show the equivalent keyboard
key sequence (if any) to invoke the same command. To save time on
recalculation, menu display caches this information in a sublist in the
binding, like this:
(ITEM-STRING [HELP-STRING] (KEY-BINDING-DATA) . REAL-BINDING)
Don't put these sublists in the menu item yourself; menu display
calculates them automatically. Don't mention keyboard equivalents in
the item strings themselves, since that is redundant.
Extended Menu Items
...................
An extended-format menu item is a more flexible and also cleaner
alternative to the simple format. It consists of a list that starts
with the symbol `menu-item'. To define a non-selectable string, the
item looks like this:
(menu-item ITEM-NAME)
A string starting with two or more dashes specifies a separator line;
see *Note Menu Separators::.
To define a real menu item which can be selected, the extended format
item looks like this:
(menu-item ITEM-NAME REAL-BINDING
. ITEM-PROPERTY-LIST)
Here, ITEM-NAME is an expression which evaluates to the menu item
string. Thus, the string need not be a constant. The third element,
REAL-BINDING, is the command to execute. The tail of the list,
ITEM-PROPERTY-LIST, has the form of a property list which contains
other information. Here is a table of the properties that are
supported:
`:enable FORM'
The result of evaluating FORM determines whether the item is
enabled (non-`nil' means yes). If the item is not enabled, you
can't really click on it.
`:visible FORM'
The result of evaluating FORM determines whether the item should
actually appear in the menu (non-`nil' means yes). If the item
does not appear, then the menu is displayed as if this item were
not defined at all.
`:help HELP'
The value of this property, HELP, specifies a "help-echo" string
to display while the mouse is on that item. This is displayed in
the same way as `help-echo' text properties (*note Help display::).
Note that this must be a constant string, unlike the `help-echo'
property for text and overlays.
`:button (TYPE . SELECTED)'
This property provides a way to define radio buttons and toggle
buttons. The CAR, TYPE, says which: it should be `:toggle' or
`:radio'. The CDR, SELECTED, should be a form; the result of
evaluating it says whether this button is currently selected.
A "toggle" is a menu item which is labeled as either "on" or "off"
according to the value of SELECTED. The command itself should
toggle SELECTED, setting it to `t' if it is `nil', and to `nil' if
it is `t'. Here is how the menu item to toggle the
`debug-on-error' flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
:button (:toggle
. (and (boundp 'debug-on-error)
debug-on-error)))
This works because `toggle-debug-on-error' is defined as a command
which toggles the variable `debug-on-error'.
"Radio buttons" are a group of menu items, in which at any time one
and only one is "selected." There should be a variable whose value
says which one is selected at any time. The SELECTED form for
each radio button in the group should check whether the variable
has the right value for selecting that button. Clicking on the
button should set the variable so that the button you clicked on
becomes selected.
`:key-sequence KEY-SEQUENCE'
This property specifies which key sequence is likely to be bound
to the same command invoked by this menu item. If you specify the
right key sequence, that makes preparing the menu for display run
much faster.
If you specify the wrong key sequence, it has no effect; before
Emacs displays KEY-SEQUENCE in the menu, it verifies that
KEY-SEQUENCE is really equivalent to this menu item.
`:key-sequence nil'
This property indicates that there is normally no key binding
which is equivalent to this menu item. Using this property saves
time in preparing the menu for display, because Emacs does not
need to search the keymaps for a keyboard equivalent for this menu
item.
However, if the user has rebound this item's definition to a key
sequence, Emacs ignores the `:keys' property and finds the keyboard
equivalent anyway.
`:keys STRING'
This property specifies that STRING is the string to display as
the keyboard equivalent for this menu item. You can use the
`\\[...]' documentation construct in STRING.
`:filter FILTER-FN'
This property provides a way to compute the menu item dynamically.
The property value FILTER-FN should be a function of one argument;
when it is called, its argument will be REAL-BINDING. The
function should return the binding to use instead.
Menu Separators
...............
A menu separator is a kind of menu item that doesn't display any
text-instead, it divides the menu into subparts with a horizontal line.
A separator looks like this in the menu keymap:
(menu-item SEPARATOR-TYPE)
where SEPARATOR-TYPE is a string starting with two or more dashes.
In the simplest case, SEPARATOR-TYPE consists of only dashes. That
specifies the default kind of separator. (For compatibility, `""' and
`-' also count as separators.)
Starting in Emacs 21, certain other values of SEPARATOR-TYPE specify
a different style of separator. Here is a table of them:
`"--no-line"'
`"--space"'
An extra vertical space, with no actual line.
`"--single-line"'
A single line in the menu's foreground color.
`"--double-line"'
A double line in the menu's foreground color.
`"--single-dashed-line"'
A single dashed line in the menu's foreground color.
`"--double-dashed-line"'
A double dashed line in the menu's foreground color.
`"--shadow-etched-in"'
A single line with a 3D sunken appearance. This is the default,
used separators consisting of dashes only.
`"--shadow-etched-out"'
A single line with a 3D raised appearance.
`"--shadow-etched-in-dash"'
A single dashed line with a 3D sunken appearance.
`"--shadow-etched-out-dash"'
A single dashed line with a 3D raised appearance.
`"--shadow-double-etched-in"'
Two lines with a 3D sunken appearance.
`"--shadow-double-etched-out"'
Two lines with a 3D raised appearance.
`"--shadow-double-etched-in-dash"'
Two dashed lines with a 3D sunken appearance.
`"--shadow-double-etched-out-dash"'
Two dashed lines with a 3D raised appearance.
You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word. Thus, `"--:singleLine"', is equivalent to
`"--single-line"'.
Some systems and display toolkits don't really handle all of these
separator types. If you use a type that isn't supported, the menu
displays a similar kind of separator that is supported.
Alias Menu Items
................
Sometimes it is useful to make menu items that use the "same"
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here's an example that makes two aliases for `toggle-read-only'
and gives them different enable conditions:
(defalias 'make-read-only 'toggle-read-only)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'toggle-read-only)
(put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the "real" command name, not the aliases
(which typically don't have any key bindings except for the menu
itself). To request this, give the alias symbol a non-`nil'
`menu-alias' property. Thus,
(put 'make-read-only 'menu-alias t)
(put 'make-writable 'menu-alias t)
causes menu items for `make-read-only' and `make-writable' to show the
keyboard bindings for `toggle-read-only'.
Menus and the Mouse
-------------------
The usual way to make a menu keymap produce a menu is to make it the
definition of a prefix key. (A Lisp program can explicitly pop up a
menu and receive the user's choice--see *Note Pop-Up Menus::.)
If the prefix key ends with a mouse event, Emacs handles the menu
keymap by popping up a visible menu, so that the user can select a
choice with the mouse. When the user clicks on a menu item, the event
generated is whatever character or symbol has the binding that brought
about that menu item. (A menu item may generate a series of events if
the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then
the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly
arrange for this. The way to do this is to make a keymap for each pane,
then create a binding for each of those maps in the main keymap of the
menu. Give each of these bindings an item string that starts with `@'.
The rest of the item string becomes the name of the pane. See the
file `lisp/mouse.el' for an example of this. Any ordinary bindings
with `@'-less item strings are grouped into one pane, which appears
along with the other panes explicitly created for the submaps.
X toolkit menus don't have panes; instead, they can have submenus.
Every nested keymap becomes a submenu, whether the item string starts
with `@' or not. In a toolkit version of Emacs, the only thing special
about `@' at the beginning of an item string is that the `@' doesn't
appear in the menu item.
You can also produce multiple panes or submenus from separate
keymaps. The full definition of a prefix key always comes from merging
the definitions supplied by the various active keymaps (minor mode,
local, and global). When more than one of these keymaps is a menu,
each of them makes a separate pane or panes (when Emacs does not use an
X-toolkit) or a separate submenu (when using an X-toolkit). *Note
Active Keymaps::.
Menus and the Keyboard
----------------------
When a prefix key ending with a keyboard event (a character or
function key) has a definition that is a menu keymap, the user can use
the keyboard to choose a menu item.
Emacs displays the menu's overall prompt string followed by the
alternatives (the item strings of the bindings) in the echo area. If
the bindings don't all fit at once, the user can type <SPC> to see the
next line of alternatives. Successive uses of <SPC> eventually get to
the end of the menu and then cycle around to the beginning. (The
variable `menu-prompt-more-char' specifies which character is used for
this; <SPC> is the default.)
When the user has found the desired alternative from the menu, he or
she should type the corresponding character--the one whose binding is
that alternative.
This way of using menus in an Emacs-like editor was inspired by the
Hierarkey system.
- Variable: menu-prompt-more-char
This variable specifies the character to use to ask to see the
next line of a menu. Its initial value is 32, the code for <SPC>.
Menu Example
------------
Here is a complete example of defining a menu keymap. It is the
definition of the `Print' submenu in the `Tools' menu in the menu bar,
and it uses the simple menu item format (*note Simple Menu Items::).
First we create the keymap, and give it a name:
(defvar menu-bar-print-menu (make-sparse-keymap "Print"))
Next we define the menu items:
(define-key menu-bar-print-menu [ps-print-region]
'("Postscript Print Region" . ps-print-region-with-faces))
(define-key menu-bar-print-menu [ps-print-buffer]
'("Postscript Print Buffer" . ps-print-buffer-with-faces))
(define-key menu-bar-print-menu [separator-ps-print]
'("--"))
(define-key menu-bar-print-menu [print-region]
'("Print Region" . print-region))
(define-key menu-bar-print-menu [print-buffer]
'("Print Buffer" . print-buffer))
Note the symbols which the bindings are "made for"; these appear inside
square brackets, in the key sequence being defined. In some cases,
this symbol is the same as the command name; sometimes it is different.
These symbols are treated as "function keys", but they are not real
function keys on the keyboard. They do not affect the functioning of
the menu itself, but they are "echoed" in the echo area when the user
selects from the menu, and they appear in the output of `where-is' and
`apropos'.
The binding whose definition is `("--")' is a separator line. Like
a real menu item, the separator has a key symbol, in this case
`separator-ps-print'. If one menu has two separators, they must have
two different key symbols.
Here is code to define enable conditions for two of the commands in
the menu:
(put 'print-region 'menu-enable 'mark-active)
(put 'ps-print-region-with-faces 'menu-enable 'mark-active)
Here is how we make this menu appear as an item in the parent menu:
(define-key menu-bar-tools-menu [print]
(cons "Print" menu-bar-print-menu))
Note that this incorporates the submenu keymap, which is the value of
the variable `menu-bar-print-menu', rather than the symbol
`menu-bar-print-menu' itself. Using that symbol in the parent menu
item would be meaningless because `menu-bar-print-menu' is not a
command.
If you wanted to attach the same print menu to a mouse click, you
can do it this way:
(define-key global-map [C-S-down-mouse-1]
menu-bar-print-menu)
We could equally well use an extended menu item (*note Extended Menu
Items::) for `print-region', like this:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:enable mark-active))
With the extended menu item, the enable condition is specified inside
the menu item itself. If we wanted to make this item disappear from
the menu entirely when the mark is inactive, we could do it this way:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:visible mark-active))
The Menu Bar
------------
Most window systems allow each frame to have a "menu bar"--a
permanently displayed menu stretching horizontally across the top of the
frame. The items of the menu bar are the subcommands of the fake
"function key" `menu-bar', as defined by all the active keymaps.
To add an item to the menu bar, invent a fake "function key" of your
own (let's call it KEY), and make a binding for the key sequence
`[menu-bar KEY]'. Most often, the binding is a menu keymap, so that
pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key
for the menu bar, the item appears just once. If the user clicks on
that menu bar item, it brings up a single, combined menu containing all
the subcommands of that item--the global subcommands, the local
subcommands, and the minor mode subcommands.
The variable `overriding-local-map' is normally ignored when
determining the menu bar contents. That is, the menu bar is computed
from the keymaps that would be active if `overriding-local-map' were
`nil'. *Note Active Keymaps::.
In order for a frame to display a menu bar, its `menu-bar-lines'
parameter must be greater than zero. Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame. We
recommend 1 or 2 as the value of `menu-bar-lines'. *Note Window Frame
Parameters::.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame)
'((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Define specific subcommands in this menu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap
by rebinding the same fake function key with `undefined' as the
binding. For example, this is how Dired suppresses the `Edit' menu bar
item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
`edit' is the fake function key used by the global map for the `Edit'
menu bar item. The main reason to suppress a global menu bar item is
to regain space for mode-specific items.
- Variable: menu-bar-final-items
Normally the menu bar shows global items followed by items defined
by the local maps.
This variable holds a list of fake function keys for items to
display at the end of the menu bar rather than in normal sequence.
The default value is `(help-menu)'; thus, the `Help' menu item
normally appears at the end of the menu bar, following local menu
items.
- Variable: menu-bar-update-hook
This normal hook is run whenever the user clicks on the menu bar,
before displaying a submenu. You can use it to update submenus
whose contents should vary.
Tool bars
---------
A "tool bar" is a row of icons at the top of a frame, that execute
commands when you click on them--in effect, a kind of graphical menu
bar. Emacs supports tool bars starting with version 21.
The frame parameter `tool-bar-lines' (X resource `toolBar') controls
how many lines' worth of height to reserve for the tool bar. A zero
value suppresses the tool bar. If the value is nonzero, and
`auto-resize-tool-bars' is non-`nil', the tool bar expands and
contracts automatically as needed to hold the specified contents.
The tool bar contents are controlled by a menu keymap attached to a
fake "function key" called `tool-bar' (much like the way the menu bar
is controlled). So you define a tool bar item using `define-key', like
this:
(define-key global-map [tool-bar KEY] ITEM)
where KEY is a fake "function key" to distinguish this item from other
items, and ITEM is a menu item key binding (*note Extended Menu
Items::), which says how to display this item and how it behaves.
The usual menu keymap item properties, `:visible', `:enable',
`:button', and `:filter', are useful in tool bar bindings and have
their normal meanings. The REAL-BINDING in the item must be a command,
not a keymap; in other words, it does not work to define a tool bar
icon as a prefix key.
The `:help' property specifies a "help-echo" string to display while
the mouse is on that item. This is displayed in the same way as
`help-echo' text properties (*note Help display::).
In addition, you should use the `:image' property; this is how you
specify the image to display in the tool bar:
`:image IMAGE'
IMAGES is either a single image specification or a vector of four
image specifications. If you use a vector of four, one of them is
used, depending on circumstances:
item 0
Used when the item is enabled and selected.
item 1
Used when the item is enabled and deselected.
item 2
Used when the item is disabled and selected.
item 3
Used when the item is disabled and deselected.
If IMAGE is a single image specification, Emacs draws the tool bar
button in disabled state by applying an edge-detection algorithm to the
image.
The default tool bar is defined so that items specific to editing do
not appear for major modes whose command symbol has a `mode-class'
property of `special' (*note Major Mode Conventions::). Major modes
may add items to the global bar by binding `[tool-bar FOO]' in their
local map. It makes sense for some major modes to replace the default
tool bar items completely, since not many can be accommodated
conveniently, and the default bindings make this easy by using an
indirection through `tool-bar-map'.
- Variable: tool-bar-map
By default, the global map binds `[tool-bar]' as follows:
(global-set-key [tool-bar]
'(menu-item "tool bar" ignore
:filter (lambda (ignore) tool-bar-map)))
Thus the tool bar map is derived dynamically from the value of
variable `tool-bar-map' and you should normally adjust the default
(global) tool bar by changing that map. Major modes may replace
the global bar completely by making `tool-bar-map' buffer-local
and set to a keymap containing only the desired items. Info mode
provides an example.
There are two convenience functions for defining tool bar items, as
follows.
- Function: tool-bar-add-item icon def key &rest props
This function adds an item to the tool bar by modifying
`tool-bar-map'. The image to use is defined by ICON, which is the
base name of an XPM, XBM or PBM image file to located by
`find-image'. Given a value `"exit"', say, `exit.xpm', `exit.pbm'
and `exit.xbm' would be searched for in that order on a color
display. On a monochrome display, the search order is `.pbm',
`.xbm' and `.xpm'. The binding to use is the command DEF, and KEY
is the fake function key symbol in the prefix keymap. The
remaining arguments PROPS are additional property list elements to
add to the menu item specification.
To define items in some local map, bind ``tool-bar-map' with `let'
around calls of this function:
(defvar foo-tool-bar-map
(let ((tool-bar-map (make-sparse-keymap)))
(tool-bar-add-item ...)
...
tool-bar-map))
- Function: tool-bar-add-item-from-menu command icon &optional map
&rest props
This command is a convenience for defining tool bar items which are
consistent with existing menu bar bindings. The binding of
COMMAND is looked up in the menu bar in MAP (default `global-map')
and modified to add an image specification for ICON, which is
looked for in the same way as by `tool-bar-add-item'. The
resulting binding is then placed in `tool-bar-map'. MAP must
contain an appropriate keymap bound to `[menu-bar]'. The
remaining arguments PROPS are additional property list elements to
add to the menu item specification.
- Variable: auto-resize-tool-bar
If this variable is non-`nil', the tool bar automatically resizes
to show all defined tool bar items--but not larger than a quarter
of the frame's height.
- Variable: auto-raise-tool-bar-items
If this variable is non-`nil', tool bar items display in raised
form when the mouse moves over them.
- Variable: tool-bar-item-margin
This variable specifies an extra margin to add around tool bar
items. The value is an integer, a number of pixels. The default
is 1.
- Variable: tool-bar-item-relief
This variable specifies the shadow width for tool bar items. The
value is an integer, a number of pixels. The default is 3.
You can define a special meaning for clicking on a tool bar item with
the shift, control, meta, etc., modifiers. You do this by setting up
additional items that relate to the original item through the fake
function keys. Specifically, the additional items should use the
modified versions of the same fake function key used to name the
original item.
Thus, if the original item was defined this way,
(define-key global-map [tool-bar shell]
'(menu-item "Shell" shell
:image (image :type xpm :file "shell.xpm")))
then here is how you can define clicking on the same tool bar image with
the shift modifier:
(define-key global-map [tool-bar S-shell] 'some-command)
*Note Function Keys::, for more information about how to add
modifiers to function keys.
Modifying Menus
---------------
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use `define-key' to add the item, it normally goes at the front of the
menu. To put it elsewhere in the menu, use `define-key-after':
- Function: define-key-after map key binding &optional after
Define a binding in MAP for KEY, with value BINDING, just like
`define-key', but position the binding in MAP after the binding
for the event AFTER. The argument KEY should be of length one--a
vector or string with just one element. But AFTER should be a
single event type--a symbol or a character, not a sequence. The
new binding goes after the binding for AFTER. If AFTER is `t' or
is omitted, then the new binding goes last, at the end of the
keymap. However, new bindings are added before any inherited
keymap.
Here is an example:
(define-key-after my-menu [drink]
'("Drink" . drink-command) 'eat)
makes a binding for the fake function key <DRINK> and puts it
right after the binding for <EAT>.
Here is how to insert an item called `Work' in the `Signals' menu
of Shell mode, after the item `break':
(define-key-after
(lookup-key shell-mode-map [menu-bar signals])
[work] '("Work" . work-command) 'break)
Major and Minor Modes
*********************
A "mode" is a set of definitions that customize Emacs and can be
turned on and off while you edit. There are two varieties of modes:
"major modes", which are mutually exclusive and used for editing
particular kinds of text, and "minor modes", which provide features
that users can enable individually.
This chapter describes how to write both major and minor modes, how
to indicate them in the mode line, and how they run hooks supplied by
the user. For related topics such as keymaps and syntax tables, see
*Note Keymaps::, and *Note Syntax Tables::.
Major Modes
===========
Major modes specialize Emacs for editing particular kinds of text.
Each buffer has only one major mode at a time.
The least specialized major mode is called "Fundamental mode". This
mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
`C-j' (`eval-print-last-sexp'), <TAB> (`lisp-indent-line'), and other
keys.
When you need to write several editing commands to help you perform a
specialized editing task, creating a new major mode is usually a good
idea. In practice, writing a major mode is easy (in contrast to
writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to
modify the old one to serve two purposes, since it may become harder to
use and maintain. Instead, copy and rename an existing major mode
definition and alter the copy--or define a "derived mode" (*note
Derived Modes::). For example, Rmail Edit mode, which is in
`emacs/lisp/mail/rmailedit.el', is a major mode that is very similar to
Text mode except that it provides two additional commands. Its
definition is distinct from that of Text mode, but uses that of Text
mode.
Even if the new mode is not an obvious derivative of any other mode,
it can be convenient to define it as a derivative of
`fundamental-mode', so that `define-derived-mode' can automatically
enforce the most important coding conventions for you.
Rmail Edit mode offers an example of changing the major mode
temporarily for a buffer, so it can be edited in a different way (with
ordinary Emacs commands rather than Rmail commands). In such cases, the
temporary major mode usually provides a command to switch back to the
buffer's usual mode (Rmail mode, in this case). You might be tempted to
present the temporary redefinitions inside a recursive edit and restore
the usual ones when the user exits; but this is a bad idea because it
constrains the user's options when it is done in more than one buffer:
recursive edits must be exited most-recently-entered first. Using an
alternative major mode avoids this limitation. *Note Recursive
Editing::.
The standard GNU Emacs Lisp library directory tree contains the code
for several major modes, in files such as `text-mode.el', `texinfo.el',
`lisp-mode.el', `c-mode.el', and `rmail.el'. They are found in various
subdirectories of the `lisp' directory. You can study these libraries
to see how modes are written. Text mode is perhaps the simplest major
mode aside from Fundamental mode. Rmail mode is a complicated and
specialized mode.
Major Mode Conventions
----------------------
The code for existing major modes follows various coding conventions,
including conventions for local keymap and syntax table initialization,
global names, and hooks. Please follow these conventions when you
define a new major mode.
This list of conventions is only partial, because each major mode
should aim for consistency in general with other Emacs major modes.
This makes Emacs as a whole more coherent. It is impossible to list
here all the possible points where this issue might come up; if the
Emacs developers point out an area where your major mode deviates from
the usual conventions, please make it compatible.
* Define a command whose name ends in `-mode', with no arguments,
that switches to the new mode in the current buffer. This command
should set up the keymap, syntax table, and buffer-local variables
in an existing buffer, without changing the buffer's contents.
* Write a documentation string for this command that describes the
special commands available in this mode. `C-h m'
(`describe-mode') in your mode will display this string.
The documentation string may include the special documentation
substrings, `\[COMMAND]', `\{KEYMAP}', and `\<KEYMAP>', which
enable the documentation to adapt automatically to the user's own
key bindings. *Note Keys in Documentation::.
* The major mode command should start by calling
`kill-all-local-variables'. This is what gets rid of the
buffer-local variables of the major mode previously in effect.
* The major mode command should set the variable `major-mode' to the
major mode command symbol. This is how `describe-mode' discovers
which documentation to print.
* The major mode command should set the variable `mode-name' to the
"pretty" name of the mode, as a string. This string appears in the
mode line.
* Since all global names are in the same name space, all the global
variables, constants, and functions that are part of the mode
should have names that start with the major mode name (or with an
abbreviation of it if the name is long). *Note Coding
Conventions::.
* In a major mode for editing some kind of structured text, such as a
programming language, indentation of text according to structure is
probably useful. So the mode should set `indent-line-function' to
a suitable function, and probably customize other variables for
indentation.
* The major mode should usually have its own keymap, which is used
as the local keymap in all buffers in that mode. The major mode
command should call `use-local-map' to install this local map.
*Note Active Keymaps::, for more information.
This keymap should be stored permanently in a global variable named
`MODENAME-mode-map'. Normally the library that defines the mode
sets this variable.
*Note Tips for Defining::, for advice about how to write the code
to set up the mode's keymap variable.
* The key sequences bound in a major mode keymap should usually
start with `C-c', followed by a control character, a digit, or `{',
`}', `<', `>', `:' or `;'. The other punctuation characters are
reserved for minor modes, and ordinary letters are reserved for
users.
It is reasonable for a major mode to rebind a key sequence with a
standard meaning, if it implements a command that does "the same
job" in a way that fits the major mode better. For example, a
major mode for editing a programming language might redefine
`C-M-a' to "move to the beginning of a function" in a way that
works better for that language.
Major modes such as Dired or Rmail that do not allow
self-insertion of text can reasonably redefine letters and other
printing characters as editing commands. Dired and Rmail both do
this.
* Major modes must not define <RET> to do anything other than insert
a newline. The command to insert a newline and then indent is
`C-j'. Please keep this distinction uniform for all major modes.
* Major modes should not alter options that are primary a matter of
user preference, such as whether Auto-Fill mode is enabled. Leave
this to each user to decide. However, a major mode should
customize other variables so that Auto-Fill mode will work
usefully _if_ the user decides to use it.
* The mode may have its own syntax table or may share one with other
related modes. If it has its own syntax table, it should store
this in a variable named `MODENAME-mode-syntax-table'. *Note
Syntax Tables::.
* If the mode handles a language that has a syntax for comments, it
should set the variables that define the comment syntax. *Note
Options Controlling Comments: (emacs)Options for Comments.
* The mode may have its own abbrev table or may share one with other
related modes. If it has its own abbrev table, it should store
this in a variable named `MODENAME-mode-abbrev-table'. *Note
Abbrev Tables::.
* The mode should specify how to do highlighting for Font Lock mode,
by setting up a buffer-local value for the variable
`font-lock-defaults' (*note Font Lock Mode::).
* The mode should specify how Imenu should find the definitions or
sections of a buffer, by setting up a buffer-local value for the
variable `imenu-generic-expression' or
`imenu-create-index-function' (*note Imenu::).
* Use `defvar' or `defcustom' to set mode-related variables, so that
they are not reinitialized if they already have a value. (Such
reinitialization could discard customizations made by the user.)
* To make a buffer-local binding for an Emacs customization
variable, use `make-local-variable' in the major mode command, not
`make-variable-buffer-local'. The latter function would make the
variable local to every buffer in which it is subsequently set,
which would affect buffers that do not use this mode. It is
undesirable for a mode to have such global effects. *Note
Buffer-Local Variables::.
With rare exceptions, the only reasonable way to use
`make-variable-buffer-local' in a Lisp package is for a variable
which is used only within that package. Using it on a variable
used by other packages would interfere with them.
* Each major mode should have a "mode hook" named
`MODENAME-mode-hook'. The major mode command should run that
hook, with `run-hooks', as the very last thing it does. *Note
Hooks::.
* The major mode command may also run the hooks of some more basic
modes. For example, `indented-text-mode' runs `text-mode-hook' as
well as `indented-text-mode-hook'. It may run these other hooks
immediately before the mode's own hook (that is, after everything
else), or it may run them earlier.
* If something special should be done if the user switches a buffer
from this mode to any other major mode, this mode can set up a
buffer-local value for `change-major-mode-hook' (*note Creating
Buffer-Local::).
* If this mode is appropriate only for specially-prepared text, then
the major mode command symbol should have a property named
`mode-class' with value `special', put on as follows:
(put 'funny-mode 'mode-class 'special)
This tells Emacs that new buffers created while the current buffer
is in Funny mode should not inherit Funny mode. Modes such as
Dired, Rmail, and Buffer List use this feature.
* If you want to make the new mode the default for files with certain
recognizable names, add an element to `auto-mode-alist' to select
the mode for those file names. If you define the mode command to
autoload, you should add this element in the same file that calls
`autoload'. Otherwise, it is sufficient to add the element in the
file that contains the mode definition. *Note Auto Major Mode::.
* In the documentation, you should provide a sample `autoload' form
and an example of how to add to `auto-mode-alist', that users can
include in their init files (*note Init File::).
* The top-level forms in the file defining the mode should be
written so that they may be evaluated more than once without
adverse consequences. Even if you never load the file more than
once, someone else will.
Major Mode Examples
-------------------
Text mode is perhaps the simplest mode besides Fundamental mode.
Here are excerpts from `text-mode.el' that illustrate many of the
conventions listed above:
;; Create mode-specific tables.
(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table
() ; Do not change the table if it is already set up.
(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ". " text-mode-syntax-table)
(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
(modify-syntax-entry ?' "w " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil
"Abbrev table used while in text mode.")
(define-abbrev-table 'text-mode-abbrev-table ())
(defvar text-mode-map nil ; Create a mode-specific keymap.
"Keymap for Text mode.
Many other modes, such as Mail mode, Outline mode and Indented Text mode,
inherit all the commands defined in this map.")
(if text-mode-map
() ; Do not change the keymap if it is already set up.
(setq text-mode-map (make-sparse-keymap))
(define-key text-mode-map "\e\t" 'ispell-complete-word)
(define-key text-mode-map "\t" 'indent-relative)
(define-key text-mode-map "\es" 'center-line)
(define-key text-mode-map "\eS" 'center-paragraph))
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read...
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
(make-local-variable 'indent-line-function)
(setq indent-line-function 'indent-relative-maybe)
(setq mode-name "Text")
(setq major-mode 'text-mode)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp
Interaction mode) have more features than Text mode and the code is
correspondingly more complicated. Here are excerpts from
`lisp-mode.el' that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is `48' in the ASCII character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
(setq i (1+ i)))
...
;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
...
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
...))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
Much code is shared among the three Lisp modes. The following
function sets various variables; it is called by each of the major Lisp
mode functions:
(defun lisp-mode-variables (lisp-syntax)
(cond (lisp-syntax
(set-syntax-table lisp-mode-syntax-table)))
(setq local-abbrev-table lisp-mode-abbrev-table)
...
Functions such as `forward-paragraph' use the value of the
`paragraph-start' variable. Since Lisp code is different from ordinary
text, the `paragraph-start' variable needs to be set specially to
handle Lisp. Also, comments are indented in a special fashion in Lisp
and the Lisp modes need their own mode-specific
`comment-indent-function'. The code to set these variables is the rest
of `lisp-mode-variables'.
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat page-delimiter "\\|$" ))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
...
(make-local-variable 'comment-indent-function)
(setq comment-indent-function 'lisp-comment-indent))
...
Each of the different Lisp modes has a slightly different keymap.
For example, Lisp mode binds `C-c C-z' to `run-lisp', but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar shared-lisp-mode-map ()
"Keymap for commands shared by all sorts of Lisp modes.")
(if shared-lisp-mode-map
()
(setq shared-lisp-mode-map (make-sparse-keymap))
(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
(define-key shared-lisp-mode-map "\177"
'backward-delete-char-untabify))
And here is the code to set up the keymap for Lisp mode:
(defvar lisp-mode-map ()
"Keymap for ordinary Lisp mode...")
(if lisp-mode-map
()
(setq lisp-mode-map (make-sparse-keymap))
(set-keymap-parent lisp-mode-map shared-lisp-mode-map)
(define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun)
(define-key lisp-mode-map "\C-c\C-z" 'run-lisp))
Finally, here is the complete major mode function definition for
Lisp mode.
(defun lisp-mode ()
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(interactive)
(kill-all-local-variables)
(use-local-map lisp-mode-map) ; Select the mode's keymap.
(setq major-mode 'lisp-mode) ; This is how `describe-mode'
; finds out what to describe.
(setq mode-name "Lisp") ; This goes into the mode line.
(lisp-mode-variables t) ; This defines various variables.
(setq imenu-case-fold-search t)
(set-syntax-table lisp-mode-syntax-table)
(run-hooks 'lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
How Emacs Chooses a Major Mode
------------------------------
Based on information in the file name or in the file itself, Emacs
automatically selects a major mode for the new buffer when a file is
visited. It also processes local variables specified in the file text.
- Command: fundamental-mode
Fundamental mode is a major mode that is not specialized for
anything in particular. Other major modes are defined in effect
by comparison with this one--their definitions say what to change,
starting from Fundamental mode. The `fundamental-mode' function
does _not_ run any hooks; you're not supposed to customize it.
(If you want Emacs to behave differently in Fundamental mode,
change the _global_ state of Emacs.)
- Command: normal-mode &optional find-file
This function establishes the proper major mode and buffer-local
variable bindings for the current buffer. First it calls
`set-auto-mode', then it runs `hack-local-variables' to parse, and
bind or evaluate as appropriate, the file's local variables.
If the FIND-FILE argument to `normal-mode' is non-`nil',
`normal-mode' assumes that the `find-file' function is calling it.
In this case, it may process a local variables list at the end of
the file and in the `-*-' line. The variable
`enable-local-variables' controls whether to do so. *Note Local
Variables in Files: (emacs)File variables, for the syntax of the
local variables section of a file.
If you run `normal-mode' interactively, the argument FIND-FILE is
normally `nil'. In this case, `normal-mode' unconditionally
processes any local variables list.
`normal-mode' uses `condition-case' around the call to the major
mode function, so errors are caught and reported as a `File mode
specification error', followed by the original error message.
- Function: set-auto-mode
This function selects the major mode that is appropriate for the
current buffer. It may base its decision on the value of the `-*-'
line, on the visited file name (using `auto-mode-alist'), on the
`#!' line (using `interpreter-mode-alist'), or on the file's local
variables list. However, this function does not look for the
`mode:' local variable near the end of a file; the
`hack-local-variables' function does that. *Note How Major Modes
are Chosen: (emacs)Choosing Modes.
- User Option: default-major-mode
This variable holds the default major mode for new buffers. The
standard value is `fundamental-mode'.
If the value of `default-major-mode' is `nil', Emacs uses the
(previously) current buffer's major mode for the major mode of a
new buffer. However, if that major mode symbol has a `mode-class'
property with value `special', then it is not used for new buffers;
Fundamental mode is used instead. The modes that have this
property are those such as Dired and Rmail that are useful only
with text that has been specially prepared.
- Function: set-buffer-major-mode buffer
This function sets the major mode of BUFFER to the value of
`default-major-mode'. If that variable is `nil', it uses the
current buffer's major mode (if that is suitable).
The low-level primitives for creating buffers do not use this
function, but medium-level commands such as `switch-to-buffer' and
`find-file-noselect' use it whenever they create buffers.
- Variable: initial-major-mode
The value of this variable determines the major mode of the initial
`*scratch*' buffer. The value should be a symbol that is a major
mode command. The default value is `lisp-interaction-mode'.
- Variable: auto-mode-alist
This variable contains an association list of file name patterns
(regular expressions; *note Regular Expressions::) and
corresponding major mode commands. Usually, the file name
patterns test for suffixes, such as `.el' and `.c', but this need
not be the case. An ordinary element of the alist looks like
`(REGEXP . MODE-FUNCTION)'.
For example,
(("\\`/tmp/fol/" . text-mode)
("\\.texinfo\\'" . texinfo-mode)
("\\.texi\\'" . texinfo-mode)
("\\.el\\'" . emacs-lisp-mode)
("\\.c\\'" . c-mode)
("\\.h\\'" . c-mode)
...)
When you visit a file whose expanded file name (*note File Name
Expansion::) matches a REGEXP, `set-auto-mode' calls the
corresponding MODE-FUNCTION. This feature enables Emacs to select
the proper major mode for most files.
If an element of `auto-mode-alist' has the form `(REGEXP FUNCTION
t)', then after calling FUNCTION, Emacs searches `auto-mode-alist'
again for a match against the portion of the file name that did
not match before. This feature is useful for uncompression
packages: an entry of the form `("\\.gz\\'" FUNCTION t)' can
uncompress the file and then put the uncompressed file in the
proper mode according to the name sans `.gz'.
Here is an example of how to prepend several pattern pairs to
`auto-mode-alist'. (You might use this sort of expression in your
init file.)
(setq auto-mode-alist
(append
;; File name (within directory) starts with a dot.
'(("/\\.[^/]*\\'" . fundamental-mode)
;; File name has no dot.
("[^\\./]*\\'" . fundamental-mode)
;; File name ends in `.C'.
("\\.C\\'" . c++-mode))
auto-mode-alist))
- Variable: interpreter-mode-alist
This variable specifies major modes to use for scripts that
specify a command interpreter in a `#!' line. Its value is a list
of elements of the form `(INTERPRETER . MODE)'; for example,
`("perl" . perl-mode)' is one element present by default. The
element says to use mode MODE if the file specifies an interpreter
which matches INTERPRETER. The value of INTERPRETER is actually a
regular expression.
This variable is applicable only when the `auto-mode-alist' does
not indicate which major mode to use.
Getting Help about a Major Mode
-------------------------------
The `describe-mode' function is used to provide information about
major modes. It is normally called with `C-h m'. The `describe-mode'
function uses the value of `major-mode', which is why every major mode
function needs to set the `major-mode' variable.
- Command: describe-mode
This function displays the documentation of the current major mode.
The `describe-mode' function calls the `documentation' function
using the value of `major-mode' as an argument. Thus, it displays
the documentation string of the major mode function. (*Note
Accessing Documentation::.)
- Variable: major-mode
This variable holds the symbol for the current buffer's major mode.
This symbol should have a function definition that is the command
to switch to that major mode. The `describe-mode' function uses
the documentation string of the function as the documentation of
the major mode.
Defining Derived Modes
----------------------
It's often useful to define a new major mode in terms of an existing
one. An easy way to do this is to use `define-derived-mode'.
- Macro: define-derived-mode variant parent name docstring body...
This construct defines VARIANT as a major mode command, using NAME
as the string form of the mode name.
The new command VARIANT is defined to call the function PARENT,
then override certain aspects of that parent mode:
* The new mode has its own keymap, named `VARIANT-map'.
`define-derived-mode' initializes this map to inherit from
`PARENT-map', if it is not already set.
* The new mode has its own syntax table, kept in the variable
`VARIANT-syntax-table'. `define-derived-mode' initializes
this variable by copying `PARENT-syntax-table', if it is not
already set.
* The new mode has its own abbrev table, kept in the variable
`VARIANT-abbrev-table'. `define-derived-mode' initializes
this variable by copying `PARENT-abbrev-table', if it is not
already set.
* The new mode has its own mode hook, `VARIANT-hook', which it
runs in standard fashion as the very last thing that it does.
(The new mode also runs the mode hook of PARENT as part of
calling PARENT.)
In addition, you can specify how to override other aspects of
PARENT with BODY. The command VARIANT evaluates the forms in BODY
after setting up all its usual overrides, just before running
`VARIANT-hook'.
The argument DOCSTRING specifies the documentation string for the
new mode. If you omit DOCSTRING, `define-derived-mode' generates
a documentation string.
Here is a hypothetical example:
(define-derived-mode hypertext-mode
text-mode "Hypertext"
"Major mode for hypertext.
\\{hypertext-mode-map}"
(setq case-fold-search nil))
(define-key hypertext-mode-map
[down-mouse-3] 'do-hyper-link)
Do not write an `interactive' spec in the definition;
`define-derived-mode' does that automatically.
Minor Modes
===========
A "minor mode" provides features that users may enable or disable
independently of the choice of major mode. Minor modes can be enabled
individually or in combination. Minor modes would be better named
"generally available, optional feature modes," except that such a name
would be unwieldy.
A minor mode is not usually meant as a variation of a single major
mode. Usually they are general and can apply to many major modes. For
example, Auto Fill mode works with any major mode that permits text
insertion. To be general, a minor mode must be effectively independent
of the things major modes do.
A minor mode is often much more difficult to implement than a major
mode. One reason is that you should be able to activate and deactivate
minor modes in any order. A minor mode should be able to have its
desired effect regardless of the major mode and regardless of the other
minor modes in effect.
Often the biggest problem in implementing a minor mode is finding a
way to insert the necessary hook into the rest of Emacs. Minor mode
keymaps make this easier than it used to be.
Conventions for Writing Minor Modes
-----------------------------------
There are conventions for writing minor modes just as there are for
major modes. Several of the major mode conventions apply to minor
modes as well: those regarding the name of the mode initialization
function, the names of global symbols, and the use of keymaps and other
tables.
In addition, there are several conventions that are specific to
minor modes.
* Make a variable whose name ends in `-mode' to control the minor
mode. We call this the "mode variable". The minor mode command
should set this variable (`nil' to disable; anything else to
enable).
If possible, implement the mode so that setting the variable
automatically enables or disables the mode. Then the minor mode
command does not need to do anything except set the variable.
This variable is used in conjunction with the `minor-mode-alist' to
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can
also check the variable's value.
If you want the minor mode to be enabled separately in each buffer,
make the variable buffer-local.
* Define a command whose name is the same as the mode variable. Its
job is to enable and disable the mode by setting the variable.
The command should accept one optional argument. If the argument
is `nil', it should toggle the mode (turn it on if it is off, and
off if it is on). Otherwise, it should turn the mode on if the
argument is a positive integer, a symbol other than `nil' or `-',
or a list whose CAR is such an integer or symbol; it should turn
the mode off otherwise.
Here is an example taken from the definition of
`transient-mark-mode'. It shows the use of `transient-mark-mode'
as a variable that enables or disables the mode's behavior, and
also shows the proper way to toggle, enable or disable the minor
mode based on the raw prefix argument value.
(setq transient-mark-mode
(if (null arg) (not transient-mark-mode)
(> (prefix-numeric-value arg) 0)))
* Add an element to `minor-mode-alist' for each minor mode (*note
Mode Line Variables::), if you want to indicate the minor mode in
the mode line. This element should be a list of the following
form:
(MODE-VARIABLE STRING)
Here MODE-VARIABLE is the variable that controls enabling of the
minor mode, and STRING is a short string, starting with a space,
to represent the mode in the mode line. These strings must be
short so that there is room for several of them at once.
When you add an element to `minor-mode-alist', use `assq' to check
for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
or like this, using `add-to-list' (*note Setting Variables::):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (*note Customization::). To do this,
the first step is to define the mode variable with `defcustom', and
specify `:type boolean'.
If just setting the variable is not sufficient to enable the mode,
you should also specify a `:set' method which enables the mode by
invoke the mode command. Note in the variable's documentation string
that setting the variable other than via Custom may not take effect.
Also mark the definition with an autoload cookie (*note Autoload::),
and specify a `:require' so that customizing the variable will load the
library that defines the mode. This will copy suitable definitions
into `loaddefs.el' so that users can use `customize-option' to enable
the mode. For example:
;;;###autoload
(defcustom msb-mode nil
"Toggle msb-mode.
Setting this variable directly does not take effect;
use either \\[customize] or the function `msb-mode'."
:set (lambda (symbol value)
(msb-mode (or value 0)))
:initialize 'custom-initialize-default
:version "20.4"
:type 'boolean
:group 'msb
:require 'msb)
Keymaps and Minor Modes
-----------------------
Each minor mode can have its own keymap, which is active when the
mode is enabled. To set up a keymap for a minor mode, add an element
to the alist `minor-mode-map-alist'. *Note Active Keymaps::.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. In general, this is the only way to do that, since the
facilities for customizing `self-insert-command' are limited to special
cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of `self-insert-command' for the
standard one. The editor command loop handles this function specially.)
The key sequences bound in a minor mode should consist of `C-c'
followed by a punctuation character _other than_ `{', `}', `<', `>',
`:', and `;'. (Those few punctuation characters are reserved for major
modes.)
Defining Minor Modes
--------------------
The macro `define-minor-mode' offers a convenient way of
implementing a mode in one self-contained definition. It supports only
buffer-local minor modes, not global ones.
- Macro: define-minor-mode mode doc &optional init-value
mode-indicator keymap body...
This macro defines a new minor mode whose name is MODE (a symbol).
It defines a command named MODE to toggle the minor mode, with DOC
as its documentation string. It also defines a variable named
MODE, which is set to `t' or `nil' by enabling or disabling the
mode. The variable is initialized to INIT-VALUE.
The command named MODE finishes by executing the BODY forms, if
any, after it has performed the standard actions such as setting
the variable named MODE.
The string MODE-INDICATOR says what to display in the mode line
when the mode is enabled; if it is `nil', the mode is not displayed
in the mode line.
The optional argument KEYMAP specifies the keymap for the minor
mode. It can be a variable name, whose value is the keymap, or it
can be an alist specifying bindings in this form:
(KEY-SEQUENCE . DEFINITION)
Here is an example of using `define-minor-mode':
(define-minor-mode hungry-mode
"Toggle Hungry mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
nil
;; The indicator for the mode line.
" Hungry"
;; The minor mode bindings.
'(("\C-\^?" . hungry-electric-delete)
("\C-\M-\^?"
. (lambda ()
(interactive)
(hungry-electric-delete t)))))
This defines a minor mode named "Hungry mode", a command named
`hungry-mode' to toggle it, a variable named `hungry-mode' which
indicates whether the mode is enabled, and a variable named
`hungry-mode-map' which holds the keymap that is active when the mode
is enabled. It initializes the keymap with key bindings for `C-<DEL>'
and `C-M-<DEL>'.
The name `easy-mmode-define-minor-mode' is an alias for this macro.
Mode Line Format
================
Each Emacs window (aside from minibuffer windows) typically has a
mode line at the bottom, which displays status information about the
buffer displayed in the window. The mode line contains information
about the buffer, such as its name, associated file, depth of recursive
editing, and major and minor modes. A window can also have a "header
line", which is much like the mode line but appears at the top of the
window (starting in Emacs 21).
This section describes how to control the contents of the mode line
and header line. We include it in this chapter because much of the
information displayed in the mode line relates to the enabled major and
minor modes.
`mode-line-format' is a buffer-local variable that holds a template
used to display the mode line of the current buffer. All windows for
the same buffer use the same `mode-line-format', so their mode lines
appear the same--except for scrolling percentages, and line and column
numbers, since those depend on point and on how the window is scrolled.
`header-line-format' is used likewise for header lines.
The mode line and header line of a window are normally updated
whenever a different buffer is shown in the window, or when the buffer's
modified-status changes from `nil' to `t' or vice-versa. If you modify
any of the variables referenced by `mode-line-format' (*note Mode Line
Variables::), or any other variables and data structures that affect
how text is displayed (*note Display::), you may want to force an
update of the mode line so as to display the new information or display
it in the new way.
- Function: force-mode-line-update
Force redisplay of the current buffer's mode line and header line.
The mode line is usually displayed in inverse video; see
`mode-line-inverse-video' in *Note Inverse Video::.
The Data Structure of the Mode Line
-----------------------------------
The mode line contents are controlled by a data structure of lists,
strings, symbols, and numbers kept in buffer-local variables. The data
structure is called a "mode line construct", and it is built in
recursive fashion out of simpler mode line constructs. The same data
structure is used for constructing frame titles (*note Frame Titles::)
and header lines (*note Header Lines::).
- Variable: mode-line-format
The value of this variable is a mode line construct with overall
responsibility for the mode line format. The value of this
variable controls which other variables are used to form the mode
line text, and where they appear.
If you set this variable to `nil' in a buffer, that buffer does not
have a mode line. (This feature was added in Emacs 21.)
A mode line construct may be as simple as a fixed string of text, but
it usually specifies how to use other variables to construct the text.
Many of these variables are themselves defined to have mode line
constructs as their values.
The default value of `mode-line-format' incorporates the values of
variables such as `mode-name' and `minor-mode-alist'. Because of this,
very few modes need to alter `mode-line-format' itself. For most
purposes, it is sufficient to alter some of the variables that
`mode-line-format' refers to.
A mode line construct may be a list, a symbol, or a string. If the
value is a list, each element may be a list, a symbol, or a string.
The mode line can display various faces, if the strings that control
it have the `face' property. *Note Properties in Mode::. In addition,
the face `mode-line' is used as a default for the whole mode line
(*note Standard Faces::).
`STRING'
A string as a mode line construct is displayed verbatim in the
mode line except for "`%'-constructs". Decimal digits after the
`%' specify the field width for space filling on the right (i.e.,
the data is left justified). *Note %-Constructs::.
`SYMBOL'
A symbol as a mode line construct stands for its value. The value
of SYMBOL is used as a mode line construct, in place of SYMBOL.
However, the symbols `t' and `nil' are ignored, as is any symbol
whose value is void.
There is one exception: if the value of SYMBOL is a string, it is
displayed verbatim: the `%'-constructs are not recognized.
`(STRING REST...) or (LIST REST...)'
A list whose first element is a string or list means to process
all the elements recursively and concatenate the results. This is
the most common form of mode line construct.
`(:eval FORM)'
A list whose first element is the symbol `:eval' says to evaluate
FORM, and use the result as a string to display. (This feature is
new as of Emacs 21.)
`(SYMBOL THEN ELSE)'
A list whose first element is a symbol that is not a keyword
specifies a conditional. Its meaning depends on the value of
SYMBOL. If the value is non-`nil', the second element, THEN, is
processed recursively as a mode line element. But if the value of
SYMBOL is `nil', the third element, ELSE, is processed recursively.
You may omit ELSE; then the mode line element displays nothing if
the value of SYMBOL is `nil'.
`(WIDTH REST...)'
A list whose first element is an integer specifies truncation or
padding of the results of REST. The remaining elements REST are
processed recursively as mode line constructs and concatenated
together. Then the result is space filled (if WIDTH is positive)
or truncated (to -WIDTH columns, if WIDTH is negative) on the
right.
For example, the usual way to show what percentage of a buffer is
above the top of the window is to use a list like this: `(-3
"%p")'.
If you do alter `mode-line-format' itself, the new value should use
the same variables that appear in the default value (*note Mode Line
Variables::), rather than duplicating their contents or displaying the
information in another fashion. This way, customizations made by the
user or by Lisp programs (such as `display-time' and major modes) via
changes to those variables remain effective.
Here is an example of a `mode-line-format' that might be useful for
`shell-mode', since it contains the host name and default directory.
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'(:eval (mode-line-mode-name))
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 . "%p")
"-%-"))
(The variables `line-number-mode', `column-number-mode' and
`which-func-mode' enable particular minor modes; as usual, these
variable names are also the minor mode command names.)
Variables Used in the Mode Line
-------------------------------
This section describes variables incorporated by the standard value
of `mode-line-format' into the text of the mode line. There is nothing
inherently special about these variables; any other variables could
have the same effects on the mode line if `mode-line-format' were
changed to use them.
- Variable: mode-line-mule-info
This variable holds the value of the mode-line construct that
displays information about the language environment, buffer coding
system, and current input method. *Note Non-ASCII Characters::.
- Variable: mode-line-modified
This variable holds the value of the mode-line construct that
displays whether the current buffer is modified.
The default value of `mode-line-modified' is `("%1*%1+")'. This
means that the mode line displays `**' if the buffer is modified,
`--' if the buffer is not modified, `%%' if the buffer is read
only, and `%*' if the buffer is read only and modified.
Changing this variable does not force an update of the mode line.
- Variable: mode-line-frame-identification
This variable identifies the current frame. The default value is
`" "' if you are using a window system which can show multiple
frames, or `"-%F "' on an ordinary terminal which shows only one
frame at a time.
- Variable: mode-line-buffer-identification
This variable identifies the buffer being displayed in the window.
Its default value is `("%12b")', which displays the buffer name,
padded with spaces to at least 12 columns.
- Variable: global-mode-string
This variable holds a mode line spec that appears in the mode line
by default, just after the buffer name. The command `display-time'
sets `global-mode-string' to refer to the variable
`display-time-string', which holds a string containing the time and
load information.
The `%M' construct substitutes the value of `global-mode-string',
but that is obsolete, since the variable is included in the mode
line from `mode-line-format'.
- Variable: mode-name
This buffer-local variable holds the "pretty" name of the current
buffer's major mode. Each major mode should set this variable so
that the mode name will appear in the mode line.
- Variable: minor-mode-alist
This variable holds an association list whose elements specify how
the mode line should indicate that a minor mode is active. Each
element of the `minor-mode-alist' should be a two-element list:
(MINOR-MODE-VARIABLE MODE-LINE-STRING)
More generally, MODE-LINE-STRING can be any mode line spec. It
appears in the mode line when the value of MINOR-MODE-VARIABLE is
non-`nil', and not otherwise. These strings should begin with
spaces so that they don't run together. Conventionally, the
MINOR-MODE-VARIABLE for a specific mode is set to a non-`nil'
value when that minor mode is activated.
The default value of `minor-mode-alist' is:
minor-mode-alist
=> ((vc-mode vc-mode)
(abbrev-mode " Abbrev")
(overwrite-mode overwrite-mode)
(auto-fill-function " Fill")
(defining-kbd-macro " Def")
(isearch-mode isearch-mode))
`minor-mode-alist' itself is not buffer-local. Each variable
mentioned in the alist should be buffer-local if its minor mode
can be enabled separately in each buffer.
- Variable: mode-line-process
This buffer-local variable contains the mode line information on
process status in modes used for communicating with subprocesses.
It is displayed immediately following the major mode name, with no
intervening space. For example, its value in the `*shell*' buffer
is `(":%s")', which allows the shell to display its status along
with the major mode as: `(Shell:run)'. Normally this variable is
`nil'.
Some variables are used by `minor-mode-alist' to display a string
for various minor modes when enabled. This is a typical example:
- Variable: vc-mode
The variable `vc-mode', buffer-local in each buffer, records
whether the buffer's visited file is maintained with version
control, and, if so, which kind. Its value is a string that
appears in the mode line, or `nil' for no version control.
The variable `default-mode-line-format' is where `mode-line-format'
usually gets its value:
- Variable: default-mode-line-format
This variable holds the default `mode-line-format' for buffers
that do not override it. This is the same as `(default-value
'mode-line-format)'.
The default value of `default-mode-line-format' is this list:
("-"
mode-line-mule-info
mode-line-modified
mode-line-frame-identification
mode-line-buffer-identification
" "
global-mode-string
" %[("
;; `mode-line-mode-name' is a function
;; that copies the mode name and adds text
;; properties to make it mouse-sensitive.
(:eval (mode-line-mode-name))
mode-line-process
minor-mode-alist
"%n"
")%]--"
(which-func-mode ("" which-func-format "--"))
(line-number-mode "L%l--")
(column-number-mode "C%c--")
(-3 . "%p")
"-%-")
`%'-Constructs in the Mode Line
-------------------------------
The following table lists the recognized `%'-constructs and what
they mean. In any construct except `%%', you can add a decimal integer
after the `%' to specify how many characters to display.
`%b'
The current buffer name, obtained with the `buffer-name' function.
*Note Buffer Names::.
`%c'
The current column number of point.
`%f'
The visited file name, obtained with the `buffer-file-name'
function. *Note Buffer File Name::.
`%F'
The title (only on a window system) or the name of the selected
frame. *Note Window Frame Parameters::.
`%l'
The current line number of point, counting within the accessible
portion of the buffer.
`%n'
`Narrow' when narrowing is in effect; nothing otherwise (see
`narrow-to-region' in *Note Narrowing::).
`%p'
The percentage of the buffer text above the *top* of window, or
`Top', `Bottom' or `All'. Note that the default mode-line
specification truncates this to three characters.
`%P'
The percentage of the buffer text that is above the *bottom* of
the window (which includes the text visible in the window, as well
as the text above the top), plus `Top' if the top of the buffer is
visible on screen; or `Bottom' or `All'.
`%s'
The status of the subprocess belonging to the current buffer,
obtained with `process-status'. *Note Process Information::.
`%t'
Whether the visited file is a text file or a binary file. This is
a meaningful distinction only on certain operating systems (*note
MS-DOS File Types::).
`%*'
`%' if the buffer is read only (see `buffer-read-only');
`*' if the buffer is modified (see `buffer-modified-p');
`-' otherwise. *Note Buffer Modification::.
`%+'
`*' if the buffer is modified (see `buffer-modified-p');
`%' if the buffer is read only (see `buffer-read-only');
`-' otherwise. This differs from `%*' only for a modified
read-only buffer. *Note Buffer Modification::.
`%&'
`*' if the buffer is modified, and `-' otherwise.
`%['
An indication of the depth of recursive editing levels (not
counting minibuffer levels): one `[' for each editing level.
*Note Recursive Editing::.
`%]'
One `]' for each recursive editing level (not counting minibuffer
levels).
`%-'
Dashes sufficient to fill the remainder of the mode line.
`%%'
The character `%'--this is how to include a literal `%' in a
string in which `%'-constructs are allowed.
The following two `%'-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
`mode-name' and `global-mode-string'.
`%m'
The value of `mode-name'.
`%M'
The value of `global-mode-string'. Currently, only `display-time'
modifies the value of `global-mode-string'.
Properties in the Mode Line
---------------------------
Starting in Emacs 21, certain text properties are meaningful in the
mode line. The `face' property affects the appearance of text; the
`help-echo' property associate help strings with the text, and
`local-map' can make the text mouse-sensitive.
There are three ways to specify text properties for text in the mode
line:
1. Put a string with the `local-map' property directly into the
mode-line data structure.
2. Put a `local-map' property on a mode-line %-construct such as
`%12b'; then the expansion of the %-construct will have that same
text property.
3. Use a list containing `:eval FORM' in the mode-line data
structure, and make FORM evaluate to a string that has a
`local-map' property.
You use the `local-map' property to specify a keymap. Like any
keymap, it can bind character keys and function keys; but that has no
effect, since it is impossible to move point into the mode line. This
keymap can only take real effect for mouse clicks.
Window Header Lines
-------------------
Starting in Emacs 21, a window can have a "header line" at the top,
just as it can have a mode line at the bottom. The header line feature
works just like the mode line feature, except that it's controlled by
different variables.
- Variable: header-line-format
This variable, local in every buffer, specifies how to display the
header line, for windows displaying the buffer. The format of the
value is the same as for `mode-line-format' (*note Mode Line
Data::).
- Variable: default-header-line-format
This variable holds the default `header-line-format' for buffers
that do not override it. This is the same as `(default-value
'header-line-format)'.
It is normally `nil', so that ordinary buffers have no header line.
Imenu
=====
"Imenu" is a feature that lets users select a definition or section
in the buffer, from a menu which lists all of them, to go directly to
that location in the buffer. Imenu works by constructing a buffer
index which lists the names and buffer positions of the definitions, or
other named portions of the buffer; then the user can choose one of
them and move point to it. This section explains how to customize how
Imenu finds the definitions or buffer portions for a particular major
mode.
The usual and simplest way is to set the variable
`imenu-generic-expression':
- Variable: imenu-generic-expression
This variable, if non-`nil', specifies regular expressions for
finding definitions for Imenu. In the simplest case, elements
should look like this:
(MENU-TITLE REGEXP SUBEXP)
Here, if MENU-TITLE is non-`nil', it says that the matches for
this element should go in a submenu of the buffer index;
MENU-TITLE itself specifies the name for the submenu. If
MENU-TITLE is `nil', the matches for this element go directly in
the top level of the buffer index.
The second item in the list, REGEXP, is a regular expression
(*note Regular Expressions::); anything in the buffer that it
matches is considered a definition, something to mention in the
buffer index. The third item, SUBEXP, indicates which
subexpression in REGEXP matches the definition's name.
An element can also look like this:
(MENU-TITLE REGEXP INDEX FUNCTION ARGUMENTS...)
Each match for this element creates a special index item which, if
selected by the user, calls FUNCTION with arguments consisting of
the item name, the buffer position, and ARGUMENTS.
For Emacs Lisp mode, PATTERN could look like this:
((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Vars*" "^\\s-*(def\\(var\\|const\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Types*"
"^\\s-*\
(def\\(type\\|struct\\|class\\|ine-condition\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2))
Setting this variable makes it buffer-local in the current buffer.
- Variable: imenu-case-fold-search
This variable controls whether matching against
IMENU-GENERIC-EXPRESSION is case-sensitive: `t', the default,
means matching should ignore case.
Setting this variable makes it buffer-local in the current buffer.
- Variable: imenu-syntax-alist
This variable is an alist of syntax table modifiers to use while
processing `imenu-generic-expression', to override the syntax table
of the current buffer. Each element should have this form:
(CHARACTERS . SYNTAX-DESCRIPTION)
The CAR, CHARACTERS, can be either a character or a string. The
element says to give that character or characters the syntax
specified by SYNTAX-DESCRIPTION, which is passed to
`modify-syntax-entry' (*note Syntax Table Functions::).
This feature is typically used to give word syntax to characters
which normally have symbol syntax, and thus to simplify
`imenu-generic-expression' and speed up matching. For example,
Fortran mode uses it this way:
(setq imenu-syntax-alist '(("_$" . "w")))
The `imenu-generic-expression' patterns can then use `\\sw+'
instead of `\\(\\sw\\|\\s_\\)+'. Note that this technique may be
inconvenient when the mode needs to limit the initial character of
a name to a smaller set of characters than are allowed in the rest
of a name.
Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the
variables `imenu-prev-index-position-function' and
`imenu-extract-index-name-function':
- Variable: imenu-prev-index-position-function
If this variable is non-`nil', its value should be a function that
finds the next "definition" to put in the buffer index, scanning
backward in the buffer from point. It should return `nil' if it
doesn't find another "definition" before point. Otherwise it
shuould leave point at the place it finds a "definition," and
return any non-`nil' value.
Setting this variable makes it buffer-local in the current buffer.
- Variable: imenu-extract-index-name-function
If this variable is non-`nil', its value should be a function to
return the name for a definition, assuming point is in that
definition as the `imenu-prev-index-position-function' function
would leave it.
Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variable `imenu-create-index-function':
- Variable: imenu-create-index-function
This variable specifies the function to use for creating a buffer
index. The function should take no arguments, and return an index
for the current buffer. It is called within `save-excursion', so
where it leaves point makes no difference.
The default value is a function that uses
`imenu-generic-expression' to produce the index alist. If you
specify a different function, then `imenu-generic-expression' is
not used.
Setting this variable makes it buffer-local in the current buffer.
- Variable: imenu-index-alist
This variable holds the index alist for the current buffer.
Setting it makes it buffer-local in the current buffer.
Simple elements in the alist look like `(INDEX-NAME .
INDEX-POSITION)'. Selecting a simple element has the effect of
moving to position INDEX-POSITION in the buffer.
Special elements look like `(INDEX-NAME POSITION FUNCTION
ARGUMENTS...)'. Selecting a special element performs
(funcall FUNCTION INDEX-NAME POSITION ARGUMENTS...)
A nested sub-alist element looks like `(INDEX-NAME SUB-ALIST)'.
Font Lock Mode
==============
"Font Lock mode" is a feature that automatically attaches `face'
properties to certain parts of the buffer based on their syntactic
role. How it parses the buffer depends on the major mode; most major
modes define syntactic criteria for which faces to use in which
contexts. This section explains how to customize Font Lock for a
particular major mode.
Font Lock mode finds text to highlight in two ways: through syntactic
parsing based on the syntax table, and through searching (usually for
regular expressions). Syntactic fontification happens first; it finds
comments and string constants, and highlights them using
`font-lock-comment-face' and `font-lock-string-face' (*note Faces for
Font Lock::). Search-based fontification follows.
Font Lock Basics
----------------
There are several variables that control how Font Lock mode
highlights text. But major modes should not set any of these variables
directly. Instead, they should set `font-lock-defaults' as a
buffer-local variable. The value assigned to this variable is used, if
and when Font Lock mode is enabled, to set all the other variables.
- Variable: font-lock-defaults
This variable is set by major modes, as a buffer-local variable, to
specify how to fontify text in that mode. The value should look
like this:
(KEYWORDS KEYWORDS-ONLY CASE-FOLD
SYNTAX-ALIST SYNTAX-BEGIN OTHER-VARS...)
The first element, KEYWORDS, indirectly specifies the value of
`font-lock-keywords'. It can be a symbol, a variable whose value
is the list to use for `font-lock-keywords'. It can also be a
list of several such symbols, one for each possible level of
fontification. The first symbol specifies how to do level 1
fontification, the second symbol how to do level 2, and so on.
The second element, KEYWORDS-ONLY, specifies the value of the
variable `font-lock-keywords-only'. If this is non-`nil',
syntactic fontification (of strings and comments) is not performed.
The third element, CASE-FOLD, specifies the value of
`font-lock-case-fold-search'. If it is non-`nil', Font Lock mode
ignores case when searching as directed by `font-lock-keywords'.
If the fourth element, SYNTAX-ALIST, is non-`nil', it should be a
list of cons cells of the form `(CHAR-OR-STRING . STRING)'. These
are used to set up a syntax table for fontification (*note Syntax
Table Functions::). The resulting syntax table is stored in
`font-lock-syntax-table'.
The fifth element, SYNTAX-BEGIN, specifies the value of
`font-lock-beginning-of-syntax-function' (see below).
All the remaining elements (if any) are collectively called
OTHER-VARS. Each of these elements should have the form
`(VARIABLE . VALUE)'--which means, make VARIABLE buffer-local and
then set it to VALUE. You can use these OTHER-VARS to set other
variables that affect fontification, aside from those you can
control with the first five elements.
Search-based Fontification
--------------------------
The most important variable for customizing Font Lock mode is
`font-lock-keywords'. It specifies the search criteria for
search-based fontification.
- Variable: font-lock-keywords
This variable's value is a list of the keywords to highlight. Be
careful when composing regular expressions for this list; a poorly
written pattern can dramatically slow things down!
Each element of `font-lock-keywords' specifies how to find certain
cases of text, and how to highlight those cases. Font Lock mode
processes the elements of `font-lock-keywords' one by one, and for each
element, it finds and handles all matches. Ordinarily, once part of
the text has been fontified already, this cannot be overridden by a
subsequent match in the same text; but you can specify different
behavior using the OVERRIDE element of a HIGHLIGHTER.
Each element of `font-lock-keywords' should have one of these forms:
`REGEXP'
Highlight all matches for REGEXP using `font-lock-keyword-face'.
For example,
;; Highlight discrete occurrences of `foo'
;; using `font-lock-keyword-face'.
"\\<foo\\>"
The function `regexp-opt' (*note Syntax of Regexps::) is useful for
calculating optimal regular expressions to match a number of
different keywords.
`FUNCTION'
Find text by calling FUNCTION, and highlight the matches it finds
using `font-lock-keyword-face'.
When FUNCTION is called, it receives one argument, the limit of
the search. It should return non-`nil' if it succeeds, and set the
match data to describe the match that was found.
`(MATCHER . MATCH)'
In this kind of element, MATCHER is either a regular expression or
a function, as described above. The CDR, MATCH, specifies which
subexpression of MATCHER should be highlighted (instead of the
entire text that MATCHER matched).
;; Highlight the `bar' in each occurrence of `fubar',
;; using `font-lock-keyword-face'.
("fu\\(bar\\)" . 1)
If you use `regexp-opt' to produce the regular expression MATCHER,
then you can use `regexp-opt-depth' (*note Syntax of Regexps::) to
calculate the value for MATCH.
`(MATCHER . FACENAME)'
In this kind of element, FACENAME is an expression whose value
specifies the face name to use for highlighting.
;; Highlight occurrences of `fubar',
;; using the face which is the value of `fubar-face'.
("fubar" . fubar-face)
`(MATCHER . HIGHLIGHTER)'
In this kind of element, HIGHLIGHTER is a list which specifies how
to highlight matches found by MATCHER. It has the form
(SUBEXP FACENAME OVERRIDE LAXMATCH)
The CAR, SUBEXP, is an integer specifying which subexpression of
the match to fontify (0 means the entire matching text). The
second subelement, FACENAME, specifies the face, as described
above.
The last two values in HIGHLIGHTER, OVERRIDE and LAXMATCH, are
flags. If OVERRIDE is `t', this element can override existing
fontification made by previous elements of `font-lock-keywords'.
If it is `keep', then each character is fontified if it has not
been fontified already by some other element. If it is `prepend',
the face FACENAME is added to the beginning of the `face'
property. If it is `append', the face FACENAME is added to the
end of the `face' property.
If LAXMATCH is non-`nil', it means there should be no error if
there is no subexpression numbered SUBEXP in MATCHER. Obviously,
fontification of the subexpression numbered SUBEXP will not occur.
However, fontification of other subexpressions (and other
regexps) will continue. If LAXMATCH is `nil', and the specified
subexpression is missing, then an error is signalled which
terminates search-based fontification.
Here are some examples of elements of this kind, and what they do:
;; Highlight occurrences of either `foo' or `bar',
;; using `foo-bar-face', even if they have already been highlighted.
;; `foo-bar-face' should be a variable whose value is a face.
("foo\\|bar" 0 foo-bar-face t)
;; Highlight the first subexpression within each occurrence
;; that the function `fubar-match' finds,
;; using the face which is the value of `fubar-face'.
(fubar-match 1 fubar-face)
`(MATCHER HIGHLIGHTERS...)'
This sort of element specifies several HIGHLIGHTER lists for a
single MATCHER. In order for this to be useful, each HIGHLIGHTER
should have a different value of SUBEXP; that is, each one should
apply to a different subexpression of MATCHER.
`(eval . FORM)'
Here FORM is an expression to be evaluated the first time this
value of `font-lock-keywords' is used in a buffer. Its value
should have one of the forms described in this table.
*Warning:* Do not design an element of `font-lock-keywords' to match
text which spans lines; this does not work reliably. While
`font-lock-fontify-buffer' handles multi-line patterns correctly,
updating when you edit the buffer does not, since it considers text one
line at a time.
Other Font Lock Variables
-------------------------
This section describes additional variables that a major mode can
set by means of `font-lock-defaults'.
- Variable: font-lock-keywords-only
Non-`nil' means Font Lock should not fontify comments or strings
syntactically; it should only fontify based on
`font-lock-keywords'.
- Variable: font-lock-keywords-case-fold-search
Non-`nil' means that regular expression matching for the sake of
`font-lock-keywords' should be case-insensitive.
- Variable: font-lock-syntax-table
This variable specifies the syntax table to use for fontification
of comments and strings.
- Variable: font-lock-beginning-of-syntax-function
If this variable is non-`nil', it should be a function to move
point back to a position that is syntactically at "top level" and
outside of strings or comments. Font Lock uses this when necessary
to get the right results for syntactic fontification.
This function is called with no arguments. It should leave point
at the beginning of any enclosing syntactic block. Typical values
are `beginning-of-line' (i.e., the start of the line is known to be
outside a syntactic block), or `beginning-of-defun' for programming
modes or `backward-paragraph' for textual modes (i.e., the
mode-dependent function is known to move outside a syntactic
block).
If the value is `nil', the beginning of the buffer is used as a
position outside of a syntactic block. This cannot be wrong, but
it can be slow.
- Variable: font-lock-mark-block-function
If this variable is non-`nil', it should be a function that is
called with no arguments, to choose an enclosing range of text for
refontification for the command `M-g M-g'
(`font-lock-fontify-block').
The function should report its choice by placing the region around
it. A good choice is a range of text large enough to give proper
results, but not too large so that refontification becomes slow.
Typical values are `mark-defun' for programming modes or
`mark-paragraph' for textual modes.
Levels of Font Lock
-------------------
Many major modes offer three different levels of fontification. You
can define multiple levels by using a list of symbols for KEYWORDS in
`font-lock-defaults'. Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels. The
chosen level's symbol value is used to initialize `font-lock-keywords'.
Here are the conventions for how to define the levels of
fontification:
* Level 1: highlight function declarations, file directives (such as
include or import directives), strings and comments. The idea is
speed, so only the most important and top-level components are
fontified.
* Level 2: in addition to level 1, highlight all language keywords,
including type names that act like keywords, as well as named
constant values. The idea is that all keywords (either syntactic
or semantic) should be fontified appropriately.
* Level 3: in addition to level 2, highlight the symbols being
defined in function and variable declarations, and all builtin
function names, wherever they appear.
Faces for Font Lock
-------------------
You can make Font Lock mode use any face, but several faces are
defined specifically for Font Lock mode. Each of these symbols is both
a face name, and a variable whose default value is the symbol itself.
Thus, the default value of `font-lock-comment-face' is
`font-lock-comment-face'. This means you can write
`font-lock-comment-face' in a context such as `font-lock-keywords'
where a face-name-valued expression is used.
`font-lock-comment-face'
Used (typically) for comments.
`font-lock-string-face'
Used (typically) for string constants.
`font-lock-keyword-face'
Used (typically) for keywords--names that have special syntactic
significance, like `for' and `if' in C.
`font-lock-builtin-face'
Used (typically) for built-in function names.
`font-lock-function-name-face'
Used (typically) for the name of a function being defined or
declared, in a function definition or declaration.
`font-lock-variable-name-face'
Used (typically) for the name of a variable being defined or
declared, in a variable definition or declaration.
`font-lock-type-face'
Used (typically) for names of user-defined data types, where they
are defined and where they are used.
`font-lock-constant-face'
Used (typically) for constant names.
`font-lock-warning-face'
Used (typically) for constructs that are peculiar, or that greatly
change the meaning of other text. For example, this is used for
`;;;###autoload' cookies in Emacs Lisp, and for `#error'
directives in C.
Syntactic Font Lock
-------------------
Font Lock mode can be used to update `syntax-table' properties
automatically. This is useful in languages for which a single syntax
table by itself is not sufficient.
- Variable: font-lock-syntactic-keywords
This variable enables and controls syntactic Font Lock. Its value
should be a list of elements of this form:
(MATCHER SUBEXP SYNTAX OVERRIDE LAXMATCH)
The parts of this element have the same meanings as in the
corresponding sort of element of `font-lock-keywords',
(MATCHER SUBEXP FACENAME OVERRIDE LAXMATCH)
However, instead of specifying the value FACENAME to use for the
`face' property, it specifies the value SYNTAX to use for the
`syntax-table' property. Here, SYNTAX can be a variable whose
value is a syntax table, a syntax entry of the form `(SYNTAX-CODE
. MATCHING-CHAR)', or an expression whose value is one of those
two types.
Hooks
=====
A "hook" is a variable where you can store a function or functions
to be called on a particular occasion by an existing program. Emacs
provides hooks for the sake of customization. Most often, hooks are set
up in the init file (*note Init File::), but Lisp programs can set them
also. *Note Standard Hooks::, for a list of standard hook variables.
Most of the hooks in Emacs are "normal hooks". These variables
contain lists of functions to be called with no arguments. When the
hook name ends in `-hook', that tells you it is normal. We try to make
all hooks normal, as much as possible, so that you can use them in a
uniform way.
Every major mode function is supposed to run a normal hook called the
"mode hook" as the last step of initialization. This makes it easy for
a user to customize the behavior of the mode, by overriding the
buffer-local variable assignments already made by the mode. But hooks
are used in other contexts too. For example, the hook `suspend-hook'
runs just before Emacs suspends itself (*note Suspending Emacs::).
The recommended way to add a hook function to a normal hook is by
calling `add-hook' (see below). The hook functions may be any of the
valid kinds of functions that `funcall' accepts (*note What Is a
Function::). Most normal hook variables are initially void; `add-hook'
knows how to deal with this.
If the hook variable's name does not end with `-hook', that
indicates it is probably an "abnormal hook". Then you should look at
its documentation to see how to use the hook properly.
If the variable's name ends in `-functions' or `-hooks', then the
value is a list of functions, but it is abnormal in that either these
functions are called with arguments or their values are used in some
way. You can use `add-hook' to add a function to the list, but you
must take care in writing the function. (A few of these variables are
actually normal hooks which were named before we established the
convention of using `-hook' for them.)
If the variable's name ends in `-function', then its value is just a
single function, not a list of functions.
Here's an example that uses a mode hook to turn on Auto Fill mode
when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
At the appropriate time, Emacs uses the `run-hooks' function to run
particular hooks. This function calls the hook functions that have
been added with `add-hook'.
- Function: run-hooks &rest hookvars
This function takes one or more hook variable names as arguments,
and runs each hook in turn. Each argument should be a symbol that
is a hook variable. These arguments are processed in the order
specified.
If a hook variable has a non-`nil' value, that value may be a
function or a list of functions. If the value is a function
(either a lambda expression or a symbol with a function
definition), it is called. If it is a list, the elements are
called, in order. The hook functions are called with no
arguments. Nowadays, storing a single function in the hook
variable is semi-obsolete; you should always use a list of
functions.
For example, here's how `emacs-lisp-mode' runs its mode hook:
(run-hooks 'emacs-lisp-mode-hook)
- Function: run-hook-with-args hook &rest args
This function is the way to run an abnormal hook which passes
arguments to the hook functions. It calls each of the hook
functions, passing each of them the arguments ARGS.
- Function: run-hook-with-args-until-failure hook &rest args
This function is the way to run an abnormal hook which passes
arguments to the hook functions, and stops as soon as any hook
function fails. It calls each of the hook functions, passing each
of them the arguments ARGS, until some hook function returns
`nil'. Then it stops, and returns `nil' if some hook function
returned `nil'. Otherwise it returns a non-`nil' value.
- Function: run-hook-with-args-until-success hook &rest args
This function is the way to run an abnormal hook which passes
arguments to the hook functions, and stops as soon as any hook
function succeeds. It calls each of the hook functions, passing
each of them the arguments ARGS, until some hook function returns
non-`nil'. Then it stops, and returns whatever was returned by
the last hook function that was called.
- Function: add-hook hook function &optional append local
This function is the handy way to add function FUNCTION to hook
variable HOOK. The argument FUNCTION may be any valid Lisp
function with the proper number of arguments. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)
adds `my-text-hook-function' to the hook called `text-mode-hook'.
You can use `add-hook' for abnormal hooks as well as for normal
hooks.
It is best to design your hook functions so that the order in
which they are executed does not matter. Any dependence on the
order is "asking for trouble." However, the order is predictable:
normally, FUNCTION goes at the front of the hook list, so it will
be executed first (barring another `add-hook' call). If the
optional argument APPEND is non-`nil', the new hook function goes
at the end of the hook list and will be executed last.
If LOCAL is non-`nil', that says to make the new hook function
buffer-local in the current buffer and automatically calls
`make-local-hook' to make the hook itself buffer-local.
- Function: remove-hook hook function &optional local
This function removes FUNCTION from the hook variable HOOK.
If LOCAL is non-`nil', that says to remove FUNCTION from the
buffer-local hook list instead of from the global hook list. If
the hook variable itself is not buffer-local, then the value of
LOCAL makes no difference.
- Function: make-local-hook hook
This function makes the hook variable `hook' buffer-local in the
current buffer. When a hook variable is buffer-local, it can have
buffer-local and global hook functions, and `run-hooks' runs all of
them.
This function works by adding `t' as an element of the buffer-local
value. That serves as a flag to use the hook functions listed in
the default value of the hook variable, as well as those listed in
the buffer-local value. Since `run-hooks' understands this flag,
`make-local-hook' works with all normal hooks. It works for only
some non-normal hooks--those whose callers have been updated to
understand this meaning of `t'.
Do not use `make-local-variable' directly for hook variables; it is
not sufficient.
Documentation
*************
GNU Emacs Lisp has convenient on-line help facilities, most of which
derive their information from the documentation strings associated with
functions and variables. This chapter describes how to write good
documentation strings for your Lisp programs, as well as how to write
programs to access documentation.
Note that the documentation strings for Emacs are not the same thing
as the Emacs manual. Manuals have their own source files, written in
the Texinfo language; documentation strings are specified in the
definitions of the functions and variables they apply to. A collection
of documentation strings is not sufficient as a manual because a good
manual is not organized in that fashion; it is organized in terms of
topics of discussion.
Documentation Basics
====================
A documentation string is written using the Lisp syntax for strings,
with double-quote characters surrounding the text of the string. This
is because it really is a Lisp string object. The string serves as
documentation when it is written in the proper place in the definition
of a function or variable. In a function definition, the documentation
string follows the argument list. In a variable definition, the
documentation string follows the initial value of the variable.
When you write a documentation string, make the first line a complete
sentence (or two complete sentences) since some commands, such as
`apropos', show only the first line of a multi-line documentation
string. Also, you should not indent the second line of a documentation
string, if it has one, because that looks odd when you use `C-h f'
(`describe-function') or `C-h v' (`describe-variable') to view the
documentation string. *Note Documentation Tips::.
Documentation strings can contain several special substrings, which
stand for key bindings to be looked up in the current keymaps when the
documentation is displayed. This allows documentation strings to refer
to the keys for related commands and be accurate even when a user
rearranges the key bindings. (*Note Accessing Documentation::.)
In Emacs Lisp, a documentation string is accessible through the
function or variable that it describes:
* The documentation for a function is stored in the function
definition itself (*note Lambda Expressions::). The function
`documentation' knows how to extract it.
* The documentation for a variable is stored in the variable's
property list under the property name `variable-documentation'.
The function `documentation-property' knows how to retrieve it.
To save space, the documentation for preloaded functions and
variables (including primitive functions and autoloaded functions) is
stored in the file `emacs/etc/DOC-VERSION'--not inside Emacs. The
documentation strings for functions and variables loaded during the
Emacs session from byte-compiled files are stored in those files (*note
Docs and Compilation::).
The data structure inside Emacs has an integer offset into the file,
or a list containing a file name and an integer, in place of the
documentation string. The functions `documentation' and
`documentation-property' use that information to fetch the
documentation string from the appropriate file; this is transparent to
the user.
For information on the uses of documentation strings, see *Note
Help: (emacs)Help.
The `emacs/lib-src' directory contains two utilities that you can
use to print nice-looking hardcopy for the file
`emacs/etc/DOC-VERSION'. These are `sorted-doc' and `digest-doc'.
Access to Documentation Strings
===============================
- Function: documentation-property symbol property &optional verbatim
This function returns the documentation string that is recorded in
SYMBOL's property list under property PROPERTY. It retrieves the
text from a file if the value calls for that. If the property
value isn't `nil', isn't a string, and doesn't refer to text in a
file, then it is evaluated to obtain a string.
Finally, `documentation-property' passes the string through
`substitute-command-keys' to substitute actual key bindings,
unless VERBATIM is non-`nil'.
(documentation-property 'command-line-processed
'variable-documentation)
=> "Non-nil once command line has been processed"
(symbol-plist 'command-line-processed)
=> (variable-documentation 188902)
- Function: documentation function &optional verbatim
This function returns the documentation string of FUNCTION.
If FUNCTION is a symbol, this function first looks for the
`function-documentation' property of that symbol; if that has a
non-`nil' value, the documentation comes from that value (if the
value is not a string, it is evaluated). If FUNCTION is not a
symbol, or if it has no `function-documentation' property, then
`documentation' extracts the documentation string from the actual
function definition, reading it from a file if called for.
Finally, unless VERBATIM is non-`nil', it calls
`substitute-command-keys' so as to return a value containing the
actual (current) key bindings.
The function `documentation' signals a `void-function' error if
FUNCTION has no function definition. However, it is OK if the
function definition has no documentation string. In that case,
`documentation' returns `nil'.
Here is an example of using the two functions, `documentation' and
`documentation-property', to display the documentation strings for
several symbols in a `*Help*' buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (user-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(with-output-to-temp-buffer "*Help*"
(mapcar describe-func (sort sym-list 'string<))
(print-help-return-message))))
The `describe-symbols' function works like `apropos', but provides
more information.
(describe-symbols "goal")
---------- Buffer: *Help* ----------
goal-column Option
*Semipermanent goal column for vertical motion, as set by ...
set-goal-column Keys: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable `goal-column'.
temporary-goal-column Variable
Current goal column for vertical motion.
It is the column where point was
at the start of current run of vertical motion commands.
When the `track-eol' feature is doing its job, the value is 9999.
---------- Buffer: *Help* ----------
The asterisk `*' as the first character of a variable's doc string,
as shown above for the `goal-column' variable, means that it is a user
option; see the description of `defvar' in *Note Defining Variables::.
- Function: Snarf-documentation filename
This function is used only during Emacs initialization, just before
the runnable Emacs is dumped. It finds the file offsets of the
documentation strings stored in the file FILENAME, and records
them in the in-core function definitions and variable property
lists in place of the actual strings. *Note Building Emacs::.
Emacs reads the file FILENAME from the `emacs/etc' directory.
When the dumped Emacs is later executed, the same file will be
looked for in the directory `doc-directory'. Usually FILENAME is
`"DOC-VERSION"'.
- Variable: doc-directory
This variable holds the name of the directory which should contain
the file `"DOC-VERSION"' that contains documentation strings for
built-in and preloaded functions and variables.
In most cases, this is the same as `data-directory'. They may be
different when you run Emacs from the directory where you built it,
without actually installing it. See `data-directory' in *Note
Help Functions::.
In older Emacs versions, `exec-directory' was used for this.
Substituting Key Bindings in Documentation
==========================================
When documentation strings refer to key sequences, they should use
the current, actual key bindings. They can do so using certain special
text sequences described below. Accessing documentation strings in the
usual way substitutes current key binding information for these special
sequences. This works by calling `substitute-command-keys'. You can
also call that function yourself.
Here is a list of the special sequences and what they mean:
`\[COMMAND]'
stands for a key sequence that will invoke COMMAND, or `M-x
COMMAND' if COMMAND has no key bindings.
`\{MAPVAR}'
stands for a summary of the keymap which is the value of the
variable MAPVAR. The summary is made using `describe-bindings'.
`\<MAPVAR>'
stands for no text itself. It is used only for a side effect: it
specifies MAPVAR's value as the keymap for any following
`\[COMMAND]' sequences in this documentation string.
`\='
quotes the following character and is discarded; thus, `\=\[' puts
`\[' into the output, and `\=\=' puts `\=' into the output.
*Please note:* Each `\' must be doubled when written in a string in
Emacs Lisp.
- Function: substitute-command-keys string
This function scans STRING for the above special sequences and
replaces them by what they stand for, returning the result as a
string. This permits display of documentation that refers
accurately to the user's own customized key bindings.
Here are examples of the special sequences:
(substitute-command-keys
"To abort recursive edit, type: \\[abort-recursive-edit]")
=> "To abort recursive edit, type: C-]"
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
=> "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
C-j minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
=> "To abort a recursive edit from the minibuffer, type C-g."
Describing Characters for Help Messages
=======================================
These functions convert events, key sequences, or characters to
textual descriptions. These descriptions are useful for including
arbitrary text characters or key sequences in messages, because they
convert non-printing and whitespace characters to sequences of printing
characters. The description of a non-whitespace printing character is
the character itself.
- Function: key-description sequence
This function returns a string containing the Emacs standard
notation for the input events in SEQUENCE. The argument SEQUENCE
may be a string, vector or list. *Note Input Events::, for more
information about valid events. See also the examples for
`single-key-description', below.
- Function: single-key-description event &optional no-angles
This function returns a string describing EVENT in the standard
Emacs notation for keyboard input. A normal printing character
appears as itself, but a control character turns into a string
starting with `C-', a meta character turns into a string starting
with `M-', and space, tab, etc. appear as `SPC', `TAB', etc. A
function key symbol appears inside angle brackets `<...>'. An
event that is a list appears as the name of the symbol in the CAR
of the list, inside angle brackets.
If the optional argument NO-ANGLES is non-`nil', the angle
brackets around function keys and event symbols are omitted; this
is for compatibility with old versions of Emacs which didn't use
the brackets.
(single-key-description ?\C-x)
=> "C-x"
(key-description "\C-x \M-y \n \t \r \f123")
=> "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
(single-key-description 'delete)
=> "<delete>"
(single-key-description 'C-mouse-1)
=> "<C-mouse-1>"
(single-key-description 'C-mouse-1 t)
=> "C-mouse-1"
- Function: text-char-description character
This function returns a string describing CHARACTER in the
standard Emacs notation for characters that appear in text--like
`single-key-description', except that control characters are
represented with a leading caret (which is how control characters
in Emacs buffers are usually displayed).
(text-char-description ?\C-c)
=> "^C"
(text-char-description ?\M-m)
=> "M-m"
(text-char-description ?\C-\M-m)
=> "M-^M"
- Function: read-kbd-macro string
This function is used mainly for operating on keyboard macros, but
it can also be used as a rough inverse for `key-description'. You
call it with a string containing key descriptions, separated by
spaces; it returns a string or vector containing the corresponding
events. (This may or may not be a single valid key sequence,
depending on what events you use; *note Keymap Terminology::.)
Help Functions
==============
Emacs provides a variety of on-line help functions, all accessible to
the user as subcommands of the prefix `C-h'. For more information
about them, see *Note Help: (emacs)Help. Here we describe some
program-level interfaces to the same information.
- Command: apropos regexp &optional do-all
This function finds all symbols whose names contain a match for the
regular expression REGEXP, and returns a list of them (*note
Regular Expressions::). It also displays the symbols in a buffer
named `*Help*', each with a one-line description taken from the
beginning of its documentation string.
If DO-ALL is non-`nil', then `apropos' also shows key bindings for
the functions that are found; it also shows all symbols, even
those that are neither functions nor variables.
In the first of the following examples, `apropos' finds all the
symbols with names containing `exec'. (We don't show here the
output that results in the `*Help*' buffer.)
(apropos "exec")
=> (Buffer-menu-execute command-execute exec-directory
exec-path execute-extended-command execute-kbd-macro
executing-kbd-macro executing-macro)
- Variable: help-map
The value of this variable is a local keymap for characters
following the Help key, `C-h'.
- Prefix Command: help-command
This symbol is not a function; its function definition cell holds
the keymap known as `help-map'. It is defined in `help.el' as
follows:
(define-key global-map "\C-h" 'help-command)
(fset 'help-command help-map)
- Function: print-help-return-message &optional function
This function builds a string that explains how to restore the
previous state of the windows after a help command. After
building the message, it applies FUNCTION to it if FUNCTION is
non-`nil'. Otherwise it calls `message' to display it in the echo
area.
This function expects to be called inside a
`with-output-to-temp-buffer' special form, and expects
`standard-output' to have the value bound by that special form.
For an example of its use, see the long example in *Note Accessing
Documentation::.
- Variable: help-char
The value of this variable is the help character--the character
that Emacs recognizes as meaning Help. By default, its value is
8, which stands for `C-h'. When Emacs reads this character, if
`help-form' is a non-`nil' Lisp expression, it evaluates that
expression, and displays the result in a window if it is a string.
Usually the value of `help-form' is `nil'. Then the help
character has no special meaning at the level of command input, and
it becomes part of a key sequence in the normal way. The standard
key binding of `C-h' is a prefix key for several general-purpose
help features.
The help character is special after prefix keys, too. If it has no
binding as a subcommand of the prefix key, it runs
`describe-prefix-bindings', which displays a list of all the
subcommands of the prefix key.
- Variable: help-event-list
The value of this variable is a list of event types that serve as
alternative "help characters." These events are handled just like
the event specified by `help-char'.
- Variable: help-form
If this variable is non-`nil', its value is a form to evaluate
whenever the character `help-char' is read. If evaluating the form
produces a string, that string is displayed.
A command that calls `read-event' or `read-char' probably should
bind `help-form' to a non-`nil' expression while it does input.
(The time when you should not do this is when `C-h' has some other
meaning.) Evaluating this expression should result in a string
that explains what the input is for and how to enter it properly.
Entry to the minibuffer binds this variable to the value of
`minibuffer-help-form' (*note Minibuffer Misc::).
- Variable: prefix-help-command
This variable holds a function to print help for a prefix key. The
function is called when the user types a prefix key followed by
the help character, and the help character has no binding after
that prefix. The variable's default value is
`describe-prefix-bindings'.
- Function: describe-prefix-bindings
This function calls `describe-bindings' to display a list of all
the subcommands of the prefix key of the most recent key sequence.
The prefix described consists of all but the last event of that
key sequence. (The last event is, presumably, the help character.)
The following two functions are meant for modes that want to provide
help without relinquishing control, such as the "electric" modes.
Their names begin with `Helper' to distinguish them from the ordinary
help functions.
- Command: Helper-describe-bindings
This command pops up a window displaying a help buffer containing a
listing of all of the key bindings from both the local and global
keymaps. It works by calling `describe-bindings'.
- Command: Helper-help
This command provides help for the current mode. It prompts the
user in the minibuffer with the message `Help (Type ? for further
options)', and then provides assistance in finding out what the key
bindings are, and what the mode is intended for. It returns `nil'.
This can be customized by changing the map `Helper-help-map'.
- Variable: data-directory
This variable holds the name of the directory in which Emacs finds
certain documentation and text files that come with Emacs. In
older Emacs versions, `exec-directory' was used for this.
- Macro: make-help-screen fname help-line help-text help-map
This macro defines a help command named FNAME that acts like a
prefix key that shows a list of the subcommands it offers.
When invoked, FNAME displays HELP-TEXT in a window, then reads and
executes a key sequence according to HELP-MAP. The string
HELP-TEXT should describe the bindings available in HELP-MAP.
The command FNAME is defined to handle a few events itself, by
scrolling the display of HELP-TEXT. When FNAME reads one of those
special events, it does the scrolling and then reads another
event. When it reads an event that is not one of those few, and
which has a binding in HELP-MAP, it executes that key's binding and
then returns.
The argument HELP-LINE should be a single-line summary of the
alternatives in HELP-MAP. In the current version of Emacs, this
argument is used only if you set the option `three-step-help' to
`t'.
This macro is used in the command `help-for-help' which is the
binding of `C-h C-h'.
- User Option: three-step-help
If this variable is non-`nil', commands defined with
`make-help-screen' display their HELP-LINE strings in the echo
area at first, and display the longer HELP-TEXT strings only if
the user types the help character again.
Files
*****
In Emacs, you can find, create, view, save, and otherwise work with
files and file directories. This chapter describes most of the
file-related functions of Emacs Lisp, but a few others are described in
*Note Buffers::, and those related to backups and auto-saving are
described in *Note Backups and Auto-Saving::.
Many of the file functions take one or more arguments that are file
names. A file name is actually a string. Most of these functions
expand file name arguments by calling `expand-file-name', so that `~'
is handled correctly, as are relative file names (including `../').
These functions don't recognize environment variable substitutions such
as `$HOME'. *Note File Name Expansion::.
When file I/O functions signal Lisp errors, they usually use the
condition `file-error' (*note Handling Errors::). The error message is
in most cases obtained from the operating system, according to locale
`system-message-locale', and decoded using coding system
`locale-coding-system' (*note Locales::).
Visiting Files
==============
Visiting a file means reading a file into a buffer. Once this is
done, we say that the buffer is "visiting" that file, and call the file
"the visited file" of the buffer.
A file and a buffer are two different things. A file is information
recorded permanently in the computer (unless you delete it). A buffer,
on the other hand, is information inside of Emacs that will vanish at
the end of the editing session (or when you kill the buffer). Usually,
a buffer contains information that you have copied from a file; then we
say the buffer is visiting that file. The copy in the buffer is what
you modify with editing commands. Such changes to the buffer do not
change the file; therefore, to make the changes permanent, you must
"save" the buffer, which means copying the altered buffer contents back
into the file.
In spite of the distinction between files and buffers, people often
refer to a file when they mean a buffer and vice-versa. Indeed, we say,
"I am editing a file," rather than, "I am editing a buffer that I will
soon save as a file of the same name." Humans do not usually need to
make the distinction explicit. When dealing with a computer program,
however, it is good to keep the distinction in mind.
Functions for Visiting Files
----------------------------
This section describes the functions normally used to visit files.
For historical reasons, these functions have names starting with
`find-' rather than `visit-'. *Note Buffer File Name::, for functions
and variables that access the visited file name of a buffer or that
find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use `insert-file-contents' in a
temporary buffer. Visiting the file is not necessary and takes longer.
*Note Reading from Files::.
- Command: find-file filename &optional wildcards
This command selects a buffer visiting the file FILENAME, using an
existing buffer if there is one, and otherwise creating a new
buffer and reading the file into it. It also returns that buffer.
The body of the `find-file' function is very simple and looks like
this:
(switch-to-buffer (find-file-noselect filename))
(See `switch-to-buffer' in *Note Displaying Buffers::.)
If WILDCARDS is non-`nil', which is always true in an interactive
call, then `find-file' expands wildcard characters in FILENAME and
visits all the matching files.
When `find-file' is called interactively, it prompts for FILENAME
in the minibuffer.
- Function: find-file-noselect filename &optional nowarn rawfile
wildcards
This function is the guts of all the file-visiting functions. It
finds or creates a buffer visiting the file FILENAME, and returns
it. It uses an existing buffer if there is one, and otherwise
creates a new buffer and reads the file into it. You may make the
buffer current or display it in a window if you wish, but this
function does not do so.
If WILDCARDS is non-`nil', then `find-file-noselect' expands
wildcard characters in FILENAME and visits all the matching files.
When `find-file-noselect' uses an existing buffer, it first
verifies that the file has not changed since it was last visited or
saved in that buffer. If the file has changed, then this function
asks the user whether to reread the changed file. If the user says
`yes', any changes previously made in the buffer are lost.
This function displays warning or advisory messages in various
peculiar cases, unless the optional argument NOWARN is non-`nil'.
For example, if it needs to create a buffer, and there is no file
named FILENAME, it displays the message `(New file)' in the echo
area, and leaves the buffer empty.
The `find-file-noselect' function normally calls `after-find-file'
after reading the file (*note Subroutines of Visiting::). That
function sets the buffer major mode, parses local variables, warns
the user if there exists an auto-save file more recent than the
file just visited, and finishes by running the functions in
`find-file-hooks'.
If the optional argument RAWFILE is non-`nil', then
`after-find-file' is not called, and the
`find-file-not-found-hooks' are not run in case of failure. What's
more, a non-`nil' RAWFILE value suppresses coding system
conversion (*note Coding Systems::) and format conversion (*note
Format Conversion::).
The `find-file-noselect' function usually returns the buffer that
is visiting the file FILENAME. But, if wildcards are actually
used and expanded, it returns a list of buffers that are visiting
the various files.
(find-file-noselect "/etc/fstab")
=> #<buffer fstab>
- Command: find-file-other-window filename &optional wildcards
This command selects a buffer visiting the file FILENAME, but does
so in a window other than the selected window. It may use another
existing window or split a window; see *Note Displaying Buffers::.
When this command is called interactively, it prompts for FILENAME.
- Command: find-file-read-only filename &optional wildcards
This command selects a buffer visiting the file FILENAME, like
`find-file', but it marks the buffer as read-only. *Note Read
Only Buffers::, for related functions and variables.
When this command is called interactively, it prompts for FILENAME.
- Command: view-file filename
This command visits FILENAME using View mode, returning to the
previous buffer when you exit View mode. View mode is a minor
mode that provides commands to skim rapidly through the file, but
does not let you modify the text. Entering View mode runs the
normal hook `view-mode-hook'. *Note Hooks::.
When `view-file' is called interactively, it prompts for FILENAME.
- Variable: find-file-wildcards
If this variable is non-`nil', then the various `find-file'
commands check for wildcard characters and visit all the files that
match them. If this is `nil', then wildcard characters are not
treated specially.
- Variable: find-file-hooks
The value of this variable is a list of functions to be called
after a file is visited. The file's local-variables specification
(if any) will have been processed before the hooks are run. The
buffer visiting the file is current when the hook functions are
run.
This variable works just like a normal hook, but we think that
renaming it would not be advisable. *Note Hooks::.
- Variable: find-file-not-found-hooks
The value of this variable is a list of functions to be called when
`find-file' or `find-file-noselect' is passed a nonexistent file
name. `find-file-noselect' calls these functions as soon as it
detects a nonexistent file. It calls them in the order of the
list, until one of them returns non-`nil'. `buffer-file-name' is
already set up.
This is not a normal hook because the values of the functions are
used, and in many cases only some of the functions are called.
Subroutines of Visiting
-----------------------
The `find-file-noselect' function uses two important subroutines
which are sometimes useful in user Lisp code: `create-file-buffer' and
`after-find-file'. This section explains how to use them.
- Function: create-file-buffer filename
This function creates a suitably named buffer for visiting
FILENAME, and returns it. It uses FILENAME (sans directory) as
the name if that name is free; otherwise, it appends a string such
as `<2>' to get an unused name. See also *Note Creating Buffers::.
*Please note:* `create-file-buffer' does _not_ associate the new
buffer with a file and does not select the buffer. It also does
not use the default major mode.
(create-file-buffer "foo")
=> #<buffer foo>
(create-file-buffer "foo")
=> #<buffer foo<2>>
(create-file-buffer "foo")
=> #<buffer foo<3>>
This function is used by `find-file-noselect'. It uses
`generate-new-buffer' (*note Creating Buffers::).
- Function: after-find-file &optional error warn noauto
after-find-file-from-revert-buffer nomodes
This function sets the buffer major mode, and parses local
variables (*note Auto Major Mode::). It is called by
`find-file-noselect' and by the default revert function (*note
Reverting::).
If reading the file got an error because the file does not exist,
but its directory does exist, the caller should pass a non-`nil'
value for ERROR. In that case, `after-find-file' issues a warning:
`(New file)'. For more serious errors, the caller should usually
not call `after-find-file'.
If WARN is non-`nil', then this function issues a warning if an
auto-save file exists and is more recent than the visited file.
If NOAUTO is non-`nil', that says not to enable or disable
Auto-Save mode. The mode remains enabled if it was enabled before.
If AFTER-FIND-FILE-FROM-REVERT-BUFFER is non-`nil', that means
this call was from `revert-buffer'. This has no direct effect,
but some mode functions and hook functions check the value of this
variable.
If NOMODES is non-`nil', that means don't alter the buffer's major
mode, don't process local variables specifications in the file,
and don't run `find-file-hooks'. This feature is used by
`revert-buffer' in some cases.
The last thing `after-find-file' does is call all the functions in
the list `find-file-hooks'.
Saving Buffers
==============
When you edit a file in Emacs, you are actually working on a buffer
that is visiting that file--that is, the contents of the file are
copied into the buffer and the copy is what you edit. Changes to the
buffer do not change the file until you "save" the buffer, which means
copying the contents of the buffer into the file.
- Command: save-buffer &optional backup-option
This function saves the contents of the current buffer in its
visited file if the buffer has been modified since it was last
visited or saved. Otherwise it does nothing.
`save-buffer' is responsible for making backup files. Normally,
BACKUP-OPTION is `nil', and `save-buffer' makes a backup file only
if this is the first save since visiting the file. Other values
for BACKUP-OPTION request the making of backup files in other
circumstances:
* With an argument of 4 or 64, reflecting 1 or 3 `C-u''s, the
`save-buffer' function marks this version of the file to be
backed up when the buffer is next saved.
* With an argument of 16 or 64, reflecting 2 or 3 `C-u''s, the
`save-buffer' function unconditionally backs up the previous
version of the file before saving it.
- Command: save-some-buffers &optional save-silently-p pred
This command saves some modified file-visiting buffers. Normally
it asks the user about each buffer. But if SAVE-SILENTLY-P is
non-`nil', it saves all the file-visiting buffers without querying
the user.
The optional PRED argument controls which buffers to ask about.
If it is `nil', that means to ask only about file-visiting buffers.
If it is `t', that means also offer to save certain other non-file
buffers--those that have a non-`nil' buffer-local value of
`buffer-offer-save'. (A user who says `yes' to saving a non-file
buffer is asked to specify the file name to use.) The
`save-buffers-kill-emacs' function passes the value `t' for PRED.
If PRED is neither `t' nor `nil', then it should be a function of
no arguments. It will be called in each buffer to decide whether
to offer to save that buffer. If it returns a non-`nil' value in
a certain buffer, that means do offer to save that buffer.
- Command: write-file filename &optional confirm
This function writes the current buffer into file FILENAME, makes
the buffer visit that file, and marks it not modified. Then it
renames the buffer based on FILENAME, appending a string like `<2>'
if necessary to make a unique buffer name. It does most of this
work by calling `set-visited-file-name' (*note Buffer File Name::)
and `save-buffer'.
If CONFIRM is non-`nil', that means to ask for confirmation before
overwriting an existing file.
Saving a buffer runs several hooks. It also performs format
conversion (*note Format Conversion::), and may save text properties in
"annotations" (*note Saving Properties::).
- Variable: write-file-hooks
The value of this variable is a list of functions to be called
before writing out a buffer to its visited file. If one of them
returns non-`nil', the file is considered already written and the
rest of the functions are not called, nor is the usual code for
writing the file executed.
If a function in `write-file-hooks' returns non-`nil', it is
responsible for making a backup file (if that is appropriate). To
do so, execute the following code:
(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by
`backup-buffer' and use that to set the mode bits of the file that
you write. This is what `save-buffer' normally does.
The hook functions in `write-file-hooks' are also responsible for
encoding the data (if desired): they must choose a suitable coding
system (*note Lisp and Coding Systems::), perform the encoding
(*note Explicit Encoding::), and set `last-coding-system-used' to
the coding system that was used (*note Encoding and I/O::).
Do not make this variable buffer-local. To set up buffer-specific
hook functions, use `write-contents-hooks' instead.
Even though this is not a normal hook, you can use `add-hook' and
`remove-hook' to manipulate the list. *Note Hooks::.
- Variable: local-write-file-hooks
This works just like `write-file-hooks', but it is intended to be
made buffer-local in particular buffers, and used for hooks that
pertain to the file name or the way the buffer contents were
obtained.
The variable is marked as a permanent local, so that changing the
major mode does not alter a buffer-local value. This is
convenient for packages that read "file" contents in special ways,
and set up hooks to save the data in a corresponding way.
- Variable: write-contents-hooks
This works just like `write-file-hooks', but it is intended for
hooks that pertain to the contents of the file, as opposed to
hooks that pertain to where the file came from. Such hooks are
usually set up by major modes, as buffer-local bindings for this
variable.
This variable automatically becomes buffer-local whenever it is
set; switching to a new major mode always resets this variable.
When you use `add-hooks' to add an element to this hook, you
should _not_ specify a non-`nil' LOCAL argument, since this
variable is used _only_ buffer-locally.
- Variable: after-save-hook
This normal hook runs after a buffer has been saved in its visited
file. One use of this hook is in Fast Lock mode; it uses this
hook to save the highlighting information in a cache file.
- Variable: file-precious-flag
If this variable is non-`nil', then `save-buffer' protects against
I/O errors while saving by writing the new file to a temporary
name instead of the name it is supposed to have, and then renaming
it to the intended name after it is clear there are no errors.
This procedure prevents problems such as a lack of disk space from
resulting in an invalid file.
As a side effect, backups are necessarily made by copying. *Note
Rename or Copy::. Yet, at the same time, saving a precious file
always breaks all hard links between the file you save and other
file names.
Some modes give this variable a non-`nil' buffer-local value in
particular buffers.
- User Option: require-final-newline
This variable determines whether files may be written out that do
_not_ end with a newline. If the value of the variable is `t',
then `save-buffer' silently adds a newline at the end of the file
whenever the buffer being saved does not already end in one. If
the value of the variable is non-`nil', but not `t', then
`save-buffer' asks the user whether to add a newline each time the
case arises.
If the value of the variable is `nil', then `save-buffer' doesn't
add newlines at all. `nil' is the default value, but a few major
modes set it to `t' in particular buffers.
See also the function `set-visited-file-name' (*note Buffer File
Name::).
Reading from Files
==================
You can copy a file from the disk and insert it into a buffer using
the `insert-file-contents' function. Don't use the user-level command
`insert-file' in a Lisp program, as that sets the mark.
- Function: insert-file-contents filename &optional visit beg end
replace
This function inserts the contents of file FILENAME into the
current buffer after point. It returns a list of the absolute
file name and the length of the data inserted. An error is
signaled if FILENAME is not the name of a file that can be read.
The function `insert-file-contents' checks the file contents
against the defined file formats, and converts the file contents if
appropriate. *Note Format Conversion::. It also calls the
functions in the list `after-insert-file-functions'; see *Note
Saving Properties::. Normally, one of the functions in the
`after-insert-file-functions' list determines the coding system
(*note Coding Systems::) used for decoding the file's contents.
If VISIT is non-`nil', this function additionally marks the buffer
as unmodified and sets up various fields in the buffer so that it
is visiting the file FILENAME: these include the buffer's visited
file name and its last save file modtime. This feature is used by
`find-file-noselect' and you probably should not use it yourself.
If BEG and END are non-`nil', they should be integers specifying
the portion of the file to insert. In this case, VISIT must be
`nil'. For example,
(insert-file-contents filename nil 0 500)
inserts the first 500 characters of a file.
If the argument REPLACE is non-`nil', it means to replace the
contents of the buffer (actually, just the accessible portion)
with the contents of the file. This is better than simply
deleting the buffer contents and inserting the whole file, because
(1) it preserves some marker positions and (2) it puts less data
in the undo list.
It is possible to read a special file (such as a FIFO or an I/O
device) with `insert-file-contents', as long as REPLACE and VISIT
are `nil'.
- Function: insert-file-contents-literally filename &optional visit
beg end replace
This function works like `insert-file-contents' except that it does
not do format decoding (*note Format Conversion::), does not do
character code conversion (*note Coding Systems::), does not run
`find-file-hooks', does not perform automatic uncompression, and so
on.
If you want to pass a file name to another process so that another
program can read the file, use the function `file-local-copy'; see
*Note Magic File Names::.
Writing to Files
================
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the `append-to-file' and `write-region'
functions. Don't use these functions to write to files that are being
visited; that could cause confusion in the mechanisms for visiting.
- Command: append-to-file start end filename
This function appends the contents of the region delimited by
START and END in the current buffer to the end of file FILENAME.
If that file does not exist, it is created. This function returns
`nil'.
An error is signaled if FILENAME specifies a nonwritable file, or
a nonexistent file in a directory where files cannot be created.
- Command: write-region start end filename &optional append visit
lockname mustbenew
This function writes the region delimited by START and END in the
current buffer into the file specified by FILENAME.
If START is a string, then `write-region' writes or appends that
string, rather than text from the buffer. END is ignored in this
case.
If APPEND is non-`nil', then the specified text is appended to the
existing file contents (if any). Starting in Emacs 21, if APPEND
is an integer, then `write-region' seeks to that byte offset from
the start of the file and writes the data from there.
If MUSTBENEW is non-`nil', then `write-region' asks for
confirmation if FILENAME names an existing file. Starting in
Emacs 21, if MUSTBENEW is the symbol `excl', then `write-region'
does not ask for confirmation, but instead it signals an error
`file-already-exists' if the file already exists.
The test for an existing file, when MUSTBENEW is `excl', uses a
special system feature. At least for files on a local disk, there
is no chance that some other program could create a file of the
same name before Emacs does, without Emacs's noticing.
If VISIT is `t', then Emacs establishes an association between the
buffer and the file: the buffer is then visiting that file. It
also sets the last file modification time for the current buffer to
FILENAME's modtime, and marks the buffer as not modified. This
feature is used by `save-buffer', but you probably should not use
it yourself.
If VISIT is a string, it specifies the file name to visit. This
way, you can write the data to one file (FILENAME) while recording
the buffer as visiting another file (VISIT). The argument VISIT
is used in the echo area message and also for file locking; VISIT
is stored in `buffer-file-name'. This feature is used to
implement `file-precious-flag'; don't use it yourself unless you
really know what you're doing.
The optional argument LOCKNAME, if non-`nil', specifies the file
name to use for purposes of locking and unlocking, overriding
FILENAME and VISIT for that purpose.
The function `write-region' converts the data which it writes to
the appropriate file formats specified by `buffer-file-format'.
*Note Format Conversion::. It also calls the functions in the list
`write-region-annotate-functions'; see *Note Saving Properties::.
Normally, `write-region' displays the message `Wrote FILENAME' in
the echo area. If VISIT is neither `t' nor `nil' nor a string,
then this message is inhibited. This feature is useful for
programs that use files for internal purposes, files that the user
does not need to know about.
- Macro: with-temp-file file body...
The `with-temp-file' macro evaluates the BODY forms with a
temporary buffer as the current buffer; then, at the end, it
writes the buffer contents into file FILE. It kills the temporary
buffer when finished, restoring the buffer that was current before
the `with-temp-file' form. Then it returns the value of the last
form in BODY.
The current buffer is restored even in case of an abnormal exit via
`throw' or error (*note Nonlocal Exits::).
See also `with-temp-buffer' in *Note Current Buffer::.
File Locks
==========
When two users edit the same file at the same time, they are likely
to interfere with each other. Emacs tries to prevent this situation
from arising by recording a "file lock" when a file is being modified.
Emacs can then detect the first attempt to modify a buffer visiting a
file that is locked by another Emacs job, and ask the user what to do.
The file lock is really a file, a symbolic link with a special name,
stored in the same directory as the file you are editing.
When you access files using NFS, there may be a small probability
that you and another user will both lock the same file "simultaneously".
If this happens, it is possible for the two users to make changes
simultaneously, but Emacs will still warn the user who saves second.
Also, the detection of modification of a buffer visiting a file changed
on disk catches some cases of simultaneous editing; see *Note
Modification Time::.
- Function: file-locked-p filename
This function returns `nil' if the file FILENAME is not locked.
It returns `t' if it is locked by this Emacs process, and it
returns the name of the user who has locked it if it is locked by
some other job.
(file-locked-p "foo")
=> nil
- Function: lock-buffer &optional filename
This function locks the file FILENAME, if the current buffer is
modified. The argument FILENAME defaults to the current buffer's
visited file. Nothing is done if the current buffer is not
visiting a file, or is not modified.
- Function: unlock-buffer
This function unlocks the file being visited in the current buffer,
if the buffer is modified. If the buffer is not modified, then
the file should not be locked, so this function does nothing. It
also does nothing if the current buffer is not visiting a file.
File locking is not supported on some systems. On systems that do
not support it, the functions `lock-buffer', `unlock-buffer' and
`file-locked-p' do nothing and return `nil'.
- Function: ask-user-about-lock file other-user
This function is called when the user tries to modify FILE, but it
is locked by another user named OTHER-USER. The default
definition of this function asks the user to say what to do. The
value this function returns determines what Emacs does next:
* A value of `t' says to grab the lock on the file. Then this
user may edit the file and OTHER-USER loses the lock.
* A value of `nil' says to ignore the lock and let this user
edit the file anyway.
* This function may instead signal a `file-locked' error, in
which case the change that the user was about to make does
not take place.
The error message for this error looks like this:
error--> File is locked: FILE OTHER-USER
where `file' is the name of the file and OTHER-USER is the
name of the user who has locked the file.
If you wish, you can replace the `ask-user-about-lock' function
with your own version that makes the decision in another way. The
code for its usual definition is in `userlock.el'.
Information about Files
=======================
The functions described in this section all operate on strings that
designate file names. All the functions have names that begin with the
word `file'. These functions all return information about actual files
or directories, so their arguments must all exist as actual files or
directories unless otherwise noted.
Testing Accessibility
---------------------
These functions test for permission to access a file in specific
ways.
- Function: file-exists-p filename
This function returns `t' if a file named FILENAME appears to
exist. This does not mean you can necessarily read the file, only
that you can find out its attributes. (On Unix and GNU/Linux,
this is true if the file exists and you have execute permission on
the containing directories, regardless of the protection of the
file itself.)
If the file does not exist, or if fascist access control policies
prevent you from finding the attributes of the file, this function
returns `nil'.
- Function: file-readable-p filename
This function returns `t' if a file named FILENAME exists and you
can read it. It returns `nil' otherwise.
(file-readable-p "files.texi")
=> t
(file-exists-p "/usr/spool/mqueue")
=> t
(file-readable-p "/usr/spool/mqueue")
=> nil
- Function: file-executable-p filename
This function returns `t' if a file named FILENAME exists and you
can execute it. It returns `nil' otherwise. On Unix and
GNU/Linux, if the file is a directory, execute permission means
you can check the existence and attributes of files inside the
directory, and open those files if their modes permit.
- Function: file-writable-p filename
This function returns `t' if the file FILENAME can be written or
created by you, and `nil' otherwise. A file is writable if the
file exists and you can write it. It is creatable if it does not
exist, but the specified directory does exist and you can write in
that directory.
In the third example below, `foo' is not writable because the
parent directory does not exist, even though the user could create
such a directory.
(file-writable-p "~/foo")
=> t
(file-writable-p "/foo")
=> nil
(file-writable-p "~/no-such-dir/foo")
=> nil
- Function: file-accessible-directory-p dirname
This function returns `t' if you have permission to open existing
files in the directory whose name as a file is DIRNAME; otherwise
(or if there is no such directory), it returns `nil'. The value
of DIRNAME may be either a directory name or the file name of a
file which is a directory.
Example: after the following,
(file-accessible-directory-p "/foo")
=> nil
we can deduce that any attempt to read a file in `/foo/' will give
an error.
- Function: access-file filename string
This function opens file FILENAME for reading, then closes it and
returns `nil'. However, if the open fails, it signals an error
using STRING as the error message text.
- Function: file-ownership-preserved-p filename
This function returns `t' if deleting the file FILENAME and then
creating it anew would keep the file's owner unchanged.
- Function: file-newer-than-file-p filename1 filename2
This function returns `t' if the file FILENAME1 is newer than file
FILENAME2. If FILENAME1 does not exist, it returns `nil'. If
FILENAME2 does not exist, it returns `t'.
In the following example, assume that the file `aug-19' was written
on the 19th, `aug-20' was written on the 20th, and the file
`no-file' doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20")
=> nil
(file-newer-than-file-p "aug-20" "aug-19")
=> t
(file-newer-than-file-p "aug-19" "no-file")
=> t
(file-newer-than-file-p "no-file" "aug-19")
=> nil
You can use `file-attributes' to get a file's last modification
time as a list of two numbers. *Note File Attributes::.
Distinguishing Kinds of Files
-----------------------------
This section describes how to distinguish various kinds of files,
such as directories, symbolic links, and ordinary files.
- Function: file-symlink-p filename
If the file FILENAME is a symbolic link, the `file-symlink-p'
function returns the file name to which it is linked. This may be
the name of a text file, a directory, or even another symbolic
link, or it may be a nonexistent file name.
If the file FILENAME is not a symbolic link (or there is no such
file), `file-symlink-p' returns `nil'.
(file-symlink-p "foo")
=> nil
(file-symlink-p "sym-link")
=> "foo"
(file-symlink-p "sym-link2")
=> "sym-link"
(file-symlink-p "/bin")
=> "/pub/bin"
- Function: file-directory-p filename
This function returns `t' if FILENAME is the name of an existing
directory, `nil' otherwise.
(file-directory-p "~rms")
=> t
(file-directory-p "~rms/lewis/files.texi")
=> nil
(file-directory-p "~rms/lewis/no-such-file")
=> nil
(file-directory-p "$HOME")
=> nil
(file-directory-p
(substitute-in-file-name "$HOME"))
=> t
- Function: file-regular-p filename
This function returns `t' if the file FILENAME exists and is a
regular file (not a directory, named pipe, terminal, or other I/O
device).
Truenames
---------
The "truename" of a file is the name that you get by following
symbolic links at all levels until none remain, then simplifying away
`.' and `..' appearing as name components. This results in a sort of
canonical name for the file. A file does not always have a unique
truename; the number of distinct truenames a file has is equal to the
number of hard links to the file. However, truenames are useful
because they eliminate symbolic links as a cause of name variation.
- Function: file-truename filename
The function `file-truename' returns the truename of the file
FILENAME. The argument must be an absolute file name.
- Function: file-chase-links filename
This function follows symbolic links, starting with FILENAME,
until it finds a file name which is not the name of a symbolic
link. Then it returns that file name.
To illustrate the difference between `file-chase-links' and
`file-truename', suppose that `/usr/foo' is a symbolic link to the
directory `/home/foo', and `/home/foo/hello' is an ordinary file (or at
least, not a symbolic link) or nonexistent. Then we would have:
(file-chase-links "/usr/foo/hello")
;; This does not follow the links in the parent directories.
=> "/usr/foo/hello"
(file-truename "/usr/foo/hello")
;; Assuming that `/home' is not a symbolic link.
=> "/home/foo/hello"
*Note Buffer File Name::, for related information.
Other Information about Files
-----------------------------
This section describes the functions for getting detailed information
about a file, other than its contents. This information includes the
mode bits that control access permission, the owner and group numbers,
the number of names, the inode number, the size, and the times of access
and modification.
- Function: file-modes filename
This function returns the mode bits of FILENAME, as an integer.
The mode bits are also called the file permissions, and they
specify access control in the usual Unix fashion. If the
low-order bit is 1, then the file is executable by all users, if
the second-lowest-order bit is 1, then the file is writable by all
users, etc.
The highest value returnable is 4095 (7777 octal), meaning that
everyone has read, write, and execute permission, that the SUID bit
is set for both others and group, and that the sticky bit is set.
(file-modes "~/junk/diffs")
=> 492 ; Decimal integer.
(format "%o" 492)
=> "754" ; Convert to octal.
(set-file-modes "~/junk/diffs" 438)
=> nil
(format "%o" 438)
=> "666" ; Convert to octal.
% ls -l diffs
-rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
- Function: file-nlinks filename
This functions returns the number of names (i.e., hard links) that
file FILENAME has. If the file does not exist, then this function
returns `nil'. Note that symbolic links have no effect on this
function, because they are not considered to be names of the files
they link to.
% ls -l foo*
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
(file-nlinks "foo")
=> 2
(file-nlinks "doesnt-exist")
=> nil
- Function: file-attributes filename
This function returns a list of attributes of file FILENAME. If
the specified file cannot be opened, it returns `nil'.
The elements of the list, in order, are:
0. `t' for a directory, a string for a symbolic link (the name
linked to), or `nil' for a text file.
1. The number of names the file has. Alternate names, also
known as hard links, can be created by using the
`add-name-to-file' function (*note Changing Files::).
2. The file's UID.
3. The file's GID.
4. The time of last access, as a list of two integers. The
first integer has the high-order 16 bits of time, the second
has the low 16 bits. (This is similar to the value of
`current-time'; see *Note Time of Day::.)
5. The time of last modification as a list of two integers (as
above).
6. The time of last status change as a list of two integers (as
above).
7. The size of the file in bytes. If the size is too large to
fit in a Lisp integer, this is a floating point number.
8. The file's modes, as a string of ten letters or dashes, as in
`ls -l'.
9. `t' if the file's GID would change if file were deleted and
recreated; `nil' otherwise.
10. The file's inode number. If possible, this is an integer.
If the inode number is too large to be represented as an
integer in Emacs Lisp, then the value has the form `(HIGH .
LOW)', where LOW holds the low 16 bits.
11. The file system number of the file system that the file is in.
Depending on the magnitude of the value, this can be either
an integer or a cons cell, in the same manner as the inode
number. This element and the file's inode number together
give enough information to distinguish any two files on the
system--no two files can have the same values for both of
these numbers.
For example, here are the file attributes for `files.texi':
(file-attributes "files.texi")
=> (nil 1 2235 75
(8489 20284)
(8489 20284)
(8489 20285)
14906 "-rw-rw-rw-"
nil 129500 -32252)
and here is how the result is interpreted:
`nil'
is neither a directory nor a symbolic link.
`1'
has only one name (the name `files.texi' in the current
default directory).
`2235'
is owned by the user with UID 2235.
`75'
is in the group with GID 75.
`(8489 20284)'
was last accessed on Aug 19 00:09.
`(8489 20284)'
was last modified on Aug 19 00:09.
`(8489 20285)'
last had its inode changed on Aug 19 00:09.
`14906'
is 14906 bytes long. (It may not contain 14906 characters,
though, if some of the bytes belong to multibyte sequences.)
`"-rw-rw-rw-"'
has a mode of read and write access for the owner, group, and
world.
`nil'
would retain the same GID if it were recreated.
`129500'
has an inode number of 129500.
`-32252'
is on file system number -32252.
Changing File Names and Attributes
==================================
The functions in this section rename, copy, delete, link, and set the
modes of files.
In the functions that have an argument NEWNAME, if a file by the
name of NEWNAME already exists, the actions taken depend on the value
of the argument OK-IF-ALREADY-EXISTS:
* Signal a `file-already-exists' error if OK-IF-ALREADY-EXISTS is
`nil'.
* Request confirmation if OK-IF-ALREADY-EXISTS is a number.
* Replace the old file without confirmation if OK-IF-ALREADY-EXISTS
is any other value.
- Function: add-name-to-file oldname newname &optional
ok-if-already-exists
This function gives the file named OLDNAME the additional name
NEWNAME. This means that NEWNAME becomes a new "hard link" to
OLDNAME.
In the first part of the following example, we list two files,
`foo' and `foo3'.
% ls -li fo*
81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo
84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Now we create a hard link, by calling `add-name-to-file', then list
the files again. This shows two names for one file, `foo' and
`foo2'.
(add-name-to-file "foo" "foo2")
=> nil
% ls -li fo*
81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Finally, we evaluate the following:
(add-name-to-file "foo" "foo3" t)
and list the files again. Now there are three names for one file:
`foo', `foo2', and `foo3'. The old contents of `foo3' are lost.
(add-name-to-file "foo1" "foo3")
=> nil
% ls -li fo*
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
This function is meaningless on operating systems where multiple
names for one file are not allowed. Some systems implement
multiple names by copying the file instead.
See also `file-nlinks' in *Note File Attributes::.
- Command: rename-file filename newname &optional ok-if-already-exists
This command renames the file FILENAME as NEWNAME.
If FILENAME has additional names aside from FILENAME, it continues
to have those names. In fact, adding the name NEWNAME with
`add-name-to-file' and then deleting FILENAME has the same effect
as renaming, aside from momentary intermediate states.
In an interactive call, this function prompts for FILENAME and
NEWNAME in the minibuffer; also, it requests confirmation if
NEWNAME already exists.
- Command: copy-file oldname newname &optional ok-if-exists time
This command copies the file OLDNAME to NEWNAME. An error is
signaled if OLDNAME does not exist.
If TIME is non-`nil', then this function gives the new file the
same last-modified time that the old one has. (This works on only
some operating systems.) If setting the time gets an error,
`copy-file' signals a `file-date-error' error.
In an interactive call, this function prompts for FILENAME and
NEWNAME in the minibuffer; also, it requests confirmation if
NEWNAME already exists.
- Command: delete-file filename
This command deletes the file FILENAME, like the shell command `rm
FILENAME'. If the file has multiple names, it continues to exist
under the other names.
A suitable kind of `file-error' error is signaled if the file does
not exist, or is not deletable. (On Unix and GNU/Linux, a file is
deletable if its directory is writable.)
See also `delete-directory' in *Note Create/Delete Dirs::.
- Command: make-symbolic-link filename newname &optional ok-if-exists
This command makes a symbolic link to FILENAME, named NEWNAME.
This is like the shell command `ln -s FILENAME NEWNAME'.
In an interactive call, this function prompts for FILENAME and
NEWNAME in the minibuffer; also, it requests confirmation if
NEWNAME already exists.
This function is not available on systems that don't support
symbolic links.
- Function: define-logical-name varname string
This function defines the logical name NAME to have the value
STRING. It is available only on VMS.
- Function: set-file-modes filename mode
This function sets mode bits of FILENAME to MODE (which must be an
integer). Only the low 12 bits of MODE are used.
- Function: set-default-file-modes mode
This function sets the default file protection for new files
created by Emacs and its subprocesses. Every file created with
Emacs initially has this protection, or a subset of it
(`write-region' will not give a file execute permission even if
the default file protection allows execute permission). On Unix
and GNU/Linux, the default protection is the bitwise complement of
the "umask" value.
The argument MODE must be an integer. On most systems, only the
low 9 bits of MODE are meaningful. You can use the Lisp construct
for octal character codes to enter MODE; for example,
(set-default-file-modes ?\644)
Saving a modified version of an existing file does not count as
creating the file; it preserves the existing file's mode, whatever
that is. So the default file protection has no effect.
- Function: default-file-modes
This function returns the current default protection value.
On MS-DOS, there is no such thing as an "executable" file mode bit.
So Emacs considers a file executable if its name ends in one of the
standard executable extensions, such as `.com', `.bat', `.exe', and
some others. Files that begin with the Unix-standard `#!' signature,
such as shell and Perl scripts, are also considered as executable
files. This is reflected in the values returned by `file-modes' and
`file-attributes'. Directories are also reported with executable bit
set, for compatibility with Unix.
File Names
==========
Files are generally referred to by their names, in Emacs as
elsewhere. File names in Emacs are represented as strings. The
functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs
often need to operate on file names; i.e., to take them apart and to use
part of a name to construct related file names. This section describes
how to manipulate file names.
The functions in this section do not actually access files, so they
can operate on file names that do not refer to an existing file or
directory.
On MS-DOS and MS-Windows, these functions (like the function that
actually operate on files) accept MS-DOS or MS-Windows file-name syntax,
where backslashes separate the components, as well as Unix syntax; but
they always return Unix syntax. On VMS, these functions (and the ones
that operate on files) understand both VMS file-name syntax and Unix
syntax. This enables Lisp programs to specify file names in Unix syntax
and work properly on all systems without change.
File Name Components
--------------------
The operating system groups files into directories. To specify a
file, you must specify the directory and the file's name within that
directory. Therefore, Emacs considers a file name as having two main
parts: the "directory name" part, and the "nondirectory" part (or "file
name within the directory"). Either part may be empty. Concatenating
these two parts reproduces the original file name.
On most systems, the directory part is everything up to and including
the last slash (backslash is also allowed in input on MS-DOS or
MS-Windows); the nondirectory part is the rest. The rules in VMS syntax
are complicated.
For some purposes, the nondirectory part is further subdivided into
the name proper and the "version number". On most systems, only backup
files have version numbers in their names. On VMS, every file has a
version number, but most of the time the file name actually used in
Emacs omits the version number, so that version numbers in Emacs are
found mostly in directory lists.
- Function: file-name-directory filename
This function returns the directory part of FILENAME (or `nil' if
FILENAME does not include a directory part). On most systems, the
function returns a string ending in a slash. On VMS, it returns a
string ending in one of the three characters `:', `]', or `>'.
(file-name-directory "lewis/foo") ; Unix example
=> "lewis/"
(file-name-directory "foo") ; Unix example
=> nil
(file-name-directory "[X]FOO.TMP") ; VMS example
=> "[X]"
- Function: file-name-nondirectory filename
This function returns the nondirectory part of FILENAME.
(file-name-nondirectory "lewis/foo")
=> "foo"
(file-name-nondirectory "foo")
=> "foo"
;; The following example is accurate only on VMS.
(file-name-nondirectory "[X]FOO.TMP")
=> "FOO.TMP"
- Function: file-name-sans-versions filename &optional
keep-backup-version
This function returns FILENAME with any file version numbers,
backup version numbers, or trailing tildes discarded.
If KEEP-BACKUP-VERSION is non-`nil', then true file version
numbers understood as such by the file system are discarded from
the return value, but backup version numbers are kept.
(file-name-sans-versions "~rms/foo.~1~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo")
=> "~rms/foo"
;; The following example applies to VMS only.
(file-name-sans-versions "foo;23")
=> "foo"
- Function: file-name-sans-extension filename
This function returns FILENAME minus its "extension," if any. The
extension, in a file name, is the part that starts with the last
`.' in the last name component. For example,
(file-name-sans-extension "foo.lose.c")
=> "foo.lose"
(file-name-sans-extension "big.hack/foo")
=> "big.hack/foo"
- Function: file-name-extension filename &optional period
This function returns FILENAME's final "extension," if any, after
applying `file-name-sans-versions' to remove any version/backup
part. If PERIOD is non-nil, then the returned value includes the
period that delimits the extension, and if FILENAME has no
extension, the value is `""'.
Directory Names
---------------
A "directory name" is the name of a directory. A directory is a
kind of file, and it has a file name, which is related to the directory
name but not identical to it. (This is not quite the same as the usual
Unix terminology.) These two different names for the same entity are
related by a syntactic transformation. On most systems, this is simple:
a directory name ends in a slash (or backslash), whereas the directory's
name as a file lacks that slash. On VMS, the relationship is more
complicated.
The difference between a directory name and its name as a file is
subtle but crucial. When an Emacs variable or function argument is
described as being a directory name, a file name of a directory is not
acceptable.
The following two functions convert between directory names and file
names. They do nothing special with environment variable substitutions
such as `$HOME', and the constructs `~', and `..'.
- Function: file-name-as-directory filename
This function returns a string representing FILENAME in a form
that the operating system will interpret as the name of a
directory. On most systems, this means appending a slash to the
string (if it does not already end in one). On VMS, the function
converts a string of the form `[X]Y.DIR.1' to the form `[X.Y]'.
(file-name-as-directory "~rms/lewis")
=> "~rms/lewis/"
- Function: directory-file-name dirname
This function returns a string representing DIRNAME in a form that
the operating system will interpret as the name of a file. On most
systems, this means removing the final slash (or backslash) from
the string. On VMS, the function converts a string of the form
`[X.Y]' to `[X]Y.DIR.1'.
(directory-file-name "~lewis/")
=> "~lewis"
Directory name abbreviations are useful for directories that are
normally accessed through symbolic links. Sometimes the users recognize
primarily the link's name as "the name" of the directory, and find it
annoying to see the directory's "real" name. If you define the link
name as an abbreviation for the "real" name, Emacs shows users the
abbreviation instead.
- Variable: directory-abbrev-alist
The variable `directory-abbrev-alist' contains an alist of
abbreviations to use for file directories. Each element has the
form `(FROM . TO)', and says to replace FROM with TO when it
appears in a directory name. The FROM string is actually a
regular expression; it should always start with `^'. The function
`abbreviate-file-name' performs these substitutions.
You can set this variable in `site-init.el' to describe the
abbreviations appropriate for your site.
Here's an example, from a system on which file system `/home/fsf'
and so on are normally accessed through symbolic links named `/fsf'
and so on.
(("^/home/fsf" . "/fsf")
("^/home/gp" . "/gp")
("^/home/gd" . "/gd"))
To convert a directory name to its abbreviation, use this function:
- Function: abbreviate-file-name dirname
This function applies abbreviations from `directory-abbrev-alist'
to its argument, and substitutes `~' for the user's home directory.
Absolute and Relative File Names
--------------------------------
All the directories in the file system form a tree starting at the
root directory. A file name can specify all the directory names
starting from the root of the tree; then it is called an "absolute"
file name. Or it can specify the position of the file in the tree
relative to a default directory; then it is called a "relative" file
name. On Unix and GNU/Linux, an absolute file name starts with a slash
or a tilde (`~'), and a relative one does not. On MS-DOS and
MS-Windows, an absolute file name starts with a slash or a backslash, or
with a drive specification `X:/', where X is the "drive letter". The
rules on VMS are complicated.
- Function: file-name-absolute-p filename
This function returns `t' if file FILENAME is an absolute file
name, `nil' otherwise. On VMS, this function understands both
Unix syntax and VMS syntax.
(file-name-absolute-p "~rms/foo")
=> t
(file-name-absolute-p "rms/foo")
=> nil
(file-name-absolute-p "/user/rms/foo")
=> t
Functions that Expand Filenames
-------------------------------
"Expansion" of a file name means converting a relative file name to
an absolute one. Since this is done relative to a default directory,
you must specify the default directory name as well as the file name to
be expanded. Expansion also simplifies file names by eliminating
redundancies such as `./' and `NAME/../'.
- Function: expand-file-name filename &optional directory
This function converts FILENAME to an absolute file name. If
DIRECTORY is supplied, it is the default directory to start with
if FILENAME is relative. (The value of DIRECTORY should itself be
an absolute directory name; it may start with `~'.) Otherwise,
the current buffer's value of `default-directory' is used. For
example:
(expand-file-name "foo")
=> "/xcssun/users/rms/lewis/foo"
(expand-file-name "../foo")
=> "/xcssun/users/rms/foo"
(expand-file-name "foo" "/usr/spool/")
=> "/usr/spool/foo"
(expand-file-name "$HOME/foo")
=> "/xcssun/users/rms/lewis/$HOME/foo"
Filenames containing `.' or `..' are simplified to their canonical
form:
(expand-file-name "bar/../foo")
=> "/xcssun/users/rms/lewis/foo"
Note that `expand-file-name' does _not_ expand environment
variables; only `substitute-in-file-name' does that.
- Function: file-relative-name filename &optional directory
This function does the inverse of expansion--it tries to return a
relative name that is equivalent to FILENAME when interpreted
relative to DIRECTORY. If DIRECTORY is omitted or `nil', it
defaults to the current buffer's default directory.
On some operating systems, an absolute file name begins with a
device name. On such systems, FILENAME has no relative equivalent
based on DIRECTORY if they start with two different device names.
In this case, `file-relative-name' returns FILENAME in absolute
form.
(file-relative-name "/foo/bar" "/foo/")
=> "bar"
(file-relative-name "/foo/bar" "/hack/")
=> "../foo/bar"
- Variable: default-directory
The value of this buffer-local variable is the default directory
for the current buffer. It should be an absolute directory name;
it may start with `~'. This variable is buffer-local in every
buffer.
`expand-file-name' uses the default directory when its second
argument is `nil'.
Aside from VMS, the value is always a string ending with a slash.
default-directory
=> "/user/lewis/manual/"
- Function: substitute-in-file-name filename
This function replaces environment variables references in
FILENAME with the environment variable values. Following standard
Unix shell syntax, `$' is the prefix to substitute an environment
variable value.
The environment variable name is the series of alphanumeric
characters (including underscores) that follow the `$'. If the
character following the `$' is a `{', then the variable name is
everything up to the matching `}'.
Here we assume that the environment variable `HOME', which holds
the user's home directory name, has value `/xcssun/users/rms'.
(substitute-in-file-name "$HOME/foo")
=> "/xcssun/users/rms/foo"
After substitution, if a `~' or a `/' appears following a `/',
everything before the following `/' is discarded:
(substitute-in-file-name "bar/~/foo")
=> "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
=> "/xcssun/users/rms/foo"
;; `/usr/local/' has been discarded.
On VMS, `$' substitution is not done, so this function does nothing
on VMS except discard superfluous initial components as shown
above.
Generating Unique File Names
----------------------------
Some programs need to write temporary files. Here is the usual way
to construct a name for such a file, starting in Emacs 21:
(make-temp-file NAME-OF-APPLICATION)
The job of `make-temp-file' is to prevent two different users or two
different jobs from trying to use the exact same file name.
- Function: make-temp-file prefix &optional dir-flag
This function creates a temporary file and returns its name. The
name starts with PREFIX; it also contains a number that is
different in each Emacs job. If PREFIX is a relative file name,
it is expanded against `temporary-file-directory'.
(make-temp-file "foo")
=> "/tmp/foo232J6v"
When `make-temp-file' returns, the file has been created and is
empty. At that point, you should write the intended contents into
the file.
If DIR-FLAG is non-`nil', `make-temp-file' creates an empty
directory instead of an empty file.
To prevent conflicts among different libraries running in the same
Emacs, each Lisp program that uses `make-temp-file' should have its
own PREFIX. The number added to the end of PREFIX distinguishes
between the same application running in different Emacs jobs.
Additional added characters permit a large number of distinct
names even in one Emacs job.
The default directory for temporary files is controlled by the
variable `temporary-file-directory'. This variable gives the user a
uniform way to specify the directory for all temporary files. Some
programs use `small-temporary-file-directory' instead, if that is
non-`nil'. To use it, you should expand the prefix against the proper
directory before calling `make-temp-file'.
In older Emacs versions where `make-temp-file' does not exist, you
should use `make-temp-name' instead:
(make-temp-name
(expand-file-name NAME-OF-APPLICATION
temporary-file-directory))
- Function: make-temp-name string
This function generates a string that can be used as a unique file
name. The name starts with STRING, and contains a number that is
different in each Emacs job. It is like `make-temp-file' except
that it just constructs a name, and does not create a file. On
MS-DOS, the STRING prefix can be truncated to fit into the 8+3
file-name limits.
- Variable: temporary-file-directory
This variable specifies the directory name for creating temporary
files. Its value should be a directory name (*note Directory
Names::), but it is good for Lisp programs to cope if the value is
a directory's file name instead. Using the value as the second
argument to `expand-file-name' is a good way to achieve that.
The default value is determined in a reasonable way for your
operating system; it is based on the `TMPDIR', `TMP' and `TEMP'
environment variables, with a fall-back to a system-dependent name
if none of these variables is defined.
Even if you do not use `make-temp-name' to choose the temporary
file's name, you should still use this variable to decide which
directory to put the file in. However, if you expect the file to
be small, you should use `small-temporary-file-directory' first if
that is non-`nil'.
- Variable: small-temporary-file-directory
This variable (new in Emacs 21) specifies the directory name for
creating certain temporary files, which are likely to be small.
If you want to write a temporary file which is likely to be small,
you should compute the directory like this:
(make-temp-file
(expand-file-name PREFIX
(or small-temporary-file-directory
temporary-file-directory)))
File Name Completion
--------------------
This section describes low-level subroutines for completing a file
name. For other completion functions, see *Note Completion::.
- Function: file-name-all-completions partial-filename directory
This function returns a list of all possible completions for a file
whose name starts with PARTIAL-FILENAME in directory DIRECTORY.
The order of the completions is the order of the files in the
directory, which is unpredictable and conveys no useful
information.
The argument PARTIAL-FILENAME must be a file name containing no
directory part and no slash (or backslash on some systems). The
current buffer's default directory is prepended to DIRECTORY, if
DIRECTORY is not absolute.
In the following example, suppose that `~rms/lewis' is the current
default directory, and has five files whose names begin with `f':
`foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-all-completions "f" "")
=> ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
(file-name-all-completions "fo" "")
=> ("foo")
- Function: file-name-completion filename directory
This function completes the file name FILENAME in directory
DIRECTORY. It returns the longest prefix common to all file names
in directory DIRECTORY that start with FILENAME.
If only one match exists and FILENAME matches it exactly, the
function returns `t'. The function returns `nil' if directory
DIRECTORY contains no name starting with FILENAME.
In the following example, suppose that the current default
directory has five files whose names begin with `f': `foo',
`file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-completion "fi" "")
=> "file"
(file-name-completion "file.c.~1" "")
=> "file.c.~1~"
(file-name-completion "file.c.~1~" "")
=> t
(file-name-completion "file.c.~3" "")
=> nil
- User Option: completion-ignored-extensions
`file-name-completion' usually ignores file names that end in any
string in this list. It does not ignore them when all the possible
completions end in one of these suffixes or when a buffer showing
all possible completions is displayed.
A typical value might look like this:
completion-ignored-extensions
=> (".o" ".elc" "~" ".dvi")
Standard File Names
-------------------
Most of the file names used in Lisp programs are entered by the user.
But occasionally a Lisp program needs to specify a standard file name
for a particular use--typically, to hold customization information
about each user. For example, abbrev definitions are stored (by
default) in the file `~/.abbrev_defs'; the `completion' package stores
completions in the file `~/.completions'. These are two of the many
standard file names used by parts of Emacs for certain purposes.
Various operating systems have their own conventions for valid file
names and for which file names to use for user profile data. A Lisp
program which reads a file using a standard file name ought to use, on
each type of system, a file name suitable for that system. The function
`convert-standard-filename' makes this easy to do.
- Function: convert-standard-filename filename
This function alters the file name FILENAME to fit the conventions
of the operating system in use, and returns the result as a new
string.
The recommended way to specify a standard file name in a Lisp program
is to choose a name which fits the conventions of GNU and Unix systems,
usually with a nondirectory part that starts with a period, and pass it
to `convert-standard-filename' instead of using it directly. Here is
an example from the `completion' package:
(defvar save-completions-file-name
(convert-standard-filename "~/.completions")
"*The file name to save completions to.")
On GNU and Unix systems, and on some other systems as well,
`convert-standard-filename' returns its argument unchanged. On some
other systems, it alters the name to fit the system's conventions.
For example, on MS-DOS the alterations made by this function include
converting a leading `.' to `_', converting a `_' in the middle of the
name to `.' if there is no other `.', inserting a `.' after eight
characters if there is none, and truncating to three characters after
the `.'. (It makes other changes as well.) Thus, `.abbrev_defs'
becomes `_abbrev.def', and `.completions' becomes `_complet.ion'.
Contents of Directories
=======================
A directory is a kind of file that contains other files entered under
various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the `ls' shell command. In the
latter case, it can optionally display information about each file,
depending on the options passed to the `ls' command.
- Function: directory-files directory &optional full-name match-regexp
nosort
This function returns a list of the names of the files in the
directory DIRECTORY. By default, the list is in alphabetical
order.
If FULL-NAME is non-`nil', the function returns the files'
absolute file names. Otherwise, it returns the names relative to
the specified directory.
If MATCH-REGEXP is non-`nil', this function returns only those
file names that contain a match for that regular expression--the
other file names are excluded from the list.
If NOSORT is non-`nil', `directory-files' does not sort the list,
so you get the file names in no particular order. Use this if you
want the utmost possible speed and don't care what order the files
are processed in. If the order of processing is visible to the
user, then the user will probably be happier if you do sort the
names.
(directory-files "~lewis")
=> ("#foo#" "#foo.el#" "." ".."
"dired-mods.el" "files.texi"
"files.texi.~1~")
An error is signaled if DIRECTORY is not the name of a directory
that can be read.
- Function: file-name-all-versions file dirname
This function returns a list of all versions of the file named
FILE in directory DIRNAME.
- Function: file-expand-wildcards pattern &optional full
This function expands the wildcard pattern PATTERN, returning a
list of file names that match it.
If PATTERN is written as an absolute file name, the values are
absolute also.
If PATTERN is written as a relative file name, it is interpreted
relative to the current default directory. The file names
returned are normally also relative to the current default
directory. However, if FULL is non-`nil', they are absolute.
- Function: insert-directory file switches &optional wildcard
full-directory-p
This function inserts (in the current buffer) a directory listing
for directory FILE, formatted with `ls' according to SWITCHES. It
leaves point after the inserted text.
The argument FILE may be either a directory name or a file
specification including wildcard characters. If WILDCARD is
non-`nil', that means treat FILE as a file specification with
wildcards.
If FULL-DIRECTORY-P is non-`nil', that means the directory listing
is expected to show the full contents of a directory. You should
specify `t' when FILE is a directory and switches do not contain
`-d'. (The `-d' option to `ls' says to describe a directory
itself as a file, rather than showing its contents.)
On most systems, this function works by running a directory listing
program whose name is in the variable `insert-directory-program'.
If WILDCARD is non-`nil', it also runs the shell specified by
`shell-file-name', to expand the wildcards.
MS-DOS and MS-Windows systems usually lack the standard Unix
program `ls', so this function emulates the standard Unix program
`ls' with Lisp code.
- Variable: insert-directory-program
This variable's value is the program to run to generate a
directory listing for the function `insert-directory'. It is
ignored on systems which generate the listing with Lisp code.
Creating and Deleting Directories
=================================
Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with `delete-file'. These special functions exist to create and delete
directories.
- Function: make-directory dirname &optional parents
This function creates a directory named DIRNAME. If PARENTS is
non-`nil', that means to create the parent directories first, if
they don't already exist.
- Function: delete-directory dirname
This function deletes the directory named DIRNAME. The function
`delete-file' does not work for files that are directories; you
must use `delete-directory' for them. If the directory contains
any files, `delete-directory' signals an error.
Making Certain File Names "Magic"
=================================
You can implement special handling for certain file names. This is
called making those names "magic". The principal use for this feature
is in implementing remote file names (*note Remote Files: (emacs)Remote
Files.).
To define a kind of magic file name, you must supply a regular
expression to define the class of names (all those that match the
regular expression), plus a handler that implements all the primitive
Emacs file operations for file names that do match.
The variable `file-name-handler-alist' holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
(REGEXP . HANDLER)
All the Emacs primitives for file access and file name transformation
check the given file name against `file-name-handler-alist'. If the
file name matches REGEXP, the primitives handle that file by calling
HANDLER.
The first argument given to HANDLER is the name of the primitive;
the remaining arguments are the arguments that were passed to that
primitive. (The first of these arguments is most often the file name
itself.) For example, if you do this:
(file-exists-p FILENAME)
and FILENAME has handler HANDLER, then HANDLER is called like this:
(funcall HANDLER 'file-exists-p FILENAME)
When a function takes two or more arguments that must be file names,
it checks each of those names for a handler. For example, if you do
this:
(expand-file-name FILENAME DIRNAME)
then it checks for a handler for FILENAME and then for a handler for
DIRNAME. In either case, the HANDLER is called like this:
(funcall HANDLER 'expand-file-name FILENAME DIRNAME)
The HANDLER then needs to figure out whether to handle FILENAME or
DIRNAME.
Here are the operations that a magic file name handler gets to
handle:
`add-name-to-file', `copy-file', `delete-directory', `delete-file',
`diff-latest-backup-file', `directory-file-name', `directory-files',
`dired-call-process', `dired-compress-file', `dired-uncache',
`expand-file-name', `file-accessible-directory-p',
`file-attributes', `file-directory-p', `file-executable-p',
`file-exists-p',
`file-local-copy', `file-modes', `file-name-all-completions',
`file-name-as-directory', `file-name-completion', `file-name-directory',
`file-name-nondirectory', `file-name-sans-versions',
`file-newer-than-file-p', `file-ownership-preserved-p',
`file-readable-p', `file-regular-p', `file-symlink-p', `file-truename',
`file-writable-p', `find-backup-file-name', `get-file-buffer',
`insert-directory', `insert-file-contents', `load', `make-directory',
`make-symbolic-link', `rename-file', `set-file-modes',
`set-visited-file-modtime', `shell-command',
`unhandled-file-name-directory', `vc-registered',
`verify-visited-file-modtime',
`write-region'.
Handlers for `insert-file-contents' typically need to clear the
buffer's modified flag, with `(set-buffer-modified-p nil)', if the
VISIT argument is non-`nil'. This also has the effect of unlocking the
buffer if it is locked.
The handler function must handle all of the above operations, and
possibly others to be added in the future. It need not implement all
these operations itself--when it has nothing special to do for a
certain operation, it can reinvoke the primitive, to handle the
operation "in the usual way". It should always reinvoke the primitive
for an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
When a handler function decides to call the ordinary Emacs primitive
for the operation at hand, it needs to prevent the primitive from
calling the same handler once again, thus leading to an infinite
recursion. The example above shows how to do this, with the variables
`inhibit-file-name-handlers' and `inhibit-file-name-operation'. Be
careful to use them exactly as shown above; the details are crucial for
proper behavior in the case of multiple handlers, and for operations
that have two file names that may each have handlers.
- Variable: inhibit-file-name-handlers
This variable holds a list of handlers whose use is presently
inhibited for a certain operation.
- Variable: inhibit-file-name-operation
The operation for which certain handlers are presently inhibited.
- Function: find-file-name-handler file operation
This function returns the handler function for file name FILE, or
`nil' if there is none. The argument OPERATION should be the
operation to be performed on the file--the value you will pass to
the handler as its first argument when you call it. The operation
is needed for comparison with `inhibit-file-name-operation'.
- Function: file-local-copy filename
This function copies file FILENAME to an ordinary non-magic file,
if it isn't one already.
If FILENAME specifies a magic file name, which programs outside
Emacs cannot directly read or write, this copies the contents to
an ordinary file and returns that file's name.
If FILENAME is an ordinary file name, not magic, then this function
does nothing and returns `nil'.
- Function: unhandled-file-name-directory filename
This function returns the name of a directory that is not magic.
It uses the directory part of FILENAME if that is not magic. For a
magic file name, it invokes the file name handler, which therefore
decides what value to return.
This is useful for running a subprocess; every subprocess must
have a non-magic directory to serve as its current directory, and
this function is a good way to come up with one.
File Format Conversion
======================
The variable `format-alist' defines a list of "file formats", which
describe textual representations used in files for the data (text,
text-properties, and possibly other information) in an Emacs buffer.
Emacs performs format conversion if appropriate when reading and writing
files.
- Variable: format-alist
This list contains one format definition for each defined file
format.
Each format definition is a list of this form:
(NAME DOC-STRING REGEXP FROM-FN TO-FN MODIFY MODE-FN)
Here is what the elements in a format definition mean:
NAME
The name of this format.
DOC-STRING
A documentation string for the format.
REGEXP
A regular expression which is used to recognize files represented
in this format.
FROM-FN
A shell command or function to decode data in this format (to
convert file data into the usual Emacs data representation).
A shell command is represented as a string; Emacs runs the command
as a filter to perform the conversion.
If FROM-FN is a function, it is called with two arguments, BEGIN
and END, which specify the part of the buffer it should convert.
It should convert the text by editing it in place. Since this can
change the length of the text, FROM-FN should return the modified
end position.
One responsibility of FROM-FN is to make sure that the beginning
of the file no longer matches REGEXP. Otherwise it is likely to
get called again.
TO-FN
A shell command or function to encode data in this format--that
is, to convert the usual Emacs data representation into this
format.
If TO-FN is a string, it is a shell command; Emacs runs the
command as a filter to perform the conversion.
If TO-FN is a function, it is called with two arguments, BEGIN and
END, which specify the part of the buffer it should convert.
There are two ways it can do the conversion:
* By editing the buffer in place. In this case, TO-FN should
return the end-position of the range of text, as modified.
* By returning a list of annotations. This is a list of
elements of the form `(POSITION . STRING)', where POSITION is
an integer specifying the relative position in the text to be
written, and STRING is the annotation to add there. The list
must be sorted in order of position when TO-FN returns it.
When `write-region' actually writes the text from the buffer
to the file, it intermixes the specified annotations at the
corresponding positions. All this takes place without
modifying the buffer.
MODIFY
A flag, `t' if the encoding function modifies the buffer, and
`nil' if it works by returning a list of annotations.
MODE-FN
A minor-mode function to call after visiting a file converted from
this format. The function is called with one argument, the
integer 1; that tells a minor-mode function to enable the mode.
The function `insert-file-contents' automatically recognizes file
formats when it reads the specified file. It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format. Then it checks all the known formats over again. It
keeps checking them until none of them is applicable.
Visiting a file, with `find-file-noselect' or the commands that use
it, performs conversion likewise (because it calls
`insert-file-contents'); it also calls the mode function for each
format that it decodes. It stores a list of the format names in the
buffer-local variable `buffer-file-format'.
- Variable: buffer-file-format
This variable states the format of the visited file. More
precisely, this is a list of the file format names that were
decoded in the course of visiting the current buffer's file. It
is always buffer-local in all buffers.
When `write-region' writes data into a file, it first calls the
encoding functions for the formats listed in `buffer-file-format', in
the order of appearance in the list.
- Command: format-write-file file format
This command writes the current buffer contents into the file FILE
in format FORMAT, and makes that format the default for future
saves of the buffer. The argument FORMAT is a list of format
names.
- Command: format-find-file file format
This command finds the file FILE, converting it according to
format FORMAT. It also makes FORMAT the default if the buffer is
saved later.
The argument FORMAT is a list of format names. If FORMAT is
`nil', no conversion takes place. Interactively, typing just
<RET> for FORMAT specifies `nil'.
- Command: format-insert-file file format &optional beg end
This command inserts the contents of file FILE, converting it
according to format FORMAT. If BEG and END are non-`nil', they
specify which part of the file to read, as in
`insert-file-contents' (*note Reading from Files::).
The return value is like what `insert-file-contents' returns: a
list of the absolute file name and the length of the data inserted
(after conversion).
The argument FORMAT is a list of format names. If FORMAT is
`nil', no conversion takes place. Interactively, typing just
<RET> for FORMAT specifies `nil'.
- Variable: auto-save-file-format
This variable specifies the format to use for auto-saving. Its
value is a list of format names, just like the value of
`buffer-file-format'; however, it is used instead of
`buffer-file-format' for writing auto-save files. This variable is
always buffer-local in all buffers.
Backups and Auto-Saving
***********************
Backup files and auto-save files are two methods by which Emacs tries
to protect the user from the consequences of crashes or of the user's
own errors. Auto-saving preserves the text from earlier in the current
editing session; backup files preserve file contents prior to the
current session.
Backup Files
============
A "backup file" is a copy of the old contents of a file you are
editing. Emacs makes a backup file the first time you save a buffer
into its visited file. Normally, this means that the backup file
contains the contents of the file as it was before the current editing
session. The contents of the backup file normally remain unchanged once
it exists.
Backups are usually made by renaming the visited file to a new name.
Optionally, you can specify that backup files should be made by copying
the visited file. This choice makes a difference for files with
multiple names; it also can affect whether the edited file remains owned
by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited.
You can alternatively request numbered backups; then each new backup
file gets a new name. You can delete old numbered backups when you
don't want them any more, or Emacs can delete them automatically.
Making Backup Files
-------------------
- Function: backup-buffer
This function makes a backup of the file visited by the current
buffer, if appropriate. It is called by `save-buffer' before
saving the buffer the first time.
- Variable: buffer-backed-up
This buffer-local variable indicates whether this buffer's file has
been backed up on account of this buffer. If it is non-`nil', then
the backup file has been written. Otherwise, the file should be
backed up when it is next saved (if backups are enabled). This is
a permanent local; `kill-all-local-variables' does not alter it.
- User Option: make-backup-files
This variable determines whether or not to make backup files. If
it is non-`nil', then Emacs creates a backup of each file when it
is saved for the first time--provided that `backup-inhibited' is
`nil' (see below).
The following example shows how to change the `make-backup-files'
variable only in the Rmail buffers and not elsewhere. Setting it
`nil' stops Emacs from making backups of these files, which may
save disk space. (You would put this code in your init file.)
(add-hook 'rmail-mode-hook
(function (lambda ()
(make-local-variable
'make-backup-files)
(setq make-backup-files nil))))
- Variable: backup-enable-predicate
This variable's value is a function to be called on certain
occasions to decide whether a file should have backup files. The
function receives one argument, a file name to consider. If the
function returns `nil', backups are disabled for that file.
Otherwise, the other variables in this section say whether and how
to make backups.
The default value is `normal-backup-enable-predicate', which checks
for files in `temporary-file-directory' and
`small-temporary-file-directory'.
- Variable: backup-inhibited
If this variable is non-`nil', backups are inhibited. It records
the result of testing `backup-enable-predicate' on the visited file
name. It can also coherently be used by other mechanisms that
inhibit backups based on which file is visited. For example, VC
sets this variable non-`nil' to prevent making backups for files
managed with a version control system.
This is a permanent local, so that changing the major mode does
not lose its value. Major modes should not set this
variable--they should set `make-backup-files' instead.
- Variable: backup-directory-alist
This variable's value is an alist of filename patterns and backup
directory names. Each element looks like
(REGEXP . DIRECTORY)
Backups of files with names matching REGEXP will be made in
DIRECTORY. DIRECTORY may be relative or absolute. If it is
absolute, so that all matching files are backed up into the same
directory, the file names in this directory will be the full name
of the file backed up with all directory separators changed to `!'
to prevent clashes. This will not work correctly if your
filesystem truncates the resulting name.
For the common case of all backups going into one directory, the
alist should contain a single element pairing `"."' with the
appropriate directory name.
If this variable is `nil', or it fails to match a filename, the
backup is made in the original file's directory.
On MS-DOS filesystems without long names this variable is always
ignored.
- Variable: make-backup-file-name-function
This variable's value is a function to use for making backups
instead of the default `make-backup-file-name'. A value of nil
gives the default `make-backup-file-name' behaviour.
This could be buffer-local to do something special for specific
files. If you define it, you may need to change
`backup-file-name-p' and `file-name-sans-versions' too.
Backup by Renaming or by Copying?
---------------------------------
There are two ways that Emacs can make a backup file:
* Emacs can rename the original file so that it becomes a backup
file, and then write the buffer being saved into a new file.
After this procedure, any other names (i.e., hard links) of the
original file now refer to the backup file. The new file is owned
by the user doing the editing, and its group is the default for
new files written by the user in that directory.
* Emacs can copy the original file into a backup file, and then
overwrite the original file with new contents. After this
procedure, any other names (i.e., hard links) of the original file
continue to refer to the current (updated) version of the file.
The file's owner and group will be unchanged.
The first method, renaming, is the default.
The variable `backup-by-copying', if non-`nil', says to use the
second method, which is to copy the original file and overwrite it with
the new buffer contents. The variable `file-precious-flag', if
non-`nil', also has this effect (as a sideline of its main
significance). *Note Saving Buffers::.
- Variable: backup-by-copying
If this variable is non-`nil', Emacs always makes backup files by
copying.
The following two variables, when non-`nil', cause the second method
to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
- Variable: backup-by-copying-when-linked
If this variable is non-`nil', Emacs makes backups by copying for
files with multiple names (hard links).
This variable is significant only if `backup-by-copying' is `nil',
since copying is always used when that variable is non-`nil'.
- Variable: backup-by-copying-when-mismatch
If this variable is non-`nil', Emacs makes backups by copying in
cases where renaming would change either the owner or the group of
the file.
The value has no effect when renaming would not alter the owner or
group of the file; that is, for files which are owned by the user
and whose group matches the default for a new file created there
by the user.
This variable is significant only if `backup-by-copying' is `nil',
since copying is always used when that variable is non-`nil'.
- Variable: backup-by-copying-when-privileged-mismatch
This variable, if non-`nil', specifies the same behavior as
`backup-by-copying-when-mismatch', but only for certain user-id
values: namely, those less than or equal to a certain number. You
set this variable to that number.
Thus, if you set `backup-by-copying-when-privileged-mismatch' to
0, backup by copying is done for the superuser only, when
necessary to prevent a change in the owner of the file.
The default is 200.
Making and Deleting Numbered Backup Files
-----------------------------------------
If a file's name is `foo', the names of its numbered backup versions
are `foo.~V~', for various integers V, like this: `foo.~1~', `foo.~2~',
`foo.~3~', ..., `foo.~259~', and so on.
- User Option: version-control
This variable controls whether to make a single non-numbered backup
file or multiple numbered backups.
`nil'
Make numbered backups if the visited file already has
numbered backups; otherwise, do not.
`never'
Do not make numbered backups.
ANYTHING ELSE
Make numbered backups.
The use of numbered backups ultimately leads to a large number of
backup versions, which must then be deleted. Emacs can do this
automatically or it can ask the user whether to delete them.
- User Option: kept-new-versions
The value of this variable is the number of newest versions to keep
when a new numbered backup is made. The newly made backup is
included in the count. The default value is 2.
- User Option: kept-old-versions
The value of this variable is the number of oldest versions to keep
when a new numbered backup is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function `find-backup-file-name'
(*note Backup Names::) is responsible for determining which backup
versions to delete, but does not delete them itself.
- User Option: delete-old-versions
If this variable is `t', then saving a file deletes excess backup
versions silently. If it is `nil', that means to ask for
confirmation before deleting excess backups. Otherwise, they are
not deleted at all.
- User Option: dired-kept-versions
This variable specifies how many of the newest backup versions to
keep in the Dired command `.' (`dired-clean-directory'). That's
the same thing `kept-new-versions' specifies when you make a new
backup file. The default value is 2.
Naming Backup Files
-------------------
The functions in this section are documented mainly because you can
customize the naming conventions for backup files by redefining them.
If you change one, you probably need to change the rest.
- Function: backup-file-name-p filename
This function returns a non-`nil' value if FILENAME is a possible
name for a backup file. A file with the name FILENAME need not
exist; the function just checks the name.
(backup-file-name-p "foo")
=> nil
(backup-file-name-p "foo~")
=> 3
The standard definition of this function is as follows:
(defun backup-file-name-p (file)
"Return non-nil if FILE is a backup file \
name (numeric or not)..."
(string-match "~\\'" file))
Thus, the function returns a non-`nil' value if the file name ends
with a `~'. (We use a backslash to split the documentation
string's first line into two lines in the text, but produce just
one line in the string itself.)
This simple expression is placed in a separate function to make it
easy to redefine for customization.
- Function: make-backup-file-name filename
This function returns a string that is the name to use for a
non-numbered backup file for file FILENAME. On Unix, this is just
FILENAME with a tilde appended.
The standard definition of this function, on most operating
systems, is as follows:
(defun make-backup-file-name (file)
"Create the non-numeric backup file name for FILE..."
(concat file "~"))
You can change the backup-file naming convention by redefining this
function. The following example redefines `make-backup-file-name'
to prepend a `.' in addition to appending a tilde:
(defun make-backup-file-name (filename)
(expand-file-name
(concat "." (file-name-nondirectory filename) "~")
(file-name-directory filename)))
(make-backup-file-name "backups.texi")
=> ".backups.texi~"
Some parts of Emacs, including some Dired commands, assume that
backup file names end with `~'. If you do not follow that
convention, it will not cause serious problems, but these commands
may give less-than-desirable results.
- Function: find-backup-file-name filename
This function computes the file name for a new backup file for
FILENAME. It may also propose certain existing backup files for
deletion. `find-backup-file-name' returns a list whose CAR is the
name for the new backup file and whose CDR is a list of backup
files whose deletion is proposed.
Two variables, `kept-old-versions' and `kept-new-versions',
determine which backup versions should be kept. This function
keeps those versions by excluding them from the CDR of the value.
*Note Numbered Backups::.
In this example, the value says that `~rms/foo.~5~' is the name to
use for the new backup file, and `~rms/foo.~3~' is an "excess"
version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo")
=> ("~rms/foo.~5~" "~rms/foo.~3~")
- Function: file-newest-backup filename
This function returns the name of the most recent backup file for
FILENAME, or `nil' if that file has no backup files.
Some file comparison commands use this function so that they can
automatically compare a file with its most recent backup.
Auto-Saving
===========
Emacs periodically saves all files that you are visiting; this is
called "auto-saving". Auto-saving prevents you from losing more than a
limited amount of work if the system crashes. By default, auto-saves
happen every 300 keystrokes, or after around 30 seconds of idle time.
*Note Auto-Save: (emacs)Auto-Save, for information on auto-save for
users. Here we describe the functions used to implement auto-saving
and the variables that control them.
- Variable: buffer-auto-save-file-name
This buffer-local variable is the name of the file used for
auto-saving the current buffer. It is `nil' if the buffer should
not be auto-saved.
buffer-auto-save-file-name
=> "/xcssun/users/rms/lewis/#backups.texi#"
- Command: auto-save-mode arg
When used interactively without an argument, this command is a
toggle switch: it turns on auto-saving of the current buffer if it
is off, and vice versa. With an argument ARG, the command turns
auto-saving on if the value of ARG is `t', a nonempty list, or a
positive integer. Otherwise, it turns auto-saving off.
- Function: auto-save-file-name-p filename
This function returns a non-`nil' value if FILENAME is a string
that could be the name of an auto-save file. It assumes the usual
naming convention for auto-save files: a name that begins and ends
with hash marks (`#') is a possible auto-save file name. The
argument FILENAME should not contain a directory part.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#backups.texi#"
(auto-save-file-name-p "#backups.texi#")
=> 0
(auto-save-file-name-p "backups.texi")
=> nil
The standard definition of this function is as follows:
(defun auto-save-file-name-p (filename)
"Return non-nil if FILENAME can be yielded by..."
(string-match "^#.*#$" filename))
This function exists so that you can customize it if you wish to
change the naming convention for auto-save files. If you redefine
it, be sure to redefine the function `make-auto-save-file-name'
correspondingly.
- Function: make-auto-save-file-name
This function returns the file name to use for auto-saving the
current buffer. This is just the file name with hash marks (`#')
prepended and appended to it. This function does not look at the
variable `auto-save-visited-file-name' (described below); callers
of this function should check that variable first.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#backups.texi#"
The standard definition of this function is as follows:
(defun make-auto-save-file-name ()
"Return file name to use for auto-saves \
of current buffer.."
(if buffer-file-name
(concat
(file-name-directory buffer-file-name)
"#"
(file-name-nondirectory buffer-file-name)
"#")
(expand-file-name
(concat "#%" (buffer-name) "#"))))
This exists as a separate function so that you can redefine it to
customize the naming convention for auto-save files. Be sure to
change `auto-save-file-name-p' in a corresponding way.
- Variable: auto-save-visited-file-name
If this variable is non-`nil', Emacs auto-saves buffers in the
files they are visiting. That is, the auto-save is done in the
same file that you are editing. Normally, this variable is `nil',
so auto-save files have distinct names that are created by
`make-auto-save-file-name'.
When you change the value of this variable, the new value does not
take effect in an existing buffer until the next time auto-save
mode is reenabled in it. If auto-save mode is already enabled,
auto-saves continue to go in the same file name until
`auto-save-mode' is called again.
- Function: recent-auto-save-p
This function returns `t' if the current buffer has been
auto-saved since the last time it was read in or saved.
- Function: set-buffer-auto-saved
This function marks the current buffer as auto-saved. The buffer
will not be auto-saved again until the buffer text is changed
again. The function returns `nil'.
- User Option: auto-save-interval
The value of this variable specifies how often to do auto-saving,
in terms of number of input events. Each time this many
additional input events are read, Emacs does auto-saving for all
buffers in which that is enabled.
- User Option: auto-save-timeout
The value of this variable is the number of seconds of idle time
that should cause auto-saving. Each time the user pauses for this
long, Emacs does auto-saving for all buffers in which that is
enabled. (If the current buffer is large, the specified timeout
is multiplied by a factor that increases as the size increases;
for a million-byte buffer, the factor is almost 4.)
If the value is zero or nil, then auto-saving is not done as a
result of idleness, only after a certain number of input events as
specified by `auto-save-interval'.
- Variable: auto-save-hook
This normal hook is run whenever an auto-save is about to happen.
- User Option: auto-save-default
If this variable is non-`nil', buffers that are visiting files
have auto-saving enabled by default. Otherwise, they do not.
- Command: do-auto-save &optional no-message current-only
This function auto-saves all buffers that need to be auto-saved.
It saves all buffers for which auto-saving is enabled and that
have been changed since the previous auto-save.
Normally, if any buffers are auto-saved, a message that says
`Auto-saving...' is displayed in the echo area while auto-saving is
going on. However, if NO-MESSAGE is non-`nil', the message is
inhibited.
If CURRENT-ONLY is non-`nil', only the current buffer is
auto-saved.
- Function: delete-auto-save-file-if-necessary
This function deletes the current buffer's auto-save file if
`delete-auto-save-files' is non-`nil'. It is called every time a
buffer is saved.
- Variable: delete-auto-save-files
This variable is used by the function
`delete-auto-save-file-if-necessary'. If it is non-`nil', Emacs
deletes auto-save files when a true save is done (in the visited
file). This saves disk space and unclutters your directory.
- Function: rename-auto-save-file
This function adjusts the current buffer's auto-save file name if
the visited file name has changed. It also renames an existing
auto-save file. If the visited file name has not changed, this
function does nothing.
- Variable: buffer-saved-size
The value of this buffer-local variable is the length of the
current buffer, when it was last read in, saved, or auto-saved.
This is used to detect a substantial decrease in size, and turn
off auto-saving in response.
If it is -1, that means auto-saving is temporarily shut off in
this buffer due to a substantial decrease in size. Explicitly
saving the buffer stores a positive value in this variable, thus
reenabling auto-saving. Turning auto-save mode off or on also
updates this variable, so that the substantial decrease in size is
forgotten.
- Variable: auto-save-list-file-name
This variable (if non-`nil') specifies a file for recording the
names of all the auto-save files. Each time Emacs does
auto-saving, it writes two lines into this file for each buffer
that has auto-saving enabled. The first line gives the name of
the visited file (it's empty if the buffer has none), and the
second gives the name of the auto-save file.
When Emacs exits normally, it deletes this file; if Emacs crashes,
you can look in the file to find all the auto-save files that
might contain work that was otherwise lost. The `recover-session'
command uses this file to find them.
The default name for this file specifies your home directory and
starts with `.saves-'. It also contains the Emacs process ID and
the host name.
- Variable: auto-save-list-file-prefix
After Emacs reads your init file, it initializes
`auto-save-list-file-name' (if you have not already set it
non-`nil') based on this prefix, adding the host name and process
ID. If you set this to `nil' in your init file, then Emacs does
not initialize `auto-save-list-file-name'.
Reverting
=========
If you have made extensive changes to a file and then change your
mind about them, you can get rid of them by reading in the previous
version of the file with the `revert-buffer' command. *Note Reverting
a Buffer: (emacs)Reverting.
- Command: revert-buffer &optional ignore-auto noconfirm
This command replaces the buffer text with the text of the visited
file on disk. This action undoes all changes since the file was
visited or saved.
By default, if the latest auto-save file is more recent than the
visited file, and the argument IGNORE-AUTO is `nil',
`revert-buffer' asks the user whether to use that auto-save
instead. When you invoke this command interactively, IGNORE-AUTO
is `t' if there is no numeric prefix argument; thus, the
interactive default is not to check the auto-save file.
Normally, `revert-buffer' asks for confirmation before it changes
the buffer; but if the argument NOCONFIRM is non-`nil',
`revert-buffer' does not ask for confirmation.
Reverting tries to preserve marker positions in the buffer by
using the replacement feature of `insert-file-contents'. If the
buffer contents and the file contents are identical before the
revert operation, reverting preserves all the markers. If they
are not identical, reverting does change the buffer; in that case,
it preserves the markers in the unchanged text (if any) at the
beginning and end of the buffer. Preserving any additional
markers would be problematical.
You can customize how `revert-buffer' does its work by setting the
variables described in the rest of this section.
- Variable: revert-without-query
This variable holds a list of files that should be reverted without
query. The value is a list of regular expressions. If the
visited file name matches one of these regular expressions, and
the file has changed on disk but the buffer is not modified, then
`revert-buffer' reverts the file without asking the user for
confirmation.
Some major modes customize `revert-buffer' by making buffer-local
bindings for these variables:
- Variable: revert-buffer-function
The value of this variable is the function to use to revert this
buffer. If non-`nil', it is called as a function with no
arguments to do the work of reverting. If the value is `nil',
reverting works the usual way.
Modes such as Dired mode, in which the text being edited does not
consist of a file's contents but can be regenerated in some other
fashion, can give this variable a buffer-local value that is a
function to regenerate the contents.
- Variable: revert-buffer-insert-file-contents-function
The value of this variable, if non-`nil', specifies the function
to use to insert the updated contents when reverting this buffer.
The function receives two arguments: first the file name to use;
second, `t' if the user has asked to read the auto-save file.
The reason for a mode to set this variable instead of
`revert-buffer-function' is to avoid duplicating or replacing the
rest of what `revert-buffer' does: asking for confirmation,
clearing the undo list, deciding the proper major mode, and
running the hooks listed below.
- Variable: before-revert-hook
This normal hook is run by `revert-buffer' before inserting the
modified contents--but only if `revert-buffer-function' is `nil'.
- Variable: after-revert-hook
This normal hook is run by `revert-buffer' after inserting the
modified contents--but only if `revert-buffer-function' is `nil'.
Buffers
*******
A "buffer" is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there may
also be buffers that are not visiting files. While several buffers may
exist at one time, only one buffer is designated the "current buffer"
at any time. Most editing commands act on the contents of the current
buffer. Each buffer, including the current buffer, may or may not be
displayed in any windows.
Buffer Basics
=============
A "buffer" is a Lisp object containing text to be edited. Buffers
are used to hold the contents of files that are being visited; there may
also be buffers that are not visiting files. Although several buffers
normally exist, only one buffer is designated the "current buffer" at
any time. Most editing commands act on the contents of the current
buffer. Each buffer, including the current buffer, may or may not be
displayed in any windows.
Buffers in Emacs editing are objects that have distinct names and
hold text that can be edited. Buffers appear to Lisp programs as a
special data type. You can think of the contents of a buffer as a
string that you can extend; insertions and deletions may occur in any
part of the buffer. *Note Text::.
A Lisp buffer object contains numerous pieces of information. Some
of this information is directly accessible to the programmer through
variables, while other information is accessible only through
special-purpose functions. For example, the visited file name is
directly accessible through a variable, while the value of point is
accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
"buffer-local" variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as `fill-column' or `comment-column' in this way. For
more information about buffer-local variables and functions related to
them, see *Note Buffer-Local Variables::.
For functions and variables related to visiting files in buffers, see
*Note Visiting Files:: and *Note Saving Buffers::. For functions and
variables related to the display of buffers in windows, see *Note
Buffers and Windows::.
- Function: bufferp object
This function returns `t' if OBJECT is a buffer, `nil' otherwise.
The Current Buffer
==================
There are, in general, many buffers in an Emacs session. At any
time, one of them is designated as the "current buffer". This is the
buffer in which most editing takes place, because most of the primitives
for examining or changing text in a buffer operate implicitly on the
current buffer (*note Text::). Normally the buffer that is displayed on
the screen in the selected window is the current buffer, but this is not
always so: a Lisp program can temporarily designate any buffer as
current in order to operate on its contents, without changing what is
displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
`set-buffer'. The specified buffer remains current until a new one is
designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in when
Emacs reads a command is the buffer that the command will apply to.
(*Note Command Loop::.) Therefore, `set-buffer' is not the way to
switch visibly to a different buffer so that the user can edit it. For
that, you must use the functions described in *Note Displaying
Buffers::.
*Note:* Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop; it is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
normally use `set-buffer' within a `save-current-buffer' or
`save-excursion' (*note Excursions::) form that will restore the
current buffer when your function is done. Here is an example, the
code for the command `append-to-buffer' (with the documentation string
abridged):
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region.
..."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
This function binds a local variable to record the current buffer, and
then `save-current-buffer' arranges to make it current again. Next,
`set-buffer' makes the specified buffer current. Finally,
`insert-buffer-substring' copies the string from the original current
buffer to the specified (and now current) buffer.
If the buffer appended to happens to be displayed in some window,
the next redisplay will show how its text has changed. Otherwise, you
will not see the change immediately on the screen. The buffer becomes
current temporarily during the execution of the command, but this does
not cause it to be displayed.
If you make local bindings (with `let' or function arguments) for a
variable that may also have buffer-local bindings, make sure that the
same buffer is current at the beginning and at the end of the local
binding's scope. Otherwise you might bind it in one buffer and unbind
it in another! There are two ways to do this. In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
binding. Otherwise, use `save-current-buffer' or `save-excursion' to
make sure that the buffer current at the beginning is current again
whenever the variable is unbound.
Do not rely on using `set-buffer' to change the current buffer back,
because that won't do the job if a quit happens while the wrong buffer
is current. Here is what _not_ to do:
(let (buffer-read-only
(obuf (current-buffer)))
(set-buffer ...)
...
(set-buffer obuf))
Using `save-current-buffer', as shown here, handles quitting, errors,
and `throw', as well as ordinary evaluation.
(let (buffer-read-only)
(save-current-buffer
(set-buffer ...)
...))
- Function: current-buffer
This function returns the current buffer.
(current-buffer)
=> #<buffer buffers.texi>
- Function: set-buffer buffer-or-name
This function makes BUFFER-OR-NAME the current buffer. This does
not display the buffer in any window, so the user cannot
necessarily see the buffer. But Lisp programs will now operate on
it.
This function returns the buffer identified by BUFFER-OR-NAME. An
error is signaled if BUFFER-OR-NAME does not identify an existing
buffer.
- Special Form: save-current-buffer body...
The `save-current-buffer' macro saves the identity of the current
buffer, evaluates the BODY forms, and finally restores that buffer
as current. The return value is the value of the last form in
BODY. The current buffer is restored even in case of an abnormal
exit via `throw' or error (*note Nonlocal Exits::).
If the buffer that used to be current has been killed by the time
of exit from `save-current-buffer', then it is not made current
again, of course. Instead, whichever buffer was current just
before exit remains current.
- Macro: with-current-buffer buffer body...
The `with-current-buffer' macro saves the identity of the current
buffer, makes BUFFER current, evaluates the BODY forms, and
finally restores the buffer. The return value is the value of the
last form in BODY. The current buffer is restored even in case of
an abnormal exit via `throw' or error (*note Nonlocal Exits::).
- Macro: with-temp-buffer body...
The `with-temp-buffer' macro evaluates the BODY forms with a
temporary buffer as the current buffer. It saves the identity of
the current buffer, creates a temporary buffer and makes it
current, evaluates the BODY forms, and finally restores the
previous current buffer while killing the temporary buffer.
The return value is the value of the last form in BODY. You can
return the contents of the temporary buffer by using
`(buffer-string)' as the last form.
The current buffer is restored even in case of an abnormal exit via
`throw' or error (*note Nonlocal Exits::).
See also `with-temp-file' in *Note Writing to Files::.
Buffer Names
============
Each buffer has a unique name, which is a string. Many of the
functions that work on buffers accept either a buffer or a buffer name
as an argument. Any argument called BUFFER-OR-NAME is of this sort,
and an error is signaled if it is neither a string nor a buffer. Any
argument called BUFFER must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the `list-buffers' and
`buffer-menu' commands don't mention them. A name starting with space
also initially disables recording undo information; see *Note Undo::.
- Function: buffer-name &optional buffer
This function returns the name of BUFFER as a string. If BUFFER
is not supplied, it defaults to the current buffer.
If `buffer-name' returns `nil', it means that BUFFER has been
killed. *Note Killing Buffers::.
(buffer-name)
=> "buffers.texi"
(setq foo (get-buffer "temp"))
=> #<buffer temp>
(kill-buffer foo)
=> nil
(buffer-name foo)
=> nil
foo
=> #<killed buffer>
- Command: rename-buffer newname &optional unique
This function renames the current buffer to NEWNAME. An error is
signaled if NEWNAME is not a string, or if there is already a
buffer with that name. The function returns NEWNAME.
Ordinarily, `rename-buffer' signals an error if NEWNAME is already
in use. However, if UNIQUE is non-`nil', it modifies NEWNAME to
make a name that is not in use. Interactively, you can make
UNIQUE non-`nil' with a numeric prefix argument. (This is how the
command `rename-uniquely' is implemented.)
- Function: get-buffer buffer-or-name
This function returns the buffer specified by BUFFER-OR-NAME. If
BUFFER-OR-NAME is a string and there is no buffer with that name,
the value is `nil'. If BUFFER-OR-NAME is a buffer, it is returned
as given; that is not very useful, so the argument is usually a
name. For example:
(setq b (get-buffer "lewis"))
=> #<buffer lewis>
(get-buffer b)
=> #<buffer lewis>
(get-buffer "Frazzle-nots")
=> nil
See also the function `get-buffer-create' in *Note Creating
Buffers::.
- Function: generate-new-buffer-name starting-name &rest ignore
This function returns a name that would be unique for a new
buffer--but does not create the buffer. It starts with
STARTING-NAME, and produces a name not currently in use for any
buffer by appending a number inside of `<...>'.
If the optional second argument IGNORE is non-`nil', it should be
a string; it makes a difference if it is a name in the sequence of
names to be tried. That name will be considered acceptable, if it
is tried, even if a buffer with that name exists. Thus, if
buffers named `foo', `foo<2>', `foo<3>' and `foo<4>' exist,
(generate-new-buffer-name "foo")
=> "foo<5>"
(generate-new-buffer-name "foo" "foo<3>")
=> "foo<3>"
(generate-new-buffer-name "foo" "foo<6>")
=> "foo<5>"
See the related function `generate-new-buffer' in *Note Creating
Buffers::.
Buffer File Name
================
The "buffer file name" is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is `nil'. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently. *Note
Visiting Files::.
- Function: buffer-file-name &optional buffer
This function returns the absolute file name of the file that
BUFFER is visiting. If BUFFER is not visiting any file,
`buffer-file-name' returns `nil'. If BUFFER is not supplied, it
defaults to the current buffer.
(buffer-file-name (other-buffer))
=> "/usr/user/lewis/manual/files.texi"
- Variable: buffer-file-name
This buffer-local variable contains the name of the file being
visited in the current buffer, or `nil' if it is not visiting a
file. It is a permanent local variable, unaffected by
`kill-all-local-variables'.
buffer-file-name
=> "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable's value without doing various
other things. Normally it is better to use
`set-visited-file-name' (see below); some of the things done
there, such as changing the buffer name, are not strictly
necessary, but others are essential to avoid confusing Emacs.
- Variable: buffer-file-truename
This buffer-local variable holds the truename of the file visited
in the current buffer, or `nil' if no file is visited. It is a
permanent local, unaffected by `kill-all-local-variables'. *Note
Truenames::.
- Variable: buffer-file-number
This buffer-local variable holds the file number and directory
device number of the file visited in the current buffer, or `nil'
if no file or a nonexistent file is visited. It is a permanent
local, unaffected by `kill-all-local-variables'.
The value is normally a list of the form `(FILENUM DEVNUM)'. This
pair of numbers uniquely identifies the file among all files
accessible on the system. See the function `file-attributes', in
*Note File Attributes::, for more information about them.
- Function: get-file-buffer filename
This function returns the buffer visiting file FILENAME. If there
is no such buffer, it returns `nil'. The argument FILENAME, which
must be a string, is expanded (*note File Name Expansion::), then
compared against the visited file names of all live buffers.
(get-file-buffer "buffers.texi")
=> #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer
visiting the same file name. In such cases, this function returns
the first such buffer in the buffer list.
- Command: set-visited-file-name filename &optional no-query
along-with-file
If FILENAME is a non-empty string, this function changes the name
of the file visited in the current buffer to FILENAME. (If the
buffer had no visited file, this gives it one.) The _next time_
the buffer is saved it will go in the newly-specified file. This
command marks the buffer as modified, since it does not (as far as
Emacs knows) match the contents of FILENAME, even if it matched the
former visited file.
If FILENAME is `nil' or the empty string, that stands for "no
visited file". In this case, `set-visited-file-name' marks the
buffer as having no visited file.
Normally, this function asks the user for confirmation if the
specified file already exists. If NO-QUERY is non-`nil', that
prevents asking this question.
If ALONG-WITH-FILE is non-`nil', that means to assume that the
former visited file has been renamed to FILENAME.
When the function `set-visited-file-name' is called interactively,
it prompts for FILENAME in the minibuffer.
- Variable: list-buffers-directory
This buffer-local variable specifies a string to display in a
buffer listing where the visited file name would go, for buffers
that don't have a visited file name. Dired buffers use this
variable.
Buffer Modification
===================
Emacs keeps a flag called the "modified flag" for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to `t' whenever you alter the contents of the buffer, and cleared
to `nil' when you save it. Thus, the flag shows whether there are
unsaved changes. The flag value is normally shown in the mode line
(*note Mode Line Variables::), and controls saving (*note Saving
Buffers::) and auto-saving (*note Auto-Saving::).
Some Lisp programs set the flag explicitly. For example, the
function `set-visited-file-name' sets the flag to `t', because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in
*Note Text::.
- Function: buffer-modified-p &optional buffer
This function returns `t' if the buffer BUFFER has been modified
since it was last read in from a file or saved, or `nil'
otherwise. If BUFFER is not supplied, the current buffer is
tested.
- Function: set-buffer-modified-p flag
This function marks the current buffer as modified if FLAG is
non-`nil', or as unmodified if the flag is `nil'.
Another effect of calling this function is to cause unconditional
redisplay of the mode line for the current buffer. In fact, the
function `force-mode-line-update' works by doing this:
(set-buffer-modified-p (buffer-modified-p))
- Command: not-modified
This command marks the current buffer as unmodified, and not
needing to be saved. With prefix arg, it marks the buffer as
modified, so that it will be saved at the next suitable occasion.
Don't use this function in programs, since it prints a message in
the echo area; use `set-buffer-modified-p' (above) instead.
- Function: buffer-modified-tick &optional buffer
This function returns BUFFER's modification-count. This is a
counter that increments every time the buffer is modified. If
BUFFER is `nil' (or omitted), the current buffer is used.
Comparison of Modification Time
===============================
Suppose that you visit a file and make changes in its buffer, and
meanwhile the file itself is changed on disk. At this point, saving the
buffer would overwrite the changes in the file. Occasionally this may
be what you want, but usually it would lose valuable information. Emacs
therefore checks the file's modification time using the functions
described below before saving the file.
- Function: verify-visited-file-modtime buffer
This function compares what BUFFER has recorded for the
modification time of its visited file against the actual
modification time of the file as recorded by the operating system.
The two should be the same unless some other process has written
the file since Emacs visited or saved it.
The function returns `t' if the last actual modification time and
Emacs's recorded modification time are the same, `nil' otherwise.
- Function: clear-visited-file-modtime
This function clears out the record of the last modification time
of the file being visited by the current buffer. As a result, the
next attempt to save this buffer will not complain of a
discrepancy in file modification times.
This function is called in `set-visited-file-name' and other
exceptional places where the usual test to avoid overwriting a
changed file should not be done.
- Function: visited-file-modtime
This function returns the buffer's recorded last file modification
time, as a list of the form `(HIGH . LOW)'. (This is the same
format that `file-attributes' uses to return time values; see
*Note File Attributes::.)
- Function: set-visited-file-modtime &optional time
This function updates the buffer's record of the last modification
time of the visited file, to the value specified by TIME if TIME
is not `nil', and otherwise to the last modification time of the
visited file.
If TIME is not `nil', it should have the form `(HIGH . LOW)' or
`(HIGH LOW)', in either case containing two integers, each of
which holds 16 bits of the time.
This function is useful if the buffer was not read from the file
normally, or if the file itself has been changed for some known
benign reason.
- Function: ask-user-about-supersession-threat filename
This function is used to ask a user how to proceed after an
attempt to modify an obsolete buffer visiting file FILENAME. An
"obsolete buffer" is an unmodified buffer for which the associated
file on disk is newer than the last save-time of the buffer. This
means some other program has probably altered the file.
Depending on the user's answer, the function may return normally,
in which case the modification of the buffer proceeds, or it may
signal a `file-supersession' error with data `(FILENAME)', in which
case the proposed buffer modification is not allowed.
This function is called automatically by Emacs on the proper
occasions. It exists so you can customize Emacs by redefining it.
See the file `userlock.el' for the standard definition.
See also the file locking mechanism in *Note File Locks::.
Read-Only Buffers
=================
If a buffer is "read-only", then you cannot change its contents,
although you may change your view of the contents by scrolling and
narrowing.
Read-only buffers are used in two kinds of situations:
* A buffer visiting a write-protected file is normally read-only.
Here, the purpose is to inform the user that editing the buffer
with the aim of saving it in the file may be futile or
undesirable. The user who wants to change the buffer text despite
this can do so after clearing the read-only flag with `C-x C-q'.
* Modes such as Dired and Rmail make buffers read-only when altering
the contents with the usual editing commands would probably be a
mistake.
The special commands of these modes bind `buffer-read-only' to
`nil' (with `let') or bind `inhibit-read-only' to `t' around the
places where they themselves change the text.
- Variable: buffer-read-only
This buffer-local variable specifies whether the buffer is
read-only. The buffer is read-only if this variable is non-`nil'.
- Variable: inhibit-read-only
If this variable is non-`nil', then read-only buffers and read-only
characters may be modified. Read-only characters in a buffer are
those that have non-`nil' `read-only' properties (either text
properties or overlay properties). *Note Special Properties::,
for more information about text properties. *Note Overlays::, for
more information about overlays and their properties.
If `inhibit-read-only' is `t', all `read-only' character
properties have no effect. If `inhibit-read-only' is a list, then
`read-only' character properties have no effect if they are members
of the list (comparison is done with `eq').
- Command: toggle-read-only
This command changes whether the current buffer is read-only. It
is intended for interactive use; do not use it in programs. At
any given point in a program, you should know whether you want the
read-only flag on or off; so you can set `buffer-read-only'
explicitly to the proper value, `t' or `nil'.
- Function: barf-if-buffer-read-only
This function signals a `buffer-read-only' error if the current
buffer is read-only. *Note Interactive Call::, for another way to
signal an error if the current buffer is read-only.
The Buffer List
===============
The "buffer list" is a list of all live buffers. Creating a buffer
adds it to this list, and killing a buffer excises it. The order of
the buffers in the list is based primarily on how recently each buffer
has been displayed in the selected window. Buffers move to the front
of the list when they are selected and to the end when they are buried
(see `bury-buffer', below). Several functions, notably `other-buffer',
use this ordering. A buffer list displayed for the user also follows
this order.
In addition to the fundamental Emacs buffer list, each frame has its
own version of the buffer list, in which the buffers that have been
selected in that frame come first, starting with the buffers most
recently selected _in that frame_. (This order is recorded in FRAME's
`buffer-list' frame parameter; see *Note Window Frame Parameters::.)
The buffers that were never selected in FRAME come afterward, ordered
according to the fundamental Emacs buffer list.
- Function: buffer-list &optional frame
This function returns the buffer list, including all buffers, even
those whose names begin with a space. The elements are actual
buffers, not their names.
If FRAME is a frame, this returns FRAME's buffer list. If FRAME
is `nil', the fundamental Emacs buffer list is used: all the
buffers appear in order of most recent selection, regardless of
which frames they were selected in.
(buffer-list)
=> (#<buffer buffers.texi>
#<buffer *Minibuf-1*> #<buffer buffer.c>
#<buffer *Help*> #<buffer TAGS>)
;; Note that the name of the minibuffer
;; begins with a space!
(mapcar (function buffer-name) (buffer-list))
=> ("buffers.texi" " *Minibuf-1*"
"buffer.c" "*Help*" "TAGS")
The list that `buffer-list' returns is constructed specifically by
`buffer-list'; it is not an internal Emacs data structure, and
modifying it has no effect on the order of buffers. If you want to
change the order of buffers in the frame-independent buffer list, here
is an easy way:
(defun reorder-buffer-list (new-list)
(while new-list
(bury-buffer (car new-list))
(setq new-list (cdr new-list))))
With this method, you can specify any order for the list, but there
is no danger of losing a buffer or adding something that is not a valid
live buffer.
To change the order or value of a frame's buffer list, set the
frame's `buffer-list' frame parameter with `modify-frame-parameters'
(*note Parameter Access::).
- Function: other-buffer &optional buffer visible-ok frame
This function returns the first buffer in the buffer list other
than BUFFER. Usually this is the buffer selected most recently (in
frame FRAME or else the currently selected frame, *note Input
Focus::), aside from BUFFER. Buffers whose names start with a
space are not considered at all.
If BUFFER is not supplied (or if it is not a buffer), then
`other-buffer' returns the first buffer in the selected frame's
buffer list that is not now visible in any window in a visible
frame.
If FRAME has a non-`nil' `buffer-predicate' parameter, then
`other-buffer' uses that predicate to decide which buffers to
consider. It calls the predicate once for each buffer, and if the
value is `nil', that buffer is ignored. *Note Window Frame
Parameters::.
If VISIBLE-OK is `nil', `other-buffer' avoids returning a buffer
visible in any window on any visible frame, except as a last
resort. If VISIBLE-OK is non-`nil', then it does not matter
whether a buffer is displayed somewhere or not.
If no suitable buffer exists, the buffer `*scratch*' is returned
(and created, if necessary).
- Command: bury-buffer &optional buffer-or-name
This function puts BUFFER-OR-NAME at the end of the buffer list,
without changing the order of any of the other buffers on the list.
This buffer therefore becomes the least desirable candidate for
`other-buffer' to return.
`bury-buffer' operates on each frame's `buffer-list' parameter as
well as the frame-independent Emacs buffer list; therefore, the
buffer that you bury will come last in the value of `(buffer-list
FRAME)' and in the value of `(buffer-list nil)'.
If BUFFER-OR-NAME is `nil' or omitted, this means to bury the
current buffer. In addition, if the buffer is displayed in the
selected window, this switches to some other buffer (obtained using
`other-buffer') in the selected window. But if the buffer is
displayed in some other window, it remains displayed there.
To replace a buffer in all the windows that display it, use
`replace-buffer-in-windows'. *Note Buffers and Windows::.
Creating Buffers
================
This section describes the two primitives for creating buffers.
`get-buffer-create' creates a buffer if it finds no existing buffer
with the specified name; `generate-new-buffer' always creates a new
buffer and gives it a unique name.
Other functions you can use to create buffers include
`with-output-to-temp-buffer' (*note Temporary Displays::) and
`create-file-buffer' (*note Visiting Files::). Starting a subprocess
can also create a buffer (*note Processes::).
- Function: get-buffer-create name
This function returns a buffer named NAME. It returns an existing
buffer with that name, if one exists; otherwise, it creates a new
buffer. The buffer does not become the current buffer--this
function does not change which buffer is current.
An error is signaled if NAME is not a string.
(get-buffer-create "foo")
=> #<buffer foo>
The major mode for the new buffer is set to Fundamental mode. The
variable `default-major-mode' is handled at a higher level. *Note
Auto Major Mode::.
- Function: generate-new-buffer name
This function returns a newly created, empty buffer, but does not
make it current. If there is no buffer named NAME, then that is
the name of the new buffer. If that name is in use, this function
adds suffixes of the form `<N>' to NAME, where N is an integer.
It tries successive integers starting with 2 until it finds an
available name.
An error is signaled if NAME is not a string.
(generate-new-buffer "bar")
=> #<buffer bar>
(generate-new-buffer "bar")
=> #<buffer bar<2>>
(generate-new-buffer "bar")
=> #<buffer bar<3>>
The major mode for the new buffer is set to Fundamental mode. The
variable `default-major-mode' is handled at a higher level. *Note
Auto Major Mode::.
See the related function `generate-new-buffer-name' in *Note
Buffer Names::.
Killing Buffers
===============
"Killing a buffer" makes its name unknown to Emacs and makes its
text space available for other use.
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; if you kill two distinct buffers, they remain
distinct according to `eq' although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs
automatically selects or displays some other buffer instead. This means
that killing a buffer can in general change the current buffer.
Therefore, when you kill a buffer, you should also take the precautions
associated with changing the current buffer (unless you happen to know
that the buffer being killed isn't current). *Note Current Buffer::.
If you kill a buffer that is the base buffer of one or more indirect
buffers, the indirect buffers are automatically killed as well.
The `buffer-name' of a killed buffer is `nil'. You can use this
feature to test whether a buffer has been killed:
(defun buffer-killed-p (buffer)
"Return t if BUFFER is killed."
(not (buffer-name buffer)))
- Command: kill-buffer buffer-or-name
This function kills the buffer BUFFER-OR-NAME, freeing all its
memory for other uses or to be returned to the operating system.
It returns `nil'.
Any processes that have this buffer as the `process-buffer' are
sent the `SIGHUP' signal, which normally causes them to terminate.
(The basic meaning of `SIGHUP' is that a dialup line has been
disconnected.) *Note Deleting Processes::.
If the buffer is visiting a file and contains unsaved changes,
`kill-buffer' asks the user to confirm before the buffer is killed.
It does this even if not called interactively. To prevent the
request for confirmation, clear the modified flag before calling
`kill-buffer'. *Note Buffer Modification::.
Killing a buffer that is already dead has no effect.
(kill-buffer "foo.unchanged")
=> nil
(kill-buffer "foo.changed")
---------- Buffer: Minibuffer ----------
Buffer foo.changed modified; kill anyway? (yes or no) yes
---------- Buffer: Minibuffer ----------
=> nil
- Variable: kill-buffer-query-functions
After confirming unsaved changes, `kill-buffer' calls the functions
in the list `kill-buffer-query-functions', in order of appearance,
with no arguments. The buffer being killed is the current buffer
when they are called. The idea of this feature is that these
functions will ask for confirmation from the user. If any of them
returns `nil', `kill-buffer' spares the buffer's life.
- Variable: kill-buffer-hook
This is a normal hook run by `kill-buffer' after asking all the
questions it is going to ask, just before actually killing the
buffer. The buffer to be killed is current when the hook
functions run. *Note Hooks::.
- Variable: buffer-offer-save
This variable, if non-`nil' in a particular buffer, tells
`save-buffers-kill-emacs' and `save-some-buffers' to offer to save
that buffer, just as they offer to save file-visiting buffers. The
variable `buffer-offer-save' automatically becomes buffer-local
when set for any reason. *Note Buffer-Local Variables::.
Indirect Buffers
================
An "indirect buffer" shares the text of some other buffer, which is
called the "base buffer" of the indirect buffer. In some ways it is
the analogue, for buffers, of a symbolic link among files. The base
buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of
its base buffer; changes made by editing either one are visible
immediately in the other. This includes the text properties as well as
the characters themselves.
In all other respects, the indirect buffer and its base buffer are
completely separate. They have different names, different values of
point, different narrowing, different markers and overlays (though
inserting or deleting text in either buffer relocates the markers and
overlays for both), different major modes, and different buffer-local
variables.
An indirect buffer cannot visit a file, but its base buffer can. If
you try to save the indirect buffer, that actually saves the base
buffer.
Killing an indirect buffer has no effect on its base buffer. Killing
the base buffer effectively kills the indirect buffer in that it cannot
ever again be the current buffer.
- Command: make-indirect-buffer base-buffer name
This creates an indirect buffer named NAME whose base buffer is
BASE-BUFFER. The argument BASE-BUFFER may be a buffer or a string.
If BASE-BUFFER is an indirect buffer, its base buffer is used as
the base for the new buffer.
- Function: buffer-base-buffer buffer
This function returns the base buffer of BUFFER. If BUFFER is not
indirect, the value is `nil'. Otherwise, the value is another
buffer, which is never an indirect buffer.
The Buffer Gap
==============
Emacs buffers are implemented using an invisible "gap" to make
insertion and deletion faster. Insertion works by filling in part of
the gap, and deletion adds to the gap. Of course, this means that the
gap must first be moved to the locus of the insertion or deletion.
Emacs moves the gap only when you try to insert or delete. This is why
your first editing command in one part of a large buffer, after
previously editing in another far-away part, sometimes involves a
noticeable delay.
This mechanism works invisibly, and Lisp code should never be
affected by the gap's current location, but these functions are
available for getting information about the gap status.
- Function: gap-position
This function returns the current gap position in the current
buffer.
- Function: gap-size
This function returns the current gap size of the current buffer.
Windows
*******
This chapter describes most of the functions and variables related to
Emacs windows. See *Note Display::, for information on how text is
displayed in windows.
Basic Concepts of Emacs Windows
===============================
A "window" in Emacs is the physical area of the screen in which a
buffer is displayed. The term is also used to refer to a Lisp object
that represents that screen area in Emacs Lisp. It should be clear
from the context which is meant.
Emacs groups windows into frames. A frame represents an area of
screen available for Emacs to use. Each frame always contains at least
one window, but you can subdivide it vertically or horizontally into
multiple nonoverlapping Emacs windows.
In each frame, at any time, one and only one window is designated as
"selected within the frame". The frame's cursor appears in that
window. At any time, one frame is the selected frame; and the window
selected within that frame is "the selected window". The selected
window's buffer is usually the current buffer (except when `set-buffer'
has been used). *Note Current Buffer::.
For practical purposes, a window exists only while it is displayed in
a frame. Once removed from the frame, the window is effectively deleted
and should not be used, _even though there may still be references to
it_ from other Lisp objects. Restoring a saved window configuration is
the only way for a window no longer on the screen to come back to life.
(*Note Deleting Windows::.)
Each window has the following attributes:
* containing frame
* window height
* window width
* window edges with respect to the screen or frame
* the buffer it displays
* position within the buffer at the upper left of the window
* amount of horizontal scrolling, in columns
* point
* the mark
* how recently the window was selected
Users create multiple windows so they can look at several buffers at
once. Lisp libraries use multiple windows for a variety of reasons, but
most often to display related information. In Rmail, for example, you
can move through a summary buffer in one window while the other window
shows messages one at a time as they are reached.
The meaning of "window" in Emacs is similar to what it means in the
context of general-purpose window systems such as X, but not identical.
The X Window System places X windows on the screen; Emacs uses one or
more X windows as frames, and subdivides them into Emacs windows. When
you use Emacs on a character-only terminal, Emacs treats the whole
terminal screen as one frame.
Most window systems support arbitrarily located overlapping windows.
In contrast, Emacs windows are "tiled"; they never overlap, and
together they fill the whole screen or frame. Because of the way in
which Emacs creates new windows and resizes them, not all conceivable
tilings of windows on an Emacs frame are actually possible. *Note
Splitting Windows::, and *Note Size of Window::.
*Note Display::, for information on how the contents of the window's
buffer are displayed in the window.
- Function: windowp object
This function returns `t' if OBJECT is a window.
Splitting Windows
=================
The functions described here are the primitives used to split a
window into two windows. Two higher level functions sometimes split a
window, but not always: `pop-to-buffer' and `display-buffer' (*note
Displaying Buffers::).
The functions described here do not accept a buffer as an argument.
The two "halves" of the split window initially display the same buffer
previously visible in the window that was split.
- Command: split-window &optional window size horizontal
This function splits WINDOW into two windows. The original window
WINDOW remains the selected window, but occupies only part of its
former screen area. The rest is occupied by a newly created
window which is returned as the value of this function.
If HORIZONTAL is non-`nil', then WINDOW splits into two side by
side windows. The original window WINDOW keeps the leftmost SIZE
columns, and gives the rest of the columns to the new window.
Otherwise, it splits into windows one above the other, and WINDOW
keeps the upper SIZE lines and gives the rest of the lines to the
new window. The original window is therefore the left-hand or
upper of the two, and the new window is the right-hand or lower.
If WINDOW is omitted or `nil', then the selected window is split.
If SIZE is omitted or `nil', then WINDOW is divided evenly into
two parts. (If there is an odd line, it is allocated to the new
window.) When `split-window' is called interactively, all its
arguments are `nil'.
The following example starts with one window on a screen that is 50
lines high by 80 columns wide; then the window is split.
(setq w (selected-window))
=> #<window 8 on windows.texi>
(window-edges) ; Edges in order:
=> (0 0 80 50) ; left-top-right-bottom
;; Returns window created
(setq w2 (split-window w 15))
=> #<window 28 on windows.texi>
(window-edges w2)
=> (0 15 80 50) ; Bottom window;
; top is line 15
(window-edges w)
=> (0 0 80 15) ; Top window
The screen looks like this:
__________
| | line 0
| w |
|__________|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Next, the top window is split horizontally:
(setq w3 (split-window w 35 t))
=> #<window 32 on windows.texi>
(window-edges w3)
=> (35 0 80 15) ; Left edge at column 35
(window-edges w)
=> (0 0 35 15) ; Right edge at column 35
(window-edges w2)
=> (0 15 80 50) ; Bottom window unchanged
Now, the screen looks like this:
column 35
__________
| | | line 0
| w | w3 |
|___|______|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Normally, Emacs indicates the border between two side-by-side
windows with a scroll bar (*note Scroll Bars: Window Frame
Parameters.) or `|' characters. The display table can specify
alternative border characters; see *Note Display Tables::.
- Command: split-window-vertically &optional size
This function splits the selected window into two windows, one
above the other, leaving the upper of the two windows selected,
with SIZE lines. (If SIZE is negative, then the lower of the two
windows gets - SIZE lines and the upper window gets the rest, but
the upper window is still the one selected.)
- Command: split-window-horizontally &optional size
This function splits the selected window into two windows
side-by-side, leaving the selected window with SIZE columns.
This function is basically an interface to `split-window'. You
could define a simplified version of the function like this:
(defun split-window-horizontally (&optional arg)
"Split selected window into two windows, side by side..."
(interactive "P")
(let ((size (and arg (prefix-numeric-value arg))))
(and size (< size 0)
(setq size (+ (window-width) size)))
(split-window nil size t)))
- Function: one-window-p &optional no-mini all-frames
This function returns non-`nil' if there is only one window. The
argument NO-MINI, if non-`nil', means don't count the minibuffer
even if it is active; otherwise, the minibuffer window is
included, if active, in the total number of windows, which is
compared against one.
The argument ALL-FRAMES specifies which frames to consider. Here
are the possible values and their meanings:
`nil'
Count the windows in the selected frame, plus the minibuffer
used by that frame even if it lies in some other frame.
`t'
Count all windows in all existing frames.
`visible'
Count all windows in all visible frames.
0
Count all windows in all visible or iconified frames.
anything else
Count precisely the windows in the selected frame, and no
others.
Deleting Windows
================
A window remains visible on its frame unless you "delete" it by
calling certain functions that delete windows. A deleted window cannot
appear on the screen, but continues to exist as a Lisp object until
there are no references to it. There is no way to cancel the deletion
of a window aside from restoring a saved window configuration (*note
Window Configurations::). Restoring a window configuration also
deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one
adjacent sibling.
- Function: window-live-p window
This function returns `nil' if WINDOW is deleted, and `t'
otherwise.
*Warning:* Erroneous information or fatal errors may result from
using a deleted window as if it were live.
- Command: delete-window &optional window
This function removes WINDOW from display, and returns `nil'. If
WINDOW is omitted, then the selected window is deleted. An error
is signaled if there is only one window when `delete-window' is
called.
- Command: delete-other-windows &optional window
This function makes WINDOW the only window on its frame, by
deleting the other windows in that frame. If WINDOW is omitted or
`nil', then the selected window is used by default.
The return value is `nil'.
- Command: delete-windows-on buffer &optional frame
This function deletes all windows showing BUFFER. If there are no
windows showing BUFFER, it does nothing.
`delete-windows-on' operates frame by frame. If a frame has
several windows showing different buffers, then those showing
BUFFER are removed, and the others expand to fill the space. If
all windows in some frame are showing BUFFER (including the case
where there is only one window), then the frame reverts to having a
single window showing another buffer chosen with `other-buffer'.
*Note The Buffer List::.
The argument FRAME controls which frames to operate on. This
function does not use it in quite the same way as the other
functions which scan all windows; specifically, the values `t' and
`nil' have the opposite of their meanings in other functions.
Here are the full details:
* If it is `nil', operate on all frames.
* If it is `t', operate on the selected frame.
* If it is `visible', operate on all visible frames.
* If it is 0, operate on all visible or iconified frames.
* If it is a frame, operate on that frame.
This function always returns `nil'.
Selecting Windows
=================
When a window is selected, the buffer in the window becomes the
current buffer, and the cursor will appear in it.
- Function: selected-window
This function returns the selected window. This is the window in
which the cursor appears and to which many commands apply.
- Function: select-window window
This function makes WINDOW the selected window. The cursor then
appears in WINDOW (on redisplay). The buffer being displayed in
WINDOW is immediately designated the current buffer.
The return value is WINDOW.
(setq w (next-window))
(select-window w)
=> #<window 65 on windows.texi>
- Macro: save-selected-window forms...
This macro records the selected window, executes FORMS in
sequence, then restores the earlier selected window, unless it is
no longer alive.
This macro does not save or restore anything about the sizes,
arrangement or contents of windows; therefore, if the FORMS change
them, the change persists.
Each frame, at any time, has a window selected within the frame.
This macro saves only _the_ selected window; it does not save
anything about other frames. If the FORMS select some other frame
and alter the window selected within it, the change persists.
The following functions choose one of the windows on the screen,
offering various criteria for the choice.
- Function: get-lru-window &optional frame
This function returns the window least recently "used" (that is,
selected). The selected window is always the most recently used
window.
The selected window can be the least recently used window if it is
the only window. A newly created window becomes the least
recently used window until it is selected. A minibuffer window is
never a candidate.
The argument FRAME controls which windows are considered.
* If it is `nil', consider windows on the selected frame.
* If it is `t', consider windows on all frames.
* If it is `visible', consider windows on all visible frames.
* If it is 0, consider windows on all visible or iconified
frames.
* If it is a frame, consider windows on that frame.
- Function: get-largest-window &optional frame
This function returns the window with the largest area (height
times width). If there are no side-by-side windows, then this is
the window with the most lines. A minibuffer window is never a
candidate.
If there are two windows of the same size, then the function
returns the window that is first in the cyclic ordering of windows
(see following section), starting from the selected window.
The argument FRAME controls which set of windows to consider. See
`get-lru-window', above.
- Function: get-window-with-predicate predicate &optional minibuf
all-frames default
This function returns a window satisfying PREDICATE. It cycles
through all visible windows using `walk-windows' (*note Cyclic
Window Ordering::), calling PREDICATE on each one one of them with
that window as its argument. The function returns the first
window for which PREDICATE returns a non-`nil' value; if that
never happens, it returns DEFAULT.
The optional arguments MINIBUF and ALL-FRAMES specify the set of
windows to include in the scan. See the description of
`next-window' in *Note Cyclic Window Ordering::, for details.
Cyclic Ordering of Windows
==========================
When you use the command `C-x o' (`other-window') to select the next
window, it moves through all the windows on the screen in a specific
cyclic order. For any given configuration of windows, this order never
varies. It is called the "cyclic ordering of windows".
This ordering generally goes from top to bottom, and from left to
right. But it may go down first or go right first, depending on the
order in which the windows were split.
If the first split was vertical (into windows one above each other),
and then the subwindows were split horizontally, then the ordering is
left to right in the top of the frame, and then left to right in the
next lower part of the frame, and so on. If the first split was
horizontal, the ordering is top to bottom in the left part, and so on.
In general, within each set of siblings at any level in the window tree,
the order is left to right, or top to bottom.
- Function: next-window &optional window minibuf all-frames
This function returns the window following WINDOW in the cyclic
ordering of windows. This is the window that `C-x o' would select
if typed when WINDOW is selected. If WINDOW is the only window
visible, then this function returns WINDOW. If omitted, WINDOW
defaults to the selected window.
The value of the argument MINIBUF determines whether the
minibuffer is included in the window order. Normally, when
MINIBUF is `nil', the minibuffer is included if it is currently
active; this is the behavior of `C-x o'. (The minibuffer window
is active while the minibuffer is in use. *Note Minibuffers::.)
If MINIBUF is `t', then the cyclic ordering includes the
minibuffer window even if it is not active.
If MINIBUF is neither `t' nor `nil', then the minibuffer window is
not included even if it is active.
The argument ALL-FRAMES specifies which frames to consider. Here
are the possible values and their meanings:
`nil'
Consider all the windows in WINDOW's frame, plus the
minibuffer used by that frame even if it lies in some other
frame.
`t'
Consider all windows in all existing frames.
`visible'
Consider all windows in all visible frames. (To get useful
results, you must ensure WINDOW is in a visible frame.)
0
Consider all windows in all visible or iconified frames.
anything else
Consider precisely the windows in WINDOW's frame, and no
others.
This example assumes there are two windows, both displaying the
buffer `windows.texi':
(selected-window)
=> #<window 56 on windows.texi>
(next-window (selected-window))
=> #<window 52 on windows.texi>
(next-window (next-window (selected-window)))
=> #<window 56 on windows.texi>
- Function: previous-window &optional window minibuf all-frames
This function returns the window preceding WINDOW in the cyclic
ordering of windows. The other arguments specify which windows to
include in the cycle, as in `next-window'.
- Command: other-window count &optional all-frames
This function selects the COUNTth following window in the cyclic
order. If count is negative, then it moves back -COUNT windows in
the cycle, rather than forward. It returns `nil'.
The argument ALL-FRAMES has the same meaning as in `next-window',
but the MINIBUF argument of `next-window' is always effectively
`nil'.
In an interactive call, COUNT is the numeric prefix argument.
- Function: walk-windows proc &optional minibuf all-frames
This function cycles through all windows, calling `proc' once for
each window with the window as its sole argument.
The optional arguments MINIBUF and ALL-FRAMES specify the set of
windows to include in the scan. See `next-window', above, for
details.
- Function: window-list &optional frame minibuf window
This function returns a list of the windows on FRAME, starting
with WINDOW. If FRAME is `nil' or omitted, the selected frame is
used instead; if WINDOW is `nil' or omitted, the selected window
is used instead.
The value of MINIBUF determines if the minibuffer window will be
included in the result list. If MINIBUF is `t', the minibuffer
window will be included, even if it isn't active. If MINIBUF is
`nil' or omitted, the minibuffer window will only be included in
the list if it is active. If MINIBUF is neither `nil' nor `t',
the minibuffer window is not included, whether or not it is active.
Buffers and Windows
===================
This section describes low-level functions to examine windows or to
display buffers in windows in a precisely controlled fashion. *Note
Displaying Buffers::, for related functions that find a window to use
and specify a buffer for it. The functions described there are easier
to use than these, but they employ heuristics in choosing or creating a
window; use these functions when you need complete control.
- Function: set-window-buffer window buffer-or-name
This function makes WINDOW display BUFFER-OR-NAME as its contents.
It returns `nil'. This is the fundamental primitive for changing
which buffer is displayed in a window, and all ways of doing that
call this function.
(set-window-buffer (selected-window) "foo")
=> nil
- Function: window-buffer &optional window
This function returns the buffer that WINDOW is displaying. If
WINDOW is omitted, this function returns the buffer for the
selected window.
(window-buffer)
=> #<buffer windows.texi>
- Function: get-buffer-window buffer-or-name &optional all-frames
This function returns a window currently displaying
BUFFER-OR-NAME, or `nil' if there is none. If there are several
such windows, then the function returns the first one in the
cyclic ordering of windows, starting from the selected window.
*Note Cyclic Window Ordering::.
The argument ALL-FRAMES controls which windows to consider.
* If it is `nil', consider windows on the selected frame.
* If it is `t', consider windows on all frames.
* If it is `visible', consider windows on all visible frames.
* If it is 0, consider windows on all visible or iconified
frames.
* If it is a frame, consider windows on that frame.
- Function: get-buffer-window-list buffer-or-name &optional minibuf
all-frames
This function returns a list of all the windows currently
displaying BUFFER-OR-NAME.
The two optional arguments work like the optional arguments of
`next-window' (*note Cyclic Window Ordering::); they are _not_
like the single optional argument of `get-buffer-window'. Perhaps
we should change `get-buffer-window' in the future to make it
compatible with the other functions.
The argument ALL-FRAMES controls which windows to consider.
* If it is `nil', consider windows on the selected frame.
* If it is `t', consider windows on all frames.
* If it is `visible', consider windows on all visible frames.
* If it is 0, consider windows on all visible or iconified
frames.
* If it is a frame, consider windows on that frame.
- Variable: buffer-display-time
This variable records the time at which a buffer was last made
visible in a window. It is always local in each buffer; each time
`set-window-buffer' is called, it sets this variable to
`(current-time)' in the specified buffer (*note Time of Day::).
When a buffer is first created, `buffer-display-time' starts out
with the value `nil'.
Displaying Buffers in Windows
=============================
In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer. These functions
can also split an existing window in certain circumstances. We also
describe variables that parameterize the heuristics used for choosing a
window. *Note Buffers and Windows::, for low-level functions that give
you more precise control. All of these functions work by calling
`set-window-buffer'.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user. Instead, use
`set-buffer' and `save-current-buffer' (*note Current Buffer::), which
designate buffers as current for programmed access without affecting
the display of buffers in windows.
- Command: switch-to-buffer buffer-or-name &optional norecord
This function makes BUFFER-OR-NAME the current buffer, and also
displays the buffer in the selected window. This means that a
human can see the buffer and subsequent keyboard commands will
apply to it. Contrast this with `set-buffer', which makes
BUFFER-OR-NAME the current buffer but does not display it in the
selected window. *Note Current Buffer::.
If BUFFER-OR-NAME does not identify an existing buffer, then a new
buffer by that name is created. The major mode for the new buffer
is set according to the variable `default-major-mode'. *Note Auto
Major Mode::.
Normally the specified buffer is put at the front of the buffer
list (both the selected frame's buffer list and the
frame-independent buffer list). This affects the operation of
`other-buffer'. However, if NORECORD is non-`nil', this is not
done. *Note The Buffer List::.
The `switch-to-buffer' function is often used interactively, as
the binding of `C-x b'. It is also used frequently in programs.
It always returns `nil'.
- Command: switch-to-buffer-other-window buffer-or-name &optional
norecord
This function makes BUFFER-OR-NAME the current buffer and displays
it in a window not currently selected. It then selects that
window. The handling of the buffer is the same as in
`switch-to-buffer'.
The currently selected window is absolutely never used to do the
job. If it is the only window, then it is split to make a
distinct window for this purpose. If the selected window is
already displaying the buffer, then it continues to do so, but
another window is nonetheless found to display it in as well.
This function updates the buffer list just like `switch-to-buffer'
unless NORECORD is non-`nil'.
- Function: pop-to-buffer buffer-or-name &optional other-window
norecord
This function makes BUFFER-OR-NAME the current buffer and switches
to it in some window, preferably not the window previously
selected. The "popped-to" window becomes the selected window
within its frame.
If the variable `pop-up-frames' is non-`nil', `pop-to-buffer'
looks for a window in any visible frame already displaying the
buffer; if there is one, it returns that window and makes it be
selected within its frame. If there is none, it creates a new
frame and displays the buffer in it.
If `pop-up-frames' is `nil', then `pop-to-buffer' operates
entirely within the selected frame. (If the selected frame has
just a minibuffer, `pop-to-buffer' operates within the most
recently selected frame that was not just a minibuffer.)
If the variable `pop-up-windows' is non-`nil', windows may be
split to create a new window that is different from the original
window. For details, see *Note Choosing Window::.
If OTHER-WINDOW is non-`nil', `pop-to-buffer' finds or creates
another window even if BUFFER-OR-NAME is already visible in the
selected window. Thus BUFFER-OR-NAME could end up displayed in
two windows. On the other hand, if BUFFER-OR-NAME is already
displayed in the selected window and OTHER-WINDOW is `nil', then
the selected window is considered sufficient display for
BUFFER-OR-NAME, so that nothing needs to be done.
All the variables that affect `display-buffer' affect
`pop-to-buffer' as well. *Note Choosing Window::.
If BUFFER-OR-NAME is a string that does not name an existing
buffer, a buffer by that name is created. The major mode for the
new buffer is set according to the variable `default-major-mode'.
*Note Auto Major Mode::.
This function updates the buffer list just like `switch-to-buffer'
unless NORECORD is non-`nil'.
- Command: replace-buffer-in-windows buffer
This function replaces BUFFER with some other buffer in all
windows displaying it. The other buffer used is chosen with
`other-buffer'. In the usual applications of this function, you
don't care which other buffer is used; you just want to make sure
that BUFFER is no longer displayed.
This function returns `nil'.
Choosing a Window for Display
=============================
This section describes the basic facility that chooses a window to
display a buffer in--`display-buffer'. All the higher-level functions
and commands use this subroutine. Here we describe how to use
`display-buffer' and how to customize it.
- Command: display-buffer buffer-or-name &optional not-this-window
frame
This command makes BUFFER-OR-NAME appear in some window, like
`pop-to-buffer', but it does not select that window and does not
make the buffer current. The identity of the selected window is
unaltered by this function.
If NOT-THIS-WINDOW is non-`nil', it means to display the specified
buffer in a window other than the selected one, even if it is
already on display in the selected window. This can cause the
buffer to appear in two windows at once. Otherwise, if
BUFFER-OR-NAME is already being displayed in any window, that is
good enough, so this function does nothing.
`display-buffer' returns the window chosen to display
BUFFER-OR-NAME.
If the argument FRAME is non-`nil', it specifies which frames to
check when deciding whether the buffer is already displayed. If
the buffer is already displayed in some window on one of these
frames, `display-buffer' simply returns that window. Here are the
possible values of FRAME:
* If it is `nil', consider windows on the selected frame.
* If it is `t', consider windows on all frames.
* If it is `visible', consider windows on all visible frames.
* If it is 0, consider windows on all visible or iconified
frames.
* If it is a frame, consider windows on that frame.
Precisely how `display-buffer' finds or creates a window depends on
the variables described below.
- User Option: display-buffer-reuse-frames
If this variable is non-`nil', `display-buffer' searches existing
frames for a window displaying the buffer. If the buffer is
already displayed in a window in some frame, `display-buffer' makes
the frame visible and raises it, to use that window. If the
buffer is not already displayed, or if
`display-buffer-reuse-frames' is `nil', `display-buffer''s
behavior is determined by other variables, described below.
- User Option: pop-up-windows
This variable controls whether `display-buffer' makes new windows.
If it is non-`nil' and there is only one window, then that window
is split. If it is `nil', then `display-buffer' does not split
the single window, but uses it whole.
- User Option: split-height-threshold
This variable determines when `display-buffer' may split a window,
if there are multiple windows. `display-buffer' always splits the
largest window if it has at least this many lines. If the largest
window is not this tall, it is split only if it is the sole window
and `pop-up-windows' is non-`nil'.
- User Option: even-window-heights
This variable determines if `display-buffer' should even out window
heights if the buffer gets displayed in an existing window, above
or beneath another existing window. If `even-window-heights' is
`t', the default, window heights will be evened out. If
`even-window-heights' is `nil', the orginal window heights will be
left alone.
- User Option: pop-up-frames
This variable controls whether `display-buffer' makes new frames.
If it is non-`nil', `display-buffer' looks for an existing window
already displaying the desired buffer, on any visible frame. If
it finds one, it returns that window. Otherwise it makes a new
frame. The variables `pop-up-windows' and
`split-height-threshold' do not matter if `pop-up-frames' is
non-`nil'.
If `pop-up-frames' is `nil', then `display-buffer' either splits a
window or reuses one.
*Note Frames::, for more information.
- Variable: pop-up-frame-function
This variable specifies how to make a new frame if `pop-up-frames'
is non-`nil'.
Its value should be a function of no arguments. When
`display-buffer' makes a new frame, it does so by calling that
function, which should return a frame. The default value of the
variable is a function that creates a frame using parameters from
`pop-up-frame-alist'.
- User Option: pop-up-frame-alist
This variable holds an alist specifying frame parameters used when
`display-buffer' makes a new frame. *Note Frame Parameters::, for
more information about frame parameters.
- User Option: special-display-buffer-names
A list of buffer names for buffers that should be displayed
specially. If the buffer's name is in this list, `display-buffer'
handles the buffer specially.
By default, special display means to give the buffer a dedicated
frame.
If an element is a list, instead of a string, then the CAR of the
list is the buffer name, and the rest of the list says how to
create the frame. There are two possibilities for the rest of the
list. It can be an alist, specifying frame parameters, or it can
contain a function and arguments to give to it. (The function's
first argument is always the buffer to be displayed; the arguments
from the list come after that.)
- User Option: special-display-regexps
A list of regular expressions that specify buffers that should be
displayed specially. If the buffer's name matches any of the
regular expressions in this list, `display-buffer' handles the
buffer specially.
By default, special display means to give the buffer a dedicated
frame.
If an element is a list, instead of a string, then the CAR of the
list is the regular expression, and the rest of the list says how
to create the frame. See above, under
`special-display-buffer-names'.
- Variable: special-display-function
This variable holds the function to call to display a buffer
specially. It receives the buffer as an argument, and should
return the window in which it is displayed.
The default value of this variable is
`special-display-popup-frame'.
- Function: special-display-popup-frame buffer &rest args
This function makes BUFFER visible in a frame of its own. If
BUFFER is already displayed in a window in some frame, it makes
the frame visible and raises it, to use that window. Otherwise, it
creates a frame that will be dedicated to BUFFER.
If ARGS is an alist, it specifies frame parameters for the new
frame.
If ARGS is a list whose CAR is a symbol, then `(car ARGS)' is
called as a function to actually create and set up the frame; it
is called with BUFFER as first argument, and `(cdr ARGS)' as
additional arguments.
This function always uses an existing window displaying BUFFER,
whether or not it is in a frame of its own; but if you set up the
above variables in your init file, before BUFFER was created, then
presumably the window was previously made by this function.
- User Option: special-display-frame-alist
This variable holds frame parameters for
`special-display-popup-frame' to use when it creates a frame.
- User Option: same-window-buffer-names
A list of buffer names for buffers that should be displayed in the
selected window. If the buffer's name is in this list,
`display-buffer' handles the buffer by switching to it in the
selected window.
- User Option: same-window-regexps
A list of regular expressions that specify buffers that should be
displayed in the selected window. If the buffer's name matches
any of the regular expressions in this list, `display-buffer'
handles the buffer by switching to it in the selected window.
- Variable: display-buffer-function
This variable is the most flexible way to customize the behavior of
`display-buffer'. If it is non-`nil', it should be a function
that `display-buffer' calls to do the work. The function should
accept two arguments, the same two arguments that `display-buffer'
received. It should choose or create a window, display the
specified buffer, and then return the window.
This hook takes precedence over all the other options and hooks
described above.
A window can be marked as "dedicated" to its buffer. Then
`display-buffer' will not try to use that window to display any other
buffer.
- Function: window-dedicated-p window
This function returns `t' if WINDOW is marked as dedicated;
otherwise `nil'.
- Function: set-window-dedicated-p window flag
This function marks WINDOW as dedicated if FLAG is non-`nil', and
nondedicated otherwise.
Windows and Point
=================
Each window has its own value of point, independent of the value of
point in other windows displaying the same buffer. This makes it useful
to have multiple windows showing one buffer.
* The window point is established when a window is first created; it
is initialized from the buffer's point, or from the window point
of another window opened on the buffer if such a window exists.
* Selecting a window sets the value of point in its buffer from the
window's value of point. Conversely, deselecting a window sets the
window's value of point from that of the buffer. Thus, when you
switch between windows that display a given buffer, the point
value for the selected window is in effect in the buffer, while
the point values for the other windows are stored in those windows.
* As long as the selected window displays the current buffer, the
window's point and the buffer's point always move together; they
remain equal.
* *Note Positions::, for more details on buffer positions.
As far as the user is concerned, point is where the cursor is, and
when the user switches to another buffer, the cursor jumps to the
position of point in that buffer.
- Function: window-point &optional window
This function returns the current position of point in WINDOW.
For a nonselected window, this is the value point would have (in
that window's buffer) if that window were selected. If WINDOW is
`nil', the selected window is used.
When WINDOW is the selected window and its buffer is also the
current buffer, the value returned is the same as point in that
buffer.
Strictly speaking, it would be more correct to return the
"top-level" value of point, outside of any `save-excursion' forms.
But that value is hard to find.
- Function: set-window-point window position
This function positions point in WINDOW at position POSITION in
WINDOW's buffer.
The Window Start Position
=========================
Each window contains a marker used to keep track of a buffer position
that specifies where in the buffer display should start. This position
is called the "display-start" position of the window (or just the
"start"). The character after this position is the one that appears at
the upper left corner of the window. It is usually, but not
inevitably, at the beginning of a text line.
- Function: window-start &optional window
This function returns the display-start position of window WINDOW.
If WINDOW is `nil', the selected window is used. For example,
(window-start)
=> 7058
When you create a window, or display a different buffer in it, the
display-start position is set to a display-start position recently
used for the same buffer, or 1 if the buffer doesn't have any.
Redisplay updates the window-start position (if you have not
specified it explicitly since the previous redisplay)--for
example, to make sure point appears on the screen. Nothing except
redisplay automatically changes the window-start position; if you
move point, do not expect the window-start position to change in
response until after the next redisplay.
For a realistic example of using `window-start', see the
description of `count-lines' in *Note Text Lines::.
- Function: window-end &optional window update
This function returns the position of the end of the display in
window WINDOW. If WINDOW is `nil', the selected window is used.
Simply changing the buffer text or moving point does not update the
value that `window-end' returns. The value is updated only when
Emacs redisplays and redisplay completes without being preempted.
If the last redisplay of WINDOW was preempted, and did not finish,
Emacs does not know the position of the end of display in that
window. In that case, this function returns `nil'.
If UPDATE is non-`nil', `window-end' always returns an up-to-date
value for where the window ends, based on the current
`window-start' value. If the saved value is valid, `window-end'
returns that; otherwise it computes the correct value by scanning
the buffer text.
Even if UPDATE is non-`nil', `window-end' does not attempt to
scroll the display if point has moved off the screen, the way real
redisplay would do. It does not alter the `window-start' value.
In effect, it reports where the displayed text will end if
scrolling is not required.
- Function: set-window-start window position &optional noforce
This function sets the display-start position of WINDOW to
POSITION in WINDOW's buffer. It returns POSITION.
The display routines insist that the position of point be visible
when a buffer is displayed. Normally, they change the
display-start position (that is, scroll the window) whenever
necessary to make point visible. However, if you specify the
start position with this function using `nil' for NOFORCE, it
means you want display to start at POSITION even if that would put
the location of point off the screen. If this does place point
off screen, the display routines move point to the left margin on
the middle line in the window.
For example, if point is 1 and you set the start of the window
to 2, then point would be "above" the top of the window. The
display routines will automatically move point if it is still 1
when redisplay occurs. Here is an example:
;; Here is what `foo' looks like before executing
;; the `set-window-start' expression.
---------- Buffer: foo ----------
-!-This is the contents of buffer foo.
2
3
4
5
6
---------- Buffer: foo ----------
(set-window-start
(selected-window)
(1+ (window-start)))
=> 2
;; Here is what `foo' looks like after executing
;; the `set-window-start' expression.
---------- Buffer: foo ----------
his is the contents of buffer foo.
2
3
-!-4
5
6
---------- Buffer: foo ----------
If NOFORCE is non-`nil', and POSITION would place point off screen
at the next redisplay, then redisplay computes a new window-start
position that works well with point, and thus POSITION is not used.
- Function: pos-visible-in-window-p &optional position window partially
This function returns `t' if POSITION is within the range of text
currently visible on the screen in WINDOW. It returns `nil' if
POSITION is scrolled vertically or horizontally out of view.
Locations that are partially obscured are not considered visible
unless PARTIALLY is non-`nil'. The argument POSITION defaults to
the current position of point in WINDOW; WINDOW, to the selected
window.
Here is an example:
(or (pos-visible-in-window-p
(point) (selected-window))
(recenter 0))
Textual Scrolling
=================
"Textual scrolling" means moving the text up or down though a
window. It works by changing the value of the window's display-start
location. It may also change the value of `window-point' to keep point
on the screen.
Textual scrolling was formerly called "vertical scrolling," but we
changed its name to distinguish it from the new vertical fractional
scrolling feature (*note Vertical Scrolling::).
In the commands `scroll-up' and `scroll-down', the directions "up"
and "down" refer to the motion of the text in the buffer at which you
are looking through the window. Imagine that the text is written on a
long roll of paper and that the scrolling commands move the paper up
and down. Thus, if you are looking at text in the middle of a buffer
and repeatedly call `scroll-down', you will eventually see the
beginning of the buffer.
Some people have urged that the opposite convention be used: they
imagine that the window moves over text that remains in place. Then
"down" commands would take you to the end of the buffer. This view is
more consistent with the actual relationship between windows and the
text in the buffer, but it is less like what the user sees. The
position of a window on the terminal does not move, and short scrolling
commands clearly move the text up or down on the screen. We have chosen
names that fit the user's point of view.
The textual scrolling functions (aside from `scroll-other-window')
have unpredictable results if the current buffer is different from the
buffer that is displayed in the selected window. *Note Current
Buffer::.
- Command: scroll-up &optional count
This function scrolls the text in the selected window upward COUNT
lines. If COUNT is negative, scrolling is actually downward.
If COUNT is `nil' (or omitted), then the length of scroll is
`next-screen-context-lines' lines less than the usable height of
the window (not counting its mode line).
`scroll-up' returns `nil'.
- Command: scroll-down &optional count
This function scrolls the text in the selected window downward
COUNT lines. If COUNT is negative, scrolling is actually upward.
If COUNT is omitted or `nil', then the length of the scroll is
`next-screen-context-lines' lines less than the usable height of
the window (not counting its mode line).
`scroll-down' returns `nil'.
- Command: scroll-other-window &optional count
This function scrolls the text in another window upward COUNT
lines. Negative values of COUNT, or `nil', are handled as in
`scroll-up'.
You can specify which buffer to scroll by setting the variable
`other-window-scroll-buffer' to a buffer. If that buffer isn't
already displayed, `scroll-other-window' displays it in some
window.
When the selected window is the minibuffer, the next window is
normally the one at the top left corner. You can specify a
different window to scroll, when the minibuffer is selected, by
setting the variable `minibuffer-scroll-window'. This variable
has no effect when any other window is selected. *Note Minibuffer
Misc::.
When the minibuffer is active, it is the next window if the
selected window is the one at the bottom right corner. In this
case, `scroll-other-window' attempts to scroll the minibuffer. If
the minibuffer contains just one line, it has nowhere to scroll
to, so the line reappears after the echo area momentarily displays
the message "Beginning of buffer".
- Variable: other-window-scroll-buffer
If this variable is non-`nil', it tells `scroll-other-window'
which buffer to scroll.
- User Option: scroll-margin
This option specifies the size of the scroll margin--a minimum
number of lines between point and the top or bottom of a window.
Whenever point gets within this many lines of the top or bottom of
the window, the window scrolls automatically (if possible) to move
point out of the margin, closer to the center of the window.
- User Option: scroll-conservatively
This variable controls how scrolling is done automatically when
point moves off the screen (or into the scroll margin). If the
value is zero, then redisplay scrolls the text to center point
vertically in the window. If the value is a positive integer N,
then redisplay scrolls the window up to N lines in either
direction, if that will bring point back into view. Otherwise, it
centers point. The default value is zero.
- User Option: scroll-down-aggressively
The value of this variable should be either `nil' or a fraction F
between 0 and 1. If it is a fraction, that specifies where on the
screen to put point when scrolling down. More precisely, when a
window scrolls down because point is above the window start, the
new start position is chosen to put point F part of the window
height from the top. The larger F, the more aggressive the
scrolling.
A value of `nil' is equivalent to .5, since its effect is to center
point. This variable automatically becomes buffer-local when set
in any fashion.
- User Option: scroll-up-aggressively
Likewise, for scrolling up. The value, F, specifies how far point
should be placed from the bottom of the window; thus, as with
`scroll-up-aggressively', a larger value scrolls more aggressively.
- User Option: scroll-step
This variable is an older variant of `scroll-conservatively'. The
difference is that it if its value is N, that permits scrolling
only by precisely N lines, not a smaller number. This feature
does not work with `scroll-margin'. The default value is zero.
- User Option: scroll-preserve-screen-position
If this option is non-`nil', the scroll functions move point so
that the vertical position of the cursor is unchanged, when that is
possible.
- User Option: next-screen-context-lines
The value of this variable is the number of lines of continuity to
retain when scrolling by full screens. For example, `scroll-up'
with an argument of `nil' scrolls so that this many lines at the
bottom of the window appear instead at the top. The default value
is `2'.
- Command: recenter &optional count
This function scrolls the selected window to put the text where
point is located at a specified vertical position within the
window.
If COUNT is a nonnegative number, it puts the line containing
point COUNT lines down from the top of the window. If COUNT is a
negative number, then it counts upward from the bottom of the
window, so that -1 stands for the last usable line in the window.
If COUNT is a non-`nil' list, then it stands for the line in the
middle of the window.
If COUNT is `nil', `recenter' puts the line containing point in
the middle of the window, then clears and redisplays the entire
selected frame.
When `recenter' is called interactively, COUNT is the raw prefix
argument. Thus, typing `C-u' as the prefix sets the COUNT to a
non-`nil' list, while typing `C-u 4' sets COUNT to 4, which
positions the current line four lines from the top.
With an argument of zero, `recenter' positions the current line at
the top of the window. This action is so handy that some people
make a separate key binding to do this. For example,
(defun line-to-top-of-window ()
"Scroll current line to top of window.
Replaces three keystroke sequence C-u 0 C-l."
(interactive)
(recenter 0))
(global-set-key [kp-multiply] 'line-to-top-of-window)
Vertical Fractional Scrolling
=============================
"Vertical fractional scrolling" means shifting the image in the
window up or down by a specified multiple or fraction of a line.
Starting in Emacs 21, each window has a "vertical scroll position",
which is a number, never less than zero. It specifies how far to raise
the contents of the window. Raising the window contents generally makes
all or part of some lines disappear off the top, and all or part of some
other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line
height, which is the height of the default font. Thus, if the value is
.5, that means the window contents are scrolled up half the normal line
height. If it is 3.3, that means the window contents are scrolled up
somewhat over three times the normal line height.
What fraction of a line the vertical scrolling covers, or how many
lines, depends on what the lines contain. A value of .5 could scroll a
line whose height is very short off the screen, while a value of 3.3
could scroll just part of the way through a tall line or an image.
- Function: window-vscroll &optional window
This function returns the current vertical scroll position of
WINDOW, If WINDOW is `nil', the selected window is used.
(window-vscroll)
=> 0
- Function: set-window-vscroll window lines
This function sets WINDOW's vertical scroll position to LINES.
The argument LINES should be zero or positive; if not, it is taken
as zero.
The actual vertical scroll position must always correspond to an
integral number of pixels, so the value you specify is rounded
accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2)
=> 1.13
Horizontal Scrolling
====================
"Horizontal scrolling" means shifting the image in the window left
or right by a specified multiple of the normal character width. Each
window has a "vertical scroll position", which is a number, never less
than zero. It specifies how far to shift the contents left. Shifting
the window contents left generally makes all or part of some characters
disappear off the left, and all or part of some other characters appear
at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal
character width, which is the width of space in the default font. Thus,
if the value is 5, that means the window contents are scrolled left by 5
times the normal character width. How many characters actually
disappear off to the left depends on their width, and could vary from
line to line.
Because we read from side to side in the "inner loop", and from top
to bottom in the "outer loop", the effect of horizontal scrolling is
not like that of textual or vertical scrolling. Textual scrolling
involves selection of a portion of text to display, and vertical
scrolling moves the window contents contiguously; but horizontal
scrolling causes part of _each line_ to go off screen.
Usually, no horizontal scrolling is in effect; then the leftmost
column is at the left edge of the window. In this state, scrolling to
the right is meaningless, since there is no data to the left of the edge
to be revealed by it; so this is not allowed. Scrolling to the left is
allowed; it scrolls the first columns of text off the edge of the window
and can reveal additional columns on the right that were truncated
before. Once a window has a nonzero amount of leftward horizontal
scrolling, you can scroll it back to the right, but only so far as to
reduce the net horizontal scroll to zero. There is no limit to how far
left you can scroll, but eventually all the text will disappear off the
left edge.
In Emacs 21, redisplay automatically alters the horizontal scrolling
of a window as necessary to ensure that point is always visible, if
`automatic-hscrolling' is set. However, you can still set the
horizontal scrolling value explicitly. The value you specify serves as
a lower bound for automatic scrolling, i.e. automatic scrolling will
not scroll a window to a column less than the specified one.
- Command: scroll-left &optional count
This function scrolls the selected window COUNT columns to the
left (or to the right if COUNT is negative). The default for
COUNT is the window width, minus 2.
The return value is the total amount of leftward horizontal
scrolling in effect after the change--just like the value returned
by `window-hscroll' (below).
- Command: scroll-right &optional count
This function scrolls the selected window COUNT columns to the
right (or to the left if COUNT is negative). The default for
COUNT is the window width, minus 2.
The return value is the total amount of leftward horizontal
scrolling in effect after the change--just like the value returned
by `window-hscroll' (below).
Once you scroll a window as far right as it can go, back to its
normal position where the total leftward scrolling is zero,
attempts to scroll any farther right have no effect.
- Function: window-hscroll &optional window
This function returns the total leftward horizontal scrolling of
WINDOW--the number of columns by which the text in WINDOW is
scrolled left past the left margin.
The value is never negative. It is zero when no horizontal
scrolling has been done in WINDOW (which is usually the case).
If WINDOW is `nil', the selected window is used.
(window-hscroll)
=> 0
(scroll-left 5)
=> 5
(window-hscroll)
=> 5
- Function: set-window-hscroll window columns
This function sets the number of columns from the left margin that
WINDOW is scrolled from the value of COLUMNS. The argument
COLUMNS should be zero or positive; if not, it is taken as zero.
Fractional values of COLUMNS are not supported at present.
The value returned is COLUMNS.
(set-window-hscroll (selected-window) 10)
=> 10
Here is how you can determine whether a given position POSITION is
off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
The Size of a Window
====================
An Emacs window is rectangular, and its size information consists of
the height (the number of lines) and the width (the number of character
positions in each line). The mode line is included in the height. But
the width does not count the scroll bar or the column of `|' characters
that separates side-by-side windows.
The following three functions return size information about a window:
- Function: window-height &optional window
This function returns the number of lines in WINDOW, including its
mode line. If WINDOW fills its entire frame, this is typically
one less than the value of `frame-height' on that frame (since the
last line is always reserved for the minibuffer).
If WINDOW is `nil', the function uses the selected window.
(window-height)
=> 23
(split-window-vertically)
=> #<window 4 on windows.texi>
(window-height)
=> 11
- Function: window-width &optional window
This function returns the number of columns in WINDOW. If WINDOW
fills its entire frame, this is the same as the value of
`frame-width' on that frame. The width does not include the
window's scroll bar or the column of `|' characters that separates
side-by-side windows.
If WINDOW is `nil', the function uses the selected window.
(window-width)
=> 80
- Function: window-edges &optional window
This function returns a list of the edge coordinates of WINDOW.
If WINDOW is `nil', the selected window is used.
The order of the list is `(LEFT TOP RIGHT BOTTOM)', all elements
relative to 0, 0 at the top left corner of the frame. The element
RIGHT of the value is one more than the rightmost column used by
WINDOW, and BOTTOM is one more than the bottommost row used by
WINDOW and its mode-line.
If a window has a scroll bar, the right edge value includes the
width of the scroll bar. Otherwise, if the window has a neighbor
on the right, its right edge value includes the width of the
separator line between the window and that neighbor. Since the
width of the window does not include this separator, the width
does not usually equal the difference between the right and left
edges.
Here is the result obtained on a typical 24-line terminal with
just one window:
(window-edges (selected-window))
=> (0 0 80 23)
The bottom edge is at line 23 because the last line is the echo
area.
If WINDOW is at the upper left corner of its frame, then BOTTOM is
the same as the value of `(window-height)', RIGHT is almost the
same as the value of `(window-width)', and TOP and LEFT are zero.
For example, the edges of the following window are `0 0 8 5'.
Assuming that the frame has more than 8 columns, the last column
of the window (column 7) holds a border rather than text. The
last row (row 4) holds the mode line, shown here with `xxxxxxxxx'.
0
_______
0 | |
| |
| |
| |
xxxxxxxxx 4
7
In the following example, let's suppose that the frame is 7
columns wide. Then the edges of the left window are `0 0 4 3' and
the edges of the right window are `4 0 8 3'.
___ ___
| | |
| | |
xxxxxxxxx
0 34 7
Changing the Size of a Window
=============================
The window size functions fall into two classes: high-level commands
that change the size of windows and low-level functions that access
window size. Emacs does not permit overlapping windows or gaps between
windows, so resizing one window affects other windows.
- Command: enlarge-window size &optional horizontal
This function makes the selected window SIZE lines taller,
stealing lines from neighboring windows. It takes the lines from
one window at a time until that window is used up, then takes from
another. If a window from which lines are stolen shrinks below
`window-min-height' lines, that window disappears.
If HORIZONTAL is non-`nil', this function makes WINDOW wider by
SIZE columns, stealing columns instead of lines. If a window from
which columns are stolen shrinks below `window-min-width' columns,
that window disappears.
If the requested size would exceed that of the window's frame,
then the function makes the window occupy the entire height (or
width) of the frame.
If there are various other windows from which lines or columns can
be stolen, and some of them specify fixed size (using
`window-size-fixed', see below), they are left untouched while
other windows are "robbed." If it would be necessary to alter the
size of a fixed-size window, `enlarge-window' gets an error
instead.
If SIZE is negative, this function shrinks the window by -SIZE
lines or columns. If that makes the window smaller than the
minimum size (`window-min-height' and `window-min-width'),
`enlarge-window' deletes the window.
`enlarge-window' returns `nil'.
- Command: enlarge-window-horizontally columns
This function makes the selected window COLUMNS wider. It could
be defined as follows:
(defun enlarge-window-horizontally (columns)
(enlarge-window columns t))
- Command: shrink-window size &optional horizontal
This function is like `enlarge-window' but negates the argument
SIZE, making the selected window smaller by giving lines (or
columns) to the other windows. If the window shrinks below
`window-min-height' or `window-min-width', then it disappears.
If SIZE is negative, the window is enlarged by -SIZE lines or
columns.
- Command: shrink-window-horizontally columns
This function makes the selected window COLUMNS narrower. It
could be defined as follows:
(defun shrink-window-horizontally (columns)
(shrink-window columns t))
- Command: shrink-window-if-larger-than-buffer &optional window
This command shrinks WINDOW to be as small as possible while still
showing the full contents of its buffer--but not less than
`window-min-height' lines. If WINDOW is not given, it defaults to
the selected window.
However, the command does nothing if the window is already too
small to display the whole text of the buffer, or if part of the
contents are currently scrolled off screen, or if the window is
not the full width of its frame, or if the window is the only
window in its frame.
- Variable: window-size-fixed
If this variable is non-`nil', in any given buffer, then the size
of any window displaying the buffer remains fixed unless you
explicitly change it or Emacs has no other choice. (This feature
is new in Emacs 21.)
If the value is `height', then only the window's height is fixed;
if the value is `width', then only the window's width is fixed.
Any other non-`nil' value fixes both the width and the height.
The usual way to use this variable is to give it a buffer-local
value in a particular buffer. That way, the windows (but usually
there is only one) displaying that buffer have fixed size.
Explicit size-change functions such as `enlarge-window' get an
error if they would have to change a window size which is fixed.
Therefore, when you want to change the size of such a window, you
should bind `window-size-fixed' to `nil', like this:
(let ((window-size-fixed nil))
(enlarge-window 10))
Note that changing the frame size will change the size of a
fixed-size window, if there is no other alternative.
The following two variables constrain the window-size-changing
functions to a minimum height and width.
- User Option: window-min-height
The value of this variable determines how short a window may become
before it is automatically deleted. Making a window smaller than
`window-min-height' automatically deletes it, and no window may be
created shorter than this. The absolute minimum height is two
(allowing one line for the mode line, and one line for the buffer
display). Actions that change window sizes reset this variable to
two if it is less than two. The default value is 4.
- User Option: window-min-width
The value of this variable determines how narrow a window may
become before it is automatically deleted. Making a window
smaller than `window-min-width' automatically deletes it, and no
window may be created narrower than this. The absolute minimum
width is one; any value below that is ignored. The default value
is 10.
Coordinates and Windows
=======================
This section describes how to relate screen coordinates to windows.
- Function: window-at x y &optional frame
This function returns the window containing the specified cursor
position in the frame FRAME. The coordinates X and Y are measured
in characters and count from the top left corner of the frame. If
they are out of range, `window-at' returns `nil'.
If you omit FRAME, the selected frame is used.
- Function: coordinates-in-window-p coordinates window
This function checks whether a particular frame position falls
within the window WINDOW.
The argument COORDINATES is a cons cell of the form `(X . Y)'.
The coordinates X and Y are measured in characters, and count from
the top left corner of the screen or frame.
The value returned by `coordinates-in-window-p' is non-`nil' if
the coordinates are inside WINDOW. The value also indicates what
part of the window the position is in, as follows:
`(RELX . RELY)'
The coordinates are inside WINDOW. The numbers RELX and RELY
are the equivalent window-relative coordinates for the
specified position, counting from 0 at the top left corner of
the window.
`mode-line'
The coordinates are in the mode line of WINDOW.
`header-line'
The coordinates are in the header line of WINDOW.
`vertical-line'
The coordinates are in the vertical line between WINDOW and
its neighbor to the right. This value occurs only if the
window doesn't have a scroll bar; positions in a scroll bar
are considered outside the window for these purposes.
`nil'
The coordinates are not in any part of WINDOW.
The function `coordinates-in-window-p' does not require a frame as
argument because it always uses the frame that WINDOW is on.
Window Configurations
=====================
A "window configuration" records the entire layout of one frame--all
windows, their sizes, which buffers they contain, what part of each
buffer is displayed, and the values of point and the mark. You can
bring back an entire previous layout by restoring a window
configuration previously saved.
If you want to record all frames instead of just one, use a frame
configuration instead of a window configuration. *Note Frame
Configurations::.
- Function: current-window-configuration &optional frame
This function returns a new object representing FRAME's current
window configuration, including the number of windows, their sizes
and current buffers, which window is the selected window, and for
each window the displayed buffer, the display-start position, and
the positions of point and the mark. It also includes the values
of `window-min-height', `window-min-width' and
`minibuffer-scroll-window'. An exception is made for point in the
current buffer, whose value is not saved.
If FRAME is omitted, the selected frame is used.
- Function: set-window-configuration configuration
This function restores the configuration of windows and buffers as
specified by CONFIGURATION, for the frame that CONFIGURATION was
created for.
The argument CONFIGURATION must be a value that was previously
returned by `current-window-configuration'. This configuration is
restored in the frame from which CONFIGURATION was made, whether
that frame is selected or not. This always counts as a window size
change and triggers execution of the `window-size-change-functions'
(*note Window Hooks::), because `set-window-configuration' doesn't
know how to tell whether the new configuration actually differs
from the old one.
If the frame which CONFIGURATION was saved from is dead, all this
function does is restore the three variables `window-min-height',
`window-min-width' and `minibuffer-scroll-window'.
Here is a way of using this function to get the same effect as
`save-window-excursion':
(let ((config (current-window-configuration)))
(unwind-protect
(progn (split-window-vertically nil)
...)
(set-window-configuration config)))
- Special Form: save-window-excursion forms...
This special form records the window configuration, executes FORMS
in sequence, then restores the earlier window configuration. The
window configuration includes the value of point and the portion
of the buffer that is visible. It also includes the choice of
selected window. However, it does not include the value of point
in the current buffer; use `save-excursion' also, if you wish to
preserve that.
Don't use this construct when `save-selected-window' is all you
need.
Exit from `save-window-excursion' always triggers execution of the
`window-size-change-functions'. (It doesn't know how to tell
whether the restored configuration actually differs from the one in
effect at the end of the FORMS.)
The return value is the value of the final form in FORMS. For
example:
(split-window)
=> #<window 25 on control.texi>
(setq w (selected-window))
=> #<window 19 on control.texi>
(save-window-excursion
(delete-other-windows w)
(switch-to-buffer "foo")
'do-something)
=> do-something
;; The screen is now split again.
- Function: window-configuration-p object
This function returns `t' if OBJECT is a window configuration.
- Function: compare-window-configurations config1 config2
This function compares two window configurations as regards the
structure of windows, but ignores the values of point and mark and
the saved scrolling positions--it can return `t' even if those
aspects differ.
The function `equal' can also compare two window configurations; it
regards configurations as unequal if they differ in any respect,
even a saved point or mark.
Primitives to look inside of window configurations would make sense,
but none are implemented. It is not clear they are useful enough to be
worth implementing.
Hooks for Window Scrolling and Changes
======================================
This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run `window-scroll-functions'; the last runs
`window-size-change-functions'. The paradigmatic use of these hooks is
in the implementation of Lazy Lock mode; see *Note Lazy Lock:
(emacs)Support Modes.
- Variable: window-scroll-functions
This variable holds a list of functions that Emacs should call
before redisplaying a window with scrolling. It is not a normal
hook, because each function is called with two arguments: the
window, and its new display-start position.
Displaying a different buffer in the window also runs these
functions.
These functions must be careful in using `window-end' (*note
Window Start::); if you need an up-to-date value, you must use the
UPDATE argument to ensure you get it.
- Variable: window-size-change-functions
This variable holds a list of functions to be called if the size
of any window changes for any reason. The functions are called
just once per redisplay, and just once for each frame on which
size changes have occurred.
Each function receives the frame as its sole argument. There is no
direct way to find out which windows on that frame have changed
size, or precisely how. However, if a size-change function
records, at each call, the existing windows and their sizes, it
can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore
causes these functions to be called. Changing the frame size also
counts, because it changes the sizes of the existing windows.
It is not a good idea to use `save-window-excursion' (*note Window
Configurations::) in these functions, because that always counts
as a size change, and it would cause these functions to be called
over and over. In most cases, `save-selected-window' (*note
Selecting Windows::) is what you need here.
- Variable: redisplay-end-trigger-functions
This abnormal hook is run whenever redisplay in a window uses text
that extends past a specified end trigger position. You set the
end trigger position with the function
`set-window-redisplay-end-trigger'. The functions are called with
two arguments: the window, and the end trigger position. Storing
`nil' for the end trigger position turns off the feature, and the
trigger value is automatically reset to `nil' just after the hook
is run.
- Function: set-window-redisplay-end-trigger window position
This function sets WINDOW's end trigger position at POSITION.
- Function: window-redisplay-end-trigger &optional window
This function returns WINDOW's current end trigger position.
- Variable: window-configuration-change-hook
A normal hook that is run every time you change the window
configuration of an existing frame. This includes splitting or
deleting windows, changing the sizes of windows, or displaying a
different buffer in a window. The frame whose window
configuration has changed is the selected frame when this hook
runs.
Frames
******
A "frame" is a rectangle on the screen that contains one or more
Emacs windows. A frame initially contains a single main window (plus
perhaps a minibuffer window), which you can subdivide vertically or
horizontally into smaller windows.
When Emacs runs on a text-only terminal, it starts with one
"terminal frame". If you create additional ones, Emacs displays one
and only one at any given time--on the terminal screen, of course.
When Emacs communicates directly with a supported window system, such
as X, it does not have a terminal frame; instead, it starts with a
single "window frame", but you can create more, and Emacs can display
several such frames at once as is usual for window systems.
- Function: framep object
This predicate returns a non-`nil' value if OBJECT is a frame, and
`nil' otherwise. For a frame, the value indicates which kind of
display the frame uses:
`x'
The frame is displayed in an X window.
`t'
A terminal frame on a character display.
`mac'
The frame is displayed on a Macintosh.
`w32'
The frame is displayed on MS-Windows 9X/NT.
`pc'
The frame is displayed on an MS-DOS terminal.
*Note Display::, for information about the related topic of
controlling Emacs redisplay.
Creating Frames
===============
To create a new frame, call the function `make-frame'.
- Function: make-frame &optional alist
This function creates a new frame. If you are using a supported
window system, it makes a window frame; otherwise, it makes a
terminal frame.
The argument is an alist specifying frame parameters. Any
parameters not mentioned in ALIST default according to the value
of the variable `default-frame-alist'; parameters not specified
even there default from the standard X resources or whatever is
used instead on your system.
The set of possible parameters depends in principle on what kind of
window system Emacs uses to display its frames. *Note Window
Frame Parameters::, for documentation of individual parameters you
can specify.
- Variable: before-make-frame-hook
A normal hook run by `make-frame' before it actually creates the
frame.
- Variable: after-make-frame-functions
An abnormal hook run by `make-frame' after it creates the frame.
Each function in `after-make-frame-functions' receives one
argument, the frame just created.
Multiple Displays
=================
A single Emacs can talk to more than one X display. Initially,
Emacs uses just one display--the one chosen with the `DISPLAY'
environment variable or with the `--display' option (*note Initial
Options: (emacs)Initial Options.). To connect to another display, use
the command `make-frame-on-display' or specify the `display' frame
parameter when you create the frame.
Emacs treats each X server as a separate terminal, giving each one
its own selected frame and its own minibuffer windows. However, only
one of those frames is "_the_ selected frame" at any given moment, see
*Note Input Focus::.
A few Lisp variables are "terminal-local"; that is, they have a
separate binding for each terminal. The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to. These variables include `default-minibuffer-frame',
`defining-kbd-macro', `last-kbd-macro', and `system-key-alist'. They
are always terminal-local, and can never be buffer-local (*note
Buffer-Local Variables::) or frame-local.
A single X server can handle more than one screen. A display name
`HOST:SERVER.SCREEN' has three parts; the last part specifies the
screen number for a given server. When you use two screens belonging
to one server, Emacs knows by the similarity in their names that they
share a single keyboard, and it treats them as a single terminal.
- Command: make-frame-on-display display &optional parameters
This creates a new frame on display DISPLAY, taking the other
frame parameters from PARAMETERS. Aside from the DISPLAY
argument, it is like `make-frame' (*note Creating Frames::).
- Function: x-display-list
This returns a list that indicates which X displays Emacs has a
connection to. The elements of the list are strings, and each one
is a display name.
- Function: x-open-connection display &optional xrm-string must-succeed
This function opens a connection to the X display DISPLAY. It
does not create a frame on that display, but it permits you to
check that communication can be established with that display.
The optional argument XRM-STRING, if not `nil', is a string of
resource names and values, in the same format used in the
`.Xresources' file. The values you specify override the resource
values recorded in the X server itself; they apply to all Emacs
frames created on this display. Here's an example of what this
string might look like:
"*BorderWidth: 3\n*InternalBorder: 2\n"
*Note Resources::.
If MUST-SUCCEED is non-`nil', failure to open the connection
terminates Emacs. Otherwise, it is an ordinary Lisp error.
- Function: x-close-connection display
This function closes the connection to display DISPLAY. Before
you can do this, you must first delete all the frames that were
open on that display (*note Deleting Frames::).
Frame Parameters
================
A frame has many parameters that control its appearance and behavior.
Just what parameters a frame has depends on what display mechanism it
uses.
Frame parameters exist mostly for the sake of window systems. A
terminal frame has a few parameters, mostly for compatibility's sake;
only the `height', `width', `name', `title', `menu-bar-lines',
`buffer-list' and `buffer-predicate' parameters do something special.
If the terminal supports colors, the parameters `foreground-color',
`background-color', `background-mode' and `display-type' are also
meaningful.
Access to Frame Parameters
--------------------------
These functions let you read and change the parameter values of a
frame.
- Function: frame-parameter frame parameter
This function returns the value of the parameter named PARAMETER
of FRAME. If FRAME is `nil', it returns the selected frame's
parameter.
- Function: frame-parameters frame
The function `frame-parameters' returns an alist listing all the
parameters of FRAME and their values.
- Function: modify-frame-parameters frame alist
This function alters the parameters of frame FRAME based on the
elements of ALIST. Each element of ALIST has the form `(PARM .
VALUE)', where PARM is a symbol naming a parameter. If you don't
mention a parameter in ALIST, its value doesn't change.
Initial Frame Parameters
------------------------
You can specify the parameters for the initial startup frame by
setting `initial-frame-alist' in your init file (*note Init File::).
- Variable: initial-frame-alist
This variable's value is an alist of parameter values used when
creating the initial window frame. You can set this variable to
specify the appearance of the initial frame without altering
subsequent frames. Each element has the form:
(PARAMETER . VALUE)
Emacs creates the initial frame before it reads your init file.
After reading that file, Emacs checks `initial-frame-alist', and
applies the parameter settings in the altered value to the already
created initial frame.
If these settings affect the frame geometry and appearance, you'll
see the frame appear with the wrong ones and then change to the
specified ones. If that bothers you, you can specify the same
geometry and appearance with X resources; those do take effect
before the frame is created. *Note X Resources: (emacs)Resources
X.
X resource settings typically apply to all frames. If you want to
specify some X resources solely for the sake of the initial frame,
and you don't want them to apply to subsequent frames, here's how
to achieve this. Specify parameters in `default-frame-alist' to
override the X resources for subsequent frames; then, to prevent
these from affecting the initial frame, specify the same
parameters in `initial-frame-alist' with values that match the X
resources.
If these parameters specify a separate minibuffer-only frame with
`(minibuffer . nil)', and you have not created one, Emacs creates one
for you.
- Variable: minibuffer-frame-alist
This variable's value is an alist of parameter values used when
creating an initial minibuffer-only frame--if such a frame is
needed, according to the parameters for the main initial frame.
- Variable: default-frame-alist
This is an alist specifying default values of frame parameters for
all Emacs frames--the first frame, and subsequent frames. When
using the X Window System, you can get the same results by means
of X resources in many cases.
See also `special-display-frame-alist', in *Note Choosing Window::.
If you use options that specify window appearance when you invoke
Emacs, they take effect by adding elements to `default-frame-alist'.
One exception is `-geometry', which adds the specified position to
`initial-frame-alist' instead. *Note Command Arguments: (emacs)Command
Arguments.
Window Frame Parameters
-----------------------
Just what parameters a frame has depends on what display mechanism it
uses. Here is a table of the parameters that have special meanings in a
window frame; of these, `name', `title', `height', `width',
`buffer-list' and `buffer-predicate' provide meaningful information in
terminal frames.
`display'
The display on which to open this frame. It should be a string of
the form `"HOST:DPY.SCREEN"', just like the `DISPLAY' environment
variable.
`title'
If a frame has a non-`nil' title, it appears in the window system's
border for the frame, and also in the mode line of windows in that
frame if `mode-line-frame-identification' uses `%F' (*note
%-Constructs::). This is normally the case when Emacs is not
using a window system, and can only display one frame at a time.
*Note Frame Titles::.
`name'
The name of the frame. The frame name serves as a default for the
frame title, if the `title' parameter is unspecified or `nil'. If
you don't specify a name, Emacs sets the frame name automatically
(*note Frame Titles::).
If you specify the frame name explicitly when you create the
frame, the name is also used (instead of the name of the Emacs
executable) when looking up X resources for the frame.
`left'
The screen position of the left edge, in pixels, with respect to
the left edge of the screen. The value may be a positive number
POS, or a list of the form `(+ POS)' which permits specifying a
negative POS value.
A negative number -POS, or a list of the form `(- POS)', actually
specifies the position of the right edge of the window with
respect to the right edge of the screen. A positive value of POS
counts toward the left. *Reminder:* if the parameter is a
negative integer -POS, then POS is positive.
Some window managers ignore program-specified positions. If you
want to be sure the position you specify is not ignored, specify a
non-`nil' value for the `user-position' parameter as well.
`top'
The screen position of the top edge, in pixels, with respect to the
top edge of the screen. The value may be a positive number POS,
or a list of the form `(+ POS)' which permits specifying a
negative POS value.
A negative number -POS, or a list of the form `(- POS)', actually
specifies the position of the bottom edge of the window with
respect to the bottom edge of the screen. A positive value of POS
counts toward the top. *Reminder:* if the parameter is a negative
integer -POS, then POS is positive.
Some window managers ignore program-specified positions. If you
want to be sure the position you specify is not ignored, specify a
non-`nil' value for the `user-position' parameter as well.
`icon-left'
The screen position of the left edge _of the frame's icon_, in
pixels, counting from the left edge of the screen. This takes
effect if and when the frame is iconified.
`icon-top'
The screen position of the top edge _of the frame's icon_, in
pixels, counting from the top edge of the screen. This takes
effect if and when the frame is iconified.
`user-position'
When you create a frame and specify its screen position with the
`left' and `top' parameters, use this parameter to say whether the
specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a
program). A non-`nil' value says the position was user-specified.
Window managers generally heed user-specified positions, and some
heed program-specified positions too. But many ignore
program-specified positions, placing the window in a default
fashion or letting the user place it with the mouse. Some window
managers, including `twm', let the user specify whether to obey
program-specified positions or ignore them.
When you call `make-frame', you should specify a non-`nil' value
for this parameter if the values of the `left' and `top'
parameters represent the user's stated preference; otherwise, use
`nil'.
`height'
The height of the frame contents, in characters. (To get the
height in pixels, call `frame-pixel-height'; see *Note Size and
Position::.)
`width'
The width of the frame contents, in characters. (To get the
height in pixels, call `frame-pixel-width'; see *Note Size and
Position::.)
`window-id'
The number of the window-system window used by the frame to
contain the actual Emacs windows.
`outer-window-id'
The number of the outermost window-system window used for the
whole frame.
`minibuffer'
Whether this frame has its own minibuffer. The value `t' means
yes, `nil' means no, `only' means this frame is just a minibuffer.
If the value is a minibuffer window (in some other frame), the
new frame uses that minibuffer.
`buffer-predicate'
The buffer-predicate function for this frame. The function
`other-buffer' uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
`nil'. It calls the predicate with one argument, a buffer, once
for each buffer; if the predicate returns a non-`nil' value, it
considers that buffer.
`buffer-list'
A list of buffers that have been selected in this frame, ordered
most-recently-selected first.
`font'
The name of the font for displaying text in the frame. This is a
string, either a valid font name for your system or the name of an
Emacs fontset (*note Fontsets::). Changing this frame parameter
on a frame also changes the font-related attributes of the default
face on that frame.
`auto-raise'
Whether selecting the frame raises it (non-`nil' means yes).
`auto-lower'
Whether deselecting the frame lowers it (non-`nil' means yes).
`vertical-scroll-bars'
Whether the frame has scroll bars for vertical scrolling, and
which side of the frame they should be on. The possible values
are `left', `right', and `nil' for no scroll bars.
`horizontal-scroll-bars'
Whether the frame has scroll bars for horizontal scrolling
(non-`nil' means yes). (Horizontal scroll bars are not currently
implemented.)
`scroll-bar-width'
The width of the vertical scroll bar, in pixels.
`icon-type'
The type of icon to use for this frame when it is iconified. If
the value is a string, that specifies a file containing a bitmap
to use. Any other non-`nil' value specifies the default bitmap
icon (a picture of a gnu); `nil' specifies a text icon.
`icon-name'
The name to use in the icon for this frame, when and if the icon
appears. If this is `nil', the frame's title is used.
`foreground-color'
The color to use for the image of a character. This is a string;
the window system defines the meaningful color names. Changing
this parameter is equivalent to changing the foreground color of
the face `default' on the frame in question.
`background-color'
The color to use for the background of characters. Changing this
parameter is equivalent to changing the foreground color of the
face `default' on the frame in question.
`background-mode'
This parameter is either `dark' or `light', according to whether
the background color is a light one or a dark one.
`mouse-color'
The color for the mouse pointer. Changing this parameter is
equivalent to changing the background color of face `mouse'.
`cursor-color'
The color for the cursor that shows point. Changing this parameter
is equivalent to changing the background color of face `cursor'.
`border-color'
The color for the border of the frame. Changing this parameter is
equivalent to changing the background color of face `border'.
`scroll-bar-foreground'
If non-`nil', the color for the foreground of scroll bars.
Changing this parameter is equivalent to setting the foreground
color of face `scroll-bar'.
`scroll-bar-background'
If non-`nil', the color for the background of scroll bars.
Changing this parameter is equivalent to setting the foreground
color of face `scroll-bar'.
`display-type'
This parameter describes the range of possible colors that can be
used in this frame. Its value is `color', `grayscale' or `mono'.
`cursor-type'
The way to display the cursor. The legitimate values are `bar',
`box', and `(bar . WIDTH)'. The symbol `box' specifies an
ordinary black box overlaying the character after point; that is
the default. The symbol `bar' specifies a vertical bar between
characters as the cursor. `(bar . WIDTH)' specifies a bar WIDTH
pixels wide.
The buffer-local variable `cursor-type' overrides the value of the
`cursor-type' frame parameter, and can in addition have values `t'
(use the cursor specified for the frame) and `nil' (don't display
a cursor).
`border-width'
The width in pixels of the window border.
`internal-border-width'
The distance in pixels between text and border.
`unsplittable'
If non-`nil', this frame's window is never split automatically.
`visibility'
The state of visibility of the frame. There are three
possibilities: `nil' for invisible, `t' for visible, and `icon' for
iconified. *Note Visibility of Frames::.
`menu-bar-lines'
The number of lines to allocate at the top of the frame for a menu
bar. The default is 1. *Note Menu Bar::. (In Emacs versions
that use the X toolkit, there is only one menu bar line; all that
matters about the number you specify is whether it is greater than
zero.)
`screen-gamma'
If this is a number, Emacs performs "gamma correction" on colors.
The value should be the screen gamma of your display, a floating
point number. Usual PC monitors have a screen gamma of 2.2, so
the default is to display for that gamma value. Specifying a
smaller value results in darker colors, which is desirable for a
monitor that tends to display colors too light. A screen gamma
value of 1.5 may give good results for LCD color displays.
`tool-bar-lines'
The number of lines to use for the toolbar. A value of `nil' means
don't display a tool bar.
`line-spacing'
Additional space put below text lines in pixels (a positive
integer).
Frame Size And Position
-----------------------
You can read or change the size and position of a frame using the
frame parameters `left', `top', `height', and `width'. Whatever
geometry parameters you don't specify are chosen by the window manager
in its usual fashion.
Here are some special features for working with sizes and positions.
(For the precise meaning of "selected frame" used by these functions,
see *Note Input Focus::.)
- Function: set-frame-position frame left top
This function sets the position of the top left corner of FRAME to
LEFT and TOP. These arguments are measured in pixels, and
normally count from the top left corner of the screen.
Negative parameter values position the bottom edge of the window
up from the bottom edge of the screen, or the right window edge to
the left of the right edge of the screen. It would probably be
better if the values were always counted from the left and top, so
that negative arguments would position the frame partly off the
top or left edge of the screen, but it seems inadvisable to change
that now.
- Function: frame-height &optional frame
- Function: frame-width &optional frame
These functions return the height and width of FRAME, measured in
lines and columns. If you don't supply FRAME, they use the
selected frame.
- Function: screen-height
- Function: screen-width
These functions are old aliases for `frame-height' and
`frame-width'. When you are using a non-window terminal, the size
of the frame is normally the same as the size of the terminal
screen.
- Function: frame-pixel-height &optional frame
- Function: frame-pixel-width &optional frame
These functions return the height and width of FRAME, measured in
pixels. If you don't supply FRAME, they use the selected frame.
- Function: frame-char-height &optional frame
- Function: frame-char-width &optional frame
These functions return the height and width of a character in
FRAME, measured in pixels. The values depend on the choice of
font. If you don't supply FRAME, these functions use the selected
frame.
- Function: set-frame-size frame cols rows
This function sets the size of FRAME, measured in characters; COLS
and ROWS specify the new width and height.
To set the size based on values measured in pixels, use
`frame-char-height' and `frame-char-width' to convert them to
units of characters.
- Function: set-frame-height frame lines &optional pretend
This function resizes FRAME to a height of LINES lines. The sizes
of existing windows in FRAME are altered proportionally to fit.
If PRETEND is non-`nil', then Emacs displays LINES lines of output
in FRAME, but does not change its value for the actual height of
the frame. This is only useful for a terminal frame. Using a
smaller height than the terminal actually implements may be useful
to reproduce behavior observed on a smaller screen, or if the
terminal malfunctions when using its whole screen. Setting the
frame height "for real" does not always work, because knowing the
correct actual size may be necessary for correct cursor
positioning on a terminal frame.
- Function: set-frame-width frame width &optional pretend
This function sets the width of FRAME, measured in characters.
The argument PRETEND has the same meaning as in `set-frame-height'.
The older functions `set-screen-height' and `set-screen-width' were
used to specify the height and width of the screen, in Emacs versions
that did not support multiple frames. They are semi-obsolete, but
still work; they apply to the selected frame.
- Function: x-parse-geometry geom
The function `x-parse-geometry' converts a standard X window
geometry string to an alist that you can use as part of the
argument to `make-frame'.
The alist describes which parameters were specified in GEOM, and
gives the values specified for them. Each element looks like
`(PARAMETER . VALUE)'. The possible PARAMETER values are `left',
`top', `width', and `height'.
For the size parameters, the value must be an integer. The
position parameter names `left' and `top' are not totally accurate,
because some values indicate the position of the right or bottom
edges instead. These are the VALUE possibilities for the position
parameters:
an integer
A positive integer relates the left edge or top edge of the
window to the left or top edge of the screen. A negative
integer relates the right or bottom edge of the window to the
right or bottom edge of the screen.
`(+ POSITION)'
This specifies the position of the left or top edge of the
window relative to the left or top edge of the screen. The
integer POSITION may be positive or negative; a negative
value specifies a position outside the screen.
`(- POSITION)'
This specifies the position of the right or bottom edge of
the window relative to the right or bottom edge of the
screen. The integer POSITION may be positive or negative; a
negative value specifies a position outside the screen.
Here is an example:
(x-parse-geometry "35x70+0-0")
=> ((height . 70) (width . 35)
(top - 0) (left . 0))
Frame Titles
============
Every frame has a `name' parameter; this serves as the default for
the frame title which window systems typically display at the top of
the frame. You can specify a name explicitly by setting the `name'
frame property.
Normally you don't specify the name explicitly, and Emacs computes
the frame name automatically based on a template stored in the variable
`frame-title-format'. Emacs recomputes the name each time the frame is
redisplayed.
- Variable: frame-title-format
This variable specifies how to compute a name for a frame when you
have not explicitly specified one. The variable's value is
actually a mode line construct, just like `mode-line-format'.
*Note Mode Line Data::.
- Variable: icon-title-format
This variable specifies how to compute the name for an iconified
frame, when you have not explicitly specified the frame title.
This title appears in the icon itself.
- Variable: multiple-frames
This variable is set automatically by Emacs. Its value is `t' when
there are two or more frames (not counting minibuffer-only frames
or invisible frames). The default value of `frame-title-format'
uses `multiple-frames' so as to put the buffer name in the frame
title only when there is more than one frame.
Deleting Frames
===============
Frames remain potentially visible until you explicitly "delete"
them. A deleted frame cannot appear on the screen, but continues to
exist as a Lisp object until there are no references to it. There is no
way to cancel the deletion of a frame aside from restoring a saved frame
configuration (*note Frame Configurations::); this is similar to the
way windows behave.
- Command: delete-frame &optional frame force
This function deletes the frame FRAME after running the hook
`delete-frame-hook'. By default, FRAME is the selected frame.
A frame cannot be deleted if its minibuffer is used by other
frames. Normally, you cannot delete a frame if all other frames
are invisible, but if the FORCE is non-`nil', then you are allowed
to do so.
- Function: frame-live-p frame
The function `frame-live-p' returns non-`nil' if the frame FRAME
has not been deleted.
Some window managers provide a command to delete a window. These
work by sending a special message to the program that operates the
window. When Emacs gets one of these commands, it generates a
`delete-frame' event, whose normal definition is a command that calls
the function `delete-frame'. *Note Misc Events::.
Finding All Frames
==================
- Function: frame-list
The function `frame-list' returns a list of all the frames that
have not been deleted. It is analogous to `buffer-list' for
buffers, and includes frames on all terminals. The list that you
get is newly created, so modifying the list doesn't have any
effect on the internals of Emacs.
- Function: visible-frame-list
This function returns a list of just the currently visible frames.
*Note Visibility of Frames::. (Terminal frames always count as
"visible", even though only the selected one is actually
displayed.)
- Function: next-frame &optional frame minibuf
The function `next-frame' lets you cycle conveniently through all
the frames on the current display from an arbitrary starting
point. It returns the "next" frame after FRAME in the cycle. If
FRAME is omitted or `nil', it defaults to the selected frame
(*note Input Focus::).
The second argument, MINIBUF, says which frames to consider:
`nil'
Exclude minibuffer-only frames.
`visible'
Consider all visible frames.
0
Consider all visible or iconified frames.
a window
Consider only the frames using that particular window as their
minibuffer.
anything else
Consider all frames.
- Function: previous-frame &optional frame minibuf
Like `next-frame', but cycles through all frames in the opposite
direction.
See also `next-window' and `previous-window', in *Note Cyclic Window
Ordering::.
Frames and Windows
==================
Each window is part of one and only one frame; you can get the frame
with `window-frame'.
- Function: window-frame window
This function returns the frame that WINDOW is on.
All the non-minibuffer windows in a frame are arranged in a cyclic
order. The order runs from the frame's top window, which is at the
upper left corner, down and to the right, until it reaches the window at
the lower right corner (always the minibuffer window, if the frame has
one), and then it moves back to the top. *Note Cyclic Window
Ordering::.
- Function: frame-first-window frame
This returns the topmost, leftmost window of frame FRAME.
At any time, exactly one window on any frame is "selected within the
frame". The significance of this designation is that selecting the
frame also selects this window. You can get the frame's current
selected window with `frame-selected-window'.
- Function: frame-selected-window frame
This function returns the window on FRAME that is selected within
FRAME.
Conversely, selecting a window for Emacs with `select-window' also
makes that window selected within its frame. *Note Selecting Windows::.
Another function that (usually) returns one of the windows in a given
frame is `minibuffer-window'. *Note Minibuffer Misc::.
Minibuffers and Frames
======================
Normally, each frame has its own minibuffer window at the bottom,
which is used whenever that frame is selected. If the frame has a
minibuffer, you can get it with `minibuffer-window' (*note Minibuffer
Misc::).
However, you can also create a frame with no minibuffer. Such a
frame must use the minibuffer window of some other frame. When you
create the frame, you can specify explicitly the minibuffer window to
use (in some other frame). If you don't, then the minibuffer is found
in the frame which is the value of the variable
`default-minibuffer-frame'. Its value should be a frame that does have
a minibuffer.
If you use a minibuffer-only frame, you might want that frame to
raise when you enter the minibuffer. If so, set the variable
`minibuffer-auto-raise' to `t'. *Note Raising and Lowering::.
- Variable: default-minibuffer-frame
This variable specifies the frame to use for the minibuffer
window, by default. It is always local to the current terminal
and cannot be buffer-local. *Note Multiple Displays::.
Input Focus
===========
At any time, one frame in Emacs is the "selected frame". The
selected window always resides on the selected frame.
When Emacs displays its frames on several terminals (*note Multiple
Displays::), each terminal has its own selected frame. But only one of
these is "_the_ selected frame": it's the frame that belongs to the
terminal from which the most recent input came. That is, when Emacs
runs a command that came from a certain terminal, the selected frame is
the one of that terminal. Since Emacs runs only a single command at any
given time, it needs to consider only one selected frame at a time; this
frame is what we call "the selected frame" in this manual. The display
on which the selected frame is displayed is the "selected frame's
display".
- Function: selected-frame
This function returns the selected frame.
Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to "shift the focus" to various window objects. Either way,
Emacs automatically keeps track of which frame has the focus.
Lisp programs can also switch frames "temporarily" by calling the
function `select-frame'. This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.
When using a text-only terminal, only the selected terminal frame is
actually displayed on the terminal. `switch-frame' is the only way to
switch frames, and the change lasts until overridden by a subsequent
call to `switch-frame'. Each terminal screen except for the initial
one has a number, and the number of the selected frame appears in the
mode line before the buffer name (*note Mode Line Variables::).
- Function: select-frame frame
This function selects frame FRAME, temporarily disregarding the
focus of the X server if any. The selection of FRAME lasts until
the next time the user does something to select a different frame,
or until the next time this function is called. The specified
FRAME becomes the selected frame, as explained above, and the
terminal that FRAME is on becomes the selected terminal.
In general, you should never use `select-frame' in a way that could
switch to a different terminal without switching back when you're
done.
Emacs cooperates with the window system by arranging to select
frames as the server and window manager request. It does so by
generating a special kind of input event, called a "focus" event, when
appropriate. The command loop handles a focus event by calling
`handle-switch-frame'. *Note Focus Events::.
- Command: handle-switch-frame frame
This function handles a focus event by selecting frame FRAME.
Focus events normally do their job by invoking this command.
Don't call it for any other reason.
- Function: redirect-frame-focus frame focus-frame
This function redirects focus from FRAME to FOCUS-FRAME. This
means that FOCUS-FRAME will receive subsequent keystrokes and
events intended for FRAME. After such an event, the value of
`last-event-frame' will be FOCUS-FRAME. Also, switch-frame events
specifying FRAME will instead select FOCUS-FRAME.
If FOCUS-FRAME is `nil', that cancels any existing redirection for
FRAME, which therefore once again receives its own events.
One use of focus redirection is for frames that don't have
minibuffers. These frames use minibuffers on other frames.
Activating a minibuffer on another frame redirects focus to that
frame. This puts the focus on the minibuffer's frame, where it
belongs, even though the mouse remains in the frame that activated
the minibuffer.
Selecting a frame can also change focus redirections. Selecting
frame `bar', when `foo' had been selected, changes any redirections
pointing to `foo' so that they point to `bar' instead. This
allows focus redirection to work properly when the user switches
from one frame to another using `select-window'.
This means that a frame whose focus is redirected to itself is
treated differently from a frame whose focus is not redirected.
`select-frame' affects the former but not the latter.
The redirection lasts until `redirect-frame-focus' is called to
change it.
- User Option: focus-follows-mouse
This option is how you inform Emacs whether the window manager
transfers focus when the user moves the mouse. Non-`nil' says
that it does. When this is so, the command `other-frame' moves
the mouse to a position consistent with the new selected frame.
Visibility of Frames
====================
A window frame may be "visible", "invisible", or "iconified". If it
is visible, you can see its contents. If it is iconified, the frame's
contents do not appear on the screen, but an icon does. If the frame
is invisible, it doesn't show on the screen, not even as an icon.
Visibility is meaningless for terminal frames, since only the
selected one is actually displayed in any case.
- Command: make-frame-visible &optional frame
This function makes frame FRAME visible. If you omit FRAME, it
makes the selected frame visible.
- Command: make-frame-invisible &optional frame
This function makes frame FRAME invisible. If you omit FRAME, it
makes the selected frame invisible.
- Command: iconify-frame &optional frame
This function iconifies frame FRAME. If you omit FRAME, it
iconifies the selected frame.
- Function: frame-visible-p frame
This returns the visibility status of frame FRAME. The value is
`t' if FRAME is visible, `nil' if it is invisible, and `icon' if
it is iconified.
The visibility status of a frame is also available as a frame
parameter. You can read or change it as such. *Note Window Frame
Parameters::.
The user can iconify and deiconify frames with the window manager.
This happens below the level at which Emacs can exert any control, but
Emacs does provide events that you can use to keep track of such
changes. *Note Misc Events::.
Raising and Lowering Frames
===========================
Most window systems use a desktop metaphor. Part of this metaphor is
the idea that windows are stacked in a notional third dimension
perpendicular to the screen surface, and thus ordered from "highest" to
"lowest". Where two windows overlap, the one higher up covers the one
underneath. Even a window at the bottom of the stack can be seen if no
other window overlaps it.
A window's place in this ordering is not fixed; in fact, users tend
to change the order frequently. "Raising" a window means moving it
"up", to the top of the stack. "Lowering" a window means moving it to
the bottom of the stack. This motion is in the notional third
dimension only, and does not change the position of the window on the
screen.
You can raise and lower Emacs frame Windows with these functions:
- Command: raise-frame &optional frame
This function raises frame FRAME (default, the selected frame).
- Command: lower-frame &optional frame
This function lowers frame FRAME (default, the selected frame).
- User Option: minibuffer-auto-raise
If this is non-`nil', activation of the minibuffer raises the frame
that the minibuffer window is in.
You can also enable auto-raise (raising automatically when a frame is
selected) or auto-lower (lowering automatically when it is deselected)
for any frame using frame parameters. *Note Window Frame Parameters::.
Frame Configurations
====================
A "frame configuration" records the current arrangement of frames,
all their properties, and the window configuration of each one. (*Note
Window Configurations::.)
- Function: current-frame-configuration
This function returns a frame configuration list that describes
the current arrangement of frames and their contents.
- Function: set-frame-configuration configuration &optional nodelete
This function restores the state of frames described in
CONFIGURATION.
Ordinarily, this function deletes all existing frames not listed in
CONFIGURATION. But if NODELETE is non-`nil', the unwanted frames
are iconified instead.
Mouse Tracking
==============
Sometimes it is useful to "track" the mouse, which means to display
something to indicate where the mouse is and move the indicator as the
mouse moves. For efficient mouse tracking, you need a way to wait until
the mouse actually moves.
The convenient way to track the mouse is to ask for events to
represent mouse motion. Then you can wait for motion by waiting for an
event. In addition, you can easily handle any other sorts of events
that may occur. That is useful, because normally you don't want to
track the mouse forever--only until some other event, such as the
release of a button.
- Special Form: track-mouse body...
This special form executes BODY, with generation of mouse motion
events enabled. Typically BODY would use `read-event' to read the
motion events and modify the display accordingly. *Note Motion
Events::, for the format of mouse motion events.
The value of `track-mouse' is that of the last form in BODY. You
should design BODY to return when it sees the up-event that
indicates the release of the button, or whatever kind of event
means it is time to stop tracking.
The usual purpose of tracking mouse motion is to indicate on the
screen the consequences of pushing or releasing a button at the current
position.
In many cases, you can avoid the need to track the mouse by using
the `mouse-face' text property (*note Special Properties::). That
works at a much lower level and runs more smoothly than Lisp-level
mouse tracking.
Mouse Position
==============
The functions `mouse-position' and `set-mouse-position' give access
to the current position of the mouse.
- Function: mouse-position
This function returns a description of the position of the mouse.
The value looks like `(FRAME X . Y)', where X and Y are integers
giving the position in characters relative to the top left corner
of the inside of FRAME.
- Variable: mouse-position-function
If non-`nil', the value of this variable is a function for
`mouse-position' to call. `mouse-position' calls this function
just before returning, with its normal return value as the sole
argument, and it returns whatever this function returns to it.
This abnormal hook exists for the benefit of packages like
`xt-mouse.el' that need to do mouse handling at the Lisp level.
- Function: set-mouse-position frame x y
This function "warps the mouse" to position X, Y in frame FRAME.
The arguments X and Y are integers, giving the position in
characters relative to the top left corner of the inside of FRAME.
If FRAME is not visible, this function does nothing. The return
value is not significant.
- Function: mouse-pixel-position
This function is like `mouse-position' except that it returns
coordinates in units of pixels rather than units of characters.
- Function: set-mouse-pixel-position frame x y
This function warps the mouse like `set-mouse-position' except that
X and Y are in units of pixels rather than units of characters.
These coordinates are not required to be within the frame.
If FRAME is not visible, this function does nothing. The return
value is not significant.
Pop-Up Menus
============
When using a window system, a Lisp program can pop up a menu so that
the user can choose an alternative with the mouse.
- Function: x-popup-menu position menu
This function displays a pop-up menu and returns an indication of
what selection the user makes.
The argument POSITION specifies where on the screen to put the
menu. It can be either a mouse button event (which says to put
the menu where the user actuated the button) or a list of this
form:
((XOFFSET YOFFSET) WINDOW)
where XOFFSET and YOFFSET are coordinates, measured in pixels,
counting from the top left corner of WINDOW's frame.
If POSITION is `t', it means to use the current mouse position.
If POSITION is `nil', it means to precompute the key binding
equivalents for the keymaps specified in MENU, without actually
displaying or popping up the menu.
The argument MENU says what to display in the menu. It can be a
keymap or a list of keymaps (*note Menu Keymaps::).
Alternatively, it can have the following form:
(TITLE PANE1 PANE2...)
where each pane is a list of form
(TITLE (LINE . ITEM)...)
Each LINE should be a string, and each ITEM should be the value to
return if that LINE is chosen.
*Usage note:* Don't use `x-popup-menu' to display a menu if you
could do the job with a prefix key defined with a menu keymap. If you
use a menu keymap to implement a menu, `C-h c' and `C-h a' can see the
individual items in that menu and provide help for them. If instead
you implement the menu by defining a command that calls `x-popup-menu',
the help facilities cannot know what happens inside that command, so
they cannot give any help for the menu's items.
The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls `x-popup-menu'. Therefore, if you try to implement a
submenu using `x-popup-menu', it cannot work with the menu bar in an
integrated fashion. This is why all menu bar submenus are implemented
with menu keymaps within the parent menu, and never with
`x-popup-menu'. *Note Menu Bar::,
If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it. To make the contents vary, add
a hook function to `menu-bar-update-hook' to update the contents of the
menu keymap as necessary.
Dialog Boxes
============
A dialog box is a variant of a pop-up menu--it looks a little
different, it always appears in the center of a frame, and it has just
one level and one pane. The main use of dialog boxes is for asking
questions that the user can answer with "yes", "no", and a few other
alternatives. The functions `y-or-n-p' and `yes-or-no-p' use dialog
boxes instead of the keyboard, when called from commands invoked by
mouse clicks.
- Function: x-popup-dialog position contents
This function displays a pop-up dialog box and returns an
indication of what selection the user makes. The argument
CONTENTS specifies the alternatives to offer; it has this format:
(TITLE (STRING . VALUE)...)
which looks like the list that specifies a single pane for
`x-popup-menu'.
The return value is VALUE from the chosen alternative.
An element of the list may be just a string instead of a cons cell
`(STRING . VALUE)'. That makes a box that cannot be selected.
If `nil' appears in the list, it separates the left-hand items from
the right-hand items; items that precede the `nil' appear on the
left, and items that follow the `nil' appear on the right. If you
don't include a `nil' in the list, then approximately half the
items appear on each side.
Dialog boxes always appear in the center of a frame; the argument
POSITION specifies which frame. The possible values are as in
`x-popup-menu', but the precise coordinates don't matter; only the
frame matters.
In some configurations, Emacs cannot display a real dialog box; so
instead it displays the same items in a pop-up menu in the center
of the frame.
Pointer Shapes
==============
These variables specify which shape to use for the mouse pointer in
various situations, when using the X Window System:
`x-pointer-shape'
This variable specifies the pointer shape to use ordinarily in the
Emacs frame.
`x-sensitive-text-pointer-shape'
This variable specifies the pointer shape to use when the mouse is
over mouse-sensitive text.
These variables affect newly created frames. They do not normally
affect existing frames; however, if you set the mouse color of a frame,
that also updates its pointer shapes based on the current values of
these variables. *Note Window Frame Parameters::.
The values you can use, to specify either of these pointer shapes,
are defined in the file `lisp/term/x-win.el'. Use `M-x apropos <RET>
x-pointer <RET>' to see a list of them.
Window System Selections
========================
The X server records a set of "selections" which permit transfer of
data between application programs. The various selections are
distinguished by "selection types", represented in Emacs by symbols. X
clients including Emacs can read or set the selection for any given
type.
- Function: x-set-selection type data
This function sets a "selection" in the X server. It takes two
arguments: a selection type TYPE, and the value to assign to it,
DATA. If DATA is `nil', it means to clear out the selection.
Otherwise, DATA may be a string, a symbol, an integer (or a cons
of two integers or list of two integers), an overlay, or a cons of
two markers pointing to the same buffer. An overlay or a pair of
markers stands for text in the overlay or between the markers.
The argument DATA may also be a vector of valid non-vector
selection values.
Each possible TYPE has its own selection value, which changes
independently. The usual values of TYPE are `PRIMARY' and
`SECONDARY'; these are symbols with upper-case names, in accord
with X Window System conventions. The default is `PRIMARY'.
- Function: x-get-selection &optional type data-type
This function accesses selections set up by Emacs or by other X
clients. It takes two optional arguments, TYPE and DATA-TYPE.
The default for TYPE, the selection type, is `PRIMARY'.
The DATA-TYPE argument specifies the form of data conversion to
use, to convert the raw data obtained from another X client into
Lisp data. Meaningful values include `TEXT', `STRING', `TARGETS',
`LENGTH', `DELETE', `FILE_NAME', `CHARACTER_POSITION',
`LINE_NUMBER', `COLUMN_NUMBER', `OWNER_OS', `HOST_NAME', `USER',
`CLASS', `NAME', `ATOM', and `INTEGER'. (These are symbols with
upper-case names in accord with X conventions.) The default for
DATA-TYPE is `STRING'.
The X server also has a set of numbered "cut buffers" which can
store text or other data being moved between applications. Cut buffers
are considered obsolete, but Emacs supports them for the sake of X
clients that still use them.
- Function: x-get-cut-buffer n
This function returns the contents of cut buffer number N.
- Function: x-set-cut-buffer string &optional push
This function stores STRING into the first cut buffer (cut buffer
0). If PUSH is `nil', only the first cut buffer is changed. If
PUSH is non-`nil', that says to move the values down through the
series of cut buffers, much like the way successive kills in Emacs
move down the kill ring. In other words, the previous value of
the first cut buffer moves into the second cut buffer, and the
second to the third, and so on through all eight cut buffers.
- Variable: selection-coding-system
This variable specifies the coding system to use when reading and
writing selections, the clipboard, or a cut buffer. *Note Coding
Systems::. The default is `compound-text', which converts to the
text representation that X11 normally uses.
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard. `x-get-selection' and
`x-set-selection' on MS-Windows support the text data type only; if the
clipboard holds other types of data, Emacs treats the clipboard as
empty.
- User Option: x-select-enable-clipboard
If this is non-`nil', the Emacs yank functions consult the
clipboard before the primary selection, and the kill functions
store in the clipboard as well as the primary selection.
Otherwise they do not access the clipboard at all. The default is
`nil' on most systems, but `t' on MS-Windows.
Color Names
===========
These functions provide a way to determine which color names are
valid, and what they look like. In some cases, the value depends on the
"selected frame", as described below; see *Note Input Focus::, for the
meaning of the term "selected frame".
- Function: color-defined-p color &optional frame
This function reports whether a color name is meaningful. It
returns `t' if so; otherwise, `nil'. The argument FRAME says
which frame's display to ask about; if FRAME is omitted or `nil',
the selected frame is used.
Note that this does not tell you whether the display you are using
really supports that color. When using X, you can ask for any
defined color on any kind of display, and you will get some
result--typically, the closest it can do. To determine whether a
frame can really display a certain color, use `color-supported-p'
(see below).
This function used to be called `x-color-defined-p', and that name
is still supported as an alias.
- Function: defined-colors &optional frame
This function returns a list of the color names that are defined
and supported on frame FRAME (default, the selected frame).
This function used to be called `x-defined-colors', and that name
is still supported as an alias.
- Function: color-supported-p color &optional frame background-p
This returns `t' if FRAME can really display the color COLOR (or
at least something close to it). If FRAME is omitted or `nil',
the question applies to the selected frame.
Some terminals support a different set of colors for foreground and
background. If BACKGROUND-P is non-`nil', that means you are
asking whether COLOR can be used as a background; otherwise you
are asking whether it can be used as a foreground.
The argument COLOR must be a valid color name.
- Function: color-gray-p color &optional frame
This returns `t' if COLOR is a shade of gray, as defined on
FRAME's display. If FRAME is omitted or `nil', the question
applies to the selected frame. The argument COLOR must be a valid
color name.
- Function: color-values color &optional frame
This function returns a value that describes what COLOR should
ideally look like. If COLOR is defined, the value is a list of
three integers, which give the amount of red, the amount of green,
and the amount of blue. Each integer ranges in principle from 0
to 65535, but in practice no value seems to be above 65280. This
kind of three-element list is called an "rgb value".
If COLOR is not defined, the value is `nil'.
(color-values "black")
=> (0 0 0)
(color-values "white")
=> (65280 65280 65280)
(color-values "red")
=> (65280 0 0)
(color-values "pink")
=> (65280 49152 51968)
(color-values "hungry")
=> nil
The color values are returned for FRAME's display. If FRAME is
omitted or `nil', the information is returned for the selected
frame's display.
This function used to be called `x-color-values', and that name is
still supported as an alias.
Text Terminal Colors
====================
Emacs can display color on text-only terminals, starting with version
21. These terminals support only a small number of colors, and the
computer uses small integers to select colors on the terminal. This
means that the computer cannot reliably tell what the selected color
looks like; instead, you have to inform your application which small
integers correspond to which colors. However, Emacs does know the
standard set of colors and will try to use them automatically.
Several of these functions use or return "rgb values". An rgb value
is a list of three integers, which give the amount of red, the amount
of green, and the amount of blue. Each integer ranges in principle
from 0 to 65535, but in practice the largest value used is 65280.
These functions accept a display (either a frame or the name of a
terminal) as an optional argument. We hope in the future to make Emacs
support more than one text-only terminal at one time; then this argument
will specify which terminal to operate on (the default being the
selected frame's terminal; *note Input Focus::). At present, though,
the DISPLAY argument has no effect.
- Function: tty-color-define name number &optional rgb display
This function associates the color name NAME with color number
NUMBER on the terminal.
The optional argument RGB, if specified, is an rgb value; it says
what the color actually looks like. If you do not specify RGB,
then this color cannot be used by `tty-color-approximate' to
approximate other colors, because Emacs does not know what it looks
like.
- Function: tty-color-clear &optional display
This function clears the table of defined colors for a text-only
terminal.
- Function: tty-color-alist &optional display
This function returns an alist recording the known colors
supported by a text-only terminal.
Each element has the form `(NAME NUMBER . RGB)' or `(NAME
NUMBER)'. Here, NAME is the color name, NUMBER is the number used
to specify it to the terminal. If present, RGB is an rgb value
that says what the color actually looks like.
- Function: tty-color-approximate rgb &optional display
This function finds the closest color, among the known colors
supported for DISPLAY, to that described by the rgb value RGB.
- Function: tty-color-translate color &optional display
This function finds the closest color to COLOR among the known
colors supported for DISPLAY. If the name COLOR is not defined,
the value is `nil'.
COLOR can be an X-style `"#XXXYYYZZZ"' specification instead of an
actual name. The format `"RGB:XX/YY/ZZ"' is also supported.
X Resources
===========
- Function: x-get-resource attribute class &optional component subclass
The function `x-get-resource' retrieves a resource value from the X
Windows defaults database.
Resources are indexed by a combination of a "key" and a "class".
This function searches using a key of the form
`INSTANCE.ATTRIBUTE' (where INSTANCE is the name under which Emacs
was invoked), and using `Emacs.CLASS' as the class.
The optional arguments COMPONENT and SUBCLASS add to the key and
the class, respectively. You must specify both of them or neither.
If you specify them, the key is `INSTANCE.COMPONENT.ATTRIBUTE',
and the class is `Emacs.CLASS.SUBCLASS'.
- Variable: x-resource-class
This variable specifies the application name that `x-get-resource'
should look up. The default value is `"Emacs"'. You can examine X
resources for application names other than "Emacs" by binding this
variable to some other string, around a call to `x-get-resource'.
*Note X Resources: (emacs)Resources X.
Display Feature Testing
=======================
The functions in this section describe the basic capabilities of a
particular display. Lisp programs can use them to adapt their behavior
to what the display can do. For example, a program that ordinarly uses
a popup menu could use the minibuffer if popup menus are not supported.
The optional argument DISPLAY in these functions specifies which
display to ask the question about. It can be a display name, a frame
(which designates the display that frame is on), or `nil' (which refers
to the selected frame's display, *note Input Focus::).
*Note Color Names::, *Note Text Terminal Colors::, for other
functions to obtain information about displays.
- Function: display-popup-menus-p &optional display
This function returns `t' if popup menus are supported on DISPLAY,
`nil' if not. Support for popup menus requires that the mouse be
available, since the user cannot choose menu items without a mouse.
- Function: display-graphic-p &optional display
This function returns `t' if DISPLAY is a graphic display capable
of displaying several frames and several different fonts at once.
This is true for displays that use a window system such as X, and
false for text-only terminals.
- Function: display-mouse-p &optional display
This function returns `t' if DISPLAY has a mouse available, `nil'
if not.
- Function: display-color-p &optional display
This function returns `t' if the screen is a color screen. It
used to be called `x-display-color-p', and that name is still
supported as an alias.
- Function: display-grayscale-p &optional display
This function returns `t' if the screen can display shades of gray.
(All color displays can do this.)
- Function: display-selections-p &optional display
This function returns `t' if DISPLAY supports selections.
Windowed displays normally support selections, but they may also be
supported in some other cases.
- Function: display-images-p &optional display
This function returns `t' if DISPLAY can display images. Windowed
displays ought in principle to handle images, but some systems
lack the support for that. On a display that does not support
images, Emacs cannot display a tool bar.
- Function: display-screens &optional display
This function returns the number of screens associated with the
display.
- Function: display-pixel-height &optional display
This function returns the height of the screen in pixels.
- Function: display-mm-height &optional display
This function returns the height of the screen in millimeters, or
`nil' if Emacs cannot get that information.
- Function: display-pixel-width &optional display
This function returns the width of the screen in pixels.
- Function: display-mm-width &optional display
This function returns the width of the screen in millimeters, or
`nil' if Emacs cannot get that information.
- Function: display-backing-store &optional display
This function returns the backing store capability of the display.
Backing store means recording the pixels of windows (and parts of
windows) that are not exposed, so that when exposed they can be
displayed very quickly.
Values can be the symbols `always', `when-mapped', or
`not-useful'. The function can also return `nil' when the
question is inapplicable to a certain kind of display.
- Function: display-save-under &optional display
This function returns non-`nil' if the display supports the
SaveUnder feature. That feature is used by pop-up windows to save
the pixels they obscure, so that they can pop down quickly.
- Function: display-planes &optional display
This function returns the number of planes the display supports.
This is typically the number of bits per pixel. For a tty
display, it is log to base two of the number of colours supported.
- Function: display-visual-class &optional display
This function returns the visual class for the screen. The value
is one of the symbols `static-gray', `gray-scale', `static-color',
`pseudo-color', `true-color', and `direct-color'.
- Function: display-color-cells &optional display
This function returns the number of color cells the screen
supports.
These functions obtain additional information specifically about X
displays.
- Function: x-server-version &optional display
This function returns the list of version numbers of the X server
running the display.
- Function: x-server-vendor &optional display
This function returns the vendor that provided the X server
software.
Positions
*********
A "position" is the index of a character in the text of a buffer.
More precisely, a position identifies the place between two characters
(or before the first character, or after the last character), so we can
speak of the character before or after a given position. However, we
often speak of the character "at" a position, meaning the character
after that position.
Positions are usually represented as integers starting from 1, but
can also be represented as "markers"--special objects that relocate
automatically when text is inserted or deleted so they stay with the
surrounding characters. *Note Markers::.
See also the "field" feature (*note Fields::), which provides
functions that are used by many cursur-motion commands.
Point
=====
"Point" is a special buffer position used by many editing commands,
including the self-inserting typed characters and text insertion
functions. Other commands move point through the text to allow editing
and insertion at different places.
Like other positions, point designates a place between two characters
(or before the first character, or after the last character), rather
than a particular character. Usually terminals display the cursor over
the character that immediately follows point; point is actually before
the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than
the buffer size plus 1. If narrowing is in effect (*note Narrowing::),
then point is constrained to fall within the accessible portion of the
buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the
value of point in other buffers. Each window also has a value of point,
which is independent of the value of point in other windows on the same
buffer. This is why point can have different values in various windows
that display the same buffer. When a buffer appears in only one window,
the buffer's point and the window's point normally have the same value,
so the distinction is rarely important. *Note Window Point::, for more
details.
- Function: point
This function returns the value of point in the current buffer, as
an integer.
(point)
=> 175
- Function: point-min
This function returns the minimum accessible value of point in the
current buffer. This is normally 1, but if narrowing is in
effect, it is the position of the start of the region that you
narrowed to. (*Note Narrowing::.)
- Function: point-max
This function returns the maximum accessible value of point in the
current buffer. This is `(1+ (buffer-size))', unless narrowing is
in effect, in which case it is the position of the end of the
region that you narrowed to. (*Note Narrowing::.)
- Function: buffer-end flag
This function returns `(point-min)' if FLAG is less than 1,
`(point-max)' otherwise. The argument FLAG must be a number.
- Function: buffer-size &optional buffer
This function returns the total number of characters in the current
buffer. In the absence of any narrowing (*note Narrowing::),
`point-max' returns a value one larger than this.
If you specify a buffer, BUFFER, then the value is the size of
BUFFER.
(buffer-size)
=> 35
(point-max)
=> 36
Motion
======
Motion functions change the value of point, either relative to the
current value of point, relative to the beginning or end of the buffer,
or relative to the edges of the selected window. *Note Point::.
Motion by Characters
--------------------
These functions move point based on a count of characters.
`goto-char' is the fundamental primitive; the other functions use that.
- Command: goto-char position
This function sets point in the current buffer to the value
POSITION. If POSITION is less than 1, it moves point to the
beginning of the buffer. If POSITION is greater than the length
of the buffer, it moves point to the end.
If narrowing is in effect, POSITION still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion. If POSITION is out of range, `goto-char' moves point to
the beginning or the end of the accessible portion.
When this function is called interactively, POSITION is the
numeric prefix argument, if provided; otherwise it is read from the
minibuffer.
`goto-char' returns POSITION.
- Command: forward-char &optional count
This function moves point COUNT characters forward, towards the
end of the buffer (or backward, towards the beginning of the
buffer, if COUNT is negative). If the function attempts to move
point past the beginning or end of the buffer (or the limits of
the accessible portion, when narrowing is in effect), an error is
signaled with error code `beginning-of-buffer' or `end-of-buffer'.
In an interactive call, COUNT is the numeric prefix argument.
- Command: backward-char &optional count
This function moves point COUNT characters backward, towards the
beginning of the buffer (or forward, towards the end of the
buffer, if COUNT is negative). If the function attempts to move
point past the beginning or end of the buffer (or the limits of
the accessible portion, when narrowing is in effect), an error is
signaled with error code `beginning-of-buffer' or `end-of-buffer'.
In an interactive call, COUNT is the numeric prefix argument.
Motion by Words
---------------
These functions for parsing words use the syntax table to decide
whether a given character is part of a word. *Note Syntax Tables::.
- Command: forward-word count
This function moves point forward COUNT words (or backward if
COUNT is negative). "Moving one word" means moving until point
crosses a word-constituent character and then encounters a
word-separator character. However, this function cannot move
point past the boundary of the accessible portion of the buffer,
or across a field boundary (*note Fields::). The most common case
of a field boundary is the end of the prompt in the minibuffer.
If it is possible to move COUNT words, without being stopped
prematurely by the buffer boundary or a field boundary, the value
is `t'. Otherwise, the return value is `nil' and point stops at
the buffer boundary or field boundary.
If `inhibit-field-text-motion' is non-`nil', this function ignores
field boundaries.
In an interactive call, COUNT is specified by the numeric prefix
argument.
- Command: backward-word count
This function is just like `forward-word', except that it moves
backward until encountering the front of a word, rather than
forward.
In an interactive call, COUNT is set to the numeric prefix
argument.
- Variable: words-include-escapes
This variable affects the behavior of `forward-word' and everything
that uses it. If it is non-`nil', then characters in the "escape"
and "character quote" syntax classes count as part of words.
Otherwise, they do not.
- Variable: inhibit-field-text-motion
If this variable is non-`nil', certain motion functions including
`forward-word', `forward-sentence', and `forward-paragraph' ignore
field boundaries.
Motion to an End of the Buffer
------------------------------
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands that users use to do these things. They are
documented here to warn you not to use them in Lisp programs, because
they set the mark and display messages in the echo area.
- Command: beginning-of-buffer &optional n
This function moves point to the beginning of the buffer (or the
limits of the accessible portion, when narrowing is in effect),
setting the mark at the previous position. If N is non-`nil',
then it puts point N tenths of the way from the beginning of the
accessible portion of the buffer.
In an interactive call, N is the numeric prefix argument, if
provided; otherwise N defaults to `nil'.
*Warning:* Don't use this function in Lisp programs!
- Command: end-of-buffer &optional n
This function moves point to the end of the buffer (or the limits
of the accessible portion, when narrowing is in effect), setting
the mark at the previous position. If N is non-`nil', then it
puts point N tenths of the way from the end of the accessible
portion of the buffer.
In an interactive call, N is the numeric prefix argument, if
provided; otherwise N defaults to `nil'.
*Warning:* Don't use this function in Lisp programs!
Motion by Text Lines
--------------------
Text lines are portions of the buffer delimited by newline
characters, which are regarded as part of the previous line. The first
text line begins at the beginning of the buffer, and the last text line
ends at the end of the buffer whether or not the last character is a
newline. The division of the buffer into text lines is not affected by
the width of the window, by line continuation in display, or by how
tabs and control characters are displayed.
- Command: goto-line line
This function moves point to the front of the LINEth line,
counting from line 1 at beginning of the buffer. If LINE is less
than 1, it moves point to the beginning of the buffer. If LINE is
greater than the number of lines in the buffer, it moves point to
the end of the buffer--that is, the _end of the last line_ of the
buffer. This is the only case in which `goto-line' does not
necessarily move to the beginning of a line.
If narrowing is in effect, then LINE still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion. So `goto-line' moves point to the beginning or end of the
accessible portion, if the line number specifies an inaccessible
position.
The return value of `goto-line' is the difference between LINE and
the line number of the line to which point actually was able to
move (in the full buffer, before taking account of narrowing).
Thus, the value is positive if the scan encounters the real end of
the buffer before finding the specified line. The value is zero
if scan encounters the end of the accessible portion but not the
real end of the buffer.
In an interactive call, LINE is the numeric prefix argument if one
has been provided. Otherwise LINE is read in the minibuffer.
- Command: beginning-of-line &optional count
This function moves point to the beginning of the current line.
With an argument COUNT not `nil' or 1, it moves forward COUNT-1
lines and then to the beginning of the line.
This function does not move point across a field boundary (*note
Fields::) unless doing so would move beyond there to a different
line; therefore, if COUNT is `nil' or 1, and point starts at a
field boundary, point does not move. To ignore field boundaries,
either bind `inhibit-field-text-motion' to `t', or use the
`forward-line' function instead. For instance, `(forward-line 0)'
does the same thing as `(beginning-of-line)', except that it
ignores field boundaries.
If this function reaches the end of the buffer (or of the
accessible portion, if narrowing is in effect), it positions point
there. No error is signaled.
- Function: line-beginning-position &optional count
Return the position that `(beginning-of-line COUNT)' would move to.
- Command: end-of-line &optional count
This function moves point to the end of the current line. With an
argument COUNT not `nil' or 1, it moves forward COUNT-1 lines and
then to the end of the line.
This function does not move point across a field boundary (*note
Fields::) unless doing so would move beyond there to a different
line; therefore, if COUNT is `nil' or 1, and point starts at a
field boundary, point does not move. To ignore field boundaries,
bind `inhibit-field-text-motion' to `t'.
If this function reaches the end of the buffer (or of the
accessible portion, if narrowing is in effect), it positions point
there. No error is signaled.
- Function: line-end-position &optional count
Return the position that `(end-of-line COUNT)' would move to.
- Command: forward-line &optional count
This function moves point forward COUNT lines, to the beginning of
the line. If COUNT is negative, it moves point -COUNT lines
backward, to the beginning of a line. If COUNT is zero, it moves
point to the beginning of the current line.
If `forward-line' encounters the beginning or end of the buffer (or
of the accessible portion) before finding that many lines, it sets
point there. No error is signaled.
`forward-line' returns the difference between COUNT and the number
of lines actually moved. If you attempt to move down five lines
from the beginning of a buffer that has only three lines, point
stops at the end of the last line, and the value will be 2.
In an interactive call, COUNT is the numeric prefix argument.
- Function: count-lines start end
This function returns the number of lines between the positions
START and END in the current buffer. If START and END are equal,
then it returns 0. Otherwise it returns at least 1, even if START
and END are on the same line. This is because the text between
them, considered in isolation, must contain at least one line
unless it is empty.
Here is an example of using `count-lines':
(defun current-line ()
"Return the vertical position of point..."
(+ (count-lines (window-start) (point))
(if (= (current-column) 0) 1 0)
-1))
Also see the functions `bolp' and `eolp' in *Note Near Point::.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
Motion by Screen Lines
----------------------
The line functions in the previous section count text lines,
delimited only by newline characters. By contrast, these functions
count screen lines, which are defined by the way the text appears on
the screen. A text line is a single screen line if it is short enough
to fit the width of the selected window, but otherwise it may occupy
several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. In these cases,
`vertical-motion' moves point much like `forward-line'. *Note
Truncation::.
Because the width of a given string depends on the flags that control
the appearance of certain characters, `vertical-motion' behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). *Note Usual
Display::.
These functions scan text to determine where screen lines break, and
thus take time proportional to the distance scanned. If you intend to
use them heavily, Emacs provides caches which may improve the
performance of your code. *Note cache-long-line-scans: Truncation.
- Function: vertical-motion count &optional window
This function moves point to the start of the screen line COUNT
screen lines down from the screen line containing point. If COUNT
is negative, it moves up instead.
`vertical-motion' returns the number of screen lines over which it
moved point. The value may be less in absolute value than COUNT
if the beginning or end of the buffer was reached.
The window WINDOW is used for obtaining parameters such as the
width, the horizontal scrolling, and the display table. But
`vertical-motion' always operates on the current buffer, even if
WINDOW currently displays some other buffer.
- Function: count-screen-lines &optional beg end count-final-newline
window
This function returns the number of screen lines in the text from
BEG to END. The number of screen lines may be different from the
number of actual lines, due to line continuation, the display
table, etc. If BEG and END are `nil' or omitted, they default to
the beginning and end of the accessible portion of the buffer.
If the region ends with a newline, that is ignored unless the
optional third argument COUNT-FINAL-NEWLINE is non-`nil'.
The optional fourth argument WINDOW specifies the window for
obtaining parameters such as width, horizontal scrolling, and so
on. The default is to use the selected window's parameters.
Like `vertical-motion', `count-screen-lines' always uses the
current buffer, regardless of which buffer is displayed in WINDOW.
This makes possible to use `count-screen-lines' in any buffer,
whether or not it is currently displayed in some window.
- Command: move-to-window-line count
This function moves point with respect to the text currently
displayed in the selected window. It moves point to the beginning
of the screen line COUNT screen lines from the top of the window.
If COUNT is negative, that specifies a position -COUNT lines from
the bottom (or the last line of the buffer, if the buffer ends
above the specified screen position).
If COUNT is `nil', then point moves to the beginning of the line
in the middle of the window. If the absolute value of COUNT is
greater than the size of the window, then point moves to the place
that would appear on that screen line if the window were tall
enough. This will probably cause the next redisplay to scroll to
bring that location onto the screen.
In an interactive call, COUNT is the numeric prefix argument.
The value returned is the window line number point has moved to,
with the top line in the window numbered 0.
- Function: compute-motion from frompos to topos width offsets window
This function scans the current buffer, calculating screen
positions. It scans the buffer forward from position FROM,
assuming that is at screen coordinates FROMPOS, to position TO or
coordinates TOPOS, whichever comes first. It returns the ending
buffer position and screen coordinates.
The coordinate arguments FROMPOS and TOPOS are cons cells of the
form `(HPOS . VPOS)'.
The argument WIDTH is the number of columns available to display
text; this affects handling of continuation lines. Use the value
returned by `window-width' for the window of your choice;
normally, use `(window-width WINDOW)'.
The argument OFFSETS is either `nil' or a cons cell of the form
`(HSCROLL . TAB-OFFSET)'. Here HSCROLL is the number of columns
not being displayed at the left margin; most callers get this by
calling `window-hscroll'. Meanwhile, TAB-OFFSET is the offset
between column numbers on the screen and column numbers in the
buffer. This can be nonzero in a continuation line, when the
previous screen lines' widths do not add up to a multiple of
`tab-width'. It is always zero in a non-continuation line.
The window WINDOW serves only to specify which display table to
use. `compute-motion' always operates on the current buffer,
regardless of what buffer is displayed in WINDOW.
The return value is a list of five elements:
(POS VPOS HPOS PREVHPOS CONTIN)
Here POS is the buffer position where the scan stopped, VPOS is
the vertical screen position, and HPOS is the horizontal screen
position.
The result PREVHPOS is the horizontal position one character back
from POS. The result CONTIN is `t' if the last line was continued
after (or within) the previous character.
For example, to find the buffer position of column COL of screen
line LINE of a certain window, pass the window's display start
location as FROM and the window's upper-left coordinates as
FROMPOS. Pass the buffer's `(point-max)' as TO, to limit the scan
to the end of the accessible portion of the buffer, and pass LINE
and COL as TOPOS. Here's a function that does this:
(defun coordinates-of-position (col line)
(car (compute-motion (window-start)
'(0 . 0)
(point-max)
(cons col line)
(window-width)
(cons (window-hscroll) 0)
(selected-window))))
When you use `compute-motion' for the minibuffer, you need to use
`minibuffer-prompt-width' to get the horizontal position of the
beginning of the first screen line. *Note Minibuffer Misc::.
Moving over Balanced Expressions
--------------------------------
Here are several functions concerned with balanced-parenthesis
expressions (also called "sexps" in connection with moving across them
in Emacs). The syntax table controls how these functions interpret
various characters; see *Note Syntax Tables::. *Note Parsing
Expressions::, for lower-level primitives for scanning sexps or parts of
sexps. For user-level commands, see *Note Lists Commands: (emacs)Lists
Commands.
- Command: forward-list &optional arg
This function moves forward across ARG (default 1) balanced groups
of parentheses. (Other syntactic entities such as words or paired
string quotes are ignored.)
- Command: backward-list &optional arg
This function moves backward across ARG (default 1) balanced
groups of parentheses. (Other syntactic entities such as words or
paired string quotes are ignored.)
- Command: up-list &optional arg
This function moves forward out of ARG (default 1) levels of
parentheses. A negative argument means move backward but still to
a less deep spot.
- Command: down-list &optional arg
This function moves forward into ARG (default 1) levels of
parentheses. A negative argument means move backward but still go
deeper in parentheses (-ARG levels).
- Command: forward-sexp &optional arg
This function moves forward across ARG (default 1) balanced
expressions. Balanced expressions include both those delimited by
parentheses and other kinds, such as words and string constants.
For example,
---------- Buffer: foo ----------
(concat-!- "foo " (car x) y z)
---------- Buffer: foo ----------
(forward-sexp 3)
=> nil
---------- Buffer: foo ----------
(concat "foo " (car x) y-!- z)
---------- Buffer: foo ----------
- Command: backward-sexp &optional arg
This function moves backward across ARG (default 1) balanced
expressions.
- Command: beginning-of-defun arg
This function moves back to the ARGth beginning of a defun. If
ARG is negative, this actually moves forward, but it still moves
to the beginning of a defun, not to the end of one.
- Command: end-of-defun arg
This function moves forward to the ARGth end of a defun. If ARG
is negative, this actually moves backward, but it still moves to
the end of a defun, not to the beginning of one.
- User Option: defun-prompt-regexp
If non-`nil', this variable holds a regular expression that
specifies what text can appear before the open-parenthesis that
starts a defun. That is to say, a defun begins on a line that
starts with a match for this regular expression, followed by a
character with open-parenthesis syntax.
- User Option: open-paren-in-column-0-is-defun-start
If this variable's value is non-`nil', an open parenthesis in
column 0 is considered to be the start of a defun. If it is
`nil', an open parenthesis in column 0 has no special meaning.
The default is `t'.
- Variable: beginning-of-defun-function
If non-`nil', this variable holds a function for finding the
beginning of a defun. The function `beginning-of-defun' calls
this function instead of using its normal method.
- Variable: end-of-defun-function
If non-`nil', this variable holds a function for finding the end of
a defun. The function `end-of-defun' calls this function instead
of using its normal method.
Skipping Characters
-------------------
The following two functions move point over a specified set of
characters. For example, they are often used to skip whitespace. For
related functions, see *Note Motion and Syntax::.
- Function: skip-chars-forward character-set &optional limit
This function moves point in the current buffer forward, skipping
over a given set of characters. It examines the character
following point, then advances point if the character matches
CHARACTER-SET. This continues until it reaches a character that
does not match. The function returns the number of characters
moved over.
The argument CHARACTER-SET is like the inside of a `[...]' in a
regular expression except that `]' is never special and `\' quotes
`^', `-' or `\'. Thus, `"a-zA-Z"' skips over all letters,
stopping before the first nonletter, and `"^a-zA-Z"' skips
nonletters stopping before the first letter. *Note Regular
Expressions::.
If LIMIT is supplied (it must be a number or a marker), it
specifies the maximum position in the buffer that point can be
skipped to. Point will stop at or before LIMIT.
In the following example, point is initially located directly
before the `T'. After the form is evaluated, point is located at
the end of that line (between the `t' of `hat' and the newline).
The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(skip-chars-forward "a-zA-Z ")
=> nil
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
- Function: skip-chars-backward character-set &optional limit
This function moves point backward, skipping characters that match
CHARACTER-SET, until LIMIT. It is just like `skip-chars-forward'
except for the direction of motion.
The return value indicates the distance traveled. It is an
integer that is zero or less.
Excursions
==========
It is often useful to move point "temporarily" within a localized
portion of the program, or to switch buffers temporarily. This is
called an "excursion", and it is done with the `save-excursion' special
form. This construct initially remembers the identity of the current
buffer, and its values of point and the mark, and restores them after
the completion of the excursion.
The forms for saving and restoring the configuration of windows are
described elsewhere (see *Note Window Configurations::, and *note Frame
Configurations::).
- Special Form: save-excursion forms...
The `save-excursion' special form saves the identity of the current
buffer and the values of point and the mark in it, evaluates
FORMS, and finally restores the buffer and its saved values of
point and the mark. All three saved values are restored even in
case of an abnormal exit via `throw' or error (*note Nonlocal
Exits::).
The `save-excursion' special form is the standard way to switch
buffers or move point within one part of a program and avoid
affecting the rest of the program. It is used more than 4000
times in the Lisp sources of Emacs.
`save-excursion' does not save the values of point and the mark for
other buffers, so changes in other buffers remain in effect after
`save-excursion' exits.
Likewise, `save-excursion' does not restore window-buffer
correspondences altered by functions such as `switch-to-buffer'.
One way to restore these correspondences, and the selected window,
is to use `save-window-excursion' inside `save-excursion' (*note
Window Configurations::).
The value returned by `save-excursion' is the result of the last of
FORMS, or `nil' if no FORMS are given.
(save-excursion FORMS)
==
(let ((old-buf (current-buffer))
(old-pnt (point-marker))
(old-mark (copy-marker (mark-marker))))
(unwind-protect
(progn FORMS)
(set-buffer old-buf)
(goto-char old-pnt)
(set-marker (mark-marker) old-mark)))
*Warning:* Ordinary insertion of text adjacent to the saved point
value relocates the saved value, just as it relocates all markers.
Therefore, when the saved point value is restored, it normally comes
before the inserted text.
Although `save-excursion' saves the location of the mark, it does
not prevent functions which modify the buffer from setting
`deactivate-mark', and thus causing the deactivation of the mark after
the command finishes. *Note The Mark::.
Narrowing
=========
"Narrowing" means limiting the text addressable by Emacs editing
commands to a limited range of characters in a buffer. The text that
remains addressable is called the "accessible portion" of the buffer.
Narrowing is specified with two buffer positions which become the
beginning and end of the accessible portion. For most editing commands
and most Emacs primitives, these positions replace the values of the
beginning and end of the buffer. While narrowing is in effect, no text
outside the accessible portion is displayed, and point cannot move
outside the accessible portion.
Values such as positions or line numbers, which usually count from
the beginning of the buffer, do so despite narrowing, but the functions
which use them refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; they
save the entire buffer regardless of any narrowing.
- Command: narrow-to-region start end
This function sets the accessible portion of the current buffer to
start at START and end at END. Both arguments should be character
positions.
In an interactive call, START and END are set to the bounds of the
current region (point and the mark, with the smallest first).
- Command: narrow-to-page move-count
This function sets the accessible portion of the current buffer to
include just the current page. An optional first argument
MOVE-COUNT non-`nil' means to move forward or backward by
MOVE-COUNT pages and then narrow to one page. The variable
`page-delimiter' specifies where pages start and end (*note
Standard Regexps::).
In an interactive call, MOVE-COUNT is set to the numeric prefix
argument.
- Command: widen
This function cancels any narrowing in the current buffer, so that
the entire contents are accessible. This is called "widening".
It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
- Special Form: save-restriction body...
This special form saves the current bounds of the accessible
portion, evaluates the BODY forms, and finally restores the saved
bounds, thus restoring the same state of narrowing (or absence
thereof) formerly in effect. The state of narrowing is restored
even in the event of an abnormal exit via `throw' or error (*note
Nonlocal Exits::). Therefore, this construct is a clean way to
narrow a buffer temporarily.
The value returned by `save-restriction' is that returned by the
last form in BODY, or `nil' if no body forms were given.
*Caution:* it is easy to make a mistake when using the
`save-restriction' construct. Read the entire description here
before you try it.
If BODY changes the current buffer, `save-restriction' still
restores the restrictions on the original buffer (the buffer whose
restrictions it saved from), but it does not restore the identity
of the current buffer.
`save-restriction' does _not_ restore point and the mark; use
`save-excursion' for that. If you use both `save-restriction' and
`save-excursion' together, `save-excursion' should come first (on
the outside). Otherwise, the old point value would be restored
with temporary narrowing still in effect. If the old point value
were outside the limits of the temporary narrowing, this would
fail to restore it accurately.
Here is a simple example of correct use of `save-restriction':
---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo-!-
---------- Buffer: foo ----------
(save-excursion
(save-restriction
(goto-char 1)
(forward-line 2)
(narrow-to-region 1 (point))
(goto-char (point-min))
(replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo-!-
---------- Buffer: foo ----------
Markers
*******
A "marker" is a Lisp object used to specify a position in a buffer
relative to the surrounding text. A marker changes its offset from the
beginning of the buffer automatically whenever text is inserted or
deleted, so that it stays with the two characters on either side of it.
Overview of Markers
===================
A marker specifies a buffer and a position in that buffer. The
marker can be used to represent a position in the functions that
require one, just as an integer could be used. *Note Positions::, for
a complete description of positions.
A marker has two attributes: the marker position, and the marker
buffer. The marker position is an integer that is equivalent (at a
given time) to the marker as a position in that buffer. But the
marker's position value can change often during the life of the marker.
Insertion and deletion of text in the buffer relocate the marker. The
idea is that a marker positioned between two characters remains between
those two characters despite insertion and deletion elsewhere in the
buffer. Relocation changes the integer equivalent of the marker.
Deleting text around a marker's position leaves the marker between
the characters immediately before and after the deleted text. Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's "insertion
type" (*note Marker Insertion Types::)--unless the insertion is done
with `insert-before-markers' (*note Insertion::).
Insertion and deletion in a buffer must check all the markers and
relocate them if necessary. This slows processing in a buffer with a
large number of markers. For this reason, it is a good idea to make a
marker point nowhere if you are sure you don't need it any more.
Unreferenced markers are garbage collected eventually, but until then
will continue to use time if they do point somewhere.
Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including `+' and `-')
accept markers as arguments. In such cases, the marker stands for its
current position.
Here are examples of creating markers, setting markers, and moving
point to markers:
;; Make a new marker that initially does not point anywhere:
(setq m1 (make-marker))
=> #<marker in no buffer>
;; Set `m1' to point between the 99th and 100th characters
;; in the current buffer:
(set-marker m1 100)
=> #<marker at 100 in markers.texi>
;; Now insert one character at the beginning of the buffer:
(goto-char (point-min))
=> 1
(insert "Q")
=> nil
;; `m1' is updated appropriately.
m1
=> #<marker at 101 in markers.texi>
;; Two markers that point to the same position
;; are not `eq', but they are `equal'.
(setq m2 (copy-marker m1))
=> #<marker at 101 in markers.texi>
(eq m1 m2)
=> nil
(equal m1 m2)
=> t
;; When you are finished using a marker, make it point nowhere.
(set-marker m1 nil)
=> #<marker in no buffer>
Predicates on Markers
=====================
You can test an object to see whether it is a marker, or whether it
is either an integer or a marker. The latter test is useful in
connection with the arithmetic functions that work with both markers
and integers.
- Function: markerp object
This function returns `t' if OBJECT is a marker, `nil' otherwise.
Note that integers are not markers, even though many functions
will accept either a marker or an integer.
- Function: integer-or-marker-p object
This function returns `t' if OBJECT is an integer or a marker,
`nil' otherwise.
- Function: number-or-marker-p object
This function returns `t' if OBJECT is a number (either integer or
floating point) or a marker, `nil' otherwise.
Functions that Create Markers
=============================
When you create a new marker, you can make it point nowhere, or point
to the present position of point, or to the beginning or end of the
accessible portion of the buffer, or to the same place as another given
marker.
- Function: make-marker
This function returns a newly created marker that does not point
anywhere.
(make-marker)
=> #<marker in no buffer>
- Function: point-marker
This function returns a new marker that points to the present
position of point in the current buffer. *Note Point::. For an
example, see `copy-marker', below.
- Function: point-min-marker
This function returns a new marker that points to the beginning of
the accessible portion of the buffer. This will be the beginning
of the buffer unless narrowing is in effect. *Note Narrowing::.
- Function: point-max-marker
This function returns a new marker that points to the end of the
accessible portion of the buffer. This will be the end of the
buffer unless narrowing is in effect. *Note Narrowing::.
Here are examples of this function and `point-min-marker', shown in
a buffer containing a version of the source file for the text of
this chapter.
(point-min-marker)
=> #<marker at 1 in markers.texi>
(point-max-marker)
=> #<marker at 15573 in markers.texi>
(narrow-to-region 100 200)
=> nil
(point-min-marker)
=> #<marker at 100 in markers.texi>
(point-max-marker)
=> #<marker at 200 in markers.texi>
- Function: copy-marker marker-or-integer insertion-type
If passed a marker as its argument, `copy-marker' returns a new
marker that points to the same place and the same buffer as does
MARKER-OR-INTEGER. If passed an integer as its argument,
`copy-marker' returns a new marker that points to position
MARKER-OR-INTEGER in the current buffer.
The new marker's insertion type is specified by the argument
INSERTION-TYPE. *Note Marker Insertion Types::.
If passed an integer argument less than 1, `copy-marker' returns a
new marker that points to the beginning of the current buffer. If
passed an integer argument greater than the length of the buffer,
`copy-marker' returns a new marker that points to the end of the
buffer.
(copy-marker 0)
=> #<marker at 1 in markers.texi>
(copy-marker 20000)
=> #<marker at 7572 in markers.texi>
An error is signaled if MARKER is neither a marker nor an integer.
Two distinct markers are considered `equal' (even though not `eq')
to each other if they have the same position and buffer, or if they
both point nowhere.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
Information from Markers
========================
This section describes the functions for accessing the components of
a marker object.
- Function: marker-position marker
This function returns the position that MARKER points to, or `nil'
if it points nowhere.
- Function: marker-buffer marker
This function returns the buffer that MARKER points into, or `nil'
if it points nowhere.
(setq m (make-marker))
=> #<marker in no buffer>
(marker-position m)
=> nil
(marker-buffer m)
=> nil
(set-marker m 3770 (current-buffer))
=> #<marker at 3770 in markers.texi>
(marker-buffer m)
=> #<buffer markers.texi>
(marker-position m)
=> 3770
- Function: buffer-has-markers-at position
This function returns `t' if one or more markers point at position
POSITION in the current buffer.
Marker Insertion Types
======================
When you insert text directly at the place where a marker points,
there are two possible ways to relocate that marker: it can point before
the inserted text, or point after it. You can specify which one a given
marker should do by setting its "insertion type". Note that use of
`insert-before-markers' ignores markers' insertion types, always
relocating a marker to point after the inserted text.
- Function: set-marker-insertion-type marker type
This function sets the insertion type of marker MARKER to TYPE.
If TYPE is `t', MARKER will advance when text is inserted at its
position. If TYPE is `nil', MARKER does not advance when text is
inserted there.
- Function: marker-insertion-type marker
This function reports the current insertion type of MARKER.
Moving Marker Positions
=======================
This section describes how to change the position of an existing
marker. When you do this, be sure you know whether the marker is used
outside of your program, and, if so, what effects will result from
moving it--otherwise, confusing things may happen in other parts of
Emacs.
- Function: set-marker marker position &optional buffer
This function moves MARKER to POSITION in BUFFER. If BUFFER is
not provided, it defaults to the current buffer.
If POSITION is less than 1, `set-marker' moves MARKER to the
beginning of the buffer. If POSITION is greater than the size of
the buffer, `set-marker' moves marker to the end of the buffer.
If POSITION is `nil' or a marker that points nowhere, then MARKER
is set to point nowhere.
The value returned is MARKER.
(setq m (point-marker))
=> #<marker at 4714 in markers.texi>
(set-marker m 55)
=> #<marker at 55 in markers.texi>
(setq b (get-buffer "foo"))
=> #<buffer foo>
(set-marker m 0 b)
=> #<marker at 1 in foo>
- Function: move-marker marker position &optional buffer
This is another name for `set-marker'.
The Mark
========
One special marker in each buffer is designated "the mark". It
records a position for the user for the sake of commands such as
`kill-region' and `indent-rigidly'. Lisp programs should set the mark
only to values that have a potential use to the user, and never for
their own internal purposes. For example, the `replace-regexp' command
sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after the
replace is finished.
Many commands are designed so that when called interactively they
operate on the text between point and the mark. If you are writing such
a command, don't examine the mark directly; instead, use `interactive'
with the `r' specification. This provides the values of point and the
mark as arguments to the command in an interactive call, but permits
other Lisp programs to specify arguments explicitly. *Note Interactive
Codes::.
Each buffer has its own value of the mark that is independent of the
value of the mark in other buffers. When a buffer is created, the mark
exists but does not point anywhere. We consider this state as "the
absence of a mark in that buffer."
Once the mark "exists" in a buffer, it normally never ceases to
exist. However, it may become "inactive", if Transient Mark mode is
enabled. The variable `mark-active', which is always buffer-local in
all buffers, indicates whether the mark is active: non-`nil' means yes.
A command can request deactivation of the mark upon return to the
editor command loop by setting `deactivate-mark' to a non-`nil' value
(but this causes deactivation only if Transient Mark mode is enabled).
The main motivation for using Transient Mark mode is that this mode
also enables highlighting of the region when the mark is active. *Note
Display::.
In addition to the mark, each buffer has a "mark ring" which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable `mark-ring-max' specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
There is also a separate global mark ring, but that is used only in a
few particular user-level commands, and is not relevant to Lisp
programming. So we do not describe it here.
- Function: mark &optional force
This function returns the current buffer's mark position as an
integer.
If the mark is inactive, `mark' normally signals an error.
However, if FORCE is non-`nil', then `mark' returns the mark
position anyway--or `nil', if the mark is not yet set for this
buffer.
- Function: mark-marker
This function returns the current buffer's mark. This is the very
marker that records the mark location inside Emacs, not a copy.
Therefore, changing this marker's position will directly affect
the position of the mark. Don't do it unless that is the effect
you want.
(setq m (mark-marker))
=> #<marker at 3420 in markers.texi>
(set-marker m 100)
=> #<marker at 100 in markers.texi>
(mark-marker)
=> #<marker at 100 in markers.texi>
Like any marker, this marker can be set to point at any buffer you
like. We don't recommend that you make it point at any buffer
other than the one of which it is the mark. If you do, it will
yield perfectly consistent, but rather odd, results.
- Function: set-mark position
This function sets the mark to POSITION, and activates the mark.
The old value of the mark is _not_ pushed onto the mark ring.
*Please note:* Use this function only if you want the user to see
that the mark has moved, and you want the previous mark position to
be lost. Normally, when a new mark is set, the old one should go
on the `mark-ring'. For this reason, most applications should use
`push-mark' and `pop-mark', not `set-mark'.
Novice Emacs Lisp programmers often try to use the mark for the
wrong purposes. The mark saves a location for the user's
convenience. An editing command should not alter the mark unless
altering the mark is part of the user-level functionality of the
command. (And, in that case, this effect should be documented.)
To remember a location for internal use in the Lisp program, store
it in a Lisp variable. For example:
(let ((beg (point)))
(forward-line 1)
(delete-region beg (point))).
- Function: push-mark &optional position nomsg activate
This function sets the current buffer's mark to POSITION, and
pushes a copy of the previous mark onto `mark-ring'. If POSITION
is `nil', then the value of point is used. `push-mark' returns
`nil'.
The function `push-mark' normally _does not_ activate the mark.
To do that, specify `t' for the argument ACTIVATE.
A `Mark set' message is displayed unless NOMSG is non-`nil'.
- Function: pop-mark
This function pops off the top element of `mark-ring' and makes
that mark become the buffer's actual mark. This does not move
point in the buffer, and it does nothing if `mark-ring' is empty.
It deactivates the mark.
The return value is not meaningful.
- User Option: transient-mark-mode
This variable if non-`nil' enables Transient Mark mode, in which
every buffer-modifying primitive sets `deactivate-mark'. The
consequence of this is that commands that modify the buffer
normally make the mark inactive.
- User Option: mark-even-if-inactive
If this is non-`nil', Lisp programs and the Emacs user can use the
mark even when it is inactive. This option affects the behavior of
Transient Mark mode. When the option is non-`nil', deactivation of
the mark turns off region highlighting, but commands that use the
mark behave as if the mark were still active.
- Variable: deactivate-mark
If an editor command sets this variable non-`nil', then the editor
command loop deactivates the mark after the command returns (if
Transient Mark mode is enabled). All the primitives that change
the buffer set `deactivate-mark', to deactivate the mark when the
command is finished.
- Function: deactivate-mark
This function deactivates the mark, if Transient Mark mode is
enabled. Otherwise it does nothing.
- Variable: mark-active
The mark is active when this variable is non-`nil'. This variable
is always buffer-local in each buffer.
- Variable: activate-mark-hook
- Variable: deactivate-mark-hook
These normal hooks are run, respectively, when the mark becomes
active and when it becomes inactive. The hook
`activate-mark-hook' is also run at the end of a command if the
mark is active and it is possible that the region may have changed.
- Variable: mark-ring
The value of this buffer-local variable is the list of saved former
marks of the current buffer, most recent first.
mark-ring
=> (#<marker at 11050 in markers.texi>
#<marker at 10832 in markers.texi>
...)
- User Option: mark-ring-max
The value of this variable is the maximum size of `mark-ring'. If
more marks than this are pushed onto the `mark-ring', `push-mark'
discards an old mark when it adds a new one.
The Region
==========
The text between point and the mark is known as "the region".
Various functions operate on text delimited by point and the mark, but
only those functions specifically related to the region itself are
described here.
- Function: region-beginning
This function returns the position of the beginning of the region
(as an integer). This is the position of either point or the mark,
whichever is smaller.
If the mark does not point anywhere, an error is signaled.
- Function: region-end
This function returns the position of the end of the region (as an
integer). This is the position of either point or the mark,
whichever is larger.
If the mark does not point anywhere, an error is signaled.
Few programs need to use the `region-beginning' and `region-end'
functions. A command designed to operate on a region should normally
use `interactive' with the `r' specification to find the beginning and
end of the region. This lets other Lisp programs specify the bounds
explicitly as arguments. (*Note Interactive Codes::.)
Text
****
This chapter describes the functions that deal with the text in a
buffer. Most examine, insert, or delete text in the current buffer,
often operating at point or on text adjacent to point. Many are
interactive. All the functions that change the text provide for undoing
the changes (*note Undo::).
Many text-related functions operate on a region of text defined by
two buffer positions passed in arguments named START and END. These
arguments should be either markers (*note Markers::) or numeric
character positions (*note Positions::). The order of these arguments
does not matter; it is all right for START to be the end of the region
and END the beginning. For example, `(delete-region 1 10)' and
`(delete-region 10 1)' are equivalent. An `args-out-of-range' error is
signaled if either START or END is outside the accessible portion of
the buffer. In an interactive call, point and the mark are used for
these arguments.
Throughout this chapter, "text" refers to the characters in the
buffer, together with their properties (when relevant). Keep in mind
that point is always between two characters, and the cursor appears on
the character after point.
Examining Text Near Point
=========================
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also `looking-at' in
*Note Regexp Search::.
- Function: char-after &optional position
This function returns the character in the current buffer at (i.e.,
immediately after) position POSITION. If POSITION is out of range
for this purpose, either before the beginning of the buffer, or at
or beyond the end, then the value is `nil'. The default for
POSITION is point.
In the following example, assume that the first character in the
buffer is `@':
(char-to-string (char-after 1))
=> "@"
- Function: char-before &optional position
This function returns the character in the current buffer
immediately before position POSITION. If POSITION is out of range
for this purpose, either before the beginning of the buffer, or at
or beyond the end, then the value is `nil'. The default for
POSITION is point.
- Function: following-char
This function returns the character following point in the current
buffer. This is similar to `(char-after (point))'. However, if
point is at the end of the buffer, then `following-char' returns 0.
Remember that point is always between characters, and the terminal
cursor normally appears over the character following point.
Therefore, the character returned by `following-char' is the
character the cursor is over.
In this example, point is between the `a' and the `c'.
---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(char-to-string (preceding-char))
=> "a"
(char-to-string (following-char))
=> "c"
- Function: preceding-char
This function returns the character preceding point in the current
buffer. See above, under `following-char', for an example. If
point is at the beginning of the buffer, `preceding-char' returns
0.
- Function: bobp
This function returns `t' if point is at the beginning of the
buffer. If narrowing is in effect, this means the beginning of the
accessible portion of the text. See also `point-min' in *Note
Point::.
- Function: eobp
This function returns `t' if point is at the end of the buffer.
If narrowing is in effect, this means the end of accessible
portion of the text. See also `point-max' in *Note Point::.
- Function: bolp
This function returns `t' if point is at the beginning of a line.
*Note Text Lines::. The beginning of the buffer (or of its
accessible portion) always counts as the beginning of a line.
- Function: eolp
This function returns `t' if point is at the end of a line. The
end of the buffer (or of its accessible portion) is always
considered the end of a line.
Examining Buffer Contents
=========================
This section describes two functions that allow a Lisp program to
convert any portion of the text in the buffer into a string.
- Function: buffer-substring start end
This function returns a string containing a copy of the text of the
region defined by positions START and END in the current buffer.
If the arguments are not positions in the accessible portion of
the buffer, `buffer-substring' signals an `args-out-of-range'
error.
It is not necessary for START to be less than END; the arguments
can be given in either order. But most often the smaller argument
is written first.
If the text being copied has any text properties, these are copied
into the string along with the characters they belong to. *Note
Text Properties::. However, overlays (*note Overlays::) in the
buffer and their properties are ignored, not copied.
---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-substring 1 10)
=> "This is t"
(buffer-substring (point-max) 10)
=> "he contents of buffer foo
"
- Function: buffer-substring-no-properties start end
This is like `buffer-substring', except that it does not copy text
properties, just the characters themselves. *Note Text
Properties::.
- Function: buffer-string
This function returns the contents of the entire accessible
portion of the current buffer as a string. It is equivalent to
(buffer-substring (point-min) (point-max))
---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-string)
=> "This is the contents of buffer foo
"
- Function: thing-at-point thing
Return the THING around or next to point, as a string.
The argument THING is a symbol which specifies a kind of syntactic
entity. Possibilities include `symbol', `list', `sexp', `defun',
`filename', `url', `word', `sentence', `whitespace', `line',
`page', and others.
---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(thing-at-point 'word)
=> "Peace"
(thing-at-point 'line)
=> "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
=> nil
Comparing Text
==============
This function lets you compare portions of the text in a buffer,
without copying them into strings first.
- Function: compare-buffer-substrings buffer1 start1 end1 buffer2
start2 end2
This function lets you compare two substrings of the same buffer
or two different buffers. The first three arguments specify one
substring, giving a buffer and two positions within the buffer.
The last three arguments specify the other substring in the same
way. You can use `nil' for BUFFER1, BUFFER2, or both to stand for
the current buffer.
The value is negative if the first substring is less, positive if
the first is greater, and zero if they are equal. The absolute
value of the result is one plus the index of the first differing
characters within the substrings.
This function ignores case when comparing characters if
`case-fold-search' is non-`nil'. It always ignores text
properties.
Suppose the current buffer contains the text `foobarbar
haha!rara!'; then in this example the two substrings are `rbar '
and `rara!'. The value is 2 because the first substring is greater
at the second character.
(compare-buffer-substrings nil 6 11 nil 16 21)
=> 2
Inserting Text
==============
"Insertion" means adding new text to a buffer. The inserted text
goes at point--between the character before point and the character
after point. Some insertion functions leave point before the inserted
text, while other functions leave it after. We call the former
insertion "after point" and the latter insertion "before point".
Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text (*note
Markers::). When a marker points at the place of insertion, insertion
may or may not relocate the marker, depending on the marker's insertion
type (*note Marker Insertion Types::). Certain special functions such
as `insert-before-markers' relocate all such markers to point after the
inserted text, regardless of the markers' insertion type.
Insertion functions signal an error if the current buffer is
read-only or if they insert within read-only text.
These functions copy text characters from strings and buffers along
with their properties. The inserted characters have exactly the same
properties as the characters they were copied from. By contrast,
characters specified as separate arguments, not part of a string or
buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in
order to insert in a multibyte buffer, and vice versa--if the text
comes from a string or from a buffer. However, they do not convert
unibyte character codes 128 through 255 to multibyte characters, not
even if the current buffer is a multibyte buffer. *Note Converting
Representations::.
- Function: insert &rest args
This function inserts the strings and/or characters ARGS into the
current buffer, at point, moving point forward. In other words, it
inserts the text before point. An error is signaled unless all
ARGS are either strings or characters. The value is `nil'.
- Function: insert-before-markers &rest args
This function inserts the strings and/or characters ARGS into the
current buffer, at point, moving point forward. An error is
signaled unless all ARGS are either strings or characters. The
value is `nil'.
This function is unlike the other insertion functions in that it
relocates markers initially pointing at the insertion point, to
point after the inserted text. If an overlay begins the insertion
point, the inserted text falls outside the overlay; if a nonempty
overlay ends at the insertion point, the inserted text falls
inside that overlay.
- Function: insert-char character &optional count inherit
This function inserts COUNT instances of CHARACTER into the
current buffer before point. The argument COUNT should be a
number (`nil' means 1), and CHARACTER must be a character. The
value is `nil'.
This function does not convert unibyte character codes 128 through
255 to multibyte characters, not even if the current buffer is a
multibyte buffer. *Note Converting Representations::.
If INHERIT is non-`nil', then the inserted characters inherit
sticky text properties from the two characters before and after the
insertion point. *Note Sticky Properties::.
- Function: insert-buffer-substring from-buffer-or-name &optional
start end
This function inserts a portion of buffer FROM-BUFFER-OR-NAME
(which must already exist) into the current buffer before point.
The text inserted is the region from START and END. (These
arguments default to the beginning and end of the accessible
portion of that buffer.) This function returns `nil'.
In this example, the form is executed with buffer `bar' as the
current buffer. We assume that buffer `bar' is initially empty.
---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
(insert-buffer-substring "foo" 1 20)
=> nil
---------- Buffer: bar ----------
We hold these truth-!-
---------- Buffer: bar ----------
*Note Sticky Properties::, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it.
Whitespace inserted by indentation functions also inherits text
properties.
User-Level Insertion Commands
=============================
This section describes higher-level commands for inserting text,
commands intended primarily for the user but useful also in Lisp
programs.
- Command: insert-buffer from-buffer-or-name
This command inserts the entire contents of FROM-BUFFER-OR-NAME
(which must exist) into the current buffer after point. It leaves
the mark after the inserted text. The value is `nil'.
- Command: self-insert-command count
This command inserts the last character typed; it does so COUNT
times, before point, and returns `nil'. Most printing characters
are bound to this command. In routine use, `self-insert-command'
is the most frequently called function in Emacs, but programs
rarely use it except to install it on a keymap.
In an interactive call, COUNT is the numeric prefix argument.
This command calls `auto-fill-function' whenever that is non-`nil'
and the character inserted is in the table `auto-fill-chars'
(*note Auto Filling::).
This command performs abbrev expansion if Abbrev mode is enabled
and the inserted character does not have word-constituent syntax.
(*Note Abbrevs::, and *Note Syntax Class Table::.)
This is also responsible for calling `blink-paren-function' when
the inserted character has close parenthesis syntax (*note
Blinking::).
Do not try substituting your own definition of
`self-insert-command' for the standard one. The editor command
loop handles this function specially.
- Command: newline &optional number-of-newlines
This command inserts newlines into the current buffer before point.
If NUMBER-OF-NEWLINES is supplied, that many newline characters
are inserted.
This function calls `auto-fill-function' if the current column
number is greater than the value of `fill-column' and
NUMBER-OF-NEWLINES is `nil'. Typically what `auto-fill-function'
does is insert a newline; thus, the overall result in this case is
to insert two newlines at different places: one at point, and
another earlier in the line. `newline' does not auto-fill if
NUMBER-OF-NEWLINES is non-`nil'.
This command indents to the left margin if that is not zero.
*Note Margins::.
The value returned is `nil'. In an interactive call, COUNT is the
numeric prefix argument.
- Command: split-line
This command splits the current line, moving the portion of the
line after point down vertically so that it is on the next line
directly below where it was before. Whitespace is inserted as
needed at the beginning of the lower line, using the `indent-to'
function. `split-line' returns the position of point.
Programs hardly ever use this function.
- Variable: overwrite-mode
This variable controls whether overwrite mode is in effect. The
value should be `overwrite-mode-textual', `overwrite-mode-binary',
or `nil'. `overwrite-mode-textual' specifies textual overwrite
mode (treats newlines and tabs specially), and
`overwrite-mode-binary' specifies binary overwrite mode (treats
newlines and tabs like any other characters).
Deleting Text
=============
Deletion means removing part of the text in a buffer, without saving
it in the kill ring (*note The Kill Ring::). Deleted text can't be
yanked, but can be reinserted using the undo mechanism (*note Undo::).
Some deletion functions do save text in the kill ring in some special
cases.
All of the deletion functions operate on the current buffer, and all
return a value of `nil'.
- Command: erase-buffer
This function deletes the entire text of the current buffer,
leaving it empty. If the buffer is read-only, it signals a
`buffer-read-only' error; if some of the text in it is read-only,
it signals a `text-read-only' error. Otherwise, it deletes the
text without asking for any confirmation. It returns `nil'.
Normally, deleting a large amount of text from a buffer inhibits
further auto-saving of that buffer "because it has shrunk".
However, `erase-buffer' does not do this, the idea being that the
future text is not really related to the former text, and its size
should not be compared with that of the former text.
- Command: delete-region start end
This command deletes the text between positions START and END in
the current buffer, and returns `nil'. If point was inside the
deleted region, its value afterward is START. Otherwise, point
relocates with the surrounding text, as markers do.
- Function: delete-and-extract-region start end
This function deletes the text between positions START and END in
the current buffer, and returns a string containing the text just
deleted.
If point was inside the deleted region, its value afterward is
START. Otherwise, point relocates with the surrounding text, as
markers do.
- Command: delete-char count &optional killp
This command deletes COUNT characters directly after point, or
before point if COUNT is negative. If KILLP is non-`nil', then it
saves the deleted characters in the kill ring.
In an interactive call, COUNT is the numeric prefix argument, and
KILLP is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no
prefix argument is supplied, then one character is deleted, but
not saved in the kill ring.
The value returned is always `nil'.
- Command: delete-backward-char count &optional killp
This command deletes COUNT characters directly before point, or
after point if COUNT is negative. If KILLP is non-`nil', then it
saves the deleted characters in the kill ring.
In an interactive call, COUNT is the numeric prefix argument, and
KILLP is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no
prefix argument is supplied, then one character is deleted, but
not saved in the kill ring.
The value returned is always `nil'.
- Command: backward-delete-char-untabify count &optional killp
This command deletes COUNT characters backward, changing tabs into
spaces. When the next character to be deleted is a tab, it is
first replaced with the proper number of spaces to preserve
alignment and then one of those spaces is deleted instead of the
tab. If KILLP is non-`nil', then the command saves the deleted
characters in the kill ring.
Conversion of tabs to spaces happens only if COUNT is positive.
If it is negative, exactly -COUNT characters after point are
deleted.
In an interactive call, COUNT is the numeric prefix argument, and
KILLP is the unprocessed prefix argument. Therefore, if a prefix
argument is supplied, the text is saved in the kill ring. If no
prefix argument is supplied, then one character is deleted, but
not saved in the kill ring.
The value returned is always `nil'.
- User Option: backward-delete-char-untabify-method
This option specifies how `backward-delete-char-untabify' should
deal with whitespace. Possible values include `untabify', the
default, meaning convert a tab to many spaces and delete one;
`hungry', meaning delete all the whitespace characters before point
with one command, and `nil', meaning do nothing special for
whitespace characters.
User-Level Deletion Commands
============================
This section describes higher-level commands for deleting text,
commands intended primarily for the user but useful also in Lisp
programs.
- Command: delete-horizontal-space
This function deletes all spaces and tabs around point. It returns
`nil'.
In the following examples, we call `delete-horizontal-space' four
times, once on each line, with point between the second and third
characters on the line each time.
---------- Buffer: foo ----------
I -!-thought
I -!- thought
We-!- thought
Yo-!-u thought
---------- Buffer: foo ----------
(delete-horizontal-space) ; Four times.
=> nil
---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
- Command: delete-indentation &optional join-following-p
This function joins the line point is on to the previous line,
deleting any whitespace at the join and in some cases replacing it
with one space. If JOIN-FOLLOWING-P is non-`nil',
`delete-indentation' joins this line to the following line
instead. The function returns `nil'.
If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then `delete-indentation' deletes the fill
prefix before joining the lines. *Note Margins::.
In the example below, point is located on the line starting
`events', and it makes no difference if there are trailing spaces
in the preceding line.
---------- Buffer: foo ----------
When in the course of human
-!- events, it becomes necessary
---------- Buffer: foo ----------
(delete-indentation)
=> nil
---------- Buffer: foo ----------
When in the course of human-!- events, it becomes necessary
---------- Buffer: foo ----------
After the lines are joined, the function `fixup-whitespace' is
responsible for deciding whether to leave a space at the junction.
- Function: fixup-whitespace
This function replaces all the whitespace surrounding point with
either one space or no space, according to the context. It
returns `nil'.
At the beginning or end of a line, the appropriate amount of space
is none. Before a character with close parenthesis syntax, or
after a character with open parenthesis or expression-prefix
syntax, no space is also appropriate. Otherwise, one space is
appropriate. *Note Syntax Class Table::.
In the example below, `fixup-whitespace' is called the first time
with point before the word `spaces' in the first line. For the
second invocation, point is directly after the `('.
---------- Buffer: foo ----------
This has too many -!-spaces
This has too many spaces at the start of (-!- this list)
---------- Buffer: foo ----------
(fixup-whitespace)
=> nil
(fixup-whitespace)
=> nil
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
- Command: just-one-space
This command replaces any spaces and tabs around point with a
single space. It returns `nil'.
- Command: delete-blank-lines
This function deletes blank lines surrounding point. If point is
on a blank line with one or more blank lines before or after it,
then all but one of them are deleted. If point is on an isolated
blank line, then it is deleted. If point is on a nonblank line,
the command deletes all blank lines following it.
A blank line is defined as a line containing only tabs and spaces.
`delete-blank-lines' returns `nil'.
The Kill Ring
=============
"Kill functions" delete text like the deletion functions, but save
it so that the user can reinsert it by "yanking". Most of these
functions have `kill-' in their name. By contrast, the functions whose
names start with `delete-' normally do not save text for yanking
(though they can still be undone); these are "deletion" functions.
Most of the kill commands are primarily for interactive use, and are
not described here. What we do describe are the functions provided for
use in writing such commands. You can use these functions to write
commands for killing text. When you need to delete text for internal
purposes within a Lisp function, you should normally use deletion
functions, so as not to disturb the kill ring contents. *Note
Deletion::.
Killed text is saved for later yanking in the "kill ring". This is
a list that holds a number of recent kills, not just the last text
kill. We call this a "ring" because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
`kill-ring', and can be operated on with the usual functions for lists;
there are also specialized functions, described in this section, that
treat it as a ring.
Some people think this use of the word "kill" is unfortunate, since
it refers to operations that specifically _do not_ destroy the entities
"killed". This is in sharp contrast to ordinary life, in which death
is permanent and "killed" entities do not come back to life.
Therefore, other metaphors have been proposed. For example, the term
"cut ring" makes sense to people who, in pre-computer days, used
scissors and paste to cut up and rearrange manuscripts. However, it
would be difficult to change the terminology now.
Kill Ring Concepts
------------------
The kill ring records killed text as strings in a list, most recent
first. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "even older text")
When the list reaches `kill-ring-max' entries in length, adding a new
entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill
command makes a new entry in the kill ring. Multiple kill commands in
succession build up a single kill-ring entry, which would be yanked as a
unit; the second and subsequent consecutive kill commands add text to
the entry made by the first one.
For yanking, one entry in the kill ring is designated the "front" of
the ring. Some yank commands "rotate" the ring by designating a
different element as the "front." But this virtual rotation doesn't
change the list itself--the most recent entry always comes first in the
list.
Functions for Killing
---------------------
`kill-region' is the usual subroutine for killing text. Any command
that calls this function is a "kill command" (and should probably have
`kill' in its name). `kill-region' puts the newly killed text in a new
element at the beginning of the kill ring or adds it to the most recent
element. It determines automatically (using `last-command') whether
the previous command was a kill command, and if so appends the killed
text to the most recent entry.
- Command: kill-region start end
This function kills the text in the region defined by START and
END. The text is deleted but saved in the kill ring, along with
its text properties. The value is always `nil'.
In an interactive call, START and END are point and the mark.
If the buffer or text is read-only, `kill-region' modifies the kill
ring just the same, then signals an error without modifying the
buffer. This is convenient because it lets the user use a series
of kill commands to copy text from a read-only buffer into the
kill ring.
- User Option: kill-read-only-ok
If this option is non-`nil', `kill-region' does not signal an
error if the buffer or text is read-only. Instead, it simply
returns, updating the kill ring but not changing the buffer.
- Command: copy-region-as-kill start end
This command saves the region defined by START and END on the kill
ring (including text properties), but does not delete the text
from the buffer. It returns `nil'. It also indicates the extent
of the text copied by moving the cursor momentarily, or by
displaying a message in the echo area.
The command does not set `this-command' to `kill-region', so a
subsequent kill command does not append to the same kill ring
entry.
Don't call `copy-region-as-kill' in Lisp programs unless you aim to
support Emacs 18. For newer Emacs versions, it is better to use
`kill-new' or `kill-append' instead. *Note Low-Level Kill Ring::.
Functions for Yanking
---------------------
"Yanking" means reinserting an entry of previously killed text from
the kill ring. The text properties are copied too.
- Command: yank &optional arg
This command inserts before point the text in the first entry in
the kill ring. It positions the mark at the beginning of that
text, and point at the end.
If ARG is a list (which occurs interactively when the user types
`C-u' with no digits), then `yank' inserts the text as described
above, but puts point before the yanked text and puts the mark
after it.
If ARG is a number, then `yank' inserts the ARGth most recently
killed text--the ARGth element of the kill ring list.
`yank' does not alter the contents of the kill ring or rotate it.
It returns `nil'.
- Command: yank-pop arg
This command replaces the just-yanked entry from the kill ring
with a different entry from the kill ring.
This is allowed only immediately after a `yank' or another
`yank-pop'. At such a time, the region contains text that was just
inserted by yanking. `yank-pop' deletes that text and inserts in
its place a different piece of killed text. It does not add the
deleted text to the kill ring, since it is already in the kill
ring somewhere.
If ARG is `nil', then the replacement text is the previous element
of the kill ring. If ARG is numeric, the replacement is the ARGth
previous kill. If ARG is negative, a more recent kill is the
replacement.
The sequence of kills in the kill ring wraps around, so that after
the oldest one comes the newest one, and before the newest one
goes the oldest.
The return value is always `nil'.
Low-Level Kill Ring
-------------------
These functions and variables provide access to the kill ring at a
lower level, but still convenient for use in Lisp programs, because they
take care of interaction with window system selections (*note Window
System Selections::).
- Function: current-kill n &optional do-not-move
The function `current-kill' rotates the yanking pointer, which
designates the "front" of the kill ring, by N places (from newer
kills to older ones), and returns the text at that place in the
ring.
If the optional second argument DO-NOT-MOVE is non-`nil', then
`current-kill' doesn't alter the yanking pointer; it just returns
the Nth kill, counting from the current yanking pointer.
If N is zero, indicating a request for the latest kill,
`current-kill' calls the value of `interprogram-paste-function'
(documented below) before consulting the kill ring.
- Function: kill-new string
This function puts the text STRING into the kill ring as a new
entry at the front of the ring. It discards the oldest entry if
appropriate. It also invokes the value of
`interprogram-cut-function' (see below).
- Function: kill-append string before-p
This function appends the text STRING to the first entry in the
kill ring. Normally STRING goes at the end of the entry, but if
BEFORE-P is non-`nil', it goes at the beginning. This function
also invokes the value of `interprogram-cut-function' (see below).
- Variable: interprogram-paste-function
This variable provides a way of transferring killed text from other
programs, when you are using a window system. Its value should be
`nil' or a function of no arguments.
If the value is a function, `current-kill' calls it to get the
"most recent kill". If the function returns a non-`nil' value,
then that value is used as the "most recent kill". If it returns
`nil', then the first element of `kill-ring' is used.
The normal use of this hook is to get the window system's primary
selection as the most recent kill, even if the selection belongs to
another application. *Note Window System Selections::.
- Variable: interprogram-cut-function
This variable provides a way of communicating killed text to other
programs, when you are using a window system. Its value should be
`nil' or a function of one argument.
If the value is a function, `kill-new' and `kill-append' call it
with the new first element of the kill ring as an argument.
The normal use of this hook is to set the window system's primary
selection from the newly killed text. *Note Window System
Selections::.
Internals of the Kill Ring
--------------------------
The variable `kill-ring' holds the kill ring contents, in the form
of a list of strings. The most recent kill is always at the front of
the list.
The `kill-ring-yank-pointer' variable points to a link in the kill
ring list, whose CAR is the text to yank next. We say it identifies
the "front" of the ring. Moving `kill-ring-yank-pointer' to a
different link is called "rotating the kill ring". We call the kill
ring a "ring" because the functions that move the yank pointer wrap
around from the end of the list to the beginning, or vice-versa.
Rotation of the kill ring is virtual; it does not change the value of
`kill-ring'.
Both `kill-ring' and `kill-ring-yank-pointer' are Lisp variables
whose values are normally lists. The word "pointer" in the name of the
`kill-ring-yank-pointer' indicates that the variable's purpose is to
identify one element of the list for use by the next yank command.
The value of `kill-ring-yank-pointer' is always `eq' to one of the
links in the kill ring list. The element it identifies is the CAR of
that link. Kill commands, which change the kill ring, also set this
variable to the value of `kill-ring'. The effect is to rotate the ring
so that the newly killed text is at the front.
Here is a diagram that shows the variable `kill-ring-yank-pointer'
pointing to the second entry in the kill ring `("some text" "a
different piece of text" "yet older text")'.
kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
This state of affairs might occur after `C-y' (`yank') immediately
followed by `M-y' (`yank-pop').
- Variable: kill-ring
This variable holds the list of killed text sequences, most
recently killed first.
- Variable: kill-ring-yank-pointer
This variable's value indicates which element of the kill ring is
at the "front" of the ring for yanking. More precisely, the value
is a tail of the value of `kill-ring', and its CAR is the kill
string that `C-y' should yank.
- User Option: kill-ring-max
The value of this variable is the maximum length to which the kill
ring can grow, before elements are thrown away at the end. The
default value for `kill-ring-max' is 30.
Undo
====
Most buffers have an "undo list", which records all changes made to
the buffer's text so that they can be undone. (The buffers that don't
have one are usually special-purpose buffers for which Emacs assumes
that undoing is not useful.) All the primitives that modify the text
in the buffer automatically add elements to the front of the undo list,
which is in the variable `buffer-undo-list'.
- Variable: buffer-undo-list
This variable's value is the undo list of the current buffer. A
value of `t' disables the recording of undo information.
Here are the kinds of elements an undo list can have:
`POSITION'
This kind of element records a previous value of point; undoing
this element moves point to POSITION. Ordinary cursor motion does
not make any sort of undo record, but deletion operations use
these entries to record where point was before the command.
`(BEG . END)'
This kind of element indicates how to delete text that was
inserted. Upon insertion, the text occupied the range BEG-END in
the buffer.
`(TEXT . POSITION)'
This kind of element indicates how to reinsert text that was
deleted. The deleted text itself is the string TEXT. The place to
reinsert it is `(abs POSITION)'.
`(t HIGH . LOW)'
This kind of element indicates that an unmodified buffer became
modified. The elements HIGH and LOW are two integers, each
recording 16 bits of the visited file's modification time as of
when it was previously visited or saved. `primitive-undo' uses
those values to determine whether to mark the buffer as unmodified
once again; it does so only if the file's modification time
matches those numbers.
`(nil PROPERTY VALUE BEG . END)'
This kind of element records a change in a text property. Here's
how you might undo the change:
(put-text-property BEG END PROPERTY VALUE)
`(MARKER . ADJUSTMENT)'
This kind of element records the fact that the marker MARKER was
relocated due to deletion of surrounding text, and that it moved
ADJUSTMENT character positions. Undoing this element moves MARKER
- ADJUSTMENT characters.
`nil'
This element is a boundary. The elements between two boundaries
are called a "change group"; normally, each change group
corresponds to one keyboard command, and undo commands normally
undo an entire group as a unit.
- Function: undo-boundary
This function places a boundary element in the undo list. The undo
command stops at such a boundary, and successive undo commands undo
to earlier and earlier boundaries. This function returns `nil'.
The editor command loop automatically creates an undo boundary
before each key sequence is executed. Thus, each undo normally
undoes the effects of one command. Self-inserting input
characters are an exception. The command loop makes a boundary
for the first such character; the next 19 consecutive
self-inserting input characters do not make boundaries, and then
the 20th does, and so on as long as self-inserting characters
continue.
All buffer modifications add a boundary whenever the previous
undoable change was made in some other buffer. This is to ensure
that each command makes a boundary in each buffer where it makes
changes.
Calling this function explicitly is useful for splitting the
effects of a command into more than one unit. For example,
`query-replace' calls `undo-boundary' after each replacement, so
that the user can undo individual replacements one by one.
- Function: primitive-undo count list
This is the basic function for undoing elements of an undo list.
It undoes the first COUNT elements of LIST, returning the rest of
LIST. You could write this function in Lisp, but it is convenient
to have it in C.
`primitive-undo' adds elements to the buffer's undo list when it
changes the buffer. Undo commands avoid confusion by saving the
undo list value at the beginning of a sequence of undo operations.
Then the undo operations use and update the saved value. The new
elements added by undoing are not part of this saved value, so
they don't interfere with continuing to undo.
Maintaining Undo Lists
======================
This section describes how to enable and disable undo information for
a given buffer. It also explains how the undo list is truncated
automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
`buffer-undo-list' yourself.
- Command: buffer-enable-undo &optional buffer-or-name
This command enables recording undo information for buffer
BUFFER-OR-NAME, so that subsequent changes can be undone. If no
argument is supplied, then the current buffer is used. This
function does nothing if undo recording is already enabled in the
buffer. It returns `nil'.
In an interactive call, BUFFER-OR-NAME is the current buffer. You
cannot specify any other buffer.
- Command: buffer-disable-undo &optional buffer
- Command: buffer-flush-undo &optional buffer
This function discards the undo list of BUFFER, and disables
further recording of undo information. As a result, it is no
longer possible to undo either previous changes or any subsequent
changes. If the undo list of BUFFER is already disabled, this
function has no effect.
This function returns `nil'.
The name `buffer-flush-undo' is not considered obsolete, but the
preferred name is `buffer-disable-undo'.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the "size" of
an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Two variables control the range of acceptable
sizes: `undo-limit' and `undo-strong-limit'.
- Variable: undo-limit
This is the soft limit for the acceptable size of an undo list.
The change group at which this size is exceeded is the last one
kept.
- Variable: undo-strong-limit
This is the upper limit for the acceptable size of an undo list.
The change group at which this size is exceeded is discarded
itself (along with all older change groups). There is one
exception: the very latest change group is never discarded no
matter how big it is.
Filling
=======
"Filling" means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be "justified", which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable `fill-column'. For
ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (*note Auto Filling::) to fill text
automatically as you insert it, but changes to existing text may leave
it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(*note Margins::). If the current justification style is `none', the
filling functions don't actually do anything.
Several of the filling functions have an argument JUSTIFY. If it is
non-`nil', that requests some kind of justification. It can be `left',
`right', `full', or `center', to request a specific style of
justification. If it is `t', that means to use the current
justification style for this part of the text (see
`current-justification', below). Any other value is treated as `full'.
When you call the filling functions interactively, using a prefix
argument implies the value `full' for JUSTIFY.
- Command: fill-paragraph justify
This command fills the paragraph at or after point. If JUSTIFY is
non-`nil', each line is justified as well. It uses the ordinary
paragraph motion commands to find paragraph boundaries. *Note
Paragraphs: (emacs)Paragraphs.
- Command: fill-region start end &optional justify nosqueeze to-eop
This command fills each of the paragraphs in the region from START
to END. It justifies as well if JUSTIFY is non-`nil'.
If NOSQUEEZE is non-`nil', that means to leave whitespace other
than line breaks untouched. If TO-EOP is non-`nil', that means to
keep filling to the end of the paragraph--or the next hard
newline, if `use-hard-newlines' is enabled (see below).
The variable `paragraph-separate' controls how to distinguish
paragraphs. *Note Standard Regexps::.
- Command: fill-individual-paragraphs start end &optional justify
citation-regexp
This command fills each paragraph in the region according to its
individual fill prefix. Thus, if the lines of a paragraph were
indented with spaces, the filled paragraph will remain indented in
the same fashion.
The first two arguments, START and END, are the beginning and end
of the region to be filled. The third and fourth arguments,
JUSTIFY and CITATION-REGEXP, are optional. If JUSTIFY is
non-`nil', the paragraphs are justified as well as filled. If
CITATION-REGEXP is non-`nil', it means the function is operating
on a mail message and therefore should not fill the header lines.
If CITATION-REGEXP is a string, it is used as a regular
expression; if it matches the beginning of a line, that line is
treated as a citation marker.
Ordinarily, `fill-individual-paragraphs' regards each change in
indentation as starting a new paragraph. If
`fill-individual-varying-indent' is non-`nil', then only separator
lines separate paragraphs. That mode can handle indented
paragraphs with additional indentation on the first line.
- User Option: fill-individual-varying-indent
This variable alters the action of `fill-individual-paragraphs' as
described above.
- Command: fill-region-as-paragraph start end &optional justify
nosqueeze squeeze-after
This command considers a region of text as a single paragraph and
fills it. If the region was made up of many paragraphs, the blank
lines between paragraphs are removed. This function justifies as
well as filling when JUSTIFY is non-`nil'.
In an interactive call, any prefix argument requests justification.
If NOSQUEEZE is non-`nil', that means to leave whitespace other
than line breaks untouched. If SQUEEZE-AFTER is non-`nil', it
specifies a position in the region, and means don't canonicalize
spaces before that position.
In Adaptive Fill mode, this command calls `fill-context-prefix' to
choose a fill prefix by default. *Note Adaptive Fill::.
- Command: justify-current-line &optional how eop nosqueeze
This command inserts spaces between the words of the current line
so that the line ends exactly at `fill-column'. It returns `nil'.
The argument HOW, if non-`nil' specifies explicitly the style of
justification. It can be `left', `right', `full', `center', or
`none'. If it is `t', that means to do follow specified
justification style (see `current-justification', below). `nil'
means to do full justification.
If EOP is non-`nil', that means do left-justification if
`current-justification' specifies full justification. This is used
for the last line of a paragraph; even if the paragraph as a whole
is fully justified, the last line should not be.
If NOSQUEEZE is non-`nil', that means do not change interior
whitespace.
- User Option: default-justification
This variable's value specifies the style of justification to use
for text that doesn't specify a style with a text property. The
possible values are `left', `right', `full', `center', or `none'.
The default value is `left'.
- Function: current-justification
This function returns the proper justification style to use for
filling the text around point.
- User Option: sentence-end-double-space
If this variable is non-`nil', a period followed by just one space
does not count as the end of a sentence, and the filling functions
avoid breaking the line at such a place.
- Variable: fill-paragraph-function
This variable provides a way for major modes to override the
filling of paragraphs. If the value is non-`nil',
`fill-paragraph' calls this function to do the work. If the
function returns a non-`nil' value, `fill-paragraph' assumes the
job is done, and immediately returns that value.
The usual use of this feature is to fill comments in programming
language modes. If the function needs to fill a paragraph in the
usual way, it can do so as follows:
(let ((fill-paragraph-function nil))
(fill-paragraph arg))
- Variable: use-hard-newlines
If this variable is non-`nil', the filling functions do not delete
newlines that have the `hard' text property. These "hard
newlines" act as paragraph separators.
Margins for Filling
===================
- User Option: fill-prefix
This buffer-local variable specifies a string of text that appears
at the beginning of normal text lines and should be disregarded
when filling them. Any line that fails to start with the fill
prefix is considered the start of a paragraph; so is any line that
starts with the fill prefix followed by additional whitespace.
Lines that start with the fill prefix but no additional whitespace
are ordinary text lines that can be filled together. The
resulting filled lines also start with the fill prefix.
The fill prefix follows the left margin whitespace, if any.
- User Option: fill-column
This buffer-local variable specifies the maximum width of filled
lines. Its value should be an integer, which is a number of
columns. All the filling, justification, and centering commands
are affected by this variable, including Auto Fill mode (*note
Auto Filling::).
As a practical matter, if you are writing text for other people to
read, you should set `fill-column' to no more than 70. Otherwise
the line will be too long for people to read comfortably, and this
can make the text seem clumsy.
- Variable: default-fill-column
The value of this variable is the default value for `fill-column'
in buffers that do not override it. This is the same as
`(default-value 'fill-column)'.
The default value for `default-fill-column' is 70.
- Command: set-left-margin from to margin
This sets the `left-margin' property on the text from FROM to TO
to the value MARGIN. If Auto Fill mode is enabled, this command
also refills the region to fit the new margin.
- Command: set-right-margin from to margin
This sets the `right-margin' property on the text from FROM to TO
to the value MARGIN. If Auto Fill mode is enabled, this command
also refills the region to fit the new margin.
- Function: current-left-margin
This function returns the proper left margin value to use for
filling the text around point. The value is the sum of the
`left-margin' property of the character at the start of the
current line (or zero if none), and the value of the variable
`left-margin'.
- Function: current-fill-column
This function returns the proper fill column value to use for
filling the text around point. The value is the value of the
`fill-column' variable, minus the value of the `right-margin'
property of the character after point.
- Command: move-to-left-margin &optional n force
This function moves point to the left margin of the current line.
The column moved to is determined by calling the function
`current-left-margin'. If the argument N is non-`nil',
`move-to-left-margin' moves forward N-1 lines first.
If FORCE is non-`nil', that says to fix the line's indentation if
that doesn't match the left margin value.
- Function: delete-to-left-margin &optional from to
This function removes left margin indentation from the text between
FROM and TO. The amount of indentation to delete is determined by
calling `current-left-margin'. In no case does this function
delete non-whitespace. If FROM and TO are omitted, they default
to the whole buffer.
- Function: indent-to-left-margin
This is the default `indent-line-function', used in Fundamental
mode, Text mode, etc. Its effect is to adjust the indentation at
the beginning of the current line to the value specified by the
variable `left-margin'. This may involve either inserting or
deleting whitespace.
- Variable: left-margin
This variable specifies the base left margin column. In
Fundamental mode, `C-j' indents to this column. This variable
automatically becomes buffer-local when set in any fashion.
- Variable: fill-nobreak-predicate
This variable gives major modes a way to specify not to break a
line at certain places. Its value should be a function. This
function is called during filling, with no arguments and with
point located at the place where a break is being considered. If
the function returns non-`nil', then the line won't be broken
there.
Adaptive Fill Mode
==================
Adaptive Fill mode chooses a fill prefix automatically from the text
in each paragraph being filled.
- User Option: adaptive-fill-mode
Adaptive Fill mode is enabled when this variable is non-`nil'. It
is `t' by default.
- Function: fill-context-prefix from to
This function implements the heart of Adaptive Fill mode; it
chooses a fill prefix based on the text between FROM and TO. It
does this by looking at the first two lines of the paragraph,
based on the variables described below.
- User Option: adaptive-fill-regexp
This variable holds a regular expression to control Adaptive Fill
mode. Adaptive Fill mode matches this regular expression against
the text starting after the left margin whitespace (if any) on a
line; the characters it matches are that line's candidate for the
fill prefix.
- User Option: adaptive-fill-first-line-regexp
In a one-line paragraph, if the candidate fill prefix matches this
regular expression, or if it matches `comment-start-skip', then it
is used--otherwise, spaces amounting to the same width are used
instead.
However, the fill prefix is never taken from a one-line paragraph
if it would act as a paragraph starter on subsequent lines.
- User Option: adaptive-fill-function
You can specify more complex ways of choosing a fill prefix
automatically by setting this variable to a function. The
function is called when `adaptive-fill-regexp' does not match,
with point after the left margin of a line, and it should return
the appropriate fill prefix based on that line. If it returns
`nil', that means it sees no fill prefix in that line.
Auto Filling
============
Auto Fill mode is a minor mode that fills lines automatically as text
is inserted. This section describes the hook used by Auto Fill mode.
For a description of functions that you can call explicitly to fill and
justify existing text, see *Note Filling::.
Auto Fill mode also enables the functions that change the margins and
justification style to refill portions of the text. *Note Margins::.
- Variable: auto-fill-function
The value of this variable should be a function (of no arguments)
to be called after self-inserting a character from the table
`auto-fill-chars'. It may be `nil', in which case nothing special
is done in that case.
The value of `auto-fill-function' is `do-auto-fill' when Auto-Fill
mode is enabled. That is a function whose sole purpose is to
implement the usual strategy for breaking a line.
In older Emacs versions, this variable was named
`auto-fill-hook', but since it is not called with the
standard convention for hooks, it was renamed to
`auto-fill-function' in version 19.
- Variable: normal-auto-fill-function
This variable specifies the function to use for
`auto-fill-function', if and when Auto Fill is turned on. Major
modes can set buffer-local values for this variable to alter how
Auto Fill works.
- Variable: auto-fill-chars
A char table of characters which invoke `auto-fill-function' when
self-inserted--space and newline in most language environments.
They have an entry `t' in the table.
Sorting Text
============
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function `sort', which rearranges
the order of the elements of a list (*note Rearrangement::). The
values returned by these functions are not meaningful.
- Function: sort-subr reverse nextrecfun endrecfun &optional
startkeyfun endkeyfun
This function is the general text-sorting routine that subdivides a
buffer into records and then sorts them. Most of the commands in
this section use this function.
To understand how `sort-subr' works, consider the whole accessible
portion of the buffer as being divided into disjoint pieces called
"sort records". The records may or may not be contiguous, but they
must not overlap. A portion of each sort record (perhaps all of
it) is designated as the sort key. Sorting rearranges the records
in order by their sort keys.
Usually, the records are rearranged in order of ascending sort key.
If the first argument to the `sort-subr' function, REVERSE, is
non-`nil', the sort records are rearranged in order of descending
sort key.
The next four arguments to `sort-subr' are functions that are
called to move point across a sort record. They are called many
times from within `sort-subr'.
1. NEXTRECFUN is called with point at the end of a record. This
function moves point to the start of the next record. The
first record is assumed to start at the position of point
when `sort-subr' is called. Therefore, you should usually
move point to the beginning of the buffer before calling
`sort-subr'.
This function can indicate there are no more sort records by
leaving point at the end of the buffer.
2. ENDRECFUN is called with point within a record. It moves
point to the end of the record.
3. STARTKEYFUN is called to move point from the start of a
record to the start of the sort key. This argument is
optional; if it is omitted, the whole record is the sort key.
If supplied, the function should either return a non-`nil'
value to be used as the sort key, or return `nil' to indicate
that the sort key is in the buffer starting at point. In the
latter case, ENDKEYFUN is called to find the end of the sort
key.
4. ENDKEYFUN is called to move point from the start of the sort
key to the end of the sort key. This argument is optional.
If STARTKEYFUN returns `nil' and this argument is omitted (or
`nil'), then the sort key extends to the end of the record.
There is no need for ENDKEYFUN if STARTKEYFUN returns a
non-`nil' value.
As an example of `sort-subr', here is the complete function
definition for `sort-lines':
;; Note that the first two lines of doc string
;; are effectively one line when viewed by a user.
(defun sort-lines (reverse beg end)
"Sort lines in region alphabetically;\
argument means descending order.
Called from a program, there are three arguments:
REVERSE (non-nil means reverse order),\
BEG and END (region to sort).
The variable `sort-fold-case' determines\
whether alphabetic case affects
the sort order.
(interactive "P\nr")
(save-excursion
(save-restriction
(narrow-to-region beg end)
(goto-char (point-min))
(sort-subr reverse 'forward-line 'end-of-line))))
Here `forward-line' moves point to the start of the next record,
and `end-of-line' moves point to the end of record. We do not pass
the arguments STARTKEYFUN and ENDKEYFUN, because the entire record
is used as the sort key.
The `sort-paragraphs' function is very much the same, except that
its `sort-subr' call looks like this:
(sort-subr reverse
(function
(lambda ()
(while (and (not (eobp))
(looking-at paragraph-separate))
(forward-line 1))))
'forward-paragraph)
Markers pointing into any sort records are left with no useful
position after `sort-subr' returns.
- User Option: sort-fold-case
If this variable is non-`nil', `sort-subr' and the other buffer
sorting functions ignore case when comparing strings.
- Command: sort-regexp-fields reverse record-regexp key-regexp start
end
This command sorts the region between START and END alphabetically
as specified by RECORD-REGEXP and KEY-REGEXP. If REVERSE is a
negative integer, then sorting is in reverse order.
Alphabetical sorting means that two sort keys are compared by
comparing the first characters of each, the second characters of
each, and so on. If a mismatch is found, it means that the sort
keys are unequal; the sort key whose character is less at the
point of first mismatch is the lesser sort key. The individual
characters are compared according to their numerical character
codes in the Emacs character set.
The value of the RECORD-REGEXP argument specifies how to divide
the buffer into sort records. At the end of each record, a search
is done for this regular expression, and the text that matches it
is taken as the next record. For example, the regular expression
`^.+$', which matches lines with at least one character besides a
newline, would make each such line into a sort record. *Note
Regular Expressions::, for a description of the syntax and meaning
of regular expressions.
The value of the KEY-REGEXP argument specifies what part of each
record is the sort key. The KEY-REGEXP could match the whole
record, or only a part. In the latter case, the rest of the
record has no effect on the sorted order of records, but it is
carried along when the record moves to its new position.
The KEY-REGEXP argument can refer to the text matched by a
subexpression of RECORD-REGEXP, or it can be a regular expression
on its own.
If KEY-REGEXP is:
`\DIGIT'
then the text matched by the DIGITth `\(...\)' parenthesis
grouping in RECORD-REGEXP is the sort key.
`\&'
then the whole record is the sort key.
a regular expression
then `sort-regexp-fields' searches for a match for the regular
expression within the record. If such a match is found, it
is the sort key. If there is no match for KEY-REGEXP within
a record then that record is ignored, which means its
position in the buffer is not changed. (The other records
may move around it.)
For example, if you plan to sort all the lines in the region by the
first word on each line starting with the letter `f', you should
set RECORD-REGEXP to `^.*$' and set KEY-REGEXP to `\<f\w*\>'. The
resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
(region-beginning)
(region-end))
If you call `sort-regexp-fields' interactively, it prompts for
RECORD-REGEXP and KEY-REGEXP in the minibuffer.
- Command: sort-lines reverse start end
This command alphabetically sorts lines in the region between
START and END. If REVERSE is non-`nil', the sort is in reverse
order.
- Command: sort-paragraphs reverse start end
This command alphabetically sorts paragraphs in the region between
START and END. If REVERSE is non-`nil', the sort is in reverse
order.
- Command: sort-pages reverse start end
This command alphabetically sorts pages in the region between
START and END. If REVERSE is non-`nil', the sort is in reverse
order.
- Command: sort-fields field start end
This command sorts lines in the region between START and END,
comparing them alphabetically by the FIELDth field of each line.
Fields are separated by whitespace and numbered starting from 1.
If FIELD is negative, sorting is by the -FIELDth field from the
end of the line. This command is useful for sorting tables.
- Command: sort-numeric-fields field start end
This command sorts lines in the region between START and END,
comparing them numerically by the FIELDth field of each line. The
specified field must contain a number in each line of the region.
Fields are separated by whitespace and numbered starting from 1.
If FIELD is negative, sorting is by the -FIELDth field from the
end of the line. This command is useful for sorting tables.
- Command: sort-columns reverse &optional beg end
This command sorts the lines in the region between BEG and END,
comparing them alphabetically by a certain range of columns. The
column positions of BEG and END bound the range of columns to sort
on.
If REVERSE is non-`nil', the sort is in reverse order.
One unusual thing about this command is that the entire line
containing position BEG, and the entire line containing position
END, are included in the region sorted.
Note that `sort-columns' uses the `sort' utility program, and so
cannot work properly on text containing tab characters. Use `M-x
untabify' to convert tabs to spaces before sorting.
Counting Columns
================
The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of `ctl-arrow',
and tabs count as occupying a number of columns that depends on the
value of `tab-width' and on the column where the tab begins. *Note
Usual Display::.
Column number computations ignore the width of the window and the
amount of horizontal scrolling. Consequently, a column value can be
arbitrarily high. The first (or leftmost) column is numbered 0.
- Function: current-column
This function returns the horizontal position of point, measured in
columns, counting from 0 at the left margin. The column position
is the sum of the widths of all the displayed representations of
the characters between the start of the current line and point.
For an example of using `current-column', see the description of
`count-lines' in *Note Text Lines::.
- Function: move-to-column column &optional force
This function moves point to COLUMN in the current line. The
calculation of COLUMN takes into account the widths of the
displayed representations of the characters between the start of
the line and point.
If column COLUMN is beyond the end of the line, point moves to the
end of the line. If COLUMN is negative, point moves to the
beginning of the line.
If it is impossible to move to column COLUMN because that is in
the middle of a multicolumn character such as a tab, point moves
to the end of that character. However, if FORCE is non-`nil', and
COLUMN is in the middle of a tab, then `move-to-column' converts
the tab into spaces so that it can move precisely to column
COLUMN. Other multicolumn characters can cause anomalies despite
FORCE, since there is no way to split them.
The argument FORCE also has an effect if the line isn't long
enough to reach column COLUMN; if it is `t', that means to add
whitespace at the end of the line to reach that column.
If COLUMN is not an integer, an error is signaled.
The return value is the column number actually moved to.
Indentation
===========
The indentation functions are used to examine, move to, and change
whitespace that is at the beginning of a line. Some of the functions
can also change whitespace elsewhere on a line. Columns and indentation
count from zero at the left margin.
Indentation Primitives
----------------------
This section describes the primitive functions used to count and
insert indentation. The functions in the following sections use these
primitives. *Note Width::, for related functions.
- Function: current-indentation
This function returns the indentation of the current line, which is
the horizontal position of the first nonblank character. If the
contents are entirely blank, then this is the horizontal position
of the end of the line.
- Command: indent-to column &optional minimum
This function indents from point with tabs and spaces until COLUMN
is reached. If MINIMUM is specified and non-`nil', then at least
that many spaces are inserted even if this requires going beyond
COLUMN. Otherwise the function does nothing if point is already
beyond COLUMN. The value is the column at which the inserted
indentation ends.
The inserted whitespace characters inherit text properties from the
surrounding text (usually, from the preceding text only). *Note
Sticky Properties::.
- User Option: indent-tabs-mode
If this variable is non-`nil', indentation functions can insert
tabs as well as spaces. Otherwise, they insert only spaces.
Setting this variable automatically makes it buffer-local in the
current buffer.
Indentation Controlled by Major Mode
------------------------------------
An important function of each major mode is to customize the <TAB>
key to indent properly for the language being edited. This section
describes the mechanism of the <TAB> key and how to control it. The
functions in this section return unpredictable values.
- Variable: indent-line-function
This variable's value is the function to be used by <TAB> (and
various commands) to indent the current line. The command
`indent-according-to-mode' does no more than call this function.
In Lisp mode, the value is the symbol `lisp-indent-line'; in C
mode, `c-indent-line'; in Fortran mode, `fortran-indent-line'. In
Fundamental mode, Text mode, and many other modes with no standard
for indentation, the value is `indent-to-left-margin' (which is the
default value).
- Command: indent-according-to-mode
This command calls the function in `indent-line-function' to
indent the current line in a way appropriate for the current major
mode.
- Command: indent-for-tab-command
This command calls the function in `indent-line-function' to indent
the current line; however, if that function is
`indent-to-left-margin', `insert-tab' is called instead. (That is
a trivial command that inserts a tab character.)
- Command: newline-and-indent
This function inserts a newline, then indents the new line (the one
following the newline just inserted) according to the major mode.
It does indentation by calling the current `indent-line-function'.
In programming language modes, this is the same thing <TAB> does,
but in some text modes, where <TAB> inserts a tab,
`newline-and-indent' indents to the column specified by
`left-margin'.
- Command: reindent-then-newline-and-indent
This command reindents the current line, inserts a newline at
point, and then indents the new line (the one following the
newline just inserted).
This command does indentation on both lines according to the
current major mode, by calling the current value of
`indent-line-function'. In programming language modes, this is
the same thing <TAB> does, but in some text modes, where <TAB>
inserts a tab, `reindent-then-newline-and-indent' indents to the
column specified by `left-margin'.
Indenting an Entire Region
--------------------------
This section describes commands that indent all the lines in the
region. They return unpredictable values.
- Command: indent-region start end to-column
This command indents each nonblank line starting between START
(inclusive) and END (exclusive). If TO-COLUMN is `nil',
`indent-region' indents each nonblank line by calling the current
mode's indentation function, the value of `indent-line-function'.
If TO-COLUMN is non-`nil', it should be an integer specifying the
number of columns of indentation; then this function gives each
line exactly that much indentation, by either adding or deleting
whitespace.
If there is a fill prefix, `indent-region' indents each line by
making it start with the fill prefix.
- Variable: indent-region-function
The value of this variable is a function that can be used by
`indent-region' as a short cut. It should take two arguments, the
start and end of the region. You should design the function so
that it will produce the same results as indenting the lines of the
region one by one, but presumably faster.
If the value is `nil', there is no short cut, and `indent-region'
actually works line by line.
A short-cut function is useful in modes such as C mode and Lisp
mode, where the `indent-line-function' must scan from the
beginning of the function definition: applying it to each line
would be quadratic in time. The short cut can update the scan
information as it moves through the lines indenting them; this
takes linear time. In a mode where indenting a line individually
is fast, there is no need for a short cut.
`indent-region' with a non-`nil' argument TO-COLUMN has a
different meaning and does not use this variable.
- Command: indent-rigidly start end count
This command indents all lines starting between START (inclusive)
and END (exclusive) sideways by COUNT columns. This "preserves
the shape" of the affected region, moving it as a rigid unit.
Consequently, this command is useful not only for indenting
regions of unindented text, but also for indenting regions of
formatted code.
For example, if COUNT is 3, this command adds 3 columns of
indentation to each of the lines beginning in the region specified.
In Mail mode, `C-c C-y' (`mail-yank-original') uses
`indent-rigidly' to indent the text copied from the message being
replied to.
- Function: indent-code-rigidly start end columns &optional
nochange-regexp
This is like `indent-rigidly', except that it doesn't alter lines
that start within strings or comments.
In addition, it doesn't alter a line if NOCHANGE-REGEXP matches at
the beginning of the line (if NOCHANGE-REGEXP is non-`nil').
Indentation Relative to Previous Lines
--------------------------------------
This section describes two commands that indent the current line
based on the contents of previous lines.
- Command: indent-relative &optional unindented-ok
This command inserts whitespace at point, extending to the same
column as the next "indent point" of the previous nonblank line.
An indent point is a non-whitespace character following
whitespace. The next indent point is the first one at a column
greater than the current column of point. For example, if point
is underneath and to the left of the first non-blank character of
a line of text, it moves to that column by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none
at a great enough column position), `indent-relative' either does
nothing (if UNINDENTED-OK is non-`nil') or calls
`tab-to-tab-stop'. Thus, if point is underneath and to the right
of the last column of a short line of text, this command ordinarily
moves point to the next tab stop by inserting whitespace.
The return value of `indent-relative' is unpredictable.
In the following example, point is at the beginning of the second
line:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
Evaluation of the expression `(indent-relative nil)' produces the
following:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
In this next example, point is between the `m' and `p' of `jumped':
This line is indented twelve spaces.
The quick brown fox jum-!-ped.
Evaluation of the expression `(indent-relative nil)' produces the
following:
This line is indented twelve spaces.
The quick brown fox jum -!-ped.
- Command: indent-relative-maybe
This command indents the current line like the previous nonblank
line, by calling `indent-relative' with `t' as the UNINDENTED-OK
argument. The return value is unpredictable.
If the previous nonblank line has no indent points beyond the
current column, this command does nothing.
Adjustable "Tab Stops"
----------------------
This section explains the mechanism for user-specified "tab stops"
and the mechanisms that use and set them. The name "tab stops" is used
because the feature is similar to that of the tab stops on a
typewriter. The feature works by inserting an appropriate number of
spaces and tab characters to reach the next tab stop column; it does not
affect the display of tab characters in the buffer (*note Usual
Display::). Note that the <TAB> character as input uses this tab stop
feature only in a few major modes, such as Text mode.
- Command: tab-to-tab-stop
This command inserts spaces or tabs before point, up to the next
tab stop column defined by `tab-stop-list'. It searches the list
for an element greater than the current column number, and uses
that element as the column to indent to. It does nothing if no
such element is found.
- User Option: tab-stop-list
This variable is the list of tab stop columns used by
`tab-to-tab-stops'. The elements should be integers in increasing
order. The tab stop columns need not be evenly spaced.
Use `M-x edit-tab-stops' to edit the location of tab stops
interactively.
Indentation-Based Motion Commands
---------------------------------
These commands, primarily for interactive use, act based on the
indentation in the text.
- Command: back-to-indentation
This command moves point to the first non-whitespace character in
the current line (which is the line in which point is located).
It returns `nil'.
- Command: backward-to-indentation arg
This command moves point backward ARG lines and then to the first
nonblank character on that line. It returns `nil'.
- Command: forward-to-indentation arg
This command moves point forward ARG lines and then to the first
nonblank character on that line. It returns `nil'.
Case Changes
============
The case change commands described here work on text in the current
buffer. *Note Case Conversion::, for case conversion functions that
work on strings and characters. *Note Case Tables::, for how to
customize which characters are upper or lower case and how to convert
them.
- Command: capitalize-region start end
This function capitalizes all words in the region defined by START
and END. To capitalize means to convert each word's first
character to upper case and convert the rest of each word to lower
case. The function returns `nil'.
If one end of the region is in the middle of a word, the part of
the word within the region is treated as an entire word.
When `capitalize-region' is called interactively, START and END
are point and the mark, with the smallest first.
---------- Buffer: foo ----------
This is the contents of the 5th foo.
---------- Buffer: foo ----------
(capitalize-region 1 44)
=> nil
---------- Buffer: foo ----------
This Is The Contents Of The 5th Foo.
---------- Buffer: foo ----------
- Command: downcase-region start end
This function converts all of the letters in the region defined by
START and END to lower case. The function returns `nil'.
When `downcase-region' is called interactively, START and END are
point and the mark, with the smallest first.
- Command: upcase-region start end
This function converts all of the letters in the region defined by
START and END to upper case. The function returns `nil'.
When `upcase-region' is called interactively, START and END are
point and the mark, with the smallest first.
- Command: capitalize-word count
This function capitalizes COUNT words after point, moving point
over as it does. To capitalize means to convert each word's first
character to upper case and convert the rest of each word to lower
case. If COUNT is negative, the function capitalizes the -COUNT
previous words but does not move point. The value is `nil'.
If point is in the middle of a word, the part of the word before
point is ignored when moving forward. The rest is treated as an
entire word.
When `capitalize-word' is called interactively, COUNT is set to
the numeric prefix argument.
- Command: downcase-word count
This function converts the COUNT words after point to all lower
case, moving point over as it does. If COUNT is negative, it
converts the -COUNT previous words but does not move point. The
value is `nil'.
When `downcase-word' is called interactively, COUNT is set to the
numeric prefix argument.
- Command: upcase-word count
This function converts the COUNT words after point to all upper
case, moving point over as it does. If COUNT is negative, it
converts the -COUNT previous words but does not move point. The
value is `nil'.
When `upcase-word' is called interactively, COUNT is set to the
numeric prefix argument.
Text Properties
===============
Each character position in a buffer or a string can have a "text
property list", much like the property list of a symbol (*note Property
Lists::). The properties belong to a particular character at a
particular place, such as, the letter `T' at the beginning of this
sentence or the first `o' in `foo'--if the same character occurs in two
different places, the two occurrences generally have different
properties.
Each property has a name and a value. Both of these can be any Lisp
object, but the name is normally a symbol. The usual way to access the
property list is to specify a name and ask what value corresponds to it.
If a character has a `category' property, we call it the "category"
of the character. It should be a symbol. The properties of the symbol
serve as defaults for the properties of the character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
`substring', `insert', and `buffer-substring'.
Examining Text Properties
-------------------------
The simplest way to examine text properties is to ask for the value
of a particular property of a particular character. For that, use
`get-text-property'. Use `text-properties-at' to get the entire
property list of a character. *Note Property Search::, for functions
to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that
positions in a string start from 0, whereas positions in a buffer start
from 1.
- Function: get-text-property pos prop &optional object
This function returns the value of the PROP property of the
character after position POS in OBJECT (a buffer or string). The
argument OBJECT is optional and defaults to the current buffer.
If there is no PROP property strictly speaking, but the character
has a category that is a symbol, then `get-text-property' returns
the PROP property of that symbol.
- Function: get-char-property pos prop &optional object
This function is like `get-text-property', except that it checks
overlays first and then text properties. *Note Overlays::.
The argument OBJECT may be a string, a buffer, or a window. If it
is a window, then the buffer displayed in that window is used for
text properties and overlays, but only the overlays active for
that window are considered. If OBJECT is a buffer, then all
overlays in that buffer are considered, as well as text
properties. If OBJECT is a string, only text properties are
considered, since strings never have overlays.
- Function: text-properties-at position &optional object
This function returns the entire property list of the character at
POSITION in the string or buffer OBJECT. If OBJECT is `nil', it
defaults to the current buffer.
- Variable: default-text-properties
This variable holds a property list giving default values for text
properties. Whenever a character does not specify a value for a
property, neither directly nor through a category symbol, the value
stored in this list is used instead. Here is an example:
(setq default-text-properties '(foo 69))
;; Make sure character 1 has no properties of its own.
(set-text-properties 1 2 nil)
;; What we get, when we ask, is the default value.
(get-text-property 1 'foo)
=> 69
Changing Text Properties
------------------------
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function `set-text-properties' (see
end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the
buffer (or string), and can affect how a buffer looks on the screen, any
change in buffer text properties marks the buffer as modified. Buffer
text property changes are undoable also (*note Undo::).
- Function: put-text-property start end prop value &optional object
This function sets the PROP property to VALUE for the text between
START and END in the string or buffer OBJECT. If OBJECT is `nil',
it defaults to the current buffer.
- Function: add-text-properties start end props &optional object
This function adds or overrides text properties for the text
between START and END in the string or buffer OBJECT. If OBJECT
is `nil', it defaults to the current buffer.
The argument PROPS specifies which properties to add. It should
have the form of a property list (*note Property Lists::): a list
whose elements include the property names followed alternately by
the corresponding values.
The return value is `t' if the function actually changed some
property's value; `nil' otherwise (if PROPS is `nil' or its values
agree with those in the text).
For example, here is how to set the `comment' and `face'
properties of a range of text:
(add-text-properties START END
'(comment t face highlight))
- Function: remove-text-properties start end props &optional object
This function deletes specified text properties from the text
between START and END in the string or buffer OBJECT. If OBJECT
is `nil', it defaults to the current buffer.
The argument PROPS specifies which properties to delete. It
should have the form of a property list (*note Property Lists::):
a list whose elements are property names alternating with
corresponding values. But only the names matter--the values that
accompany them are ignored. For example, here's how to remove the
`face' property.
(remove-text-properties START END '(face nil))
The return value is `t' if the function actually changed some
property's value; `nil' otherwise (if PROPS is `nil' or if no
character in the specified text had any of those properties).
To remove all text properties from certain text, use
`set-text-properties' and specify `nil' for the new property list.
- Function: set-text-properties start end props &optional object
This function completely replaces the text property list for the
text between START and END in the string or buffer OBJECT. If
OBJECT is `nil', it defaults to the current buffer.
The argument PROPS is the new property list. It should be a list
whose elements are property names alternating with corresponding
values.
After `set-text-properties' returns, all the characters in the
specified range have identical properties.
If PROPS is `nil', the effect is to get rid of all properties from
the specified range of text. Here's an example:
(set-text-properties START END nil)
The easiest way to make a string with text properties is with
`propertize':
- Function: propertize string &rest properties
This function returns a copy of STRING which has the text
properties PROPERTIES. These properties apply to all the
characters in the string that is returned. Here is an example that
constructs a string with a `face' property and a `mouse-face'
property:
(propertize "foo" 'face 'italic
'mouse-face 'bold-italic)
=> #("foo" 0 3 (mouse-face bold-italic face italic))
To put different properties on various parts of a string, you can
construct each part with `propertize' and then combine them with
`concat':
(concat
(propertize "foo" 'face 'italic
'mouse-face 'bold-italic)
" and "
(propertize "bar" 'face 'italic
'mouse-face 'bold-italic))
=> #("foo and bar"
0 3 (face italic mouse-face bold-italic)
3 8 nil
8 11 (face italic mouse-face bold-italic))
See also the function `buffer-substring-no-properties' (*note Buffer
Contents::) which copies text from the buffer but does not copy its
properties.
Text Property Search Functions
------------------------------
In typical use of text properties, most of the time several or many
consecutive characters have the same value for a property. Rather than
writing your programs to examine characters one by one, it is much
faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use `eq' for
comparing property values. In all cases, OBJECT defaults to the
current buffer.
For high performance, it's very important to use the LIMIT argument
to these functions, especially the ones that search for a single
property--otherwise, they may spend a long time scanning to the end of
the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position
(or `nil'). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
- Function: next-property-change pos &optional object limit
The function scans the text forward from position POS in the
string or buffer OBJECT till it finds a change in some text
property, then returns the position of the change. In other
words, it returns the position of the first character beyond POS
whose properties are not identical to those of the character just
after POS.
If LIMIT is non-`nil', then the scan ends at position LIMIT. If
there is no property change before that point,
`next-property-change' returns LIMIT.
The value is `nil' if the properties remain unchanged all the way
to the end of OBJECT and LIMIT is `nil'. If the value is
non-`nil', it is a position greater than or equal to POS. The
value equals POS only when LIMIT equals POS.
Here is an example of how to scan the buffer by chunks of text
within which all properties are constant:
(while (not (eobp))
(let ((plist (text-properties-at (point)))
(next-change
(or (next-property-change (point) (current-buffer))
(point-max))))
Process text from point to NEXT-CHANGE...
(goto-char next-change)))
- Function: next-single-property-change pos prop &optional object limit
The function scans the text forward from position POS in the
string or buffer OBJECT till it finds a change in the PROP
property, then returns the position of the change. In other
words, it returns the position of the first character beyond POS
whose PROP property differs from that of the character just after
POS.
If LIMIT is non-`nil', then the scan ends at position LIMIT. If
there is no property change before that point,
`next-single-property-change' returns LIMIT.
The value is `nil' if the property remains unchanged all the way to
the end of OBJECT and LIMIT is `nil'. If the value is non-`nil',
it is a position greater than or equal to POS; it equals POS only
if LIMIT equals POS.
- Function: previous-property-change pos &optional object limit
This is like `next-property-change', but scans back from POS
instead of forward. If the value is non-`nil', it is a position
less than or equal to POS; it equals POS only if LIMIT equals POS.
- Function: previous-single-property-change pos prop &optional object
limit
This is like `next-single-property-change', but scans back from
POS instead of forward. If the value is non-`nil', it is a
position less than or equal to POS; it equals POS only if LIMIT
equals POS.
- Function: next-char-property-change pos &optional limit
This is like `next-property-change' except that it considers
overlay properties as well as text properties, and if no change is
found before the end of the buffer, it returns the maximum buffer
position rather than `nil' (in this sense, it resembles the
corresponding overlay function `next-overlay-change', rather than
`next-property-change'). There is no OBJECT operand because this
function operates only on the current buffer. It returns the next
address at which either kind of property changes.
- Function: previous-char-property-change pos &optional limit
This is like `next-char-property-change', but scans back from POS
instead of forward, and returns the minimum buffer position if no
change is found.
- Function: next-single-char-property-change pos prop &optional object
limit
This is like `next-single-property-change' except that it
considers overlay properties as well as text properties, and if no
change is found before the end of the OBJECT, it returns the
maximum valid position in OBJECT rather than `nil'. Unlike
`next-char-property-change', this function _does_ have an OBJECT
operand; if OBJECT is not a buffer, only text-properties are
considered.
- Function: previous-single-char-property-change pos prop &optional
object limit
This is like `next-single-char-property-change', but scans back
from POS instead of forward, and returns the minimum valid
position in OBJECT if no change is found.
- Function: text-property-any start end prop value &optional object
This function returns non-`nil' if at least one character between
START and END has a property PROP whose value is VALUE. More
precisely, it returns the position of the first such character.
Otherwise, it returns `nil'.
The optional fifth argument, OBJECT, specifies the string or
buffer to scan. Positions are relative to OBJECT. The default
for OBJECT is the current buffer.
- Function: text-property-not-all start end prop value &optional object
This function returns non-`nil' if at least one character between
START and END does not have a property PROP with value VALUE.
More precisely, it returns the position of the first such
character. Otherwise, it returns `nil'.
The optional fifth argument, OBJECT, specifies the string or
buffer to scan. Positions are relative to OBJECT. The default
for OBJECT is the current buffer.
Properties with Special Meanings
--------------------------------
Here is a table of text property names that have special built-in
meanings. The following sections list a few additional special property
names that control filling and property inheritance. All other names
have no standard meaning, and you can use them as you like.
`category'
If a character has a `category' property, we call it the
"category" of the character. It should be a symbol. The
properties of the symbol serve as defaults for the properties of
the character.
`face'
You can use the property `face' to control the font and color of
text. *Note Faces::, for more information.
In the simplest case, the value is a face name. It can also be a
list; then each element can be any of these possibilities;
* A face name (a symbol or string).
* Starting in Emacs 21, a property list of face attributes.
This has the form (KEYWORD VALUE ...), where each KEYWORD is a
face attribute name and VALUE is a meaningful value for that
attribute. With this feature, you do not need to create a
face each time you want to specify a particular attribute for
certain text. *Note Face Attributes::.
* A cons cell of the form `(foreground-color . COLOR-NAME)' or
`(background-color . COLOR-NAME)'. These elements specify
just the foreground color or just the background color.
`(foreground-color . COLOR-NAME)' is equivalent to
`(:foreground COLOR-NAME)', and likewise for the background.
*Note Font Lock Mode::, for information on how to update `face'
properties automatically based on the contents of the text.
`mouse-face'
The property `mouse-face' is used instead of `face' when the mouse
is on or near the character. For this purpose, "near" means that
all text between the character and where the mouse is have the same
`mouse-face' property value.
`fontified'
This property, if non-`nil', says that text in the buffer has had
faces assigned automatically by a feature such as Font-Lock mode.
*Note Auto Faces::.
`display'
This property activates various features that change the way text
is displayed. For example, it can make text appear taller or
shorter, higher or lower, wider or narrow, or replaced with an
image. *Note Display Property::.
`help-echo'
If text has a string as its `help-echo' property, then when you
move the mouse onto that text, Emacs displays that string in the
echo area, or in the tooltip window.
If the value of the `help-echo' property is a function, that
function is called with three arguments, WINDOW, OBJECT and
POSITION and should return a help string or NIL for none. The
first argument, WINDOW is the window in which the help was found.
The second, OBJECT, is the buffer, overlay or string which had the
`help-echo' property. The POSITION argument is as follows:
* If OBJECT is a buffer, POS is the position in the buffer
where the `help-echo' text property was found.
* If OBJECT is an overlay, that overlay has a `help-echo'
property, and POS is the position in the overlay's buffer
under the mouse.
* If OBJECT is a string (an overlay string or a string displayed
with the `display' property), POS is the position in that
string under the mouse.
If the value of the `help-echo' property is neither a function nor
a string, it is evaluated to obtain a help string.
You can alter the way help text is displayed by setting the
variable `show-help-function' (*note Help display::).
This feature is used in the mode line and for other active text.
It is available starting in Emacs 21.
`local-map'
You can specify a different keymap for some of the text in a
buffer by means of the `local-map' property. The property's value
for the character after point, if non-`nil', is used for key
lookup instead of the buffer's local map. If the property value
is a symbol, the symbol's function definition is used as the
keymap. *Note Active Keymaps::.
`keymap'
The `keymap' property is similar to `local-map' but overrides the
buffer's local map (and the map specified by the `local-map'
property) rather than replacing it.
`syntax-table'
The `syntax-table' property overrides what the syntax table says
about this particular character. *Note Syntax Properties::.
`read-only'
If a character has the property `read-only', then modifying that
character is not allowed. Any command that would do so gets an
error, `text-read-only'.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the `read-only' property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. *Note Sticky
Properties::.
Since changing properties counts as modifying the buffer, it is not
possible to remove a `read-only' property unless you know the
special trick: bind `inhibit-read-only' to a non-`nil' value and
then remove the property. *Note Read Only Buffers::.
`invisible'
A non-`nil' `invisible' property can make a character invisible on
the screen. *Note Invisible Text::, for details.
`intangible'
If a group of consecutive characters have equal and non-`nil'
`intangible' properties, then you cannot place point between them.
If you try to move point forward into the group, point actually
moves to the end of the group. If you try to move point backward
into the group, point actually moves to the start of the group.
When the variable `inhibit-point-motion-hooks' is non-`nil', the
`intangible' property is ignored.
`field'
Consecutive characters with the same `field' property constitute a
"field". Some motion functions including `forward-word' and
`beginning-of-line' stop moving at a field boundary. *Note
Fields::.
`modification-hooks'
If a character has the property `modification-hooks', then its
value should be a list of functions; modifying that character
calls all of those functions. Each function receives two
arguments: the beginning and end of the part of the buffer being
modified. Note that if a particular modification hook function
appears on several characters being modified by a single
primitive, you can't predict how many times the function will be
called.
`insert-in-front-hooks'
`insert-behind-hooks'
The operation of inserting text in a buffer also calls the
functions listed in the `insert-in-front-hooks' property of the
following character and in the `insert-behind-hooks' property of
the preceding character. These functions receive two arguments,
the beginning and end of the inserted text. The functions are
called _after_ the actual insertion takes place.
See also *Note Change Hooks::, for other hooks that are called
when you change text in a buffer.
`point-entered'
`point-left'
The special properties `point-entered' and `point-left' record
hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
* the `point-left' property of the character after the old
location, and
* the `point-entered' property of the character after the new
location.
If these two values differ, each of them is called (if not `nil')
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and
new locations. The result may be to execute two `point-left'
functions (which may be the same function) and/or two
`point-entered' functions (which may be the same function). In
any case, all the `point-left' functions are called first,
followed by all the `point-entered' functions.
It is possible using `char-after' to examine characters at various
positions without moving point to those positions. Only an actual
change in the value of point runs these hook functions.
- Variable: inhibit-point-motion-hooks
When this variable is non-`nil', `point-left' and `point-entered'
hooks are not run, and the `intangible' property has no effect.
Do not set this variable globally; bind it with `let'.
- Variable: show-help-function
If this variable is non-`nil', it specifies a function called to
display help strings. These may be `help-echo' properties, menu
help strings (*note Simple Menu Items::, *note Extended Menu
Items::), or tool bar help strings (*note Tool Bar::). The
specified function is called with one argument, the help string to
display. Tooltip mode (*note Tooltips: (emacs)Tooltips.) provides
an example.
Formatted Text Properties
-------------------------
These text properties affect the behavior of the fill commands. They
are used for representing formatted text. *Note Filling::, and *Note
Margins::.
`hard'
If a newline character has this property, it is a "hard" newline.
The fill commands do not alter hard newlines and do not move words
across them. However, this property takes effect only if the
variable `use-hard-newlines' is non-`nil'.
`right-margin'
This property specifies an extra right margin for filling this
part of the text.
`left-margin'
This property specifies an extra left margin for filling this part
of the text.
`justification'
This property specifies the style of justification for filling
this part of the text.
Stickiness of Text Properties
-----------------------------
Self-inserting characters normally take on the same properties as the
preceding character. This is called "inheritance" of properties.
In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive. The ordinary text
insertion functions such as `insert' do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text
from one context to another--for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section. Self-inserting characters inherit properties because they work
using these primitives.
When you do insertion with inheritance, _which_ properties are
inherited, and from where, depends on which properties are "sticky".
Insertion after a character inherits those of its properties that are
"rear-sticky". Insertion before a character inherits those of its
properties that are "front-sticky". When both sides offer different
sticky values for the same property, the previous character's value
takes precedence.
By default, a text property is rear-sticky but not front-sticky;
thus, the default is to inherit all the properties of the preceding
character, and nothing from the following character.
You can control the stickiness of various text properties with two
specific text properties, `front-sticky' and `rear-nonsticky', and with
the variable `text-property-default-nonsticky'. You can use the
variable to specify a different default for a given property. You can
use those two text properties to make any specific properties sticky or
nonsticky in any particular part of the text.
If a character's `front-sticky' property is `t', then all its
properties are front-sticky. If the `front-sticky' property is a list,
then the sticky properties of the character are those whose names are
in the list. For example, if a character has a `front-sticky' property
whose value is `(face read-only)', then insertion before the character
can inherit its `face' property and its `read-only' property, but no
others.
The `rear-nonsticky' property works the opposite way. Most
properties are rear-sticky by default, so the `rear-nonsticky' property
says which properties are _not_ rear-sticky. If a character's
`rear-nonsticky' property is `t', then none of its properties are
rear-sticky. If the `rear-nonsticky' property is a list, properties
are rear-sticky _unless_ their names are in the list.
- Variable: text-property-default-nonsticky
This variable holds an alist which defines the default
rear-stickiness of various text properties. Each element has the
form `(PROPERTY . NONSTICKINESS)', and it defines the stickiness
of a particular text property, PROPERTY.
If NONSTICKINESS is non-`nil', this means that the property
PROPERTY is rear-nonsticky by default. Since all properties are
front-nonsticky by default, this makes PROPERTY nonsticky in both
directions by default.
The text properties `front-sticky' and `rear-nonsticky', when
used, take precedence over the default NONSTICKINESS specifed in
`text-property-default-nonsticky'.
Here are the functions that insert text with inheritance of
properties:
- Function: insert-and-inherit &rest strings
Insert the strings STRINGS, just like the function `insert', but
inherit any sticky properties from the adjoining text.
- Function: insert-before-markers-and-inherit &rest strings
Insert the strings STRINGS, just like the function
`insert-before-markers', but inherit any sticky properties from the
adjoining text.
*Note Insertion::, for the ordinary insertion functions which do not
inherit.
Saving Text Properties in Files
-------------------------------
You can save text properties in files (along with the text itself),
and restore the same text properties when visiting or inserting the
files, using these two hooks:
- Variable: write-region-annotate-functions
This variable's value is a list of functions for `write-region' to
run to encode text properties in some fashion as annotations to
the text being written in the file. *Note Writing to Files::.
Each function in the list is called with two arguments: the start
and end of the region to be written. These functions should not
alter the contents of the buffer. Instead, they should return
lists indicating annotations to write in the file in addition to
the text in the buffer.
Each function should return a list of elements of the form
`(POSITION . STRING)', where POSITION is an integer specifying the
relative position within the text to be written, and STRING is the
annotation to add there.
Each list returned by one of these functions must be already
sorted in increasing order by POSITION. If there is more than one
function, `write-region' merges the lists destructively into one
sorted list.
When `write-region' actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
- Variable: after-insert-file-functions
This variable holds a list of functions for `insert-file-contents'
to call after inserting a file's contents. These functions should
scan the inserted text for annotations, and convert them to the
text properties they stand for.
Each function receives one argument, the length of the inserted
text; point indicates the start of that text. The function should
scan that text for annotations, delete them, and create the text
properties that the annotations specify. The function should
return the updated length of the inserted text, as it stands after
those changes. The value returned by one function becomes the
argument to the next function.
These functions should always return with point at the beginning of
the inserted text.
The intended use of `after-insert-file-functions' is for converting
some sort of textual annotations into actual text properties. But
other uses may be possible.
We invite users to write Lisp programs to store and retrieve text
properties in files, using these hooks, and thus to experiment with
various data formats and find good ones. Eventually we hope users will
produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text
property names or values--because a program that general is probably
difficult to write, and slow. Instead, choose a set of possible data
types that are reasonably flexible, and not too hard to encode.
*Note Format Conversion::, for a related feature.
Lazy Computation of Text Properties
-----------------------------------
Instead of computing text properties for all the text in the buffer,
you can arrange to compute the text properties for parts of the text
when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is `buffer-substring'. Before examining the properties,
this function runs the abnormal hook `buffer-access-fontify-functions'.
- Variable: buffer-access-fontify-functions
This variable holds a list of functions for computing text
properties. Before `buffer-substring' copies the text and text
properties for a portion of the buffer, it calls all the functions
in this list. Each of the functions receives two arguments that
specify the range of the buffer being accessed. (The buffer
itself is always the current buffer.)
The function `buffer-substring-no-properties' does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
`buffer-access-fontified-property'.
- Variable: buffer-access-fontified-property
If this value's variable is non-`nil', it is a symbol which is used
as a text property name. A non-`nil' value for that text property
means, "the other text properties for this character have already
been computed."
If all the characters in the range specified for `buffer-substring'
have a non-`nil' value for this property, `buffer-substring' does
not call the `buffer-access-fontify-functions' functions. It
assumes these characters already have the right text properties,
and just copies the properties they already have.
The normal way to use this feature is that the
`buffer-access-fontify-functions' functions add this property, as
well as others, to the characters they operate on. That way, they
avoid being called over and over for the same text.
Defining Clickable Text
-----------------------
There are two ways to set up "clickable text" in a buffer. There
are typically two parts of this: to make the text highlight when the
mouse is over it, and to make a mouse button do something when you
click it on that part of the text.
Highlighting is done with the `mouse-face' text property. Here is
an example of how Dired does it:
(condition-case nil
(if (dired-move-to-filename)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'mouse-face 'highlight))
(error nil))
The first two arguments to `put-text-property' specify the beginning
and end of the text.
The usual way to make the mouse do something when you click it on
this text is to define `mouse-2' in the major mode's keymap. The job
of checking whether the click was on clickable text is done by the
command definition. Here is how Dired does it:
(defun dired-mouse-find-file-other-window (event)
"In dired, visit the file or directory name you click on."
(interactive "e")
(let (file)
(save-excursion
(set-buffer (window-buffer (posn-window (event-end event))))
(save-excursion
(goto-char (posn-point (event-end event)))
(setq file (dired-get-filename))))
(select-window (posn-window (event-end event)))
(find-file-other-window (file-name-sans-versions file t))))
The reason for the outer `save-excursion' construct is to avoid
changing the current buffer; the reason for the inner one is to avoid
permanently altering point in the buffer you click on. In this case,
Dired uses the function `dired-get-filename' to determine which file to
visit, based on the position found in the event.
Instead of defining a mouse command for the major mode, you can
define a key binding for the clickable text itself, using the `keymap'
text property:
(let ((map (make-sparse-keymap)))
(define-key map [mouse-2] 'operate-this-button)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'keymap map))
This method makes it possible to define different commands for various
clickable pieces of text. Also, the major mode definition (or the
global definition) remains available for the rest of the text in the
buffer.
Defining and Using Fields
-------------------------
A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with `eq') of the
`field' property (either a text-property or an overlay property). This
section describes special functions that are available for operating on
fields.
You specify a field with a buffer position, POS. We think of each
field as containing a range of buffer positions, so the position you
specify stands for the field containing that position.
When the characters before and after POS are part of the same field,
there is no doubt which field contains POS: the one those characters
both belong to. When POS is at a boundary between fields, which field
it belongs to depends on the stickiness of the `field' properties of
the two surrounding characters (*note Sticky Properties::). The field
whose property would be inherited by text inserted at POS is the field
that contains POS.
There is an anomalous case where newly inserted text at POS would
not inherit the `field' property from either side. This happens if the
previous character's `field' property is not rear-sticky, and the
following character's `field' property is not front-sticky. In this
case, POS belongs to neither the preceding field nor the following
field; the field functions treat it as belonging to an empty field
whose beginning and end are both at POS.
In all of these functions, if POS is omitted or `nil', the value of
point is used by default.
- Function: field-beginning &optional pos escape-from-edge
This function returns the beginning of the field specified by POS.
If POS is at the beginning of its field, and ESCAPE-FROM-EDGE is
non-`nil', then the return value is always the beginning of the
preceding field that _ends_ at POS, regardless of the stickiness
of the `field' properties around POS.
- Function: field-end &optional pos escape-from-edge
This function returns the end of the field specified by POS.
If POS is at the end of its field, and ESCAPE-FROM-EDGE is
non-`nil', then the return value is always the end of the following
field that _begins_ at POS, regardless of the stickiness of the
`field' properties around POS.
- Function: field-string &optional pos
This function returns the contents of the field specified by POS,
as a string.
- Function: field-string-no-properties &optional pos
This function returns the contents of the field specified by POS,
as a string, discarding text properties.
- Function: delete-field &optional pos
This function deletes the text of the field specified by POS.
- Function: constrain-to-field new-pos old-pos &optional
escape-from-edge only-in-line inhibit-capture-property
This function "constrains" NEW-POS to the field that OLD-POS
belongs to--in other words, it returns the position closest to
NEW-POS that is in the same field as OLD-POS.
If NEW-POS is `nil', then `constrain-to-field' uses the value of
point instead, and moves point to the resulting position.
If OLD-POS is at the boundary of two fields, then the acceptable
positions for NEW-POS depend on the value of the optional argument
ESCAPE-FROM-EDGE. If ESCAPE-FROM-EDGE is `nil', then NEW-POS is
constrained to the field that has the same `field' property
(either a text-property or an overlay property) that new
characters inserted at OLD-POS would get. (This depends on the
stickiness of the `field' property for the characters before and
after OLD-POS.) If ESCAPE-FROM-EDGE is non-`nil', NEW-POS is
constrained to the union of the two adjacent fields.
Additionally, if two fields are separated by another field with the
special value `boundary', then any point within this special field
is also considered to be "on the boundary."
If the optional argument ONLY-IN-LINE is non-`nil', and
constraining NEW-POS in the usual way would move it to a different
line, NEW-POS is returned unconstrained. This used in commands
that move by line, such as `next-line' and `beginning-of-line', so
that they respect field boundaries only in the case where they can
still move to the right line.
If the optional argument INHIBIT-CAPTURE-PROPERTY is non-`nil',
and OLD-POS has a non-`nil' property of that name, then any field
boundaries are ignored.
You can cause `constrain-to-field' to ignore all field boundaries
(and so never constrain anything) by binding the variable
`inhibit-field-text-motion' to a non-nil value.
Why Text Properties are not Intervals
-------------------------------------
Some editors that support adding attributes to text in the buffer do
so by letting the user specify "intervals" within the text, and adding
the properties to the intervals. Those editors permit the user or the
programmer to determine where individual intervals start and end. We
deliberately provided a different sort of interface in Emacs Lisp to
avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means
you can distinguish between a buffer that is just one interval with a
certain property, and a buffer containing the same text subdivided into
two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of
the text. The text remaining in the buffer is one interval, and the
copy in the kill ring (and the undo list) becomes a separate interval.
Then if you yank back the killed text, you get two intervals with the
same properties. Thus, editing does not preserve the distinction
between one interval and two.
Suppose we "fix" this problem by coalescing the two intervals when
the text is inserted. That works fine if the buffer originally was a
single interval. But suppose instead that we have two adjacent
intervals with the same properties, and we kill the text of one interval
and yank it back. The same interval-coalescence feature that rescues
the other case causes trouble in this one: after yanking, we have just
one interval. One again, editing does not preserve the distinction
between one interval and two.
Insertion of text at the border between intervals also raises
questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for
questions of the form, "What are the properties of this character?" So
we have decided these are the only questions that make sense; we have
not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions
in place of explicit interval boundaries. You can think of them as
finding the boundaries of intervals, assuming that intervals are always
coalesced whenever possible. *Note Property Search::.
Emacs also provides explicit intervals as a presentation feature; see
*Note Overlays::.
Substituting for a Character Code
=================================
The following functions replace characters within a specified region
based on their character codes.
- Function: subst-char-in-region start end old-char new-char &optional
noundo
This function replaces all occurrences of the character OLD-CHAR
with the character NEW-CHAR in the region of the current buffer
defined by START and END.
If NOUNDO is non-`nil', then `subst-char-in-region' does not
record the change for undo and does not mark the buffer as
modified. This was useful for controlling the old selective
display feature (*note Selective Display::).
`subst-char-in-region' does not move point and returns `nil'.
---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
(subst-char-in-region 1 20 ?i ?X)
=> nil
---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
- Function: translate-region start end table
This function applies a translation table to the characters in the
buffer between positions START and END.
The translation table TABLE is a string; `(aref TABLE OCHAR)'
gives the translated character corresponding to OCHAR. If the
length of TABLE is less than 256, any characters with codes larger
than the length of TABLE are not altered by the translation.
The return value of `translate-region' is the number of characters
that were actually changed by the translation. This does not
count characters that were mapped into themselves in the
translation table.
Registers
=========
A register is a sort of variable used in Emacs editing that can hold
a variety of different kinds of values. Each register is named by a
single character. All ASCII characters and their meta variants (but
with the exception of `C-g') can be used to name registers. Thus,
there are 255 possible registers. A register is designated in Emacs
Lisp by the character that is its name.
- Variable: register-alist
This variable is an alist of elements of the form `(NAME .
CONTENTS)'. Normally, there is one element for each Emacs
register that has been used.
The object NAME is a character (an integer) identifying the
register.
The CONTENTS of a register can have several possible types:
a number
A number stands for itself. If `insert-register' finds a number
in the register, it converts the number to decimal.
a marker
A marker represents a buffer position to jump to.
a string
A string is text saved in the register.
a rectangle
A rectangle is represented by a list of strings.
`(WINDOW-CONFIGURATION POSITION)'
This represents a window configuration to restore in one frame,
and a position to jump to in the current buffer.
`(FRAME-CONFIGURATION POSITION)'
This represents a frame configuration to restore, and a position
to jump to in the current buffer.
(file FILENAME)
This represents a file to visit; jumping to this value visits file
FILENAME.
(file-query FILENAME POSITION)
This represents a file to visit and a position in it; jumping to
this value visits file FILENAME and goes to buffer position
POSITION. Restoring this type of position asks the user for
confirmation first.
The functions in this section return unpredictable values unless
otherwise stated.
- Function: get-register reg
This function returns the contents of the register REG, or `nil'
if it has no contents.
- Function: set-register reg value
This function sets the contents of register REG to VALUE. A
register can be set to any value, but the other register functions
expect only certain data types. The return value is VALUE.
- Command: view-register reg
This command displays what is contained in register REG.
- Command: insert-register reg &optional beforep
This command inserts contents of register REG into the current
buffer.
Normally, this command puts point before the inserted text, and the
mark after it. However, if the optional second argument BEFOREP
is non-`nil', it puts the mark before and point after. You can
pass a non-`nil' second argument BEFOREP to this function
interactively by supplying any prefix argument.
If the register contains a rectangle, then the rectangle is
inserted with its upper left corner at point. This means that
text is inserted in the current line and underneath it on
successive lines.
If the register contains something other than saved text (a
string) or a rectangle (a list), currently useless things happen.
This may be changed in the future.
Transposition of Text
=====================
This subroutine is used by the transposition commands.
- Function: transpose-regions start1 end1 start2 end2 &optional
leave-markers
This function exchanges two nonoverlapping portions of the buffer.
Arguments START1 and END1 specify the bounds of one portion and
arguments START2 and END2 specify the bounds of the other portion.
Normally, `transpose-regions' relocates markers with the transposed
text; a marker previously positioned within one of the two
transposed portions moves along with that portion, thus remaining
between the same two characters in their new position. However,
if LEAVE-MARKERS is non-`nil', `transpose-regions' does not do
this--it leaves all markers unrelocated.
Base 64 Encoding
================
Base 64 code is used in email to encode a sequence of 8-bit bytes as
a longer sequence of ASCII graphic characters. It is defined in
Internet RFC(1)2045. This section describes the functions for
converting to and from this code.
- Function: base64-encode-region beg end &optional no-line-break
This function converts the region from BEG to END into base 64
code. It returns the length of the encoded text. An error is
signaled if a character in the region is multibyte, i.e. in a
multibyte buffer the region must contain only characters from the
charsets `ascii', `eight-bit-control' and `eight-bit-graphic'.
Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines. However, if the optional argument
NO-LINE-BREAK is non-`nil', these newlines are not added, so the
output is just one long line.
- Function: base64-encode-string string &optional no-line-break
This function converts the string STRING into base 64 code. It
returns a string containing the encoded text. As for
`base64-encode-region', an error is signaled if a character in the
string is multibyte.
Normally, this function inserts newline characters into the encoded
text, to avoid overlong lines. However, if the optional argument
NO-LINE-BREAK is non-`nil', these newlines are not added, so the
result string is just one long line.
- Function: base64-decode-region beg end
This function converts the region from BEG to END from base 64
code into the corresponding decoded text. It returns the length of
the decoded text.
The decoding functions ignore newline characters in the encoded
text.
- Function: base64-decode-string string
This function converts the string STRING from base 64 code into
the corresponding decoded text. It returns a string containing the
decoded text.
The decoding functions ignore newline characters in the encoded
text.
---------- Footnotes ----------
(1) An RFC, an acronym for "Request for Comments", is a numbered
Internet informational document describing a standard. RFCs are
usually written by technical experts acting on their own initiative,
and are traditionally written in a pragmatic, experience-driven manner.
MD5 Checksum
============
MD5 cryptographic checksums, or "message digests", are 128-bit
"fingerprints" of a document or program. They are used to verify that
you have an exact and unaltered copy of the data. The algorithm to
calculate the MD5 message digest is defined in Internet RFC(1)1321.
This section describes the Emacs facilities for computing message
digests.
- Function: md5 object &optional start end coding-system noerror
This function returns the MD5 message digest of OBJECT, which
should be a buffer or a string.
The two optional arguments START and END are character positions
specifying the portion of OBJECT to compute the message digest
for. If they are `nil' or omitted, the digest is computed for the
whole of OBJECT.
The function `md5' does not compute the message digest directly
from the internal Emacs representation of the text (*note Text
Representations::). Instead, it encodes the text using a coding
system, and computes the message digest from the encoded text. The
optional fourth argument CODING-SYSTEM specifies which coding
system to use for encoding the text. It should be the same coding
system that you used to read the text, or that you used or will use
when saving or sending the text. *Note Coding Systems::, for more
information about coding systems.
If CODING-SYSTEM is `nil' or omitted, the default depends on
OBJECT. If OBJECT is a buffer, the default for CODING-SYSTEM is
whatever coding system would be chosen by default for writing this
text into a file. If OBJECT is a string, the user's most
preferred coding system (*note prefer-coding-system:
(emacs)Recognize Coding.) is used.
Normally, `md5' signals an error if the text can't be encoded
using the specified or chosen coding system. However, if NOERROR
is non-`nil', it silently uses `raw-text' coding instead.
---------- Footnotes ----------
(1) For an explanation of what is an RFC, see the footnote in *Note
Base 64::.
Change Hooks
============
These hook variables let you arrange to take notice of all changes in
all buffers (or in a particular buffer, if you make them buffer-local).
See also *Note Special Properties::, for how to detect changes to
specific parts of the text.
The functions you use in these hooks should save and restore the
match data if they do anything that uses regular expressions;
otherwise, they will interfere in bizarre ways with the editing
operations that call them.
- Variable: before-change-functions
This variable holds a list of functions to call before any buffer
modification. Each function gets two arguments, the beginning and
end of the region that is about to change, represented as
integers. The buffer that is about to change is always the
current buffer.
- Variable: after-change-functions
This variable holds a list of functions to call after any buffer
modification. Each function receives three arguments: the
beginning and end of the region just changed, and the length of
the text that existed before the change. All three arguments are
integers. The buffer that's about to change is always the current
buffer.
The length of the old text is the difference between the buffer
positions before and after that text as it was before the change.
As for the changed text, its length is simply the difference
between the first two arguments.
- Macro: combine-after-change-calls body...
The macro executes BODY normally, but arranges to call the
after-change functions just once for a series of several
changes--if that seems safe.
If a program makes several text changes in the same area of the
buffer, using the macro `combine-after-change-calls' around that
part of the program can make it run considerably faster when
after-change hooks are in use. When the after-change hooks are
ultimately called, the arguments specify a portion of the buffer
including all of the changes made within the
`combine-after-change-calls' body.
*Warning:* You must not alter the values of
`after-change-functions' within the body of a
`combine-after-change-calls' form.
*Note:* If the changes you combine occur in widely scattered parts
of the buffer, this will still work, but it is not advisable,
because it may lead to inefficient behavior for some change hook
functions.
The two variables above are temporarily bound to `nil' during the
time that any of these functions is running. This means that if one of
these functions changes the buffer, that change won't run these
functions. If you do want a hook function to make changes that run
these functions, make it bind these variables back to their usual
values.
One inconvenient result of this protective feature is that you cannot
have a function in `after-change-functions' or
`before-change-functions' which changes the value of that variable.
But that's not a real limitation. If you want those functions to change
the list of functions to run, simply add one fixed function to the hook,
and code that function to look in another variable for other functions
to call. Here is an example:
(setq my-own-after-change-functions nil)
(defun indirect-after-change-function (beg end len)
(let ((list my-own-after-change-functions))
(while list
(funcall (car list) beg end len)
(setq list (cdr list)))))
(add-hooks 'after-change-functions
'indirect-after-change-function)
- Variable: first-change-hook
This variable is a normal hook that is run whenever a buffer is
changed that was previously in the unmodified state.
- Variable: inhibit-modification-hooks
If this variable is non-`nil', all of the change hooks are
disabled; none of them run. This affects all the hook variables
described above in this section, as well as the hooks attached to
certain special text properties (*note Special Properties::) and
overlay properties (*note Overlay Properties::).
This variable is available starting in Emacs 21.
Non-ASCII Characters
********************
This chapter covers the special issues relating to non-ASCII
characters and how they are stored in strings and buffers.
Text Representations
====================
Emacs has two "text representations"--two ways to represent text in
a string or buffer. These are called "unibyte" and "multibyte". Each
string, and each buffer, uses one of these two representations. For
most purposes, you can ignore the issue of representations, because
Emacs converts text between them as appropriate. Occasionally in Lisp
programming you will need to pay attention to the difference.
In unibyte representation, each character occupies one byte and
therefore the possible character codes range from 0 to 255. Codes 0
through 127 are ASCII characters; the codes from 128 through 255 are
used for one non-ASCII character set (you can choose which character
set by setting the variable `nonascii-insert-offset').
In multibyte representation, a character may occupy more than one
byte, and as a result, the full range of Emacs character codes can be
stored. The first byte of a multibyte character is always in the range
128 through 159 (octal 0200 through 0237). These values are called
"leading codes". The second and subsequent bytes of a multibyte
character are always in the range 160 through 255 (octal 0240 through
0377); these values are "trailing codes".
Some sequences of bytes are not valid in multibyte text: for example,
a single isolated byte in the range 128 through 159 is not allowed. But
character codes 128 through 159 can appear in multibyte text,
represented as two-byte sequences. All the character codes 128 through
255 are possible (though slightly abnormal) in multibyte text; they
appear in multibyte buffers and strings when you do explicit encoding
and decoding (*note Explicit Encoding::).
In a buffer, the buffer-local value of the variable
`enable-multibyte-characters' specifies the representation used. The
representation for a string is determined and recorded in the string
when the string is constructed.
- Variable: enable-multibyte-characters
This variable specifies the current buffer's text representation.
If it is non-`nil', the buffer contains multibyte text; otherwise,
it contains unibyte text.
You cannot set this variable directly; instead, use the function
`set-buffer-multibyte' to change a buffer's representation.
- Variable: default-enable-multibyte-characters
This variable's value is entirely equivalent to `(default-value
'enable-multibyte-characters)', and setting this variable changes
that default value. Setting the local binding of
`enable-multibyte-characters' in a specific buffer is not allowed,
but changing the default value is supported, and it is a reasonable
thing to do, because it has no effect on existing buffers.
The `--unibyte' command line option does its job by setting the
default value to `nil' early in startup.
- Function: position-bytes position
Return the byte-position corresponding to buffer position POSITION
in the current buffer.
- Function: byte-to-position byte-position
Return the buffer position corresponding to byte-position
BYTE-POSITION in the current buffer.
- Function: multibyte-string-p string
Return `t' if STRING is a multibyte string.
Converting Text Representations
===============================
Emacs can convert unibyte text to multibyte; it can also convert
multibyte text to unibyte, though this conversion loses information. In
general these conversions happen when inserting text into a buffer, or
when putting text from several strings together in one string. You can
also explicitly convert a string's contents to either representation.
Emacs chooses the representation for a string based on the text that
it is constructed from. The general rule is to convert unibyte text to
multibyte text when combining it with other multibyte text, because the
multibyte representation is more general and can hold whatever
characters the unibyte text has.
When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by `enable-multibyte-characters'
in that buffer. In particular, when you insert multibyte text into a
unibyte buffer, Emacs converts the text to unibyte, even though this
conversion cannot in general preserve all the characters that might be
in the multibyte text. The other natural alternative, to convert the
buffer contents to multibyte, is not acceptable because the buffer's
representation is a choice made by the user that cannot be overridden
automatically.
Converting unibyte text to multibyte text leaves ASCII characters
unchanged, and likewise character codes 128 through 159. It converts
the non-ASCII codes 160 through 255 by adding the value
`nonascii-insert-offset' to each character code. By setting this
variable, you specify which character set the unibyte characters
correspond to (*note Character Sets::). For example, if
`nonascii-insert-offset' is 2048, which is `(- (make-char
'latin-iso8859-1) 128)', then the unibyte non-ASCII characters
correspond to Latin 1. If it is 2688, which is `(- (make-char
'greek-iso8859-7) 128)', then they correspond to Greek letters.
Converting multibyte text to unibyte is simpler: it discards all but
the low 8 bits of each character code. If `nonascii-insert-offset' has
a reasonable value, corresponding to the beginning of some character
set, this conversion is the inverse of the other: converting unibyte
text to multibyte and back to unibyte reproduces the original unibyte
text.
- Variable: nonascii-insert-offset
This variable specifies the amount to add to a non-ASCII character
when converting unibyte text to multibyte. It also applies when
`self-insert-command' inserts a character in the unibyte non-ASCII
range, 128 through 255. However, the functions `insert' and
`insert-char' do not perform this conversion.
The right value to use to select character set CS is `(-
(make-char CS) 128)'. If the value of `nonascii-insert-offset' is
zero, then conversion actually uses the value for the Latin 1
character set, rather than zero.
- Variable: nonascii-translation-table
This variable provides a more general alternative to
`nonascii-insert-offset'. You can use it to specify independently
how to translate each code in the range of 128 through 255 into a
multibyte character. The value should be a char-table, or `nil'.
If this is non-`nil', it overrides `nonascii-insert-offset'.
- Function: string-make-unibyte string
This function converts the text of STRING to unibyte
representation, if it isn't already, and returns the result. If
STRING is a unibyte string, it is returned unchanged. Multibyte
character codes are converted to unibyte by using just the low 8
bits.
- Function: string-make-multibyte string
This function converts the text of STRING to multibyte
representation, if it isn't already, and returns the result. If
STRING is a multibyte string, it is returned unchanged. The
function `unibyte-char-to-multibyte' is used to convert each
unibyte character to a multibyte character.
Selecting a Representation
==========================
Sometimes it is useful to examine an existing buffer or string as
multibyte when it was unibyte, or vice versa.
- Function: set-buffer-multibyte multibyte
Set the representation type of the current buffer. If MULTIBYTE
is non-`nil', the buffer becomes multibyte. If MULTIBYTE is
`nil', the buffer becomes unibyte.
This function leaves the buffer contents unchanged when viewed as a
sequence of bytes. As a consequence, it can change the contents
viewed as characters; a sequence of two bytes which is treated as
one character in multibyte representation will count as two
characters in unibyte representation. Character codes 128 through
159 are an exception. They are represented by one byte in a
unibyte buffer, but when the buffer is set to multibyte, they are
converted to two-byte sequences, and vice versa.
This function sets `enable-multibyte-characters' to record which
representation is in use. It also adjusts various data in the
buffer (including overlays, text properties and markers) so that
they cover the same text as they did before.
You cannot use `set-buffer-multibyte' on an indirect buffer,
because indirect buffers always inherit the representation of the
base buffer.
- Function: string-as-unibyte string
This function returns a string with the same bytes as STRING but
treating each byte as a character. This means that the value may
have more characters than STRING has.
If STRING is already a unibyte string, then the value is STRING
itself. Otherwise it is a newly created string, with no text
properties. If STRING is multibyte, any characters it contains of
charset EIGHT-BIT-CONTROL or EIGHT-BIT-GRAPHIC are converted to
the corresponding single byte.
- Function: string-as-multibyte string
This function returns a string with the same bytes as STRING but
treating each multibyte sequence as one character. This means
that the value may have fewer characters than STRING has.
If STRING is already a multibyte string, then the value is STRING
itself. Otherwise it is a newly created string, with no text
properties. If STRING is unibyte and contains any individual
8-bit bytes (i.e. not part of a multibyte form), they are
converted to the corresponding multibyte character of charset
EIGHT-BIT-CONTROL or EIGHT-BIT-GRAPHIC.
Character Codes
===============
The unibyte and multibyte text representations use different
character codes. The valid character codes for unibyte representation
range from 0 to 255--the values that can fit in one byte. The valid
character codes for multibyte representation range from 0 to 524287,
but not all values in that range are valid. The values 128 through 255
are not entirely proper in multibyte text, but they can occur if you do
explicit encoding and decoding (*note Explicit Encoding::). Some other
character codes cannot occur at all in multibyte text. Only the ASCII
codes 0 through 127 are completely legitimate in both representations.
- Function: char-valid-p charcode &optional genericp
This returns `t' if CHARCODE is valid for either one of the two
text representations.
(char-valid-p 65)
=> t
(char-valid-p 256)
=> nil
(char-valid-p 2248)
=> t
If the optional argument GENERICP is non-nil, this function
returns `t' if CHARCODE is a generic character (*note Splitting
Characters::).
Character Sets
==============
Emacs classifies characters into various "character sets", each of
which has a name which is a symbol. Each character belongs to one and
only one character set.
In general, there is one character set for each distinct script. For
example, `latin-iso8859-1' is one character set, `greek-iso8859-7' is
another, and `ascii' is another. An Emacs character set can hold at
most 9025 characters; therefore, in some cases, characters that would
logically be grouped together are split into several character sets.
For example, one set of Chinese characters, generally known as Big 5,
is divided into two Emacs character sets, `chinese-big5-1' and
`chinese-big5-2'.
ASCII characters are in character set `ascii'. The non-ASCII
characters 128 through 159 are in character set `eight-bit-control',
and codes 160 through 255 are in character set `eight-bit-graphic'.
- Function: charsetp object
Returns `t' if OBJECT is a symbol that names a character set,
`nil' otherwise.
- Function: charset-list
This function returns a list of all defined character set names.
- Function: char-charset character
This function returns the name of the character set that CHARACTER
belongs to.
- Function: charset-plist charset
This function returns the charset property list of the character
set CHARSET. Although CHARSET is a symbol, this is not the same
as the property list of that symbol. Charset properties are used
for special purposes within Emacs; for example,
`preferred-coding-system' helps determine which coding system to
use to encode characters in a charset.
Characters and Bytes
====================
In multibyte representation, each character occupies one or more
bytes. Each character set has an "introduction sequence", which is
normally one or two bytes long. (Exception: the ASCII character set
and the EIGHT-BIT-GRAPHIC character set have a zero-length introduction
sequence.) The introduction sequence is the beginning of the byte
sequence for any character in the character set. The rest of the
character's bytes distinguish it from the other characters in the same
character set. Depending on the character set, there are either one or
two distinguishing bytes; the number of such bytes is called the
"dimension" of the character set.
- Function: charset-dimension charset
This function returns the dimension of CHARSET; at present, the
dimension is always 1 or 2.
- Function: charset-bytes charset
This function returns the number of bytes used to represent a
character in character set CHARSET.
This is the simplest way to determine the byte length of a character
set's introduction sequence:
(- (charset-bytes CHARSET)
(charset-dimension CHARSET))
Splitting Characters
====================
The functions in this section convert between characters and the byte
values used to represent them. For most purposes, there is no need to
be concerned with the sequence of bytes used to represent a character,
because Emacs translates automatically when necessary.
- Function: split-char character
Return a list containing the name of the character set of
CHARACTER, followed by one or two byte values (integers) which
identify CHARACTER within that character set. The number of byte
values is the character set's dimension.
(split-char 2248)
=> (latin-iso8859-1 72)
(split-char 65)
=> (ascii 65)
(split-char 128)
=> (eight-bit-control 128)
- Function: make-char charset &optional code1 code2
This function returns the character in character set CHARSET whose
position codes are CODE1 and CODE2. This is roughly the inverse
of `split-char'. Normally, you should specify either one or both
of CODE1 and CODE2 according to the dimension of CHARSET. For
example,
(make-char 'latin-iso8859-1 72)
=> 2248
If you call `make-char' with no BYTE-VALUES, the result is a
"generic character" which stands for CHARSET. A generic character is
an integer, but it is _not_ valid for insertion in the buffer as a
character. It can be used in `char-table-range' to refer to the whole
character set (*note Char-Tables::). `char-valid-p' returns `nil' for
generic characters. For example:
(make-char 'latin-iso8859-1)
=> 2176
(char-valid-p 2176)
=> nil
(char-valid-p 2176 t)
=> t
(split-char 2176)
=> (latin-iso8859-1 0)
The character sets ASCII, EIGHT-BIT-CONTROL, and EIGHT-BIT-GRAPHIC
don't have corresponding generic characters. If CHARSET is one of them
and you don't supply CODE1, `make-char' returns the character code
corresponding to the smallest code in CHARSET.
Scanning for Character Sets
===========================
Sometimes it is useful to find out which character sets appear in a
part of a buffer or a string. One use for this is in determining which
coding systems (*note Coding Systems::) are capable of representing all
of the text in question.
- Function: find-charset-region beg end &optional translation
This function returns a list of the character sets that appear in
the current buffer between positions BEG and END.
The optional argument TRANSLATION specifies a translation table to
be used in scanning the text (*note Translation of Characters::).
If it is non-`nil', then each character in the region is translated
through this table, and the value returned describes the translated
characters instead of the characters actually in the buffer.
- Function: find-charset-string string &optional translation
This function returns a list of the character sets that appear in
the string STRING. It is just like `find-charset-region', except
that it applies to the contents of STRING instead of part of the
current buffer.
Translation of Characters
=========================
A "translation table" specifies a mapping of characters into
characters. These tables are used in encoding and decoding, and for
other purposes. Some coding systems specify their own particular
translation tables; there are also default translation tables which
apply to all other coding systems.
- Function: make-translation-table &rest translations
This function returns a translation table based on the argument
TRANSLATIONS. Each element of TRANSLATIONS should be a list of
elements of the form `(FROM . TO)'; this says to translate the
character FROM into TO.
The arguments and the forms in each argument are processed in
order, and if a previous form already translates TO to some other
character, say TO-ALT, FROM is also translated to TO-ALT.
You can also map one whole character set into another character
set with the same dimension. To do this, you specify a generic
character (which designates a character set) for FROM (*note
Splitting Characters::). In this case, TO should also be a
generic character, for another character set of the same
dimension. Then the translation table translates each character
of FROM's character set into the corresponding character of TO's
character set.
In decoding, the translation table's translations are applied to the
characters that result from ordinary decoding. If a coding system has
property `character-translation-table-for-decode', that specifies the
translation table to use. Otherwise, if
`standard-translation-table-for-decode' is non-`nil', decoding uses
that table.
In encoding, the translation table's translations are applied to the
characters in the buffer, and the result of translation is actually
encoded. If a coding system has property
`character-translation-table-for-encode', that specifies the
translation table to use. Otherwise the variable
`standard-translation-table-for-encode' specifies the translation table.
- Variable: standard-translation-table-for-decode
This is the default translation table for decoding, for coding
systems that don't specify any other translation table.
- Variable: standard-translation-table-for-encode
This is the default translation table for encoding, for coding
systems that don't specify any other translation table.
Coding Systems
==============
When Emacs reads or writes a file, and when Emacs sends text to a
subprocess or receives text from a subprocess, it normally performs
character code conversion and end-of-line conversion as specified by a
particular "coding system".
How to define a coding system is an arcane matter, and is not
documented here.
Basic Concepts of Coding Systems
--------------------------------
"Character code conversion" involves conversion between the encoding
used inside Emacs and some other encoding. Emacs supports many
different encodings, in that it can convert to and from them. For
example, it can convert text to or from encodings such as Latin 1, Latin
2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some
cases, Emacs supports several alternative encodings for the same
characters; for example, there are three coding systems for the Cyrillic
(Russian) alphabet: ISO, Alternativnyj, and KOI8.
Most coding systems specify a particular character code for
conversion, but some of them leave the choice unspecified--to be chosen
heuristically for each file, based on the data.
"End of line conversion" handles three different conventions used on
various systems for representing end of line in files. The Unix
convention is to use the linefeed character (also called newline). The
DOS convention is to use a carriage-return and a linefeed at the end of
a line. The Mac convention is to use just carriage-return.
"Base coding systems" such as `latin-1' leave the end-of-line
conversion unspecified, to be chosen based on the data. "Variant
coding systems" such as `latin-1-unix', `latin-1-dos' and `latin-1-mac'
specify the end-of-line conversion explicitly as well. Most base
coding systems have three corresponding variants whose names are formed
by adding `-unix', `-dos' and `-mac'.
The coding system `raw-text' is special in that it prevents
character code conversion, and causes the buffer visited with that
coding system to be a unibyte buffer. It does not specify the
end-of-line conversion, allowing that to be determined as usual by the
data, and has the usual three variants which specify the end-of-line
conversion. `no-conversion' is equivalent to `raw-text-unix': it
specifies no conversion of either character codes or end-of-line.
The coding system `emacs-mule' specifies that the data is
represented in the internal Emacs encoding. This is like `raw-text' in
that no code conversion happens, but different in that the result is
multibyte data.
- Function: coding-system-get coding-system property
This function returns the specified property of the coding system
CODING-SYSTEM. Most coding system properties exist for internal
purposes, but one that you might find useful is `mime-charset'.
That property's value is the name used in MIME for the character
coding which this coding system can read and write. Examples:
(coding-system-get 'iso-latin-1 'mime-charset)
=> iso-8859-1
(coding-system-get 'iso-2022-cn 'mime-charset)
=> iso-2022-cn
(coding-system-get 'cyrillic-koi8 'mime-charset)
=> koi8-r
The value of the `mime-charset' property is also defined as an
alias for the coding system.
Encoding and I/O
----------------
The principal purpose of coding systems is for use in reading and
writing files. The function `insert-file-contents' uses a coding
system for decoding the file data, and `write-region' uses one to
encode the buffer contents.
You can specify the coding system to use either explicitly (*note
Specifying Coding Systems::), or implicitly using the defaulting
mechanism (*note Default Coding Systems::). But these methods may not
completely specify what to do. For example, they may choose a coding
system such as `undefined' which leaves the character code conversion
to be determined from the data. In these cases, the I/O operation
finishes the job of choosing a coding system. Very often you will want
to find out afterwards which coding system was chosen.
- Variable: buffer-file-coding-system
This variable records the coding system that was used for visiting
the current buffer. It is used for saving the buffer, and for
writing part of the buffer with `write-region'. When those
operations ask the user to specify a different coding system,
`buffer-file-coding-system' is updated to the coding system
specified.
However, `buffer-file-coding-system' does not affect sending text
to a subprocess.
- Variable: save-buffer-coding-system
This variable specifies the coding system for saving the buffer (by
overriding `buffer-file-coding-system'). Note that it is not used
for `write-region'.
When a command to save the buffer starts out to use
`buffer-file-coding-system' (or `save-buffer-coding-system'), and
that coding system cannot handle the actual text in the buffer,
the command asks the user to choose another coding system. After
that happens, the command also updates `buffer-file-coding-system'
to represent the coding system that the user specified.
- Variable: last-coding-system-used
I/O operations for files and subprocesses set this variable to the
coding system name that was used. The explicit encoding and
decoding functions (*note Explicit Encoding::) set it too.
*Warning:* Since receiving subprocess output sets this variable,
it can change whenever Emacs waits; therefore, you should copy the
value shortly after the function call that stores the value you are
interested in.
The variable `selection-coding-system' specifies how to encode
selections for the window system. *Note Window System Selections::.
Coding Systems in Lisp
----------------------
Here are the Lisp facilities for working with coding systems:
- Function: coding-system-list &optional base-only
This function returns a list of all coding system names (symbols).
If BASE-ONLY is non-`nil', the value includes only the base
coding systems. Otherwise, it includes alias and variant coding
systems as well.
- Function: coding-system-p object
This function returns `t' if OBJECT is a coding system name.
- Function: check-coding-system coding-system
This function checks the validity of CODING-SYSTEM. If that is
valid, it returns CODING-SYSTEM. Otherwise it signals an error
with condition `coding-system-error'.
- Function: coding-system-change-eol-conversion coding-system eol-type
This function returns a coding system which is like CODING-SYSTEM
except for its eol conversion, which is specified by `eol-type'.
EOL-TYPE should be `unix', `dos', `mac', or `nil'. If it is
`nil', the returned coding system determines the end-of-line
conversion from the data.
- Function: coding-system-change-text-conversion eol-coding text-coding
This function returns a coding system which uses the end-of-line
conversion of EOL-CODING, and the text conversion of TEXT-CODING.
If TEXT-CODING is `nil', it returns `undecided', or one of its
variants according to EOL-CODING.
- Function: find-coding-systems-region from to
This function returns a list of coding systems that could be used
to encode a text between FROM and TO. All coding systems in the
list can safely encode any multibyte characters in that portion of
the text.
If the text contains no multibyte characters, the function returns
the list `(undecided)'.
- Function: find-coding-systems-string string
This function returns a list of coding systems that could be used
to encode the text of STRING. All coding systems in the list can
safely encode any multibyte characters in STRING. If the text
contains no multibyte characters, this returns the list
`(undecided)'.
- Function: find-coding-systems-for-charsets charsets
This function returns a list of coding systems that could be used
to encode all the character sets in the list CHARSETS.
- Function: detect-coding-region start end &optional highest
This function chooses a plausible coding system for decoding the
text from START to END. This text should be a byte sequence
(*note Explicit Encoding::).
Normally this function returns a list of coding systems that could
handle decoding the text that was scanned. They are listed in
order of decreasing priority. But if HIGHEST is non-`nil', then
the return value is just one coding system, the one that is
highest in priority.
If the region contains only ASCII characters, the value is
`undecided' or `(undecided)'.
- Function: detect-coding-string string highest
This function is like `detect-coding-region' except that it
operates on the contents of STRING instead of bytes in the buffer.
*Note Process Information::, for how to examine or set the coding
systems used for I/O to a subprocess.
User-Chosen Coding Systems
--------------------------
- Function: select-safe-coding-system from to &optional
default-coding-system accept-default-p
This function selects a coding system for encoding specified text,
asking the user to choose if necessary. Normally the specified
text is the text in the current buffer between FROM and TO,
defaulting to the whole buffer if they are `nil'. If FROM is a
string, the string is the specified text, and TO is ignored.
If DEFAULT-CODING-SYSTEM is non-`nil', that is the first coding
system to try; if that can handle the text,
`select-safe-coding-system' returns that coding system. It can
also be a list of coding systems; then the function tries each of
them one by one. After trying all of them, it next tries the
user's most preferred coding system (*note prefer-coding-system:
(emacs)Recognize Coding.), and after that the current buffer's
value of `buffer-file-coding-system' (if it is not `undecided').
If one of those coding systems can safely encode all the specified
text, `select-safe-coding-system' chooses it and returns it.
Otherwise, it asks the user to choose from a list of coding systems
which can encode all the text, and returns the user's choice.
The optional argument ACCEPT-DEFAULT-P, if non-`nil', should be a
function to determine whether the coding system selected without
user interaction is acceptable. If this function returns `nil',
the silently selected coding system is rejected, and the user is
asked to select a coding system from a list of possible candidates.
If the variable `select-safe-coding-system-accept-default-p' is
non-`nil', its value overrides the value of ACCEPT-DEFAULT-P.
Here are two functions you can use to let the user specify a coding
system, with completion. *Note Completion::.
- Function: read-coding-system prompt &optional default
This function reads a coding system using the minibuffer,
prompting with string PROMPT, and returns the coding system name
as a symbol. If the user enters null input, DEFAULT specifies
which coding system to return. It should be a symbol or a string.
- Function: read-non-nil-coding-system prompt
This function reads a coding system using the minibuffer,
prompting with string PROMPT, and returns the coding system name
as a symbol. If the user tries to enter null input, it asks the
user to try again. *Note Coding Systems::.
Default Coding Systems
----------------------
This section describes variables that specify the default coding
system for certain files or when running certain subprograms, and the
function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to
the defaults you want, and then do not change them again. To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
`coding-system-for-read' and `coding-system-for-write' (*note
Specifying Coding Systems::).
- Variable: auto-coding-regexp-alist
This variable is an alist of text patterns and corresponding coding
systems. Each element has the form `(REGEXP . CODING-SYSTEM)'; a
file whose first few kilobytes match REGEXP is decoded with
CODING-SYSTEM when its contents are read into a buffer. The
settings in this alist take priority over `coding:' tags in the
files and the contents of `file-coding-system-alist' (see below).
The default value is set so that Emacs automatically recognizes
mail files in Babyl format and reads them with no code conversions.
- Variable: file-coding-system-alist
This variable is an alist that specifies the coding systems to use
for reading and writing particular files. Each element has the
form `(PATTERN . CODING)', where PATTERN is a regular expression
that matches certain file names. The element applies to file
names that match PATTERN.
The CDR of the element, CODING, should be either a coding system,
a cons cell containing two coding systems, or a function name (a
symbol with a function definition). If CODING is a coding system,
that coding system is used for both reading the file and writing
it. If CODING is a cons cell containing two coding systems, its
CAR specifies the coding system for decoding, and its CDR
specifies the coding system for encoding.
If CODING is a function name, the function must return a coding
system or a cons cell containing two coding systems. This value
is used as described above.
- Variable: process-coding-system-alist
This variable is an alist specifying which coding systems to use
for a subprocess, depending on which program is running in the
subprocess. It works like `file-coding-system-alist', except that
PATTERN is matched against the program name used to start the
subprocess. The coding system or systems specified in this alist
are used to initialize the coding systems used for I/O to the
subprocess, but you can specify other coding systems later using
`set-process-coding-system'.
*Warning:* Coding systems such as `undecided', which determine the
coding system from the data, do not work entirely reliably with
asynchronous subprocess output. This is because Emacs handles
asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion--that is, one like `latin-1-unix', rather
than `undecided' or `latin-1'.
- Variable: network-coding-system-alist
This variable is an alist that specifies the coding system to use
for network streams. It works much like
`file-coding-system-alist', with the difference that the PATTERN
in an element may be either a port number or a regular expression.
If it is a regular expression, it is matched against the network
service name used to open the network stream.
- Variable: default-process-coding-system
This variable specifies the coding systems to use for subprocess
(and network stream) input and output, when nothing else specifies
what to do.
The value should be a cons cell of the form `(INPUT-CODING .
OUTPUT-CODING)'. Here INPUT-CODING applies to input from the
subprocess, and OUTPUT-CODING applies to output to it.
- Function: find-operation-coding-system operation &rest arguments
This function returns the coding system to use (by default) for
performing OPERATION with ARGUMENTS. The value has this form:
(DECODING-SYSTEM ENCODING-SYSTEM)
The first element, DECODING-SYSTEM, is the coding system to use
for decoding (in case OPERATION does decoding), and
ENCODING-SYSTEM is the coding system for encoding (in case
OPERATION does encoding).
The argument OPERATION should be a symbol, one of
`insert-file-contents', `write-region', `call-process',
`call-process-region', `start-process', or `open-network-stream'.
These are the names of the Emacs I/O primitives that can do coding
system conversion.
The remaining arguments should be the same arguments that might be
given to that I/O primitive. Depending on the primitive, one of
those arguments is selected as the "target". For example, if
OPERATION does file I/O, whichever argument specifies the file
name is the target. For subprocess primitives, the process name
is the target. For `open-network-stream', the target is the
service name or port number.
This function looks up the target in `file-coding-system-alist',
`process-coding-system-alist', or `network-coding-system-alist',
depending on OPERATION. *Note Default Coding Systems::.
Specifying a Coding System for One Operation
--------------------------------------------
You can specify the coding system for a specific operation by binding
the variables `coding-system-for-read' and/or `coding-system-for-write'.
- Variable: coding-system-for-read
If this variable is non-`nil', it specifies the coding system to
use for reading a file, or for input from a synchronous subprocess.
It also applies to any asynchronous subprocess or network stream,
but in a different way: the value of `coding-system-for-read' when
you start the subprocess or open the network stream specifies the
input decoding method for that subprocess or network stream. It
remains in use for that subprocess or network stream unless and
until overridden.
The right way to use this variable is to bind it with `let' for a
specific I/O operation. Its global value is normally `nil', and
you should not globally set it to any other value. Here is an
example of the right way to use the variable:
;; Read the file with no character code conversion.
;; Assume CRLF represents end-of-line.
(let ((coding-system-for-write 'emacs-mule-dos))
(insert-file-contents filename))
When its value is non-`nil', `coding-system-for-read' takes
precedence over all other methods of specifying a coding system to
use for input, including `file-coding-system-alist',
`process-coding-system-alist' and `network-coding-system-alist'.
- Variable: coding-system-for-write
This works much like `coding-system-for-read', except that it
applies to output rather than input. It affects writing to files,
as well as sending output to subprocesses and net connections.
When a single operation does both input and output, as do
`call-process-region' and `start-process', both
`coding-system-for-read' and `coding-system-for-write' affect it.
- Variable: inhibit-eol-conversion
When this variable is non-`nil', no end-of-line conversion is done,
no matter which coding system is specified. This applies to all
the Emacs I/O and subprocess primitives, and to the explicit
encoding and decoding functions (*note Explicit Encoding::).
Explicit Encoding and Decoding
------------------------------
All the operations that transfer text in and out of Emacs have the
ability to use a coding system to encode or decode the text. You can
also explicitly encode and decode text using the functions in this
section.
The result of encoding, and the input to decoding, are not ordinary
text. They logically consist of a series of byte values; that is, a
series of characters whose codes are in the range 0 through 255. In a
multibyte buffer or string, character codes 128 through 159 are
represented by multibyte sequences, but this is invisible to Lisp
programs.
The usual way to read a file into a buffer as a sequence of bytes, so
you can decode the contents explicitly, is with
`insert-file-contents-literally' (*note Reading from Files::);
alternatively, specify a non-`nil' RAWFILE argument when visiting a
file with `find-file-noselect'. These methods result in a unibyte
buffer.
The usual way to use the byte sequence that results from explicitly
encoding text is to copy it to a file or process--for example, to write
it with `write-region' (*note Writing to Files::), and suppress
encoding by binding `coding-system-for-write' to `no-conversion'.
Here are the functions to perform explicit encoding or decoding. The
decoding functions produce sequences of bytes; the encoding functions
are meant to operate on sequences of bytes. All of these functions
discard text properties.
- Function: encode-coding-region start end coding-system
This function encodes the text from START to END according to
coding system CODING-SYSTEM. The encoded text replaces the
original text in the buffer. The result of encoding is logically a
sequence of bytes, but the buffer remains multibyte if it was
multibyte before.
- Function: encode-coding-string string coding-system
This function encodes the text in STRING according to coding
system CODING-SYSTEM. It returns a new string containing the
encoded text. The result of encoding is a unibyte string.
- Function: decode-coding-region start end coding-system
This function decodes the text from START to END according to
coding system CODING-SYSTEM. The decoded text replaces the
original text in the buffer. To make explicit decoding useful,
the text before decoding ought to be a sequence of byte values,
but both multibyte and unibyte buffers are acceptable.
- Function: decode-coding-string string coding-system
This function decodes the text in STRING according to coding
system CODING-SYSTEM. It returns a new string containing the
decoded text. To make explicit decoding useful, the contents of
STRING ought to be a sequence of byte values, but a multibyte
string is acceptable.
Terminal I/O Encoding
---------------------
Emacs can decode keyboard input using a coding system, and encode
terminal output. This is useful for terminals that transmit or display
text using a particular encoding such as Latin-1. Emacs does not set
`last-coding-system-used' for encoding or decoding for the terminal.
- Function: keyboard-coding-system
This function returns the coding system that is in use for decoding
keyboard input--or `nil' if no coding system is to be used.
- Function: set-keyboard-coding-system coding-system
This function specifies CODING-SYSTEM as the coding system to use
for decoding keyboard input. If CODING-SYSTEM is `nil', that
means do not decode keyboard input.
- Function: terminal-coding-system
This function returns the coding system that is in use for encoding
terminal output--or `nil' for no encoding.
- Function: set-terminal-coding-system coding-system
This function specifies CODING-SYSTEM as the coding system to use
for encoding terminal output. If CODING-SYSTEM is `nil', that
means do not encode terminal output.
MS-DOS File Types
-----------------
On MS-DOS and Microsoft Windows, Emacs guesses the appropriate
end-of-line conversion for a file by looking at the file's name. This
feature classifies files as "text files" and "binary files". By
"binary file" we mean a file of literal byte values that are not
necessarily meant to be characters; Emacs does no end-of-line conversion
and no character code conversion for them. On the other hand, the bytes
in a text file are intended to represent characters; when you create a
new file whose name implies that it is a text file, Emacs uses DOS
end-of-line conversion.
- Variable: buffer-file-type
This variable, automatically buffer-local in each buffer, records
the file type of the buffer's visited file. When a buffer does
not specify a coding system with `buffer-file-coding-system', this
variable is used to determine which coding system to use when
writing the contents of the buffer. It should be `nil' for text,
`t' for binary. If it is `t', the coding system is
`no-conversion'. Otherwise, `undecided-dos' is used.
Normally this variable is set by visiting a file; it is set to
`nil' if the file was visited without any actual conversion.
- User Option: file-name-buffer-file-type-alist
This variable holds an alist for recognizing text and binary files.
Each element has the form (REGEXP . TYPE), where REGEXP is matched
against the file name, and TYPE may be `nil' for text, `t' for
binary, or a function to call to compute which. If it is a
function, then it is called with a single argument (the file name)
and should return `t' or `nil'.
When running on MS-DOS or MS-Windows, Emacs checks this alist to
decide which coding system to use when reading a file. For a text
file, `undecided-dos' is used. For a binary file, `no-conversion'
is used.
If no element in this alist matches a given file name, then
`default-buffer-file-type' says how to treat the file.
- User Option: default-buffer-file-type
This variable says how to handle files for which
`file-name-buffer-file-type-alist' says nothing about the type.
If this variable is non-`nil', then these files are treated as
binary: the coding system `no-conversion' is used. Otherwise,
nothing special is done for them--the coding system is deduced
solely from the file contents, in the usual Emacs fashion.
Input Methods
=============
"Input methods" provide convenient ways of entering non-ASCII
characters from the keyboard. Unlike coding systems, which translate
non-ASCII characters to and from encodings meant to be read by
programs, input methods provide human-friendly commands. (*Note Input
Methods: (emacs)Input Methods, for information on how users use input
methods to enter text.) How to define input methods is not yet
documented in this manual, but here we describe how to use them.
Each input method has a name, which is currently a string; in the
future, symbols may also be usable as input method names.
- Variable: current-input-method
This variable holds the name of the input method now active in the
current buffer. (It automatically becomes local in each buffer
when set in any fashion.) It is `nil' if no input method is
active in the buffer now.
- Variable: default-input-method
This variable holds the default input method for commands that
choose an input method. Unlike `current-input-method', this
variable is normally global.
- Function: set-input-method input-method
This function activates input method INPUT-METHOD for the current
buffer. It also sets `default-input-method' to INPUT-METHOD. If
INPUT-METHOD is `nil', this function deactivates any input method
for the current buffer.
- Function: read-input-method-name prompt &optional default
inhibit-null
This function reads an input method name with the minibuffer,
prompting with PROMPT. If DEFAULT is non-`nil', that is returned
by default, if the user enters empty input. However, if
INHIBIT-NULL is non-`nil', empty input signals an error.
The returned value is a string.
- Variable: input-method-alist
This variable defines all the supported input methods. Each
element defines one input method, and should have the form:
(INPUT-METHOD LANGUAGE-ENV ACTIVATE-FUNC
TITLE DESCRIPTION ARGS...)
Here INPUT-METHOD is the input method name, a string; LANGUAGE-ENV
is another string, the name of the language environment this input
method is recommended for. (That serves only for documentation
purposes.)
ACTIVATE-FUNC is a function to call to activate this method. The
ARGS, if any, are passed as arguments to ACTIVATE-FUNC. All told,
the arguments to ACTIVATE-FUNC are INPUT-METHOD and the ARGS.
TITLE is a string to display in the mode line while this method is
active. DESCRIPTION is a string describing this method and what
it is good for.
The fundamental interface to input methods is through the variable
`input-method-function'. *Note Reading One Event::.
Locales
=======
POSIX defines a concept of "locales" which control which language to
use in language-related features. These Emacs variables control how
Emacs interacts with these features.
- Variable: locale-coding-system
This variable specifies the coding system to use for decoding
system error messages, for encoding the format argument to
`format-time-string', and for decoding the return value of
`format-time-string'.
- Variable: system-messages-locale
This variable specifies the locale to use for generating system
error messages. Changing the locale can cause messages to come
out in a different language or in a different orthography. If the
variable is `nil', the locale is specified by environment
variables in the usual POSIX fashion.
- Variable: system-time-locale
This variable specifies the locale to use for formatting time
values. Changing the locale can cause messages to appear
according to the conventions of a different language. If the
variable is `nil', the locale is specified by environment
variables in the usual POSIX fashion.
Searching and Matching
**********************
GNU Emacs provides two ways to search through a buffer for specified
text: exact string searches and regular expression searches. After a
regular expression search, you can examine the "match data" to
determine which text matched the whole regular expression or various
portions of it.
The `skip-chars...' functions also perform a kind of searching.
*Note Skipping Characters::.
Searching for Strings
=====================
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string; the
arguments LIMIT and NOERROR are `nil', and REPEAT is 1.
These search functions convert the search string to multibyte if the
buffer is multibyte; they convert the search string to unibyte if the
buffer is unibyte. *Note Text Representations::.
- Command: search-forward string &optional limit noerror repeat
This function searches forward from point for an exact match for
STRING. If successful, it sets point to the end of the occurrence
found, and returns the new value of point. If no match is found,
the value and side effects depend on NOERROR (see below).
In the following example, point is initially at the beginning of
the line. Then `(search-forward "fox")' moves point after the last
letter of `fox':
---------- Buffer: foo ----------
-!-The quick brown fox jumped over the lazy dog.
---------- Buffer: foo ----------
(search-forward "fox")
=> 20
---------- Buffer: foo ----------
The quick brown fox-!- jumped over the lazy dog.
---------- Buffer: foo ----------
The argument LIMIT specifies the upper bound to the search. (It
must be a position in the current buffer.) No match extending
after that position is accepted. If LIMIT is omitted or `nil', it
defaults to the end of the accessible portion of the buffer.
What happens when the search fails depends on the value of
NOERROR. If NOERROR is `nil', a `search-failed' error is
signaled. If NOERROR is `t', `search-forward' returns `nil' and
does nothing. If NOERROR is neither `nil' nor `t', then
`search-forward' moves point to the upper bound and returns `nil'.
(It would be more consistent now to return the new position of
point in that case, but some existing programs may depend on a
value of `nil'.)
If REPEAT is supplied (it must be a positive number), then the
search is repeated that many times (each time starting at the end
of the previous time's match). If these successive searches
succeed, the function succeeds, moving point and returning its new
value. Otherwise the search fails.
- Command: search-backward string &optional limit noerror repeat
This function searches backward from point for STRING. It is just
like `search-forward' except that it searches backwards and leaves
point at the beginning of the match.
- Command: word-search-forward string &optional limit noerror repeat
This function searches forward from point for a "word" match for
STRING. If it finds a match, it sets point to the end of the
match found, and returns the new value of point.
Word matching regards STRING as a sequence of words, disregarding
punctuation that separates them. It searches the buffer for the
same sequence of words. Each word must be distinct in the buffer
(searching for the word `ball' does not match the word `balls'),
but the details of punctuation and spacing are ignored (searching
for `ball boy' does match `ball. Boy!').
In this example, point is initially at the beginning of the
buffer; the search leaves it between the `y' and the `!'.
---------- Buffer: foo ----------
-!-He said "Please! Find
the ball boy!"
---------- Buffer: foo ----------
(word-search-forward "Please find the ball, boy.")
=> 35
---------- Buffer: foo ----------
He said "Please! Find
the ball boy-!-!"
---------- Buffer: foo ----------
If LIMIT is non-`nil' (it must be a position in the current
buffer), then it is the upper bound to the search. The match
found must not extend after that position.
If NOERROR is `nil', then `word-search-forward' signals an error
if the search fails. If NOERROR is `t', then it returns `nil'
instead of signaling an error. If NOERROR is neither `nil' nor
`t', it moves point to LIMIT (or the end of the buffer) and
returns `nil'.
If REPEAT is non-`nil', then the search is repeated that many
times. Point is positioned at the end of the last match.
- Command: word-search-backward string &optional limit noerror repeat
This function searches backward from point for a word match to
STRING. This function is just like `word-search-forward' except
that it searches backward and normally leaves point at the
beginning of the match.
Regular Expressions
===================
A "regular expression" ("regexp", for short) is a pattern that
denotes a (possibly infinite) set of strings. Searching for matches for
a regexp is a very powerful operation. This section explains how to
write regexps; the following section says how to search for them.
Syntax of Regular Expressions
-----------------------------
Regular expressions have a syntax in which a few characters are
special constructs and the rest are "ordinary". An ordinary character
is a simple regular expression that matches that character and nothing
else. The special characters are `.', `*', `+', `?', `[', `]', `^',
`$', and `\'; no new special characters will be defined in the future.
Any other character appearing in a regular expression is ordinary,
unless a `\' precedes it.
For example, `f' is not a special character, so it is ordinary, and
therefore `f' is a regular expression that matches the string `f' and
no other string. (It does _not_ match the string `fg', but it does
match a _part_ of that string.) Likewise, `o' is a regular expression
that matches only `o'.
Any two regular expressions A and B can be concatenated. The result
is a regular expression that matches a string if A matches some amount
of the beginning of that string and B matches the rest of the string.
As a simple example, we can concatenate the regular expressions `f'
and `o' to get the regular expression `fo', which matches only the
string `fo'. Still trivial. To do something more powerful, you need
to use one of the special regular expression constructs.
Special Characters in Regular Expressions
.........................................
Here is a list of the characters that are special in a regular
expression.
`.' (Period)
is a special character that matches any single character except a
newline. Using concatenation, we can make regular expressions
like `a.b', which matches any three-character string that begins
with `a' and ends with `b'.
`*'
is not a construct by itself; it is a postfix operator that means
to match the preceding regular expression repetitively as many
times as possible. Thus, `o*' matches any number of `o's
(including no `o's).
`*' always applies to the _smallest_ possible preceding
expression. Thus, `fo*' has a repeating `o', not a repeating
`fo'. It matches `f', `fo', `foo', and so on.
The matcher processes a `*' construct by matching, immediately, as
many repetitions as can be found. Then it continues with the rest
of the pattern. If that fails, backtracking occurs, discarding
some of the matches of the `*'-modified construct in the hope that
that will make it possible to match the rest of the pattern. For
example, in matching `ca*ar' against the string `caaar', the `a*'
first tries to match all three `a's; but the rest of the pattern is
`ar' and there is only `r' left to match, so this try fails. The
next alternative is for `a*' to match only two `a's. With this
choice, the rest of the regexp matches successfully.
Nested repetition operators can be extremely slow if they specify
backtracking loops. For example, it could take hours for the
regular expression `\(x+y*\)*a' to try to match the sequence
`xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz', before it ultimately fails.
The slowness is because Emacs must try each imaginable way of
grouping the 35 `x's before concluding that none of them can work.
To make sure your regular expressions run fast, check nested
repetitions carefully.
`+'
is a postfix operator, similar to `*' except that it must match
the preceding expression at least once. So, for example, `ca+r'
matches the strings `car' and `caaaar' but not the string `cr',
whereas `ca*r' matches all three strings.
`?'
is a postfix operator, similar to `*' except that it must match the
preceding expression either once or not at all. For example,
`ca?r' matches `car' or `cr'; nothing else.
`*?', `+?', `??'
These are "non-greedy" variants of the operators `*', `+' and `?'.
Where those operators match the largest possible substring
(consistent with matching the entire containing expression), the
non-greedy variants match the smallest possible substring
(consistent with matching the entire containing expression).
For example, the regular expression `c[ad]*a' when applied to the
string `cdaaada' matches the whole string; but the regular
expression `c[ad]*?a', applied to that same string, matches just
`cda'. (The smallest possible match here for `[ad]*?' that
permits the whole expression to match is `d'.)
`[ ... ]'
is a "character alternative", which begins with `[' and is
terminated by `]'. In the simplest case, the characters between
the two brackets are what this character alternative can match.
Thus, `[ad]' matches either one `a' or one `d', and `[ad]*'
matches any string composed of just `a's and `d's (including the
empty string), from which it follows that `c[ad]*r' matches `cr',
`car', `cdr', `caddaar', etc.
You can also include character ranges in a character alternative,
by writing the starting and ending characters with a `-' between
them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges
may be intermixed freely with individual characters, as in
`[a-z$%.]', which matches any lower case ASCII letter or `$', `%'
or period.
Note that the usual regexp special characters are not special
inside a character alternative. A completely different set of
characters is special inside character alternatives: `]', `-' and
`^'.
To include a `]' in a character alternative, you must make it the
first character. For example, `[]a]' matches `]' or `a'. To
include a `-', write `-' as the first or last character of the
character alternative, or put it after a range. Thus, `[]-]'
matches both `]' and `-'.
To include `^' in a character alternative, put it anywhere but at
the beginning.
The beginning and end of a range of multibyte characters must be in
the same character set (*note Character Sets::). Thus,
`"[\x8e0-\x97c]"' is invalid because character 0x8e0 (`a' with
grave accent) is in the Emacs character set for Latin-1 but the
character 0x97c (`u' with diaeresis) is in the Emacs character set
for Latin-2. (We use Lisp string syntax to write that example,
and a few others in the next few paragraphs, in order to include
hex escape sequences in them.)
If a range starts with a unibyte character C and ends with a
multibyte character C2, the range is divided into two parts: one
is `C..?\377', the other is `C1..C2', where C1 is the first
character of the charset to which C2 belongs.
You cannot always match all non-ASCII characters with the regular
expression `"[\200-\377]"'. This works when searching a unibyte
buffer or string (*note Text Representations::), but not in a
multibyte buffer or string, because many non-ASCII characters have
codes above octal 0377. However, the regular expression
`"[^\000-\177]"' does match all non-ASCII characters (see below
regarding `^'), in both multibyte and unibyte representations,
because only the ASCII characters are excluded.
Starting in Emacs 21, a character alternative can also specify
named character classes (*note Char Classes::). This is a POSIX
feature whose syntax is `[:CLASS:]'. Using a character class is
equivalent to mentioning each of the characters in that class; but
the latter is not feasible in practice, since some classes include
thousands of different characters.
`[^ ... ]'
`[^' begins a "complemented character alternative", which matches
any character except the ones specified. Thus, `[^a-z0-9A-Z]'
matches all characters _except_ letters and digits.
`^' is not special in a character alternative unless it is the
first character. The character following the `^' is treated as if
it were first (in other words, `-' and `]' are not special there).
A complemented character alternative can match a newline, unless
newline is mentioned as one of the characters not to match. This
is in contrast to the handling of regexps in programs such as
`grep'.
`^'
is a special character that matches the empty string, but only at
the beginning of a line in the text being matched. Otherwise it
fails to match anything. Thus, `^foo' matches a `foo' that occurs
at the beginning of a line.
When matching a string instead of a buffer, `^' matches at the
beginning of the string or after a newline character.
For historical compatibility reasons, `^' can be used only at the
beginning of the regular expression, or after `\(' or `\|'.
`$'
is similar to `^' but matches only at the end of a line. Thus,
`x+$' matches a string of one `x' or more at the end of a line.
When matching a string instead of a buffer, `$' matches at the end
of the string or before a newline character.
For historical compatibility reasons, `$' can be used only at the
end of the regular expression, or before `\)' or `\|'.
`\'
has two functions: it quotes the special characters (including
`\'), and it introduces additional special constructs.
Because `\' quotes special characters, `\$' is a regular
expression that matches only `$', and `\[' is a regular expression
that matches only `[', and so on.
Note that `\' also has special meaning in the read syntax of Lisp
strings (*note String Type::), and must be quoted with `\'. For
example, the regular expression that matches the `\' character is
`\\'. To write a Lisp string that contains the characters `\\',
Lisp syntax requires you to quote each `\' with another `\'.
Therefore, the read syntax for a regular expression matching `\'
is `"\\\\"'.
*Please note:* For historical compatibility, special characters are
treated as ordinary ones if they are in contexts where their special
meanings make no sense. For example, `*foo' treats `*' as ordinary
since there is no preceding expression on which the `*' can act. It is
poor practice to depend on this behavior; quote the special character
anyway, regardless of where it appears.
Character Classes
.................
Here is a table of the classes you can use in a character
alternative, in Emacs 21, and what they mean:
`[:ascii:]'
This matches any ASCII (unibyte) character.
`[:alnum:]'
This matches any letter or digit. (At present, for multibyte
characters, it matches anything that has word syntax.)
`[:alpha:]'
This matches any letter. (At present, for multibyte characters, it
matches anything that has word syntax.)
`[:blank:]'
This matches space and tab only.
`[:cntrl:]'
This matches any ASCII control character.
`[:digit:]'
This matches `0' through `9'. Thus, `[-+[:digit:]]' matches any
digit, as well as `+' and `-'.
`[:graph:]'
This matches graphic characters--everything except ASCII control
characters, space, and the delete character.
`[:lower:]'
This matches any lower-case letter, as determined by the current
case table (*note Case Tables::).
`[:nonascii:]'
This matches any non-ASCII (multibyte) character.
`[:print:]'
This matches printing characters--everything except ASCII control
characters and the delete character.
`[:punct:]'
This matches any punctuation character. (At present, for multibyte
characters, it matches anything that has non-word syntax.)
`[:space:]'
This matches any character that has whitespace syntax (*note
Syntax Class Table::).
`[:upper:]'
This matches any upper-case letter, as determined by the current
case table (*note Case Tables::).
`[:word:]'
This matches any character that has word syntax (*note Syntax
Class Table::).
`[:xdigit:]'
This matches the hexadecimal digits: `0' through `9', `a' through
`f' and `A' through `F'.
Backslash Constructs in Regular Expressions
...........................................
For the most part, `\' followed by any character matches only that
character. However, there are several exceptions: certain
two-character sequences starting with `\' that have special meanings.
(The character after the `\' in such a sequence is always ordinary when
used on its own.) Here is a table of the special `\' constructs.
`\|'
specifies an alternative. Two regular expressions A and B with
`\|' in between form an expression that matches anything that
either A or B matches.
Thus, `foo\|bar' matches either `foo' or `bar' but no other string.
`\|' applies to the largest possible surrounding expressions.
Only a surrounding `\( ... \)' grouping can limit the grouping
power of `\|'.
Full backtracking capability exists to handle multiple uses of
`\|', if you use the POSIX regular expression functions (*note
POSIX Regexps::).
`\{M\}'
is a postfix operator that repeats the previous pattern exactly M
times. Thus, `x\{5\}' matches the string `xxxxx' and nothing
else. `c[ad]\{3\}r' matches string such as `caaar', `cdddr',
`cadar', and so on.
`\{M,N\}'
is more general postfix operator that specifies repetition with a
minimum of M repeats and a maximum of N repeats. If M is omitted,
the minimum is 0; if N is omitted, there is no maximum.
For example, `c[ad]\{1,2\}r' matches the strings `car', `cdr',
`caar', `cadr', `cdar', and `cddr', and nothing else.
`\{0,1\}' or `\{,1\}' is equivalent to `?'.
`\{0,\}' or `\{,\}' is equivalent to `*'.
`\{1,\}' is equivalent to `+'.
`\( ... \)'
is a grouping construct that serves three purposes:
1. To enclose a set of `\|' alternatives for other operations.
Thus, the regular expression `\(foo\|bar\)x' matches either
`foox' or `barx'.
2. To enclose a complicated expression for the postfix operators
`*', `+' and `?' to operate on. Thus, `ba\(na\)*' matches
`ba', `bana', `banana', `bananana', etc., with any number
(zero or more) of `na' strings.
3. To record a matched substring for future reference with
`\DIGIT' (see below).
This last application is not a consequence of the idea of a
parenthetical grouping; it is a separate feature that was assigned
as a second meaning to the same `\( ... \)' construct because, in
pratice, there was usually no conflict between the two meanings.
But occasionally there is a conflict, and that led to the
introduction of shy groups.
`\(?: ... \)'
is the "shy group" construct. A shy group serves the first two
purposes of an ordinary group (controlling the nesting of other
operators), but it does not get a number, so you cannot refer back
to its value with `\DIGIT'.
Shy groups are particulary useful for mechanically-constructed
regular expressions because they can be added automatically
without altering the numbering of any ordinary, non-shy groups.
`\DIGIT'
matches the same text that matched the DIGITth occurrence of a
grouping (`\( ... \)') construct.
In other words, after the end of a group, the matcher remembers the
beginning and end of the text matched by that group. Later on in
the regular expression you can use `\' followed by DIGIT to match
that same text, whatever it may have been.
The strings matching the first nine grouping constructs appearing
in the entire regular expression passed to a search or matching
function are assigned numbers 1 through 9 in the order that the
open parentheses appear in the regular expression. So you can use
`\1' through `\9' to refer to the text matched by the
corresponding grouping constructs.
For example, `\(.*\)\1' matches any newline-free string that is
composed of two identical halves. The `\(.*\)' matches the first
half, which may be anything, but the `\1' that follows must match
the same exact text.
If a particular grouping construct in the regular expression was
never matched--for instance, if it appears inside of an
alternative that wasn't used, or inside of a repetition that
repeated zero times--then the corresponding `\DIGIT' construct
never matches anything. To use an artificial example,,
`\(foo\(b*\)\|lose\)\2' cannot match `lose': the second
alternative inside the larger group matches it, but then `\2' is
undefined and can't match anything. But it can match `foobb',
because the first alternative matches `foob' and `\2' matches `b'.
`\w'
matches any word-constituent character. The editor syntax table
determines which characters these are. *Note Syntax Tables::.
`\W'
matches any character that is not a word constituent.
`\sCODE'
matches any character whose syntax is CODE. Here CODE is a
character that represents a syntax code: thus, `w' for word
constituent, `-' for whitespace, `(' for open parenthesis, etc.
To represent whitespace syntax, use either `-' or a space
character. *Note Syntax Class Table::, for a list of syntax codes
and the characters that stand for them.
`\SCODE'
matches any character whose syntax is not CODE.
`\cC'
matches any character whose category is C. Here C is a character
that represents a category: thus, `c' for Chinese characters or
`g' for Greek characters in the standard category table.
`\CC'
matches any character whose category is not C.
The following regular expression constructs match the empty
string--that is, they don't use up any characters--but whether they
match depends on the context.
`\`'
matches the empty string, but only at the beginning of the buffer
or string being matched against.
`\''
matches the empty string, but only at the end of the buffer or
string being matched against.
`\='
matches the empty string, but only at point. (This construct is
not defined when matching against a string.)
`\b'
matches the empty string, but only at the beginning or end of a
word. Thus, `\bfoo\b' matches any occurrence of `foo' as a
separate word. `\bballs?\b' matches `ball' or `balls' as a
separate word.
`\b' matches at the beginning or end of the buffer regardless of
what text appears next to it.
`\B'
matches the empty string, but _not_ at the beginning or end of a
word.
`\<'
matches the empty string, but only at the beginning of a word.
`\<' matches at the beginning of the buffer only if a
word-constituent character follows.
`\>'
matches the empty string, but only at the end of a word. `\>'
matches at the end of the buffer only if the contents end with a
word-constituent character.
Not every string is a valid regular expression. For example, a
string with unbalanced square brackets is invalid (with a few
exceptions, such as `[]]'), and so is a string that ends with a single
`\'. If an invalid regular expression is passed to any of the search
functions, an `invalid-regexp' error is signaled.
Complex Regexp Example
----------------------
Here is a complicated regexp, used by Emacs to recognize the end of a
sentence together with any whitespace that follows. It is the value of
the variable `sentence-end'.
First, we show the regexp as a string in Lisp syntax to distinguish
spaces from tab characters. The string constant begins and ends with a
double-quote. `\"' stands for a double-quote as part of the string,
`\\' for a backslash as part of the string, `\t' for a tab and `\n' for
a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
In contrast, if you evaluate the variable `sentence-end', you will see
the following:
sentence-end
=> "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[
]*"
In this output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be
deciphered as follows:
`[.?!]'
The first part of the pattern is a character alternative that
matches any one of three characters: period, question mark, and
exclamation mark. The match must begin with one of these three
characters.
`[]\"')}]*'
The second part of the pattern matches any closing braces and
quotation marks, zero or more of them, that may follow the period,
question mark or exclamation mark. The `\"' is Lisp syntax for a
double-quote in a string. The `*' at the end indicates that the
immediately preceding regular expression (a character alternative,
in this case) may be repeated zero or more times.
`\\($\\| $\\|\t\\| \\)'
The third part of the pattern matches the whitespace that follows
the end of a sentence: the end of a line (optionally with a
space), or a tab, or two spaces. The double backslashes mark the
parentheses and vertical bars as regular expression syntax; the
parentheses delimit a group and the vertical bars separate
alternatives. The dollar sign is used to match the end of a line.
`[ \t\n]*'
Finally, the last part of the pattern matches any additional
whitespace beyond the minimum needed to end a sentence.
Regular Expression Functions
----------------------------
These functions operate on regular expressions.
- Function: regexp-quote string
This function returns a regular expression whose only exact match
is STRING. Using this regular expression in `looking-at' will
succeed only if the next characters in the buffer are STRING;
using it in a search function will succeed if the text being
searched contains STRING.
This allows you to request an exact string match or search when
calling a function that wants a regular expression.
(regexp-quote "^The cat$")
=> "\\^The cat\\$"
One use of `regexp-quote' is to combine an exact string match with
context described as a regular expression. For example, this
searches for the string that is the value of STRING, surrounded by
whitespace:
(re-search-forward
(concat "\\s-" (regexp-quote string) "\\s-"))
- Function: regexp-opt strings &optional paren
This function returns an efficient regular expression that will
match any of the strings STRINGS. This is useful when you need to
make matching or searching as fast as possible--for example, for
Font Lock mode.
If the optional argument PAREN is non-`nil', then the returned
regular expression is always enclosed by at least one
parentheses-grouping construct.
This simplified definition of `regexp-opt' produces a regular
expression which is equivalent to the actual value (but not as
efficient):
(defun regexp-opt (strings paren)
(let ((open-paren (if paren "\\(" ""))
(close-paren (if paren "\\)" "")))
(concat open-paren
(mapconcat 'regexp-quote strings "\\|")
close-paren)))
- Function: regexp-opt-depth regexp
This function returns the total number of grouping constructs
(parenthesized expressions) in REGEXP.
Regular Expression Searching
============================
In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not. For incremental search
commands, see *Note Regular Expression Search: (emacs)Regexp Search.
Here we describe only the search functions useful in programs. The
principal one is `re-search-forward'.
These search functions convert the regular expression to multibyte if
the buffer is multibyte; they convert the regular expression to unibyte
if the buffer is unibyte. *Note Text Representations::.
- Command: re-search-forward regexp &optional limit noerror repeat
This function searches forward in the current buffer for a string
of text that is matched by the regular expression REGEXP. The
function skips over any amount of text that is not matched by
REGEXP, and leaves point at the end of the first match found. It
returns the new value of point.
If LIMIT is non-`nil' (it must be a position in the current
buffer), then it is the upper bound to the search. No match
extending after that position is accepted.
If REPEAT is supplied (it must be a positive number), then the
search is repeated that many times (each time starting at the end
of the previous time's match). If all these successive searches
succeed, the function succeeds, moving point and returning its new
value. Otherwise the function fails.
What happens when the function fails depends on the value of
NOERROR. If NOERROR is `nil', a `search-failed' error is
signaled. If NOERROR is `t', `re-search-forward' does nothing and
returns `nil'. If NOERROR is neither `nil' nor `t', then
`re-search-forward' moves point to LIMIT (or the end of the
buffer) and returns `nil'.
In the following example, point is initially before the `T'.
Evaluating the search call moves point to the end of that line
(between the `t' of `hat' and the newline).
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(re-search-forward "[a-z]+" nil t 5)
=> 27
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
- Command: re-search-backward regexp &optional limit noerror repeat
This function searches backward in the current buffer for a string
of text that is matched by the regular expression REGEXP, leaving
point at the beginning of the first text found.
This function is analogous to `re-search-forward', but they are not
simple mirror images. `re-search-forward' finds the match whose
beginning is as close as possible to the starting point. If
`re-search-backward' were a perfect mirror image, it would find the
match whose end is as close as possible. However, in fact it
finds the match whose beginning is as close as possible. The
reason for this is that matching a regular expression at a given
spot always works from beginning to end, and starts at a specified
beginning position.
A true mirror-image of `re-search-forward' would require a special
feature for matching regular expressions from end to beginning.
It's not worth the trouble of implementing that.
- Function: string-match regexp string &optional start
This function returns the index of the start of the first match for
the regular expression REGEXP in STRING, or `nil' if there is no
match. If START is non-`nil', the search starts at that index in
STRING.
For example,
(string-match
"quick" "The quick brown fox jumped quickly.")
=> 4
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
The index of the first character of the string is 0, the index of
the second character is 1, and so on.
After this function returns, the index of the first character
beyond the match is available as `(match-end 0)'. *Note Match
Data::.
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
(match-end 0)
=> 32
- Function: looking-at regexp
This function determines whether the text in the current buffer
directly following point matches the regular expression REGEXP.
"Directly following" means precisely that: the search is
"anchored" and it can succeed only starting with the first
character following point. The result is `t' if so, `nil'
otherwise.
This function does not move point, but it updates the match data,
which you can access using `match-beginning' and `match-end'.
*Note Match Data::.
In this example, point is located directly before the `T'. If it
were anywhere else, the result would be `nil'.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(looking-at "The cat in the hat$")
=> t
POSIX Regular Expression Searching
==================================
The usual regular expression functions do backtracking when necessary
to handle the `\|' and repetition constructs, but they continue this
only until they find _some_ match. Then they succeed and report the
first match found.
This section describes alternative search functions which perform the
full backtracking specified by the POSIX standard for regular expression
matching. They continue backtracking until they have tried all
possibilities and found all matches, so they can report the longest
match, as required by POSIX. This is much slower, so use these
functions only when you really need the longest match.
- Function: posix-search-forward regexp &optional limit noerror repeat
This is like `re-search-forward' except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
- Function: posix-search-backward regexp &optional limit noerror repeat
This is like `re-search-backward' except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
- Function: posix-looking-at regexp
This is like `looking-at' except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
- Function: posix-string-match regexp string &optional start
This is like `string-match' except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
Search and Replace
==================
- Function: perform-replace from-string replacements start end
query-flag regexp-flag delimited-flag &optional repeat-count
map
This function is the guts of `query-replace' and related commands.
It searches for occurrences of FROM-STRING in the text between
positions START and END and replaces some or all of them. If
START is `nil', point is used instead, and the buffer's end is
used for END.
If QUERY-FLAG is `nil', it replaces all occurrences; otherwise, it
asks the user what to do about each one.
If REGEXP-FLAG is non-`nil', then FROM-STRING is considered a
regular expression; otherwise, it must match literally. If
DELIMITED-FLAG is non-`nil', then only replacements surrounded by
word boundaries are considered.
The argument REPLACEMENTS specifies what to replace occurrences
with. If it is a string, that string is used. It can also be a
list of strings, to be used in cyclic order.
If REPLACEMENTS is a cons cell, `(FUNCTION . DATA)', this means to
call FUNCTION after each match to get the replacement text. This
function is called with two arguments: DATA, and the number of
replacements already made.
If REPEAT-COUNT is non-`nil', it should be an integer. Then it
specifies how many times to use each of the strings in the
REPLACEMENTS list before advancing cyclicly to the next one.
If FROM-STRING contains upper-case letters, then `perform-replace'
binds `case-fold-search' to `nil', and it uses the `replacements'
without altering the case of them.
Normally, the keymap `query-replace-map' defines the possible user
responses for queries. The argument MAP, if non-`nil', is a
keymap to use instead of `query-replace-map'.
- Variable: query-replace-map
This variable holds a special keymap that defines the valid user
responses for `query-replace' and related functions, as well as
`y-or-n-p' and `map-y-or-n-p'. It is unusual in two ways:
* The "key bindings" are not commands, just symbols that are
meaningful to the functions that use this map.
* Prefix keys are not supported; each key binding must be for a
single-event key sequence. This is because the functions
don't use `read-key-sequence' to get the input; instead, they
read a single event and look it up "by hand."
Here are the meaningful "bindings" for `query-replace-map'. Several
of them are meaningful only for `query-replace' and friends.
`act'
Do take the action being considered--in other words, "yes."
`skip'
Do not take action for this question--in other words, "no."
`exit'
Answer this question "no," and give up on the entire series of
questions, assuming that the answers will be "no."
`act-and-exit'
Answer this question "yes," and give up on the entire series of
questions, assuming that subsequent answers will be "no."
`act-and-show'
Answer this question "yes," but show the results--don't advance yet
to the next question.
`automatic'
Answer this question and all subsequent questions in the series
with "yes," without further user interaction.
`backup'
Move back to the previous place that a question was asked about.
`edit'
Enter a recursive edit to deal with this question--instead of any
other action that would normally be taken.
`delete-and-edit'
Delete the text being considered, then enter a recursive edit to
replace it.
`recenter'
Redisplay and center the window, then ask the same question again.
`quit'
Perform a quit right away. Only `y-or-n-p' and related functions
use this answer.
`help'
Display some help, then ask again.
The Match Data
==============
Emacs keeps track of the start and end positions of the segments of
text found during a regular expression search. This means, for example,
that you can search for a complex pattern, such as a date in an Rmail
message, and then extract parts of the match under control of the
pattern.
Because the match data normally describe the most recent search only,
you must be careful not to do another search inadvertently between the
search you wish to refer back to and the use of the match data. If you
can't avoid another intervening search, you must save and restore the
match data around it, to prevent it from being overwritten.
Replacing the Text that Matched
-------------------------------
This function replaces the text matched by the last search with
REPLACEMENT.
- Function: replace-match replacement &optional fixedcase literal
string subexp
This function replaces the text in the buffer (or in STRING) that
was matched by the last search. It replaces that text with
REPLACEMENT.
If you did the last search in a buffer, you should specify `nil'
for STRING. Then `replace-match' does the replacement by editing
the buffer; it leaves point at the end of the replacement text,
and returns `t'.
If you did the search in a string, pass the same string as STRING.
Then `replace-match' does the replacement by constructing and
returning a new string.
If FIXEDCASE is non-`nil', then the case of the replacement text
is not changed; otherwise, the replacement text is converted to a
different case depending upon the capitalization of the text to be
replaced. If the original text is all upper case, the replacement
text is converted to upper case. If the first word of the
original text is capitalized, then the first word of the
replacement text is capitalized. If the original text contains
just one word, and that word is a capital letter, `replace-match'
considers this a capitalized first word rather than all upper case.
If LITERAL is non-`nil', then REPLACEMENT is inserted exactly as
it is, the only alterations being case changes as needed. If it
is `nil' (the default), then the character `\' is treated
specially. If a `\' appears in REPLACEMENT, then it must be part
of one of the following sequences:
`\&'
`\&' stands for the entire text being replaced.
`\N'
`\N', where N is a digit, stands for the text that matched
the Nth subexpression in the original regexp. Subexpressions
are those expressions grouped inside `\(...\)'.
`\\'
`\\' stands for a single `\' in the replacement text.
If SUBEXP is non-`nil', that says to replace just subexpression
number SUBEXP of the regexp that was matched, not the entire
match. For example, after matching `foo \(ba*r\)', calling
`replace-match' with 1 as SUBEXP means to replace just the text
that matched `\(ba*r\)'.
Simple Match Data Access
------------------------
This section explains how to use the match data to find out what was
matched by the last search or match operation.
You can ask about the entire matching text, or about a particular
parenthetical subexpression of a regular expression. The COUNT
argument in the functions below specifies which. If COUNT is zero, you
are asking about the entire match. If COUNT is positive, it specifies
which subexpression you want.
Recall that the subexpressions of a regular expression are those
expressions grouped with escaped parentheses, `\(...\)'. The COUNTth
subexpression is found by counting occurrences of `\(' from the
beginning of the whole regular expression. The first subexpression is
numbered 1, the second 2, and so on. Only regular expressions can have
subexpressions--after a simple string search, the only information
available is about the entire match.
A search which fails may or may not alter the match data. In the
past, a failing search did not do this, but we may change it in the
future.
- Function: match-string count &optional in-string
This function returns, as a string, the text matched in the last
search or match operation. It returns the entire text if COUNT is
zero, or just the portion corresponding to the COUNTth
parenthetical subexpression, if COUNT is positive.
If the last such operation was done against a string with
`string-match', then you should pass the same string as the
argument IN-STRING. After a buffer search or match, you should
omit IN-STRING or pass `nil' for it; but you should make sure that
the current buffer when you call `match-string' is the one in
which you did the searching or matching.
The value is `nil' if COUNT is out of range, or for a
subexpression inside a `\|' alternative that wasn't used or a
repetition that repeated zero times.
- Function: match-string-no-properties count &optional in-string
This function is like `match-string' except that the result has no
text properties.
- Function: match-beginning count
This function returns the position of the start of text matched by
the last regular expression searched for, or a subexpression of it.
If COUNT is zero, then the value is the position of the start of
the entire match. Otherwise, COUNT specifies a subexpression in
the regular expression, and the value of the function is the
starting position of the match for that subexpression.
The value is `nil' for a subexpression inside a `\|' alternative
that wasn't used or a repetition that repeated zero times.
- Function: match-end count
This function is like `match-beginning' except that it returns the
position of the end of the match, rather than the position of the
beginning.
Here is an example of using the match data, with a comment showing
the positions within the text:
(string-match "\\(qu\\)\\(ick\\)"
"The quick fox jumped quickly.")
;0123456789
=> 4
(match-string 0 "The quick fox jumped quickly.")
=> "quick"
(match-string 1 "The quick fox jumped quickly.")
=> "qu"
(match-string 2 "The quick fox jumped quickly.")
=> "ick"
(match-beginning 1) ; The beginning of the match
=> 4 ; with `qu' is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with `ick' is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with `qu' is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with `ick' is at index 9.
Here is another example. Point is initially located at the beginning
of the line. Searching moves point to between the space and the word
`in'. The beginning of the entire match is at the 9th character of the
buffer (`T'), and the beginning of the match for the first
subexpression is at the 13th character (`c').
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (9 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(In this case, the index returned is a buffer position; the first
character of the buffer counts as 1.)
Accessing the Entire Match Data
-------------------------------
The functions `match-data' and `set-match-data' read or write the
entire match data, all at once.
- Function: match-data
This function returns a newly constructed list containing all the
information on what text the last search matched. Element zero is
the position of the beginning of the match for the whole
expression; element one is the position of the end of the match
for the expression. The next two elements are the positions of
the beginning and end of the match for the first subexpression,
and so on. In general, element number 2N corresponds to
`(match-beginning N)'; and element number 2N + 1 corresponds to
`(match-end N)'.
All the elements are markers or `nil' if matching was done on a
buffer, and all are integers or `nil' if matching was done on a
string with `string-match'.
As always, there must be no possibility of intervening searches
between the call to a search function and the call to `match-data'
that is intended to access the match data for that search.
(match-data)
=> (#<marker at 9 in foo>
#<marker at 17 in foo>
#<marker at 13 in foo>
#<marker at 17 in foo>)
- Function: set-match-data match-list
This function sets the match data from the elements of MATCH-LIST,
which should be a list that was the value of a previous call to
`match-data'.
If MATCH-LIST refers to a buffer that doesn't exist, you don't get
an error; that sets the match data in a meaningless but harmless
way.
`store-match-data' is a semi-obsolete alias for `set-match-data'.
Saving and Restoring the Match Data
-----------------------------------
When you call a function that may do a search, you may need to save
and restore the match data around that call, if you want to preserve the
match data from an earlier search for later use. Here is an example
that shows the problem that arises if you fail to save the match data:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; Perhaps `foo' does
; more searching.
(match-end 0)
=> 61 ; Unexpected result--not 48!
You can save and restore the match data with `save-match-data':
- Macro: save-match-data body...
This macro executes BODY, saving and restoring the match data
around it.
You could use `set-match-data' together with `match-data' to imitate
the effect of the special form `save-match-data'. Here is how:
(let ((data (match-data)))
(unwind-protect
... ; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs
process filter functions (*note Filter Functions::) and process
sentinels (*note Sentinels::).
Searching and Case
==================
By default, searches in Emacs ignore the case of the text they are
searching through; if you specify searching for `FOO', then `Foo' or
`foo' is also considered a match. This applies to regular expressions,
too; thus, `[aB]' would match `a' or `A' or `b' or `B'.
If you do not want this feature, set the variable `case-fold-search'
to `nil'. Then all letters must match exactly, including case. This
is a buffer-local variable; altering the variable affects only the
current buffer. (*Note Intro to Buffer-Local::.) Alternatively, you
may change the value of `default-case-fold-search', which is the
default value of `case-fold-search' for buffers that do not override it.
Note that the user-level incremental search feature handles case
distinctions differently. When given a lower case letter, it looks for
a match of either case, but when given an upper case letter, it looks
for an upper case letter only. But this has nothing to do with the
searching functions used in Lisp code.
- User Option: case-replace
This variable determines whether the replacement functions should
preserve case. If the variable is `nil', that means to use the
replacement text verbatim. A non-`nil' value means to convert the
case of the replacement text according to the text being replaced.
This variable is used by passing it as an argument to the function
`replace-match'. *Note Replacing Match::.
- User Option: case-fold-search
This buffer-local variable determines whether searches should
ignore case. If the variable is `nil' they do not ignore case;
otherwise they do ignore case.
- Variable: default-case-fold-search
The value of this variable is the default value for
`case-fold-search' in buffers that do not override it. This is the
same as `(default-value 'case-fold-search)'.
Standard Regular Expressions Used in Editing
============================================
This section describes some variables that hold regular expressions
used for certain purposes in editing:
- Variable: page-delimiter
This is the regular expression describing line-beginnings that
separate pages. The default value is `"^\014"' (i.e., `"^^L"' or
`"^\C-l"'); this matches a line that starts with a formfeed
character.
The following two regular expressions should _not_ assume the match
always starts at the beginning of a line; they should not use `^' to
anchor the match. Most often, the paragraph commands do check for a
match only at the beginning of a line, which means that `^' would be
superfluous. When there is a nonzero left margin, they accept matches
that start after the left margin. In that case, a `^' would be
incorrect. However, a `^' is harmless in modes where a left margin is
never used.
- Variable: paragraph-separate
This is the regular expression for recognizing the beginning of a
line that separates paragraphs. (If you change this, you may have
to change `paragraph-start' also.) The default value is
`"[ \t\f]*$"', which matches a line that consists entirely of
spaces, tabs, and form feeds (after its left margin).
- Variable: paragraph-start
This is the regular expression for recognizing the beginning of a
line that starts _or_ separates paragraphs. The default value is
`"[ \t\n\f]"', which matches a line starting with a space, tab,
newline, or form feed (after its left margin).
- Variable: sentence-end
This is the regular expression describing the end of a sentence.
(All paragraph boundaries also end sentences, regardless.) The
default value is:
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
This means a period, question mark or exclamation mark, followed
optionally by a closing parenthetical character, followed by tabs,
spaces or new lines.
For a detailed explanation of this regular expression, see *Note
Regexp Example::.
Syntax Tables
*************
A "syntax table" specifies the syntactic textual function of each
character. This information is used by the "parsing functions", the
complex movement commands, and others to determine where words, symbols,
and other syntactic constructs begin and end. The current syntax table
controls the meaning of the word motion functions (*note Word Motion::)
and the list motion functions (*note List Motion::), as well as the
functions in this chapter.
Syntax Table Concepts
=====================
A "syntax table" provides Emacs with the information that determines
the syntactic use of each character in a buffer. This information is
used by the parsing commands, the complex movement commands, and others
to determine where words, symbols, and other syntactic constructs begin
and end. The current syntax table controls the meaning of the word
motion functions (*note Word Motion::) and the list motion functions
(*note List Motion::) as well as the functions in this chapter.
A syntax table is a char-table (*note Char-Tables::). The element at
index C describes the character with code C. The element's value
should be a list that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the Emacs
Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp
expressions, and these rules cannot be changed. (Some Lisp systems
provide ways to redefine the read syntax, but we decided to leave this
feature out of Emacs Lisp for simplicity.)
Each buffer has its own major mode, and each major mode has its own
idea of the syntactic class of various characters. For example, in Lisp
mode, the character `;' begins a comment, but in C mode, it terminates
a statement. To support these variations, Emacs makes the choice of
syntax table local to each buffer. Typically, each major mode has its
own syntax table and installs that table in each buffer that uses that
mode. Changing this table alters the syntax in all those buffers as
well as in any buffers subsequently put in that mode. Occasionally
several similar modes share one syntax table. *Note Example Major
Modes::, for an example of how to set up a syntax table.
A syntax table can inherit the data for some characters from the
standard syntax table, while specifying other characters itself. The
"inherit" syntax class means "inherit this character's syntax from the
standard syntax table." Just changing the standard syntax for a
character affects all syntax tables that inherit from it.
- Function: syntax-table-p object
This function returns `t' if OBJECT is a syntax table.
Syntax Descriptors
==================
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a "syntax
descriptor", which is a Lisp string that you pass to
`modify-syntax-entry' to specify the syntax you want.
The syntax table specifies a syntax class for each character. There
is no necessary relationship between the class of a character in one
syntax table and its class in any other table.
Each class is designated by a mnemonic character, which serves as the
name of the class when you need to specify a class. Usually the
designator character is one that is often assigned that class; however,
its meaning as a designator is unvarying and independent of what syntax
that character currently has. Thus, `\' as a designator character
always gives "escape character" syntax, regardless of what syntax `\'
currently has.
A syntax descriptor is a Lisp string that specifies a syntax class, a
matching character (used only for the parenthesis classes) and flags.
The first character is the designator for a syntax class. The second
character is the character to match; if it is unused, put a space there.
Then come the characters for any desired flags. If no matching
character or flags are needed, one character is sufficient.
For example, the syntax descriptor for the character `*' in C mode
is `. 23' (i.e., punctuation, matching character slot unused, second
character of a comment-starter, first character of a comment-ender),
and the entry for `/' is `. 14' (i.e., punctuation, matching character
slot unused, first character of a comment-starter, second character of
a comment-ender).
Table of Syntax Classes
-----------------------
Here is a table of syntax classes, the characters that stand for
them, their meanings, and examples of their use.
- Syntax class: whitespace character
"Whitespace characters" (designated by ` ' or `-') separate
symbols and words from each other. Typically, whitespace
characters have no other syntactic significance, and multiple
whitespace characters are syntactically equivalent to a single
one. Space, tab, newline and formfeed are classified as
whitespace in almost all major modes.
- Syntax class: word constituent
"Word constituents" (designated by `w') are parts of normal
English words and are typically used in variable and command names
in programs. All upper- and lower-case letters, and the digits,
are typically word constituents.
- Syntax class: symbol constituent
"Symbol constituents" (designated by `_') are the extra characters
that are used in variable and command names along with word
constituents. For example, the symbol constituents class is used
in Lisp mode to indicate that certain characters may be part of
symbol names even though they are not part of English words.
These characters are `$&*+-_<>'. In standard C, the only
non-word-constituent character that is valid in symbols is
underscore (`_').
- Syntax class: punctuation character
"Punctuation characters" (designated by `.') are those characters
that are used as punctuation in English, or are used in some way
in a programming language to separate symbols from one another.
Most programming language modes, including Emacs Lisp mode, have no
characters in this class since the few characters that are not
symbol or word constituents all have other uses.
- Syntax class: open parenthesis character
- Syntax class: close parenthesis character
Open and close "parenthesis characters" are characters used in
dissimilar pairs to surround sentences or expressions. Such a
grouping is begun with an open parenthesis character and
terminated with a close. Each open parenthesis character matches
a particular close parenthesis character, and vice versa.
Normally, Emacs indicates momentarily the matching open
parenthesis when you insert a close parenthesis. *Note Blinking::.
The class of open parentheses is designated by `(', and that of
close parentheses by `)'.
In English text, and in C code, the parenthesis pairs are `()',
`[]', and `{}'. In Emacs Lisp, the delimiters for lists and
vectors (`()' and `[]') are classified as parenthesis characters.
- Syntax class: string quote
"String quote characters" (designated by `"') are used in many
languages, including Lisp and C, to delimit string constants. The
same string quote character appears at the beginning and the end
of a string. Such quoted strings do not nest.
The parsing facilities of Emacs consider a string as a single
token. The usual syntactic meanings of the characters in the
string are suppressed.
The Lisp modes have two string quote characters: double-quote (`"')
and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is
used in Common Lisp. C also has two string quote characters:
double-quote for strings, and single-quote (`'') for character
constants.
English text has no string quote characters because English is not
a programming language. Although quotation marks are used in
English, we do not want them to turn off the usual syntactic
properties of other characters in the quotation.
- Syntax class: escape
An "escape character" (designated by `\') starts an escape
sequence such as is used in C string and character constants. The
character `\' belongs to this class in both C and Lisp. (In C, it
is used thus only inside strings, but it turns out to cause no
trouble to treat it this way throughout C code.)
Characters in this class count as part of words if
`words-include-escapes' is non-`nil'. *Note Word Motion::.
- Syntax class: character quote
A "character quote character" (designated by `/') quotes the
following character so that it loses its normal syntactic meaning.
This differs from an escape character in that only the character
immediately following is ever affected.
Characters in this class count as part of words if
`words-include-escapes' is non-`nil'. *Note Word Motion::.
This class is used for backslash in TeX mode.
- Syntax class: paired delimiter
"Paired delimiter characters" (designated by `$') are like string
quote characters except that the syntactic properties of the
characters between the delimiters are not suppressed. Only TeX
mode uses a paired delimiter presently--the `$' that both enters
and leaves math mode.
- Syntax class: expression prefix
An "expression prefix operator" (designated by `'') is used for
syntactic operators that are considered as part of an expression
if they appear next to one. In Lisp modes, these characters
include the apostrophe, `'' (used for quoting), the comma, `,'
(used in macros), and `#' (used in the read syntax for certain
data types).
- Syntax class: comment starter
- Syntax class: comment ender
The "comment starter" and "comment ender" characters are used in
various languages to delimit comments. These classes are
designated by `<' and `>', respectively.
English text has no comment characters. In Lisp, the semicolon
(`;') starts a comment and a newline or formfeed ends one.
- Syntax class: inherit
This syntax class does not specify a particular syntax. It says
to look in the standard syntax table to find the syntax of this
character. The designator for this syntax code is `@'.
- Syntax class: generic comment delimiter
A "generic comment delimiter" (designated by `!') starts or ends a
special kind of comment. _Any_ generic comment delimiter matches
_any_ generic comment delimiter, but they cannot match a comment
starter or comment ender; generic comment delimiters can only
match each other.
This syntax class is primarily meant for use with the
`syntax-table' text property (*note Syntax Properties::). You can
mark any range of characters as forming a comment, by giving the
first and last characters of the range `syntax-table' properties
identifying them as generic comment delimiters.
- Syntax class: generic string delimiter
A "generic string delimiter" (designated by `|') starts or ends a
string. This class differs from the string quote class in that
_any_ generic string delimiter can match any other generic string
delimiter; but they do not match ordinary string quote characters.
This syntax class is primarily meant for use with the
`syntax-table' text property (*note Syntax Properties::). You can
mark any range of characters as forming a string constant, by
giving the first and last characters of the range `syntax-table'
properties identifying them as generic string delimiters.
Syntax Flags
------------
In addition to the classes, entries for characters in a syntax table
can specify flags. There are seven possible flags, represented by the
characters `1', `2', `3', `4', `b', `n', and `p'.
All the flags except `n' and `p' are used to describe
multi-character comment delimiters. The digit flags indicate that a
character can _also_ be part of a comment sequence, in addition to the
syntactic properties associated with its character class. The flags
are independent of the class and each other for the sake of characters
such as `*' in C mode, which is a punctuation character, _and_ the
second character of a start-of-comment sequence (`/*'), _and_ the first
character of an end-of-comment sequence (`*/').
Here is a table of the possible flags for a character C, and what
they mean:
* `1' means C is the start of a two-character comment-start sequence.
* `2' means C is the second character of such a sequence.
* `3' means C is the start of a two-character comment-end sequence.
* `4' means C is the second character of such a sequence.
* `b' means that C as a comment delimiter belongs to the alternative
"b" comment style.
Emacs supports two comment styles simultaneously in any one syntax
table. This is for the sake of C++. Each style of comment syntax
has its own comment-start sequence and its own comment-end
sequence. Each comment must stick to one style or the other;
thus, if it starts with the comment-start sequence of style "b",
it must also end with the comment-end sequence of style "b".
The two comment-start sequences must begin with the same
character; only the second character may differ. Mark the second
character of the "b"-style comment-start sequence with the `b'
flag.
A comment-end sequence (one or two characters) applies to the "b"
style if its first character has the `b' flag set; otherwise, it
applies to the "a" style.
The appropriate comment syntax settings for C++ are as follows:
`/'
`124b'
`*'
`23'
newline
`>b'
This defines four comment-delimiting sequences:
`/*'
This is a comment-start sequence for "a" style because the
second character, `*', does not have the `b' flag.
`//'
This is a comment-start sequence for "b" style because the
second character, `/', does have the `b' flag.
`*/'
This is a comment-end sequence for "a" style because the first
character, `*', does not have the `b' flag.
newline
This is a comment-end sequence for "b" style, because the
newline character has the `b' flag.
* `n' on a comment delimiter character specifies that this kind of
comment can be nested. For a two-character comment delimiter, `n'
on either character makes it nestable.
* `p' identifies an additional "prefix character" for Lisp syntax.
These characters are treated as whitespace when they appear between
expressions. When they appear within an expression, they are
handled according to their usual syntax codes.
The function `backward-prefix-chars' moves back over these
characters, as well as over characters whose primary syntax class
is prefix (`''). *Note Motion and Syntax::.
Syntax Table Functions
======================
In this section we describe functions for creating, accessing and
altering syntax tables.
- Function: make-syntax-table
This function creates a new syntax table. It inherits the syntax
for letters and control characters from the standard syntax table.
For other characters, the syntax is copied from the standard
syntax table.
Most major mode syntax tables are created in this way.
- Function: copy-syntax-table &optional table
This function constructs a copy of TABLE and returns it. If TABLE
is not supplied (or is `nil'), it returns a copy of the current
syntax table. Otherwise, an error is signaled if TABLE is not a
syntax table.
- Command: modify-syntax-entry char syntax-descriptor &optional table
This function sets the syntax entry for CHAR according to
SYNTAX-DESCRIPTOR. The syntax is changed only for TABLE, which
defaults to the current buffer's syntax table, and not in any
other syntax table. The argument SYNTAX-DESCRIPTOR specifies the
desired syntax; this is a string beginning with a class designator
character, and optionally containing a matching character and
flags as well. *Note Syntax Descriptors::.
This function always returns `nil'. The old syntax information in
the table for this character is discarded.
An error is signaled if the first character of the syntax
descriptor is not one of the twelve syntax class designator
characters. An error is also signaled if CHAR is not a character.
Examples:
;; Put the space character in class whitespace.
(modify-syntax-entry ?\ " ")
=> nil
;; Make `$' an open parenthesis character,
;; with `^' as its matching close.
(modify-syntax-entry ?$ "(^")
=> nil
;; Make `^' a close parenthesis character,
;; with `$' as its matching open.
(modify-syntax-entry ?^ ")$")
=> nil
;; Make `/' a punctuation character,
;; the first character of a start-comment sequence,
;; and the second character of an end-comment sequence.
;; This is used in C mode.
(modify-syntax-entry ?/ ". 14")
=> nil
- Function: char-syntax character
This function returns the syntax class of CHARACTER, represented
by its mnemonic designator character. This returns _only_ the
class, not any matching parenthesis or flags.
An error is signaled if CHAR is not a character.
The following examples apply to C mode. The first example shows
that the syntax class of space is whitespace (represented by a
space). The second example shows that the syntax of `/' is
punctuation. This does not show the fact that it is also part of
comment-start and -end sequences. The third example shows that
open parenthesis is in the class of open parentheses. This does
not show the fact that it has a matching character, `)'.
(string (char-syntax ?\ ))
=> " "
(string (char-syntax ?/))
=> "."
(string (char-syntax ?\())
=> "("
We use `string' to make it easier to see the character returned by
`char-syntax'.
- Function: set-syntax-table table
This function makes TABLE the syntax table for the current buffer.
It returns TABLE.
- Function: syntax-table
This function returns the current syntax table, which is the table
for the current buffer.
- Macro: with-syntax-table TABLE BODY...
This macro executes BODY using TABLE as the current syntax table.
It returns the value of the last form in BODY, after restoring the
old current syntax table.
Since each buffer has its own current syntax table, we should make
that more precise: `with-syntax-table' temporarily alters the
current syntax table of whichever buffer is current at the time
the macro execution starts. Other buffers are not affected.
Syntax Properties
=================
When the syntax table is not flexible enough to specify the syntax
of a language, you can use `syntax-table' text properties to override
the syntax table for specific character occurrences in the buffer.
*Note Text Properties::.
The valid values of `syntax-table' text property are:
SYNTAX-TABLE
If the property value is a syntax table, that table is used
instead of the current buffer's syntax table to determine the
syntax for this occurrence of the character.
`(SYNTAX-CODE . MATCHING-CHAR)'
A cons cell of this format specifies the syntax for this
occurrence of the character. (*note Syntax Table Internals::)
`nil'
If the property is `nil', the character's syntax is determined from
the current syntax table in the usual way.
- Variable: parse-sexp-lookup-properties
If this is non-`nil', the syntax scanning functions pay attention
to syntax text properties. Otherwise they use only the current
syntax table.
Motion and Syntax
=================
This section describes functions for moving across characters that
have certain syntax classes.
- Function: skip-syntax-forward syntaxes &optional limit
This function moves point forward across characters having syntax
classes mentioned in SYNTAXES. It stops when it encounters the
end of the buffer, or position LIMIT (if specified), or a
character it is not supposed to skip.
If SYNTAXES starts with `^', then the function skips characters
whose syntax is _not_ in SYNTAXES.
The return value is the distance traveled, which is a nonnegative
integer.
- Function: skip-syntax-backward syntaxes &optional limit
This function moves point backward across characters whose syntax
classes are mentioned in SYNTAXES. It stops when it encounters
the beginning of the buffer, or position LIMIT (if specified), or
a character it is not supposed to skip.
If SYNTAXES starts with `^', then the function skips characters
whose syntax is _not_ in SYNTAXES.
The return value indicates the distance traveled. It is an
integer that is zero or less.
- Function: backward-prefix-chars
This function moves point backward over any number of characters
with expression prefix syntax. This includes both characters in
the expression prefix syntax class, and characters with the `p'
flag.
Parsing Balanced Expressions
============================
Here are several functions for parsing and scanning balanced
expressions, also known as "sexps", in which parentheses match in
pairs. The syntax table controls the interpretation of characters, so
these functions can be used for Lisp expressions when in Lisp mode and
for C expressions when in C mode. *Note List Motion::, for convenient
higher-level functions for moving over balanced expressions.
- Function: parse-partial-sexp start limit &optional target-depth
stop-before state stop-comment
This function parses a sexp in the current buffer starting at
START, not scanning past LIMIT. It stops at position LIMIT or
when certain criteria described below are met, and sets point to
the location where parsing stops. It returns a value describing
the status of the parse at the point where it stops.
If STATE is `nil', START is assumed to be at the top level of
parenthesis structure, such as the beginning of a function
definition. Alternatively, you might wish to resume parsing in the
middle of the structure. To do this, you must provide a STATE
argument that describes the initial status of parsing.
If the third argument TARGET-DEPTH is non-`nil', parsing stops if
the depth in parentheses becomes equal to TARGET-DEPTH. The depth
starts at 0, or at whatever is given in STATE.
If the fourth argument STOP-BEFORE is non-`nil', parsing stops
when it comes to any character that starts a sexp. If
STOP-COMMENT is non-`nil', parsing stops when it comes to the
start of a comment. If STOP-COMMENT is the symbol `syntax-table',
parsing stops after the start of a comment or a string, or the end
of a comment or a string, whichever comes first.
The fifth argument STATE is a nine-element list of the same form
as the value of this function, described below. (It is OK to omit
the last element of the nine.) The return value of one call may
be used to initialize the state of the parse on another call to
`parse-partial-sexp'.
The result is a list of nine elements describing the final state of
the parse:
0. The depth in parentheses, counting from 0.
1. The character position of the start of the innermost
parenthetical grouping containing the stopping point; `nil'
if none.
2. The character position of the start of the last complete
subexpression terminated; `nil' if none.
3. Non-`nil' if inside a string. More precisely, this is the
character that will terminate the string, or `t' if a generic
string delimiter character should terminate it.
4. `t' if inside a comment (of either style), or the comment
nesting level if inside a kind of comment that can be nested.
5. `t' if point is just after a quote character.
6. The minimum parenthesis depth encountered during this scan.
7. What kind of comment is active: `nil' for a comment of style
"a", `t' for a comment of style "b", and `syntax-table' for a
comment that should be ended by a generic comment delimiter
character.
8. The string or comment start position. While inside a
comment, this is the position where the comment began; while
inside a string, this is the position where the string began.
When outside of strings and comments, this element is `nil'.
Elements 0, 3, 4, 5 and 7 are significant in the argument STATE.
This function is most often used to compute indentation for
languages that have nested parentheses.
- Function: scan-lists from count depth
This function scans forward COUNT balanced parenthetical groupings
from position FROM. It returns the position where the scan stops.
If COUNT is negative, the scan moves backwards.
If DEPTH is nonzero, parenthesis depth counting begins from that
value. The only candidates for stopping are places where the
depth in parentheses becomes zero; `scan-lists' counts COUNT such
places and then stops. Thus, a positive value for DEPTH means go
out DEPTH levels of parenthesis.
Scanning ignores comments if `parse-sexp-ignore-comments' is
non-`nil'.
If the scan reaches the beginning or end of the buffer (or its
accessible portion), and the depth is not zero, an error is
signaled. If the depth is zero but the count is not used up,
`nil' is returned.
- Function: scan-sexps from count
This function scans forward COUNT sexps from position FROM. It
returns the position where the scan stops. If COUNT is negative,
the scan moves backwards.
Scanning ignores comments if `parse-sexp-ignore-comments' is
non-`nil'.
If the scan reaches the beginning or end of (the accessible part
of) the buffer while in the middle of a parenthetical grouping, an
error is signaled. If it reaches the beginning or end between
groupings but before count is used up, `nil' is returned.
- Variable: multibyte-syntax-as-symbol
If this variable is non-`nil', `scan-sexps' treats all non-ASCII
characters as symbol constituents regardless of what the syntax
table says about them. (However, text properties can still
override the syntax.)
- Variable: parse-sexp-ignore-comments
If the value is non-`nil', then comments are treated as whitespace
by the functions in this section and by `forward-sexp'.
In older Emacs versions, this feature worked only when the comment
terminator is something like `*/', and appears only to end a
comment. In languages where newlines terminate comments, it was
necessary make this variable `nil', since not every newline is the
end of a comment. This limitation no longer exists.
You can use `forward-comment' to move forward or backward over one
comment or several comments.
- Function: forward-comment count
This function moves point forward across COUNT comments (backward,
if COUNT is negative). If it finds anything other than a comment
or whitespace, it stops, leaving point at the place where it
stopped. It also stops after satisfying COUNT.
To move forward over all comments and whitespace following point, use
`(forward-comment (buffer-size))'. `(buffer-size)' is a good argument
to use, because the number of comments in the buffer cannot exceed that
many.
Some Standard Syntax Tables
===========================
Most of the major modes in Emacs have their own syntax tables. Here
are several of them:
- Function: standard-syntax-table
This function returns the standard syntax table, which is the
syntax table used in Fundamental mode.
- Variable: text-mode-syntax-table
The value of this variable is the syntax table used in Text mode.
- Variable: c-mode-syntax-table
The value of this variable is the syntax table for C-mode buffers.
- Variable: emacs-lisp-mode-syntax-table
The value of this variable is the syntax table used in Emacs Lisp
mode by editing commands. (It has no effect on the Lisp `read'
function.)
Syntax Table Internals
======================
Lisp programs don't usually work with the elements directly; the
Lisp-level syntax table functions usually work with syntax descriptors
(*note Syntax Descriptors::). Nonetheless, here we document the
internal format. This format is used mostly when manipulating syntax
properties.
Each element of a syntax table is a cons cell of the form
`(SYNTAX-CODE . MATCHING-CHAR)'. The CAR, SYNTAX-CODE, is an integer
that encodes the syntax class, and any flags. The CDR, MATCHING-CHAR,
is non-`nil' if a character to match was specified.
This table gives the value of SYNTAX-CODE which corresponds to each
syntactic type.
Integer Class Integer Class Integer Class
0 whitespace 5 close parenthesis 10 character quote
1 punctuation 6 expression prefix 11 comment-start
2 word 7 string quote 12 comment-end
3 symbol 8 paired delimiter 13 inherit
4 open parenthesis 9 escape 14 comment-fence
15 string-fence
For example, the usual syntax value for `(' is `(4 . 41)'. (41 is
the character code for `)'.)
The flags are encoded in higher order bits, starting 16 bits from the
least significant bit. This table gives the power of two which
corresponds to each syntax flag.
Prefix Flag Prefix Flag Prefix Flag
`1' `(lsh 1 16)' `4' `(lsh 1 19)' `b' `(lsh 1 21)'
`2' `(lsh 1 17)' `p' `(lsh 1 20)' `n' `(lsh 1 22)'
`3' `(lsh 1 18)'
- Function: string-to-syntax DESC
This function returns the internal form `(SYNTAX-CODE .
MATCHING-CHAR)' corresponding to the syntax descriptor DESC.
Categories
==========
"Categories" provide an alternate way of classifying characters
syntactically. You can define several categories as needed, then
independently assign each character to one or more categories. Unlike
syntax classes, categories are not mutually exclusive; it is normal for
one character to belong to several categories.
Each buffer has a "category table" which records which categories
are defined and also which characters belong to each category. Each
category table defines its own categories, but normally these are
initialized by copying from the standard categories table, so that the
standard categories are available in all modes.
Each category has a name, which is an ASCII printing character in
the range ` ' to `~'. You specify the name of a category when you
define it with `define-category'.
The category table is actually a char-table (*note Char-Tables::).
The element of the category table at index C is a "category set"--a
bool-vector--that indicates which categories character C belongs to.
In this category set, if the element at index CAT is `t', that means
category CAT is a member of the set, and that character C belongs to
category CAT.
- Function: define-category char docstring &optional table
This function defines a new category, with name CHAR and
documentation DOCSTRING.
The new category is defined for category table TABLE, which
defaults to the current buffer's category table.
- Function: category-docstring category &optional table
This function returns the documentation string of category CATEGORY
in category table TABLE.
(category-docstring ?a)
=> "ASCII"
(category-docstring ?l)
=> "Latin"
- Function: get-unused-category table
This function returns a category name (a character) which is not
currently defined in TABLE. If all possible categories are in use
in TABLE, it returns `nil'.
- Function: category-table
This function returns the current buffer's category table.
- Function: category-table-p object
This function returns `t' if OBJECT is a category table, otherwise
`nil'.
- Function: standard-category-table
This function returns the standard category table.
- Function: copy-category-table &optional table
This function constructs a copy of TABLE and returns it. If TABLE
is not supplied (or is `nil'), it returns a copy of the current
category table. Otherwise, an error is signaled if TABLE is not a
category table.
- Function: set-category-table table
This function makes TABLE the category table for the current
buffer. It returns TABLE.
- Function: make-category-table
This creates and returns an empty category table. In an empty
category table, no categories have been allocated, and no
characters belong to any categories.
- Function: make-category-set categories
This function returns a new category set--a bool-vector--whose
initial contents are the categories listed in the string
CATEGORIES. The elements of CATEGORIES should be category names;
the new category set has `t' for each of those categories, and
`nil' for all other categories.
(make-category-set "al")
=> #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
- Function: char-category-set char
This function returns the category set for character CHAR. This
is the bool-vector which records which categories the character
CHAR belongs to. The function `char-category-set' does not
allocate storage, because it returns the same bool-vector that
exists in the category table.
(char-category-set ?a)
=> #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
- Function: category-set-mnemonics category-set
This function converts the category set CATEGORY-SET into a string
containing the characters that designate the categories that are
members of the set.
(category-set-mnemonics (char-category-set ?a))
=> "al"
- Function: modify-category-entry character category &optional table
reset
This function modifies the category set of CHARACTER in category
table TABLE (which defaults to the current buffer's category
table).
Normally, it modifies the category set by adding CATEGORY to it.
But if RESET is non-`nil', then it deletes CATEGORY instead.
- Command: describe-categories
This function describes the category specifications in the current
category table. The descriptions are inserted in a buffer, which
is then displayed.
Abbrevs and Abbrev Expansion
****************************
An abbreviation or "abbrev" is a string of characters that may be
expanded to a longer string. The user can insert the abbrev string and
find it replaced automatically with the expansion of the abbrev. This
saves typing.
The set of abbrevs currently in effect is recorded in an "abbrev
table". Each buffer has a local abbrev table, but normally all buffers
in the same major mode share one abbrev table. There is also a global
abbrev table. Normally both are used.
An abbrev table is represented as an obarray containing a symbol for
each abbreviation. The symbol's name is the abbreviation; its value is
the expansion; its function definition is the hook function to do the
expansion (*note Defining Abbrevs::); its property list cell contains
the use count, the number of times the abbreviation has been expanded.
Because these symbols are not interned in the usual obarray, they will
never appear as the result of reading a Lisp expression; in fact,
normally they are never used except by the code that handles abbrevs.
Therefore, it is safe to use them in an extremely nonstandard way.
*Note Creating Symbols::.
For the user-level commands for abbrevs, see *Note Abbrev Mode:
(emacs)Abbrevs.
Setting Up Abbrev Mode
======================
Abbrev mode is a minor mode controlled by the value of the variable
`abbrev-mode'.
- Variable: abbrev-mode
A non-`nil' value of this variable turns on the automatic expansion
of abbrevs when their abbreviations are inserted into a buffer.
If the value is `nil', abbrevs may be defined, but they are not
expanded automatically.
This variable automatically becomes buffer-local when set in any
fashion.
- Variable: default-abbrev-mode
This is the value of `abbrev-mode' for buffers that do not
override it. This is the same as `(default-value 'abbrev-mode)'.
Abbrev Tables
=============
This section describes how to create and manipulate abbrev tables.
- Function: make-abbrev-table
This function creates and returns a new, empty abbrev table--an
obarray containing no symbols. It is a vector filled with zeros.
- Function: clear-abbrev-table table
This function undefines all the abbrevs in abbrev table TABLE,
leaving it empty. It always returns `nil'.
- Function: define-abbrev-table tabname definitions
This function defines TABNAME (a symbol) as an abbrev table name,
i.e., as a variable whose value is an abbrev table. It defines
abbrevs in the table according to DEFINITIONS, a list of elements
of the form `(ABBREVNAME EXPANSION HOOK USECOUNT)'. The return
value is always `nil'.
- Variable: abbrev-table-name-list
This is a list of symbols whose values are abbrev tables.
`define-abbrev-table' adds the new abbrev table name to this list.
- Function: insert-abbrev-table-description name &optional human
This function inserts before point a description of the abbrev
table named NAME. The argument NAME is a symbol whose value is an
abbrev table. The return value is always `nil'.
If HUMAN is non-`nil', the description is human-oriented.
Otherwise the description is a Lisp expression--a call to
`define-abbrev-table' that would define NAME exactly as it is
currently defined.
Defining Abbrevs
================
These functions define an abbrev in a specified abbrev table.
`define-abbrev' is the low-level basic function, while `add-abbrev' is
used by commands that ask for information from the user.
- Function: add-abbrev table type arg
This function adds an abbreviation to abbrev table TABLE based on
information from the user. The argument TYPE is a string
describing in English the kind of abbrev this will be (typically,
`"global"' or `"mode-specific"'); this is used in prompting the
user. The argument ARG is the number of words in the expansion.
The return value is the symbol that internally represents the new
abbrev, or `nil' if the user declines to confirm redefining an
existing abbrev.
- Function: define-abbrev table name expansion &optional hook count
This function defines an abbrev named NAME, in TABLE, to expand to
EXPANSION and call HOOK. The value of COUNT, if specified,
initializes the abbrev's usage-count. If COUNT is not specified
or `nil', the use count is initialized to zero. The return value
is a symbol that represents the abbrev inside Emacs; its name is
NAME.
The argument NAME should be a string. The argument EXPANSION is
normally the desired expansion (a string), or `nil' to undefine
the abbrev. If it is anything but a string or `nil', then the
abbreviation "expands" solely by running HOOK.
The argument HOOK is a function or `nil'. If HOOK is non-`nil',
then it is called with no arguments after the abbrev is replaced
with EXPANSION; point is located at the end of EXPANSION when HOOK
is called.
If HOOK is a non-nil symbol whose `no-self-insert' property is
non-`nil', HOOK can explicitly control whether to insert the
self-inserting input character that triggered the expansion. If
HOOK returns non-`nil' in this case, that inhibits insertion of
the character. By contrast, if HOOK returns `nil',
`expand-abbrev' also returns `nil', as if expansion had not really
occurred.
- User Option: only-global-abbrevs
If this variable is non-`nil', it means that the user plans to use
global abbrevs only. This tells the commands that define
mode-specific abbrevs to define global ones instead. This
variable does not alter the behavior of the functions in this
section; it is examined by their callers.
Saving Abbrevs in Files
=======================
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with `load' (*note How Programs Do Loading::). However, the function
`quietly-read-abbrev-file' is provided as a more convenient interface.
User-level facilities such as `save-some-buffers' can save abbrevs
in a file automatically, under the control of variables described here.
- User Option: abbrev-file-name
This is the default file name for reading and saving abbrevs.
- Function: quietly-read-abbrev-file &optional filename
This function reads abbrev definitions from a file named FILENAME,
previously written with `write-abbrev-file'. If FILENAME is
omitted or `nil', the file specified in `abbrev-file-name' is
used. `save-abbrevs' is set to `t' so that changes will be saved.
This function does not display any messages. It returns `nil'.
- User Option: save-abbrevs
A non-`nil' value for `save-abbrev' means that Emacs should save
abbrevs when files are saved. `abbrev-file-name' specifies the
file to save the abbrevs in.
- Variable: abbrevs-changed
This variable is set non-`nil' by defining or altering any
abbrevs. This serves as a flag for various Emacs commands to
offer to save your abbrevs.
- Command: write-abbrev-file &optional filename
Save all abbrev definitions, in all abbrev tables, in the file
FILENAME, in the form of a Lisp program that when loaded will
define the same abbrevs. If FILENAME is `nil' or omitted,
`abbrev-file-name' is used. This function returns `nil'.
Looking Up and Expanding Abbreviations
======================================
Abbrevs are usually expanded by certain interactive commands,
including `self-insert-command'. This section describes the
subroutines used in writing such commands, as well as the variables they
use for communication.
- Function: abbrev-symbol abbrev &optional table
This function returns the symbol representing the abbrev named
ABBREV. The value returned is `nil' if that abbrev is not
defined. The optional second argument TABLE is the abbrev table
to look it up in. If TABLE is `nil', this function tries first
the current buffer's local abbrev table, and second the global
abbrev table.
- Function: abbrev-expansion abbrev &optional table
This function returns the string that ABBREV would expand into (as
defined by the abbrev tables used for the current buffer). The
optional argument TABLE specifies the abbrev table to use, as in
`abbrev-symbol'.
- Command: expand-abbrev
This command expands the abbrev before point, if any. If point
does not follow an abbrev, this command does nothing. The command
returns the abbrev symbol if it did expansion, `nil' otherwise.
If the abbrev symbol has a hook function which is a symbol whose
`no-self-insert' property is non-`nil', and if the hook function
returns `nil' as its value, then `expand-abbrev' returns `nil'
even though expansion did occur.
- Command: abbrev-prefix-mark &optional arg
Mark current point as the beginning of an abbrev. The next call to
`expand-abbrev' will use the text from here to point (where it is
then) as the abbrev to expand, rather than using the previous word
as usual.
- User Option: abbrev-all-caps
When this is set non-`nil', an abbrev entered entirely in upper
case is expanded using all upper case. Otherwise, an abbrev
entered entirely in upper case is expanded by capitalizing each
word of the expansion.
- Variable: abbrev-start-location
This is the buffer position for `expand-abbrev' to use as the start
of the next abbrev to be expanded. (`nil' means use the word
before point instead.) `abbrev-start-location' is set to `nil'
each time `expand-abbrev' is called. This variable is also set by
`abbrev-prefix-mark'.
- Variable: abbrev-start-location-buffer
The value of this variable is the buffer for which
`abbrev-start-location' has been set. Trying to expand an abbrev
in any other buffer clears `abbrev-start-location'. This variable
is set by `abbrev-prefix-mark'.
- Variable: last-abbrev
This is the `abbrev-symbol' of the most recent abbrev expanded.
This information is left by `expand-abbrev' for the sake of the
`unexpand-abbrev' command (*note Expanding Abbrevs:
(emacs)Expanding Abbrevs.).
- Variable: last-abbrev-location
This is the location of the most recent abbrev expanded. This
contains information left by `expand-abbrev' for the sake of the
`unexpand-abbrev' command.
- Variable: last-abbrev-text
This is the exact expansion text of the most recent abbrev
expanded, after case conversion (if any). Its value is `nil' if
the abbrev has already been unexpanded. This contains information
left by `expand-abbrev' for the sake of the `unexpand-abbrev'
command.
- Variable: pre-abbrev-expand-hook
This is a normal hook whose functions are executed, in sequence,
just before any expansion of an abbrev. *Note Hooks::. Since it
is a normal hook, the hook functions receive no arguments.
However, they can find the abbrev to be expanded by looking in the
buffer before point. Running the hook is the first thing that
`expand-abbrev' does, and so a hook function can be used to change
the current abbrev table before abbrev lookup happens.
The following sample code shows a simple use of
`pre-abbrev-expand-hook'. If the user terminates an abbrev with a
punctuation character, the hook function asks for confirmation. Thus,
this hook allows the user to decide whether to expand the abbrev, and
aborts expansion if it is not confirmed.
(add-hook 'pre-abbrev-expand-hook 'query-if-not-space)
;; This is the function invoked by `pre-abbrev-expand-hook'.
;; If the user terminated the abbrev with a space, the function does
;; nothing (that is, it returns so that the abbrev can expand). If the
;; user entered some other character, this function asks whether
;; expansion should continue.
;; If the user answers the prompt with `y', the function returns
;; `nil' (because of the `not' function), but that is
;; acceptable; the return value has no effect on expansion.
(defun query-if-not-space ()
(if (/= ?\ (preceding-char))
(if (not (y-or-n-p "Do you want to expand this abbrev? "))
(error "Not expanding this abbrev"))))
Standard Abbrev Tables
======================
Here we list the variables that hold the abbrev tables for the
preloaded major modes of Emacs.
- Variable: global-abbrev-table
This is the abbrev table for mode-independent abbrevs. The abbrevs
defined in it apply to all buffers. Each buffer may also have a
local abbrev table, whose abbrev definitions take precedence over
those in the global table.
- Variable: local-abbrev-table
The value of this buffer-local variable is the (mode-specific)
abbreviation table of the current buffer.
- Variable: fundamental-mode-abbrev-table
This is the local abbrev table used in Fundamental mode; in other
words, it is the local abbrev table in all buffers in Fundamental
mode.
- Variable: text-mode-abbrev-table
This is the local abbrev table used in Text mode.
- Variable: lisp-mode-abbrev-table
This is the local abbrev table used in Lisp mode and Emacs Lisp
mode.
Processes
*********
In the terminology of operating systems, a "process" is a space in
which a program can execute. Emacs runs in a process. Emacs Lisp
programs can invoke other programs in processes of their own. These are
called "subprocesses" or "child processes" of the Emacs process, which
is their "parent process".
A subprocess of Emacs may be "synchronous" or "asynchronous",
depending on how it is created. When you create a synchronous
subprocess, the Lisp program waits for the subprocess to terminate
before continuing execution. When you create an asynchronous
subprocess, it can run in parallel with the Lisp program. This kind of
subprocess is represented within Emacs by a Lisp object which is also
called a "process". Lisp programs can use this object to communicate
with the subprocess or to control it. For example, you can send
signals, obtain status information, receive output from the process, or
send input to it.
- Function: processp object
This function returns `t' if OBJECT is a process, `nil' otherwise.
Functions that Create Subprocesses
==================================
There are three functions that create a new subprocess in which to
run a program. One of them, `start-process', creates an asynchronous
process and returns a process object (*note Asynchronous Processes::).
The other two, `call-process' and `call-process-region', create a
synchronous process and do not return a process object (*note
Synchronous Processes::).
Synchronous and asynchronous processes are explained in the following
sections. Since the three functions are all called in a similar
fashion, their common arguments are described here.
In all cases, the function's PROGRAM argument specifies the program
to be run. An error is signaled if the file is not found or cannot be
executed. If the file name is relative, the variable `exec-path'
contains a list of directories to search. Emacs initializes
`exec-path' when it starts up, based on the value of the environment
variable `PATH'. The standard file name constructs, `~', `.', and
`..', are interpreted as usual in `exec-path', but environment variable
substitutions (`$HOME', etc.) are not recognized; use
`substitute-in-file-name' to perform them (*note File Name Expansion::).
Each of the subprocess-creating functions has a BUFFER-OR-NAME
argument which specifies where the standard output from the program will
go. It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist. It can also
be `nil', which says to discard the output unless a filter function
handles it. (*Note Filter Functions::, and *Note Read and Print::.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.
All three of the subprocess-creating functions have a `&rest'
argument, ARGS. The ARGS must all be strings, and they are supplied to
PROGRAM as separate command line arguments. Wildcard characters and
other shell constructs have no special meanings in these strings, since
the whole strings are passed directly to the specified program.
*Please note:* The argument PROGRAM contains only the name of the
program; it may not contain any command-line arguments. You must use
ARGS to provide those.
The subprocess gets its current directory from the value of
`default-directory' (*note File Name Expansion::).
The subprocess inherits its environment from Emacs, but you can
specify overrides for it with `process-environment'. *Note System
Environment::.
- Variable: exec-directory
The value of this variable is a string, the name of a directory
that contains programs that come with GNU Emacs, programs intended
for Emacs to invoke. The program `movemail' is an example of such
a program; Rmail uses it to fetch new mail from an inbox.
- User Option: exec-path
The value of this variable is a list of directories to search for
programs to run in subprocesses. Each element is either the name
of a directory (i.e., a string), or `nil', which stands for the
default directory (which is the value of `default-directory').
The value of `exec-path' is used by `call-process' and
`start-process' when the PROGRAM argument is not an absolute file
name.
Shell Arguments
===============
Lisp programs sometimes need to run a shell and give it a command
that contains file names that were specified by the user. These
programs ought to be able to support any valid file name. But the shell
gives special treatment to certain characters, and if these characters
occur in the file name, they will confuse the shell. To handle these
characters, use the function `shell-quote-argument':
- Function: shell-quote-argument argument
This function returns a string which represents, in shell syntax,
an argument whose actual contents are ARGUMENT. It should work
reliably to concatenate the return value into a shell command and
then pass it to a shell for execution.
Precisely what this function does depends on your operating
system. The function is designed to work with the syntax of your
system's standard shell; if you use an unusual shell, you will
need to redefine this function.
;; This example shows the behavior on GNU and Unix systems.
(shell-quote-argument "foo > bar")
=> "foo\\ \\>\\ bar"
;; This example shows the behavior on MS-DOS and MS-Windows systems.
(shell-quote-argument "foo > bar")
=> "\"foo > bar\""
Here's an example of using `shell-quote-argument' to construct a
shell command:
(concat "diff -c "
(shell-quote-argument oldfile)
" "
(shell-quote-argument newfile))
Creating a Synchronous Process
==============================
After a "synchronous process" is created, Emacs waits for the
process to terminate before continuing. Starting Dired on GNU or
Unix(1) is an example of this: it runs `ls' in a synchronous process,
then modifies the output slightly. Because the process is synchronous,
the entire directory listing arrives in the buffer before Emacs tries
to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing `C-g'. The first `C-g' tries to kill the
subprocess with a `SIGINT' signal; but it waits until the subprocess
actually terminates before quitting. If during that time the user
types another `C-g', that kills the subprocess instantly with `SIGKILL'
and quits immediately (except on MS-DOS, where killing other processes
doesn't work). *Note Quitting::.
The synchronous subprocess functions return an indication of how the
process terminated.
The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file. The input sent to a
subprocess by `call-process-region' is encoded using a coding system,
much like text written into a file. *Note Coding Systems::.
- Function: call-process program &optional infile destination display
&rest args
This function calls PROGRAM in a separate process and waits for it
to finish.
The standard input for the process comes from file INFILE if
INFILE is not `nil', and from the null device otherwise. The
argument DESTINATION says where to put the process output. Here
are the possibilities:
a buffer
Insert the output in that buffer, before point. This
includes both the standard output stream and the standard
error stream of the process.
a string
Insert the output in a buffer with that name, before point.
`t'
Insert the output in the current buffer, before point.
`nil'
Discard the output.
0
Discard the output, and return `nil' immediately without
waiting for the subprocess to finish.
In this case, the process is not truly synchronous, since it
can run in parallel with Emacs; but you can think of it as
synchronous in that Emacs is essentially finished with the
subprocess as soon as this function returns.
MS-DOS doesn't support asynchronous subprocesses, so this
option doesn't work there.
`(REAL-DESTINATION ERROR-DESTINATION)'
Keep the standard output stream separate from the standard
error stream; deal with the ordinary output as specified by
REAL-DESTINATION, and dispose of the error output according
to ERROR-DESTINATION. If ERROR-DESTINATION is `nil', that
means to discard the error output, `t' means mix it with the
ordinary output, and a string specifies a file name to
redirect error output into.
You can't directly specify a buffer to put the error output
in; that is too difficult to implement. But you can achieve
this result by sending the error output to a temporary file
and then inserting the file into a buffer.
If DISPLAY is non-`nil', then `call-process' redisplays the buffer
as output is inserted. (However, if the coding system chosen for
decoding output is `undecided', meaning deduce the encoding from
the actual data, then redisplay sometimes cannot continue once
non-ASCII characters are encountered. There are fundamental
reasons why it is hard to fix this; see *Note Output from
Processes::.)
Otherwise the function `call-process' does no redisplay, and the
results become visible on the screen only when Emacs redisplays
that buffer in the normal course of events.
The remaining arguments, ARGS, are strings that specify command
line arguments for the program.
The value returned by `call-process' (unless you told it not to
wait) indicates the reason for process termination. A number
gives the exit status of the subprocess; 0 means success, and any
other value means failure. If the process terminated with a
signal, `call-process' returns a string describing the signal.
In the examples below, the buffer `foo' is current.
(call-process "pwd" nil t)
=> 0
---------- Buffer: foo ----------
/usr/user/lewis/manual
---------- Buffer: foo ----------
(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
=> 0
---------- Buffer: bar ----------
lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
---------- Buffer: bar ----------
Here is a good example of the use of `call-process', which used to
be found in the definition of `insert-directory':
(call-process insert-directory-program nil t nil SWITCHES
(if full-directory-p
(concat (file-name-as-directory file) ".")
file))
- Function: call-process-region start end program &optional delete
destination display &rest args
This function sends the text from START to END as standard input
to a process running PROGRAM. It deletes the text sent if DELETE
is non-`nil'; this is useful when DESTINATION is `t', to insert
the output in the current buffer in place of the input.
The arguments DESTINATION and DISPLAY control what to do with the
output from the subprocess, and whether to update the display as
it comes in. For details, see the description of `call-process',
above. If DESTINATION is the integer 0, `call-process-region'
discards the output and returns `nil' immediately, without waiting
for the subprocess to finish (this only works if asynchronous
subprocesses are supported).
The remaining arguments, ARGS, are strings that specify command
line arguments for the program.
The return value of `call-process-region' is just like that of
`call-process': `nil' if you told it to return without waiting;
otherwise, a number or string which indicates how the subprocess
terminated.
In the following example, we use `call-process-region' to run the
`cat' utility, with standard input being the first five characters
in buffer `foo' (the word `input'). `cat' copies its standard
input into its standard output. Since the argument DESTINATION is
`t', this output is inserted in the current buffer.
---------- Buffer: foo ----------
input-!-
---------- Buffer: foo ----------
(call-process-region 1 6 "cat" nil t)
=> 0
---------- Buffer: foo ----------
inputinput-!-
---------- Buffer: foo ----------
The `shell-command-on-region' command uses `call-process-region'
like this:
(call-process-region
start end
shell-file-name ; Name of program.
nil ; Do not delete region.
buffer ; Send output to `buffer'.
nil ; No redisplay during output.
"-c" command) ; Arguments for the shell.
- Function: shell-command-to-string command
This function executes COMMAND (a string) as a shell command, then
returns the command's output as a string.
---------- Footnotes ----------
(1) On other systems, Emacs uses a Lisp emulation of `ls'; see *Note
Contents of Directories::.
Creating an Asynchronous Process
================================
After an "asynchronous process" is created, Emacs and the subprocess
both continue running immediately. The process thereafter runs in
parallel with Emacs, and the two can communicate with each other using
the functions described in the following sections. However,
communication is only partially asynchronous: Emacs sends data to the
process only when certain functions are called, and Emacs accepts data
from the process only when Emacs is waiting for input or for a time
delay.
Here we describe how to create an asynchronous process.
- Function: start-process name buffer-or-name program &rest args
This function creates a new asynchronous subprocess and starts the
program PROGRAM running in it. It returns a process object that
stands for the new subprocess in Lisp. The argument NAME
specifies the name for the process object; if a process with this
name already exists, then NAME is modified (by appending `<1>',
etc.) to be unique. The buffer BUFFER-OR-NAME is the buffer to
associate with the process.
The remaining arguments, ARGS, are strings that specify command
line arguments for the program.
In the example below, the first process is started and runs
(rather, sleeps) for 100 seconds. Meanwhile, the second process
is started, and given the name `my-process<1>' for the sake of
uniqueness. It inserts the directory listing at the end of the
buffer `foo', before the first process finishes. Then it
finishes, and a message to that effect is inserted in the buffer.
Much later, the first process finishes, and another message is
inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100")
=> #<process my-process>
(start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
=> #<process my-process<1>>
---------- Buffer: foo ----------
total 2
lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs
-rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon
Process my-process<1> finished
Process my-process finished
---------- Buffer: foo ----------
- Function: start-process-shell-command name buffer-or-name command
&rest command-args
This function is like `start-process' except that it uses a shell
to execute the specified command. The argument COMMAND is a shell
command name, and COMMAND-ARGS are the arguments for the shell
command. The variable `shell-file-name' specifies which shell to
use.
The point of running a program through the shell, rather than
directly with `start-process', is so that you can employ shell
features such as wildcards in the arguments. It follows that if
you include an arbitrary user-specified arguments in the command,
you should quote it with `shell-quote-argument' first, so that any
special shell characters do _not_ have their special shell
meanings. *Note Shell Arguments::.
- Variable: process-connection-type
This variable controls the type of device used to communicate with
asynchronous subprocesses. If it is non-`nil', then PTYs are
used, when available. Otherwise, pipes are used.
PTYs are usually preferable for processes visible to the user, as
in Shell mode, because they allow job control (`C-c', `C-z', etc.)
to work between the process and its children, whereas pipes do
not. For subprocesses used for internal purposes by programs, it
is often better to use a pipe, because they are more efficient. In
addition, the total number of PTYs is limited on many systems and
it is good not to waste them.
The value of `process-connection-type' is used when
`start-process' is called. So you can specify how to communicate
with one subprocess by binding the variable around the call to
`start-process'.
(let ((process-connection-type nil)) ; Use a pipe.
(start-process ...))
To determine whether a given subprocess actually got a pipe or a
PTY, use the function `process-tty-name' (*note Process
Information::).
Deleting Processes
==================
"Deleting a process" disconnects Emacs immediately from the
subprocess, and removes it from the list of active processes. It sends
a signal to the subprocess to make the subprocess terminate, but this is
not guaranteed to happen immediately. The process object itself
continues to exist as long as other Lisp objects point to it. The
process mark continues to point to the same place as before (usually
into a buffer where output from the process was being inserted).
You can delete a process explicitly at any time. Processes are
deleted automatically after they terminate, but not necessarily right
away. If you delete a terminated process explicitly before it is
deleted automatically, no harm results.
- User Option: delete-exited-processes
This variable controls automatic deletion of processes that have
terminated (due to calling `exit' or to a signal). If it is
`nil', then they continue to exist until the user runs
`list-processes'. Otherwise, they are deleted immediately after
they exit.
- Function: delete-process name
This function deletes the process associated with NAME, killing it
with a `SIGHUP' signal. The argument NAME may be a process, the
name of a process, a buffer, or the name of a buffer.
(delete-process "*shell*")
=> nil
- Function: process-kill-without-query process &optional do-query
This function specifies whether Emacs should query the user if
PROCESS is still running when Emacs is exited. If DO-QUERY is
`nil', the process will be deleted silently. Otherwise, Emacs
will query about killing it.
The value is `t' if the process was formerly set up to require
query, `nil' otherwise. A newly-created process always requires
query.
(process-kill-without-query (get-process "shell"))
=> t
Process Information
===================
Several functions return information about processes.
`list-processes' is provided for interactive use.
- Command: list-processes
This command displays a listing of all living processes. In
addition, it finally deletes any process whose status was `Exited'
or `Signaled'. It returns `nil'.
- Function: process-list
This function returns a list of all processes that have not been
deleted.
(process-list)
=> (#<process display-time> #<process shell>)
- Function: get-process name
This function returns the process named NAME, or `nil' if there is
none. An error is signaled if NAME is not a string.
(get-process "shell")
=> #<process shell>
- Function: process-command process
This function returns the command that was executed to start
PROCESS. This is a list of strings, the first string being the
program executed and the rest of the strings being the arguments
that were given to the program.
(process-command (get-process "shell"))
=> ("/bin/csh" "-i")
- Function: process-id process
This function returns the PID of PROCESS. This is an integer that
distinguishes the process PROCESS from all other processes running
on the same computer at the current time. The PID of a process is
chosen by the operating system kernel when the process is started
and remains constant as long as the process exists.
- Function: process-name process
This function returns the name of PROCESS.
- Function: process-contact process
This function returns `t' for an ordinary child process, and
`(HOSTNAME SERVICE)' for a net connection (*note Network::).
- Function: process-status process-name
This function returns the status of PROCESS-NAME as a symbol. The
argument PROCESS-NAME must be a process, a buffer, a process name
(string) or a buffer name (string).
The possible values for an actual subprocess are:
`run'
for a process that is running.
`stop'
for a process that is stopped but continuable.
`exit'
for a process that has exited.
`signal'
for a process that has received a fatal signal.
`open'
for a network connection that is open.
`closed'
for a network connection that is closed. Once a connection
is closed, you cannot reopen it, though you might be able to
open a new connection to the same place.
`nil'
if PROCESS-NAME is not the name of an existing process.
(process-status "shell")
=> run
(process-status (get-buffer "*shell*"))
=> run
x
=> #<process xx<1>>
(process-status x)
=> exit
For a network connection, `process-status' returns one of the
symbols `open' or `closed'. The latter means that the other side
closed the connection, or Emacs did `delete-process'.
- Function: process-exit-status process
This function returns the exit status of PROCESS or the signal
number that killed it. (Use the result of `process-status' to
determine which of those it is.) If PROCESS has not yet
terminated, the value is 0.
- Function: process-tty-name process
This function returns the terminal name that PROCESS is using for
its communication with Emacs--or `nil' if it is using pipes
instead of a terminal (see `process-connection-type' in *Note
Asynchronous Processes::).
- Function: process-coding-system process
This function returns a cons cell describing the coding systems in
use for decoding output from PROCESS and for encoding input to
PROCESS (*note Coding Systems::). The value has this form:
(CODING-SYSTEM-FOR-DECODING . CODING-SYSTEM-FOR-ENCODING)
- Function: set-process-coding-system process decoding-system
encoding-system
This function specifies the coding systems to use for subsequent
output from and input to PROCESS. It will use DECODING-SYSTEM to
decode subprocess output, and ENCODING-SYSTEM to encode subprocess
input.
Sending Input to Processes
==========================
Asynchronous subprocesses receive input when it is sent to them by
Emacs, which is done with the functions in this section. You must
specify the process to send input to, and the input data to send. The
data appears on the "standard input" of the subprocess.
Some operating systems have limited space for buffered input in a
PTY. On these systems, Emacs sends an EOF periodically amidst the
other characters, to force them through. For most programs, these EOFs
do no harm.
Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file. You can use
`set-process-coding-system' to specify which coding system to use
(*note Process Information::). Otherwise, the coding system comes from
`coding-system-for-write', if that is non-`nil'; or else from the
defaulting mechanism (*note Default Coding Systems::).
Sometimes the system is unable to accept input for that process,
because the input buffer is full. When this happens, the send functions
wait a short while, accepting output from subprocesses, and then try
again. This gives the subprocess a chance to read more of its pending
input and make space in the buffer. It also allows filters, sentinels
and timers to run--so take account of that in writing your code.
- Function: process-send-string process-name string
This function sends PROCESS-NAME the contents of STRING as
standard input. The argument PROCESS-NAME must be a process or
the name of a process. If it is `nil', the current buffer's
process is used.
The function returns `nil'.
(process-send-string "shell<1>" "ls\n")
=> nil
---------- Buffer: *shell* ----------
...
introduction.texi syntax-tables.texi~
introduction.texi~ text.texi
introduction.txt text.texi~
...
---------- Buffer: *shell* ----------
- Function: process-send-region process-name start end
This function sends the text in the region defined by START and
END as standard input to PROCESS-NAME, which is a process or a
process name. (If it is `nil', the current buffer's process is
used.)
An error is signaled unless both START and END are integers or
markers that indicate positions in the current buffer. (It is
unimportant which number is larger.)
- Function: process-send-eof &optional process-name
This function makes PROCESS-NAME see an end-of-file in its input.
The EOF comes after any text already sent to it.
If PROCESS-NAME is not supplied, or if it is `nil', then this
function sends the EOF to the current buffer's process. An error
is signaled if the current buffer has no process.
The function returns PROCESS-NAME.
(process-send-eof "shell")
=> "shell"
- Function: process-running-child-p process
This function will tell you whether a subprocess has given control
of its terminal to its own child process. The value is `t' if
this is true, or if Emacs cannot tell; it is `nil' if Emacs can be
certain that this is not so.
Sending Signals to Processes
============================
"Sending a signal" to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. The set of signals and their names is defined by the operating
system. For example, the signal `SIGINT' means that the user has typed
`C-c', or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals
kill the subprocess, but some stop or resume execution instead. Most
signals can optionally be handled by programs; if the program handles
the signal, then we can say nothing in general about its effects.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a `SIGHUP' signal to all its associated
processes; killing Emacs sends a `SIGHUP' signal to all remaining
processes. (`SIGHUP' is a signal that usually indicates that the user
hung up the phone.)
Each of the signal-sending functions takes two optional arguments:
PROCESS-NAME and CURRENT-GROUP.
The argument PROCESS-NAME must be either a process, the name of one,
or `nil'. If it is `nil', the process defaults to the process
associated with the current buffer. An error is signaled if
PROCESS-NAME does not identify a process.
The argument CURRENT-GROUP is a flag that makes a difference when
you are running a job-control shell as an Emacs subprocess. If it is
non-`nil', then the signal is sent to the current process-group of the
terminal that Emacs uses to communicate with the subprocess. If the
process is a job-control shell, this means the shell's current subjob.
If it is `nil', the signal is sent to the process group of the
immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag CURRENT-GROUP has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
`process-connection-type' in *Note Asynchronous Processes::.
- Function: interrupt-process &optional process-name current-group
This function interrupts the process PROCESS-NAME by sending the
signal `SIGINT'. Outside of Emacs, typing the "interrupt
character" (normally `C-c' on some systems, and `DEL' on others)
sends this signal. When the argument CURRENT-GROUP is non-`nil',
you can think of this function as "typing `C-c'" on the terminal
by which Emacs talks to the subprocess.
- Function: kill-process &optional process-name current-group
This function kills the process PROCESS-NAME by sending the signal
`SIGKILL'. This signal kills the subprocess immediately, and
cannot be handled by the subprocess.
- Function: quit-process &optional process-name current-group
This function sends the signal `SIGQUIT' to the process
PROCESS-NAME. This signal is the one sent by the "quit character"
(usually `C-b' or `C-\') when you are not inside Emacs.
- Function: stop-process &optional process-name current-group
This function stops the process PROCESS-NAME by sending the signal
`SIGTSTP'. Use `continue-process' to resume its execution.
Outside of Emacs, on systems with job control, the "stop character"
(usually `C-z') normally sends this signal. When CURRENT-GROUP is
non-`nil', you can think of this function as "typing `C-z'" on the
terminal Emacs uses to communicate with the subprocess.
- Function: continue-process &optional process-name current-group
This function resumes execution of the process PROCESS by sending
it the signal `SIGCONT'. This presumes that PROCESS-NAME was
stopped previously.
- Function: signal-process pid signal
This function sends a signal to process PID, which need not be a
child of Emacs. The argument SIGNAL specifies which signal to
send; it should be an integer.
Receiving Output from Processes
===============================
There are two ways to receive the output that a subprocess writes to
its standard output stream. The output can be inserted in a buffer,
which is called the associated buffer of the process, or a function
called the "filter function" can be called to act on the output. If
the process has no buffer and no filter function, its output is
discarded.
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input, in `sit-for' and `sleep-for' (*note Waiting::),
and in `accept-process-output' (*note Accepting Output::). This
minimizes the problem of timing errors that usually plague parallel
programming. For example, you can safely create a process and only
then specify its buffer or filter function; no output can arrive before
you finish, if the code in between does not call any primitive that
waits.
It is impossible to separate the standard output and standard error
streams of the subprocess, because Emacs normally spawns the subprocess
inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
you want to keep the output to those streams separate, you should
redirect one of them to a file-for example, by using an appropriate
shell command.
Subprocess output is normally decoded using a coding system before
the buffer or filter function receives it, much like text read from a
file. You can use `set-process-coding-system' to specify which coding
system to use (*note Process Information::). Otherwise, the coding
system comes from `coding-system-for-read', if that is non-`nil'; or
else from the defaulting mechanism (*note Default Coding Systems::).
*Warning:* Coding systems such as `undecided' which determine the
coding system from the data do not work entirely reliably with
asynchronous subprocess output. This is because Emacs has to process
asynchronous subprocess output in batches, as it arrives. Emacs must
try to detect the proper coding system from one batch at a time, and
this does not always work. Therefore, if at all possible, use a coding
system which determines both the character code conversion and the end
of line conversion--that is, one like `latin-1-unix', rather than
`undecided' or `latin-1'.
Process Buffers
---------------
A process can (and usually does) have an "associated buffer", which
is an ordinary Emacs buffer that is used for two purposes: storing the
output from the process, and deciding when to kill the process. You
can also use the buffer to identify a process to operate on, since in
normal practice only one process is associated with any given buffer.
Many applications of processes also use the buffer for editing input to
be sent to the process, but this is not built into Emacs Lisp.
Unless the process has a filter function (*note Filter Functions::),
its output is inserted in the associated buffer. The position to insert
the output is determined by the `process-mark', which is then updated
to point to the end of the text just inserted. Usually, but not
always, the `process-mark' is at the end of the buffer.
- Function: process-buffer process
This function returns the associated buffer of the process PROCESS.
(process-buffer (get-process "shell"))
=> #<buffer *shell*>
- Function: process-mark process
This function returns the process marker for PROCESS, which is the
marker that says where to insert output from the process.
If PROCESS does not have a buffer, `process-mark' returns a marker
that points nowhere.
Insertion of process output in a buffer uses this marker to decide
where to insert, and updates it to point after the inserted text.
That is why successive batches of output are inserted
consecutively.
Filter functions normally should use this marker in the same
fashion as is done by direct insertion of output in the buffer. A
good example of a filter function that uses `process-mark' is
found at the end of the following section.
When the user is expected to enter input in the process buffer for
transmission to the process, the process marker separates the new
input from previous output.
- Function: set-process-buffer process buffer
This function sets the buffer associated with PROCESS to BUFFER.
If BUFFER is `nil', the process becomes associated with no buffer.
- Function: get-buffer-process buffer-or-name
This function returns the process associated with BUFFER-OR-NAME.
If there are several processes associated with it, then one is
chosen. (Currently, the one chosen is the one most recently
created.) It is usually a bad idea to have more than one process
associated with the same buffer.
(get-buffer-process "*shell*")
=> #<process shell>
Killing the process's buffer deletes the process, which kills the
subprocess with a `SIGHUP' signal (*note Signals to Processes::).
Process Filter Functions
------------------------
A process "filter function" is a function that receives the standard
output from the associated process. If a process has a filter, then
_all_ output from that process is passed to the filter. The process
buffer is used directly for output from the process only when there is
no filter.
The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times. Emacs
waits when reading terminal input, in `sit-for' and `sleep-for' (*note
Waiting::), and in `accept-process-output' (*note Accepting Output::).
A filter function must accept two arguments: the associated process
and a string, which is output just received from it. The function is
then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function--otherwise,
the effect of typing `C-g' at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a filter
function, bind `inhibit-quit' to `nil'. *Note Quitting::.
If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started. However, if
`debug-on-error' is non-`nil', the error-catching is turned off. This
makes it possible to use the Lisp debugger to debug the filter
function. *Note Debugger::.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use `set-buffer' in order to be
sure to insert in that buffer. To avoid setting the current buffer
semipermanently, these filter functions must save and restore the
current buffer. They should also update the process marker, and in some
cases update the value of point. Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))))
The reason to use `with-current-buffer', rather than using
`save-excursion' to save and restore the current buffer, is so as to
preserve the change in point made by the second call to `goto-char'.
To make the filter force the process buffer to be visible whenever
new text arrives, insert the following line just before the
`with-current-buffer' construct:
(display-buffer (process-buffer proc))
To force point to the end of the new output, no matter where it was
previously, eliminate the variable `moving' and call `goto-char'
unconditionally.
In earlier Emacs versions, every filter function that did regular
expression searching or matching had to explicitly save and restore the
match data. Now Emacs does this automatically for filter functions;
they never need to do it explicitly. *Note Match Data::.
A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive. If it tries to
insert into a dead buffer, it will get an error. The expression
`(buffer-name (process-buffer PROCESS))' returns `nil' if the buffer is
dead.
The output to the function may come in chunks of any size. A program
that produces the same output twice in a row may send it as one batch of
200 characters one time, and five batches of 40 characters the next. If
the filter looks for certain text strings in the subprocess output, make
sure to handle the case where one of these strings is split across two
or more batches of output.
- Function: set-process-filter process filter
This function gives PROCESS the filter function FILTER. If FILTER
is `nil', it gives the process no filter.
- Function: process-filter process
This function returns the filter function of PROCESS, or `nil' if
it has none.
Here is an example of use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
=> keep-output
(setq kept nil)
=> nil
(set-process-filter (get-process "shell") 'keep-output)
=> keep-output
(process-send-string "shell" "ls ~/other\n")
=> nil
kept
=> ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
Accepting Output from Processes
-------------------------------
Output from asynchronous subprocesses normally arrives only while
Emacs is waiting for some sort of external event, such as elapsed time
or terminal input. Occasionally it is useful in a Lisp program to
explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.
- Function: accept-process-output &optional process seconds millisec
This function allows Emacs to read pending output from processes.
The output is inserted in the associated buffers or given to their
filter functions. If PROCESS is non-`nil' then this function does
not return until some output has been received from PROCESS.
The arguments SECONDS and MILLISEC let you specify timeout
periods. The former specifies a period measured in seconds and the
latter specifies one measured in milliseconds. The two time
periods thus specified are added together, and
`accept-process-output' returns after that much time whether or
not there has been any subprocess output.
The argument SECONDS need not be an integer. If it is a floating
point number, this function waits for a fractional number of
seconds. Some systems support only a whole number of seconds; on
these systems, SECONDS is rounded down.
Not all operating systems support waiting periods other than
multiples of a second; on those that do not, you get an error if
you specify nonzero MILLISEC.
The function `accept-process-output' returns non-`nil' if it did
get some output, or `nil' if the timeout expired before output
arrived.
Sentinels: Detecting Process Status Changes
===========================================
A "process sentinel" is a function that is called whenever the
associated process changes status for any reason, including signals
(whether sent by Emacs or caused by the process's own actions) that
terminate, stop, or continue the process. The process sentinel is also
called if the process exits. The sentinel receives two arguments: the
process for which the event occurred, and a string describing the type
of event.
The string describing the event looks like one of the following:
* `"finished\n"'.
* `"exited abnormally with code EXITCODE\n"'.
* `"NAME-OF-SIGNAL\n"'.
* `"NAME-OF-SIGNAL (core dumped)\n"'.
A sentinel runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output). This avoids the
timing errors that could result from running them at random places in
the middle of other Lisp programs. A program can wait, so that
sentinels will run, by calling `sit-for' or `sleep-for' (*note
Waiting::), or `accept-process-output' (*note Accepting Output::).
Emacs also allows sentinels to run when the command loop is reading
input.
Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing `C-g' at command level or to quit a user command would
be unpredictable. If you want to permit quitting inside a sentinel,
bind `inhibit-quit' to `nil'. *Note Quitting::.
A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
`(buffer-name (process-buffer PROCESS))' returns `nil'.
If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started. However, if
`debug-on-error' is non-`nil', the error-catching is turned off. This
makes it possible to use the Lisp debugger to debug the sentinel.
*Note Debugger::.
In earlier Emacs versions, every sentinel that did regular expression
searching or matching had to explicitly save and restore the match data.
Now Emacs does this automatically for sentinels; they never need to do
it explicitly. *Note Match Data::.
- Function: set-process-sentinel process sentinel
This function associates SENTINEL with PROCESS. If SENTINEL is
`nil', then the process will have no sentinel. The default
behavior when there is no sentinel is to insert a message in the
process's buffer when the process status changes.
(defun msg-me (process event)
(princ
(format "Process: %s had the event `%s'" process event)))
(set-process-sentinel (get-process "shell") 'msg-me)
=> msg-me
(kill-process (get-process "shell"))
-| Process: #<process shell> had the event `killed'
=> #<process shell>
- Function: process-sentinel process
This function returns the sentinel of PROCESS, or `nil' if it has
none.
- Function: waiting-for-user-input-p
While a sentinel or filter function is running, this function
returns non-`nil' if Emacs was waiting for keyboard input from the
user at the time the sentinel or filter function was called, `nil'
if it was not.
Transaction Queues
==================
You can use a "transaction queue" to communicate with a subprocess
using transactions. First use `tq-create' to create a transaction
queue communicating with a specified process. Then you can call
`tq-enqueue' to send a transaction.
- Function: tq-create process
This function creates and returns a transaction queue
communicating with PROCESS. The argument PROCESS should be a
subprocess capable of sending and receiving streams of bytes. It
may be a child process, or it may be a TCP connection to a server,
possibly on another machine.
- Function: tq-enqueue queue question regexp closure fn
This function sends a transaction to queue QUEUE. Specifying the
queue has the effect of specifying the subprocess to talk to.
The argument QUESTION is the outgoing message that starts the
transaction. The argument FN is the function to call when the
corresponding answer comes back; it is called with two arguments:
CLOSURE, and the answer received.
The argument REGEXP is a regular expression that should match text
at the end of the entire answer, but nothing before; that's how
`tq-enqueue' determines where the answer ends.
The return value of `tq-enqueue' itself is not meaningful.
- Function: tq-close queue
Shut down transaction queue QUEUE, waiting for all pending
transactions to complete, and then terminate the connection or
child process.
Transaction queues are implemented by means of a filter function.
*Note Filter Functions::.
Network Connections
===================
Emacs Lisp programs can open TCP network connections to other
processes on the same machine or other machines. A network connection
is handled by Lisp much like a subprocess, and is represented by a
process object. However, the process you are communicating with is not
a child of the Emacs process, so you can't kill it or send it signals.
All you can do is send and receive data. `delete-process' closes the
connection, but does not kill the process at the other end; that
process must decide what to do about closure of the connection.
You can distinguish process objects representing network connections
from those representing subprocesses with the `process-status'
function. It always returns either `open' or `closed' for a network
connection, and it never returns either of those values for a real
subprocess. *Note Process Information::.
- Function: open-network-stream name buffer-or-name host service
This function opens a TCP connection for a service to a host. It
returns a process object to represent the connection.
The NAME argument specifies the name for the process object. It
is modified as necessary to make it unique.
The BUFFER-OR-NAME argument is the buffer to associate with the
connection. Output from the connection is inserted in the buffer,
unless you specify a filter function to handle the output. If
BUFFER-OR-NAME is `nil', it means that the connection is not
associated with any buffer.
The arguments HOST and SERVICE specify where to connect to; HOST
is the host name (a string), and SERVICE is the name of a defined
network service (a string) or a port number (an integer).
Emacs Display
*************
This chapter describes a number of features related to the display
that Emacs presents to the user.
Refreshing the Screen
=====================
The function `redraw-frame' redisplays the entire contents of a
given frame (*note Frames::).
- Function: redraw-frame frame
This function clears and redisplays frame FRAME.
Even more powerful is `redraw-display':
- Command: redraw-display
This function clears and redisplays all visible frames.
Processing user input takes absolute priority over redisplay. If you
call these functions when input is available, they do nothing
immediately, but a full redisplay does happen eventually--after all the
input has been processed.
Normally, suspending and resuming Emacs also refreshes the screen.
Some terminal emulators record separate contents for display-oriented
programs such as Emacs and for ordinary sequential display. If you are
using such a terminal, you might want to inhibit the redisplay on
resumption.
- Variable: no-redraw-on-reenter
This variable controls whether Emacs redraws the entire screen
after it has been suspended and resumed. Non-`nil' means there is
no need to redraw, `nil' means redrawing is needed. The default
is `nil'.
Forcing Redisplay
=================
Emacs redisplay normally stops if input arrives, and does not happen
at all if input is available before it starts. Most of the time, this
is exactly what you want. However, you can prevent preemption by
binding `redisplay-dont-pause' to a non-`nil' value.
- Variable: redisplay-dont-pause
If this variable is non-`nil', pending input does not prevent or
halt redisplay; redisplay occurs, and finishes, regardless of
whether input is available. This feature is available as of Emacs
21.
You can request a display update, but only if no input is pending,
with `(sit-for 0)'. To force a display update even when input is
pending, do this:
(let ((redisplay-dont-pause t))
(sit-for 0))
Truncation
==========
When a line of text extends beyond the right edge of a window, the
line can either be continued on the next screen line, or truncated to
one screen line. The additional screen lines used to display a long
text line are called "continuation" lines. Normally, a `$' in the
rightmost column of the window indicates truncation; a `\' on the
rightmost column indicates a line that "wraps" onto the next line,
which is also called "continuing" the line. (The display table can
specify alternative indicators; see *Note Display Tables::.)
Note that continuation is different from filling; continuation
happens on the screen only, not in the buffer contents, and it breaks a
line precisely at the right margin, not at a word boundary. *Note
Filling::.
- User Option: truncate-lines
This buffer-local variable controls how Emacs displays lines that
extend beyond the right edge of the window. The default is `nil',
which specifies continuation. If the value is non-`nil', then
these lines are truncated.
If the variable `truncate-partial-width-windows' is non-`nil',
then truncation is always used for side-by-side windows (within one
frame) regardless of the value of `truncate-lines'.
- User Option: default-truncate-lines
This variable is the default value for `truncate-lines', for
buffers that do not have buffer-local values for it.
- User Option: truncate-partial-width-windows
This variable controls display of lines that extend beyond the
right edge of the window, in side-by-side windows (*note Splitting
Windows::). If it is non-`nil', these lines are truncated;
otherwise, `truncate-lines' says what to do with them.
When horizontal scrolling (*note Horizontal Scrolling::) is in use in
a window, that forces truncation.
You can override the glyphs that indicate continuation or truncation
using the display table; see *Note Display Tables::.
If your buffer contains _very_ long lines, and you use continuation
to display them, just thinking about them can make Emacs redisplay
slow. The column computation and indentation functions also become
slow. Then you might find it advisable to set `cache-long-line-scans'
to `t'.
- Variable: cache-long-line-scans
If this variable is non-`nil', various indentation and motion
functions, and Emacs redisplay, cache the results of scanning the
buffer, and consult the cache to avoid rescanning regions of the
buffer unless they are modified.
Turning on the cache slows down processing of short lines somewhat.
This variable is automatically buffer-local in every buffer.
The Echo Area
=============
The "echo area" is used for displaying messages made with the
`message' primitive, and for echoing keystrokes. It is not the same as
the minibuffer, despite the fact that the minibuffer appears (when
active) in the same place on the screen as the echo area. The `GNU
Emacs Manual' specifies the rules for resolving conflicts between the
echo area and the minibuffer for use of that screen space (*note The
Minibuffer: (emacs)Minibuffer.). Error messages appear in the echo
area; see *Note Errors::.
You can write output in the echo area by using the Lisp printing
functions with `t' as the stream (*note Output Functions::), or as
follows:
- Function: message string &rest arguments
This function displays a message in the echo area. The argument
STRING is similar to a C language `printf' control string. See
`format' in *Note String Conversion::, for the details on the
conversion specifications. `message' returns the constructed
string.
In batch mode, `message' prints the message text on the standard
error stream, followed by a newline.
If STRING, or strings among the ARGUMENTS, have `face' text
properties, these affect the way the message is displayed.
If STRING is `nil', `message' clears the echo area; if the echo
area has been expanded automatically, this brings it back to its
normal size. If the minibuffer is active, this brings the
minibuffer contents back onto the screen immediately.
Normally, displaying a long message resizes the echo area to
display the entire message. But if the variable
`message-truncate-lines' is non-`nil', the echo area does not
resize, and the message is truncated to fit it, as in Emacs 20 and
before.
(message "Minibuffer depth is %d."
(minibuffer-depth))
-| Minibuffer depth is 0.
=> "Minibuffer depth is 0."
---------- Echo Area ----------
Minibuffer depth is 0.
---------- Echo Area ----------
To automatically display a message in the echo area or in a
pop-buffer, depending on its size, use `display-message-or-buffer'.
- Macro: with-temp-message message &rest body
This construct displays a message in the echo area temporarily,
during the execution of BODY. It displays MESSAGE, executes BODY,
then returns the value of the last body form while restoring the
previous echo area contents.
- Function: message-or-box string &rest arguments
This function displays a message like `message', but may display it
in a dialog box instead of the echo area. If this function is
called in a command that was invoked using the mouse--more
precisely, if `last-nonmenu-event' (*note Command Loop Info::) is
either `nil' or a list--then it uses a dialog box or pop-up menu to
display the message. Otherwise, it uses the echo area. (This is
the same criterion that `y-or-n-p' uses to make a similar
decision; see *Note Yes-or-No Queries::.)
You can force use of the mouse or of the echo area by binding
`last-nonmenu-event' to a suitable value around the call.
- Function: message-box string &rest arguments
This function displays a message like `message', but uses a dialog
box (or a pop-up menu) whenever that is possible. If it is
impossible to use a dialog box or pop-up menu, because the
terminal does not support them, then `message-box' uses the echo
area, like `message'.
- Function: display-message-or-buffer message &optional buffer-name
not-this-window frame
This function displays the message MESSAGE, which may be either a
string or a buffer. If it is shorter than the maximum height of
the echo area, as defined by `max-mini-window-height', it is
displayed in the echo area, using `message'. Otherwise,
`display-buffer' is used to show it in a pop-up buffer.
Returns either the string shown in the echo area, or when a pop-up
buffer is used, the window used to display it.
If MESSAGE is a string, then the optional argument BUFFER-NAME is
the name of the buffer used to display it when a pop-up buffer is
used, defaulting to `*Message*'. In the case where MESSAGE is a
string and displayed in the echo area, it is not specified whether
the contents are inserted into the buffer anyway.
The optional arguments NOT-THIS-WINDOW and FRAME are as for
`display-buffer', and only used if a buffer is displayed.
- Function: current-message
This function returns the message currently being displayed in the
echo area, or `nil' if there is none.
- Variable: cursor-in-echo-area
This variable controls where the cursor appears when a message is
displayed in the echo area. If it is non-`nil', then the cursor
appears at the end of the message. Otherwise, the cursor appears
at point--not in the echo area at all.
The value is normally `nil'; Lisp programs bind it to `t' for
brief periods of time.
- Variable: echo-area-clear-hook
This normal hook is run whenever the echo area is cleared--either
by `(message nil)' or for any other reason.
Almost all the messages displayed in the echo area are also recorded
in the `*Messages*' buffer.
- User Option: message-log-max
This variable specifies how many lines to keep in the `*Messages*'
buffer. The value `t' means there is no limit on how many lines to
keep. The value `nil' disables message logging entirely. Here's
how to display a message and prevent it from being logged:
(let (message-log-max)
(message ...))
- Variable: echo-keystrokes
This variable determines how much time should elapse before command
characters echo. Its value must be an integer or floating point
number, which specifies the number of seconds to wait before
echoing. If the user types a prefix key (such as `C-x') and then
delays this many seconds before continuing, the prefix key is
echoed in the echo area. (Once echoing begins in a key sequence,
all subsequent characters in the same key sequence are echoed
immediately.)
If the value is zero, then command input is not echoed.
Invisible Text
==============
You can make characters "invisible", so that they do not appear on
the screen, with the `invisible' property. This can be either a text
property (*note Text Properties::) or a property of an overlay (*note
Overlays::).
In the simplest case, any non-`nil' `invisible' property makes a
character invisible. This is the default case--if you don't alter the
default value of `buffer-invisibility-spec', this is how the
`invisible' property works.
More generally, you can use the variable `buffer-invisibility-spec'
to control which values of the `invisible' property make text
invisible. This permits you to classify the text into different subsets
in advance, by giving them different `invisible' values, and
subsequently make various subsets visible or invisible by changing the
value of `buffer-invisibility-spec'.
Controlling visibility with `buffer-invisibility-spec' is especially
useful in a program to display the list of entries in a database. It
permits the implementation of convenient filtering commands to view
just a part of the entries in the database. Setting this variable is
very fast, much faster than scanning all the text in the buffer looking
for properties to change.
- Variable: buffer-invisibility-spec
This variable specifies which kinds of `invisible' properties
actually make a character invisible.
`t'
A character is invisible if its `invisible' property is
non-`nil'. This is the default.
a list
Each element of the list specifies a criterion for
invisibility; if a character's `invisible' property fits any
one of these criteria, the character is invisible. The list
can have two kinds of elements:
`ATOM'
A character is invisible if its `invisible' property
value is ATOM or if it is a list with ATOM as a member.
`(ATOM . t)'
A character is invisible if its `invisible' property
value is ATOM or if it is a list with ATOM as a member.
Moreover, if this character is at the end of a line and
is followed by a visible newline, it displays an
ellipsis.
Two functions are specifically provided for adding elements to
`buffer-invisibility-spec' and removing elements from it.
- Function: add-to-invisibility-spec element
Add the element ELEMENT to `buffer-invisibility-spec' (if it is
not already present in that list).
- Function: remove-from-invisibility-spec element
Remove the element ELEMENT from `buffer-invisibility-spec'. This
does nothing if ELEMENT is not in the list.
One convention about the use of `buffer-invisibility-spec' is that a
major mode should use the mode's own name as an element of
`buffer-invisibility-spec' and as the value of the `invisible' property:
;; If you want to display an ellipsis:
(add-to-invisibility-spec '(my-symbol . t))
;; If you don't want ellipsis:
(add-to-invisibility-spec 'my-symbol)
(overlay-put (make-overlay beginning end)
'invisible 'my-symbol)
;; When done with the overlays:
(remove-from-invisibility-spec '(my-symbol . t))
;; Or respectively:
(remove-from-invisibility-spec 'my-symbol)
Ordinarily, commands that operate on text or move point do not care
whether the text is invisible. The user-level line motion commands
explicitly ignore invisible newlines if `line-move-ignore-invisible' is
non-`nil', but only because they are explicitly programmed to do so.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-`nil' `isearch-open-invisible'
property. The property value should be a function to be called with
the overlay as an argument. This function should make the overlay
visible permanently; it is used when the match overlaps the overlay on
exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
`isearch-open-invisible-temporary' property which is a function. The
function is called with two arguments: the first is the overlay, and
the second is `nil' to make the overlay visible, or `t' to make it
invisible again.
Selective Display
=================
"Selective display" refers to a pair of related features for hiding
certain lines on the screen.
The first variant, explicit selective display, is designed for use in
a Lisp program: it controls which lines are hidden by altering the text.
The invisible text feature (*note Invisible Text::) has partially
replaced this feature.
In the second variant, the choice of lines to hide is made
automatically based on indentation. This variant is designed to be a
user-level feature.
The way you control explicit selective display is by replacing a
newline (control-j) with a carriage return (control-m). The text that
was formerly a line following that newline is now invisible. Strictly
speaking, it is temporarily no longer a line at all, since only newlines
can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, `C-f' (`forward-char') moves point unhesitatingly into
invisible text. However, the replacement of newline characters with
carriage return characters affects some editing commands. For example,
`next-line' skips invisible lines, since it searches only for newlines.
Modes that use selective display can also define commands that take
account of the newlines, or that make parts of the text visible or
invisible.
When you write a selectively displayed buffer into a file, all the
control-m's are output as newlines. This means that when you next read
in the file, it looks OK, with nothing invisible. The selective display
effect is seen only within Emacs.
- Variable: selective-display
This buffer-local variable enables selective display. This means
that lines, or portions of lines, may be made invisible.
* If the value of `selective-display' is `t', then the character
control-m marks the start of invisible text; the control-m,
and the rest of the line following it, are not displayed.
This is explicit selective display.
* If the value of `selective-display' is a positive integer,
then lines that start with more than that many columns of
indentation are not displayed.
When some portion of a buffer is invisible, the vertical movement
commands operate as if that portion did not exist, allowing a
single `next-line' command to skip any number of invisible lines.
However, character movement commands (such as `forward-char') do
not skip the invisible portion, and it is possible (if tricky) to
insert or delete text in an invisible portion.
In the examples below, we show the _display appearance_ of the
buffer `foo', which changes with the value of `selective-display'.
The _contents_ of the buffer do not change.
(setq selective-display nil)
=> nil
---------- Buffer: foo ----------
1 on this column
2on this column
3n this column
3n this column
2on this column
1 on this column
---------- Buffer: foo ----------
(setq selective-display 2)
=> 2
---------- Buffer: foo ----------
1 on this column
2on this column
2on this column
1 on this column
---------- Buffer: foo ----------
- Variable: selective-display-ellipses
If this buffer-local variable is non-`nil', then Emacs displays
`...' at the end of a line that is followed by invisible text.
This example is a continuation of the previous one.
(setq selective-display-ellipses t)
=> t
---------- Buffer: foo ----------
1 on this column
2on this column ...
2on this column
1 on this column
---------- Buffer: foo ----------
You can use a display table to substitute other text for the
ellipsis (`...'). *Note Display Tables::.
The Overlay Arrow
=================
The "overlay arrow" is useful for directing the user's attention to
a particular line in a buffer. For example, in the modes used for
interface to debuggers, the overlay arrow indicates the line of code
about to be executed.
- Variable: overlay-arrow-string
This variable holds the string to display to call attention to a
particular line, or `nil' if the arrow feature is not in use. On
a graphical display the contents of the string are ignored;
instead a glyph is displayed in the fringe area to the left of the
display area.
- Variable: overlay-arrow-position
This variable holds a marker that indicates where to display the
overlay arrow. It should point at the beginning of a line. On a
non-graphical display the arrow text appears at the beginning of
that line, overlaying any text that would otherwise appear. Since
the arrow is usually short, and the line usually begins with
indentation, normally nothing significant is overwritten.
The overlay string is displayed only in the buffer that this marker
points into. Thus, only one buffer can have an overlay arrow at
any given time.
You can do a similar job by creating an overlay with a
`before-string' property. *Note Overlay Properties::.
Temporary Displays
==================
Temporary displays are used by Lisp programs to put output into a
buffer and then present it to the user for perusal rather than for
editing. Many help commands use this feature.
- Special Form: with-output-to-temp-buffer buffer-name forms...
This function executes FORMS while arranging to insert any output
they print into the buffer named BUFFER-NAME, which is first
created if necessary, and put into Help mode. Finally, the buffer
is displayed in some window, but not selected.
If the FORMS do not change the major mode in the output buffer, so
that it is still Help mode at the end of their execution, then
`with-output-to-temp-buffer' makes this buffer read-only at the
end, and also scans it for function and variable names to make
them into clickable cross-references.
The string BUFFER-NAME specifies the temporary buffer, which need
not already exist. The argument must be a string, not a buffer.
The buffer is erased initially (with no questions asked), and it is
marked as unmodified after `with-output-to-temp-buffer' exits.
`with-output-to-temp-buffer' binds `standard-output' to the
temporary buffer, then it evaluates the forms in FORMS. Output
using the Lisp output functions within FORMS goes by default to
that buffer (but screen display and messages in the echo area,
although they are "output" in the general sense of the word, are
not affected). *Note Output Functions::.
Several hooks are available for customizing the behavior of this
construct; they are listed below.
The value of the last form in FORMS is returned.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(with-output-to-temp-buffer "foo"
(print 20)
(print standard-output))
=> #<buffer foo>
---------- Buffer: foo ----------
20
#<buffer foo>
---------- Buffer: foo ----------
- Variable: temp-buffer-show-function
If this variable is non-`nil', `with-output-to-temp-buffer' calls
it as a function to do the job of displaying a help buffer. The
function gets one argument, which is the buffer it should display.
It is a good idea for this function to run `temp-buffer-show-hook'
just as `with-output-to-temp-buffer' normally would, inside of
`save-selected-window' and with the chosen window and buffer
selected.
- Variable: temp-buffer-setup-hook
This normal hook is run by `with-output-to-temp-buffer' before
evaluating BODY. When the hook runs, the help buffer is current.
This hook is normally set up with a function to put the buffer in
Help mode.
- Variable: temp-buffer-show-hook
This normal hook is run by `with-output-to-temp-buffer' after
displaying the help buffer. When the hook runs, the help buffer is
current, and the window it was displayed in is selected. This
hook is normally set up with a function to make the buffer read
only, and find function names and variable names in it, provided
the major mode is still Help mode.
- Function: momentary-string-display string position &optional char
message
This function momentarily displays STRING in the current buffer at
POSITION. It has no effect on the undo list or on the buffer's
modification status.
The momentary display remains until the next input event. If the
next input event is CHAR, `momentary-string-display' ignores it
and returns. Otherwise, that event remains buffered for
subsequent use as input. Thus, typing CHAR will simply remove the
string from the display, while typing (say) `C-f' will remove the
string from the display and later (presumably) move point forward.
The argument CHAR is a space by default.
The return value of `momentary-string-display' is not meaningful.
If the string STRING does not contain control characters, you can
do the same job in a more general way by creating (and then
subsequently deleting) an overlay with a `before-string' property.
*Note Overlay Properties::.
If MESSAGE is non-`nil', it is displayed in the echo area while
STRING is displayed in the buffer. If it is `nil', a default
message says to type CHAR to continue.
In this example, point is initially located at the beginning of the
second line:
---------- Buffer: foo ----------
This is the contents of foo.
-!-Second line.
---------- Buffer: foo ----------
(momentary-string-display
"**** Important Message! ****"
(point) ?\r
"Type RET when done reading")
=> t
---------- Buffer: foo ----------
This is the contents of foo.
**** Important Message! ****Second line.
---------- Buffer: foo ----------
---------- Echo Area ----------
Type RET when done reading
---------- Echo Area ----------
Overlays
========
You can use "overlays" to alter the appearance of a buffer's text on
the screen, for the sake of presentation features. An overlay is an
object that belongs to a particular buffer, and has a specified
beginning and end. It also has properties that you can examine and set;
these affect the display of the text within the overlay.
Overlay Properties
------------------
Overlay properties are like text properties in that the properties
that alter how a character is displayed can come from either source.
But in most respects they are different. Text properties are
considered a part of the text; overlays are specifically considered not
to be part of the text. Thus, copying text between various buffers and
strings preserves text properties, but does not try to preserve
overlays. Changing a buffer's text properties marks the buffer as
modified, while moving an overlay or changing its properties does not.
Unlike text property changes, overlay changes are not recorded in the
buffer's undo list. *Note Text Properties::, for comparison.
These functions are used for reading and writing the properties of an
overlay:
- Function: overlay-get overlay prop
This function returns the value of property PROP recorded in
OVERLAY, if any. If OVERLAY does not record any value for that
property, but it does have a `category' property which is a
symbol, that symbol's PROP property is used. Otherwise, the value
is `nil'.
- Function: overlay-put overlay prop value
This function sets the value of property PROP recorded in OVERLAY
to VALUE. It returns VALUE.
See also the function `get-char-property' which checks both overlay
properties and text properties for a given character. *Note Examining
Properties::.
Many overlay properties have special meanings; here is a table of
them:
`priority'
This property's value (which should be a nonnegative number)
determines the priority of the overlay. The priority matters when
two or more overlays cover the same character and both specify a
face for display; the one whose `priority' value is larger takes
priority over the other, and its face attributes override the face
attributes of the lower priority overlay.
Currently, all overlays take priority over text properties. Please
avoid using negative priority values, as we have not yet decided
just what they should mean.
`window'
If the `window' property is non-`nil', then the overlay applies
only on that window.
`category'
If an overlay has a `category' property, we call it the "category"
of the overlay. It should be a symbol. The properties of the
symbol serve as defaults for the properties of the overlay.
`face'
This property controls the way text is displayed--for example,
which font and which colors. *Note Faces::, for more information.
In the simplest case, the value is a face name. It can also be a
list; then each element can be any of these possibilities:
* A face name (a symbol or string).
* Starting in Emacs 21, a property list of face attributes.
This has the form (KEYWORD VALUE ...), where each KEYWORD is a
face attribute name and VALUE is a meaningful value for that
attribute. With this feature, you do not need to create a
face each time you want to specify a particular attribute for
certain text. *Note Face Attributes::.
* A cons cell of the form `(foreground-color . COLOR-NAME)' or
`(background-color . COLOR-NAME)'. These elements specify
just the foreground color or just the background color.
`(foreground-color . COLOR-NAME)' is equivalent to
`(:foreground COLOR-NAME)', and likewise for the background.
`mouse-face'
This property is used instead of `face' when the mouse is within
the range of the overlay.
`display'
This property activates various features that change the way text
is displayed. For example, it can make text appear taller or
shorter, higher or lower, wider or narrower, or replaced with an
image. *Note Display Property::.
`help-echo'
If an overlay has a `help-echo' property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string
in the echo area, or in the tooltip window. For details see *Note
Text help-echo::. This feature is available starting in Emacs 21.
`modification-hooks'
This property's value is a list of functions to be called if any
character within the overlay is changed or if text is inserted
strictly within the overlay.
The hook functions are called both before and after each change.
If the functions save the information they receive, and compare
notes between calls, they can determine exactly what change has
been made in the buffer text.
When called before a change, each function receives four
arguments: the overlay, `nil', and the beginning and end of the
text range to be modified.
When called after a change, each function receives five arguments:
the overlay, `t', the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that
range. (For an insertion, the pre-change length is zero; for a
deletion, that length is the number of characters deleted, and the
post-change beginning and end are equal.)
`insert-in-front-hooks'
This property's value is a list of functions to be called before
and after inserting text right at the beginning of the overlay.
The calling conventions are the same as for the
`modification-hooks' functions.
`insert-behind-hooks'
This property's value is a list of functions to be called before
and after inserting text right at the end of the overlay. The
calling conventions are the same as for the `modification-hooks'
functions.
`invisible'
The `invisible' property can make the text in the overlay
invisible, which means that it does not appear on the screen.
*Note Invisible Text::, for details.
`intangible'
The `intangible' property on an overlay works just like the
`intangible' text property. *Note Special Properties::, for
details.
`isearch-open-invisible'
This property tells incremental search how to make an invisible
overlay visible, permanently, if the final match overlaps it.
*Note Invisible Text::.
`isearch-open-invisible-temporary'
This property tells incremental search how to make an invisible
overlay visible, temporarily, during the search. *Note Invisible
Text::.
`before-string'
This property's value is a string to add to the display at the
beginning of the overlay. The string does not appear in the
buffer in any sense--only on the screen.
`after-string'
This property's value is a string to add to the display at the end
of the overlay. The string does not appear in the buffer in any
sense--only on the screen.
`evaporate'
If this property is non-`nil', the overlay is deleted automatically
if it ever becomes empty (i.e., if it spans no characters).
`local-map'
If this property is non-`nil', it specifies a keymap for a portion
of the text. The property's value replaces the buffer's local
map, when the character after point is within the overlay. *Note
Active Keymaps::.
`keymap'
The `keymap' property is similar to `local-map' but overrides the
buffer's local map (and the map specified by the `local-map'
property) rather than replacing it.
Managing Overlays
-----------------
This section describes the functions to create, delete and move
overlays, and to examine their contents.
- Function: make-overlay start end &optional buffer front-advance
rear-advance
This function creates and returns an overlay that belongs to
BUFFER and ranges from START to END. Both START and END must
specify buffer positions; they may be integers or markers. If
BUFFER is omitted, the overlay is created in the current buffer.
The arguments FRONT-ADVANCE and REAR-ADVANCE specify the insertion
type for the start of the overlay and for the end of the overlay,
respectively. *Note Marker Insertion Types::.
- Function: overlay-start overlay
This function returns the position at which OVERLAY starts, as an
integer.
- Function: overlay-end overlay
This function returns the position at which OVERLAY ends, as an
integer.
- Function: overlay-buffer overlay
This function returns the buffer that OVERLAY belongs to.
- Function: delete-overlay overlay
This function deletes OVERLAY. The overlay continues to exist as
a Lisp object, and its property list is unchanged, but it ceases
to be attached to the buffer it belonged to, and ceases to have
any effect on display.
A deleted overlay is not permanently disconnected. You can give
it a position in a buffer again by calling `move-overlay'.
- Function: move-overlay overlay start end &optional buffer
This function moves OVERLAY to BUFFER, and places its bounds at
START and END. Both arguments START and END must specify buffer
positions; they may be integers or markers.
If BUFFER is omitted, OVERLAY stays in the same buffer it was
already associated with; if OVERLAY was deleted, it goes into the
current buffer.
The return value is OVERLAY.
This is the only valid way to change the endpoints of an overlay.
Do not try modifying the markers in the overlay by hand, as that
fails to update other vital data structures and can cause some
overlays to be "lost".
Here are some examples:
;; Create an overlay.
(setq foo (make-overlay 1 10))
=> #<overlay from 1 to 10 in display.texi>
(overlay-start foo)
=> 1
(overlay-end foo)
=> 10
(overlay-buffer foo)
=> #<buffer display.texi>
;; Give it a property we can check later.
(overlay-put foo 'happy t)
=> t
;; Verify the property is present.
(overlay-get foo 'happy)
=> t
;; Move the overlay.
(move-overlay foo 5 20)
=> #<overlay from 5 to 20 in display.texi>
(overlay-start foo)
=> 5
(overlay-end foo)
=> 20
;; Delete the overlay.
(delete-overlay foo)
=> nil
;; Verify it is deleted.
foo
=> #<overlay in no buffer>
;; A deleted overlay has no position.
(overlay-start foo)
=> nil
(overlay-end foo)
=> nil
(overlay-buffer foo)
=> nil
;; Undelete the overlay.
(move-overlay foo 1 20)
=> #<overlay from 1 to 20 in display.texi>
;; Verify the results.
(overlay-start foo)
=> 1
(overlay-end foo)
=> 20
(overlay-buffer foo)
=> #<buffer display.texi>
;; Moving and deleting the overlay does not change its properties.
(overlay-get foo 'happy)
=> t
Searching for Overlays
----------------------
- Function: overlays-at pos
This function returns a list of all the overlays that cover the
character at position POS in the current buffer. The list is in
no particular order. An overlay contains position POS if it
begins at or before POS, and ends after POS.
To illustrate usage, here is a Lisp function that returns a list
of the overlays that specify property PROP for the character at
point:
(defun find-overlays-specifying (prop)
(let ((overlays (overlays-at (point)))
found)
(while overlays
(let ((overlay (car overlays)))
(if (overlay-get overlay prop)
(setq found (cons overlay found))))
(setq overlays (cdr overlays)))
found))
- Function: overlays-in beg end
This function returns a list of the overlays that overlap the
region BEG through END. "Overlap" means that at least one
character is contained within the overlay and also contained
within the specified region; however, empty overlays are included
in the result if they are located at BEG, or strictly between BEG
and END.
- Function: next-overlay-change pos
This function returns the buffer position of the next beginning or
end of an overlay, after POS.
- Function: previous-overlay-change pos
This function returns the buffer position of the previous
beginning or end of an overlay, before POS.
Here's an easy way to use `next-overlay-change' to search for the
next character which gets a non-`nil' `happy' property from either its
overlays or its text properties (*note Property Search::):
(defun find-overlay-prop (prop)
(save-excursion
(while (and (not (eobp))
(not (get-char-property (point) 'happy)))
(goto-char (min (next-overlay-change (point))
(next-single-property-change (point) 'happy))))
(point)))
Width
=====
Since not all characters have the same width, these functions let you
check the width of a character. *Note Primitive Indent::, and *Note
Screen Lines::, for related functions.
- Function: char-width char
This function returns the width in columns of the character CHAR,
if it were displayed in the current buffer and the selected window.
- Function: string-width string
This function returns the width in columns of the string STRING,
if it were displayed in the current buffer and the selected window.
- Function: truncate-string-to-width string width &optional
start-column padding
This function returns the part of STRING that fits within WIDTH
columns, as a new string.
If STRING does not reach WIDTH, then the result ends where STRING
ends. If one multi-column character in STRING extends across the
column WIDTH, that character is not included in the result. Thus,
the result can fall short of WIDTH but cannot go beyond it.
The optional argument START-COLUMN specifies the starting column.
If this is non-`nil', then the first START-COLUMN columns of the
string are omitted from the value. If one multi-column character
in STRING extends across the column START-COLUMN, that character
is not included.
The optional argument PADDING, if non-`nil', is a padding
character added at the beginning and end of the result string, to
extend it to exactly WIDTH columns. The padding character is used
at the end of the result if it falls short of WIDTH. It is also
used at the beginning of the result if one multi-column character
in STRING extends across the column START-COLUMN.
(truncate-string-to-width "\tab\t" 12 4)
=> "ab"
(truncate-string-to-width "\tab\t" 12 4 ?\ )
=> " ab "
Faces
=====
A "face" is a named collection of graphical attributes: font family,
foreground color, background color, optional underlining, and many
others. Faces are used in Emacs to control the style of display of
particular parts of the text or the frame.
Each face has its own "face number", which distinguishes faces at
low levels within Emacs. However, for most purposes, you refer to
faces in Lisp programs by their names.
- Function: facep object
This function returns `t' if OBJECT is a face name symbol (or if
it is a vector of the kind used internally to record face data).
It returns `nil' otherwise.
Each face name is meaningful for all frames, and by default it has
the same meaning in all frames. But you can arrange to give a
particular face name a special meaning in one frame if you wish.
Standard Faces
--------------
This table lists all the standard faces and their uses. Most of them
are used for displaying certain parts of the frames or certain kinds of
text; you can control how those places look by customizing these faces.
`default'
This face is used for ordinary text.
`mode-line'
This face is used for mode lines, and for menu bars when toolkit
menus are not used--but only if `mode-line-inverse-video' is
non-`nil'.
`modeline'
This is an alias for the `mode-line' face, for compatibility with
old Emacs versions.
`header-line'
This face is used for the header lines of windows that have them.
`menu'
This face controls the display of menus, both their colors and
their font. (This works only on certain systems.)
`fringe'
This face controls the colors of window fringes, the thin areas on
either side that are used to display continuation and truncation
glyphs.
`scroll-bar'
This face controls the colors for display of scroll bars.
`tool-bar'
This face is used for display of the tool bar, if any.
`region'
This face is used for highlighting the region in Transient Mark
mode.
`secondary-selection'
This face is used to show any secondary selection you have made.
`highlight'
This face is meant to be used for highlighting for various
purposes.
`trailing-whitespace'
This face is used to display excess whitespace at the end of a
line, if `show-trailing-whitespace' is non-`nil'.
In contrast, these faces are provided to change the appearance of
text in specific ways. You can use them on specific text, when you want
the effects they produce.
`bold'
This face uses a bold font, if possible. It uses the bold variant
of the frame's font, if it has one. It's up to you to choose a
default font that has a bold variant, if you want to use one.
`italic'
This face uses the italic variant of the frame's font, if it has
one.
`bold-italic'
This face uses the bold italic variant of the frame's font, if it
has one.
`underline'
This face underlines text.
`fixed-pitch'
This face forces use of a particular fixed-width font.
`variable-pitch'
This face forces use of a particular variable-width font. It's
reasonable to customize this to use a different variable-width
font, if you like, but you should not make it a fixed-width font.
- Variable: show-trailing-whitespace
If this variable is non-`nil', Emacs uses the
`trailing-whitespace' face to display any spaces and tabs at the
end of a line.
Defining Faces
--------------
The way to define a new face is with `defface'. This creates a kind
of customization item (*note Customization::) which the user can
customize using the Customization buffer (*note Easy Customization:
(emacs)Easy Customization.).
- Macro: defface face spec doc [keyword value]...
This declares FACE as a customizable face that defaults according
to SPEC. You should not quote the symbol FACE. The argument DOC
specifies the face documentation. The keywords you can use in
`defface' are the same ones that are meaningful in both `defgroup'
and `defcustom' (*note Common Keywords::).
When `defface' executes, it defines the face according to SPEC,
then uses any customizations that were read from the init file
(*note Init File::) to override that specification.
The purpose of SPEC is to specify how the face should appear on
different kinds of terminals. It should be an alist whose
elements have the form `(DISPLAY ATTS)'. Each element's CAR,
DISPLAY, specifies a class of terminals. The element's second
element, ATTS, is a list of face attributes and their values; it
specifies what the face should look like on that kind of terminal.
The possible attributes are defined in the value of
`custom-face-attributes'.
The DISPLAY part of an element of SPEC determines which frames the
element applies to. If more than one element of SPEC matches a
given frame, the first matching element is the only one used for
that frame. There are two possibilities for DISPLAY:
`t'
This element of SPEC matches all frames. Therefore, any
subsequent elements of SPEC are never used. Normally `t' is
used in the last (or only) element of SPEC.
a list
If DISPLAY is a list, each element should have the form
`(CHARACTERISTIC VALUE...)'. Here CHARACTERISTIC specifies a
way of classifying frames, and the VALUEs are possible
classifications which DISPLAY should apply to. Here are the
possible values of CHARACTERISTIC:
`type'
The kind of window system the frame uses--either
`graphic' (any graphics-capable display), `x', `pc' (for
the MS-DOS console), `w32' (for MS Windows 9X/NT), or
`tty' (a non-graphics-capable display).
`class'
What kinds of colors the frame supports--either `color',
`grayscale', or `mono'.
`background'
The kind of background--either `light' or `dark'.
If an element of DISPLAY specifies more than one VALUE for a
given CHARACTERISTIC, any of those values is acceptable. If
DISPLAY has more than one element, each element should
specify a different CHARACTERISTIC; then _each_
characteristic of the frame must match one of the VALUEs
specified for it in DISPLAY.
Here's how the standard face `region' is defined:
(defface region
`((((type tty) (class color))
(:background "blue" :foreground "white"))
(((type tty) (class mono))
(:inverse-video t))
(((class color) (background dark))
(:background "blue"))
(((class color) (background light))
(:background "lightblue"))
(t (:background "gray")))
"Basic face for highlighting the region."
:group 'basic-faces)
Internally, `defface' uses the symbol property `face-defface-spec'
to record the face attributes specified in `defface', `saved-face' for
the attributes saved by the user with the customization buffer, and
`face-documentation' for the documentation string.
- User Option: frame-background-mode
This option, if non-`nil', specifies the background type to use for
interpreting face definitions. If it is `dark', then Emacs treats
all frames as if they had a dark background, regardless of their
actual background colors. If it is `light', then Emacs treats all
frames as if they had a light background.
Face Attributes
---------------
The effect of using a face is determined by a fixed set of "face
attributes". This table lists all the face attributes, and what they
mean. Note that in general, more than one face can be specified for a
given piece of text; when that happens, the attributes of all the faces
are merged to specify how to display the text. *Note Merging Faces::.
In Emacs 21, any attribute in a face can have the value
`unspecified'. This means the face doesn't specify that attribute. In
face merging, when the first face fails to specify a particular
attribute, that means the next face gets a chance. However, the
`default' face must specify all attributes.
Some of these font attributes are meaningful only on certain kinds of
displays--if your display cannot handle a certain attribute, the
attribute is ignored. (The attributes `:family', `:width', `:height',
`:weight', and `:slant' correspond to parts of an X Logical Font
Descriptor.)
`:family'
Font family name, or fontset name (*note Fontsets::). If you
specify a font family name, the wild-card characters `*' and `?'
are allowed.
`:width'
Relative proportionate width, also known as the character set
width or set width. This should be one of the symbols
`ultra-condensed', `extra-condensed', `condensed',
`semi-condensed', `normal', `semi-expanded', `expanded',
`extra-expanded', or `ultra-expanded'.
`:height'
Either the font height, an integer in units of 1/10 point, a
floating point number specifying the amount by which to scale the
height of any underlying face, or a function, which is called with
the old height (from the underlying face), and should return the
new height.
`:weight'
Font weight--a symbol from this series (from most dense to most
faint): `ultra-bold', `extra-bold', `bold', `semi-bold', `normal',
`semi-light', `light', `extra-light', or `ultra-light'.
On a text-only terminal, any weight greater than normal is
displayed as extra bright, and any weight less than normal is
displayed as half-bright (provided the terminal supports the
feature).
`:slant'
Font slant--one of the symbols `italic', `oblique', `normal',
`reverse-italic', or `reverse-oblique'.
On a text-only terminal, slanted text is displayed as half-bright,
if the terminal supports the feature.
`:foreground'
Foreground color, a string.
`:background'
Background color, a string.
`:inverse-video'
Whether or not characters should be displayed in inverse video.
The value should be `t' (yes) or `nil' (no).
`:stipple'
The background stipple, a bitmap.
The value can be a string; that should be the name of a file
containing external-format X bitmap data. The file is found in
the directories listed in the variable `x-bitmap-file-path'.
Alternatively, the value can specify the bitmap directly, with a
list of the form `(WIDTH HEIGHT DATA)'. Here, WIDTH and HEIGHT
specify the size in pixels, and DATA is a string containing the
raw bits of the bitmap, row by row. Each row occupies (WIDTH + 7)
/ 8 consecutie bytes in the string (which should be a unibyte
string for best results).
If the value is `nil', that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it
is used automatically to handle certain shades of gray.
`:underline'
Whether or not characters should be underlined, and in what color.
If the value is `t', underlining uses the foreground color of the
face. If the value is a string, underlining uses that color. The
value `nil' means do not underline.
`:overline'
Whether or not characters should be overlined, and in what color.
The value is used like that of `:underline'.
`:strike-through'
Whether or not characters should be strike-through, and in what
color. The value is used like that of `:underline'.
`:inherit'
The name of a face from which to inherit attributes, or a list of
face names. Attributes from inherited faces are merged into the
face like an underlying face would be, with higher priority than
underlying faces.
`:box'
Whether or not a box should be drawn around characters, its color,
the width of the box lines, and 3D appearance.
Here are the possible values of the `:box' attribute, and what they
mean:
`nil'
Don't draw a box.
`t'
Draw a box with lines of width 1, in the foreground color.
COLOR
Draw a box with lines of width 1, in color COLOR.
`(:line-width WIDTH :color COLOR :style STYLE)'
This way you can explicitly specify all aspects of the box. The
value WIDTH specifies the width of the lines to draw; it defaults
to 1.
The value COLOR specifies the color to draw with. The default is
the foreground color of the face for simple boxes, and the
background color of the face for 3D boxes.
The value STYLE specifies whether to draw a 3D box. If it is
`released-button', the box looks like a 3D button that is not being
pressed. If it is `pressed-button', the box looks like a 3D button
that is being pressed. If it is `nil' or omitted, a plain 2D box
is used.
The attributes `:overline', `:strike-through' and `:box' are new in
Emacs 21. The attributes `:family', `:height', `:width', `:weight',
`:slant' are also new; previous versions used the following attributes,
now semi-obsolete, to specify some of the same information:
`:font'
This attribute specifies the font name.
`:bold'
A non-`nil' value specifies a bold font.
`:italic'
A non-`nil' value specifies an italic font.
For compatibility, you can still set these "attributes" in Emacs 21,
even though they are not real face attributes. Here is what that does:
`:font'
You can specify an X font name as the "value" of this "attribute";
that sets the `:family', `:width', `:height', `:weight', and
`:slant' attributes according to the font name.
If the value is a pattern with wildcards, the first font that
matches the pattern is used to set these attributes.
`:bold'
A non-`nil' makes the face bold; `nil' makes it normal. This
actually works by setting the `:weight' attribute.
`:italic'
A non-`nil' makes the face italic; `nil' makes it normal. This
actually works by setting the `:slant' attribute.
- Variable: x-bitmap-file-path
This variable specifies a list of directories for searching for
bitmap files, for the `:stipple' attribute.
- Function: bitmap-spec-p object
This returns `t' if OBJECT is a valid bitmap specification,
suitable for use with `:stipple'. It returns `nil' otherwise.
Face Attribute Functions
------------------------
You can modify the attributes of an existing face with the following
functions. If you specify FRAME, they affect just that frame;
otherwise, they affect all frames as well as the defaults that apply to
new frames.
- Function: set-face-attribute face frame &rest arguments
This function sets one or more attributes of face FACE for frame
FRAME. If FRAME is `nil', it sets the attribute for all frames,
and the defaults for new frames.
The extra arguments ARGUMENTS specify the attributes to set, and
the values for them. They should consist of alternating attribute
names (such as `:family' or `:underline') and corresponding values.
Thus,
(set-face-attribute 'foo nil
:width :extended
:weight :bold
:underline "red")
sets the attributes `:width', `:weight' and `:underline' to the
corresponding values.
- Function: face-attribute face attribute &optional frame
This returns the value of the ATTRIBUTE attribute of face FACE on
FRAME. If FRAME is `nil', that means the selected frame (*note
Input Focus::).
If FRAME is `t', the value is the default for FACE for new frames.
For example,
(face-attribute 'bold :weight)
=> bold
The functions above did not exist before Emacs 21. For compatibility
with older Emacs versions, you can use the following functions to set
and examine the face attributes which existed in those versions.
- Function: set-face-foreground face color &optional frame
- Function: set-face-background face color &optional frame
These functions set the foreground (or background, respectively)
color of face FACE to COLOR. The argument COLOR should be a
string, the name of a color.
Certain shades of gray are implemented by stipple patterns on
black-and-white screens.
- Function: set-face-stipple face pattern &optional frame
This function sets the background stipple pattern of face FACE to
PATTERN. The argument PATTERN should be the name of a stipple
pattern defined by the X server, or `nil' meaning don't use
stipple.
Normally there is no need to pay attention to stipple patterns,
because they are used automatically to handle certain shades of
gray.
- Function: set-face-font face font &optional frame
This function sets the font of face FACE.
In Emacs 21, this actually sets the attributes `:family',
`:width', `:height', `:weight', and `:slant' according to the font
name FONT.
In Emacs 20, this sets the font attribute. Once you set the font
explicitly, the bold and italic attributes cease to have any
effect, because the precise font that you specified is used.
- Function: set-face-bold-p face bold-p &optional frame
This function specifies whether FACE should be bold. If BOLD-P is
non-`nil', that means yes; `nil' means no.
In Emacs 21, this sets the `:weight' attribute. In Emacs 20, it
sets the `:bold' attribute.
- Function: set-face-italic-p face italic-p &optional frame
This function specifies whether FACE should be italic. If
ITALIC-P is non-`nil', that means yes; `nil' means no.
In Emacs 21, this sets the `:slant' attribute. In Emacs 20, it
sets the `:italic' attribute.
- Function: set-face-underline-p face underline-p &optional frame
This function sets the underline attribute of face FACE.
Non-`nil' means do underline; `nil' means don't.
- Function: invert-face face &optional frame
This function inverts the `:inverse-video' attribute of face FACE.
If the attribute is `nil', this function sets it to `t', and vice
versa.
These functions examine the attributes of a face. If you don't
specify FRAME, they refer to the default data for new frames. They
return the symbol `unspecified' if the face doesn't define any value
for that attribute.
- Function: face-foreground face &optional frame
- Function: face-background face &optional frame
These functions return the foreground color (or background color,
respectively) of face FACE, as a string.
- Function: face-stipple face &optional frame
This function returns the name of the background stipple pattern
of face FACE, or `nil' if it doesn't have one.
- Function: face-font face &optional frame
This function returns the name of the font of face FACE.
- Function: face-bold-p face &optional frame
This function returns `t' if FACE is bold--that is, if it is
bolder than normal. It returns `nil' otherwise.
- Function: face-italic-p face &optional frame
This function returns `t' if FACE is italic or oblique, `nil'
otherwise.
- Function: face-underline-p face &optional frame
This function returns the `:underline' attribute of face FACE.
- Function: face-inverse-video-p face &optional frame
This function returns the `:inverse-video' attribute of face FACE.
Merging Faces for Display
-------------------------
Here are the ways to specify which faces to use for display of text:
* With defaults. The `default' face is used as the ultimate default
for all text. (In Emacs 19 and 20, the `default' face is used
only when no other face is specified.)
For a mode line or header line, the face `modeline' or
`header-line' is used just before `default'.
* With text properties. A character can have a `face' property; if
so, the faces and face attributes specified there apply. *Note
Special Properties::.
If the character has a `mouse-face' property, that is used instead
of the `face' property when the mouse is "near enough" to the
character.
* With overlays. An overlay can have `face' and `mouse-face'
properties too; they apply to all the text covered by the overlay.
* With a region that is active. In Transient Mark mode, the region
is highlighted with the face `region' (*note Standard Faces::).
* With special glyphs. Each glyph can specify a particular face
number. *Note Glyphs::.
If these various sources together specify more than one face for a
particular character, Emacs merges the attributes of the various faces
specified. The attributes of the faces of special glyphs come first;
then comes the face for region highlighting, if appropriate; then come
attributes of faces from overlays, followed by those from text
properties, and last the default face.
When multiple overlays cover one character, an overlay with higher
priority overrides those with lower priority. *Note Overlays::.
In Emacs 20, if an attribute such as the font or a color is not
specified in any of the above ways, the frame's own font or color is
used. In newer Emacs versions, this cannot happen, because the
`default' face specifies all attributes--in fact, the frame's own font
and colors are synonymous with those of the default face.
Font Selection
--------------
"Selecting a font" means mapping the specified face attributes for a
character to a font that is available on a particular display. The
face attributes, as determined by face merging, specify most of the
font choice, but not all. Part of the choice depends on what character
it is.
For multibyte characters, typically each font covers only one
character set. So each character set (*note Character Sets::) specifies
a registry and encoding to use, with the character set's
`x-charset-registry' property. Its value is a string containing the
registry and the encoding, with a dash between them:
(plist-get (charset-plist 'latin-iso8859-1)
'x-charset-registry)
=> "ISO8859-1"
Unibyte text does not have character sets, so displaying a unibyte
character takes the registry and encoding from the variable
`face-default-registry'.
- Variable: face-default-registry
This variable specifies which registry and encoding to use in
choosing fonts for unibyte characters. The value is initialized
at Emacs startup time from the font the user specified for Emacs.
If the face specifies a fontset name, that fontset determines a
pattern for fonts of the given charset. If the face specifies a font
family, a font pattern is constructed.
Emacs tries to find an available font for the given face attributes
and character's registry and encoding. If there is a font that matches
exactly, it is used, of course. The hard case is when no available font
exactly fits the specification. Then Emacs looks for one that is
"close"--one attribute at a time. You can specify the order to
consider the attributes. In the case where a specified font family is
not available, you can specify a set of mappings for alternatives to
try.
- Variable: face-font-selection-order
This variable specifies the order of importance of the face
attributes `:width', `:height', `:weight', and `:slant'. The
value should be a list containing those four symbols, in order of
decreasing importance.
Font selection first finds the best available matches for the first
attribute listed; then, among the fonts which are best in that
way, it searches for the best matches in the second attribute, and
so on.
The attributes `:weight' and `:width' have symbolic values in a
range centered around `normal'. Matches that are more extreme
(farther from `normal') are somewhat preferred to matches that are
less extreme (closer to `normal'); this is designed to ensure that
non-normal faces contrast with normal ones, whenever possible.
The default is `(:width :height :weight :slant)', which means first
find the fonts closest to the specified `:width', then--among the
fonts with that width--find a best match for the specified font
height, and so on.
One example of a case where this variable makes a difference is
when the default font has no italic equivalent. With the default
ordering, the `italic' face will use a non-italic font that is
similar to the default one. But if you put `:slant' before
`:height', the `italic' face will use an italic font, even if its
height is not quite right.
- Variable: face-font-family-alternatives
This variable lets you specify alternative font families to try,
if a given family is specified and doesn't exist. Each element
should have this form:
(FAMILY ALTERNATE-FAMILIES...)
If FAMILY is specified but not available, Emacs will try the other
families given in ALTERNATE-FAMILIES, one by one, until it finds a
family that does exist.
- Variable: face-font-registry-alternatives
This variable lets you specify alternative font registries to try,
if a given registry is specified and doesn't exist. Each element
should have this form:
(REGISTRY ALTERNATE-REGISTRIES...)
If REGISTRY is specified but not available, Emacs will try the
other registries given in ALTERNATE-REGISTRIES, one by one, until
it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use
them, since the use of too many or too big scalable fonts can crash
XFree86 servers.
- Variable: scalable-fonts-allowed
This variable controls which scalable fonts to use. A value of
`nil', the default, means do not use scalable fonts. `t' means to
use any scalable font that seems appropriate for the text.
Otherwise, the value must be a list of regular expressions. Then a
scalable font is enabled for use if its name matches any regular
expression in the list. For example,
(setq scalable-fonts-allowed '("muleindian-2$"))
allows the use of scalable fonts with registry `muleindian-2'.
- Function: clear-face-cache &optional unload-p
This function clears the face cache for all frames. If UNLOAD-P
is non-`nil', that means to unload all unused fonts as well.
Functions for Working with Faces
--------------------------------
Here are additional functions for creating and working with faces.
- Function: make-face name
This function defines a new face named NAME, initially with all
attributes `nil'. It does nothing if there is already a face named
NAME.
- Function: face-list
This function returns a list of all defined face names.
- Function: copy-face old-face new-name &optional frame new-frame
This function defines the face NEW-NAME as a copy of the existing
face named OLD-FACE. It creates the face NEW-NAME if that doesn't
already exist.
If the optional argument FRAME is given, this function applies
only to that frame. Otherwise it applies to each frame
individually, copying attributes from OLD-FACE in each frame to
NEW-FACE in the same frame.
If the optional argument NEW-FRAME is given, then `copy-face'
copies the attributes of OLD-FACE in FRAME to NEW-NAME in
NEW-FRAME.
- Function: face-id face
This function returns the face number of face FACE.
- Function: face-documentation face
This function returns the documentation string of face FACE, or
`nil' if none was specified for it.
- Function: face-equal face1 face2 &optional frame
This returns `t' if the faces FACE1 and FACE2 have the same
attributes for display.
- Function: face-differs-from-default-p face &optional frame
This returns `t' if the face FACE displays differently from the
default face. A face is considered to be "the same" as the
default face if each attribute is either the same as that of the
default face, or unspecified (meaning to inherit from the default).
Automatic Face Assignment
-------------------------
Starting with Emacs 21, a hook is available for automatically
assigning faces to text in the buffer. This hook is used for part of
the implementation of Font-Lock mode.
- Variable: fontification-functions
This variable holds a list of functions that are called by Emacs
redisplay as needed to assign faces automatically to text in the
buffer.
The functions are called in the order listed, with one argument, a
buffer position POS. Each function should attempt to assign faces
to the text in the current buffer starting at POS.
Each function should record the faces they assign by setting the
`face' property. It should also add a non-`nil' `fontified'
property for all the text it has assigned faces to. That property
tells redisplay that faces have been assigned to that text already.
It is probably a good idea for each function to do nothing if the
character after POS already has a non-`nil' `fontified' property,
but this is not required. If one function overrides the
assignments made by a previous one, the properties as they are
after the last function finishes are the ones that really matter.
For efficiency, we recommend writing these functions so that they
usually assign faces to around 400 to 600 characters at each call.
Looking Up Fonts
----------------
- Function: x-list-fonts pattern &optional face frame maximum
This function returns a list of available font names that match
PATTERN. If the optional arguments FACE and FRAME are specified,
then the list is limited to fonts that are the same size as FACE
currently is on FRAME.
The argument PATTERN should be a string, perhaps with wildcard
characters: the `*' character matches any substring, and the `?'
character matches any single character. Pattern matching of font
names ignores case.
If you specify FACE and FRAME, FACE should be a face name (a
symbol) and FRAME should be a frame.
The optional argument MAXIMUM sets a limit on how many fonts to
return. If this is non-`nil', then the return value is truncated
after the first MAXIMUM matching fonts. Specifying a small value
for MAXIMUM can make this function much faster, in cases where
many fonts match the pattern.
These additional functions are available starting in Emacs 21.
- Function: x-family-fonts &optional family frame
This function returns a list describing the available fonts for
family FAMILY on FRAME. If FAMILY is omitted or `nil', this list
applies to all families, and therefore, it contains all available
fonts. Otherwise, FAMILY must be a string; it may contain the
wildcards `?' and `*'.
The list describes the display that FRAME is on; if FRAME is
omitted or `nil', it applies to the selected frame's display
(*note Input Focus::).
The list contains a vector of the following form for each font:
[FAMILY WIDTH POINT-SIZE WEIGHT SLANT
FIXED-P FULL REGISTRY-AND-ENCODING]
The first five elements correspond to face attributes; if you
specify these attributes for a face, it will use this font.
The last three elements give additional information about the font.
FIXED-P is non-nil if the font is fixed-pitch. FULL is the full
name of the font, and REGISTRY-AND-ENCODING is a string giving the
registry and encoding of the font.
The result list is sorted according to the current face font sort
order.
- Function: x-font-family-list &optional frame
This function returns a list of the font families available for
FRAME's display. If FRAME is omitted or `nil', it describes the
selected frame's display (*note Input Focus::).
The value is a list of elements of this form:
(FAMILY . FIXED-P)
Here FAMILY is a font family, and FIXED-P is non-`nil' if fonts of
that family are fixed-pitch.
- Variable: font-list-limit
This variable specifies maximum number of fonts to consider in font
matching. The function `x-family-fonts' will not return more than
that many fonts, and font selection will consider only that many
fonts when searching a matching font for face attributes. The
default is currently 100.
Fontsets
--------
A "fontset" is a list of fonts, each assigned to a range of
character codes. An individual font cannot display the whole range of
characters that Emacs supports, but a fontset can. Fontsets have names,
just as fonts do, and you can use a fontset name in place of a font name
when you specify the "font" for a frame or a face. Here is information
about defining a fontset under Lisp program control.
- Function: create-fontset-from-fontset-spec fontset-spec &optional
style-variant-p noerror
This function defines a new fontset according to the specification
string FONTSET-SPEC. The string should have this format:
FONTPATTERN, [CHARSETNAME:FONTNAME]...
Whitespace characters before and after the commas are ignored.
The first part of the string, FONTPATTERN, should have the form of
a standard X font name, except that the last two fields should be
`fontset-ALIAS'.
The new fontset has two names, one long and one short. The long
name is FONTPATTERN in its entirety. The short name is
`fontset-ALIAS'. You can refer to the fontset by either name. If
a fontset with the same name already exists, an error is signaled,
unless NOERROR is non-`nil', in which case this function does
nothing.
If optional argument STYLE-VARIANT-P is non-`nil', that says to
create bold, italic and bold-italic variants of the fontset as
well. These variant fontsets do not have a short name, only a
long one, which is made by altering FONTPATTERN to indicate the
bold or italic status.
The specification string also says which fonts to use in the
fontset. See below for the details.
The construct `CHARSET:FONT' specifies which font to use (in this
fontset) for one particular character set. Here, CHARSET is the name
of a character set, and FONT is the font to use for that character set.
You can use this construct any number of times in the specification
string.
For the remaining character sets, those that you don't specify
explicitly, Emacs chooses a font based on FONTPATTERN: it replaces
`fontset-ALIAS' with a value that names one character set. For the
ASCII character set, `fontset-ALIAS' is replaced with `ISO8859-1'.
In addition, when several consecutive fields are wildcards, Emacs
collapses them into a single wildcard. This is to prevent use of
auto-scaled fonts. Fonts made by scaling larger fonts are not usable
for editing, and scaling a smaller font is not useful because it is
better to use the smaller font in its own size, which Emacs does.
Thus if FONTPATTERN is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
the font specification for ASCII characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
You may not have any Chinese font matching the above font
specification. Most X distributions include only Chinese fonts that
have `song ti' or `fangsong ti' in the FAMILY field. In such a case,
`Fontset-N' can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
Then, the font specifications for all but Chinese GB2312 characters have
`fixed' in the FAMILY field, and the font specification for Chinese
GB2312 characters has a wild card `*' in the FAMILY field.
The `display' Property
======================
The `display' text property (or overlay property) is used to insert
images into text, and also control other aspects of how text displays.
These features are available starting in Emacs 21. The value of the
`display' property should be a display specification, or a list or
vector containing several display specifications. The rest of this
section describes several kinds of display specifications and what they
mean.
Specified Spaces
----------------
To display a space of specified width and/or height, use a display
specification of the form `(space . PROPS)', where PROPS is a property
list (a list of alternating properties and values). You can put this
property on one or more consecutive characters; a space of the
specified height and width is displayed in place of _all_ of those
characters. These are the properties you can use to specify the weight
of the space:
`:width WIDTH'
Specifies that the space width should be WIDTH times the normal
character width. WIDTH can be an integer or floating point number.
`:relative-width FACTOR'
Specifies that the width of the stretch should be computed from the
first character in the group of consecutive characters that have
the same `display' property. The space width is the width of that
character, multiplied by FACTOR.
`:align-to HPOS'
Specifies that the space should be wide enough to reach HPOS. The
value HPOS is measured in units of the normal character width. It
may be an interer or a floating point number.
Exactly one of the above properties should be used. You can also
specify the height of the space, with other properties:
`:height HEIGHT'
Specifies the height of the space, as HEIGHT, measured in terms of
the normal line height.
`:relative-height FACTOR'
Specifies the height of the space, multiplying the ordinary height
of the text having this display specification by FACTOR.
`:ascent ASCENT'
Specifies that ASCENT percent of the height of the space should be
considered as the ascent of the space--that is, the part above the
baseline. The value of ASCENT must be a non-negative number no
greater than 100.
You should not use both `:height' and `:relative-height' together.
Other Display Specifications
----------------------------
`(image . IMAGE-PROPS)'
This is in fact an image descriptor (*note Images::). When used
as a display specification, it means to display the image instead
of the text that has the display specification.
`((margin nil) STRING)'
`STRING'
A display specification of this form means to display STRING
instead of the text that has the display specification, at the same
position as that text. This is a special case of marginal display
(*note Display Margins::).
Recursive display specifications are not supported, i.e. string
display specifications that have a display specification property
themselves.
`(space-width FACTOR)'
This display specification affects all the space characters within
the text that has the specification. It displays all of these
spaces FACTOR times as wide as normal. The element FACTOR should
be an integer or float. Characters other than spaces are not
affected at all; in particular, this has no effect on tab
characters.
`(height HEIGHT)'
This display specification makes the text taller or shorter. Here
are the possibilities for HEIGHT:
`(+ N)'
This means to use a font that is N steps larger. A "step" is
defined by the set of available fonts--specifically, those
that match what was otherwise specified for this text, in all
attributes except height. Each size for which a suitable
font is available counts as another step. N should be an
integer.
`(- N)'
This means to use a font that is N steps smaller.
a number, FACTOR
A number, FACTOR, means to use a font that is FACTOR times as
tall as the default font.
a symbol, FUNCTION
A symbol is a function to compute the height. It is called
with the current height as argument, and should return the
new height to use.
anything else, FORM
If the HEIGHT value doesn't fit the previous possibilities,
it is a form. Emacs evaluates it to get the new height, with
the symbol `height' bound to the current specified font
height.
`(raise FACTOR)'
This kind of display specification raises or lowers the text it
applies to, relative to the baseline of the line.
FACTOR must be a number, which is interpreted as a multiple of the
height of the affected text. If it is positive, that means to
display the characters raised. If it is negative, that means to
display them lower down.
If the text also has a `height' display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
Displaying in the Margins
-------------------------
A buffer can have blank areas called "display margins" on the left
and on the right. Ordinary text never appears in these areas, but you
can put things into the display margins using the `display' property.
To put text in the left or right display margin of the window, use a
display specification of the form `(margin right-margin)' or `(margin
left-margin)' on it. To put an image in a display margin, use that
display specification along with the display specification for the
image.
Before the display margins can display anything, you must give them
a nonzero width. The usual way to do that is to set these variables:
- Variable: left-margin-width
This variable specifies the width of the left margin. It is
buffer-local in all buffers.
- Variable: right-margin-width
This variable specifies the width of the right margin. It is
buffer-local in all buffers.
Setting these variables does not immediately affect the window.
These variables are checked when a new buffer is displayed in the
window. Thus, you can make changes take effect by calling
`set-window-buffer'.
You can also set the margin widths immediately.
- Function: set-window-margins window left &optional right
This function specifies the margin widths for window WINDOW. The
argument LEFT controls the left margin and RIGHT controls the
right margin (default `0').
- Function: window-margins &optional window
This function returns the left and right margins of WINDOW as a
cons cell of the form `(LEFT . RIGHT)'. If WINDOW is `nil', the
selected window is used.
Conditional Display Specifications
----------------------------------
You can make any display specification conditional. To do that,
package it in another list of the form `(when CONDITION . SPEC)'.
Then the specification SPEC applies only when CONDITION evaluates to a
non-`nil' value. During the evaluation, `object' is bound to the
string or buffer having the conditional `display' property. `position'
and `buffer-position' are bound to the position within `object' and the
buffer position where the `display' property was found, respectively.
Both positions can be different when `object' is a string.
Images
======
To display an image in an Emacs buffer, you must first create an
image descriptor, then use it as a display specifier in the `display'
property of text that is displayed (*note Display Property::). Like the
`display' property, this feature is available starting in Emacs 21.
Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on your
machine. The supported image formats include XBM, XPM (needing the
libraries `libXpm' version 3.4k and `libz'), GIF (needing `libungif'
4.1.0), Postscript, PBM, JPEG (needing the `libjpeg' library version
v6a), TIFF (needing `libtiff' v3.4), and PNG (needing `libpng' 1.0.2).
You specify one of these formats with an image type symbol. The
image type symbols are `xbm', `xpm', `gif', `postscript', `pbm',
`jpeg', `tiff', and `png'.
- Variable: image-types
This variable contains a list of those image type symbols that are
supported in the current configuration.
Image Descriptors
-----------------
An image description is a list of the form `(image . PROPS)', where
PROPS is a property list containing alternating keyword symbols
(symbols whose names start with a colon) and their values. You can use
any Lisp object as a property, but the only properties that have any
special meaning are certain symbols, all of them keywords.
Every image descriptor must contain the property `:type TYPE' to
specify the format of the image. The value of TYPE should be an image
type symbol; for example, `xpm' for an image in XPM format.
Here is a list of other properties that are meaningful for all image
types:
`:file FILE'
The `:file' property specifies to load the image from file FILE.
If FILE is not an absolute file name, it is expanded in
`data-directory'.
`:data DATA'
The `:data' property specifies the actual contents of the image.
Each image must use either `:data' or `:file', but not both. For
most image types, the value of the `:data' property should be a
string containing the image data; we recommend using a unibyte
string.
Before using `:data', look for further information in the section
below describing the specific image format. For some image types,
`:data' may not be supported; for some, it allows other data types;
for some, `:data' alone is not enough, so you need to use other
image properties along with `:data'.
`:margin MARGIN'
The `:margin' property specifies how many pixels to add as an
extra margin around the image. The value, MARGIN, must be a a
non-negative number, or a pair `(X . Y)' of such numbers. If it
is a pair, X specifies how many pixels to add horizontally, and Y
specifies how many pixels to add vertically. If `:margin' is not
specified, the default is zero.
`:ascent ASCENT'
The `:ascent' property specifies the amount of the image's height
to use for its ascent--that is, the part above the baseline. The
value, ASCENT, must be a number in the range 0 to 100, or the
symbol `center'.
If ASCENT is a number, that percentage of the image's height is
used for its ascent.
If ASCENT is `center', the image is vertically centered around a
centerline which would be the vertical centerline of text drawn at
the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
`:relief RELIEF'
The `:relief' property, if non-`nil', adds a shadow rectangle
around the image. The value, RELIEF, specifies the width of the
shadow lines, in pixels. If RELIEF is negative, shadows are drawn
so that the image appears as a pressed button; otherwise, it
appears as an unpressed button.
`:conversion ALGORITHM'
The `:conversion' property, if non-`nil', specifies a conversion
algorithm that should be applied to the image before it is
displayed; the value, ALGORITHM, specifies which algorithm.
`laplace'
`emboss'
Specifies the Laplace edge detection algorithm, which blurs
out small differences in color while highlighting larger
differences. People sometimes consider this useful for
displaying the image for a "disabled" button.
`(edge-detection :matrix MATRIX :color-adjust ADJUST)'
Specifies a general edge-detection algorithm. MATRIX must be
either a nine-element list or a nine-element vector of
numbers. A pixel at position x/y in the transformed image is
computed from original pixels around that position. MATRIX
specifies, for each pixel in the neighborhood of x/y, a
factor with which that pixel will influence the transformed
pixel; element 0 specifies the factor for the pixel at
x-1/y-1, element 1 the factor for the pixel at x/y-1 etc., as
shown below:
(x-1/y-1 x/y-1 x+1/y-1
x-1/y x/y x+1/y
x-1/y+1 x/y+1 x+1/y+1)
The resulting pixel is computed from the color intensity of
the color resulting from summing up the RGB values of
surrounding pixels, multiplied by the specified factors, and
dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0
0 0 0
9 9 -1)
Emboss edge-detection uses a matrix of
( 2 -1 0
-1 0 1
0 1 -2)
`disabled'
Specifies transforming the image so that it looks "disabled".
`:mask MASK'
If MASK is `heuristic' or `(heuristic BG)', build a clipping mask
for the image, so that the background of a frame is visible behind
the image. If BG is not specified, or if BG is `t', determine the
background color of the image by looking at the four corners of
the image, assuming the most frequently occurring color from the
corners is the background color of the image. Otherwise, BG must
be a list `(RED GREEN BLUE)' specifying the color to assume for
the background of the image.
If MASK is nil, remove a mask from the image, if it has one.
Images in some formats include a mask which can be removed by
specifying `:mask nil'.
- Function: image-mask-p spec &optional frame
This function returns `t' if image SPEC has a mask bitmap. FRAME
is the frame on which the image will be displayed. FRAME `nil' or
omitted means to use the selected frame (*note Input Focus::).
XBM Images
----------
To use XBM format, specify `xbm' as the image type. This image
format doesn't require an external library, so images of this type are
always supported.
Additional image properties supported for the `xbm' image type are:
`:foreground FOREGROUND'
The value, FOREGROUND, should be a string specifying the image
foreground color, or `nil' for the default color. This color is
used for each pixel in the XBM that is 1. The default is the
frame's foreground color.
`:background BACKGROUND'
The value, BACKGROUND, should be a string specifying the image
background color, or `nil' for the default color. This color is
used for each pixel in the XBM that is 0. The default is the
frame's background color.
If you specify an XBM image using data within Emacs instead of an
external file, use the following three properties:
`:data DATA'
The value, DATA, specifies the contents of the image. There are
three formats you can use for DATA:
* A vector of strings or bool-vectors, each specifying one line
of the image. Do specify `:height' and `:width'.
* A string containing the same byte sequence as an XBM file
would contain. You must not specify `:height' and `:width'
in this case, because omitting them is what indicates the
data has the format of an XBM file. The file contents
specify the height and width of the image.
* A string or a bool-vector containing the bits of the image
(plus perhaps some extra bits at the end that will not be
used). It should contain at least WIDTH * `height' bits. In
this case, you must specify `:height' and `:width', both to
indicate that the string contains just the bits rather than a
whole XBM file, and to specify the size of the image.
`:width WIDTH'
The value, WIDTH, specifies the width of the image, in pixels.
`:height HEIGHT'
The value, HEIGHT, specifies the height of the image, in pixels.
XPM Images
----------
To use XPM format, specify `xpm' as the image type. The additional
image property `:color-symbols' is also meaningful with the `xpm' image
type:
`:color-symbols SYMBOLS'
The value, SYMBOLS, should be an alist whose elements have the
form `(NAME . COLOR)'. In each element, NAME is the name of a
color as it appears in the image file, and COLOR specifies the
actual color to use for displaying that name.
GIF Images
----------
For GIF images, specify image type `gif'. Because of the patents in
the US covering the LZW algorithm, the continued use of GIF format is a
problem for the whole Internet; to end this problem, it is a good idea
for everyone, even outside the US, to stop using GIFS right away
(`http://www.burnallgifs.org/'). But if you still want to use them,
Emacs can display them.
`:index INDEX'
You can use `:index' to specify one image from a GIF file that
contains more than one image. This property specifies use of image
number INDEX from the file. An error is signaled if the GIF file
doesn't contain an image with index INDEX.
Postscript Images
-----------------
To use Postscript for an image, specify image type `postscript'.
This works only if you have Ghostscript installed. You must always use
these three properties:
`:pt-width WIDTH'
The value, WIDTH, specifies the width of the image measured in
points (1/72 inch). WIDTH must be an integer.
`:pt-height HEIGHT'
The value, HEIGHT, specifies the height of the image in points
(1/72 inch). HEIGHT must be an integer.
`:bounding-box BOX'
The value, BOX, must be a list or vector of four integers, which
specifying the bounding box of the Postscript image, analogous to
the `BoundingBox' comment found in Postscript files.
%%BoundingBox: 22 171 567 738
Displaying Postscript images from Lisp data is not currently
implemented, but it may be implemented by the time you read this. See
the `etc/NEWS' file to make sure.
Other Image Types
-----------------
For PBM images, specify image type `pbm'. Color, gray-scale and
monochromatic images are supported. For mono PBM images, two
additional image properties are supported.
`:foreground FOREGROUND'
The value, FOREGROUND, should be a string specifying the image
foreground color, or `nil' for the default color. This color is
used for each pixel in the XBM that is 1. The default is the
frame's foreground color.
`:background BACKGROUND'
The value, BACKGROUND, should be a string specifying the image
background color, or `nil' for the default color. This color is
used for each pixel in the XBM that is 0. The default is the
frame's background color.
For JPEG images, specify image type `jpeg'.
For TIFF images, specify image type `tiff'.
For PNG images, specify image type `png'.
Defining Images
---------------
The functions `create-image', `defimage' and `find-image' provide
convenient ways to create image descriptors.
- Function: create-image file &optional type &rest props
This function creates and returns an image descriptor which uses
the data in FILE.
The optional argument TYPE is a symbol specifying the image type.
If TYPE is omitted or `nil', `create-image' tries to determine the
image type from the file's first few bytes, or else from the
file's name.
The remaining arguments, PROPS, specify additional image
properties--for example,
(create-image "foo.xpm" 'xpm :heuristic-mask t)
The function returns `nil' if images of this type are not
supported. Otherwise it returns an image descriptor.
- Macro: defimage variable doc &rest specs
This macro defines VARIABLE as an image name. The second argument,
DOC, is an optional documentation string. The remaining
arguments, SPECS, specify alternative ways to display the image.
Each argument in SPECS has the form of a property list, and each
one should specify at least the `:type' property and the `:file'
property. Here is an example:
(defimage test-image
'((:type xpm :file "~/test1.xpm")
(:type xbm :file "~/test1.xbm")))
`defimage' tests each argument, one by one, to see if it is
usable--that is, if the type is supported and the file exists. The
first usable argument is used to make an image descriptor which is
stored in the variable VARIABLE.
If none of the alternatives will work, then VARIABLE is defined as
`nil'.
- Function: find-image specs
This function provides a convenient way to find an image
satisfying one of a list of image specifications SPECS.
Each specification in SPECS is a property list with contents
depending on image type. All specifications must at least contain
the properties `:type TYPE' and either `:file FILE' or
`:data DATA', where TYPE is a symbol specifying the image type,
e.g. `xbm', FILE is the file to load the image from, and DATA is a
string containing the actual image data. The first specification
in the list whose TYPE is supported, and FILE exists, is used to
construct the image specification to be returned. If no
specification is satisfied, `nil' is returned.
The image is looked for first on `load-path' and then in
`data-directory'.
Showing Images
--------------
You can use an image descriptor by setting up the `display' property
yourself, but it is easier to use the functions in this section.
- Function: insert-image image &optional string area
This function inserts IMAGE in the current buffer at point. The
value IMAGE should be an image descriptor; it could be a value
returned by `create-image', or the value of a symbol defined with
`defimage'. The argument STRING specifies the text to put in the
buffer to hold the image.
The argument AREA specifies whether to put the image in a margin.
If it is `left-margin', the image appears in the left margin;
`right-margin' specifies the right margin. If AREA is `nil' or
omitted, the image is displayed at point within the buffer's text.
Internally, this function inserts STRING in the buffer, and gives
it a `display' property which specifies IMAGE. *Note Display
Property::.
- Function: put-image image pos &optional string area
This function puts image IMAGE in front of POS in the current
buffer. The argument POS should be an integer or a marker. It
specifies the buffer position where the image should appear. The
argument STRING specifies the text that should hold the image as
an alternative to the default.
The argument IMAGE must be an image descriptor, perhaps returned
by `create-image' or stored by `defimage'.
The argument AREA specifies whether to put the image in a margin.
If it is `left-margin', the image appears in the left margin;
`right-margin' specifies the right margin. If AREA is `nil' or
omitted, the image is displayed at point within the buffer's text.
Internally, this function creates an overlay, and gives it a
`before-string' property containing text that has a `display'
property whose value is the image. (Whew!)
- Function: remove-images start end &optional buffer
This function removes images in BUFFER between positions START and
END. If BUFFER is omitted or `nil', images are removed from the
current buffer.
This removes only images that were put into BUFFER the way
`put-image' does it, not images that were inserted with
`insert-image' or in other ways.
- Function: image-size spec &optional pixels frame
This function returns the size of an image as a pair
`(WIDTH . HEIGHT)'. SPEC is an image specification. PIXELS
non-nil means return sizes measured in pixels, otherwise return
sizes measured in canonical character units (fractions of the
width/height of the frame's default font). FRAME is the frame on
which the image will be displayed. FRAME null or omitted means
use the selected frame (*note Input Focus::).
Image Cache
-----------
Emacs stores images in an image cache when it displays them, so it
can display them again more efficiently. It removes an image from the
cache when it hasn't been displayed for a specified period of time.
When an image is looked up in the cache, its specification is
compared with cached image specifications using `equal'. This means
that all images with equal specifications share the same image in the
cache.
- Variable: image-cache-eviction-delay
This variable specifies the number of seconds an image can remain
in the cache without being displayed. When an image is not
displayed for this length of time, Emacs removes it from the image
cache.
If the value is `nil', Emacs does not remove images from the cache
except when you explicitly clear it. This mode can be useful for
debugging.
- Function: clear-image-cache &optional frame
This function clears the image cache. If FRAME is non-`nil', only
the cache for that frame is cleared. Otherwise all frames' caches
are cleared.
Blinking Parentheses
====================
This section describes the mechanism by which Emacs shows a matching
open parenthesis when the user inserts a close parenthesis.
- Variable: blink-paren-function
The value of this variable should be a function (of no arguments)
to be called whenever a character with close parenthesis syntax is
inserted. The value of `blink-paren-function' may be `nil', in
which case nothing is done.
- User Option: blink-matching-paren
If this variable is `nil', then `blink-matching-open' does nothing.
- User Option: blink-matching-paren-distance
This variable specifies the maximum distance to scan for a matching
parenthesis before giving up.
- User Option: blink-matching-delay
This variable specifies the number of seconds for the cursor to
remain at the matching parenthesis. A fraction of a second often
gives good results, but the default is 1, which works on all
systems.
- Command: blink-matching-open
This function is the default value of `blink-paren-function'. It
assumes that point follows a character with close parenthesis
syntax and moves the cursor momentarily to the matching opening
character. If that character is not already on the screen, it
displays the character's context in the echo area. To avoid long
delays, this function does not search farther than
`blink-matching-paren-distance' characters.
Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open ()
"Indicate momentarily the start of sexp before point."
(interactive)
(let ((blink-matching-paren-distance
(buffer-size))
(blink-matching-paren t))
(blink-matching-open)))
Inverse Video
=============
- User Option: inverse-video
This variable controls whether Emacs uses inverse video for all
text on the screen. Non-`nil' means yes, `nil' means no. The
default is `nil'.
- User Option: mode-line-inverse-video
This variable controls the use of inverse video for mode lines and
menu bars. If it is non-`nil', then these lines are displayed in
inverse video. Otherwise, these lines are displayed normally,
just like other text. The default is `t'.
For window frames, this feature actually applies the face named
`mode-line'; that face is normally set up as the inverse of the
default face, unless you change it.
Usual Display Conventions
=========================
The usual display conventions define how to display each character
code. You can override these conventions by setting up a display table
(*note Display Tables::). Here are the usual display conventions:
* Character codes 32 through 126 map to glyph codes 32 through 126.
Normally this means they display as themselves.
* Character code 9 is a horizontal tab. It displays as whitespace
up to a position determined by `tab-width'.
* Character code 10 is a newline.
* All other codes in the range 0 through 31, and code 127, display
in one of two ways according to the value of `ctl-arrow'. If it is
non-`nil', these codes map to sequences of two glyphs, where the
first glyph is the ASCII code for `^'. (A display table can
specify a glyph to use instead of `^'.) Otherwise, these codes map
just like the codes in the range 128 to 255.
On MS-DOS terminals, Emacs arranges by default for the character
code 127 to be mapped to the glyph code 127, which normally
displays as an empty polygon. This glyph is used to display
non-ASCII characters that the MS-DOS terminal doesn't support.
*Note MS-DOS and MULE: (emacs)MS-DOS and MULE.
* Character codes 128 through 255 map to sequences of four glyphs,
where the first glyph is the ASCII code for `\', and the others are
digit characters representing the character code in octal. (A
display table can specify a glyph to use instead of `\'.)
* Multibyte character codes above 256 are displayed as themselves,
or as a question mark or empty box if the terminal cannot display
that character.
The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
`nil'. Thus, when you set up a display table, you need only specify
the characters for which you want special behavior.
These display rules apply to carriage return (character code 13),
when it appears in the buffer. But that character may not appear in the
buffer where you expect it, if it was eliminated as part of end-of-line
conversion (*note Coding System Basics::).
These variables affect the way certain characters are displayed on
the screen. Since they change the number of columns the characters
occupy, they also affect the indentation functions. These variables
also affect how the mode line is displayed; if you want to force
redisplay of the mode line using the new values, call the function
`force-mode-line-update' (*note Mode Line Format::).
- User Option: ctl-arrow
This buffer-local variable controls how control characters are
displayed. If it is non-`nil', they are displayed as a caret
followed by the character: `^A'. If it is `nil', they are
displayed as a backslash followed by three octal digits: `\001'.
- Variable: default-ctl-arrow
The value of this variable is the default value for `ctl-arrow' in
buffers that do not override it. *Note Default Value::.
- User Option: indicate-empty-lines
When this is non-`nil', Emacs displays a special glyph in each
empty line at the end of the buffer, on terminals that support it
(window systems).
- User Option: tab-width
The value of this variable is the spacing between tab stops used
for displaying tab characters in Emacs buffers. The value is in
units of columns, and the default is 8. Note that this feature is
completely independent of the user-settable tab stops used by the
command `tab-to-tab-stop'. *Note Indent Tabs::.
Display Tables
==============
You can use the "display table" feature to control how all possible
character codes display on the screen. This is useful for displaying
European languages that have letters not in the ASCII character set.
The display table maps each character code into a sequence of
"glyphs", each glyph being a graphic that takes up one character
position on the screen. You can also define how to display each glyph
on your terminal, using the "glyph table".
Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
`force-mode-line-update' (*note Mode Line Format::).
Display Table Format
--------------------
A display table is actually a char-table (*note Char-Tables::) with
`display-table' as its subtype.
- Function: make-display-table
This creates and returns a display table. The table initially has
`nil' in all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index C says how to display the character code C.
The value should be `nil' or a vector of glyph values (*note
Glyphs::). If an element is `nil', it says to display that character
according to the usual display conventions (*note Usual Display::).
If you use the display table to change the display of newline
characters, the whole buffer will be displayed as one long "line."
The display table also has six "extra slots" which serve special
purposes. Here is a table of their meanings; `nil' in any slot means
to use the default for that slot, as stated below.
0
The glyph for the end of a truncated screen line (the default for
this is `$'). *Note Glyphs::. Newer Emacs versions, on some
platforms, display arrows to indicate truncation--the display
table has no effect in these situations.
1
The glyph for the end of a continued line (the default is `\').
Newer Emacs versions, on some platforms, display curved arrows to
indicate truncation--the display table has no effect in these
situations.
2
The glyph for indicating a character displayed as an octal
character code (the default is `\').
3
The glyph for indicating a control character (the default is `^').
4
A vector of glyphs for indicating the presence of invisible lines
(the default is `...'). *Note Selective Display::.
5
The glyph used to draw the border between side-by-side windows (the
default is `|'). *Note Splitting Windows::. This takes effect
only when there are no scroll bars; if scroll bars are supported
and in use, a scroll bar separates the two windows.
For example, here is how to construct a display table that mimics the
effect of setting `ctl-arrow' to a non-`nil' value:
(setq disptab (make-display-table))
(let ((i 0))
(while (< i 32)
(or (= i ?\t) (= i ?\n)
(aset disptab i (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
- Function: display-table-slot display-table slot
This function returns the value of the extra slot SLOT of
DISPLAY-TABLE. The argument SLOT may be a number from 0 to 5
inclusive, or a slot name (symbol). Valid symbols are
`truncation', `wrap', `escape', `control', `selective-display',
and `vertical-border'.
- Function: set-display-table-slot display-table slot value
This function stores VALUE in the extra slot SLOT of
DISPLAY-TABLE. The argument SLOT may be a number from 0 to 5
inclusive, or a slot name (symbol). Valid symbols are
`truncation', `wrap', `escape', `control', `selective-display',
and `vertical-border'.
- Function: describe-display-table display-table
This function displays a description of the display table
DISPLAY-TABLE in a help buffer.
- Command: describe-current-display-table
This command displays a description of the current display table
in a help buffer.
Active Display Table
--------------------
Each window can specify a display table, and so can each buffer.
When a buffer B is displayed in window W, display uses the display
table for window W if it has one; otherwise, the display table for
buffer B if it has one; otherwise, the standard display table if any.
The display table chosen is called the "active" display table.
- Function: window-display-table window
This function returns WINDOW's display table, or `nil' if WINDOW
does not have an assigned display table.
- Function: set-window-display-table window table
This function sets the display table of WINDOW to TABLE. The
argument TABLE should be either a display table or `nil'.
- Variable: buffer-display-table
This variable is automatically buffer-local in all buffers; its
value in a particular buffer specifies the display table for that
buffer. If it is `nil', that means the buffer does not have an
assigned display table.
- Variable: standard-display-table
This variable's value is the default display table, used whenever a
window has no display table and neither does the buffer displayed
in that window. This variable is `nil' by default.
If there is no display table to use for a particular window--that is,
if the window specifies none, its buffer specifies none, and
`standard-display-table' is `nil'--then Emacs uses the usual display
conventions for all character codes in that window. *Note Usual
Display::.
A number of functions for changing the standard display table are
defined in the library `disp-table'.
Glyphs
------
A "glyph" is a generalization of a character; it stands for an image
that takes up a single character position on the screen. Glyphs are
represented in Lisp as integers, just as characters are.
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable `glyph-table'.
- Variable: glyph-table
The value of this variable is the current glyph table. It should
be a vector; the Gth element defines glyph code G. If the value
is `nil' instead of a vector, then all glyphs are simple (see
below). The glyph table is not used on windowed displays.
Here are the possible types of elements in the glyph table:
STRING
Send the characters in STRING to the terminal to output this
glyph. This alternative is available on character terminals, but
not under a window system.
INTEGER
Define this glyph code as an alias for glyph code INTEGER. You
can use an alias to specify a face code for the glyph; see below.
`nil'
This glyph is simple. The glyph code mod 524288 is the character
to output, and the glyph code divided by 524288 specifies the face
number (*note Face Functions::) to use while outputting it.
(524288 is 2**19.) *Note Faces::.
If a glyph code is greater than or equal to the length of the glyph
table, that code is automatically simple.
- Function: create-glyph string
This function returns a newly-allocated glyph code which is set up
to display by sending STRING to the terminal.
Beeping
=======
This section describes how to make Emacs ring the bell (or blink the
screen) to attract the user's attention. Be conservative about how
often you do this; frequent bells can become irritating. Also be
careful not to use just beeping when signaling an error is more
appropriate. (*Note Errors::.)
- Function: ding &optional do-not-terminate
This function beeps, or flashes the screen (see `visible-bell'
below). It also terminates any keyboard macro currently executing
unless DO-NOT-TERMINATE is non-`nil'.
- Function: beep &optional do-not-terminate
This is a synonym for `ding'.
- User Option: visible-bell
This variable determines whether Emacs should flash the screen to
represent a bell. Non-`nil' means yes, `nil' means no. This is
effective on a window system, and on a character-only terminal
provided the terminal's Termcap entry defines the visible bell
capability (`vb').
- Variable: ring-bell-function
If this is non-`nil', it specifies how Emacs should "ring the
bell." Its value should be a function of no arguments. If this is
non-`nil', it takes precedence over the `visible-bell' variable.
Window Systems
==============
Emacs works with several window systems, most notably the X Window
System. Both Emacs and X use the term "window", but use it
differently. An Emacs frame is a single window as far as X is
concerned; the individual Emacs windows are not known to X at all.
- Variable: window-system
This variable tells Lisp programs what window system Emacs is
running under. The possible values are
`x'
Emacs is displaying using X.
`pc'
Emacs is displaying using MS-DOS.
`w32'
Emacs is displaying using Windows.
`mac'
Emacs is displaying using a Macintosh.
`nil'
Emacs is using a character-based terminal.
- Variable: window-setup-hook
This variable is a normal hook which Emacs runs after handling the
initialization files. Emacs runs this hook after it has completed
loading your init file, the default initialization file (if any),
and the terminal-specific Lisp code, and running the hook
`term-setup-hook'.
This hook is used for internal purposes: setting up communication
with the window system, and creating the initial window. Users
should not interfere with it.
Customizing the Calendar and Diary
**********************************
There are many customizations that you can use to make the calendar
and diary suit your personal tastes.
Customizing the Calendar
========================
If you set the variable `view-diary-entries-initially' to `t',
calling up the calendar automatically displays the diary entries for
the current date as well. The diary dates appear only if the current
date is visible. If you add both of the following lines to your init
file:
(setq view-diary-entries-initially t)
(calendar)
this displays both the calendar and diary windows whenever you start
Emacs.
Similarly, if you set the variable
`view-calendar-holidays-initially' to `t', entering the calendar
automatically displays a list of holidays for the current three-month
period. The holiday list appears in a separate window.
You can set the variable `mark-diary-entries-in-calendar' to `t' in
order to mark any dates with diary entries. This takes effect whenever
the calendar window contents are recomputed. There are two ways of
marking these dates: by changing the face (*note Faces::), or by
placing a plus sign (`+') beside the date.
Similarly, setting the variable `mark-holidays-in-calendar' to `t'
marks holiday dates, either with a change of face or with an asterisk
(`*').
The variable `calendar-holiday-marker' specifies how to mark a date
as being a holiday. Its value may be a character to insert next to the
date, or a face name to use for displaying the date. Likewise, the
variable `diary-entry-marker' specifies how to mark a date that has
diary entries. The calendar creates faces named `holiday-face' and
`diary-face' for these purposes; those symbols are the default values
of these variables.
The variable `calendar-load-hook' is a normal hook run when the
calendar package is first loaded (before actually starting to display
the calendar).
Starting the calendar runs the normal hook
`initial-calendar-window-hook'. Recomputation of the calendar display
does not run this hook. But if you leave the calendar with the `q'
command and reenter it, the hook runs again.
The variable `today-visible-calendar-hook' is a normal hook run
after the calendar buffer has been prepared with the calendar when the
current date is visible in the window. One use of this hook is to
replace today's date with asterisks; to do that, use the hook function
`calendar-star-date'.
(add-hook 'today-visible-calendar-hook 'calendar-star-date)
Another standard hook function marks the current date, either by
changing its face or by adding an asterisk. Here's how to use it:
(add-hook 'today-visible-calendar-hook 'calendar-mark-today)
The variable `calendar-today-marker' specifies how to mark today's
date. Its value should be a character to insert next to the date or a
face name to use for displaying the date. A face named
`calendar-today-face' is provided for this purpose; that symbol is the
default for this variable.
A similar normal hook, `today-invisible-calendar-hook' is run if the
current date is _not_ visible in the window.
Starting in Emacs 21, each of the calendar cursor motion commands
runs the hook `calendar-move-hook' after it moves the cursor.
Customizing the Holidays
========================
Emacs knows about holidays defined by entries on one of several
lists. You can customize these lists of holidays to your own needs,
adding or deleting holidays. The lists of holidays that Emacs uses are
for general holidays (`general-holidays'), local holidays
(`local-holidays'), Christian holidays (`christian-holidays'), Hebrew
(Jewish) holidays (`hebrew-holidays'), Islamic (Moslem) holidays
(`islamic-holidays'), and other holidays (`other-holidays').
The general holidays are, by default, holidays common throughout the
United States. To eliminate these holidays, set `general-holidays' to
`nil'.
There are no default local holidays (but sites may supply some). You
can set the variable `local-holidays' to any list of holidays, as
described below.
By default, Emacs does not include all the holidays of the religions
that it knows, only those commonly found in secular calendars. For a
more extensive collection of religious holidays, you can set any (or
all) of the variables `all-christian-calendar-holidays',
`all-hebrew-calendar-holidays', or `all-islamic-calendar-holidays' to
`t'. If you want to eliminate the religious holidays, set any or all
of the corresponding variables `christian-holidays', `hebrew-holidays',
and `islamic-holidays' to `nil'.
You can set the variable `other-holidays' to any list of holidays.
This list, normally empty, is intended for individual use.
Each of the lists (`general-holidays', `local-holidays',
`christian-holidays', `hebrew-holidays', `islamic-holidays', and
`other-holidays') is a list of "holiday forms", each holiday form
describing a holiday (or sometimes a list of holidays).
Here is a table of the possible kinds of holiday form. Day numbers
and month numbers count starting from 1, but "dayname" numbers count
Sunday as 0. The element STRING is always the name of the holiday, as
a string.
`(holiday-fixed MONTH DAY STRING)'
A fixed date on the Gregorian calendar.
`(holiday-float MONTH DAYNAME K STRING)'
The Kth DAYNAME in MONTH on the Gregorian calendar (DAYNAME=0 for
Sunday, and so on); negative K means count back from the end of
the month.
`(holiday-hebrew MONTH DAY STRING)'
A fixed date on the Hebrew calendar.
`(holiday-islamic MONTH DAY STRING)'
A fixed date on the Islamic calendar.
`(holiday-julian MONTH DAY STRING)'
A fixed date on the Julian calendar.
`(holiday-sexp SEXP STRING)'
A date calculated by the Lisp expression SEXP. The expression
should use the variable `year' to compute and return the date of a
holiday, or `nil' if the holiday doesn't happen this year. The
value of SEXP must represent the date as a list of the form
`(MONTH DAY YEAR)'.
`(if CONDITION HOLIDAY-FORM)'
A holiday that happens only if CONDITION is true.
`(FUNCTION [ARGS])'
A list of dates calculated by the function FUNCTION, called with
arguments ARGS.
For example, suppose you want to add Bastille Day, celebrated in
France on July 14. You can do this as follows:
(setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))
The holiday form `(holiday-fixed 7 14 "Bastille Day")' specifies the
fourteenth day of the seventh month (July).
Many holidays occur on a specific day of the week, at a specific time
of month. Here is a holiday form describing Hurricane Supplication Day,
celebrated in the Virgin Islands on the fourth Monday in August:
(holiday-float 8 1 4 "Hurricane Supplication Day")
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0,
Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in
the month (1 specifies the first occurrence, 2 the second occurrence,
-1 the last occurrence, -2 the second-to-last occurrence, and so on).
You can specify holidays that occur on fixed days of the Hebrew,
Islamic, and Julian calendars too. For example,
(setq other-holidays
'((holiday-hebrew 10 2 "Last day of Hanukkah")
(holiday-islamic 3 12 "Mohammed's Birthday")
(holiday-julian 4 2 "Jefferson's Birthday")))
adds the last day of Hanukkah (since the Hebrew months are numbered with
1 starting from Nisan), the Islamic feast celebrating Mohammed's
birthday (since the Islamic months are numbered from 1 starting with
Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the
Julian calendar.
To include a holiday conditionally, use either Emacs Lisp's `if' or
the `holiday-sexp' form. For example, American presidential elections
occur on the first Tuesday after the first Monday in November of years
divisible by 4:
(holiday-sexp (if (= 0 (% year 4))
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 year))))))
"US Presidential Election"))
or
(if (= 0 (% displayed-year 4))
(fixed 11
(extract-calendar-day
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 displayed-year)))))))
"US Presidential Election"))
Some holidays just don't fit into any of these forms because special
calculations are involved in their determination. In such cases you
must write a Lisp function to do the calculation. To include eclipses,
for example, add `(eclipses)' to `other-holidays' and write an Emacs
Lisp function `eclipses' that returns a (possibly empty) list of the
relevant Gregorian dates among the range visible in the calendar
window, with descriptive strings, like this:
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
Date Display Format
===================
You can customize the manner of displaying dates in the diary, in
mode lines, and in messages by setting `calendar-date-display-form'.
This variable holds a list of expressions that can involve the variables
`month', `day', and `year', which are all numbers in string form, and
`monthname' and `dayname', which are both alphabetic strings. In the
American style, the default value of this list is as follows:
((if dayname (concat dayname ", ")) monthname " " day ", " year)
while in the European style this value is the default:
((if dayname (concat dayname ", ")) day " " monthname " " year)
The ISO standard date representation is this:
(year "-" month "-" day)
This specifies a typical American format:
(month "/" day "/" (substring year -2))
Time Display Format
===================
The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either `am' or `pm'. If you prefer the European style, also known
in the US as military, in which the hours go from 00 to 23, you can
alter the variable `calendar-time-display-form'. This variable is a
list of expressions that can involve the variables `12-hours',
`24-hours', and `minutes', which are all numbers in string form, and
`am-pm' and `time-zone', which are both alphabetic strings. The
default value of `calendar-time-display-form' is as follows:
(12-hours ":" minutes am-pm
(if time-zone " (") time-zone (if time-zone ")"))
Here is a value that provides European style times:
(24-hours ":" minutes
(if time-zone " (") time-zone (if time-zone ")"))
Daylight Savings Time
=====================
Emacs understands the difference between standard time and daylight
savings time--the times given for sunrise, sunset, solstices,
equinoxes, and the phases of the moon take that into account. The rules
for daylight savings time vary from place to place and have also varied
historically from year to year. To do the job properly, Emacs needs to
know which rules to use.
Some operating systems keep track of the rules that apply to the
place where you are; on these systems, Emacs gets the information it
needs from the system automatically. If some or all of this
information is missing, Emacs fills in the gaps with the rules
currently used in Cambridge, Massachusetts, which is the center of
GNU's world.
If the default choice of rules is not appropriate for your location,
you can tell Emacs the rules to use by setting the variables
`calendar-daylight-savings-starts' and
`calendar-daylight-savings-ends'. Their values should be Lisp
expressions that refer to the variable `year', and evaluate to the
Gregorian date on which daylight savings time starts or (respectively)
ends, in the form of a list `(MONTH DAY YEAR)'. The values should be
`nil' if your area does not use daylight savings time.
Emacs uses these expressions to determine the start and end dates of
daylight savings time as holidays and for correcting times of day in the
solar and lunar calculations.
The values for Cambridge, Massachusetts are as follows:
(calendar-nth-named-day 1 0 4 year)
(calendar-nth-named-day -1 0 10 year)
i.e., the first 0th day (Sunday) of the fourth month (April) in the
year specified by `year', and the last Sunday of the tenth month
(October) of that year. If daylight savings time were changed to start
on October 1, you would set `calendar-daylight-savings-starts' to this:
(list 10 1 year)
For a more complex example, suppose daylight savings time begins on
the first of Nisan on the Hebrew calendar. You should set
`calendar-daylight-savings-starts' to this value:
(calendar-gregorian-from-absolute
(calendar-absolute-from-hebrew
(list 1 1 (+ year 3760))))
because Nisan is the first month in the Hebrew calendar and the Hebrew
year differs from the Gregorian year by 3760 at Nisan.
If there is no daylight savings time at your location, or if you want
all times in standard time, set `calendar-daylight-savings-starts' and
`calendar-daylight-savings-ends' to `nil'.
The variable `calendar-daylight-time-offset' specifies the
difference between daylight savings time and standard time, measured in
minutes. The value for Cambridge is 60.
The variable `calendar-daylight-savings-starts-time' and the
variable `calendar-daylight-savings-ends-time' specify the number of
minutes after midnight local time when the transition to and from
daylight savings time should occur. For Cambridge, both variables'
values are 120.
Customizing the Diary
=====================
Ordinarily, the mode line of the diary buffer window indicates any
holidays that fall on the date of the diary entries. The process of
checking for holidays can take several seconds, so including holiday
information delays the display of the diary buffer noticeably. If you'd
prefer to have a faster display of the diary buffer but without the
holiday information, set the variable `holidays-in-diary-buffer' to
`nil'.
The variable `number-of-diary-entries' controls the number of days
of diary entries to be displayed at one time. It affects the initial
display when `view-diary-entries-initially' is `t', as well as the
command `M-x diary'. For example, the default value is 1, which says
to display only the current day's diary entries. If the value is 2,
both the current day's and the next day's entries are displayed. The
value can also be a vector of seven elements: for example, if the value
is `[0 2 2 2 2 4 1]' then no diary entries appear on Sunday, the
current date's and the next day's diary entries appear Monday through
Thursday, Friday through Monday's entries appear on Friday, while on
Saturday only that day's entries appear.
The variable `print-diary-entries-hook' is a normal hook run after
preparation of a temporary buffer containing just the diary entries
currently visible in the diary buffer. (The other, irrelevant diary
entries are really absent from the temporary buffer; in the diary
buffer, they are merely hidden.) The default value of this hook does
the printing with the command `lpr-buffer'. If you want to use a
different command to do the printing, just change the value of this
hook. Other uses might include, for example, rearranging the lines into
order by day and time.
You can customize the form of dates in your diary file, if neither
the standard American nor European styles suits your needs, by setting
the variable `diary-date-forms'. This variable is a list of patterns
for recognizing a date. Each date pattern is a list whose elements may
be regular expressions (*note Regular Expressions::) or the symbols
`month', `day', `year', `monthname', and `dayname'. All these elements
serve as patterns that match certain kinds of text in the diary file.
In order for the date pattern, as a whole, to match, all of its
elements must match consecutively.
A regular expression in a date pattern matches in its usual fashion,
using the standard syntax table altered so that `*' is a word
constituent.
The symbols `month', `day', `year', `monthname', and `dayname' match
the month number, day number, year number, month name, and day name of
the date being considered. The symbols that match numbers allow
leading zeros; those that match names allow three-letter abbreviations
and capitalization. All the symbols can match `*'; since `*' in a
diary entry means "any day", "any month", and so on, it should match
regardless of the date being considered.
The default value of `diary-date-forms' in the American style is
this:
((month "/" day "[^/0-9]")
(month "/" day "/" year "[^0-9]")
(monthname " *" day "[^,0-9]")
(monthname " *" day ", *" year "[^0-9]")
(dayname "\\W"))
The date patterns in the list must be _mutually exclusive_ and must
not match any portion of the diary entry itself, just the date and one
character of whitespace. If, to be mutually exclusive, the pattern
must match a portion of the diary entry text--beyond the whitespace
that ends the date--then the first element of the date pattern _must_
be `backup'. This causes the date recognizer to back up to the
beginning of the current word of the diary entry, after finishing the
match. Even if you use `backup', the date pattern must absolutely not
match more than a portion of the first word of the diary entry. The
default value of `diary-date-forms' in the European style is this list:
((day "/" month "[^/0-9]")
(day "/" month "/" year "[^0-9]")
(backup day " *" monthname "\\W+\\<[^*0-9]")
(day " *" monthname " *" year "[^0-9]")
(dayname "\\W"))
Notice the use of `backup' in the third pattern, because it needs to
match part of a word beyond the date itself to distinguish it from the
fourth pattern.
Hebrew- and Islamic-Date Diary Entries
======================================
Your diary file can have entries based on Hebrew or Islamic dates, as
well as entries based on the world-standard Gregorian calendar.
However, because recognition of such entries is time-consuming and most
people don't use them, you must explicitly enable their use. If you
want the diary to recognize Hebrew-date diary entries, for example, you
must do this:
(add-hook 'nongregorian-diary-listing-hook 'list-hebrew-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)
If you want Islamic-date entries, do this:
(add-hook 'nongregorian-diary-listing-hook 'list-islamic-diary-entries)
(add-hook 'nongregorian-diary-marking-hook 'mark-islamic-diary-entries)
Hebrew- and Islamic-date diary entries have the same formats as
Gregorian-date diary entries, except that `H' precedes a Hebrew date
and `I' precedes an Islamic date. Moreover, because the Hebrew and
Islamic month names are not uniquely specified by the first three
letters, you may not abbreviate them. For example, a diary entry for
the Hebrew date Heshvan 25 could look like this:
HHeshvan 25 Happy Hebrew birthday!
and would appear in the diary for any date that corresponds to Heshvan
25 on the Hebrew calendar. And here is an Islamic-date diary entry
that matches Dhu al-Qada 25:
IDhu al-Qada 25 Happy Islamic birthday!
As with Gregorian-date diary entries, Hebrew- and Islamic-date
entries are nonmarking if they are preceded with an ampersand (`&').
Here is a table of commands used in the calendar to create diary
entries that match the selected date and other dates that are similar
in the Hebrew or Islamic calendar:
`i h d'
Add a diary entry for the Hebrew date corresponding to the
selected date (`insert-hebrew-diary-entry').
`i h m'
Add a diary entry for the day of the Hebrew month corresponding to
the selected date (`insert-monthly-hebrew-diary-entry'). This
diary entry matches any date that has the same Hebrew
day-within-month as the selected date.
`i h y'
Add a diary entry for the day of the Hebrew year corresponding to
the selected date (`insert-yearly-hebrew-diary-entry'). This diary
entry matches any date which has the same Hebrew month and
day-within-month as the selected date.
`i i d'
Add a diary entry for the Islamic date corresponding to the
selected date (`insert-islamic-diary-entry').
`i i m'
Add a diary entry for the day of the Islamic month corresponding
to the selected date (`insert-monthly-islamic-diary-entry').
`i i y'
Add a diary entry for the day of the Islamic year corresponding to
the selected date (`insert-yearly-islamic-diary-entry').
These commands work much like the corresponding commands for ordinary
diary entries: they apply to the date that point is on in the calendar
window, and what they do is insert just the date portion of a diary
entry at the end of your diary file. You must then insert the rest of
the diary entry.
Fancy Diary Display
===================
Diary display works by preparing the diary buffer and then running
the hook `diary-display-hook'. The default value of this hook
(`simple-diary-display') hides the irrelevant diary entries and then
displays the buffer. However, if you specify the hook as follows,
(add-hook 'diary-display-hook 'fancy-diary-display)
this enables fancy diary display. It displays diary entries and
holidays by copying them into a special buffer that exists only for the
sake of display. Copying to a separate buffer provides an opportunity
to change the displayed text to make it prettier--for example, to sort
the entries by the dates they apply to.
As with simple diary display, you can print a hard copy of the buffer
with `print-diary-entries'. To print a hard copy of a day-by-day diary
for a week, position point on Sunday of that week, type `7 d', and then
do `M-x print-diary-entries'. As usual, the inclusion of the holidays
slows down the display slightly; you can speed things up by setting the
variable `holidays-in-diary-buffer' to `nil'.
Ordinarily, the fancy diary buffer does not show days for which
there are no diary entries, even if that day is a holiday. If you want
such days to be shown in the fancy diary buffer, set the variable
`diary-list-include-blanks' to `t'.
If you use the fancy diary display, you can use the normal hook
`list-diary-entries-hook' to sort each day's diary entries by their
time of day. Here's how:
(add-hook 'list-diary-entries-hook 'sort-diary-entries t)
For each day, this sorts diary entries that begin with a recognizable
time of day according to their times. Diary entries without times come
first within each day.
Fancy diary display also has the ability to process included diary
files. This permits a group of people to share a diary file for events
that apply to all of them. Lines in the diary file of this form:
#include "FILENAME"
includes the diary entries from the file FILENAME in the fancy diary
buffer. The include mechanism is recursive, so that included files can
include other files, and so on; you must be careful not to have a cycle
of inclusions, of course. Here is how to enable the include facility:
(add-hook 'list-diary-entries-hook 'include-other-diary-files)
(add-hook 'mark-diary-entries-hook 'mark-included-diary-files)
The include mechanism works only with the fancy diary display,
because ordinary diary display shows the entries directly from your
diary file.
Sexp Entries and the Fancy Diary Display
========================================
Sexp diary entries allow you to do more than just have complicated
conditions under which a diary entry applies. If you use the fancy
diary display, sexp entries can generate the text of the entry depending
on the date itself. For example, an anniversary diary entry can insert
the number of years since the anniversary date into the text of the
diary entry. Thus the `%d' in this dairy entry:
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
gets replaced by the age, so on October 31, 1990 the entry appears in
the fancy diary buffer like this:
Arthur's birthday (42 years old)
If the diary file instead contains this entry:
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
the entry in the fancy diary buffer for October 31, 1990 appears like
this:
Arthur's 42nd birthday
Similarly, cyclic diary entries can interpolate the number of
repetitions that have occurred:
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
looks like this:
Renew medication (5th time)
in the fancy diary display on September 8, 1990.
There is an early reminder diary sexp that includes its entry in the
diary not only on the date of occurrence, but also on earlier dates.
For example, if you want a reminder a week before your anniversary, you
can use
%%(diary-remind '(diary-anniversary 12 22 1968) 7) Ed's anniversary
and the fancy diary will show
Ed's anniversary
both on December 15 and on December 22.
The function `diary-date' applies to dates described by a month,
day, year combination, each of which can be an integer, a list of
integers, or `t'. The value `t' means all values. For example,
%%(diary-date '(10 11 12) 22 t) Rake leaves
causes the fancy diary to show
Rake leaves
on October 22, November 22, and December 22 of every year.
The function `diary-float' allows you to describe diary entries that
apply to dates like the third Friday of November, or the last Tuesday
in April. The parameters are the MONTH, DAYNAME, and an index N. The
entry appears on the Nth DAYNAME of MONTH, where DAYNAME=0 means
Sunday, 1 means Monday, and so on. If N is negative it counts backward
from the end of MONTH. The value of MONTH can be a list of months, a
single month, or `t' to specify all months. You can also use an
optional parameter DAY to specify the Nth DAYNAME of MONTH on or
after/before DAY; the value of DAY defaults to 1 if N is positive and
to the last day of MONTH if N is negative. For example,
%%(diary-float t 1 -1) Pay rent
causes the fancy diary to show
Pay rent
on the last Monday of every month.
The generality of sexp diary entries lets you specify any diary entry
that you can describe algorithmically. A sexp diary entry contains an
expression that computes whether the entry applies to any given date.
If its value is non-`nil', the entry applies to that date; otherwise,
it does not. The expression can use the variable `date' to find the
date being considered; its value is a list (MONTH DAY YEAR) that refers
to the Gregorian calendar.
Suppose you get paid on the 21st of the month if it is a weekday, and
on the Friday before if the 21st is on a weekend. Here is how to write
a sexp diary entry that matches those dates:
&%%(let ((dayname (calendar-day-of-week date))
(day (car (cdr date))))
(or (and (= day 21) (memq dayname '(1 2 3 4 5)))
(and (memq day '(19 20)) (= dayname 5)))
) Pay check deposited
The following sexp diary entries take advantage of the ability (in
the fancy diary display) to concoct diary entries whose text varies
based on the date:
`%%(diary-sunrise-sunset)'
Make a diary entry for the local times of today's sunrise and
sunset.
`%%(diary-phases-of-moon)'
Make a diary entry for the phases (quarters) of the moon.
`%%(diary-day-of-year)'
Make a diary entry with today's day number in the current year and
the number of days remaining in the current year.
`%%(diary-iso-date)'
Make a diary entry with today's equivalent ISO commercial date.
`%%(diary-julian-date)'
Make a diary entry with today's equivalent date on the Julian
calendar.
`%%(diary-astro-day-number)'
Make a diary entry with today's equivalent astronomical (Julian)
day number.
`%%(diary-hebrew-date)'
Make a diary entry with today's equivalent date on the Hebrew
calendar.
`%%(diary-islamic-date)'
Make a diary entry with today's equivalent date on the Islamic
calendar.
`%%(diary-french-date)'
Make a diary entry with today's equivalent date on the French
Revolutionary calendar.
`%%(diary-mayan-date)'
Make a diary entry with today's equivalent date on the Mayan
calendar.
Thus including the diary entry
&%%(diary-hebrew-date)
causes every day's diary display to contain the equivalent date on the
Hebrew calendar, if you are using the fancy diary display. (With simple
diary display, the line `&%%(diary-hebrew-date)' appears in the diary
for any date, but does nothing particularly useful.)
These functions can be used to construct sexp diary entries based on
the Hebrew calendar in certain standard ways:
`%%(diary-rosh-hodesh)'
Make a diary entry that tells the occurrence and ritual
announcement of each new Hebrew month.
`%%(diary-parasha)'
Make a Saturday diary entry that tells the weekly synagogue
scripture reading.
`%%(diary-sabbath-candles)'
Make a Friday diary entry that tells the _local time_ of Sabbath
candle lighting.
`%%(diary-omer)'
Make a diary entry that gives the omer count, when appropriate.
`%%(diary-yahrzeit MONTH DAY YEAR) NAME'
Make a diary entry marking the anniversary of a date of death.
The date is the _Gregorian_ (civil) date of death. The diary
entry appears on the proper Hebrew calendar anniversary and on the
day before. (In the European style, the order of the parameters
is changed to DAY, MONTH, YEAR.)
Customizing Appointment Reminders
=================================
You can specify exactly how Emacs reminds you of an appointment, and
how far in advance it begins doing so, by setting these variables:
`appt-message-warning-time'
The time in minutes before an appointment that the reminder
begins. The default is 10 minutes.
`appt-audible'
If this is non-`nil', Emacs rings the terminal bell for
appointment reminders. The default is `t'.
`appt-visible'
If this is non-`nil', Emacs displays the appointment message in
the echo area. The default is `t'.
`appt-display-mode-line'
If this is non-`nil', Emacs displays the number of minutes to the
appointment on the mode line. The default is `t'.
`appt-msg-window'
If this is non-`nil', Emacs displays the appointment message in
another window. The default is `t'.
`appt-disp-window-function'
This variable holds a function to use to create the other window
for the appointment message.
`appt-delete-window-function'
This variable holds a function to use to get rid of the appointment
message window, when its time is up.
`appt-display-duration'
The number of seconds to display an appointment message. The
default is 5 seconds.
Operating System Interface
**************************
This chapter is about starting and getting out of Emacs, access to
values in the operating system environment, and terminal input, output,
and flow control.
*Note Building Emacs::, for related information. See also *Note
Display::, for additional operating system status information
pertaining to the terminal and the screen.
Starting Up Emacs
=================
This section describes what Emacs does when it is started, and how
you can customize these actions.
Summary: Sequence of Actions at Startup
---------------------------------------
The order of operations performed (in `startup.el') by Emacs when it
is started up is as follows:
1. It adds subdirectories to `load-path', by running the file named
`subdirs.el' in each directory in the list. Normally this file
adds the directory's subdirectories to the list, and these will be
scanned in their turn. The files `subdirs.el' are normally
generated automatically by Emacs installation.
2. It sets the language environment and the terminal coding system,
if requested by environment variables such as `LANG'.
3. It loads the initialization library for the window system, if you
are using a window system. This library's name is
`term/WINDOWSYSTEM-win.el'.
4. It processes the initial options. (Some of them are handled even
earlier than this.)
5. It initializes the window frame and faces, if appropriate.
6. It runs the normal hook `before-init-hook'.
7. It loads the library `site-start', unless the option
`-no-site-file' was specified. The library's file name is usually
`site-start.el'.
8. It loads your init file (usually `~/.emacs'), unless `-q',
`-no-init-file', or `-batch' was specified on the command line.
The `-u' option can specify another user whose home directory
should be used instead of `~'.
9. It loads the library `default', unless `inhibit-default-init' is
non-`nil'. (This is not done in `-batch' mode or if `-q' was
specified on the command line.) The library's file name is
usually `default.el'.
10. It runs the normal hook `after-init-hook'.
11. It sets the major mode according to `initial-major-mode', provided
the buffer `*scratch*' is still current and still in Fundamental
mode.
12. It loads the terminal-specific Lisp file, if any, except when in
batch mode or using a window system.
13. It displays the initial echo area message, unless you have
suppressed that with `inhibit-startup-echo-area-message'.
14. It processes the action arguments from the command line.
15. It runs `emacs-startup-hook' and then `term-setup-hook'.
16. It calls `frame-notice-user-settings', which modifies the
parameters of the selected frame according to whatever the init
files specify.
17. It runs `window-setup-hook'. *Note Window Systems::.
18. It displays copyleft, nonwarranty, and basic use information,
provided there were no remaining command-line arguments (a few
steps above), the value of `inhibit-startup-message' is `nil', and
the buffer is still empty.
- User Option: inhibit-startup-message
This variable inhibits the initial startup messages (the
nonwarranty, etc.). If it is non-`nil', then the messages are not
printed.
This variable exists so you can set it in your personal init file,
once you are familiar with the contents of the startup message.
Do not set this variable in the init file of a new user, or in a
way that affects more than one user, because that would prevent
new users from receiving the information they are supposed to see.
- User Option: inhibit-startup-echo-area-message
This variable controls the display of the startup echo area
message. You can suppress the startup echo area message by adding
text with this form to your init file:
(setq inhibit-startup-echo-area-message
"YOUR-LOGIN-NAME")
Emacs explicitly checks for an expression as shown above in your
init file; your login name must appear in the expression as a Lisp
string constant. Other methods of setting
`inhibit-startup-echo-area-message' to the same value do not
inhibit the startup message.
This way, you can easily inhibit the message for yourself if you
wish, but thoughtless copying of your init file will not inhibit
the message for someone else.
The Init File, `.emacs'
-----------------------
When you start Emacs, it normally attempts to load your "init file",
a file in your home directory. Its normal name is `.emacs', but you
can alternatively call it `.emacs.el', which enables you to
byte-compile it (*note Byte Compilation::); then the actual file loaded
will be `.emacs.elc'.
The command-line switches `-q' and `-u' control whether and where to
find the init file; `-q' says not to load an init file, and `-u USER'
says to load USER's init file instead of yours. *Note Entering Emacs:
(emacs)Entering Emacs. If neither option is specified, Emacs uses the
`LOGNAME' environment variable, or the `USER' (most systems) or
`USERNAME' (MS systems) variable, to find your home directory and thus
your init file; this way, even if you have su'd, Emacs still loads your
own init file. If those environment variables are absent, though,
Emacs uses your user-id to find your home directory.
A site may have a "default init file", which is the library named
`default.el'. Emacs finds the `default.el' file through the standard
search path for libraries (*note How Programs Do Loading::). The Emacs
distribution does not come with this file; sites may provide one for
local customizations. If the default init file exists, it is loaded
whenever you start Emacs, except in batch mode or if `-q' is specified.
But your own personal init file, if any, is loaded first; if it sets
`inhibit-default-init' to a non-`nil' value, then Emacs does not
subsequently load the `default.el' file.
Another file for site-customization is `site-start.el'. Emacs loads
this _before_ the user's init file. You can inhibit the loading of
this file with the option `-no-site-file'.
- Variable: site-run-file
This variable specifies the site-customization file to load before
the user's init file. Its normal value is `"site-start"'. The
only way you can change it with real effect is to do so before
dumping Emacs.
*Note Init File Examples: (emacs)Init File Examples, for examples of
how to make various commonly desired customizations in your `.emacs'
file.
- User Option: inhibit-default-init
This variable prevents Emacs from loading the default
initialization library file for your session of Emacs. If its
value is non-`nil', then the default library is not loaded. The
default value is `nil'.
- Variable: before-init-hook
This normal hook is run, once, just before loading all the init
files (the user's init file, `default.el', and/or `site-start.el').
(The only way to change it with real effect is before dumping
Emacs.)
- Variable: after-init-hook
This normal hook is run, once, just after loading all the init
files (the user's init file, `default.el', and/or `site-start.el'),
before loading the terminal-specific library and processing the
command-line arguments.
- Variable: emacs-startup-hook
This normal hook is run, once, just after handling the command line
arguments, just before `term-setup-hook'.
- Variable: user-init-file
This variable holds the file name of the user's init file. If the
actual init file loaded is a compiled file, such as `.emacs.elc',
the value refers to the corresponding source file.
Terminal-Specific Initialization
--------------------------------
Each terminal type can have its own Lisp library that Emacs loads
when run on that type of terminal. The library's name is constructed by
concatenating the value of the variable `term-file-prefix' and the
terminal type (specified by the environment variable `TERM').
Normally, `term-file-prefix' has the value `"term/"'; changing this is
not recommended. Emacs finds the file in the normal manner, by
searching the `load-path' directories, and trying the `.elc' and `.el'
suffixes.
The usual function of a terminal-specific library is to enable
special keys to send sequences that Emacs can recognize. It may also
need to set or add to `function-key-map' if the Termcap entry does not
specify all the terminal's function keys. *Note Terminal Input::.
When the name of the terminal type contains a hyphen, only the part
of the name before the first hyphen is significant in choosing the
library name. Thus, terminal types `aaa-48' and `aaa-30-rv' both use
the `term/aaa' library. If necessary, the library can evaluate
`(getenv "TERM")' to find the full name of the terminal type.
Your init file can prevent the loading of the terminal-specific
library by setting the variable `term-file-prefix' to `nil'. This
feature is useful when experimenting with your own peculiar
customizations.
You can also arrange to override some of the actions of the
terminal-specific library by setting the variable `term-setup-hook'.
This is a normal hook which Emacs runs using `run-hooks' at the end of
Emacs initialization, after loading both your init file and any
terminal-specific libraries. You can use this variable to define
initializations for terminals that do not have their own libraries.
*Note Hooks::.
- Variable: term-file-prefix
If the `term-file-prefix' variable is non-`nil', Emacs loads a
terminal-specific initialization file as follows:
(load (concat term-file-prefix (getenv "TERM")))
You may set the `term-file-prefix' variable to `nil' in your init
file if you do not wish to load the terminal-initialization file.
To do this, put the following in your init file: `(setq
term-file-prefix nil)'.
On MS-DOS, if the environment variable `TERM' is not set, Emacs
uses `internal' as the terminal type.
- Variable: term-setup-hook
This variable is a normal hook that Emacs runs after loading your
init file, the default initialization file (if any) and the
terminal-specific Lisp file.
You can use `term-setup-hook' to override the definitions made by a
terminal-specific file.
See `window-setup-hook' in *Note Window Systems::, for a related
feature.
Command-Line Arguments
----------------------
You can use command-line arguments to request various actions when
you start Emacs. Since you do not need to start Emacs more than once
per day, and will often leave your Emacs session running longer than
that, command-line arguments are hardly ever used. As a practical
matter, it is best to avoid making the habit of using them, since this
habit would encourage you to kill and restart Emacs unnecessarily
often. These options exist for two reasons: to be compatible with
other editors (for invocation by other programs) and to enable shell
scripts to run specific Lisp programs.
This section describes how Emacs processes command-line arguments,
and how you can customize them.
- Function: command-line
This function parses the command line that Emacs was called with,
processes it, loads the user's init file and displays the startup
messages.
- Variable: command-line-processed
The value of this variable is `t' once the command line has been
processed.
If you redump Emacs by calling `dump-emacs', you may wish to set
this variable to `nil' first in order to cause the new dumped Emacs
to process its new command-line arguments.
- Variable: command-switch-alist
The value of this variable is an alist of user-defined command-line
options and associated handler functions. This variable exists so
you can add elements to it.
A "command-line option" is an argument on the command line, which
has the form:
-OPTION
The elements of the `command-switch-alist' look like this:
(OPTION . HANDLER-FUNCTION)
The CAR, OPTION, is a string, the name of a command-line option
(not including the initial hyphen). The HANDLER-FUNCTION is
called to handle OPTION, and receives the option name as its sole
argument.
In some cases, the option is followed in the command line by an
argument. In these cases, the HANDLER-FUNCTION can find all the
remaining command-line arguments in the variable
`command-line-args-left'. (The entire list of command-line
arguments is in `command-line-args'.)
The command-line arguments are parsed by the `command-line-1'
function in the `startup.el' file. See also *Note Command Line
Switches and Arguments: (emacs)Command Switches.
- Variable: command-line-args
The value of this variable is the list of command-line arguments
passed to Emacs.
- Variable: command-line-functions
This variable's value is a list of functions for handling an
unrecognized command-line argument. Each time the next argument
to be processed has no special meaning, the functions in this list
are called, in order of appearance, until one of them returns a
non-`nil' value.
These functions are called with no arguments. They can access the
command-line argument under consideration through the variable
`argi', which is bound temporarily at this point. The remaining
arguments (not including the current one) are in the variable
`command-line-args-left'.
When a function recognizes and processes the argument in `argi', it
should return a non-`nil' value to say it has dealt with that
argument. If it has also dealt with some of the following
arguments, it can indicate that by deleting them from
`command-line-args-left'.
If all of these functions return `nil', then the argument is used
as a file name to visit.
Getting Out of Emacs
====================
There are two ways to get out of Emacs: you can kill the Emacs job,
which exits permanently, or you can suspend it, which permits you to
reenter the Emacs process later. As a practical matter, you seldom kill
Emacs--only when you are about to log out. Suspending is much more
common.
Killing Emacs
-------------
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control. The low-level primitive for
killing Emacs is `kill-emacs'.
- Function: kill-emacs &optional exit-data
This function exits the Emacs process and kills it.
If EXIT-DATA is an integer, then it is used as the exit status of
the Emacs process. (This is useful primarily in batch operation;
see *Note Batch Mode::.)
If EXIT-DATA is a string, its contents are stuffed into the
terminal input buffer so that the shell (or whatever program next
reads input) can read them.
All the information in the Emacs process, aside from files that have
been saved, is lost when the Emacs process is killed. Because killing
Emacs inadvertently can lose a lot of work, Emacs queries for
confirmation before actually terminating if you have buffers that need
saving or subprocesses that are running. This is done in the function
`save-buffers-kill-emacs'.
- Variable: kill-emacs-query-functions
After asking the standard questions, `save-buffers-kill-emacs'
calls the functions in the list `kill-emacs-query-functions', in
order of appearance, with no arguments. These functions can ask
for additional confirmation from the user. If any of them returns
`nil', Emacs is not killed.
- Variable: kill-emacs-hook
This variable is a normal hook; once `save-buffers-kill-emacs' is
finished with all file saving and confirmation, it runs the
functions in this hook.
Suspending Emacs
----------------
"Suspending Emacs" means stopping Emacs temporarily and returning
control to its superior process, which is usually the shell. This
allows you to resume editing later in the same Emacs process, with the
same buffers, the same kill ring, the same undo history, and so on. To
resume Emacs, use the appropriate command in the parent shell--most
likely `fg'.
Some operating systems do not support suspension of jobs; on these
systems, "suspension" actually creates a new shell temporarily as a
subprocess of Emacs. Then you would exit the shell to return to Emacs.
Suspension is not useful with window systems, because the Emacs job
may not have a parent that can resume it again, and in any case you can
give input to some other job such as a shell merely by moving to a
different window. Therefore, suspending is not allowed when Emacs is
using a window system (X or MS Windows).
- Function: suspend-emacs string
This function stops Emacs and returns control to the superior
process. If and when the superior process resumes Emacs,
`suspend-emacs' returns `nil' to its caller in Lisp.
If STRING is non-`nil', its characters are sent to be read as
terminal input by Emacs's superior shell. The characters in
STRING are not echoed by the superior shell; only the results
appear.
Before suspending, `suspend-emacs' runs the normal hook
`suspend-hook'.
After the user resumes Emacs, `suspend-emacs' runs the normal hook
`suspend-resume-hook'. *Note Hooks::.
The next redisplay after resumption will redraw the entire screen,
unless the variable `no-redraw-on-reenter' is non-`nil' (*note
Refresh Screen::).
In the following example, note that `pwd' is not echoed after
Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs)
=> nil
(add-hook 'suspend-hook
(function (lambda ()
(or (y-or-n-p
"Really suspend? ")
(error "Suspend cancelled")))))
=> (lambda nil
(or (y-or-n-p "Really suspend? ")
(error "Suspend cancelled")))
(add-hook 'suspend-resume-hook
(function (lambda () (message "Resumed!"))))
=> (lambda nil (message "Resumed!"))
(suspend-emacs "pwd")
=> nil
---------- Buffer: Minibuffer ----------
Really suspend? y
---------- Buffer: Minibuffer ----------
---------- Parent Shell ----------
lewis@slug[23] % /user/lewis/manual
lewis@slug[24] % fg
---------- Echo Area ----------
Resumed!
- Variable: suspend-hook
This variable is a normal hook that Emacs runs before suspending.
- Variable: suspend-resume-hook
This variable is a normal hook that Emacs runs on resuming after a
suspension.
Operating System Environment
============================
Emacs provides access to variables in the operating system
environment through various functions. These variables include the
name of the system, the user's UID, and so on.
- Variable: system-configuration
This variable holds the GNU configuration name for the
hardware/software configuration of your system, as a string. The
convenient way to test parts of this string is with `string-match'.
- Variable: system-type
The value of this variable is a symbol indicating the type of
operating system Emacs is operating on. Here is a table of the
possible values:
`alpha-vms'
VMS on the Alpha.
`aix-v3'
AIX.
`berkeley-unix'
Berkeley BSD.
`dgux'
Data General DGUX operating system.
`gnu'
the GNU system (using the GNU kernel, which consists of the
HURD and Mach).
`gnu/linux'
A GNU/Linux system--that is, a variant GNU system, using the
Linux kernel. (These systems are the ones people often call
"Linux," but actually Linux is just the kernel, not the whole
system.)
`hpux'
Hewlett-Packard HPUX operating system.
`irix'
Silicon Graphics Irix system.
`ms-dos'
Microsoft MS-DOS "operating system." Emacs compiled with
DJGPP for MS-DOS binds `system-type' to `ms-dos' even when
you run it on MS-Windows.
`next-mach'
NeXT Mach-based system.
`rtu'
Masscomp RTU, UCB universe.
`unisoft-unix'
UniSoft UniPlus.
`usg-unix-v'
AT&T System V.
`vax-vms'
VAX VMS.
`windows-nt'
Microsoft windows NT. The same executable supports Windows
9X, but the value of `system-type' is `windows-nt' in either
case.
`xenix'
SCO Xenix 386.
We do not wish to add new symbols to make finer distinctions
unless it is absolutely necessary! In fact, we hope to eliminate
some of these alternatives in the future. We recommend using
`system-configuration' to distinguish between different operating
systems.
- Function: system-name
This function returns the name of the machine you are running on.
(system-name)
=> "www.gnu.org"
The symbol `system-name' is a variable as well as a function. In
fact, the function returns whatever value the variable `system-name'
currently holds. Thus, you can set the variable `system-name' in case
Emacs is confused about the name of your system. The variable is also
useful for constructing frame titles (*note Frame Titles::).
- Variable: mail-host-address
If this variable is non-`nil', it is used instead of `system-name'
for purposes of generating email addresses. For example, it is
used when constructing the default value of `user-mail-address'.
*Note User Identification::. (Since this is done when Emacs
starts up, the value actually used is the one saved when Emacs was
dumped. *Note Building Emacs::.)
- Command: getenv var
This function returns the value of the environment variable VAR,
as a string. Within Emacs, the environment variable values are
kept in the Lisp variable `process-environment'.
(getenv "USER")
=> "lewis"
lewis@slug[10] % printenv
PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
USER=lewis
TERM=ibmapa16
SHELL=/bin/csh
HOME=/user/lewis
- Command: setenv variable value
This command sets the value of the environment variable named
VARIABLE to VALUE. Both arguments should be strings. This
function works by modifying `process-environment'; binding that
variable with `let' is also reasonable practice.
- Variable: process-environment
This variable is a list of strings, each describing one environment
variable. The functions `getenv' and `setenv' work by means of
this variable.
process-environment
=> ("l=/usr/stanford/lib/gnuemacs/lisp"
"PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
"USER=lewis"
"TERM=ibmapa16"
"SHELL=/bin/csh"
"HOME=/user/lewis")
- Variable: path-separator
This variable holds a string which says which character separates
directories in a search path (as found in an environment
variable). Its value is `":"' for Unix and GNU systems, and `";"'
for MS-DOS and MS-Windows.
- Function: parse-colon-path path
This function takes a search path string such as would be the
value of the `PATH' environment variable, and splits it at the
separators, returning a list of directory names. `nil' in this
list stands for "use the current directory." Although the
function's name says "colon," it actually uses the value of
`path-separator'.
(parse-colon-path ":/foo:/bar")
=> (nil "/foo/" "/bar/")
- Variable: invocation-name
This variable holds the program name under which Emacs was
invoked. The value is a string, and does not include a directory
name.
- Variable: invocation-directory
This variable holds the directory from which the Emacs executable
was invoked, or perhaps `nil' if that directory cannot be
determined.
- Variable: installation-directory
If non-`nil', this is a directory within which to look for the
`lib-src' and `etc' subdirectories. This is non-`nil' when Emacs
can't find those directories in their standard installed
locations, but can find them in a directory related somehow to the
one containing the Emacs executable.
- Function: load-average &optional use-float
This function returns the current 1-minute, 5-minute, and
15-minute load averages, in a list.
By default, the values are integers that are 100 times the system
load averages, which indicate the average number of processes
trying to run. If USE-FLOAT is non-`nil', then they are returned
as floating point numbers and without multiplying by 100.
(load-average)
=> (169 48 36)
(load-average t)
=> (1.69 0.48 0.36)
lewis@rocky[5] % uptime
11:55am up 1 day, 19:37, 3 users,
load average: 1.69, 0.48, 0.36
- Function: emacs-pid
This function returns the process ID of the Emacs process.
- Variable: tty-erase-char
This variable holds the erase character that was selected in the
system's terminal driver, before Emacs was started.
- Function: setprv privilege-name &optional setp getprv
This function sets or resets a VMS privilege. (It does not exist
on other systems.) The first argument is the privilege name, as a
string. The second argument, SETP, is `t' or `nil', indicating
whether the privilege is to be turned on or off. Its default is
`nil'. The function returns `t' if successful, `nil' otherwise.
If the third argument, GETPRV, is non-`nil', `setprv' does not
change the privilege, but returns `t' or `nil' indicating whether
the privilege is currently enabled.
User Identification
===================
- Variable: init-file-user
This variable says which user's init files should be used by
Emacs--or `nil' if none. The value reflects command-line options
such as `-q' or `-u USER'.
Lisp packages that load files of customizations, or any other sort
of user profile, should obey this variable in deciding where to
find it. They should load the profile of the user name found in
this variable. If `init-file-user' is `nil', meaning that the `-q'
option was used, then Lisp packages should not load any
customization files or user profile.
- Variable: user-mail-address
This holds the nominal email address of the user who is using
Emacs. Emacs normally sets this variable to a default value after
reading your init files, but not if you have already set it. So
you can set the variable to some other value in your init file if
you do not want to use the default value.
- Function: user-login-name &optional uid
If you don't specify UID, this function returns the name under
which the user is logged in. If the environment variable `LOGNAME'
is set, that value is used. Otherwise, if the environment variable
`USER' is set, that value is used. Otherwise, the value is based
on the effective UID, not the real UID.
If you specify UID, the value is the user name that corresponds to
UID (which should be an integer).
(user-login-name)
=> "lewis"
- Function: user-real-login-name
This function returns the user name corresponding to Emacs's real
UID. This ignores the effective UID and ignores the environment
variables `LOGNAME' and `USER'.
- Function: user-full-name &optional uid
This function returns the full name of the logged-in user--or the
value of the environment variable `NAME', if that is set.
(user-full-name)
=> "Bil Lewis"
If the Emacs job's user-id does not correspond to any known user
(and provided `NAME' is not set), the value is `"unknown"'.
If UID is non-`nil', then it should be an integer (a user-id) or a
string (a login name). Then `user-full-name' returns the full
name corresponding to that user-id or login name. If you specify a
user-id or login name that isn't defined, it returns `nil'.
The symbols `user-login-name', `user-real-login-name' and
`user-full-name' are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to "fake out" Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (*note Frame
Titles::).
- Function: user-real-uid
This function returns the real UID of the user.
(user-real-uid)
=> 19
- Function: user-uid
This function returns the effective UID of the user.
Time of Day
===========
This section explains how to determine the current time and the time
zone.
- Function: current-time-string &optional time-value
This function returns the current time and date as a human-readable
string. The format of the string is unvarying; the number of
characters used for each part is always the same, so you can
reliably use `substring' to extract pieces of it. It is wise to
count the characters from the beginning of the string rather than
from the end, as additional information may some day be added at
the end.
The argument TIME-VALUE, if given, specifies a time to format
instead of the current time. The argument should be a list whose
first two elements are integers. Thus, you can use times obtained
from `current-time' (see below) and from `file-attributes' (*note
File Attributes::).
(current-time-string)
=> "Wed Oct 14 22:21:05 1987"
- Function: current-time
This function returns the system's time value as a list of three
integers: `(HIGH LOW MICROSEC)'. The integers HIGH and LOW
combine to give the number of seconds since 0:00 January 1, 1970
(local time), which is HIGH * 2**16 + LOW.
The third element, MICROSEC, gives the microseconds since the
start of the current second (or 0 for systems that return time with
the resolution of only one second).
The first two elements can be compared with file time values such
as you get with the function `file-attributes'. *Note File
Attributes::.
- Function: current-time-zone &optional time-value
This function returns a list describing the time zone that the
user is in.
The value has the form `(OFFSET NAME)'. Here OFFSET is an integer
giving the number of seconds ahead of UTC (east of Greenwich). A
negative value means west of Greenwich. The second element, NAME,
is a string giving the name of the time zone. Both elements
change when daylight savings time begins or ends; if the user has
specified a time zone that does not use a seasonal time
adjustment, then the value is constant through time.
If the operating system doesn't supply all the information
necessary to compute the value, both elements of the list are
`nil'.
The argument TIME-VALUE, if given, specifies a time to analyze
instead of the current time. The argument should be a cons cell
containing two integers, or a list whose first two elements are
integers. Thus, you can use times obtained from `current-time'
(see above) and from `file-attributes' (*note File Attributes::).
- Function: float-time &optional time-value
This function returns the current time as a floating-point number
of seconds since the epoch. The argument TIME-VALUE, if given,
specifies a time to convert instead of the current time. The
argument should have the same form as for `current-time-string'
(see above), and it also accepts the output of `current-time' and
`file-attributes'.
_Warning_: Since the result is floating point, it may not be
exact. Do not use this function if precise time stamps are
required.
Time Conversion
===============
These functions convert time values (lists of two or three integers)
to strings or to calendrical information. There is also a function to
convert calendrical information to a time value. You can get time
values from the functions `current-time' (*note Time of Day::) and
`file-attributes' (*note File Attributes::).
Many operating systems are limited to time values that contain 32
bits of information; these systems typically handle only the times from
1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some
operating systems have larger time values, and can represent times far
in the past or future.
Time conversion functions always use the Gregorian calendar, even for
dates before the Gregorian calendar was introduced. Year numbers count
the number of years since the year 1 B.C., and do not skip zero as
traditional Gregorian years do; for example, the year number -37
represents the Gregorian year 38 B.C.
- Function: format-time-string format-string &optional time universal
This function converts TIME (or the current time, if TIME is
omitted) to a string according to FORMAT-STRING. The argument
FORMAT-STRING may contain `%'-sequences which say to substitute
parts of the time. Here is a table of what the `%'-sequences mean:
`%a'
This stands for the abbreviated name of the day of week.
`%A'
This stands for the full name of the day of week.
`%b'
This stands for the abbreviated name of the month.
`%B'
This stands for the full name of the month.
`%c'
This is a synonym for `%x %X'.
`%C'
This has a locale-specific meaning. In the default locale
(named C), it is equivalent to `%A, %B %e, %Y'.
`%d'
This stands for the day of month, zero-padded.
`%D'
This is a synonym for `%m/%d/%y'.
`%e'
This stands for the day of month, blank-padded.
`%h'
This is a synonym for `%b'.
`%H'
This stands for the hour (00-23).
`%I'
This stands for the hour (01-12).
`%j'
This stands for the day of the year (001-366).
`%k'
This stands for the hour (0-23), blank padded.
`%l'
This stands for the hour (1-12), blank padded.
`%m'
This stands for the month (01-12).
`%M'
This stands for the minute (00-59).
`%n'
This stands for a newline.
`%p'
This stands for `AM' or `PM', as appropriate.
`%r'
This is a synonym for `%I:%M:%S %p'.
`%R'
This is a synonym for `%H:%M'.
`%S'
This stands for the seconds (00-59).
`%t'
This stands for a tab character.
`%T'
This is a synonym for `%H:%M:%S'.
`%U'
This stands for the week of the year (01-52), assuming that
weeks start on Sunday.
`%w'
This stands for the numeric day of week (0-6). Sunday is day
0.
`%W'
This stands for the week of the year (01-52), assuming that
weeks start on Monday.
`%x'
This has a locale-specific meaning. In the default locale
(named `C'), it is equivalent to `%D'.
`%X'
This has a locale-specific meaning. In the default locale
(named `C'), it is equivalent to `%T'.
`%y'
This stands for the year without century (00-99).
`%Y'
This stands for the year with century.
`%Z'
This stands for the time zone abbreviation.
You can also specify the field width and type of padding for any of
these `%'-sequences. This works as in `printf': you write the
field width as digits in the middle of a `%'-sequences. If you
start the field width with `0', it means to pad with zeros. If you
start the field width with `_', it means to pad with spaces.
For example, `%S' specifies the number of seconds since the minute;
`%03S' means to pad this with zeros to 3 positions, `%_3S' to pad
with spaces to 3 positions. Plain `%3S' pads with zeros, because
that is how `%S' normally pads to two positions.
The characters `E' and `O' act as modifiers when used between `%'
and one of the letters in the table above. `E' specifies using
the current locale's "alternative" version of the date and time.
In a Japanese locale, for example, `%Ex' might yield a date format
based on the Japanese Emperors' reigns. `E' is allowed in `%Ec',
`%EC', `%Ex', `%EX', `%Ey', and `%EY'.
`O' means to use the current locale's "alternative" representation
of numbers, instead of the ordinary decimal digits. This is
allowed with most letters, all the ones that output numbers.
If UNIVERSAL is non-`nil', that means to describe the time as
Universal Time; `nil' means describe it using what Emacs believes
is the local time zone (see `current-time-zone').
This function uses the C library function `strftime' to do most of
the work. In order to communicate with that function, it first
encodes its argument using the coding system specified by
`locale-coding-system' (*note Locales::); after `strftime' returns
the resulting string, `format-time-string' decodes the string
using that same coding system.
- Function: decode-time time
This function converts a time value into calendrical information.
The return value is a list of nine elements, as follows:
(SECONDS MINUTES HOUR DAY MONTH YEAR DOW DST ZONE)
Here is what the elements mean:
SECONDS
The number of seconds past the minute, as an integer between
0 and 59.
MINUTES
The number of minutes past the hour, as an integer between 0
and 59.
HOUR
The hour of the day, as an integer between 0 and 23.
DAY
The day of the month, as an integer between 1 and 31.
MONTH
The month of the year, as an integer between 1 and 12.
YEAR
The year, an integer typically greater than 1900.
DOW
The day of week, as an integer between 0 and 6, where 0
stands for Sunday.
DST
`t' if daylight savings time is effect, otherwise `nil'.
ZONE
An integer indicating the time zone, as the number of seconds
east of Greenwich.
*Common Lisp Note:* Common Lisp has different meanings for DOW and
ZONE.
- Function: encode-time seconds minutes hour day month year &optional
zone
This function is the inverse of `decode-time'. It converts seven
items of calendrical data into a time value. For the meanings of
the arguments, see the table above under `decode-time'.
Year numbers less than 100 are not treated specially. If you want
them to stand for years above 1900, or years above 2000, you must
alter them yourself before you call `encode-time'.
The optional argument ZONE defaults to the current time zone and
its daylight savings time rules. If specified, it can be either a
list (as you would get from `current-time-zone'), a string as in
the `TZ' environment variable, or an integer (as you would get from
`decode-time'). The specified zone is used without any further
alteration for daylight savings time.
If you pass more than seven arguments to `encode-time', the first
six are used as SECONDS through YEAR, the last argument is used as
ZONE, and the arguments in between are ignored. This feature
makes it possible to use the elements of a list returned by
`decode-time' as the arguments to `encode-time', like this:
(apply 'encode-time (decode-time ...))
You can perform simple date arithmetic by using out-of-range
values for the SECONDS, MINUTES, HOUR, DAY, and MONTH arguments;
for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time
values; if you try to encode a time that is out of range, an error
results.
Timers for Delayed Execution
============================
You can set up a "timer" to call a function at a specified future
time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
`sit-for' or `read-event' which _can_ wait. Therefore, a timer's
execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
- Function: run-at-time time repeat function &rest args
This function arranges to call FUNCTION with arguments ARGS at
time TIME. The argument FUNCTION is a function to call later, and
ARGS are the arguments to give it when it is called. The time
TIME is specified as a string.
Absolute times may be specified in a wide variety of formats; this
function tries to accept all the commonly used date formats. Valid
formats include these two,
YEAR-MONTH-DAY HOUR:MIN:SEC TIMEZONE
HOUR:MIN:SEC TIMEZONE MONTH/DAY/YEAR
where in both examples all fields are numbers; the format that
`current-time-string' returns is also allowed, and many others as
well.
To specify a relative time, use numbers followed by units. For
example:
`1 min'
denotes 1 minute from now.
`1 min 5 sec'
denotes 65 seconds from now.
`1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year'
denotes exactly 103 months, 123 days, and 10862 seconds from
now.
For relative time values, Emacs considers a month to be exactly
thirty days, and a year to be exactly 365.25 days.
If TIME is a number (integer or floating point), that specifies a
relative time measured in seconds.
The argument REPEAT specifies how often to repeat the call. If
REPEAT is `nil', there are no repetitions; FUNCTION is called just
once, at TIME. If REPEAT is a number, it specifies a repetition
period measured in seconds.
In most cases, REPEAT has no effect on when _first_ call takes
place--TIME alone specifies that. There is one exception: if TIME
is `t', then the timer runs whenever the time is a multiple of
REPEAT seconds after the epoch. This is useful for functions like
`display-time'.
The function `run-at-time' returns a timer value that identifies
the particular scheduled future action. You can use this value to
call `cancel-timer' (see below).
- Macro: with-timeout (seconds timeout-forms...) body...
Execute BODY, but give up after SECONDS seconds. If BODY finishes
before the time is up, `with-timeout' returns the value of the
last form in BODY. If, however, the execution of BODY is cut
short by the timeout, then `with-timeout' executes all the
TIMEOUT-FORMS and returns the value of the last of them.
This macro works by setting a timer to run after SECONDS seconds.
If BODY finishes before that time, it cancels the timer. If the
timer actually runs, it terminates execution of BODY, then
executes TIMEOUT-FORMS.
Since timers can run within a Lisp program only when the program
calls a primitive that can wait, `with-timeout' cannot stop
executing BODY while it is in the midst of a computation--only
when it calls one of those primitives. So use `with-timeout' only
with a BODY that waits for input, not one that does a long
computation.
The function `y-or-n-p-with-timeout' provides a simple way to use a
timer to avoid waiting too long for an answer. *Note Yes-or-No
Queries::.
- Function: run-with-idle-timer secs repeat function &rest args
Set up a timer which runs when Emacs has been idle for SECS
seconds. The value of SECS may be an integer or a floating point
number.
If REPEAT is `nil', the timer runs just once, the first time Emacs
remains idle for a long enough time. More often REPEAT is
non-`nil', which means to run the timer _each time_ Emacs remains
idle for SECS seconds.
The function `run-with-idle-timer' returns a timer value which you
can use in calling `cancel-timer' (see below).
Emacs becomes "idle" when it starts waiting for user input, and it
remains idle until the user provides some input. If a timer is set for
five seconds of idleness, it runs approximately five seconds after Emacs
first becomes idle. Even if REPEAT is non-`nil', this timer will not
run again as long as Emacs remains idle, because the duration of
idleness will continue to increase and will not go down to five seconds
again.
Emacs can do various things while idle: garbage collect, autosave or
handle data from a subprocess. But these interludes during idleness do
not interfere with idle timers, because they do not reset the clock of
idleness to zero. An idle timer set for 600 seconds will run when ten
minutes have elapsed since the last user command was finished, even if
subprocess output has been accepted thousands of times within those ten
minutes, and even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing
the input. Then it becomes idle again, and all the idle timers that are
set up to repeat will subsequently run another time, one by one.
- Function: cancel-timer timer
Cancel the requested action for TIMER, which should be a value
previously returned by `run-at-time' or `run-with-idle-timer'.
This cancels the effect of that call to `run-at-time'; the arrival
of the specified time will not cause anything special to happen.
Terminal Input
==============
This section describes functions and variables for recording or
manipulating terminal input. See *Note Display::, for related
functions.
Input Modes
-----------
- Function: set-input-mode interrupt flow meta quit-char
This function sets the mode for reading keyboard input. If
INTERRUPT is non-null, then Emacs uses input interrupts. If it is
`nil', then it uses CBREAK mode. The default setting is
system-dependent. Some systems always use CBREAK mode regardless
of what is specified.
When Emacs communicates directly with X, it ignores this argument
and uses interrupts if that is the way it knows how to communicate.
If FLOW is non-`nil', then Emacs uses XON/XOFF (`C-q', `C-s') flow
control for output to the terminal. This has no effect except in
CBREAK mode. *Note Flow Control::.
The argument META controls support for input character codes above
127. If META is `t', Emacs converts characters with the 8th bit
set into Meta characters. If META is `nil', Emacs disregards the
8th bit; this is necessary when the terminal uses it as a parity
bit. If META is neither `t' nor `nil', Emacs uses all 8 bits of
input unchanged. This is good for terminals that use 8-bit
character sets.
If QUIT-CHAR is non-`nil', it specifies the character to use for
quitting. Normally this character is `C-g'. *Note Quitting::.
The `current-input-mode' function returns the input mode settings
Emacs is currently using.
- Function: current-input-mode
This function returns the current mode for reading keyboard input.
It returns a list, corresponding to the arguments of
`set-input-mode', of the form `(INTERRUPT FLOW META QUIT)' in
which:
INTERRUPT
is non-`nil' when Emacs is using interrupt-driven input. If
`nil', Emacs is using CBREAK mode.
FLOW
is non-`nil' if Emacs uses XON/XOFF (`C-q', `C-s') flow
control for output to the terminal. This value is meaningful
only when INTERRUPT is `nil'.
META
is `t' if Emacs treats the eighth bit of input characters as
the meta bit; `nil' means Emacs clears the eighth bit of every
input character; any other value means Emacs uses all eight
bits as the basic character code.
QUIT
is the character Emacs currently uses for quitting, usually
`C-g'.
Translating Input Events
------------------------
This section describes features for translating input events into
other input events before they become part of key sequences. These
features apply to each event in the order they are described here: each
event is first modified according to `extra-keyboard-modifiers', then
translated through `keyboard-translate-table' (if applicable), and
finally decoded with the specified keyboard coding system. If it is
being read as part of a key sequence, it is then added to the sequence
being read; then subsequences containing it are checked first with
`function-key-map' and then with `key-translation-map'.
- Variable: extra-keyboard-modifiers
This variable lets Lisp programs "press" the modifier keys on the
keyboard. The value is a bit mask:
1
The <SHIFT> key.
2
The <LOCK> key.
4
The <CTL> key.
8
The <META> key.
Each time the user types a keyboard key, it is altered as if the
modifier keys specified in the bit mask were held down.
When using a window system, the program can "press" any of the
modifier keys in this way. Otherwise, only the <CTL> and <META>
keys can be virtually pressed.
- Variable: keyboard-translate-table
This variable is the translate table for keyboard characters. It
lets you reshuffle the keys on the keyboard without changing any
command bindings. Its value is normally a char-table, or else
`nil'.
If `keyboard-translate-table' is a char-table (*note
Char-Tables::), then each character read from the keyboard is
looked up in this char-table. If the value found there is
non-`nil', then it is used instead of the actual input character.
In the example below, we set `keyboard-translate-table' to a
char-table. Then we fill it in to swap the characters `C-s' and
`C-\' and the characters `C-q' and `C-^'. Subsequently, typing
`C-\' has all the usual effects of typing `C-s', and vice versa.
(*Note Flow Control::, for more information on this subject.)
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^."
(interactive)
(setq keyboard-translate-table
(make-char-table 'keyboard-translate-table nil))
;; Swap `C-s' and `C-\'.
(aset keyboard-translate-table ?\034 ?\^s)
(aset keyboard-translate-table ?\^s ?\034)
;; Swap `C-q' and `C-^'.
(aset keyboard-translate-table ?\036 ?\^q)
(aset keyboard-translate-table ?\^q ?\036))
Note that this translation is the first thing that happens to a
character after it is read from the terminal. Record-keeping
features such as `recent-keys' and dribble files record the
characters after translation.
- Function: keyboard-translate from to
This function modifies `keyboard-translate-table' to translate
character code FROM into character code TO. It creates the
keyboard translate table if necessary.
The remaining translation features translate subsequences of key
sequences being read. They are implemented in `read-key-sequence' and
have no effect on input read with `read-event'.
- Variable: function-key-map
This variable holds a keymap that describes the character
sequences sent by function keys on an ordinary character terminal.
This keymap has the same structure as other keymaps, but is used
differently: it specifies translations to make while reading key
sequences, rather than bindings for key sequences.
If `function-key-map' "binds" a key sequence K to a vector V, then
when K appears as a subsequence _anywhere_ in a key sequence, it
is replaced with the events in V.
For example, VT100 terminals send `<ESC> O P' when the keypad
<PF1> key is pressed. Therefore, we want Emacs to translate that
sequence of events into the single event `pf1'. We accomplish
this by "binding" `<ESC> O P' to `[pf1]' in `function-key-map',
when using a VT100.
Thus, typing `C-c <PF1>' sends the character sequence `C-c <ESC> O
P'; later the function `read-key-sequence' translates this back
into `C-c <PF1>', which it returns as the vector `[?\C-c pf1]'.
Entries in `function-key-map' are ignored if they conflict with
bindings made in the minor mode, local, or global keymaps. The
intent is that the character sequences that function keys send
should not have command bindings in their own right--but if they
do, the ordinary bindings take priority.
The value of `function-key-map' is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but
sometimes those need help from terminal-specific Lisp files.
Emacs comes with terminal-specific files for many common
terminals; their main purpose is to make entries in
`function-key-map' beyond those that can be deduced from Termcap
and Terminfo. *Note Terminal-Specific::.
- Variable: key-translation-map
This variable is another keymap used just like `function-key-map'
to translate input events into other events. It differs from
`function-key-map' in two ways:
* `key-translation-map' goes to work after `function-key-map' is
finished; it receives the results of translation by
`function-key-map'.
* `key-translation-map' overrides actual key bindings. For
example, if `C-x f' has a binding in `key-translation-map',
that translation takes effect even though `C-x f' also has a
key binding in the global map.
The intent of `key-translation-map' is for users to map one
character set to another, including ordinary characters normally
bound to `self-insert-command'.
You can use `function-key-map' or `key-translation-map' for more
than simple aliases, by using a function, instead of a key sequence, as
the "translation" of a key. Then this function is called to compute
the translation of that key.
The key translation function receives one argument, which is the
prompt that was specified in `read-key-sequence'--or `nil' if the key
sequence is being read by the editor command loop. In most cases you
can ignore the prompt value.
If the function reads input itself, it can have the effect of
altering the event that follows. For example, here's how to define
`C-c h' to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
Finally, if you have enabled keyboard character set decoding using
`set-keyboard-coding-system', decoding is done after the translations
listed above. *Note Specifying Coding Systems::. In future Emacs
versions, character set decoding may be done before the other
translations.
Recording Input
---------------
- Function: recent-keys
This function returns a vector containing the last 100 input
events from the keyboard or mouse. All input events are included,
whether or not they were used as parts of key sequences. Thus,
you always get the last 100 input events, not counting events
generated by keyboard macros. (These are excluded because they
are less interesting for debugging; it should be enough to see the
events that invoked the macros.)
A call to `clear-this-command-keys' (*note Command Loop Info::)
causes this function to return an empty vector immediately
afterward.
- Command: open-dribble-file filename
This function opens a "dribble file" named FILENAME. When a
dribble file is open, each input event from the keyboard or mouse
(but not those from keyboard macros) is written in that file. A
non-character event is expressed using its printed representation
surrounded by `<...>'.
You close the dribble file by calling this function with an
argument of `nil'.
This function is normally used to record the input necessary to
trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble")
=> nil
See also the `open-termscript' function (*note Terminal Output::).
Terminal Output
===============
The terminal output functions send output to the terminal, or keep
track of output sent to the terminal. The variable `baud-rate' tells
you what Emacs thinks is the output speed of the terminal.
- Variable: baud-rate
This variable's value is the output speed of the terminal, as far
as Emacs knows. Setting this variable does not change the speed
of actual data transmission, but the value is used for
calculations such as padding. It also affects decisions about
whether to scroll part of the screen or repaint--even when using a
window system. (We designed it this way despite the fact that a
window system has no true "output speed", to give you a way to
tune these decisions.)
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set `baud-rate'.
- Function: baud-rate
This obsolete function returns the value of the variable
`baud-rate'.
- Function: send-string-to-terminal string
This function sends STRING to the terminal without alteration.
Control characters in STRING have terminal-dependent effects.
One use of this function is to define function keys on terminals
that have downloadable function key definitions. For example,
this is how (on certain terminals) to define function key 4 to
move forward four characters (by transmitting the characters `C-u
C-f' to the computer):
(send-string-to-terminal "\eF4\^U\^F")
=> nil
- Command: open-termscript filename
This function is used to open a "termscript file" that will record
all the characters sent by Emacs to the terminal. It returns
`nil'. Termscript files are useful for investigating problems
where Emacs garbles the screen, problems that are due to incorrect
Termcap entries or to undesirable settings of terminal options more
often than to actual Emacs bugs. Once you are certain which
characters were actually output, you can determine reliably
whether they correspond to the Termcap specifications in use.
See also `open-dribble-file' in *Note Terminal Input::.
(open-termscript "../junk/termscript")
=> nil
Sound Output
============
To play sound using Emacs, use the function `play-sound'. Only
certain systems are supported; if you call `play-sound' on a system
which cannot really do the job, it gives an error. Emacs version 20 and
earlier did not support sound at all.
The sound must be stored as a file in RIFF-WAVE format (`.wav') or
Sun Audio format (`.au').
- Function: play-sound sound
This function plays a specified sound. The argument, SOUND, has
the form `(sound PROPERTIES...)', where the PROPERTIES consist of
alternating keywords (particular symbols recognized specially) and
values corresponding to them.
Here is a table of the keywords that are currently meaningful in
SOUND, and their meanings:
`:file FILE'
This specifies the file containing the sound to play. If the
file name is not absolute, it is expanded against the
directory `data-directory'.
`:data DATA'
This specifies the sound to play without need to refer to a
file. The value, DATA, should be a string containing the
same bytes as a sound file. We recommend using a unibyte
string.
`:volume VOLUME'
This specifies how loud to play the sound. It should be a
number in the range of 0 to 1. The default is to use
whatever volume has been specified before.
`:device DEVICE'
This specifies the system device on which to play the sound,
as a string. The default device is system-dependent.
Before actually playing the sound, `play-sound' calls the
functions in the list `play-sound-functions'. Each function is
called with one argument, SOUND.
- Function: play-sound-file file &optional volume device
This function is an alternative interface to playing a sound FILE
specifying an optional VOLUME and DEVICE.
- Variable: play-sound-functions
A list of functions to be called before playing a sound. Each
function is called with one argument, a property list that
describes the sound.
System-Specific X11 Keysyms
===========================
To define system-specific X11 keysyms, set the variable
`system-key-alist'.
- Variable: system-key-alist
This variable's value should be an alist with one element for each
system-specific keysym. Each element has the form `(CODE .
SYMBOL)', where CODE is the numeric keysym code (not including the
"vendor specific" bit, -2**28), and SYMBOL is the name for the
function key.
For example `(168 . mute-acute)' defines a system-specific key
(used by HP X servers) whose numeric code is -2**28 + 168.
It is not crucial to exclude from the alist the keysyms of other X
servers; those do no harm, as long as they don't conflict with the
ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be
buffer-local. *Note Multiple Displays::.
Flow Control
============
This section attempts to answer the question "Why does Emacs use
flow-control characters in its command character set?" For a second
view on this issue, read the comments on flow control in the
`emacs/INSTALL' file from the distribution; for help with Termcap
entries and DEC terminal concentrators, see `emacs/etc/TERMS'.
At one time, most terminals did not need flow control, and none used
`C-s' and `C-q' for flow control. Therefore, the choice of `C-s' and
`C-q' as command characters for searching and quoting was natural and
uncontroversial. With so many commands needing key assignments, of
course we assigned meanings to nearly all ASCII control characters.
Later, some terminals were introduced which required these characters
for flow control. They were not very good terminals for full-screen
editing, so Emacs maintainers ignored them. In later years, flow
control with `C-s' and `C-q' became widespread among terminals, but by
this time it was usually an option. And the majority of Emacs users,
who can turn flow control off, did not want to switch to less mnemonic
key bindings for the sake of flow control.
So which usage is "right"--Emacs's or that of some terminal and
concentrator manufacturers? This question has no simple answer.
One reason why we are reluctant to cater to the problems caused by
`C-s' and `C-q' is that they are gratuitous. There are other
techniques (albeit less common in practice) for flow control that
preserve transparency of the character stream. Note also that their use
for flow control is not an official standard. Interestingly, on the
model 33 teletype with a paper tape punch (around 1970), `C-s' and
`C-q' were sent by the computer to turn the punch on and off!
As window systems and PC terminal emulators replace character-only
terminals, the flow control problem is gradually disappearing. For the
mean time, Emacs provides a convenient way of enabling flow control if
you want it: call the function `enable-flow-control'.
- Command: enable-flow-control
This function enables use of `C-s' and `C-q' for output flow
control, and provides the characters `C-\' and `C-^' as aliases
for them using `keyboard-translate-table' (*note Translating
Input::).
You can use the function `enable-flow-control-on' in your init file
to enable flow control automatically on certain terminal types.
- Function: enable-flow-control-on &rest termtypes
This function enables flow control, and the aliases `C-\' and
`C-^', if the terminal type is one of TERMTYPES. For example:
(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
Here is how `enable-flow-control' does its job:
1. It sets CBREAK mode for terminal input, and tells the operating
system to handle flow control, with `(set-input-mode nil t)'.
2. It sets up `keyboard-translate-table' to translate `C-\' and `C-^'
into `C-s' and `C-q'. Except at its very lowest level, Emacs
never knows that the characters typed were anything but `C-s' and
`C-q', so you can in effect type them as `C-\' and `C-^' even when
they are input for other commands. *Note Translating Input::.
If the terminal is the source of the flow control characters, then
once you enable kernel flow control handling, you probably can make do
with less padding than normal for that terminal. You can reduce the
amount of padding by customizing the Termcap entry. You can also
reduce it by setting `baud-rate' to a smaller value so that Emacs uses
a smaller speed when calculating the padding needed. *Note Terminal
Output::.
Batch Mode
==========
The command-line option `-batch' causes Emacs to run
noninteractively. In this mode, Emacs does not read commands from the
terminal, it does not alter the terminal modes, and it does not expect
to be outputting to an erasable screen. The idea is that you specify
Lisp programs to run; when they are finished, Emacs should exit. The
way to specify the programs to run is with `-l FILE', which loads the
library named FILE, and `-f FUNCTION', which calls FUNCTION with no
arguments.
Any Lisp program output that would normally go to the echo area,
either using `message', or using `prin1', etc., with `t' as the stream,
goes instead to Emacs's standard error descriptor when in batch mode.
Similarly, input that would normally come from the minibuffer is read
from the standard input descriptor. Thus, Emacs behaves much like a
noninteractive application program. (The echo area output that Emacs
itself normally generates, such as command echoing, is suppressed
entirely.)
- Variable: noninteractive
This variable is non-`nil' when Emacs is running in batch mode.
Emacs 20 Antinews
*****************
For those users who live backwards in time, here is information about
downgrading to Emacs version 20.4. We hope you will enjoy the greater
simplicity that results from the absence of many Emacs 21 features. In
the following section, we carry this information back to Emacs 20.3,
for which the previous printed edition of this manual was made.
Old Lisp Features in Emacs 20
=============================
* The `push' and `pop' macros are not defined. Neither are `dolist'
and `dotimes'.
* You can't display images in buffers. (Emacs is meant for editing
text.) With no images, there are no display margins, and no tool
bars.
* The `display' text property has no special meaning; you can use it
freely in Lisp programs, with no effects except what you implement
for yourself. With no images, who needs the `display' text
property?
* The `field' text property has no special meaning; buffers are no
longer subdivided into fields. (The division of information into
fields is always rather arbitrary.)
* Faces have fewer attributes. The attributes `:family', `:height',
`:width', `:weight', and `:slant', have been replaced with a font
name, a "bold" flag, and an "italic" flag.
The attributes `:overline', `:strike-through' and `:box' have been
eliminated too. Underlining now always has the same color as the
text--using any other color would be bad taste.
With fewer font attributes, there are no functions
`set-face-attribute' and `face-attribute'. Instead, you access
these attributes using functions such as `face-font', and set them
with functions such as `set-face-font'. (These functions were
available in Emacs 21, but are not as useful there.)
* The standard faces `scroll-bar', `menu', `border', `cursor', and
`mouse' have been eliminated. They are rather strange, as faces,
and therefore shouldn't really exist. You can use
`set-border-color', `set-cursor-color' and `set-mouse-color' to
specify the colors for the frame border, the text cursor, and the
mouse cursor. To specify menu colors, use X resources.
* Colors and other face attributes are no longer supported on
character terminals, so you no longer have to worry about
terminals making faces at you.
* Emacs will respect your peace and quiet, aside from occasional
beeps, because there are no facilities for playing sounds.
* Emacs 20 provides a complex and badly designed method for handling
character composition for languages such as Thai that display
several letters as a single combined image. We are too ashamed of
it to tell you any more than that.
* `delete-and-extract-region' has been deleted; instead, use
`buffer-substring' to extract the text, then use `delete-region'
to delete it.
* Regular expressions do not support the POSIX character classes
such as `[:alpha:]'. All characters are created equal.
* Hash tables have been eliminated; use alists instead.
* The Lisp printer does not detect and report circular structure.
That is ok, because the Lisp reader cannot recreate circular
structure anyway. However, there is a library `cust-print.el'
which can report circular structure.
* Emacs provides its own implementation of scroll bars, instead of
using those of the X toolkit. They always use the frame foreground
and background colors, so you cannot specify different colors for
the scroll bars.
* For simplicity, all ASCII characters now have the same height and
width. (Certain characters, such as Chinese characters, always
have twice the standard width.) All characters are created equal.
* You can now resize any Emacs window, and size changes in one
window can propagate to all others. Windows can no longer use
`window-size-fixed' to get special privileges.
* The function `intern-soft' no longer accepts a symbol as argument.
* The function `bitmap-spec-p' has been renamed to `pixmap-spec-p'
to encourage users to practice Emacs' help system while trying to
find it.
* Tooltips operate using ordinary Emacs frames.
* Areas of the mode line are not mouse-sensitive; however, some mouse
commands are available for the mode line as a whole.
* Windows cannot have header lines. Conversely, there is no way to
turn off the mode line of a window unless it is a minibuffer.
* Plain dashes are the only separators you can use in a menu.
* Vertical fractional scrolling does not exist.
* The functions `format' and `message' ignore and discard text
properties.
* The function `propertize' does not exist; you can get the job done
using `set-text-properties'.
* Colors are supported only on window systems, not on text-only
terminals. So the support functions for colors on text-only
terminals are not needed, and have been eliminated.
* The functions `color-values', `color-defined-p' and
`defined-colors' have been renamed to `x-color-values',
`x-color-defined-p' and `x-defined-colors'.
* Windows cannot be made fixed-width or fixed-height; Emacs will
adjust the size of all windows when it needs to.
* The string used as the value of the `before-string' or
`after-string' property must contain only characters that display
as a single column--control characters, including tabs and
newlines, will give strange results.
* The minibuffer prompt does not actually appear in content of the
minibuffer; it is displayed specially in the minibuffer window.
* The "exclusive open" feature of `write-region' has been
eliminated; any non-`nil' value for the seventh argument now means
to ask the user for confirmation.
* The function `buffer-size' always reports on the current buffer.
* The function `assq-delete-all' has itself been deleted. So there!
* The keyword `:set-after' no longer does anything in `defcustom'.
* The variable `small-temporary-file-directory' has no special
meaning. There's only one variable for specifying which directory
to use for temporary files, `temporary-file-directory', but not all
Emacs features use it anyway. Some use the `TMP' environment
variable, and some use the `TMPDIR' environment variable.
* If the second argument of `save-some-buffers', PRED, is not `nil',
then the precise value no longer matters. Any non-`nil' value
means the same as `t': offer to save each non-file buffer that has
a non-`nil' value for `buffer-offer-save'.
* The variable `inhibit-modification-hooks' has no special meaning.
* The hook `fontification-functions' has been eliminated, but there
are other hooks, such as `window-scroll-functions', that you can
use to do a similar job.
* The variable `redisplay-dont-pause' has no special meaning.
* The hook `calendar-move-hook' has been deleted.
* The function `move-to-column' treats any non-`nil' second argument
just like `t'.
Old Lisp Features in Emacs 20.3
===============================
Here are the most important of the features that you will learn to
do without in Emacs 20.3:
Here are changes in the Lisp language itself:
* The functions `line-beginning-position' and `line-end-position'
have been eliminated.
* The functions `directory-files-and-attributes',
`file-attributes-lessp', and `file-expand-wildcards', have been
eliminated.
* The functions `decode-coding-region' and `encode-coding-region'
leave text properties untouched, in case that is useful. (It
rarely makes any sense, though.)
* The functions `position-bytes' and `byte-to-position' have been
eliminated.
* Temporary buffers made with `with-output-to-temp-buffer' are now
modifiable by default, and use Fundamental mode rather than Help
mode.
* The functions `sref' interprets its INDEX argument as a number of
bytes, not a number of characters. And the function `char-bytes'
actually tries to report on the number of bytes that a character
occupies.
* The function `process-running-child-p' has been eliminated.
* The function `interrupt-process' and similar functions no longer do
anything special when the second argument is `lambda'.
* The function `define-prefix-command' accepts only two arguments.
* The meaning of the second argument to `read-char', `read-event',
and `read-char-exclusive' has been reversed: they use the current
input method if the argument is if `nil'.
* The function `with-temp-message' has been eliminated.
* The function `clear-this-command-keys' has been eliminated.
* The functions `gap-position' and `gap-size' have been eliminated.
* In `modify-face', an argument of `(nil)' has no special meaning.
* The base64 conversion functions have been eliminated.
* Wildcard support has been eliminated from `find-file' and allied
functions.
* `file-attributes' returns the file size and the file inode number
only as a simple integer.
GNU Free Documentation License
******************************
Version 1.1, March 2000
Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
written document "free" in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily,
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modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work that contains a
notice placed by the copyright holder saying it can be distributed
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A "Modified Version" of the Document means any work containing the
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The "Invariant Sections" are certain Secondary Sections whose
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The "Title Page" means, for a printed book, the title page itself,
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2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
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applies to the Document are reproduced in all copies, and that you
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may not use technical measures to obstruct or control the reading
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you may accept compensation in exchange for copies. If you
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You may also lend copies, under the same conditions stated above,
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3. COPYING IN QUANTITY
If you publish printed copies of the Document numbering more than
100, and the Document's license notice requires Cover Texts, you
must enclose the copies in covers that carry, clearly and legibly,
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If the required texts for either cover are too voluminous to fit
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If you publish or distribute Opaque copies of the Document
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It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of
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4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with
the Modified Version filling the role of the Document, thus
licensing distribution and modification of the Modified Version to
whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of previous
versions (which should, if there were any, be listed in the
History section of the Document). You may use the same title
as a previous version if the original publisher of that version
gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in the
Modified Version, together with at least five of the principal
authors of the Document (all of its principal authors, if it
has less than five).
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified Version
under the terms of this License, in the form shown in the
Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section entitled "History", and its title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page.
If there is no section entitled "History" in the Document,
create one stating the title, year, authors, and publisher of
the Document as given on its Title Page, then add an item
describing the Modified Version as stated in the previous
sentence.
J. Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in the
"History" section. You may omit a network location for a work
that was published at least four years before the Document
itself, or if the original publisher of the version it refers
to gives permission.
K. In any section entitled "Acknowledgements" or "Dedications",
preserve the section's title, and preserve in the section all the
substance and tone of each of the contributor acknowledgements
and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
M. Delete any section entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section as "Endorsements" or to
conflict in title with any Invariant Section.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
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add their titles to the list of Invariant Sections in the Modified
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You may add a section entitled "Endorsements", provided it contains
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You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end
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5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
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unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
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In the combination, you must combine any sections entitled
"History" in the various original documents, forming one section
entitled "History"; likewise combine any sections entitled
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must delete all sections entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, does not as a whole count as a
Modified Version of the Document, provided no compilation
copyright is claimed for the compilation. Such a compilation is
called an "aggregate", and this License does not apply to the
other self-contained works thus compiled with the Document, on
account of their being thus compiled, if they are not themselves
derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one
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8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License provided that you also include the
original English version of this License. In case of a
disagreement between the translation and the original English
version of this License, the original English version will prevail.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided for under this License. Any other
attempt to copy, modify, sublicense or distribute the Document is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
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have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have no Invariant Sections, write "with no Invariant
Sections" instead of saying which ones are invariant. If you have no
Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover
Texts being LIST"; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.
GNU General Public License
**************************
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
========
The licenses for most software are designed to take away your
freedom to share and change it. By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users. This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it. (Some other Free Software Foundation software is covered by
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When we speak of free software, we are referring to freedom, not
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We protect your rights with two steps: (1) copyright the software,
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The precise terms and conditions for copying, distribution and
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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License applies to any program or other work which contains a
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or any part thereof, to be licensed as a whole at no charge
to all third parties under the terms of this License.
c. If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display
an announcement including an appropriate copyright notice and
a notice that there is no warranty (or else, saying that you
provide a warranty) and that users may redistribute the
program under these conditions, and telling the user how to
view a copy of this License. (Exception: if the Program
itself is interactive but does not normally print such an
announcement, your work based on the Program is not required
to print an announcement.)
These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the
Program, and can be reasonably considered independent and separate
works in themselves, then this License, and its terms, do not
apply to those sections when you distribute them as separate
works. But when you distribute the same sections as part of a
whole which is a work based on the Program, the distribution of
the whole must be on the terms of this License, whose permissions
for other licensees extend to the entire whole, and thus to each
and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or
contest your rights to work written entirely by you; rather, the
intent is to exercise the right to control the distribution of
derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the
Program with the Program (or with a work based on the Program) on
a volume of a storage or distribution medium does not bring the
other work under the scope of this License.
3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms
of Sections 1 and 2 above provided that you also do one of the
following:
a. Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of
Sections 1 and 2 above on a medium customarily used for
software interchange; or,
b. Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a
medium customarily used for software interchange; or,
c. Accompany it with the information you received as to the offer
to distribute corresponding source code. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with
such an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for
making modifications to it. For an executable work, complete
source code means all the source code for all modules it contains,
plus any associated interface definition files, plus the scripts
used to control compilation and installation of the executable.
However, as a special exception, the source code distributed need
not include anything that is normally distributed (in either
source or binary form) with the major components (compiler,
kernel, and so on) of the operating system on which the executable
runs, unless that component itself accompanies the executable.
If distribution of executable or object code is made by offering
access to copy from a designated place, then offering equivalent
access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.
4. You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
5. You are not required to accept this License, since you have not
signed it. However, nothing else grants you permission to modify
or distribute the Program or its derivative works. These actions
are prohibited by law if you do not accept this License.
Therefore, by modifying or distributing the Program (or any work
based on the Program), you indicate your acceptance of this
License to do so, and all its terms and conditions for copying,
distributing or modifying the Program or works based on it.
6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program
subject to these terms and conditions. You may not impose any
further restrictions on the recipients' exercise of the rights
granted herein. You are not responsible for enforcing compliance
by third parties to this License.
7. If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent
issues), conditions are imposed on you (whether by court order,
agreement or otherwise) that contradict the conditions of this
License, they do not excuse you from the conditions of this
License. If you cannot distribute so as to satisfy simultaneously
your obligations under this License and any other pertinent
obligations, then as a consequence you may not distribute the
Program at all. For example, if a patent license would not permit
royalty-free redistribution of the Program by all those who
receive copies directly or indirectly through you, then the only
way you could satisfy both it and this License would be to refrain
entirely from distribution of the Program.
If any portion of this section is held invalid or unenforceable
under any particular circumstance, the balance of the section is
intended to apply and the section as a whole is intended to apply
in other circumstances.
It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of
any such claims; this section has the sole purpose of protecting
the integrity of the free software distribution system, which is
implemented by public license practices. Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is
willing to distribute software through any other system and a
licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed
to be a consequence of the rest of this License.
8. If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces,
the original copyright holder who places the Program under this
License may add an explicit geographical distribution limitation
excluding those countries, so that distribution is permitted only
in or among countries not thus excluded. In such case, this
License incorporates the limitation as if written in the body of
this License.
9. The Free Software Foundation may publish revised and/or new
versions of the General Public License from time to time. Such
new versions will be similar in spirit to the present version, but
may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the
Program specifies a version number of this License which applies
to it and "any later version", you have the option of following
the terms and conditions either of that version or of any later
version published by the Free Software Foundation. If the Program
does not specify a version number of this License, you may choose
any version ever published by the Free Software Foundation.
10. If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the
author to ask for permission. For software which is copyrighted
by the Free Software Foundation, write to the Free Software
Foundation; we sometimes make exceptions for this. Our decision
will be guided by the two goals of preserving the free status of
all derivatives of our free software and of promoting the sharing
and reuse of software generally.
NO WARRANTY
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE
QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
SERVICING, REPAIR OR CORRECTION.
12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
=============================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
Copyright (C) YEAR NAME OF AUTHOR
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
Also add information on how to contact you by electronic and paper
mail.
If the program is interactive, make it output a short notice like
this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) YEAR NAME OF AUTHOR
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.
You should also get your employer (if you work as a programmer) or
your school, if any, to sign a "copyright disclaimer" for the program,
if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
SIGNATURE OF TY COON, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Lesser General Public License instead of this License.
Tips and Conventions
********************
This chapter describes no additional features of Emacs Lisp. Instead
it gives advice on making effective use of the features described in the
previous chapters, and describes conventions Emacs Lisp programmers
should follow.
You can automatically check some of the conventions described below
by running the command `M-x checkdoc RET' when visiting a Lisp file.
It cannot check all of the conventions, and not all the warnings it
gives necessarily correspond to problems, but it is worth examining them
all.
Emacs Lisp Coding Conventions
=============================
Here are conventions that you should follow when writing Emacs Lisp
code intended for widespread use:
* Since all global variables share the same name space, and all
functions share another name space, you should choose a short word
to distinguish your program from other Lisp programs.(1) Then
take care to begin the names of all global variables, constants,
and functions in your program with the chosen prefix. This helps
avoid name conflicts.
This recommendation applies even to names for traditional Lisp
primitives that are not primitives in Emacs Lisp--even to
`copy-list'. Believe it or not, there is more than one plausible
way to define `copy-list'. Play it safe; append your name prefix
to produce a name like `foo-copy-list' or `mylib-copy-list'
instead.
If you write a function that you think ought to be added to Emacs
under a certain name, such as `twiddle-files', don't call it by
that name in your program. Call it `mylib-twiddle-files' in your
program, and send mail to `bug-gnu-emacs@gnu.org' suggesting we add
it to Emacs. If and when we do, we can change the name easily
enough.
If one prefix is insufficient, your package may use two or three
alternative common prefixes, so long as they make sense.
Separate the prefix from the rest of the symbol name with a hyphen,
`-'. This will be consistent with Emacs itself and with most Emacs
Lisp programs.
* It is often useful to put a call to `provide' in each separate
library program, at least if there is more than one entry point to
the program.
* If a file requires certain other library programs to be loaded
beforehand, then the comments at the beginning of the file should
say so. Also, use `require' to make sure they are loaded.
* If one file FOO uses a macro defined in another file BAR, FOO
should contain this expression before the first use of the macro:
(eval-when-compile (require 'BAR))
(And the library BAR should contain `(provide 'BAR)', to make the
`require' work.) This will cause BAR to be loaded when you
byte-compile FOO. Otherwise, you risk compiling FOO without the
necessary macro loaded, and that would produce compiled code that
won't work right. *Note Compiling Macros::.
Using `eval-when-compile' avoids loading BAR when the compiled
version of FOO is _used_.
* Please don't require the `cl' package of Common Lisp extensions at
run time. Use of this package is optional, and it is not part of
the standard Emacs namespace. If your package loads `cl' at run
time, that could cause name clashes for users who don't use that
package.
However, there is no problem with using the `cl' package at compile
time, for the sake of macros. You do that like this:
(eval-when-compile (require 'cl))
* When defining a major mode, please follow the major mode
conventions. *Note Major Mode Conventions::.
* When defining a minor mode, please follow the minor mode
conventions. *Note Minor Mode Conventions::.
* If the purpose of a function is to tell you whether a certain
condition is true or false, give the function a name that ends in
`p'. If the name is one word, add just `p'; if the name is
multiple words, add `-p'. Examples are `framep' and
`frame-live-p'.
* If a user option variable records a true-or-false condition, give
it a name that ends in `-flag'.
* Please do not define `C-c LETTER' as a key in your major modes.
These sequences are reserved for users; they are the *only*
sequences reserved for users, so do not block them.
Instead, define sequences consisting of `C-c' followed by a control
character, a digit, or certain punctuation characters. These
sequences are reserved for major modes.
Changing all the Emacs major modes to follow this convention was a
lot of work. Abandoning this convention would make that work go
to waste, and inconvenience users.
* Sequences consisting of `C-c' followed by `{', `}', `<', `>', `:'
or `;' are also reserved for major modes.
* Sequences consisting of `C-c' followed by any other punctuation
character are allocated for minor modes. Using them in a major
mode is not absolutely prohibited, but if you do that, the major
mode binding may be shadowed from time to time by minor modes.
* Function keys <F5> through <F9> without modifier keys are reserved
for users to define.
* Do not bind `C-h' following any prefix character (including
`C-c'). If you don't bind `C-h', it is automatically available as
a help character for listing the subcommands of the prefix
character.
* Do not bind a key sequence ending in <ESC> except following
another <ESC>. (That is, it is OK to bind a sequence ending in
`<ESC> <ESC>'.)
The reason for this rule is that a non-prefix binding for <ESC> in
any context prevents recognition of escape sequences as function
keys in that context.
* Anything which acts like a temporary mode or state which the user
can enter and leave should define `<ESC> <ESC>' or `<ESC> <ESC>
<ESC>' as a way to escape.
For a state which accepts ordinary Emacs commands, or more
generally any kind of state in which <ESC> followed by a function
key or arrow key is potentially meaningful, then you must not
define `<ESC> <ESC>', since that would preclude recognizing an
escape sequence after <ESC>. In these states, you should define
`<ESC> <ESC> <ESC>' as the way to escape. Otherwise, define
`<ESC> <ESC>' instead.
* Applications should not bind mouse events based on button 1 with
the shift key held down. These events include `S-mouse-1',
`M-S-mouse-1', `C-S-mouse-1', and so on. They are reserved for
users.
* Special major modes used for read-only text should usually redefine
`mouse-2' and <RET> to trace some sort of reference in the text.
Modes such as Dired, Info, Compilation, and Occur redefine it in
this way.
* When a package provides a modification of ordinary Emacs behavior,
it is good to include a command to enable and disable the feature,
Provide a command named `WHATEVER-mode' which turns the feature on
or off, and make it autoload (*note Autoload::). Design the
package so that simply loading it has no visible effect--that
should not enable the feature.(2) Users will request the feature
by invoking the command.
* It is a bad idea to define aliases for the Emacs primitives. Use
the standard names instead.
* If a package needs to define an alias or a new function for
compatibility with some other version of Emacs, name it with the
package prefix, not with the raw name with which it occurs in the
other version. Here is an example from Gnus, which provides many
examples of such compatibility issues.
(defalias 'gnus-point-at-bol
(if (fboundp 'point-at-bol)
'point-at-bol
'line-beginning-position))
* Redefining (or advising) an Emacs primitive is discouraged. It
may do the right thing for a particular program, but there is no
telling what other programs might break as a result.
* If a file does replace any of the functions or library programs of
standard Emacs, prominent comments at the beginning of the file
should say which functions are replaced, and how the behavior of
the replacements differs from that of the originals.
* Please keep the names of your Emacs Lisp source files to 13
characters or less. This way, if the files are compiled, the
compiled files' names will be 14 characters or less, which is
short enough to fit on all kinds of Unix systems.
* Don't use `next-line' or `previous-line' in programs; nearly
always, `forward-line' is more convenient as well as more
predictable and robust. *Note Text Lines::.
* Don't call functions that set the mark, unless setting the mark is
one of the intended features of your program. The mark is a
user-level feature, so it is incorrect to change the mark except
to supply a value for the user's benefit. *Note The Mark::.
In particular, don't use any of these functions:
* `beginning-of-buffer', `end-of-buffer'
* `replace-string', `replace-regexp'
If you just want to move point, or replace a certain string,
without any of the other features intended for interactive users,
you can replace these functions with one or two lines of simple
Lisp code.
* Use lists rather than vectors, except when there is a particular
reason to use a vector. Lisp has more facilities for manipulating
lists than for vectors, and working with lists is usually more
convenient.
Vectors are advantageous for tables that are substantial in size
and are accessed in random order (not searched front to back),
provided there is no need to insert or delete elements (only lists
allow that).
* The recommended way to print a message in the echo area is with
the `message' function, not `princ'. *Note The Echo Area::.
* When you encounter an error condition, call the function `error'
(or `signal'). The function `error' does not return. *Note
Signaling Errors::.
Do not use `message', `throw', `sleep-for', or `beep' to report
errors.
* An error message should start with a capital letter but should not
end with a period.
* In `interactive', if you use a Lisp expression to produce a list
of arguments, don't try to provide the "correct" default values for
region or position arguments. Instead, provide `nil' for those
arguments if they were not specified, and have the function body
compute the default value when the argument is `nil'. For
instance, write this:
(defun foo (pos)
(interactive
(list (if SPECIFIED SPECIFIED-POS)))
(unless pos (setq pos DEFAULT-POS))
...)
rather than this:
(defun foo (pos)
(interactive
(list (if SPECIFIED SPECIFIED-POS
DEFAULT-POS)))
...)
This is so that repetition of the command will recompute these
defaults based on the current circumstances.
You do not need to take such precautions when you use interactive
specs `d', `m' and `r', because they make special arrangements to
recompute the argument values on repetition of the command.
* Many commands that take a long time to execute display a message
that says something like `Operating...' when they start, and
change it to `Operating...done' when they finish. Please keep the
style of these messages uniform: _no_ space around the ellipsis,
and _no_ period after `done'.
* Try to avoid using recursive edits. Instead, do what the Rmail `e'
command does: use a new local keymap that contains one command
defined to switch back to the old local keymap. Or do what the
`edit-options' command does: switch to another buffer and let the
user switch back at will. *Note Recursive Editing::.
* In some other systems there is a convention of choosing variable
names that begin and end with `*'. We don't use that convention
in Emacs Lisp, so please don't use it in your programs. (Emacs
uses such names only for special-purpose buffers.) The users will
find Emacs more coherent if all libraries use the same conventions.
* Try to avoid compiler warnings about undefined free variables, by
adding `defvar' definitions for these variables.
Sometimes adding a `require' for another package is useful to avoid
compilation warnings for variables and functions defined in that
package. If you do this, often it is better if the `require' acts
only at compile time. Here's how to do that:
(eval-when-compile
(require 'foo)
(defvar bar-baz))
If you bind a variable in one function, and use it or set it in
another function, the compiler warns about the latter function
unless the variable has a definition. But often these variables
have short names, and it is not clean for Lisp packages to define
such variable names. Therefore, you should rename the variable to
start with the name prefix used for the other functions and
variables in your package.
* Indent each function with `C-M-q' (`indent-sexp') using the
default indentation parameters.
* Don't make a habit of putting close-parentheses on lines by
themselves; Lisp programmers find this disconcerting. Once in a
while, when there is a sequence of many consecutive
close-parentheses, it may make sense to split the sequence in one
or two significant places.
* Please put a copyright notice on the file if you give copies to
anyone. Use a message like this one:
;; Copyright (C) YEAR NAME
;; This program is free software; you can redistribute it and/or
;; modify it under the terms of the GNU General Public License as
;; published by the Free Software Foundation; either version 2 of
;; the License, or (at your option) any later version.
;; This program is distributed in the hope that it will be
;; useful, but WITHOUT ANY WARRANTY; without even the implied
;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
;; PURPOSE. See the GNU General Public License for more details.
;; You should have received a copy of the GNU General Public
;; License along with this program; if not, write to the Free
;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
;; MA 02111-1307 USA
If you have signed papers to assign the copyright to the
Foundation, then use `Free Software Foundation, Inc.' as NAME.
Otherwise, use your name.
---------- Footnotes ----------
(1) The benefits of a Common Lisp-style package system are
considered not to outweigh the costs.
(2) Consider that the package may be loaded arbitrarily by Custom
for instance.
Tips for Making Compiled Code Fast
==================================
Here are ways of improving the execution speed of byte-compiled Lisp
programs.
* Profile your program with the `profile' library or the `elp'
library. See the files `profile.el' and `elp.el' for instructions.
* Use iteration rather than recursion whenever possible. Function
calls are slow in Emacs Lisp even when a compiled function is
calling another compiled function.
* Using the primitive list-searching functions `memq', `member',
`assq', or `assoc' is even faster than explicit iteration. It can
be worth rearranging a data structure so that one of these
primitive search functions can be used.
* Certain built-in functions are handled specially in byte-compiled
code, avoiding the need for an ordinary function call. It is a
good idea to use these functions rather than alternatives. To see
whether a function is handled specially by the compiler, examine
its `byte-compile' property. If the property is non-`nil', then
the function is handled specially.
For example, the following input will show you that `aref' is
compiled specially (*note Array Functions::):
(get 'aref 'byte-compile)
=> byte-compile-two-args
* If calling a small function accounts for a substantial part of your
program's running time, make the function inline. This eliminates
the function call overhead. Since making a function inline reduces
the flexibility of changing the program, don't do it unless it
gives a noticeable speedup in something slow enough that users
care about the speed. *Note Inline Functions::.
Tips for Documentation Strings
==============================
Here are some tips and conventions for the writing of documentation
strings. You can check many of these conventions by running the command
`M-x checkdoc-minor-mode'.
* Every command, function, or variable intended for users to know
about should have a documentation string.
* An internal variable or subroutine of a Lisp program might as well
have a documentation string. In earlier Emacs versions, you could
save space by using a comment instead of a documentation string,
but that is no longer the case--documentation strings now take up
very little space in a running Emacs.
* The first line of the documentation string should consist of one
or two complete sentences that stand on their own as a summary.
`M-x apropos' displays just the first line, and if that line's
contents don't stand on their own, the result looks bad. In
particular, start the first line with a capital letter and end
with a period.
The documentation string is not limited to one line; use as many
lines as you need to explain the details of how to use the
function or variable. Please use complete sentences in the
additional lines.
* For consistency, phrase the verb in the first sentence of a
function's documentation string as an imperative-for instance, use
"Return the cons of A and B." in preference to "Returns the cons
of A and B." Usually it looks good to do likewise for the rest of
the first paragraph. Subsequent paragraphs usually look better if
each sentence has a proper subject.
* Write documentation strings in the active voice, not the passive,
and in the present tense, not the future. For instance, use
"Return a list containing A and B." instead of "A list containing
A and B will be returned."
* Avoid using the word "cause" (or its equivalents) unnecessarily.
Instead of, "Cause Emacs to display text in boldface," write just
"Display text in boldface."
* When a command is meaningful only in a certain mode or situation,
do mention that in the documentation string. For example, the
documentation of `dired-find-file' is:
In Dired, visit the file or directory named on this line.
* Do not start or end a documentation string with whitespace.
* Format the documentation string so that it fits in an Emacs window
on an 80-column screen. It is a good idea for most lines to be no
wider than 60 characters. The first line should not be wider than
67 characters or it will look bad in the output of `apropos'.
You can fill the text if that looks good. However, rather than
blindly filling the entire documentation string, you can often
make it much more readable by choosing certain line breaks with
care. Use blank lines between topics if the documentation string
is long.
* *Do not* indent subsequent lines of a documentation string so that
the text is lined up in the source code with the text of the first
line. This looks nice in the source code, but looks bizarre when
users view the documentation. Remember that the indentation
before the starting double-quote is not part of the string!
* When the user tries to use a disabled command, Emacs displays just
the first paragraph of its documentation string--everything
through the first blank line. If you wish, you can choose which
information to include before the first blank line so as to make
this display useful.
* A variable's documentation string should start with `*' if the
variable is one that users would often want to set interactively.
If the value is a long list, or a function, or if the variable
would be set only in init files, then don't start the
documentation string with `*'. *Note Defining Variables::.
* The documentation string for a variable that is a yes-or-no flag
should start with words such as "Non-nil means...", to make it
clear that all non-`nil' values are equivalent and indicate
explicitly what `nil' and non-`nil' mean.
* When a function's documentation string mentions the value of an
argument of the function, use the argument name in capital letters
as if it were a name for that value. Thus, the documentation
string of the function `eval' refers to its second argument as
`FORM', because the actual argument name is `form':
Evaluate FORM and return its value.
Also write metasyntactic variables in capital letters, such as
when you show the decomposition of a list or vector into subunits,
some of which may vary. `KEY' and `VALUE' in the following example
illustrate this practice:
The argument TABLE should be an alist whose elements
have the form (KEY . VALUE). Here, KEY is ...
* If a line in a documentation string begins with an
open-parenthesis, write a backslash before the open-parenthesis,
like this:
The argument FOO can be either a number
\(a buffer position) or a string (a file name).
This prevents the open-parenthesis from being treated as the start
of a defun (*note Defuns: (emacs)Defuns.).
* When a documentation string refers to a Lisp symbol, write it as it
would be printed (which usually means in lower case), with
single-quotes around it. For example: `lambda'. There are two
exceptions: write t and nil without single-quotes. (In this
manual, we use a different convention, with single-quotes for all
symbols.)
Help mode automatically creates a hyperlink when a documentation
string uses a symbol name inside single quotes, if the symbol has
either a function or a variable definition. You do not need to do
anything special to make use of this feature. However, when a
symbol has both a function definition and a variable definition,
and you want to refer to just one of them, you can specify which
one by writing one of the words `variable', `option', `function',
or `command', immediately before the symbol name. (Case makes no
difference in recognizing these indicator words.) For example, if
you write
This function sets the variable `buffer-file-name'.
then the hyperlink will refer only to the variable documentation of
`buffer-file-name', and not to its function documentation.
If a symbol has a function definition and/or a variable
definition, but those are irrelevant to the use of the symbol that
you are documenting, you can write the word `symbol' before the
symbol name to prevent making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list',
this function returns a list of all the objects
that satisfy the criterion.
does not make a hyperlink to the documentation, irrelevant here,
of the function `list'.
To make a hyperlink to Info documentation, write the name of the
Info node in single quotes, preceded by `info node' or `Info
node'. The Info file name defaults to `emacs'. For example,
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
* Don't write key sequences directly in documentation strings.
Instead, use the `\\[...]' construct to stand for them. For
example, instead of writing `C-f', write the construct
`\\[forward-char]'. When Emacs displays the documentation string,
it substitutes whatever key is currently bound to `forward-char'.
(This is normally `C-f', but it may be some other character if the
user has moved key bindings.) *Note Keys in Documentation::.
* In documentation strings for a major mode, you will want to refer
to the key bindings of that mode's local map, rather than global
ones. Therefore, use the construct `\\<...>' once in the
documentation string to specify which key map to use. Do this
before the first use of `\\[...]'. The text inside the `\\<...>'
should be the name of the variable containing the local keymap for
the major mode.
It is not practical to use `\\[...]' very many times, because
display of the documentation string will become slow. So use this
to describe the most important commands in your major mode, and
then use `\\{...}' to display the rest of the mode's keymap.
Tips on Writing Comments
========================
We recommend these conventions for where to put comments and how to
indent them:
`;'
Comments that start with a single semicolon, `;', should all be
aligned to the same column on the right of the source code. Such
comments usually explain how the code on the same line does its
job. In Lisp mode and related modes, the `M-;'
(`indent-for-comment') command automatically inserts such a `;' in
the right place, or aligns such a comment if it is already present.
This and following examples are taken from the Emacs sources.
(setq base-version-list ; there was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion
`;;'
Comments that start with two semicolons, `;;', should be aligned to
the same level of indentation as the code. Such comments usually
describe the purpose of the following lines or the state of the
program at that point. For example:
(prog1 (setq auto-fill-function
...
...
;; update mode line
(force-mode-line-update)))
We also normally use two semicolons for comments outside functions.
;; This Lisp code is run in Emacs
;; when it is to operate as a server
;; for other processes.
Every function that has no documentation string (presumably one
that is used only internally within the package it belongs to),
should instead have a two-semicolon comment right before the
function, explaining what the function does and how to call it
properly. Explain precisely what each argument means and how the
function interprets its possible values.
`;;;'
Comments that start with three semicolons, `;;;', should start at
the left margin. These are used, occasionally, for comments within
functions that should start at the margin. We also use them
sometimes for comments that are between functions--whether to use
two or three semicolons there is a matter of style.
Another use for triple-semicolon comments is for commenting out
lines within a function. We use three semicolons for this
precisely so that they remain at the left margin.
(defun foo (a)
;;; This is no longer necessary.
;;; (force-mode-line-update)
(message "Finished with %s" a))
`;;;;'
Comments that start with four semicolons, `;;;;', should be aligned
to the left margin and are used for headings of major sections of a
program. For example:
;;;; The kill ring
The indentation commands of the Lisp modes in Emacs, such as `M-;'
(`indent-for-comment') and <TAB> (`lisp-indent-line'), automatically
indent comments according to these conventions, depending on the number
of semicolons. *Note Manipulating Comments: (emacs)Comments.
Conventional Headers for Emacs Libraries
========================================
Emacs has conventions for using special comments in Lisp libraries
to divide them into sections and give information such as who wrote
them. This section explains these conventions.
We'll start with an example, a package that is included in the Emacs
distribution.
Parts of this example reflect its status as part of Emacs; for
example, the copyright notice lists the Free Software Foundation as the
copyright holder, and the copying permission says the file is part of
Emacs. When you write a package and post it, the copyright holder would
be you (unless your employer claims to own it instead), and you should
get the suggested copying permission from the end of the GNU General
Public License itself. Don't say your file is part of Emacs if we
haven't installed it in Emacs yet!
With that warning out of the way, on to the example:
;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
;; Copyright (C) 1992 Free Software Foundation, Inc.
;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
;; Created: 14 Jul 1992
;; Version: 1.2
;; Keywords: docs
;; This file is part of GNU Emacs.
...
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
The very first line should have this format:
;;; FILENAME --- DESCRIPTION
The description should be complete in one line.
After the copyright notice come several "header comment" lines, each
beginning with `;; HEADER-NAME:'. Here is a table of the conventional
possibilities for HEADER-NAME:
`Author'
This line states the name and net address of at least the principal
author of the library.
If there are multiple authors, you can list them on continuation
lines led by `;;' and a tab character, like this:
;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
;; Dave Sill <de5@ornl.gov>
;; Dave Brennan <brennan@hal.com>
;; Eric Raymond <esr@snark.thyrsus.com>
`Maintainer'
This line should contain a single name/address as in the Author
line, or an address only, or the string `FSF'. If there is no
maintainer line, the person(s) in the Author field are presumed to
be the maintainers. The example above is mildly bogus because the
maintainer line is redundant.
The idea behind the `Author' and `Maintainer' lines is to make
possible a Lisp function to "send mail to the maintainer" without
having to mine the name out by hand.
Be sure to surround the network address with `<...>' if you
include the person's full name as well as the network address.
`Created'
This optional line gives the original creation date of the file.
For historical interest only.
`Version'
If you wish to record version numbers for the individual Lisp
program, put them in this line.
`Adapted-By'
In this header line, place the name of the person who adapted the
library for installation (to make it fit the style conventions, for
example).
`Keywords'
This line lists keywords for the `finder-by-keyword' help command.
Please use that command to see a list of the meaningful keywords.
This field is important; it's how people will find your package
when they're looking for things by topic area. To separate the
keywords, you can use spaces, commas, or both.
Just about every Lisp library ought to have the `Author' and
`Keywords' header comment lines. Use the others if they are
appropriate. You can also put in header lines with other header
names--they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the
library file. These should be separated by blank lines from anything
else. Here is a table of them:
`;;; Commentary:'
This begins introductory comments that explain how the library
works. It should come right after the copying permissions,
terminated by a `Change Log', `History' or `Code' comment line.
This text is used by the Finder package, so it should make sense
in that context.
`;;; Documentation'
This has been used in some files in place of `;;; Commentary:',
but `;;; Commentary:' is preferred.
`;;; Change Log:'
This begins change log information stored in the library file (if
you store the change history there). For Lisp files distributed
with Emacs, the change history is kept in the file `ChangeLog' and
not in the source file at all; these files generally do not have a
`;;; Change Log:' line. `History' is an alternative to `Change
Log'.
`;;; Code:'
This begins the actual code of the program.
`;;; FILENAME ends here'
This is the "footer line"; it appears at the very end of the file.
Its purpose is to enable people to detect truncated versions of
the file from the lack of a footer line.
GNU Emacs Internals
*******************
This chapter describes how the runnable Emacs executable is dumped
with the preloaded Lisp libraries in it, how storage is allocated, and
some internal aspects of GNU Emacs that may be of interest to C
programmers.
Building Emacs
==============
This section explains the steps involved in building the Emacs
executable. You don't have to know this material to build and install
Emacs, since the makefiles do all these things automatically. This
information is pertinent to Emacs maintenance.
Compilation of the C source files in the `src' directory produces an
executable file called `temacs', also called a "bare impure Emacs". It
contains the Emacs Lisp interpreter and I/O routines, but not the
editing commands.
The command `temacs -l loadup' uses `temacs' to create the real
runnable Emacs executable. These arguments direct `temacs' to evaluate
the Lisp files specified in the file `loadup.el'. These files set up
the normal Emacs editing environment, resulting in an Emacs that is
still impure but no longer bare.
It takes a substantial time to load the standard Lisp files.
Luckily, you don't have to do this each time you run Emacs; `temacs' can
dump out an executable program called `emacs' that has these files
preloaded. `emacs' starts more quickly because it does not need to
load the files. This is the Emacs executable that is normally
installed.
To create `emacs', use the command `temacs -batch -l loadup dump'.
The purpose of `-batch' here is to prevent `temacs' from trying to
initialize any of its data on the terminal; this ensures that the
tables of terminal information are empty in the dumped Emacs. The
argument `dump' tells `loadup.el' to dump a new executable named
`emacs'.
Some operating systems don't support dumping. On those systems, you
must start Emacs with the `temacs -l loadup' command each time you use
it. This takes a substantial time, but since you need to start Emacs
once a day at most--or once a week if you never log out--the extra time
is not too severe a problem.
You can specify additional files to preload by writing a library
named `site-load.el' that loads them. You may need to add a definition
#define SITELOAD_PURESIZE_EXTRA N
to make N added bytes of pure space to hold the additional files. (Try
adding increments of 20000 until it is big enough.) However, the
advantage of preloading additional files decreases as machines get
faster. On modern machines, it is usually not advisable.
After `loadup.el' reads `site-load.el', it finds the documentation
strings for primitive and preloaded functions (and variables) in the
file `etc/DOC' where they are stored, by calling `Snarf-documentation'
(*note Accessing Documentation::).
You can specify other Lisp expressions to execute just before dumping
by putting them in a library named `site-init.el'. This file is
executed after the documentation strings are found.
If you want to preload function or variable definitions, there are
three ways you can do this and make their documentation strings
accessible when you subsequently run Emacs:
* Arrange to scan these files when producing the `etc/DOC' file, and
load them with `site-load.el'.
* Load the files with `site-init.el', then copy the files into the
installation directory for Lisp files when you install Emacs.
* Specify a non-`nil' value for `byte-compile-dynamic-docstrings' as
a local variable in each of these files, and load them with either
`site-load.el' or `site-init.el'. (This method has the drawback
that the documentation strings take up space in Emacs all the
time.)
It is not advisable to put anything in `site-load.el' or
`site-init.el' that would alter any of the features that users expect
in an ordinary unmodified Emacs. If you feel you must override normal
features for your site, do it with `default.el', so that users can
override your changes if they wish. *Note Startup Summary::.
- Function: dump-emacs to-file from-file
This function dumps the current state of Emacs into an executable
file TO-FILE. It takes symbols from FROM-FILE (this is normally
the executable file `temacs').
If you want to use this function in an Emacs that was already
dumped, you must run Emacs with `-batch'.
Pure Storage
============
Emacs Lisp uses two kinds of storage for user-created Lisp objects:
"normal storage" and "pure storage". Normal storage is where all the
new data created during an Emacs session are kept; see the following
section for information on normal storage. Pure storage is used for
certain data in the preloaded standard Lisp files--data that should
never change during actual use of Emacs.
Pure storage is allocated only while `temacs' is loading the
standard preloaded Lisp libraries. In the file `emacs', it is marked
as read-only (on operating systems that permit this), so that the
memory space can be shared by all the Emacs jobs running on the machine
at once. Pure storage is not expandable; a fixed amount is allocated
when Emacs is compiled, and if that is not sufficient for the preloaded
libraries, `temacs' crashes. If that happens, you must increase the
compilation parameter `PURESIZE' in the file `src/puresize.h'. This
normally won't happen unless you try to preload additional libraries or
add features to the standard ones.
- Function: purecopy object
This function makes a copy in pure storage of OBJECT, and returns
it. It copies a string by simply making a new string with the same
characters in pure storage. It recursively copies the contents of
vectors and cons cells. It does not make copies of other objects
such as symbols, but just returns them unchanged. It signals an
error if asked to copy markers.
This function is a no-op except while Emacs is being built and
dumped; it is usually called only in the file
`emacs/lisp/loaddefs.el', but a few packages call it just in case
you decide to preload them.
- Variable: pure-bytes-used
The value of this variable is the number of bytes of pure storage
allocated so far. Typically, in a dumped Emacs, this number is
very close to the total amount of pure storage available--if it
were not, we would preallocate less.
- Variable: purify-flag
This variable determines whether `defun' should make a copy of the
function definition in pure storage. If it is non-`nil', then the
function definition is copied into pure storage.
This flag is `t' while loading all of the basic functions for
building Emacs initially (allowing those functions to be sharable
and non-collectible). Dumping Emacs as an executable always writes
`nil' in this variable, regardless of the value it actually has
before and after dumping.
You should not change this flag in a running Emacs.
Garbage Collection
==================
When a program creates a list or the user defines a new function
(such as by loading a library), that data is placed in normal storage.
If normal storage runs low, then Emacs asks the operating system to
allocate more memory in blocks of 1k bytes. Each block is used for one
type of Lisp object, so symbols, cons cells, markers, etc., are
segregated in distinct blocks in memory. (Vectors, long strings,
buffers and certain other editing types, which are fairly large, are
allocated in individual blocks, one per object, while small strings are
packed into blocks of 8k bytes.)
It is quite common to use some storage for a while, then release it
by (for example) killing a buffer or deleting the last pointer to an
object. Emacs provides a "garbage collector" to reclaim this abandoned
storage. (This name is traditional, but "garbage recycler" might be a
more intuitive metaphor for this facility.)
The garbage collector operates by finding and marking all Lisp
objects that are still accessible to Lisp programs. To begin with, it
assumes all the symbols, their values and associated function
definitions, and any data presently on the stack, are accessible. Any
objects that can be reached indirectly through other accessible objects
are also accessible.
When marking is finished, all objects still unmarked are garbage. No
matter what the Lisp program or the user does, it is impossible to refer
to them, since there is no longer a way to reach them. Their space
might as well be reused, since no one will miss them. The second
("sweep") phase of the garbage collector arranges to reuse them.
The sweep phase puts unused cons cells onto a "free list" for future
allocation; likewise for symbols and markers. It compacts the
accessible strings so they occupy fewer 8k blocks; then it frees the
other 8k blocks. Vectors, buffers, windows, and other large objects are
individually allocated and freed using `malloc' and `free'.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call
the garbage collector when the free list is empty. Instead, it
simply requests the operating system to allocate more storage, and
processing continues until `gc-cons-threshold' bytes have been
used.
This means that you can make sure that the garbage collector will
not run during a certain portion of a Lisp program by calling the
garbage collector explicitly just before it (provided that portion
of the program does not use so much space as to force a second
garbage collection).
- Command: garbage-collect
This command runs a garbage collection, and returns information on
the amount of space in use. (Garbage collection can also occur
spontaneously if you use more than `gc-cons-threshold' bytes of
Lisp data since the previous garbage collection.)
`garbage-collect' returns a list containing the following
information:
((USED-CONSES . FREE-CONSES)
(USED-SYMS . FREE-SYMS)
(USED-MISCS . FREE-MISCS)
USED-STRING-CHARS
USED-VECTOR-SLOTS
(USED-FLOATS . FREE-FLOATS)
(USED-INTERVALS . FREE-INTERVALS)
(USED-STRINGS . FREE-STRINGS))
Here is an example:
(garbage-collect)
=> ((106886 . 13184) (9769 . 0)
(7731 . 4651) 347543 121628
(31 . 94) (1273 . 168)
(25474 . 3569))
Here is a table explaining each element:
USED-CONSES
The number of cons cells in use.
FREE-CONSES
The number of cons cells for which space has been obtained
from the operating system, but that are not currently being
used.
USED-SYMS
The number of symbols in use.
FREE-SYMS
The number of symbols for which space has been obtained from
the operating system, but that are not currently being used.
USED-MISCS
The number of miscellaneous objects in use. These include
markers and overlays, plus certain objects not visible to
users.
FREE-MISCS
The number of miscellaneous objects for which space has been
obtained from the operating system, but that are not
currently being used.
USED-STRING-CHARS
The total size of all strings, in characters.
USED-VECTOR-SLOTS
The total number of elements of existing vectors.
USED-FLOATS
The number of floats in use.
FREE-FLOATS
The number of floats for which space has been obtained from
the operating system, but that are not currently being used.
USED-INTERVALS
The number of intervals in use. Intervals are an internal
data structure used for representing text properties.
FREE-INTERVALS
The number of intervals for which space has been obtained
from the operating system, but that are not currently being
used.
USED-STRINGS
The number of strings in use.
FREE-STRINGS
The number of string headers for which the space was obtained
from the operating system, but which are currently not in
use. (A string object consists of a header and the storage
for the string text itself; the latter is only allocated when
the string is created.)
- User Option: garbage-collection-messages
If this variable is non-`nil', Emacs displays a message at the
beginning and end of garbage collection. The default value is
`nil', meaning there are no such messages.
- User Option: gc-cons-threshold
The value of this variable is the number of bytes of storage that
must be allocated for Lisp objects after one garbage collection in
order to trigger another garbage collection. A cons cell counts
as eight bytes, a string as one byte per character plus a few
bytes of overhead, and so on; space allocated to the contents of
buffers does not count. Note that the subsequent garbage
collection does not happen immediately when the threshold is
exhausted, but only the next time the Lisp evaluator is called.
The initial threshold value is 400,000. If you specify a larger
value, garbage collection will happen less often. This reduces the
amount of time spent garbage collecting, but increases total
memory use. You may want to do this when running a program that
creates lots of Lisp data.
You can make collections more frequent by specifying a smaller
value, down to 10,000. A value less than 10,000 will remain in
effect only until the subsequent garbage collection, at which time
`garbage-collect' will set the threshold back to 10,000.
The value return by `garbage-collect' describes the amount of memory
used by Lisp data, broken down by data type. By contrast, the function
`memory-limit' provides information on the total amount of memory Emacs
is currently using.
- Function: memory-limit
This function returns the address of the last byte Emacs has
allocated, divided by 1024. We divide the value by 1024 to make
sure it fits in a Lisp integer.
You can use this to get a general idea of how your actions affect
the memory usage.
Memory Usage
============
These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
`(garbage-collect)'; those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.
- Variable: cons-cells-consed
The total number of cons cells that have been allocated so far in
this Emacs session.
- Variable: floats-consed
The total number of floats that have been allocated so far in this
Emacs session.
- Variable: vector-cells-consed
The total number of vector cells that have been allocated so far
in this Emacs session.
- Variable: symbols-consed
The total number of symbols that have been allocated so far in
this Emacs session.
- Variable: string-chars-consed
The total number of string characters that have been allocated so
far in this Emacs session.
- Variable: misc-objects-consed
The total number of miscellaneous objects that have been allocated
so far in this Emacs session. These include markers and overlays,
plus certain objects not visible to users.
- Variable: intervals-consed
The total number of intervals that have been allocated so far in
this Emacs session.
- Variable: strings-consed
The total number of strings that have been allocated so far in this
Emacs session.
Writing Emacs Primitives
========================
Lisp primitives are Lisp functions implemented in C. The details of
interfacing the C function so that Lisp can call it are handled by a few
C macros. The only way to really understand how to write new C code is
to read the source, but we can explain some things here.
An example of a special form is the definition of `or', from
`eval.c'. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
"Eval args until one of them yields non-nil; return that value.\n\
The remaining args are not evalled at all.\n\
If all args return nil, return nil.")
(args)
Lisp_Object args;
{
register Lisp_Object val;
Lisp_Object args_left;
struct gcpro gcpro1;
if (NILP (args))
return Qnil;
args_left = args;
GCPRO1 (args_left);
do
{
val = Feval (Fcar (args_left));
if (!NILP (val))
break;
args_left = Fcdr (args_left);
}
while (!NILP (args_left));
UNGCPRO;
return val;
}
Let's start with a precise explanation of the arguments to the
`DEFUN' macro. Here is a template for them:
DEFUN (LNAME, FNAME, SNAME, MIN, MAX, INTERACTIVE, DOC)
LNAME
This is the name of the Lisp symbol to define as the function
name; in the example above, it is `or'.
FNAME
This is the C function name for this function. This is the name
that is used in C code for calling the function. The name is, by
convention, `F' prepended to the Lisp name, with all dashes (`-')
in the Lisp name changed to underscores. Thus, to call this
function from C code, call `For'. Remember that the arguments must
be of type `Lisp_Object'; various macros and functions for creating
values of type `Lisp_Object' are declared in the file `lisp.h'.
SNAME
This is a C variable name to use for a structure that holds the
data for the subr object that represents the function in Lisp.
This structure conveys the Lisp symbol name to the initialization
routine that will create the symbol and store the subr object as
its definition. By convention, this name is always FNAME with `F'
replaced with `S'.
MIN
This is the minimum number of arguments that the function
requires. The function `or' allows a minimum of zero arguments.
MAX
This is the maximum number of arguments that the function accepts,
if there is a fixed maximum. Alternatively, it can be `UNEVALLED',
indicating a special form that receives unevaluated arguments, or
`MANY', indicating an unlimited number of evaluated arguments (the
equivalent of `&rest'). Both `UNEVALLED' and `MANY' are macros.
If MAX is a number, it may not be less than MIN and it may not be
greater than seven.
INTERACTIVE
This is an interactive specification, a string such as might be
used as the argument of `interactive' in a Lisp function. In the
case of `or', it is 0 (a null pointer), indicating that `or'
cannot be called interactively. A value of `""' indicates a
function that should receive no arguments when called
interactively.
DOC
This is the documentation string. It is written just like a
documentation string for a function defined in Lisp, except you
must write `\n\' at the end of each line. In particular, the
first line should be a single sentence.
After the call to the `DEFUN' macro, you must write the argument
name list that every C function must have, followed by ordinary C
declarations for the arguments. For a function with a fixed maximum
number of arguments, declare a C argument for each Lisp argument, and
give them all type `Lisp_Object'. When a Lisp function has no upper
limit on the number of arguments, its implementation in C actually
receives exactly two arguments: the first is the number of Lisp
arguments, and the second is the address of a block containing their
values. They have types `int' and `Lisp_Object *'.
Within the function `For' itself, note the use of the macros
`GCPRO1' and `UNGCPRO'. `GCPRO1' is used to "protect" a variable from
garbage collection--to inform the garbage collector that it must look
in that variable and regard its contents as an accessible object. This
is necessary whenever you call `Feval' or anything that can directly or
indirectly call `Feval'. At such a time, any Lisp object that you
intend to refer to again must be protected somehow. `UNGCPRO' cancels
the protection of the variables that are protected in the current
function. It is necessary to do this explicitly.
For most data types, it suffices to protect at least one pointer to
the object; as long as the object is not recycled, all pointers to it
remain valid. This is not so for strings, because the garbage collector
can move them. When the garbage collector moves a string, it relocates
all the pointers it knows about; any other pointers become invalid.
Therefore, you must protect all pointers to strings across any point
where garbage collection may be possible.
The macro `GCPRO1' protects just one local variable. If you want to
protect two, use `GCPRO2' instead; repeating `GCPRO1' will not work.
Macros `GCPRO3' and `GCPRO4' also exist.
These macros implicitly use local variables such as `gcpro1'; you
must declare these explicitly, with type `struct gcpro'. Thus, if you
use `GCPRO2', you must declare `gcpro1' and `gcpro2'. Alas, we can't
explain all the tricky details here.
You must not use C initializers for static or global variables unless
the variables are never written once Emacs is dumped. These variables
with initializers are allocated in an area of memory that becomes
read-only (on certain operating systems) as a result of dumping Emacs.
*Note Pure Storage::.
Do not use static variables within functions--place all static
variables at top level in the file. This is necessary because Emacs on
some operating systems defines the keyword `static' as a null macro.
(This definition is used because those systems put all variables
declared static in a place that becomes read-only after dumping, whether
they have initializers or not.)
Defining the C function is not enough to make a Lisp primitive
available; you must also create the Lisp symbol for the primitive and
store a suitable subr object in its function cell. The code looks like
this:
defsubr (&SUBR-STRUCTURE-NAME);
Here SUBR-STRUCTURE-NAME is the name you used as the third argument to
`DEFUN'.
If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
`syms_of_SOMETHING', and add the call to `defsubr' there. If the file
doesn't have this function, or if you create a new file, add to it a
`syms_of_FILENAME' (e.g., `syms_of_myfile'). Then find the spot in
`emacs.c' where all of these functions are called, and add a call to
`syms_of_FILENAME' there.
The function `syms_of_FILENAME' is also the place to define any C
variables that are to be visible as Lisp variables. `DEFVAR_LISP'
makes a C variable of type `Lisp_Object' visible in Lisp. `DEFVAR_INT'
makes a C variable of type `int' visible in Lisp with a value that is
always an integer. `DEFVAR_BOOL' makes a C variable of type `int'
visible in Lisp with a value that is either `t' or `nil'. Note that
variables defined with `DEFVAR_BOOL' are automatically added to the list
`byte-boolean-vars' used by the byte compiler.
If you define a file-scope C variable of type `Lisp_Object', you
must protect it from garbage-collection by calling `staticpro' in
`syms_of_FILENAME', like this:
staticpro (&VARIABLE);
Here is another example function, with more complicated arguments.
This comes from the code in `window.c', and it demonstrates the use of
macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2,
"xSpecify coordinate pair: \nXExpression which evals to window: ",
"Return non-nil if COORDINATES is in WINDOW.\n\
COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
...
If they are on the border between WINDOW and its right sibling,\n\
`vertical-line' is returned.")
(coordinates, window)
register Lisp_Object coordinates, window;
{
int x, y;
CHECK_LIVE_WINDOW (window, 0);
CHECK_CONS (coordinates, 1);
x = XINT (Fcar (coordinates));
y = XINT (Fcdr (coordinates));
switch (coordinates_in_window (XWINDOW (window), &x, &y))
{
case 0: /* NOT in window at all. */
return Qnil;
case 1: /* In text part of window. */
return Fcons (make_number (x), make_number (y));
case 2: /* In mode line of window. */
return Qmode_line;
case 3: /* On right border of window. */
return Qvertical_line;
default:
abort ();
}
}
Note that C code cannot call functions by name unless they are
defined in C. The way to call a function written in Lisp is to use
`Ffuncall', which embodies the Lisp function `funcall'. Since the Lisp
function `funcall' accepts an unlimited number of arguments, in C it
takes two: the number of Lisp-level arguments, and a one-dimensional
array containing their values. The first Lisp-level argument is the
Lisp function to call, and the rest are the arguments to pass to it.
Since `Ffuncall' can call the evaluator, you must protect pointers from
garbage collection around the call to `Ffuncall'.
The C functions `call0', `call1', `call2', and so on, provide handy
ways to call a Lisp function conveniently with a fixed number of
arguments. They work by calling `Ffuncall'.
`eval.c' is a very good file to look through for examples; `lisp.h'
contains the definitions for some important macros and functions.
If you define a function which is side-effect free, update the code
in `byte-opt.el' which binds `side-effect-free-fns' and
`side-effect-and-error-free-fns' to include it. This will help the
optimizer.
Object Internals
================
GNU Emacs Lisp manipulates many different types of data. The actual
data are stored in a heap and the only access that programs have to it
is through pointers. Pointers are thirty-two bits wide in most
implementations. Depending on the operating system and type of machine
for which you compile Emacs, twenty-eight bits are used to address the
object, and the remaining four bits are used for a GC mark bit and the
tag that identifies the object's type.
Because Lisp objects are represented as tagged pointers, it is always
possible to determine the Lisp data type of any object. The C data type
`Lisp_Object' can hold any Lisp object of any data type. Ordinary
variables have type `Lisp_Object', which means they can hold any type
of Lisp value; you can determine the actual data type only at run time.
The same is true for function arguments; if you want a function to
accept only a certain type of argument, you must check the type
explicitly using a suitable predicate (*note Type Predicates::).
Buffer Internals
----------------
Buffers contain fields not directly accessible by the Lisp
programmer. We describe them here, naming them by the names used in
the C code. Many are accessible indirectly in Lisp programs via Lisp
primitives.
Two structures are used to represent buffers in C. The
`buffer_text' structure contains fields describing the text of a
buffer; the `buffer' structure holds other fields. In the case of
indirect buffers, two or more `buffer' structures reference the same
`buffer_text' structure.
Here is a list of the `struct buffer_text' fields:
`beg'
This field contains the actual address of the buffer contents.
`gpt'
This holds the character position of the gap in the buffer.
`z'
This field contains the character position of the end of the buffer
text.
`gpt_byte'
Contains the byte position of the gap.
`z_byte'
Holds the byte position of the end of the buffer text.
`gap_size'
Contains the size of buffer's gap.
`modiff'
This field counts buffer-modification events for this buffer. It
is incremented for each such event, and never otherwise changed.
`save_modiff'
Contains the previous value of `modiff', as of the last time a
buffer was visited or saved in a file.
`overlay_modiff'
Counts modifications to overlays analogous to `modiff'.
`beg_unchanged'
Holds the number of characters at the start of the text that are
known to be unchanged since the last redisplay that finished.
`end_unchanged'
Holds the number of characters at the end of the text that are
known to be unchanged since the last redisplay that finished.
`unchanged_modified'
Contains the value of `modiff' at the time of the last redisplay
that finished. If this value matches `modiff', `beg_unchanged'
and `end_unchanged' contain no useful information.
`overlay_unchanged_modified'
Contains the value of `overlay_modiff' at the time of the last
redisplay that finished. If this value matches `overlay_modiff',
`beg_unchanged' and `end_unchanged' contain no useful information.
`markers'
The markers that refer to this buffer. This is actually a single
marker, and successive elements in its marker `chain' are the other
markers referring to this buffer text.
`intervals'
Contains the interval tree which records the text properties of
this buffer.
The fields of `struct buffer' are:
`next'
Points to the next buffer, in the chain of all buffers including
killed buffers. This chain is used only for garbage collection,
in order to collect killed buffers properly. Note that vectors,
and most kinds of objects allocated as vectors, are all on one
chain, but buffers are on a separate chain of their own.
`own_text'
This is a `struct buffer_text' structure. In an ordinary buffer,
it holds the buffer contents. In indirect buffers, this field is
not used.
`text'
This points to the `buffer_text' structure that is used for this
buffer. In an ordinary buffer, this is the `own_text' field above.
In an indirect buffer, this is the `own_text' field of the base
buffer.
`pt'
Contains the character position of point in a buffer.
`pt_byte'
Contains the byte position of point in a buffer.
`begv'
This field contains the character position of the beginning of the
accessible range of text in the buffer.
`begv_byte'
This field contains the byte position of the beginning of the
accessible range of text in the buffer.
`zv'
This field contains the character position of the end of the
accessible range of text in the buffer.
`zv_byte'
This field contains the byte position of the end of the accessible
range of text in the buffer.
`base_buffer'
In an indirect buffer, this points to the base buffer. In an
ordinary buffer, it is null.
`local_var_flags'
This field contains flags indicating that certain variables are
local in this buffer. Such variables are declared in the C code
using `DEFVAR_PER_BUFFER', and their buffer-local bindings are
stored in fields in the buffer structure itself. (Some of these
fields are described in this table.)
`modtime'
This field contains the modification time of the visited file. It
is set when the file is written or read. Before writing the
buffer into a file, this field is compared to the modification
time of the file to see if the file has changed on disk. *Note
Buffer Modification::.
`auto_save_modified'
This field contains the time when the buffer was last auto-saved.
`auto_save_failure_time'
The time at which we detected a failure to auto-save, or -1 if we
didn't have a failure.
`last_window_start'
This field contains the `window-start' position in the buffer as of
the last time the buffer was displayed in a window.
`clip_changed'
This flag is set when narrowing changes in a buffer.
`prevent_redisplay_optimizations_p'
this flag indicates that redisplay optimizations should not be used
to display this buffer.
`undo_list'
This field points to the buffer's undo list. *Note Undo::.
`name'
The buffer name is a string that names the buffer. It is
guaranteed to be unique. *Note Buffer Names::.
`filename'
The name of the file visited in this buffer, or `nil'.
`directory'
The directory for expanding relative file names.
`save_length'
Length of the file this buffer is visiting, when last read or
saved. This and other fields concerned with saving are not kept
in the `buffer_text' structure because indirect buffers are never
saved.
`auto_save_file_name'
File name used for auto-saving this buffer. This is not in the
`buffer_text' because it's not used in indirect buffers at all.
`read_only'
Non-`nil' means this buffer is read-only.
`mark'
This field contains the mark for the buffer. The mark is a marker,
hence it is also included on the list `markers'. *Note The Mark::.
`local_var_alist'
This field contains the association list describing the
buffer-local variable bindings of this buffer, not including the
built-in buffer-local bindings that have special slots in the
buffer object. (Those slots are omitted from this table.) *Note
Buffer-Local Variables::.
`major_mode'
Symbol naming the major mode of this buffer, e.g., `lisp-mode'.
`mode_name'
Pretty name of major mode, e.g., `"Lisp"'.
`mode_line_format'
Mode line element that controls the format of the mode line. If
this is `nil', no mode line will be displayed.
`header_line_format'
This field is analoguous to `mode_line_format' for the mode line
displayed at the top of windows.
`keymap'
This field holds the buffer's local keymap. *Note Keymaps::.
`abbrev_table'
This buffer's local abbrevs.
`syntax_table'
This field contains the syntax table for the buffer. *Note Syntax
Tables::.
`category_table'
This field contains the category table for the buffer.
`case_fold_search'
The value of `case-fold-search' in this buffer.
`tab_width'
The value of `tab-width' in this buffer.
`fill_column'
The value of `fill-column' in this buffer.
`left_margin'
The value of `left-margin' in this buffer.
`auto_fill_function'
The value of `auto-fill-function' in this buffer.
`downcase_table'
This field contains the conversion table for converting text to
lower case. *Note Case Tables::.
`upcase_table'
This field contains the conversion table for converting text to
upper case. *Note Case Tables::.
`case_canon_table'
This field contains the conversion table for canonicalizing text
for case-folding search. *Note Case Tables::.
`case_eqv_table'
This field contains the equivalence table for case-folding search.
*Note Case Tables::.
`truncate_lines'
The value of `truncate-lines' in this buffer.
`ctl_arrow'
The value of `ctl-arrow' in this buffer.
`selective_display'
The value of `selective-display' in this buffer.
`selective_display_ellipsis'
The value of `selective-display-ellipsis' in this buffer.
`minor_modes'
An alist of the minor modes of this buffer.
`overwrite_mode'
The value of `overwrite_mode' in this buffer.
`abbrev_mode'
The value of `abbrev-mode' in this buffer.
`display_table'
This field contains the buffer's display table, or `nil' if it
doesn't have one. *Note Display Tables::.
`save_modified'
This field contains the time when the buffer was last saved, as an
integer. *Note Buffer Modification::.
`mark_active'
This field is non-`nil' if the buffer's mark is active.
`overlays_before'
This field holds a list of the overlays in this buffer that end at
or before the current overlay center position. They are sorted in
order of decreasing end position.
`overlays_after'
This field holds a list of the overlays in this buffer that end
after the current overlay center position. They are sorted in
order of increasing beginning position.
`overlay_center'
This field holds the current overlay center position. *Note
Overlays::.
`enable_multibyte_characters'
This field holds the buffer's local value of
`enable-multibyte-characters'--either `t' or `nil'.
`buffer_file_coding_system'
The value of `buffer-file-coding-system' in this buffer.
`file_format'
The value of `buffer-file-format' in this buffer.
`pt_marker'
In an indirect buffer, or a buffer that is the base of an indirect
buffer, this holds a marker that records point for this buffer
when the buffer is not current.
`begv_marker'
In an indirect buffer, or a buffer that is the base of an indirect
buffer, this holds a marker that records `begv' for this buffer
when the buffer is not current.
`zv_marker'
In an indirect buffer, or a buffer that is the base of an indirect
buffer, this holds a marker that records `zv' for this buffer when
the buffer is not current.
`file_truename'
The truename of the visited file, or `nil'.
`invisibility_spec'
The value of `buffer-invisibility-spec' in this buffer.
`last_selected_window'
This is the last window that was selected with this buffer in it,
or `nil' if that window no longer displays this buffer.
`display_count'
This field is incremented each time the buffer is displayed in a
window.
`left_margin_width'
The value of `left-margin-width' in this buffer.
`right_margin_width'
The value of `right-margin-width' in this buffer.
`indicate_empty_lines'
Non-`nil' means indicate empty lines (lines with no text) with a
small bitmap in the fringe, when using a window system that can do
it.
`display_time'
This holds a time stamp that is updated each time this buffer is
displayed in a window.
`scroll_up_aggressively'
The value of `scroll-up-aggressively' in this buffer.
`scroll_down_aggressively'
The value of `scroll-down-aggressively' in this buffer.
Window Internals
----------------
Windows have the following accessible fields:
`frame'
The frame that this window is on.
`mini_p'
Non-`nil' if this window is a minibuffer window.
`parent'
Internally, Emacs arranges windows in a tree; each group of
siblings has a parent window whose area includes all the siblings.
This field points to a window's parent.
Parent windows do not display buffers, and play little role in
display except to shape their child windows. Emacs Lisp programs
usually have no access to the parent windows; they operate on the
windows at the leaves of the tree, which actually display buffers.
The following four fields also describe the window tree structure.
`hchild'
In a window subdivided horizontally by child windows, the leftmost
child. Otherwise, `nil'.
`vchild'
In a window subdivided vertically by child windows, the topmost
child. Otherwise, `nil'.
`next'
The next sibling of this window. It is `nil' in a window that is
the rightmost or bottommost of a group of siblings.
`prev'
The previous sibling of this window. It is `nil' in a window that
is the leftmost or topmost of a group of siblings.
`left'
This is the left-hand edge of the window, measured in columns.
(The leftmost column on the screen is column 0.)
`top'
This is the top edge of the window, measured in lines. (The top
line on the screen is line 0.)
`height'
The height of the window, measured in lines.
`width'
The width of the window, measured in columns. This width includes
the scroll bar and fringes, and/or the separator line on the right
of the window (if any).
`buffer'
The buffer that the window is displaying. This may change often
during the life of the window.
`start'
The position in the buffer that is the first character to be
displayed in the window.
`pointm'
This is the value of point in the current buffer when this window
is selected; when it is not selected, it retains its previous
value.
`force_start'
If this flag is non-`nil', it says that the window has been
scrolled explicitly by the Lisp program. This affects what the
next redisplay does if point is off the screen: instead of
scrolling the window to show the text around point, it moves point
to a location that is on the screen.
`frozen_window_start_p'
This field is set temporarily to 1 to indicate to redisplay that
`start' of this window should not be changed, even if point gets
invisible.
`start_at_line_beg'
Non-`nil' means current value of `start' was the beginning of a
line when it was chosen.
`too_small_ok'
Non-`nil' means don't delete this window for becoming "too small".
`height_fixed_p'
This field is temporarily set to 1 to fix the height of the
selected window when the echo area is resized.
`use_time'
This is the last time that the window was selected. The function
`get-lru-window' uses this field.
`sequence_number'
A unique number assigned to this window when it was created.
`last_modified'
The `modiff' field of the window's buffer, as of the last time a
redisplay completed in this window.
`last_overlay_modified'
The `overlay_modiff' field of the window's buffer, as of the last
time a redisplay completed in this window.
`last_point'
The buffer's value of point, as of the last time a redisplay
completed in this window.
`last_had_star'
A non-`nil' value means the window's buffer was "modified" when the
window was last updated.
`vertical_scroll_bar'
This window's vertical scroll bar.
`left_margin_width'
The width of the left margin in this window, or `nil' not to
specify it (in which case the buffer's value of `left-margin-width'
is used.
`right_margin_width'
Likewise for the right margin.
`window_end_pos'
This is computed as `z' minus the buffer position of the last glyph
in the current matrix of the window. The value is only valid if
`window_end_valid' is not `nil'.
`window_end_bytepos'
The byte position corresponding to `window_end_pos'.
`window_end_vpos'
The window-relative vertical position of the line containing
`window_end_pos'.
`window_end_valid'
This field is set to a non-`nil' value if `window_end_pos' is truly
valid. This is `nil' if nontrivial redisplay is preempted since
in that case the display that `window_end_pos' was computed for
did not get onto the screen.
`redisplay_end_trigger'
If redisplay in this window goes beyond this buffer position, it
runs run the `redisplay-end-trigger-hook'.
`cursor'
A structure describing where the cursor is in this window.
`last_cursor'
The value of `cursor' as of the last redisplay that finished.
`phys_cursor'
A structure describing where the cursor of this window physically
is.
`phys_cursor_type'
The type of cursor that was last displayed on this window.
`phys_cursor_on_p'
This field is non-zero if the cursor is physically on.
`cursor_off_p'
Non-zero means the cursor in this window is logically on.
`last_cursor_off_p'
This field contains the value of `cursor_off_p' as of the time of
the last redisplay.
`must_be_updated_p'
This is set to 1 during redisplay when this window must be updated.
`hscroll'
This is the number of columns that the display in the window is
scrolled horizontally to the left. Normally, this is 0.
`vscroll'
Vertical scroll amount, in pixels. Normally, this is 0.
`dedicated'
Non-`nil' if this window is dedicated to its buffer.
`display_table'
The window's display table, or `nil' if none is specified for it.
`update_mode_line'
Non-`nil' means this window's mode line needs to be updated.
`base_line_number'
The line number of a certain position in the buffer, or `nil'.
This is used for displaying the line number of point in the mode
line.
`base_line_pos'
The position in the buffer for which the line number is known, or
`nil' meaning none is known.
`region_showing'
If the region (or part of it) is highlighted in this window, this
field holds the mark position that made one end of that region.
Otherwise, this field is `nil'.
`column_number_displayed'
The column number currently displayed in this window's mode line,
or `nil' if column numbers are not being displayed.
`current_matrix'
A glyph matrix describing the current display of this window.
`desired_matrix'
A glyph matrix describing the desired display of this window.
Process Internals
-----------------
The fields of a process are:
`name'
A string, the name of the process.
`command'
A list containing the command arguments that were used to start
this process.
`filter'
A function used to accept output from the process instead of a
buffer, or `nil'.
`sentinel'
A function called whenever the process receives a signal, or `nil'.
`buffer'
The associated buffer of the process.
`pid'
An integer, the Unix process ID.
`childp'
A flag, non-`nil' if this is really a child process. It is `nil'
for a network connection.
`mark'
A marker indicating the position of the end of the last output
from this process inserted into the buffer. This is often but not
always the end of the buffer.
`kill_without_query'
If this is non-`nil', killing Emacs while this process is still
running does not ask for confirmation about killing the process.
`raw_status_low'
`raw_status_high'
These two fields record 16 bits each of the process status
returned by the `wait' system call.
`status'
The process status, as `process-status' should return it.
`tick'
`update_tick'
If these two fields are not equal, a change in the status of the
process needs to be reported, either by running the sentinel or by
inserting a message in the process buffer.
`pty_flag'
Non-`nil' if communication with the subprocess uses a PTY; `nil'
if it uses a pipe.
`infd'
The file descriptor for input from the process.
`outfd'
The file descriptor for output to the process.
`subtty'
The file descriptor for the terminal that the subprocess is using.
(On some systems, there is no need to record this, so the value is
`nil'.)
`tty_name'
The name of the terminal that the subprocess is using, or `nil' if
it is using pipes.
`decode_coding_system'
Coding-system for decoding the input from this process.
`decoding_buf'
A working buffer for decoding.
`decoding_carryover'
Size of carryover in decoding.
`encode_coding_system'
Coding-system for encoding the output to this process.
`encoding_buf'
A working buffer for enecoding.
`encoding_carryover'
Size of carryover in encoding.
`inherit_coding_system_flag'
Flag to set `coding-system' of the process buffer from the coding
system used to decode process output.
Standard Errors
***************
Here is the complete list of the error symbols in standard Emacs,
grouped by concept. The list includes each symbol's message (on the
`error-message' property of the symbol) and a cross reference to a
description of how the error can occur.
Each error symbol has an `error-conditions' property that is a list
of symbols. Normally this list includes the error symbol itself and
the symbol `error'. Occasionally it includes additional symbols, which
are intermediate classifications, narrower than `error' but broader
than a single error symbol. For example, all the errors in accessing
files have the condition `file-error'. If we do not say here that a
certain error symbol has additional error conditions, that means it has
none.
As a special exception, the error symbol `quit' does not have the
condition `error', because quitting is not considered an error.
*Note Errors::, for an explanation of how errors are generated and
handled.
`SYMBOL'
STRING; REFERENCE.
`error'
`"error"'
*Note Errors::.
`quit'
`"Quit"'
*Note Quitting::.
`args-out-of-range'
`"Args out of range"'
*Note Sequences Arrays Vectors::.
`arith-error'
`"Arithmetic error"'
See `/' and `%' in *Note Numbers::.
`beginning-of-buffer'
`"Beginning of buffer"'
*Note Motion::.
`buffer-read-only'
`"Buffer is read-only"'
*Note Read Only Buffers::.
`coding-system-error'
`"Invalid coding system"'
*Note Coding Systems::.
`cyclic-function-indirection'
`"Symbol's chain of function indirections\
contains a loop"'
*Note Function Indirection::.
`end-of-buffer'
`"End of buffer"'
*Note Motion::.
`end-of-file'
`"End of file during parsing"'
Note that this is not a subcategory of `file-error', because it
pertains to the Lisp reader, not to file I/O. *Note Input
Functions::.
`file-already-exists'
This is a subcategory of `file-error'.
*Note Writing to Files::.
`file-date-error'
This is a subcategory of `file-error'. It occurs when `copy-file'
tries and fails to set the last-modification time of the output
file. *Note Changing Files::.
`file-error'
This error and its subcategories do not have error-strings,
because the error message is constructed from the data items alone
when the error condition `file-error' is present.
*Note Files::.
`file-locked'
This is a subcategory of `file-error'.
*Note File Locks::.
`file-supersession'
This is a subcategory of `file-error'.
*Note Modification Time::.
`ftp-error'
This is a subcategory of `file-error', which results from problems
in accessing a remote file using ftp.
*Note Remote Files: (emacs)Remote Files.
`invalid-function'
`"Invalid function"'
*Note Classifying Lists::.
`invalid-read-syntax'
`"Invalid read syntax"'
*Note Input Functions::.
`invalid-regexp'
`"Invalid regexp"'
*Note Regular Expressions::.
`mark-inactive'
`"Mark inactive"'
*Note The Mark::.
`no-catch'
`"No catch for tag"'
*Note Catch and Throw::.
`scan-error'
`"Scan error"'
This happens when certain syntax-parsing functions find invalid
syntax or mismatched parentheses.
*Note List Motion::, and *Note Parsing Expressions::.
`search-failed'
`"Search failed"'
*Note Searching and Matching::.
`setting-constant'
`"Attempt to set a constant symbol"'
The values of the symbols `nil' and `t', and any symbols that
start with `:', may not be changed.
*Note Variables that Never Change: Constant Variables.
`text-read-only'
`"Text is read-only"'
*Note Special Properties::.
`undefined-color'
`"Undefined color"'
*Note Color Names::.
`void-function'
`"Symbol's function definition is void"'
*Note Function Cells::.
`void-variable'
`"Symbol's value as variable is void"'
*Note Accessing Variables::.
`wrong-number-of-arguments'
`"Wrong number of arguments"'
*Note Classifying Lists::.
`wrong-type-argument'
`"Wrong type argument"'
*Note Type Predicates::.
These kinds of error, which are classified as special cases of
`arith-error', can occur on certain systems for invalid use of
mathematical functions.
`domain-error'
`"Arithmetic domain error"'
*Note Math Functions::.
`overflow-error'
`"Arithmetic overflow error"'
*Note Math Functions::.
`range-error'
`"Arithmetic range error"'
*Note Math Functions::.
`singularity-error'
`"Arithmetic singularity error"'
*Note Math Functions::.
`underflow-error'
`"Arithmetic underflow error"'
*Note Math Functions::.
Buffer-Local Variables
**********************
The table below lists the general-purpose Emacs variables that
automatically become buffer-local in each buffer. Most become
buffer-local only when set; a few of them are always local in every
buffer. Many Lisp packages define such variables for their internal
use, but we don't try to list them all here.
`abbrev-mode'
*Note Abbrevs::.
`auto-fill-function'
*Note Auto Filling::.
`buffer-auto-save-file-name'
*Note Auto-Saving::.
`buffer-backed-up'
*Note Backup Files::.
`buffer-display-count'
*Note Displaying Buffers::.
`buffer-display-table'
*Note Display Tables::.
`buffer-file-coding-system'
*Note Encoding and I/O::.
`buffer-file-format'
*Note Format Conversion::.
`buffer-file-name'
*Note Buffer File Name::.
`buffer-file-number'
*Note Buffer File Name::.
`buffer-file-truename'
*Note Buffer File Name::.
`buffer-file-type'
*Note MS-DOS File Types::.
`buffer-invisibility-spec'
*Note Invisible Text::.
`buffer-offer-save'
*Note Saving Buffers::.
`buffer-read-only'
*Note Read Only Buffers::.
`buffer-saved-size'
*Note Point::.
`buffer-undo-list'
*Note Undo::.
`cache-long-line-scans'
*Note Text Lines::.
`case-fold-search'
*Note Searching and Case::.
`ctl-arrow'
*Note Usual Display::.
`comment-column'
*Note Comments: (emacs)Comments.
`default-directory'
*Note System Environment::.
`defun-prompt-regexp'
*Note List Motion::.
`enable-multibyte-characters'
*Note Non-ASCII Characters::.
`fill-column'
*Note Auto Filling::.
`goal-column'
*Note Moving Point: (emacs)Moving Point.
`header-line-format'
*Note Mode Line Data::.
`indicate-empty-lines'
*Note Usual Display::.
`left-margin'
*Note Indentation::.
`left-margin-width'
*Note Display Margins::.
`local-abbrev-table'
*Note Abbrevs::.
`local-write-file-hooks'
*Note Saving Buffers::.
`major-mode'
*Note Mode Help::.
`mark-active'
*Note The Mark::.
`mark-ring'
*Note The Mark::.
`minor-modes'
*Note Minor Modes::.
`mode-line-buffer-identification'
*Note Mode Line Variables::.
`mode-line-format'
*Note Mode Line Data::.
`mode-line-modified'
*Note Mode Line Variables::.
`mode-line-process'
*Note Mode Line Variables::.
`mode-name'
*Note Mode Line Variables::.
`overwrite-mode'
*Note Insertion::.
`paragraph-separate'
*Note Standard Regexps::.
`paragraph-start'
*Note Standard Regexps::.
`point-before-scroll'
Used for communication between mouse commands and scroll-bar
commands.
`require-final-newline'
*Note Insertion::.
`right-margin-width'
*Note Display Margins::.
`scroll-down-aggressively'
*Note Textual Scrolling::.
`scroll-up-aggressively'
*Note Textual Scrolling::.
`selective-display'
*Note Selective Display::.
`selective-display-ellipses'
*Note Selective Display::.
`tab-width'
*Note Usual Display::.
`truncate-lines'
*Note Truncation::.
`vc-mode'
*Note Mode Line Variables::.
Standard Keymaps
****************
The following symbols are used as the names for various keymaps.
Some of these exist when Emacs is first started, others are loaded only
when their respective mode is used. This is not an exhaustive list.
Almost all of these maps are used as local maps. Indeed, of the
modes that presently exist, only Vip mode and Terminal mode ever change
the global keymap.
`Buffer-menu-mode-map'
A full keymap used by Buffer Menu mode.
`c-mode-map'
A sparse keymap used by C mode.
`command-history-map'
A full keymap used by Command History mode.
`ctl-x-4-map'
A sparse keymap for subcommands of the prefix `C-x 4'.
`ctl-x-5-map'
A sparse keymap for subcommands of the prefix `C-x 5'.
`ctl-x-map'
A full keymap for `C-x' commands.
`debugger-mode-map'
A full keymap used by Debugger mode.
`dired-mode-map'
A full keymap for `dired-mode' buffers.
`edit-abbrevs-map'
A sparse keymap used in `edit-abbrevs'.
`edit-tab-stops-map'
A sparse keymap used in `edit-tab-stops'.
`electric-buffer-menu-mode-map'
A full keymap used by Electric Buffer Menu mode.
`electric-history-map'
A full keymap used by Electric Command History mode.
`emacs-lisp-mode-map'
A sparse keymap used by Emacs Lisp mode.
`facemenu-menu'
The sparse keymap that displays the Text Properties menu.
`facemenu-background-menu'
The sparse keymap that displays the Background Color submenu of
the Text Properties menu.
`facemenu-face-menu'
The sparse keymap that displays the Face submenu of the Text
Properties menu.
`facemenu-foreground-menu'
The sparse keymap that displays the Foreground Color submenu of
the Text Properties menu.
`facemenu-indentation-menu'
The sparse keymap that displays the Indentation submenu of the Text
Properties menu.
`facemenu-justification-menu'
The sparse keymap that displays the Justification submenu of the
Text Properties menu.
`facemenu-special-menu'
The sparse keymap that displays the Special Props submenu of the
Text Properties menu.
`function-key-map'
The keymap for translating keypad and function keys.
If there are none, then it contains an empty sparse keymap. *Note
Translating Input::.
`fundamental-mode-map'
The sparse keymap for Fundamental mode.
It is empty and should not be changed.
`Helper-help-map'
A full keymap used by the help utility package.
It has the same keymap in its value cell and in its function cell.
`Info-edit-map'
A sparse keymap used by the `e' command of Info.
`Info-mode-map'
A sparse keymap containing Info commands.
`isearch-mode-map'
A keymap that defines the characters you can type within
incremental search.
`key-translation-map'
A keymap for translating keys. This one overrides ordinary key
bindings, unlike `function-key-map'. *Note Translating Input::.
`lisp-interaction-mode-map'
A sparse keymap used by Lisp Interaction mode.
`lisp-mode-map'
A sparse keymap used by Lisp mode.
`menu-bar-edit-menu'
The keymap which displays the Edit menu in the menu bar.
`menu-bar-files-menu'
The keymap which displays the Files menu in the menu bar.
`menu-bar-help-menu'
The keymap which displays the Help menu in the menu bar.
`menu-bar-mule-menu'
The keymap which displays the Mule menu in the menu bar.
`menu-bar-search-menu'
The keymap which displays the Search menu in the menu bar.
`menu-bar-tools-menu'
The keymap which displays the Tools menu in the menu bar.
`mode-specific-map'
The keymap for characters following `C-c'. Note, this is in the
global map. This map is not actually mode specific: its name was
chosen to be informative for the user in `C-h b'
(`display-bindings'), where it describes the main use of the `C-c'
prefix key.
`occur-mode-map'
A sparse keymap used by Occur mode.
`query-replace-map'
A sparse keymap used for responses in `query-replace' and related
commands; also for `y-or-n-p' and `map-y-or-n-p'. The functions
that use this map do not support prefix keys; they look up one
event at a time.
`text-mode-map'
A sparse keymap used by Text mode.
`view-mode-map'
A full keymap used by View mode.
Standard Hooks
**************
The following is a list of hook variables that let you provide
functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with `-hook'. They are
"normal hooks", run by means of `run-hooks'. The value of such a hook
is a list of functions; the functions are called with no arguments and
their values are completely ignored. The recommended way to put a new
function on such a hook is to call `add-hook'. *Note Hooks::, for more
information about using hooks.
The variables whose names end in `-hooks' or `-functions' are
usually "abnormal hooks"; their values are lists of functions, but
these functions are called in a special way (they are passed arguments,
or their values are used). A few of these variables are actually normal
hooks which were named before we established the convention that normal
hooks' names should end in `-hook'.
The variables whose names end in `-function' have single functions
as their values. (In older Emacs versions, some of these variables had
names ending in `-hook' even though they were not normal hooks;
however, we have renamed all of those.)
`activate-mark-hook'
`after-change-functions'
`after-init-hook'
`after-insert-file-functions'
`after-make-frame-functions'
`after-revert-hook'
`after-save-hook'
`apropos-mode-hook'
`auto-fill-function'
`auto-save-hook'
`before-change-functions'
`before-init-hook'
`before-make-frame-hook'
`before-revert-hook'
`blink-paren-function'
`buffer-access-fontify-functions'
`c-mode-hook'
`calendar-load-hook'
`change-major-mode-hook'
`command-history-hook'
`command-line-functions'
`comment-indent-function'
`deactivate-mark-hook'
`diary-display-hook'
`diary-hook'
`dired-mode-hook'
`disabled-command-hook'
`echo-area-clear-hook'
`edit-picture-hook'
`electric-buffer-menu-mode-hook'
`electric-command-history-hook'
`electric-help-mode-hook'
`emacs-lisp-mode-hook'
`find-file-hooks'
`find-file-not-found-hooks'
`first-change-hook'
`fortran-comment-hook'
`fortran-mode-hook'
`indent-mim-hook'
`initial-calendar-window-hook'
`kbd-macro-termination-hook'
`kill-buffer-hook'
`kill-buffer-query-functions'
`kill-emacs-hook'
`kill-emacs-query-functions'
`LaTeX-mode-hook'
`ledit-mode-hook'
`lisp-indent-function'
`lisp-interaction-mode-hook'
`lisp-mode-hook'
`list-diary-entries-hook'
`local-write-file-hooks'
`mail-mode-hook'
`mail-setup-hook'
`mark-diary-entries-hook'
`medit-mode-hook'
`menu-bar-update-hook'
`minibuffer-setup-hook'
`minibuffer-exit-hook'
`mouse-position-function'
`news-mode-hook'
`news-reply-mode-hook'
`news-setup-hook'
`nongregorian-diary-listing-hook'
`nongregorian-diary-marking-hook'
`nroff-mode-hook'
`outline-mode-hook'
`plain-TeX-mode-hook'
`post-command-hook'
`pre-abbrev-expand-hook'
`pre-command-hook'
`print-diary-entries-hook'
`prolog-mode-hook'
`protect-innocence-hook'
`redisplay-end-trigger-functions'
`rmail-edit-mode-hook'
`rmail-mode-hook'
`rmail-summary-mode-hook'
`scheme-indent-hook'
`scheme-mode-hook'
`scribe-mode-hook'
`shell-mode-hook'
`shell-set-directory-error-hook'
`suspend-hook'
`suspend-resume-hook'
`temp-buffer-show-function'
`term-setup-hook'
`terminal-mode-hook'
`terminal-mode-break-hook'
`TeX-mode-hook'
`text-mode-hook'
`today-visible-calendar-hook'
`today-invisible-calendar-hook'
`vi-mode-hook'
`view-hook'
`window-configuration-change-hook'
`window-scroll-functions'
`window-setup-hook'
`window-size-change-functions'
`write-contents-hooks'
`write-file-hooks'
`write-region-annotate-functions'
Index
*****
" in printing:
See ``Output Functions''.
" in strings:
See ``Syntax for Strings''.
#$:
See ``Documentation Strings and Compilation''.
#' syntax:
See ``Anonymous Functions''.
#@COUNT:
See ``Documentation Strings and Compilation''.
#COLON read syntax:
See ``Symbol Type''.
#N# read syntax:
See ``Read Syntax for Circular Objects''.
#N= read syntax:
See ``Read Syntax for Circular Objects''.
$ in display:
See ``Truncation''.
$ in regexp:
See ``Special Characters in Regular Expressions''.
%:
See ``Arithmetic Operations''.
% in format:
See ``Formatting Strings''.
& in replacement:
See ``Replacing the Text that Matched''.
&define (Edebug):
See ``Specification List''.
¬ (Edebug):
See ``Specification List''.
&optional:
See ``Other Features of Argument Lists''.
&optional (Edebug):
See ``Specification List''.
&or (Edebug):
See ``Specification List''.
&rest:
See ``Other Features of Argument Lists''.
&rest (Edebug):
See ``Specification List''.
' for quoting:
See ``Quoting''.
( in regexp:
See ``Backslash Constructs in Regular Expressions''.
(...) in lists:
See ``Cons Cell and List Types''.
) in regexp:
See ``Backslash Constructs in Regular Expressions''.
*:
See ``Arithmetic Operations''.
* in interactive:
See ``Using `interactive'''.
* in regexp:
See ``Special Characters in Regular Expressions''.
*scratch*:
See ``How Emacs Chooses a Major Mode''.
+:
See ``Arithmetic Operations''.
+ in regexp:
See ``Special Characters in Regular Expressions''.
, (with Backquote):
See ``Backquote''.
,@ (with Backquote):
See ``Backquote''.
-:
See ``Arithmetic Operations''.
. in lists:
See ``Dotted Pair Notation''.
. in regexp:
See ``Special Characters in Regular Expressions''.
.emacs:
See ``The Init File, `.emacs'''.
/:
See ``Arithmetic Operations''.
/=:
See ``Comparison of Numbers''.
1+:
See ``Arithmetic Operations''.
1-:
See ``Arithmetic Operations''.
2C-mode-map:
See ``Prefix Keys''.
; in comment:
See ``Comments''.
<:
See ``Comparison of Numbers''.
<=:
See ``Comparison of Numbers''.
<ESC>:
See ``Functions for Key Lookup''.
<SPC> in minibuffer:
See ``Reading Text Strings with the Minibuffer''.
<TAB> in minibuffer:
See ``Reading Text Strings with the Minibuffer''.
=:
See ``Comparison of Numbers''.
>:
See ``Comparison of Numbers''.
>=:
See ``Comparison of Numbers''.
? in character constant:
See ``Character Type''.
? in minibuffer:
See ``Reading Text Strings with the Minibuffer''.
? in regexp:
See ``Special Characters in Regular Expressions''.
@ in interactive:
See ``Using `interactive'''.
[ in regexp:
See ``Special Characters in Regular Expressions''.
[...] (Edebug):
See ``Specification List''.
\ in character constant:
See ``Character Type''.
\ in display:
See ``Truncation''.
\ in printing:
See ``Output Functions''.
\ in regexp:
See ``Special Characters in Regular Expressions''.
\ in replacement:
See ``Replacing the Text that Matched''.
\ in strings:
See ``Syntax for Strings''.
\ in symbols:
See ``Symbol Type''.
\' in regexp:
See ``Backslash Constructs in Regular Expressions''.
\< in regexp:
See ``Backslash Constructs in Regular Expressions''.
\= in regexp:
See ``Backslash Constructs in Regular Expressions''.
\> in regexp:
See ``Backslash Constructs in Regular Expressions''.
\` in regexp:
See ``Backslash Constructs in Regular Expressions''.
\a:
See ``Character Type''.
\b:
See ``Character Type''.
\B in regexp:
See ``Backslash Constructs in Regular Expressions''.
\b in regexp:
See ``Backslash Constructs in Regular Expressions''.
\e:
See ``Character Type''.
\f:
See ``Character Type''.
\n:
See ``Character Type''.
\n in print:
See ``Variables Affecting Output''.
\N in replacement:
See ``Replacing the Text that Matched''.
\r:
See ``Character Type''.
\S in regexp:
See ``Backslash Constructs in Regular Expressions''.
\s in regexp:
See ``Backslash Constructs in Regular Expressions''.
\t:
See ``Character Type''.
\v:
See ``Character Type''.
\W in regexp:
See ``Backslash Constructs in Regular Expressions''.
\w in regexp:
See ``Backslash Constructs in Regular Expressions''.
] in regexp:
See ``Special Characters in Regular Expressions''.
^ in regexp:
See ``Special Characters in Regular Expressions''.
`:
See ``Backquote''.
` (list substitution):
See ``Backquote''.
abbrev:
See ``Abbrevs and Abbrev Expansion''.
abbrev table:
See ``Abbrevs and Abbrev Expansion''.
abbrev tables in modes:
See ``Major Mode Conventions''.
abbrev-all-caps:
See ``Looking Up and Expanding Abbreviations''.
abbrev-expansion:
See ``Looking Up and Expanding Abbreviations''.
abbrev-file-name:
See ``Saving Abbrevs in Files''.
abbrev-mode:
See ``Setting Up Abbrev Mode''.
abbrev-prefix-mark:
See ``Looking Up and Expanding Abbreviations''.
abbrev-start-location:
See ``Looking Up and Expanding Abbreviations''.
abbrev-start-location-buffer:
See ``Looking Up and Expanding Abbreviations''.
abbrev-symbol:
See ``Looking Up and Expanding Abbreviations''.
abbrev-table-name-list:
See ``Abbrev Tables''.
abbreviate-file-name:
See ``Directory Names''.
abbrevs-changed:
See ``Saving Abbrevs in Files''.
abnormal hook:
See ``Hooks''.
abort-recursive-edit:
See ``Recursive Editing''.
aborting:
See ``Recursive Editing''.
abs:
See ``Comparison of Numbers''.
absolute file name:
See ``Absolute and Relative File Names''.
accept-process-output:
See ``Accepting Output from Processes''.
access-file:
See ``Testing Accessibility''.
accessibility of a file:
See ``Testing Accessibility''.
accessible portion (of a buffer):
See ``Narrowing''.
accessible-keymaps:
See ``Scanning Keymaps''.
accessing data of mouse events:
See ``Accessing Events''.
acos:
See ``Standard Mathematical Functions''.
activate-mark-hook:
See ``The Mark''.
activating advice:
See ``Activation of Advice''.
active display table:
See ``Active Display Table''.
active keymap:
See ``Active Keymaps''.
active-minibuffer-window:
See ``Minibuffer Miscellany''.
ad-activate:
See ``Activation of Advice''.
ad-activate-all:
See ``Activation of Advice''.
ad-activate-regexp:
See ``Activation of Advice''.
ad-add-advice:
See ``Computed Advice''.
ad-deactivate:
See ``Activation of Advice''.
ad-deactivate-all:
See ``Activation of Advice''.
ad-deactivate-regexp:
See ``Activation of Advice''.
ad-default-compilation-action:
See ``Activation of Advice''.
ad-define-subr-args:
See ``Definition of Subr Argument Lists''.
ad-disable-advice:
See ``Enabling and Disabling Advice''.
ad-disable-regexp:
See ``Enabling and Disabling Advice''.
ad-do-it:
See ``Around-Advice''.
ad-enable-advice:
See ``Enabling and Disabling Advice''.
ad-enable-regexp:
See ``Enabling and Disabling Advice''.
ad-get-arg:
See ``Argument Access in Advice''.
ad-get-args:
See ``Argument Access in Advice''.
ad-return-value:
See ``Defining Advice''.
ad-set-arg:
See ``Argument Access in Advice''.
ad-set-args:
See ``Argument Access in Advice''.
ad-start-advice:
See ``Activation of Advice''.
ad-stop-advice:
See ``Activation of Advice''.
ad-unadvise:
See ``Defining Advice''.
ad-unadvise-all:
See ``Defining Advice''.
ad-update:
See ``Activation of Advice''.
ad-update-all:
See ``Activation of Advice''.
ad-update-regexp:
See ``Activation of Advice''.
Adaptive Fill mode:
See ``Adaptive Fill Mode''.
adaptive-fill-first-line-regexp:
See ``Adaptive Fill Mode''.
adaptive-fill-function:
See ``Adaptive Fill Mode''.
adaptive-fill-mode:
See ``Adaptive Fill Mode''.
adaptive-fill-regexp:
See ``Adaptive Fill Mode''.
add-abbrev:
See ``Defining Abbrevs''.
add-hook:
See ``Hooks''.
add-name-to-file:
See ``Changing File Names and Attributes''.
add-text-properties:
See ``Changing Text Properties''.
add-to-invisibility-spec:
See ``Invisible Text''.
add-to-list:
See ``How to Alter a Variable Value''.
address field of register:
See ``Cons Cell and List Types''.
advice, activating:
See ``Activation of Advice''.
advice, deactivating:
See ``Activation of Advice''.
advice, defining:
See ``Defining Advice''.
advice, enabling and disabling:
See ``Enabling and Disabling Advice''.
advice, preactivating:
See ``Preactivation''.
advising functions:
See ``Advising Emacs Lisp Functions''.
after-advice:
See ``Defining Advice''.
after-change-functions:
See ``Change Hooks''.
after-find-file:
See ``Subroutines of Visiting''.
after-init-hook:
See ``The Init File, `.emacs'''.
after-insert-file-functions:
See ``Saving Text Properties in Files''.
after-load-alist:
See ``Hooks for Loading''.
after-make-frame-functions:
See ``Creating Frames''.
after-revert-hook:
See ``Reverting''.
after-save-hook:
See ``Saving Buffers''.
after-string (overlay property):
See ``Overlay Properties''.
alist:
See ``Association Lists''.
all-christian-calendar-holidays:
See ``Customizing the Holidays''.
all-completions:
See ``Basic Completion Functions''.
all-hebrew-calendar-holidays:
See ``Customizing the Holidays''.
all-islamic-calendar-holidays:
See ``Customizing the Holidays''.
alt characters:
See ``Character Type''.
and:
See ``Constructs for Combining Conditions''.
anonymous function:
See ``Anonymous Functions''.
anonymous lambda expressions (Edebug):
See ``Instrumenting for Edebug''.
apostrophe for quoting:
See ``Quoting''.
append:
See ``Building Cons Cells and Lists''.
append-to-file:
See ``Writing to Files''.
apply:
See ``Calling Functions''.
apply, and debugging:
See ``Internals of the Debugger''.
appt-audible:
See ``Customizing Appointment Reminders''.
appt-delete-window-function:
See ``Customizing Appointment Reminders''.
appt-disp-window-function:
See ``Customizing Appointment Reminders''.
appt-display-duration:
See ``Customizing Appointment Reminders''.
appt-display-mode-line:
See ``Customizing Appointment Reminders''.
appt-message-warning-time:
See ``Customizing Appointment Reminders''.
appt-msg-window:
See ``Customizing Appointment Reminders''.
appt-visible:
See ``Customizing Appointment Reminders''.
apropos:
See ``Help Functions''.
aref:
See ``Functions that Operate on Arrays''.
argument binding:
See ``Other Features of Argument Lists''.
argument descriptors:
See ``Using `interactive'''.
argument evaluation form:
See ``Using `interactive'''.
argument prompt:
See ``Using `interactive'''.
arguments, reading:
See ``Minibuffers''.
arith-error example:
See ``Writing Code to Handle Errors''.
arith-error in division:
See ``Arithmetic Operations''.
arithmetic shift:
See ``Bitwise Operations on Integers''.
around-advice:
See ``Defining Advice''.
array:
See ``Arrays''.
array elements:
See ``Functions that Operate on Arrays''.
arrayp:
See ``Functions that Operate on Arrays''.
ASCII character codes:
See ``Character Type''.
aset:
See ``Functions that Operate on Arrays''.
ash:
See ``Bitwise Operations on Integers''.
asin:
See ``Standard Mathematical Functions''.
ask-user-about-lock:
See ``File Locks''.
ask-user-about-supersession-threat:
See ``Comparison of Modification Time''.
asking the user questions:
See ``Yes-or-No Queries''.
assoc:
See ``Association Lists''.
assoc-default:
See ``Association Lists''.
assoc-ignore-case:
See ``Comparison of Characters and Strings''.
assoc-ignore-representation:
See ``Comparison of Characters and Strings''.
association list:
See ``Association Lists''.
assq:
See ``Association Lists''.
assq-delete-all:
See ``Association Lists''.
asynchronous subprocess:
See ``Creating an Asynchronous Process''.
atan:
See ``Standard Mathematical Functions''.
atom <1>:
See ``Predicates on Lists''.
atom:
See ``Cons Cell and List Types''.
atoms:
See ``Predicates on Lists''.
attributes of text:
See ``Text Properties''.
Auto Fill mode:
See ``Auto Filling''.
auto-coding-regexp-alist:
See ``Default Coding Systems''.
auto-fill-chars:
See ``Auto Filling''.
auto-fill-function:
See ``Auto Filling''.
auto-mode-alist:
See ``How Emacs Chooses a Major Mode''.
auto-raise-tool-bar-items:
See ``Tool bars''.
auto-resize-tool-bar:
See ``Tool bars''.
auto-save-default:
See ``Auto-Saving''.
auto-save-file-format:
See ``File Format Conversion''.
auto-save-file-name-p:
See ``Auto-Saving''.
auto-save-hook:
See ``Auto-Saving''.
auto-save-interval:
See ``Auto-Saving''.
auto-save-list-file-name:
See ``Auto-Saving''.
auto-save-list-file-prefix:
See ``Auto-Saving''.
auto-save-mode:
See ``Auto-Saving''.
auto-save-timeout:
See ``Auto-Saving''.
auto-save-visited-file-name:
See ``Auto-Saving''.
auto-saving:
See ``Auto-Saving''.
autoload:
See ``Autoload''.
autoload errors:
See ``Autoload''.
automatic face assignment:
See ``Automatic Face Assignment''.
automatically buffer-local:
See ``Introduction to Buffer-Local Variables''.
back-to-indentation:
See ``Indentation-Based Motion Commands''.
backquote (list substitution):
See ``Backquote''.
backslash in character constant:
See ``Character Type''.
backslash in strings:
See ``Syntax for Strings''.
backslash in symbols:
See ``Symbol Type''.
backspace:
See ``Character Type''.
backtrace:
See ``Internals of the Debugger''.
backtrace-debug:
See ``Internals of the Debugger''.
backtrace-frame:
See ``Internals of the Debugger''.
backtracking:
See ``Backtracking in Specifications''.
backup file:
See ``Backup Files''.
backup files, how to make them:
See ``Backup by Renaming or by Copying?''.
backup-buffer:
See ``Making Backup Files''.
backup-by-copying:
See ``Backup by Renaming or by Copying?''.
backup-by-copying-when-linked:
See ``Backup by Renaming or by Copying?''.
backup-by-copying-when-mismatch:
See ``Backup by Renaming or by Copying?''.
backup-by-copying-when-privileged-mismatch:
See ``Backup by Renaming or by Copying?''.
backup-directory-alist:
See ``Making Backup Files''.
backup-enable-predicate:
See ``Making Backup Files''.
backup-file-name-p:
See ``Naming Backup Files''.
backup-inhibited:
See ``Making Backup Files''.
backward-char:
See ``Motion by Characters''.
backward-delete-char-untabify:
See ``Deleting Text''.
backward-delete-char-untabify-method:
See ``Deleting Text''.
backward-list:
See ``Moving over Balanced Expressions''.
backward-prefix-chars:
See ``Motion and Syntax''.
backward-sexp:
See ``Moving over Balanced Expressions''.
backward-to-indentation:
See ``Indentation-Based Motion Commands''.
backward-word:
See ``Motion by Words''.
balancing parentheses:
See ``Blinking Parentheses''.
barf-if-buffer-read-only:
See ``Read-Only Buffers''.
base 64 encoding:
See ``Base 64 Encoding''.
base buffer:
See ``Indirect Buffers''.
base coding system:
See ``Basic Concepts of Coding Systems''.
base for reading an integer:
See ``Integer Basics''.
base64-decode-region:
See ``Base 64 Encoding''.
base64-decode-string:
See ``Base 64 Encoding''.
base64-encode-region:
See ``Base 64 Encoding''.
base64-encode-string:
See ``Base 64 Encoding''.
basic code (of input character):
See ``Keyboard Events''.
batch mode:
See ``Batch Mode''.
batch-byte-compile:
See ``The Compilation Functions''.
baud-rate:
See ``Terminal Output''.
beep:
See ``Beeping''.
beeping:
See ``Beeping''.
before point, insertion:
See ``Inserting Text''.
before-advice:
See ``Defining Advice''.
before-change-functions:
See ``Change Hooks''.
before-init-hook:
See ``The Init File, `.emacs'''.
before-make-frame-hook:
See ``Creating Frames''.
before-revert-hook:
See ``Reverting''.
before-string (overlay property):
See ``Overlay Properties''.
beginning of line:
See ``Motion by Text Lines''.
beginning of line in regexp:
See ``Special Characters in Regular Expressions''.
beginning-of-buffer:
See ``Motion to an End of the Buffer''.
beginning-of-defun:
See ``Moving over Balanced Expressions''.
beginning-of-defun-function:
See ``Moving over Balanced Expressions''.
beginning-of-line:
See ``Motion by Text Lines''.
bell:
See ``Beeping''.
bell character:
See ``Character Type''.
binary files and text files:
See ``MS-DOS File Types''.
binding arguments:
See ``Other Features of Argument Lists''.
binding local variables:
See ``Local Variables''.
binding of a key:
See ``Keymap Terminology''.
bitmap-spec-p:
See ``Face Attributes''.
bitwise and:
See ``Bitwise Operations on Integers''.
bitwise exclusive or:
See ``Bitwise Operations on Integers''.
bitwise not:
See ``Bitwise Operations on Integers''.
bitwise or:
See ``Bitwise Operations on Integers''.
blink-matching-delay:
See ``Blinking Parentheses''.
blink-matching-open:
See ``Blinking Parentheses''.
blink-matching-paren:
See ``Blinking Parentheses''.
blink-matching-paren-distance:
See ``Blinking Parentheses''.
blink-paren-function:
See ``Blinking Parentheses''.
blinking:
See ``Blinking Parentheses''.
bobp:
See ``Examining Text Near Point''.
body of function:
See ``Components of a Lambda Expression''.
bold (face name):
See ``Standard Faces''.
bold-italic (face name):
See ``Standard Faces''.
bolp:
See ``Examining Text Near Point''.
bool-vector-p:
See ``Bool-vectors''.
Bool-vectors:
See ``Bool-vectors''.
boolean:
See ```nil' and `t'''.
boundp:
See ``When a Variable is "Void"''.
box diagrams, for lists:
See ``Cons Cell and List Types''.
box representation for lists:
See ``Lists as Linked Pairs of Boxes''.
break:
See ``The Lisp Debugger''.
breakpoints:
See ``Breakpoints''.
bucket (in obarray):
See ``Creating and Interning Symbols''.
buffer:
See ``Buffers''.
buffer contents:
See ``Text''.
buffer file name:
See ``Buffer File Name''.
buffer input stream:
See ``Input Streams''.
buffer internals:
See ``Buffer Internals''.
buffer list:
See ``The Buffer List''.
buffer modification:
See ``Buffer Modification''.
buffer names:
See ``Buffer Names''.
buffer output stream:
See ``Output Streams''.
buffer text notation:
See ``Buffer Text Notation''.
buffer, read-only:
See ``Read-Only Buffers''.
buffer-access-fontified-property:
See ``Lazy Computation of Text Properties''.
buffer-access-fontify-functions:
See ``Lazy Computation of Text Properties''.
buffer-auto-save-file-name:
See ``Auto-Saving''.
buffer-backed-up:
See ``Making Backup Files''.
buffer-base-buffer:
See ``Indirect Buffers''.
buffer-disable-undo:
See ``Maintaining Undo Lists''.
buffer-display-table:
See ``Active Display Table''.
buffer-display-time:
See ``Buffers and Windows''.
buffer-enable-undo:
See ``Maintaining Undo Lists''.
buffer-end:
See ``Point''.
buffer-file-coding-system:
See ``Encoding and I/O''.
buffer-file-format:
See ``File Format Conversion''.
buffer-file-name:
See ``Buffer File Name''.
buffer-file-number:
See ``Buffer File Name''.
buffer-file-truename:
See ``Buffer File Name''.
buffer-file-type:
See ``MS-DOS File Types''.
buffer-flush-undo:
See ``Maintaining Undo Lists''.
buffer-has-markers-at:
See ``Information from Markers''.
buffer-invisibility-spec:
See ``Invisible Text''.
buffer-list:
See ``The Buffer List''.
buffer-local variables:
See ``Buffer-Local Variables''.
buffer-local variables in modes:
See ``Major Mode Conventions''.
buffer-local-variables:
See ``Creating and Deleting Buffer-Local Bindings''.
Buffer-menu-mode-map:
See ``Standard Keymaps''.
buffer-modified-p:
See ``Buffer Modification''.
buffer-modified-tick:
See ``Buffer Modification''.
buffer-name:
See ``Buffer Names''.
buffer-name-history:
See ``Minibuffer History''.
buffer-offer-save:
See ``Killing Buffers''.
buffer-read-only:
See ``Read-Only Buffers''.
buffer-saved-size:
See ``Auto-Saving''.
buffer-size:
See ``Point''.
buffer-string:
See ``Examining Buffer Contents''.
buffer-substring:
See ``Examining Buffer Contents''.
buffer-substring-no-properties:
See ``Examining Buffer Contents''.
buffer-undo-list:
See ``Undo''.
bufferp:
See ``Buffer Basics''.
buffers, controlled in windows:
See ``Buffers and Windows''.
buffers, creating:
See ``Creating Buffers''.
buffers, killing:
See ``Killing Buffers''.
building Emacs:
See ``Building Emacs''.
building lists:
See ``Building Cons Cells and Lists''.
built-in function:
See ``What Is a Function?''.
bury-buffer:
See ``The Buffer List''.
butlast:
See ``Accessing Elements of Lists''.
button-down event:
See ``Button-Down Events''.
byte-boolean-vars:
See ``Writing Emacs Primitives''.
byte-code <1>:
See ``The Compilation Functions''.
byte-code:
See ``Byte Compilation''.
byte-code function:
See ``Byte-Code Function Objects''.
byte-code interpreter:
See ``The Compilation Functions''.
byte-code-function-p:
See ``What Is a Function?''.
byte-compile:
See ``The Compilation Functions''.
byte-compile-dynamic:
See ``Dynamic Loading of Individual Functions''.
byte-compile-dynamic-docstrings:
See ``Documentation Strings and Compilation''.
byte-compile-file:
See ``The Compilation Functions''.
byte-compiling macros:
See ``Macros and Byte Compilation''.
byte-compiling require:
See ``Features''.
byte-recompile-directory:
See ``The Compilation Functions''.
byte-to-position:
See ``Text Representations''.
bytes:
See ``Strings and Characters''.
bytes and characters:
See ``Characters and Bytes''.
C-c:
See ``Prefix Keys''.
C-g:
See ``Quitting''.
C-h:
See ``Prefix Keys''.
C-M-x:
See ``Instrumenting for Edebug''.
c-mode-map:
See ``Standard Keymaps''.
c-mode-syntax-table:
See ``Some Standard Syntax Tables''.
C-q:
See ``Flow Control''.
C-s:
See ``Flow Control''.
C-x:
See ``Prefix Keys''.
C-x 4:
See ``Prefix Keys''.
C-x 5:
See ``Prefix Keys''.
C-x 6:
See ``Prefix Keys''.
C-x <RET>:
See ``Prefix Keys''.
C-x v:
See ``Prefix Keys''.
caar:
See ``Accessing Elements of Lists''.
cache-long-line-scans:
See ``Truncation''.
cadr:
See ``Accessing Elements of Lists''.
calendar-date-display-form:
See ``Date Display Format''.
calendar-daylight-savings-ends:
See ``Daylight Savings Time''.
calendar-daylight-savings-ends-time:
See ``Daylight Savings Time''.
calendar-daylight-savings-starts:
See ``Daylight Savings Time''.
calendar-daylight-savings-starts-time:
See ``Daylight Savings Time''.
calendar-daylight-time-offset:
See ``Daylight Savings Time''.
calendar-holiday-marker:
See ``Customizing the Calendar''.
calendar-holidays:
See ``Customizing the Holidays''.
calendar-load-hook:
See ``Customizing the Calendar''.
calendar-mark-today:
See ``Customizing the Calendar''.
calendar-move-hook:
See ``Customizing the Calendar''.
calendar-star-date:
See ``Customizing the Calendar''.
calendar-time-display-form:
See ``Time Display Format''.
calendar-today-marker:
See ``Customizing the Calendar''.
call stack:
See ``Internals of the Debugger''.
call-interactively:
See ``Interactive Call''.
call-process:
See ``Creating a Synchronous Process''.
call-process-region:
See ``Creating a Synchronous Process''.
calling a function:
See ``Calling Functions''.
cancel-debug-on-entry:
See ``Entering the Debugger on a Function Call''.
cancel-timer:
See ``Timers for Delayed Execution''.
candle lighting times:
See ``Sexp Entries and the Fancy Diary Display''.
capitalization:
See ``Case Conversion in Lisp''.
capitalize:
See ``Case Conversion in Lisp''.
capitalize-region:
See ``Case Changes''.
capitalize-word:
See ``Case Changes''.
car:
See ``Accessing Elements of Lists''.
car-safe:
See ``Accessing Elements of Lists''.
case conversion in buffers:
See ``Case Changes''.
case conversion in Lisp:
See ``Case Conversion in Lisp''.
case in replacements:
See ``Replacing the Text that Matched''.
case-fold-search:
See ``Searching and Case''.
case-replace:
See ``Searching and Case''.
case-table-p:
See ``The Case Table''.
catch:
See ``Explicit Nonlocal Exits: `catch' and `throw'''.
categories of characters:
See ``Categories''.
category (overlay property):
See ``Overlay Properties''.
category (text property):
See ``Properties with Special Meanings''.
category of text character:
See ``Properties with Special Meanings''.
category-docstring:
See ``Categories''.
category-set-mnemonics:
See ``Categories''.
category-table:
See ``Categories''.
category-table-p:
See ``Categories''.
CBREAK:
See ``Flow Control''.
cdar:
See ``Accessing Elements of Lists''.
cddr:
See ``Accessing Elements of Lists''.
cdr:
See ``Accessing Elements of Lists''.
cdr-safe:
See ``Accessing Elements of Lists''.
ceiling:
See ``Numeric Conversions''.
centering point:
See ``Textual Scrolling''.
change hooks:
See ``Change Hooks''.
change hooks for a character:
See ``Properties with Special Meanings''.
change-major-mode-hook:
See ``Creating and Deleting Buffer-Local Bindings''.
changing key bindings:
See ``Changing Key Bindings''.
changing to another buffer:
See ``The Current Buffer''.
changing window size:
See ``Changing the Size of a Window''.
char-after:
See ``Examining Text Near Point''.
char-before:
See ``Examining Text Near Point''.
char-category-set:
See ``Categories''.
char-charset:
See ``Character Sets''.
char-equal:
See ``Comparison of Characters and Strings''.
char-or-string-p:
See ``The Predicates for Strings''.
char-syntax:
See ``Syntax Table Functions''.
char-table-extra-slot:
See ``Char-Tables''.
char-table-p:
See ``Char-Tables''.
char-table-parent:
See ``Char-Tables''.
char-table-range:
See ``Char-Tables''.
char-table-subtype:
See ``Char-Tables''.
char-tables:
See ``Char-Tables''.
char-to-string:
See ``Conversion of Characters and Strings''.
char-valid-p:
See ``Character Codes''.
char-width:
See ``Width''.
character alternative (in regexp):
See ``Special Characters in Regular Expressions''.
character arrays:
See ``Strings and Characters''.
character case:
See ``Case Conversion in Lisp''.
character classes in regexp:
See ``Character Classes''.
character code conversion:
See ``Basic Concepts of Coding Systems''.
character codes:
See ``Character Codes''.
character insertion:
See ``User-Level Insertion Commands''.
character printing:
See ``Describing Characters for Help Messages''.
character sets:
See ``Character Sets''.
character to string:
See ``Conversion of Characters and Strings''.
character translation tables:
See ``Translation of Characters''.
characters:
See ``Strings and Characters''.
characters for interactive codes:
See ``Code Characters for `interactive'''.
character quote:
See ``Table of Syntax Classes''.
charset-bytes:
See ``Characters and Bytes''.
charset-dimension:
See ``Characters and Bytes''.
charset-list:
See ``Character Sets''.
charset-plist:
See ``Character Sets''.
charsetp:
See ``Character Sets''.
check-coding-system:
See ``Coding Systems in Lisp''.
checkdoc-minor-mode:
See ``Tips for Documentation Strings''.
child process:
See ``Processes''.
christian-holidays:
See ``Customizing the Holidays''.
circular structure, read syntax:
See ``Read Syntax for Circular Objects''.
cl:
See ``Lisp History''.
CL note--allocate more storage:
See ``Garbage Collection''.
CL note--case of letters:
See ``Symbol Type''.
CL note--default optional arg:
See ``Other Features of Argument Lists''.
CL note--integers vrs eq:
See ``Comparison of Numbers''.
CL note--interning existing symbol:
See ``Creating and Interning Symbols''.
CL note--lack union, intersection:
See ``Using Lists as Sets''.
CL note--no continuable errors:
See ``How to Signal an Error''.
CL note--only throw in Emacs:
See ``Explicit Nonlocal Exits: `catch' and `throw'''.
CL note--rplaca vrs setcar:
See ``Modifying Existing List Structure''.
CL note--set local:
See ``How to Alter a Variable Value''.
CL note--special forms compared:
See ``Special Forms''.
CL note--special variables:
See ``Scoping Rules for Variable Bindings''.
CL note--symbol in obarrays:
See ``Creating and Interning Symbols''.
cl-specs.el:
See ``Instrumenting for Edebug''.
cl.el (Edebug):
See ``Instrumenting for Edebug''.
class of advice:
See ``Defining Advice''.
cleanup forms:
See ``Cleaning Up from Nonlocal Exits''.
clear-abbrev-table:
See ``Abbrev Tables''.
clear-face-cache:
See ``Font Selection''.
clear-image-cache:
See ``Image Cache''.
clear-this-command-keys:
See ``Information from the Command Loop''.
clear-visited-file-modtime:
See ``Comparison of Modification Time''.
click event:
See ``Click Events''.
clickable text:
See ``Defining Clickable Text''.
clipboard support (for MS-Windows):
See ``Window System Selections''.
close parenthesis:
See ``Blinking Parentheses''.
close parenthesis character:
See ``Table of Syntax Classes''.
closures not available:
See ``Extent''.
clrhash:
See ``Hash Table Access''.
codes, interactive, description of:
See ``Code Characters for `interactive'''.
coding standards:
See ``Tips and Conventions''.
coding system:
See ``Coding Systems''.
coding-system-change-eol-conversion:
See ``Coding Systems in Lisp''.
coding-system-change-text-conversion:
See ``Coding Systems in Lisp''.
coding-system-for-read:
See ``Specifying a Coding System for One Operation''.
coding-system-for-write:
See ``Specifying a Coding System for One Operation''.
coding-system-get:
See ``Basic Concepts of Coding Systems''.
coding-system-list:
See ``Coding Systems in Lisp''.
coding-system-p:
See ``Coding Systems in Lisp''.
color-defined-p:
See ``Color Names''.
color-gray-p:
See ``Color Names''.
color-supported-p:
See ``Color Names''.
color-values:
See ``Color Names''.
colors on text-only terminals:
See ``Text Terminal Colors''.
columns:
See ``Counting Columns''.
combine-after-change-calls:
See ``Change Hooks''.
command:
See ``What Is a Function?''.
command descriptions:
See ``A Sample Function Description''.
command history:
See ``Command History''.
command in keymap:
See ``Key Lookup''.
command loop:
See ``Command Loop''.
command loop, recursive:
See ``Recursive Editing''.
command-debug-status:
See ``Internals of the Debugger''.
command-execute:
See ``Interactive Call''.
command-history:
See ``Command History''.
command-history-map:
See ``Standard Keymaps''.
command-line:
See ``Command-Line Arguments''.
command-line arguments:
See ``Command-Line Arguments''.
command-line options:
See ``Command-Line Arguments''.
command-line-args:
See ``Command-Line Arguments''.
command-line-functions:
See ``Command-Line Arguments''.
command-line-processed:
See ``Command-Line Arguments''.
command-switch-alist:
See ``Command-Line Arguments''.
commandp:
See ``Interactive Call''.
commandp example:
See ``High-Level Completion Functions''.
commands, defining:
See ``Defining Commands''.
comment syntax:
See ``Table of Syntax Classes''.
comments:
See ``Comments''.
comment ender:
See ``Table of Syntax Classes''.
comment starter:
See ``Table of Syntax Classes''.
Common Lisp:
See ``Lisp History''.
Common Lisp (Edebug):
See ``Instrumenting for Edebug''.
compare-buffer-substrings:
See ``Comparing Text''.
compare-strings:
See ``Comparison of Characters and Strings''.
compare-window-configurations:
See ``Window Configurations''.
comparing buffer text:
See ``Comparing Text''.
comparison of modification time:
See ``Comparison of Modification Time''.
compilation:
See ``Byte Compilation''.
compilation functions:
See ``The Compilation Functions''.
compile-defun:
See ``The Compilation Functions''.
compiled function:
See ``Byte-Code Function Objects''.
complete key:
See ``Keymap Terminology''.
completing-read:
See ``Completion and the Minibuffer''.
completion:
See ``Completion''.
completion, file name:
See ``File Name Completion''.
completion-auto-help:
See ``Minibuffer Commands that Do Completion''.
completion-ignore-case:
See ``Basic Completion Functions''.
completion-ignored-extensions:
See ``File Name Completion''.
complex arguments:
See ``Minibuffers''.
complex command:
See ``Command History''.
compute-motion:
See ``Motion by Screen Lines''.
concat:
See ``Creating Strings''.
concatenating lists:
See ``Functions that Rearrange Lists''.
concatenating strings:
See ``Creating Strings''.
cond:
See ``Conditionals''.
condition name:
See ``Error Symbols and Condition Names''.
condition-case:
See ``Writing Code to Handle Errors''.
conditional display specifications:
See ``Conditional Display Specifications''.
conditional evaluation:
See ``Conditionals''.
conditional selection of windows:
See ``Selecting Windows''.
cons:
See ``Building Cons Cells and Lists''.
cons cell as box:
See ``Lists as Linked Pairs of Boxes''.
cons cells:
See ``Building Cons Cells and Lists''.
cons-cells-consed:
See ``Memory Usage''.
consing:
See ``Building Cons Cells and Lists''.
consp:
See ``Predicates on Lists''.
constrain-to-field:
See ``Defining and Using Fields''.
continuation lines:
See ``Truncation''.
continue-process:
See ``Sending Signals to Processes''.
control character key constants:
See ``Changing Key Bindings''.
control character printing:
See ``Describing Characters for Help Messages''.
control characters:
See ``Character Type''.
control characters in display:
See ``Usual Display Conventions''.
control characters, reading:
See ``Quoted Character Input''.
control structures:
See ``Control Structures''.
Control-X-prefix:
See ``Prefix Keys''.
conventions for writing minor modes:
See ``Conventions for Writing Minor Modes''.
conversion of strings:
See ``Conversion of Characters and Strings''.
convert-standard-filename:
See ``Standard File Names''.
coordinates-in-window-p:
See ``Coordinates and Windows''.
copy-alist:
See ``Association Lists''.
copy-category-table:
See ``Categories''.
copy-face:
See ``Functions for Working with Faces''.
copy-file:
See ``Changing File Names and Attributes''.
copy-hash-table:
See ``Other Hash Table Functions''.
copy-keymap:
See ``Creating Keymaps''.
copy-marker:
See ``Functions that Create Markers''.
copy-region-as-kill:
See ``Functions for Killing''.
copy-sequence:
See ``Sequences''.
copy-syntax-table:
See ``Syntax Table Functions''.
copying alists:
See ``Association Lists''.
copying files:
See ``Changing File Names and Attributes''.
copying lists:
See ``Building Cons Cells and Lists''.
copying sequences:
See ``Sequences''.
copying strings:
See ``Creating Strings''.
copying vectors:
See ``Functions for Vectors''.
cos:
See ``Standard Mathematical Functions''.
count-lines:
See ``Motion by Text Lines''.
count-loop:
See ``A Sample Function Description''.
count-screen-lines:
See ``Motion by Screen Lines''.
counting columns:
See ``Counting Columns''.
coverage testing:
See ``Coverage Testing''.
create-file-buffer:
See ``Subroutines of Visiting''.
create-fontset-from-fontset-spec:
See ``Fontsets''.
create-glyph:
See ``Glyphs''.
create-image:
See ``Defining Images''.
creating buffers:
See ``Creating Buffers''.
creating keymaps:
See ``Creating Keymaps''.
ctl-arrow:
See ``Usual Display Conventions''.
ctl-x-4-map:
See ``Prefix Keys''.
ctl-x-5-map:
See ``Prefix Keys''.
ctl-x-map:
See ``Prefix Keys''.
current binding:
See ``Local Variables''.
current buffer:
See ``The Current Buffer''.
current buffer excursion:
See ``Excursions''.
current buffer mark:
See ``The Mark''.
current buffer point and mark (Edebug):
See ``Edebug Display Update''.
current buffer position:
See ``Point''.
current command:
See ``Information from the Command Loop''.
current stack frame:
See ``Using the Debugger''.
current-buffer:
See ``The Current Buffer''.
current-case-table:
See ``The Case Table''.
current-column:
See ``Counting Columns''.
current-fill-column:
See ``Margins for Filling''.
current-frame-configuration:
See ``Frame Configurations''.
current-global-map:
See ``Active Keymaps''.
current-indentation:
See ``Indentation Primitives''.
current-input-method:
See ``Input Methods''.
current-input-mode:
See ``Input Modes''.
current-justification:
See ``Filling''.
current-kill:
See ``Low-Level Kill Ring''.
current-left-margin:
See ``Margins for Filling''.
current-local-map:
See ``Active Keymaps''.
current-message:
See ``The Echo Area''.
current-minor-mode-maps:
See ``Active Keymaps''.
current-prefix-arg:
See ``Prefix Command Arguments''.
current-time:
See ``Time of Day''.
current-time-string:
See ``Time of Day''.
current-time-zone:
See ``Time of Day''.
current-window-configuration:
See ``Window Configurations''.
cursor-in-echo-area:
See ``The Echo Area''.
cursor-type:
See ``Window Frame Parameters''.
cust-print:
See ``Printing in Edebug''.
custom-add-option:
See ``Defining Customization Variables''.
cut buffer:
See ``Window System Selections''.
cyclic ordering of windows:
See ``Cyclic Ordering of Windows''.
data type:
See ``Lisp Data Types''.
data-directory:
See ``Help Functions''.
daylight savings time:
See ``Daylight Savings Time''.
deactivate-mark:
See ``The Mark''.
deactivate-mark-hook:
See ``The Mark''.
deactivating advice:
See ``Activation of Advice''.
debug:
See ``Invoking the Debugger''.
debug-ignored-errors:
See ``Entering the Debugger on an Error''.
debug-on-entry:
See ``Entering the Debugger on a Function Call''.
debug-on-error:
See ``Entering the Debugger on an Error''.
debug-on-error use:
See ``How Emacs Processes Errors''.
debug-on-next-call:
See ``Internals of the Debugger''.
debug-on-quit:
See ``Debugging Infinite Loops''.
debug-on-signal:
See ``Entering the Debugger on an Error''.
debugger <1>:
See ``Internals of the Debugger''.
debugger:
See ``The Lisp Debugger''.
debugger command list:
See ``Debugger Commands''.
debugger-mode-map:
See ``Standard Keymaps''.
debugging errors:
See ``Entering the Debugger on an Error''.
debugging specific functions:
See ``Entering the Debugger on a Function Call''.
decode-coding-region:
See ``Explicit Encoding and Decoding''.
decode-coding-string:
See ``Explicit Encoding and Decoding''.
decode-time:
See ``Time Conversion''.
decoding file formats:
See ``File Format Conversion''.
decoding text:
See ``Explicit Encoding and Decoding''.
decrement field of register:
See ``Cons Cell and List Types''.
dedicated window:
See ``Choosing a Window for Display''.
deep binding:
See ``Implementation of Dynamic Scoping''.
def-edebug-spec:
See ``Instrumenting Macro Calls''.
defadvice:
See ``Defining Advice''.
defalias:
See ``Defining Functions''.
default (face name):
See ``Standard Faces''.
default argument string:
See ``Code Characters for `interactive'''.
default init file:
See ``The Init File, `.emacs'''.
default key binding:
See ``Format of Keymaps''.
default value:
See ``The Default Value of a Buffer-Local Variable''.
default value of char-table:
See ``Char-Tables''.
default-abbrev-mode:
See ``Setting Up Abbrev Mode''.
default-boundp:
See ``The Default Value of a Buffer-Local Variable''.
default-buffer-file-type:
See ``MS-DOS File Types''.
default-case-fold-search:
See ``Searching and Case''.
default-ctl-arrow:
See ``Usual Display Conventions''.
default-directory:
See ``Functions that Expand Filenames''.
default-enable-multibyte-characters:
See ``Text Representations''.
default-file-modes:
See ``Changing File Names and Attributes''.
default-fill-column:
See ``Margins for Filling''.
default-frame-alist:
See ``Initial Frame Parameters''.
default-header-line-format:
See ``Window Header Lines''.
default-input-method:
See ``Input Methods''.
default-justification:
See ``Filling''.
default-major-mode:
See ``How Emacs Chooses a Major Mode''.
default-minibuffer-frame:
See ``Minibuffers and Frames''.
default-mode-line-format:
See ``Variables Used in the Mode Line''.
default-process-coding-system:
See ``Default Coding Systems''.
default-text-properties:
See ``Examining Text Properties''.
default-truncate-lines:
See ``Truncation''.
default-value:
See ``The Default Value of a Buffer-Local Variable''.
default.el:
See ``Summary: Sequence of Actions at Startup''.
defconst:
See ``Defining Global Variables''.
defcustom:
See ``Defining Customization Variables''.
defface:
See ``Defining Faces''.
defgroup:
See ``Defining Custom Groups''.
defimage:
See ``Defining Images''.
define-abbrev:
See ``Defining Abbrevs''.
define-abbrev-table:
See ``Abbrev Tables''.
define-category:
See ``Categories''.
define-derived-mode:
See ``Defining Derived Modes''.
define-hash-table-test:
See ``Defining Hash Comparisons''.
define-key:
See ``Changing Key Bindings''.
define-key-after:
See ``Modifying Menus''.
define-logical-name:
See ``Changing File Names and Attributes''.
define-minor-mode:
See ``Defining Minor Modes''.
define-prefix-command:
See ``Prefix Keys''.
defined-colors:
See ``Color Names''.
defining a function:
See ``Defining Functions''.
defining advice:
See ``Defining Advice''.
defining commands:
See ``Defining Commands''.
defining menus:
See ``Defining Menus''.
defining-kbd-macro:
See ``Keyboard Macros''.
definition of a symbol:
See ``Defining Symbols''.
defmacro:
See ``Defining Macros''.
defsubst:
See ``Inline Functions''.
defun:
See ``Defining Functions''.
defun-prompt-regexp:
See ``Moving over Balanced Expressions''.
defvar:
See ``Defining Global Variables''.
delete:
See ``Using Lists as Sets''.
delete previous char:
See ``Deleting Text''.
delete-and-extract-region:
See ``Deleting Text''.
delete-auto-save-file-if-necessary:
See ``Auto-Saving''.
delete-auto-save-files:
See ``Auto-Saving''.
delete-backward-char:
See ``Deleting Text''.
delete-blank-lines:
See ``User-Level Deletion Commands''.
delete-char:
See ``Deleting Text''.
delete-directory:
See ``Creating and Deleting Directories''.
delete-exited-processes:
See ``Deleting Processes''.
delete-field:
See ``Defining and Using Fields''.
delete-file:
See ``Changing File Names and Attributes''.
delete-frame:
See ``Deleting Frames''.
delete-frame event:
See ``Miscellaneous Window System Events''.
delete-frame-hook:
See ``Deleting Frames''.
delete-horizontal-space:
See ``User-Level Deletion Commands''.
delete-indentation:
See ``User-Level Deletion Commands''.
delete-minibuffer-contents:
See ``Minibuffer Miscellany''.
delete-old-versions:
See ``Making and Deleting Numbered Backup Files''.
delete-other-windows:
See ``Deleting Windows''.
delete-overlay:
See ``Managing Overlays''.
delete-process:
See ``Deleting Processes''.
delete-region:
See ``Deleting Text''.
delete-to-left-margin:
See ``Margins for Filling''.
delete-window:
See ``Deleting Windows''.
delete-windows-on:
See ``Deleting Windows''.
deleting files:
See ``Changing File Names and Attributes''.
deleting processes:
See ``Deleting Processes''.
deleting whitespace:
See ``User-Level Deletion Commands''.
deleting windows:
See ``Deleting Windows''.
deletion of elements:
See ``Using Lists as Sets''.
deletion of frames:
See ``Deleting Frames''.
deletion vs killing:
See ``Deleting Text''.
delq:
See ``Using Lists as Sets''.
describe-bindings:
See ``Scanning Keymaps''.
describe-buffer-case-table:
See ``The Case Table''.
describe-categories:
See ``Categories''.
describe-current-display-table:
See ``Display Table Format''.
describe-display-table:
See ``Display Table Format''.
describe-mode:
See ``Getting Help about a Major Mode''.
describe-prefix-bindings:
See ``Help Functions''.
description for interactive codes:
See ``Code Characters for `interactive'''.
description format:
See ``Format of Descriptions''.
destructive list operations:
See ``Modifying Existing List Structure''.
detect-coding-region:
See ``Coding Systems in Lisp''.
detect-coding-string:
See ``Coding Systems in Lisp''.
diagrams, boxed, for lists:
See ``Cons Cell and List Types''.
dialog boxes:
See ``Dialog Boxes''.
diary buffer:
See ``Fancy Diary Display''.
diary-anniversary:
See ``Sexp Entries and the Fancy Diary Display''.
diary-astro-day-number:
See ``Sexp Entries and the Fancy Diary Display''.
diary-cyclic:
See ``Sexp Entries and the Fancy Diary Display''.
diary-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-date-forms:
See ``Customizing the Diary''.
diary-day-of-year:
See ``Sexp Entries and the Fancy Diary Display''.
diary-display-hook:
See ``Fancy Diary Display''.
diary-entry-marker:
See ``Customizing the Calendar''.
diary-float:
See ``Sexp Entries and the Fancy Diary Display''.
diary-french-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-hebrew-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-islamic-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-iso-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-julian-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-list-include-blanks:
See ``Fancy Diary Display''.
diary-mayan-date:
See ``Sexp Entries and the Fancy Diary Display''.
diary-omer:
See ``Sexp Entries and the Fancy Diary Display''.
diary-parasha:
See ``Sexp Entries and the Fancy Diary Display''.
diary-phases-of-moon:
See ``Sexp Entries and the Fancy Diary Display''.
diary-remind:
See ``Sexp Entries and the Fancy Diary Display''.
diary-rosh-hodesh:
See ``Sexp Entries and the Fancy Diary Display''.
diary-sabbath-candles:
See ``Sexp Entries and the Fancy Diary Display''.
diary-sunrise-sunset:
See ``Sexp Entries and the Fancy Diary Display''.
diary-yahrzeit:
See ``Sexp Entries and the Fancy Diary Display''.
digit-argument:
See ``Prefix Command Arguments''.
dimension (of character set):
See ``Characters and Bytes''.
ding:
See ``Beeping''.
directory name:
See ``Directory Names''.
directory name abbreviation:
See ``Directory Names''.
directory part (of file name):
See ``File Name Components''.
directory-abbrev-alist:
See ``Directory Names''.
directory-file-name:
See ``Directory Names''.
directory-files:
See ``Contents of Directories''.
directory-oriented functions:
See ``Contents of Directories''.
dired-kept-versions:
See ``Making and Deleting Numbered Backup Files''.
dired-mode-map:
See ``Standard Keymaps''.
disable undo:
See ``Maintaining Undo Lists''.
disable-command:
See ``Disabling Commands''.
disable-point-adjustment:
See ``Adjusting Point After Commands''.
disabled:
See ``Disabling Commands''.
disabled command:
See ``Disabling Commands''.
disabled-command-hook:
See ``Disabling Commands''.
disabling advice:
See ``Enabling and Disabling Advice''.
disassemble:
See ``Disassembled Byte-Code''.
disassembled byte-code:
See ``Disassembled Byte-Code''.
discard input:
See ``Miscellaneous Event Input Features''.
discard-input:
See ``Miscellaneous Event Input Features''.
display (overlay property):
See ``Overlay Properties''.
display (text property) <1>:
See ``The `display' Property''.
display (text property):
See ``Properties with Special Meanings''.
display feature testing:
See ``Display Feature Testing''.
display margins:
See ``Displaying in the Margins''.
display specification:
See ``The `display' Property''.
display table:
See ``Display Tables''.
display-backing-store:
See ``Display Feature Testing''.
display-buffer:
See ``Choosing a Window for Display''.
display-buffer-function:
See ``Choosing a Window for Display''.
display-buffer-reuse-frames:
See ``Choosing a Window for Display''.
display-color-cells:
See ``Display Feature Testing''.
display-color-p:
See ``Display Feature Testing''.
display-completion-list:
See ``Minibuffer Commands that Do Completion''.
display-graphic-p:
See ``Display Feature Testing''.
display-grayscale-p:
See ``Display Feature Testing''.
display-images-p:
See ``Display Feature Testing''.
display-message-or-buffer:
See ``The Echo Area''.
display-mm-height:
See ``Display Feature Testing''.
display-mm-width:
See ``Display Feature Testing''.
display-mouse-p:
See ``Display Feature Testing''.
display-pixel-height:
See ``Display Feature Testing''.
display-pixel-width:
See ``Display Feature Testing''.
display-planes:
See ``Display Feature Testing''.
display-popup-menus-p:
See ``Display Feature Testing''.
display-save-under:
See ``Display Feature Testing''.
display-screens:
See ``Display Feature Testing''.
display-selections-p:
See ``Display Feature Testing''.
display-table-slot:
See ``Display Table Format''.
display-visual-class:
See ``Display Feature Testing''.
displaying a buffer:
See ``Displaying Buffers in Windows''.
displays, multiple:
See ``Multiple Displays''.
do-auto-save:
See ``Auto-Saving''.
DOC (documentation) file:
See ``Documentation Basics''.
doc-directory:
See ``Access to Documentation Strings''.
documentation:
See ``Access to Documentation Strings''.
documentation conventions:
See ``Documentation Basics''.
documentation for major mode:
See ``Getting Help about a Major Mode''.
documentation notation:
See ``Evaluation Notation''.
documentation of function:
See ``Documentation Strings of Functions''.
documentation strings:
See ``Documentation''.
documentation, keys in:
See ``Substituting Key Bindings in Documentation''.
documentation-property:
See ``Access to Documentation Strings''.
dolist:
See ``Iteration''.
DOS file types:
See ``MS-DOS File Types''.
dotimes:
See ``Iteration''.
dotted lists (Edebug):
See ``Specification List''.
dotted pair notation:
See ``Dotted Pair Notation''.
double-click events:
See ``Repeat Events''.
double-click-fuzz:
See ``Repeat Events''.
double-click-time:
See ``Repeat Events''.
double-quote in strings:
See ``Syntax for Strings''.
down-list:
See ``Moving over Balanced Expressions''.
downcase:
See ``Case Conversion in Lisp''.
downcase-region:
See ``Case Changes''.
downcase-word:
See ``Case Changes''.
downcasing in lookup-key:
See ``Key Sequence Input''.
drag event:
See ``Drag Events''.
drag-n-drop event:
See ``Miscellaneous Window System Events''.
dribble file:
See ``Recording Input''.
dump-emacs:
See ``Building Emacs''.
dynamic loading of documentation:
See ``Documentation Strings and Compilation''.
dynamic loading of functions:
See ``Dynamic Loading of Individual Functions''.
dynamic scoping:
See ``Scoping Rules for Variable Bindings''.
easy-mmode-define-minor-mode:
See ``Defining Minor Modes''.
echo area:
See ``The Echo Area''.
echo-area-clear-hook:
See ``The Echo Area''.
echo-keystrokes:
See ``The Echo Area''.
edebug:
See ``Source Breakpoints''.
Edebug:
See ``Edebug''.
Edebug execution modes:
See ``Edebug Execution Modes''.
Edebug mode:
See ``Edebug''.
Edebug specification list:
See ``Specification List''.
edebug-all-defs:
See ``Edebug Options''.
edebug-all-forms:
See ``Edebug Options''.
edebug-continue-kbd-macro:
See ``Edebug Options''.
edebug-display-freq-count:
See ``Coverage Testing''.
edebug-eval-top-level-form:
See ``Instrumenting for Edebug''.
edebug-global-break-condition:
See ``Edebug Options''.
edebug-initial-mode:
See ``Edebug Options''.
edebug-on-error:
See ``Edebug Options''.
edebug-on-quit:
See ``Edebug Options''.
edebug-print-circle:
See ``Printing in Edebug''.
edebug-print-length:
See ``Printing in Edebug''.
edebug-print-level:
See ``Printing in Edebug''.
edebug-print-trace-after:
See ``Trace Buffer''.
edebug-print-trace-before:
See ``Trace Buffer''.
edebug-save-displayed-buffer-points:
See ``Edebug Options''.
edebug-save-windows:
See ``Edebug Options''.
edebug-set-global-break-condition:
See ``Global Break Condition''.
edebug-setup-hook:
See ``Edebug Options''.
edebug-test-coverage:
See ``Edebug Options''.
edebug-trace <1>:
See ``Edebug Options''.
edebug-trace:
See ``Trace Buffer''.
edebug-tracing:
See ``Trace Buffer''.
edebug-unwrap:
See ``Specification List''.
edit-abbrevs-map:
See ``Standard Keymaps''.
edit-and-eval-command:
See ``Reading Lisp Objects with the Minibuffer''.
edit-tab-stops-map:
See ``Standard Keymaps''.
editing types:
See ``Editing Types''.
editor command loop:
See ``Command Loop''.
electric-buffer-menu-mode-map:
See ``Standard Keymaps''.
electric-future-map:
See ``A Sample Variable Description''.
electric-history-map:
See ``Standard Keymaps''.
element (of list):
See ``Lists''.
elements of sequences:
See ``Sequences''.
elp.el:
See ``Tips for Making Compiled Code Fast''.
elt:
See ``Sequences''.
Emacs event standard notation:
See ``Describing Characters for Help Messages''.
emacs-build-time:
See ``Version Information''.
emacs-lisp-mode-map:
See ``Standard Keymaps''.
emacs-lisp-mode-syntax-table:
See ``Some Standard Syntax Tables''.
emacs-major-version:
See ``Version Information''.
emacs-minor-version:
See ``Version Information''.
emacs-pid:
See ``Operating System Environment''.
emacs-startup-hook:
See ``The Init File, `.emacs'''.
emacs-version:
See ``Version Information''.
emacs/etc/DOC-VERSION:
See ``Documentation Basics''.
EMACSLOADPATH environment variable:
See ``Library Search''.
empty list:
See ``Cons Cell and List Types''.
enable-command:
See ``Disabling Commands''.
enable-flow-control:
See ``Flow Control''.
enable-flow-control-on:
See ``Flow Control''.
enable-local-eval:
See ``File Local Variables''.
enable-local-variables:
See ``File Local Variables''.
enable-multibyte-characters:
See ``Text Representations''.
enable-recursive-minibuffers:
See ``Minibuffer Miscellany''.
enabling advice:
See ``Enabling and Disabling Advice''.
encode-coding-region:
See ``Explicit Encoding and Decoding''.
encode-coding-string:
See ``Explicit Encoding and Decoding''.
encode-time:
See ``Time Conversion''.
encoding file formats:
See ``File Format Conversion''.
encoding text:
See ``Explicit Encoding and Decoding''.
end of buffer marker:
See ``Functions that Create Markers''.
end of line conversion:
See ``Basic Concepts of Coding Systems''.
end of line in regexp:
See ``Special Characters in Regular Expressions''.
end-of-buffer:
See ``Motion to an End of the Buffer''.
end-of-defun:
See ``Moving over Balanced Expressions''.
end-of-defun-function:
See ``Moving over Balanced Expressions''.
end-of-file:
See ``Input Functions''.
end-of-line:
See ``Motion by Text Lines''.
enlarge-window:
See ``Changing the Size of a Window''.
enlarge-window-horizontally:
See ``Changing the Size of a Window''.
environment:
See ``Introduction to Evaluation''.
environment variable access:
See ``Operating System Environment''.
environment variables, subprocesses:
See ``Functions that Create Subprocesses''.
eobp:
See ``Examining Text Near Point''.
eolp:
See ``Examining Text Near Point''.
eq:
See ``Equality Predicates''.
equal:
See ``Equality Predicates''.
equality:
See ``Equality Predicates''.
erase-buffer:
See ``Deleting Text''.
error:
See ``How to Signal an Error''.
error cleanup:
See ``Cleaning Up from Nonlocal Exits''.
error debugging:
See ``Entering the Debugger on an Error''.
error description:
See ``Writing Code to Handle Errors''.
error display:
See ``The Echo Area''.
error handler:
See ``Writing Code to Handle Errors''.
error in debug:
See ``Invoking the Debugger''.
error message notation:
See ``Error Messages''.
error name:
See ``Error Symbols and Condition Names''.
error symbol:
See ``Error Symbols and Condition Names''.
error-conditions:
See ``Error Symbols and Condition Names''.
error-message-string:
See ``Writing Code to Handle Errors''.
errors:
See ``Errors''.
esc-map:
See ``Prefix Keys''.
ESC-prefix:
See ``Prefix Keys''.
escape <1>:
See ``Table of Syntax Classes''.
escape:
See ``Character Type''.
escape characters:
See ``Variables Affecting Output''.
escape characters in printing:
See ``Output Functions''.
escape sequence:
See ``Character Type''.
etc/DOC-VERSION:
See ``Documentation Basics''.
eval:
See ``Eval''.
eval, and debugging:
See ``Internals of the Debugger''.
eval-after-load:
See ``Hooks for Loading''.
eval-and-compile:
See ``Evaluation During Compilation''.
eval-current-buffer:
See ``Eval''.
eval-current-buffer (Edebug):
See ``Instrumenting for Edebug''.
eval-defun (Edebug):
See ``Instrumenting for Edebug''.
eval-expression (Edebug):
See ``Instrumenting for Edebug''.
eval-minibuffer:
See ``Reading Lisp Objects with the Minibuffer''.
eval-region:
See ``Eval''.
eval-region (Edebug):
See ``Instrumenting for Edebug''.
eval-when-compile:
See ``Evaluation During Compilation''.
evaluated expression argument:
See ``Code Characters for `interactive'''.
evaluation:
See ``Evaluation''.
evaluation error:
See ``Local Variables''.
evaluation list group:
See ``Evaluation List Buffer''.
evaluation notation:
See ``Evaluation Notation''.
evaluation of buffer contents:
See ``Eval''.
evaporate (overlay property):
See ``Overlay Properties''.
even-window-heights:
See ``Choosing a Window for Display''.
event printing:
See ``Describing Characters for Help Messages''.
event type:
See ``Classifying Events''.
event, reading only one:
See ``Reading One Event''.
event-basic-type:
See ``Classifying Events''.
event-click-count:
See ``Repeat Events''.
event-convert-list:
See ``Classifying Events''.
event-end:
See ``Accessing Events''.
event-modifiers:
See ``Classifying Events''.
event-start:
See ``Accessing Events''.
eventp:
See ``Input Events''.
events:
See ``Input Events''.
examining the interactive form:
See ``Using `interactive'''.
examining windows:
See ``Buffers and Windows''.
examples of using interactive:
See ``Examples of Using `interactive'''.
excursion:
See ``Excursions''.
exec-directory:
See ``Functions that Create Subprocesses''.
exec-path:
See ``Functions that Create Subprocesses''.
execute program:
See ``Functions that Create Subprocesses''.
execute with prefix argument:
See ``Interactive Call''.
execute-extended-command:
See ``Interactive Call''.
execute-kbd-macro:
See ``Keyboard Macros''.
executing-macro:
See ``Keyboard Macros''.
execution speed:
See ``Tips for Making Compiled Code Fast''.
exit:
See ``Recursive Editing''.
exit recursive editing:
See ``Recursive Editing''.
exit-minibuffer:
See ``Minibuffer Miscellany''.
exit-recursive-edit:
See ``Recursive Editing''.
exiting Emacs:
See ``Getting Out of Emacs''.
exp:
See ``Standard Mathematical Functions''.
expand-abbrev:
See ``Looking Up and Expanding Abbreviations''.
expand-file-name:
See ``Functions that Expand Filenames''.
expansion of file names:
See ``Functions that Expand Filenames''.
expansion of macros:
See ``Expansion of a Macro Call''.
expression:
See ``Introduction to Evaluation''.
expression prefix:
See ``Table of Syntax Classes''.
expt:
See ``Standard Mathematical Functions''.
extended-command-history:
See ``Minibuffer History''.
extent:
See ``Scoping Rules for Variable Bindings''.
extra slots of char-table:
See ``Char-Tables''.
extra-keyboard-modifiers:
See ``Translating Input Events''.
face:
See ``Faces''.
face (overlay property):
See ``Overlay Properties''.
face (text property):
See ``Properties with Special Meanings''.
face attributes:
See ``Face Attributes''.
face codes of text:
See ``Properties with Special Meanings''.
face id:
See ``Faces''.
face-attribute:
See ``Face Attribute Functions''.
face-background:
See ``Face Attribute Functions''.
face-bold-p:
See ``Face Attribute Functions''.
face-default-registry:
See ``Font Selection''.
face-differs-from-default-p:
See ``Functions for Working with Faces''.
face-documentation:
See ``Functions for Working with Faces''.
face-equal:
See ``Functions for Working with Faces''.
face-font:
See ``Face Attribute Functions''.
face-font-family-alternatives:
See ``Font Selection''.
face-font-registry-alternatives:
See ``Font Selection''.
face-font-selection-order:
See ``Font Selection''.
face-foreground:
See ``Face Attribute Functions''.
face-id:
See ``Functions for Working with Faces''.
face-inverse-video-p:
See ``Face Attribute Functions''.
face-italic-p:
See ``Face Attribute Functions''.
face-list:
See ``Functions for Working with Faces''.
face-stipple:
See ``Face Attribute Functions''.
face-underline-p:
See ``Face Attribute Functions''.
facemenu-background-menu:
See ``Standard Keymaps''.
facemenu-face-menu:
See ``Standard Keymaps''.
facemenu-foreground-menu:
See ``Standard Keymaps''.
facemenu-indentation-menu:
See ``Standard Keymaps''.
facemenu-justification-menu:
See ``Standard Keymaps''.
facemenu-keymap:
See ``Prefix Keys''.
facemenu-menu:
See ``Standard Keymaps''.
facemenu-special-menu:
See ``Standard Keymaps''.
facep:
See ``Faces''.
faces, automatic choice:
See ``Automatic Face Assignment''.
false:
See ```nil' and `t'''.
fancy-diary-display:
See ``Fancy Diary Display''.
fboundp:
See ``Accessing Function Cell Contents''.
fceiling:
See ``Rounding Operations''.
FEATURE-unload-hook:
See ``Unloading''.
featurep:
See ``Features''.
features:
See ``Features''.
fetch-bytecode:
See ``Dynamic Loading of Individual Functions''.
ffloor:
See ``Rounding Operations''.
field (text property):
See ``Properties with Special Meanings''.
field width:
See ``Formatting Strings''.
field-beginning:
See ``Defining and Using Fields''.
field-end:
See ``Defining and Using Fields''.
field-string:
See ``Defining and Using Fields''.
field-string-no-properties:
See ``Defining and Using Fields''.
fields:
See ``Defining and Using Fields''.
file accessibility:
See ``Testing Accessibility''.
file age:
See ``Testing Accessibility''.
file attributes:
See ``Other Information about Files''.
file format conversion:
See ``File Format Conversion''.
file hard link:
See ``Changing File Names and Attributes''.
file locks:
See ``File Locks''.
file mode specification error:
See ``How Emacs Chooses a Major Mode''.
file modes and MS-DOS:
See ``Changing File Names and Attributes''.
file modification time:
See ``Testing Accessibility''.
file name completion subroutines:
See ``File Name Completion''.
file name of buffer:
See ``Buffer File Name''.
file name of directory:
See ``Directory Names''.
file names:
See ``File Names''.
file names in directory:
See ``Contents of Directories''.
file open error:
See ``Subroutines of Visiting''.
file symbolic links:
See ``Distinguishing Kinds of Files''.
file types on MS-DOS and Windows:
See ``MS-DOS File Types''.
file with multiple names:
See ``Changing File Names and Attributes''.
file-accessible-directory-p:
See ``Testing Accessibility''.
file-already-exists:
See ``Changing File Names and Attributes''.
file-attributes:
See ``Other Information about Files''.
file-chase-links:
See ``Truenames''.
file-coding-system-alist:
See ``Default Coding Systems''.
file-directory-p:
See ``Distinguishing Kinds of Files''.
file-error:
See ``How Programs Do Loading''.
file-executable-p:
See ``Testing Accessibility''.
file-exists-p:
See ``Testing Accessibility''.
file-expand-wildcards:
See ``Contents of Directories''.
file-local-copy:
See ``Making Certain File Names "Magic"''.
file-locked:
See ``File Locks''.
file-locked-p:
See ``File Locks''.
file-modes:
See ``Other Information about Files''.
file-name-absolute-p:
See ``Absolute and Relative File Names''.
file-name-all-completions:
See ``File Name Completion''.
file-name-all-versions:
See ``Contents of Directories''.
file-name-as-directory:
See ``Directory Names''.
file-name-buffer-file-type-alist:
See ``MS-DOS File Types''.
file-name-completion:
See ``File Name Completion''.
file-name-directory:
See ``File Name Components''.
file-name-extension:
See ``File Name Components''.
file-name-history:
See ``Minibuffer History''.
file-name-nondirectory:
See ``File Name Components''.
file-name-sans-extension:
See ``File Name Components''.
file-name-sans-versions:
See ``File Name Components''.
file-newer-than-file-p:
See ``Testing Accessibility''.
file-newest-backup:
See ``Naming Backup Files''.
file-nlinks:
See ``Other Information about Files''.
file-ownership-preserved-p:
See ``Testing Accessibility''.
file-precious-flag:
See ``Saving Buffers''.
file-readable-p:
See ``Testing Accessibility''.
file-regular-p:
See ``Distinguishing Kinds of Files''.
file-relative-name:
See ``Functions that Expand Filenames''.
file-supersession:
See ``Comparison of Modification Time''.
file-symlink-p:
See ``Distinguishing Kinds of Files''.
file-truename:
See ``Truenames''.
file-writable-p:
See ``Testing Accessibility''.
fill-column:
See ``Margins for Filling''.
fill-context-prefix:
See ``Adaptive Fill Mode''.
fill-individual-paragraphs:
See ``Filling''.
fill-individual-varying-indent:
See ``Filling''.
fill-nobreak-predicate:
See ``Margins for Filling''.
fill-paragraph:
See ``Filling''.
fill-paragraph-function:
See ``Filling''.
fill-prefix:
See ``Margins for Filling''.
fill-region:
See ``Filling''.
fill-region-as-paragraph:
See ``Filling''.
fillarray:
See ``Functions that Operate on Arrays''.
filling a paragraph:
See ``Filling''.
filling, automatic:
See ``Auto Filling''.
filling, explicit:
See ``Filling''.
filter function:
See ``Process Filter Functions''.
find-backup-file-name:
See ``Naming Backup Files''.
find-charset-region:
See ``Scanning for Character Sets''.
find-charset-string:
See ``Scanning for Character Sets''.
find-coding-systems-for-charsets:
See ``Coding Systems in Lisp''.
find-coding-systems-region:
See ``Coding Systems in Lisp''.
find-coding-systems-string:
See ``Coding Systems in Lisp''.
find-file:
See ``Functions for Visiting Files''.
find-file-hooks:
See ``Functions for Visiting Files''.
find-file-name-handler:
See ``Making Certain File Names "Magic"''.
find-file-noselect:
See ``Functions for Visiting Files''.
find-file-not-found-hooks:
See ``Functions for Visiting Files''.
find-file-other-window:
See ``Functions for Visiting Files''.
find-file-read-only:
See ``Functions for Visiting Files''.
find-file-wildcards:
See ``Functions for Visiting Files''.
find-image:
See ``Defining Images''.
find-operation-coding-system:
See ``Default Coding Systems''.
finding files:
See ``Visiting Files''.
finding windows:
See ``Selecting Windows''.
first-change-hook:
See ``Change Hooks''.
fixed-pitch (face name):
See ``Standard Faces''.
fixup-whitespace:
See ``User-Level Deletion Commands''.
float:
See ``Numeric Conversions''.
float-time:
See ``Time of Day''.
floatp:
See ``Type Predicates for Numbers''.
floats-consed:
See ``Memory Usage''.
floor:
See ``Numeric Conversions''.
flow control characters:
See ``Flow Control''.
flow control example:
See ``Translating Input Events''.
flush input:
See ``Miscellaneous Event Input Features''.
fmakunbound:
See ``Accessing Function Cell Contents''.
focus event:
See ``Focus Events''.
focus-follows-mouse:
See ``Input Focus''.
following-char:
See ``Examining Text Near Point''.
Font Lock Mode:
See ``Font Lock Mode''.
font-list-limit:
See ``Looking Up Fonts''.
Font-Lock mode:
See ``Automatic Face Assignment''.
font-lock-beginning-of-syntax-function:
See ``Other Font Lock Variables''.
font-lock-builtin-face:
See ``Faces for Font Lock''.
font-lock-comment-face:
See ``Faces for Font Lock''.
font-lock-constant-face:
See ``Faces for Font Lock''.
font-lock-defaults:
See ``Font Lock Basics''.
font-lock-function-name-face:
See ``Faces for Font Lock''.
font-lock-keyword-face:
See ``Faces for Font Lock''.
font-lock-keywords:
See ``Search-based Fontification''.
font-lock-keywords-case-fold-search:
See ``Other Font Lock Variables''.
font-lock-keywords-only:
See ``Other Font Lock Variables''.
font-lock-mark-block-function:
See ``Other Font Lock Variables''.
font-lock-string-face:
See ``Faces for Font Lock''.
font-lock-syntactic-keywords:
See ``Syntactic Font Lock''.
font-lock-syntax-table:
See ``Other Font Lock Variables''.
font-lock-type-face:
See ``Faces for Font Lock''.
font-lock-variable-name-face:
See ``Faces for Font Lock''.
font-lock-warning-face:
See ``Faces for Font Lock''.
fontification-functions:
See ``Automatic Face Assignment''.
fontified (text property):
See ``Properties with Special Meanings''.
fonts:
See ``Some Terms''.
fonts, more than one on display:
See ``Display Feature Testing''.
foo:
See ``A Sample Function Description''.
for:
See ``Evaluating Macro Arguments Repeatedly''.
force-mode-line-update:
See ``Mode Line Format''.
forcing redisplay:
See ``Forcing Redisplay''.
format:
See ``Formatting Strings''.
format definition:
See ``File Format Conversion''.
format of keymaps:
See ``Format of Keymaps''.
format specification:
See ``Formatting Strings''.
format-alist:
See ``File Format Conversion''.
format-find-file:
See ``File Format Conversion''.
format-insert-file:
See ``File Format Conversion''.
format-time-string:
See ``Time Conversion''.
format-write-file:
See ``File Format Conversion''.
formatting strings:
See ``Formatting Strings''.
formfeed:
See ``Character Type''.
forms:
See ``Introduction to Evaluation''.
forward advice:
See ``Defining Advice''.
forward-char:
See ``Motion by Characters''.
forward-comment:
See ``Parsing Balanced Expressions''.
forward-line:
See ``Motion by Text Lines''.
forward-list:
See ``Moving over Balanced Expressions''.
forward-sexp:
See ``Moving over Balanced Expressions''.
forward-to-indentation:
See ``Indentation-Based Motion Commands''.
forward-word:
See ``Motion by Words''.
frame:
See ``Frames''.
frame configuration:
See ``Frame Configurations''.
frame size:
See ``Frame Size And Position''.
frame visibility:
See ``Visibility of Frames''.
frame-background-mode:
See ``Defining Faces''.
frame-char-height:
See ``Frame Size And Position''.
frame-char-width:
See ``Frame Size And Position''.
frame-first-window:
See ``Frames and Windows''.
frame-height:
See ``Frame Size And Position''.
frame-list:
See ``Finding All Frames''.
frame-live-p:
See ``Deleting Frames''.
frame-parameter:
See ``Access to Frame Parameters''.
frame-parameters:
See ``Access to Frame Parameters''.
frame-pixel-height:
See ``Frame Size And Position''.
frame-pixel-width:
See ``Frame Size And Position''.
frame-selected-window:
See ``Frames and Windows''.
frame-title-format:
See ``Frame Titles''.
frame-visible-p:
See ``Visibility of Frames''.
frame-width:
See ``Frame Size And Position''.
framep:
See ``Frames''.
frames, more than one on display:
See ``Display Feature Testing''.
free list:
See ``Garbage Collection''.
frequency counts:
See ``Coverage Testing''.
fringe (face name):
See ``Standard Faces''.
fround:
See ``Rounding Operations''.
fset:
See ``Accessing Function Cell Contents''.
ftp-login:
See ``Cleaning Up from Nonlocal Exits''.
ftruncate:
See ``Rounding Operations''.
full keymap:
See ``Format of Keymaps''.
funcall:
See ``Calling Functions''.
funcall, and debugging:
See ``Internals of the Debugger''.
function <1>:
See ``Anonymous Functions''.
function:
See ``What Is a Function?''.
function call:
See ``Evaluation of Function Forms''.
function call debugging:
See ``Entering the Debugger on a Function Call''.
function cell:
See ``Symbol Components''.
function cell in autoload:
See ``Autoload''.
function definition:
See ``Naming a Function''.
function descriptions:
See ``A Sample Function Description''.
function form evaluation:
See ``Evaluation of Function Forms''.
function input stream:
See ``Input Streams''.
function invocation:
See ``Calling Functions''.
function keys:
See ``Function Keys''.
function name:
See ``Naming a Function''.
function output stream:
See ``Output Streams''.
function quoting:
See ``Anonymous Functions''.
function-key-map:
See ``Translating Input Events''.
functionals:
See ``Calling Functions''.
functionp:
See ``What Is a Function?''.
functions in modes:
See ``Major Mode Conventions''.
functions, making them interactive:
See ``Defining Commands''.
Fundamental mode:
See ``Major Modes''.
fundamental-mode:
See ``How Emacs Chooses a Major Mode''.
fundamental-mode-abbrev-table:
See ``Standard Abbrev Tables''.
fundamental-mode-map:
See ``Standard Keymaps''.
gamma correction:
See ``Window Frame Parameters''.
gap-position:
See ``The Buffer Gap''.
gap-size:
See ``The Buffer Gap''.
garbage collection protection:
See ``Writing Emacs Primitives''.
garbage collector:
See ``Garbage Collection''.
garbage-collect:
See ``Garbage Collection''.
garbage-collection-messages:
See ``Garbage Collection''.
gc-cons-threshold:
See ``Garbage Collection''.
general-holidays:
See ``Customizing the Holidays''.
generate-new-buffer:
See ``Creating Buffers''.
generate-new-buffer-name:
See ``Buffer Names''.
generic characters:
See ``Splitting Characters''.
generic comment delimiter:
See ``Table of Syntax Classes''.
generic string delimiter:
See ``Table of Syntax Classes''.
geometry specification:
See ``Frame Size And Position''.
get:
See ``Property List Functions for Symbols''.
get-buffer:
See ``Buffer Names''.
get-buffer-create:
See ``Creating Buffers''.
get-buffer-process:
See ``Process Buffers''.
get-buffer-window:
See ``Buffers and Windows''.
get-buffer-window-list:
See ``Buffers and Windows''.
get-char-property:
See ``Examining Text Properties''.
get-file-buffer:
See ``Buffer File Name''.
get-file-char:
See ``Input Streams''.
get-largest-window:
See ``Selecting Windows''.
get-lru-window:
See ``Selecting Windows''.
get-process:
See ``Process Information''.
get-register:
See ``Registers''.
get-text-property:
See ``Examining Text Properties''.
get-unused-category:
See ``Categories''.
get-window-with-predicate:
See ``Selecting Windows''.
getenv:
See ``Operating System Environment''.
gethash:
See ``Hash Table Access''.
GIF:
See ``GIF Images''.
global binding:
See ``Local Variables''.
global break condition:
See ``Global Break Condition''.
global keymap:
See ``Active Keymaps''.
global variable:
See ``Global Variables''.
global-abbrev-table:
See ``Standard Abbrev Tables''.
global-disable-point-adjustment:
See ``Adjusting Point After Commands''.
global-key-binding:
See ``Functions for Key Lookup''.
global-map:
See ``Active Keymaps''.
global-mode-string:
See ``Variables Used in the Mode Line''.
global-set-key:
See ``Commands for Binding Keys''.
global-unset-key:
See ``Commands for Binding Keys''.
glyph:
See ``Glyphs''.
glyph table:
See ``Glyphs''.
glyph-table:
See ``Glyphs''.
goto-char:
See ``Motion by Characters''.
goto-line:
See ``Motion by Text Lines''.
hack-local-variables:
See ``File Local Variables''.
handle-switch-frame:
See ``Input Focus''.
handling errors:
See ``Writing Code to Handle Errors''.
hash code:
See ``Defining Hash Comparisons''.
hash notation:
See ``Printed Representation and Read Syntax''.
hash tables:
See ``Hash Tables''.
hash-table-count:
See ``Other Hash Table Functions''.
hash-table-p:
See ``Other Hash Table Functions''.
hash-table-rehash-size:
See ``Other Hash Table Functions''.
hash-table-rehash-threshold:
See ``Other Hash Table Functions''.
hash-table-size:
See ``Other Hash Table Functions''.
hash-table-test:
See ``Other Hash Table Functions''.
hash-table-weakness:
See ``Other Hash Table Functions''.
hashing:
See ``Creating and Interning Symbols''.
header comments:
See ``Conventional Headers for Emacs Libraries''.
header line (of a window):
See ``Window Header Lines''.
header-line (face name):
See ``Standard Faces''.
header-line prefix key:
See ``Key Sequence Input''.
header-line-format:
See ``Window Header Lines''.
hebrew-holidays:
See ``Customizing the Holidays''.
help for major mode:
See ``Getting Help about a Major Mode''.
help-char:
See ``Help Functions''.
help-command:
See ``Help Functions''.
help-echo (text property) <1>:
See ``Overlay Properties''.
help-echo (text property):
See ``Properties with Special Meanings''.
help-event-list:
See ``Help Functions''.
help-form:
See ``Help Functions''.
help-map:
See ``Help Functions''.
Helper-describe-bindings:
See ``Help Functions''.
Helper-help:
See ``Help Functions''.
Helper-help-map:
See ``Standard Keymaps''.
highlight (face name):
See ``Standard Faces''.
highlighting:
See ``Inverse Video''.
history list:
See ``Minibuffer History''.
history of commands:
See ``Command History''.
holiday forms:
See ``Customizing the Holidays''.
holidays-in-diary-buffer:
See ``Customizing the Diary''.
HOME environment variable:
See ``Functions that Create Subprocesses''.
hooks:
See ``Hooks''.
hooks for changing a character:
See ``Properties with Special Meanings''.
hooks for loading:
See ``Hooks for Loading''.
hooks for motion of point:
See ``Properties with Special Meanings''.
hooks for text changes:
See ``Change Hooks''.
horizontal position:
See ``Counting Columns''.
horizontal scrolling:
See ``Horizontal Scrolling''.
horizontal-scroll-bar prefix key:
See ``Key Sequence Input''.
hyper characters:
See ``Character Type''.
icon-title-format:
See ``Frame Titles''.
iconified frame:
See ``Visibility of Frames''.
iconify-frame:
See ``Visibility of Frames''.
iconify-frame event:
See ``Miscellaneous Window System Events''.
identity:
See ``Calling Functions''.
idleness:
See ``Timers for Delayed Execution''.
IEEE floating point:
See ``Floating Point Basics''.
if:
See ``Conditionals''.
ignore:
See ``Calling Functions''.
ignored-local-variables:
See ``File Local Variables''.
image descriptor:
See ``Image Descriptors''.
image-cache-eviction-delay:
See ``Image Cache''.
image-mask-p:
See ``Image Descriptors''.
image-size:
See ``Showing Images''.
image-types:
See ``Images''.
images in buffers:
See ``Images''.
Imenu:
See ``Imenu''.
imenu-case-fold-search:
See ``Imenu''.
imenu-create-index-function:
See ``Imenu''.
imenu-extract-index-name-function:
See ``Imenu''.
imenu-generic-expression:
See ``Imenu''.
imenu-index-alist:
See ``Imenu''.
imenu-prev-index-position-function:
See ``Imenu''.
imenu-syntax-alist:
See ``Imenu''.
implicit progn:
See ``Sequencing''.
inc:
See ``A Simple Example of a Macro''.
include-other-diary-files:
See ``Fancy Diary Display''.
indent-according-to-mode:
See ``Indentation Controlled by Major Mode''.
indent-code-rigidly:
See ``Indenting an Entire Region''.
indent-for-tab-command:
See ``Indentation Controlled by Major Mode''.
indent-line-function:
See ``Indentation Controlled by Major Mode''.
indent-region:
See ``Indenting an Entire Region''.
indent-region-function:
See ``Indenting an Entire Region''.
indent-relative:
See ``Indentation Relative to Previous Lines''.
indent-relative-maybe:
See ``Indentation Relative to Previous Lines''.
indent-rigidly:
See ``Indenting an Entire Region''.
indent-tabs-mode:
See ``Indentation Primitives''.
indent-to:
See ``Indentation Primitives''.
indent-to-left-margin:
See ``Margins for Filling''.
indentation:
See ``Indentation''.
indenting with parentheses:
See ``Parsing Balanced Expressions''.
indicate-empty-lines:
See ``Usual Display Conventions''.
indirect buffers:
See ``Indirect Buffers''.
indirect specifications:
See ``Specification List''.
indirect-function:
See ``Symbol Function Indirection''.
indirection:
See ``Symbol Function Indirection''.
infinite loops:
See ``Debugging Infinite Loops''.
infinite recursion:
See ``Local Variables''.
infinity:
See ``Floating Point Basics''.
Info-edit-map:
See ``Standard Keymaps''.
Info-mode-map:
See ``Standard Keymaps''.
inherit:
See ``Table of Syntax Classes''.
inheritance of text properties:
See ``Stickiness of Text Properties''.
inheriting a keymap's bindings:
See ``Inheritance and Keymaps''.
inhibit-default-init:
See ``The Init File, `.emacs'''.
inhibit-eol-conversion:
See ``Specifying a Coding System for One Operation''.
inhibit-field-text-motion:
See ``Motion by Words''.
inhibit-file-name-handlers:
See ``Making Certain File Names "Magic"''.
inhibit-file-name-operation:
See ``Making Certain File Names "Magic"''.
inhibit-modification-hooks:
See ``Change Hooks''.
inhibit-point-motion-hooks:
See ``Properties with Special Meanings''.
inhibit-quit:
See ``Quitting''.
inhibit-read-only:
See ``Read-Only Buffers''.
inhibit-startup-echo-area-message:
See ``Summary: Sequence of Actions at Startup''.
inhibit-startup-message:
See ``Summary: Sequence of Actions at Startup''.
init file:
See ``The Init File, `.emacs'''.
init-file-user:
See ``User Identification''.
initial-calendar-window-hook:
See ``Customizing the Calendar''.
initial-frame-alist:
See ``Initial Frame Parameters''.
initial-major-mode:
See ``How Emacs Chooses a Major Mode''.
initialization:
See ``Summary: Sequence of Actions at Startup''.
inline functions:
See ``Inline Functions''.
innermost containing parentheses:
See ``Parsing Balanced Expressions''.
input events:
See ``Input Events''.
input focus:
See ``Input Focus''.
input methods:
See ``Input Methods''.
input modes:
See ``Input Modes''.
input stream:
See ``Input Streams''.
input-method-alist:
See ``Input Methods''.
input-method-function:
See ``Invoking the Input Method''.
input-pending-p:
See ``Miscellaneous Event Input Features''.
insert:
See ``Inserting Text''.
insert-abbrev-table-description:
See ``Abbrev Tables''.
insert-and-inherit:
See ``Stickiness of Text Properties''.
insert-before-markers:
See ``Inserting Text''.
insert-before-markers-and-inherit:
See ``Stickiness of Text Properties''.
insert-behind-hooks (overlay property):
See ``Overlay Properties''.
insert-behind-hooks (text property):
See ``Properties with Special Meanings''.
insert-buffer:
See ``User-Level Insertion Commands''.
insert-buffer-substring:
See ``Inserting Text''.
insert-char:
See ``Inserting Text''.
insert-default-directory:
See ``Reading File Names''.
insert-directory:
See ``Contents of Directories''.
insert-directory-program:
See ``Contents of Directories''.
insert-file-contents:
See ``Reading from Files''.
insert-file-contents-literally:
See ``Reading from Files''.
insert-hebrew-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
insert-image:
See ``Showing Images''.
insert-in-front-hooks (overlay property):
See ``Overlay Properties''.
insert-in-front-hooks (text property):
See ``Properties with Special Meanings''.
insert-islamic-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
insert-monthly-hebrew-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
insert-monthly-islamic-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
insert-register:
See ``Registers''.
insert-yearly-hebrew-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
insert-yearly-islamic-diary-entry:
See ``Hebrew- and Islamic-Date Diary Entries''.
inserting killed text:
See ``Functions for Yanking''.
insertion before point:
See ``Inserting Text''.
insertion of text:
See ``Inserting Text''.
insertion type of a marker:
See ``Marker Insertion Types''.
inside comment:
See ``Parsing Balanced Expressions''.
inside string:
See ``Parsing Balanced Expressions''.
installation-directory:
See ``Operating System Environment''.
int-to-string:
See ``Conversion of Characters and Strings''.
intangible (overlay property):
See ``Overlay Properties''.
intangible (text property):
See ``Properties with Special Meanings''.
integer to decimal:
See ``Conversion of Characters and Strings''.
integer to hexadecimal:
See ``Formatting Strings''.
integer to octal:
See ``Formatting Strings''.
integer to string:
See ``Conversion of Characters and Strings''.
integer-or-marker-p:
See ``Predicates on Markers''.
integerp:
See ``Type Predicates for Numbers''.
integers:
See ``Numbers''.
integers in specific radix:
See ``Integer Basics''.
interactive:
See ``Using `interactive'''.
interactive call:
See ``Interactive Call''.
interactive code description:
See ``Code Characters for `interactive'''.
interactive commands (Edebug):
See ``Instrumenting for Edebug''.
interactive completion:
See ``Code Characters for `interactive'''.
interactive function:
See ``Defining Commands''.
interactive, examples of using:
See ``Examples of Using `interactive'''.
interactive-form:
See ``Using `interactive'''.
interactive-p:
See ``Interactive Call''.
intern:
See ``Creating and Interning Symbols''.
intern-soft:
See ``Creating and Interning Symbols''.
internals, of buffer:
See ``Buffer Internals''.
internals, of process:
See ``Process Internals''.
internals, of window:
See ``Window Internals''.
interning:
See ``Creating and Interning Symbols''.
interpreter:
See ``Evaluation''.
interpreter-mode-alist:
See ``How Emacs Chooses a Major Mode''.
interprogram-cut-function:
See ``Low-Level Kill Ring''.
interprogram-paste-function:
See ``Low-Level Kill Ring''.
interrupt-process:
See ``Sending Signals to Processes''.
intervals:
See ``Why Text Properties are not Intervals''.
intervals-consed:
See ``Memory Usage''.
introduction sequence:
See ``Characters and Bytes''.
invalid function:
See ``Symbol Function Indirection''.
invalid prefix key error:
See ``Changing Key Bindings''.
invalid-function:
See ``Symbol Function Indirection''.
invalid-read-syntax:
See ``Printed Representation and Read Syntax''.
invalid-regexp:
See ``Backslash Constructs in Regular Expressions''.
Inverse Video:
See ``Inverse Video''.
inverse-video:
See ``Inverse Video''.
invert-face:
See ``Face Attribute Functions''.
invisible (overlay property):
See ``Overlay Properties''.
invisible (text property):
See ``Properties with Special Meanings''.
invisible frame:
See ``Visibility of Frames''.
invisible text:
See ``Invisible Text''.
invocation-directory:
See ``Operating System Environment''.
invocation-name:
See ``Operating System Environment''.
isearch-mode-map:
See ``Standard Keymaps''.
islamic-holidays:
See ``Customizing the Holidays''.
italic (face name):
See ``Standard Faces''.
iteration:
See ``Iteration''.
joining lists:
See ``Functions that Rearrange Lists''.
just-one-space:
See ``User-Level Deletion Commands''.
justify-current-line:
See ``Filling''.
kbd-macro-termination-hook:
See ``Keyboard Macros''.
kept-new-versions:
See ``Making and Deleting Numbered Backup Files''.
kept-old-versions:
See ``Making and Deleting Numbered Backup Files''.
key:
See ``Keymap Terminology''.
key binding:
See ``Keymap Terminology''.
key lookup:
See ``Key Lookup''.
key sequence:
See ``Key Sequence Input''.
key sequence error:
See ``Changing Key Bindings''.
key sequence input:
See ``Key Sequence Input''.
key translation function:
See ``Translating Input Events''.
key-binding:
See ``Functions for Key Lookup''.
key-description:
See ``Describing Characters for Help Messages''.
key-translation-map:
See ``Translating Input Events''.
keyboard events in strings:
See ``Putting Keyboard Events in Strings''.
keyboard macro execution:
See ``Interactive Call''.
keyboard macro termination:
See ``Beeping''.
keyboard macros:
See ``Keyboard Macros''.
keyboard macros (Edebug):
See ``Edebug Execution Modes''.
keyboard-coding-system:
See ``Terminal I/O Encoding''.
keyboard-quit:
See ``Quitting''.
keyboard-translate:
See ``Translating Input Events''.
keyboard-translate-table:
See ``Translating Input Events''.
keymap:
See ``Keymaps''.
keymap (overlay property):
See ``Overlay Properties''.
keymap (text property):
See ``Properties with Special Meanings''.
keymap entry:
See ``Key Lookup''.
keymap format:
See ``Format of Keymaps''.
keymap in keymap:
See ``Key Lookup''.
keymap inheritance:
See ``Inheritance and Keymaps''.
keymap of character:
See ``Properties with Special Meanings''.
keymap of character (and overlays):
See ``Overlay Properties''.
keymap prompt string:
See ``Format of Keymaps''.
keymap-parent:
See ``Inheritance and Keymaps''.
keymapp:
See ``Format of Keymaps''.
keymaps in modes:
See ``Major Mode Conventions''.
keys in documentation strings:
See ``Substituting Key Bindings in Documentation''.
keys, reserved:
See ``Emacs Lisp Coding Conventions''.
keystroke:
See ``Keymap Terminology''.
keystroke command:
See ``What Is a Function?''.
keyword symbol:
See ``Variables that Never Change''.
keywordp:
See ``Variables that Never Change''.
kill command repetition:
See ``Information from the Command Loop''.
kill ring:
See ``The Kill Ring''.
kill-all-local-variables:
See ``Creating and Deleting Buffer-Local Bindings''.
kill-append:
See ``Low-Level Kill Ring''.
kill-buffer:
See ``Killing Buffers''.
kill-buffer-hook:
See ``Killing Buffers''.
kill-buffer-query-functions:
See ``Killing Buffers''.
kill-emacs:
See ``Killing Emacs''.
kill-emacs-hook:
See ``Killing Emacs''.
kill-emacs-query-functions:
See ``Killing Emacs''.
kill-local-variable:
See ``Creating and Deleting Buffer-Local Bindings''.
kill-new:
See ``Low-Level Kill Ring''.
kill-process:
See ``Sending Signals to Processes''.
kill-read-only-ok:
See ``Functions for Killing''.
kill-region:
See ``Functions for Killing''.
kill-ring:
See ``Internals of the Kill Ring''.
kill-ring-max:
See ``Internals of the Kill Ring''.
kill-ring-yank-pointer:
See ``Internals of the Kill Ring''.
killing buffers:
See ``Killing Buffers''.
killing Emacs:
See ``Killing Emacs''.
lambda expression:
See ``Lambda Expressions''.
lambda in debug:
See ``Invoking the Debugger''.
lambda in keymap:
See ``Key Lookup''.
lambda list:
See ``Components of a Lambda Expression''.
lambda-list (Edebug):
See ``Specification List''.
last:
See ``Accessing Elements of Lists''.
last-abbrev:
See ``Looking Up and Expanding Abbreviations''.
last-abbrev-location:
See ``Looking Up and Expanding Abbreviations''.
last-abbrev-text:
See ``Looking Up and Expanding Abbreviations''.
last-coding-system-used:
See ``Encoding and I/O''.
last-command:
See ``Information from the Command Loop''.
last-command-char:
See ``Information from the Command Loop''.
last-command-event:
See ``Information from the Command Loop''.
last-event-frame:
See ``Information from the Command Loop''.
last-input-char:
See ``Miscellaneous Event Input Features''.
last-input-event:
See ``Miscellaneous Event Input Features''.
last-kbd-macro:
See ``Keyboard Macros''.
last-nonmenu-event:
See ``Information from the Command Loop''.
last-prefix-arg:
See ``Prefix Command Arguments''.
lazy loading:
See ``Dynamic Loading of Individual Functions''.
leading code:
See ``Text Representations''.
left-margin:
See ``Margins for Filling''.
left-margin-width:
See ``Displaying in the Margins''.
length:
See ``Sequences''.
let:
See ``Local Variables''.
let*:
See ``Local Variables''.
lexical binding (Edebug):
See ``Evaluation''.
lexical comparison:
See ``Comparison of Characters and Strings''.
library:
See ``Loading''.
library compilation:
See ``The Compilation Functions''.
library header comments:
See ``Conventional Headers for Emacs Libraries''.
line wrapping:
See ``Truncation''.
line-beginning-position:
See ``Motion by Text Lines''.
line-end-position:
See ``Motion by Text Lines''.
line-move-ignore-invisible:
See ``Invisible Text''.
lines:
See ``Motion by Text Lines''.
lines in region:
See ``Motion by Text Lines''.
linking files:
See ``Changing File Names and Attributes''.
Lisp debugger:
See ``The Lisp Debugger''.
Lisp expression motion:
See ``Moving over Balanced Expressions''.
Lisp history:
See ``Lisp History''.
Lisp library:
See ``Loading''.
Lisp nesting error:
See ``Eval''.
Lisp object:
See ``Lisp Data Types''.
Lisp printer:
See ``Output Functions''.
Lisp reader:
See ``Introduction to Reading and Printing''.
lisp-interaction-mode-map:
See ``Standard Keymaps''.
lisp-mode-abbrev-table:
See ``Standard Abbrev Tables''.
lisp-mode-map:
See ``Standard Keymaps''.
lisp-mode.el:
See ``Major Mode Examples''.
list <1>:
See ``Building Cons Cells and Lists''.
list:
See ``Lists''.
list elements:
See ``Accessing Elements of Lists''.
list form evaluation:
See ``Classification of List Forms''.
list in keymap:
See ``Key Lookup''.
list length:
See ``Sequences''.
list motion:
See ``Moving over Balanced Expressions''.
list structure:
See ``Lists and Cons Cells''.
list-buffers-directory:
See ``Buffer File Name''.
list-diary-entries-hook:
See ``Fancy Diary Display''.
list-hebrew-diary-entries:
See ``Hebrew- and Islamic-Date Diary Entries''.
list-islamic-diary-entries:
See ``Hebrew- and Islamic-Date Diary Entries''.
list-processes:
See ``Process Information''.
listify-key-sequence:
See ``Miscellaneous Event Input Features''.
listp:
See ``Predicates on Lists''.
lists and cons cells:
See ``Lists and Cons Cells''.
lists as sets:
See ``Using Lists as Sets''.
lists represented as boxes:
See ``Lists as Linked Pairs of Boxes''.
literal evaluation:
See ``Self-Evaluating Forms''.
ln:
See ``Changing File Names and Attributes''.
load:
See ``How Programs Do Loading''.
load error with require:
See ``Features''.
load errors:
See ``How Programs Do Loading''.
load-average:
See ``Operating System Environment''.
load-file:
See ``How Programs Do Loading''.
load-history:
See ``Unloading''.
load-in-progress:
See ``How Programs Do Loading''.
load-library:
See ``How Programs Do Loading''.
load-path:
See ``Library Search''.
load-read-function:
See ``How Programs Do Loading''.
loadhist-special-hooks:
See ``Unloading''.
loading:
See ``Loading''.
loading hooks:
See ``Hooks for Loading''.
loadup.el:
See ``Building Emacs''.
local binding:
See ``Local Variables''.
local keymap:
See ``Active Keymaps''.
local variables:
See ``Local Variables''.
local-abbrev-table:
See ``Standard Abbrev Tables''.
local-holidays:
See ``Customizing the Holidays''.
local-key-binding:
See ``Functions for Key Lookup''.
local-map (overlay property):
See ``Overlay Properties''.
local-map (text property):
See ``Properties with Special Meanings''.
local-set-key:
See ``Commands for Binding Keys''.
local-unset-key:
See ``Commands for Binding Keys''.
local-variable-p:
See ``Creating and Deleting Buffer-Local Bindings''.
local-write-file-hooks:
See ``Saving Buffers''.
locale:
See ``Locales''.
locale-coding-system:
See ``Locales''.
locate-library:
See ``Library Search''.
lock-buffer:
See ``File Locks''.
log:
See ``Standard Mathematical Functions''.
log10:
See ``Standard Mathematical Functions''.
logand:
See ``Bitwise Operations on Integers''.
logb:
See ``Floating Point Basics''.
logical and:
See ``Bitwise Operations on Integers''.
logical exclusive or:
See ``Bitwise Operations on Integers''.
logical inclusive or:
See ``Bitwise Operations on Integers''.
logical not:
See ``Bitwise Operations on Integers''.
logical shift:
See ``Bitwise Operations on Integers''.
logior:
See ``Bitwise Operations on Integers''.
lognot:
See ``Bitwise Operations on Integers''.
logxor:
See ``Bitwise Operations on Integers''.
looking-at:
See ``Regular Expression Searching''.
lookup-key:
See ``Functions for Key Lookup''.
loops, infinite:
See ``Debugging Infinite Loops''.
lower case:
See ``Case Conversion in Lisp''.
lower-frame:
See ``Raising and Lowering Frames''.
lowering a frame:
See ``Raising and Lowering Frames''.
lsh:
See ``Bitwise Operations on Integers''.
M-g:
See ``Prefix Keys''.
M-x:
See ``Interactive Call''.
Maclisp:
See ``Lisp History''.
macro:
See ``What Is a Function?''.
macro argument evaluation:
See ``Evaluating Macro Arguments Repeatedly''.
macro call:
See ``Expansion of a Macro Call''.
macro call evaluation:
See ``Lisp Macro Evaluation''.
macro compilation:
See ``The Compilation Functions''.
macro descriptions:
See ``A Sample Function Description''.
macro expansion:
See ``Expansion of a Macro Call''.
macroexpand:
See ``Expansion of a Macro Call''.
macros:
See ``Macros''.
magic file names:
See ``Making Certain File Names "Magic"''.
mail-host-address:
See ``Operating System Environment''.
major mode:
See ``Major Modes''.
major mode hook:
See ``Major Mode Conventions''.
major mode keymap:
See ``Active Keymaps''.
major-mode:
See ``Getting Help about a Major Mode''.
make-abbrev-table:
See ``Abbrev Tables''.
make-auto-save-file-name:
See ``Auto-Saving''.
make-backup-file-name:
See ``Naming Backup Files''.
make-backup-file-name-function:
See ``Making Backup Files''.
make-backup-files:
See ``Making Backup Files''.
make-bool-vector:
See ``Bool-vectors''.
make-byte-code:
See ``Byte-Code Function Objects''.
make-category-set:
See ``Categories''.
make-category-table:
See ``Categories''.
make-char:
See ``Splitting Characters''.
make-char-table:
See ``Char-Tables''.
make-directory:
See ``Creating and Deleting Directories''.
make-display-table:
See ``Display Table Format''.
make-face:
See ``Functions for Working with Faces''.
make-frame:
See ``Creating Frames''.
make-frame-invisible:
See ``Visibility of Frames''.
make-frame-on-display:
See ``Multiple Displays''.
make-frame-visible:
See ``Visibility of Frames''.
make-frame-visible event:
See ``Miscellaneous Window System Events''.
make-hash-table:
See ``Creating Hash Tables''.
make-help-screen:
See ``Help Functions''.
make-indirect-buffer:
See ``Indirect Buffers''.
make-keymap:
See ``Creating Keymaps''.
make-list:
See ``Building Cons Cells and Lists''.
make-local-hook:
See ``Hooks''.
make-local-variable:
See ``Creating and Deleting Buffer-Local Bindings''.
make-marker:
See ``Functions that Create Markers''.
make-overlay:
See ``Managing Overlays''.
make-sparse-keymap:
See ``Creating Keymaps''.
make-string:
See ``Creating Strings''.
make-symbol:
See ``Creating and Interning Symbols''.
make-symbolic-link:
See ``Changing File Names and Attributes''.
make-syntax-table:
See ``Syntax Table Functions''.
make-temp-file:
See ``Generating Unique File Names''.
make-temp-name:
See ``Generating Unique File Names''.
make-translation-table:
See ``Translation of Characters''.
make-variable-buffer-local:
See ``Creating and Deleting Buffer-Local Bindings''.
make-variable-frame-local:
See ``Frame-Local Variables''.
make-vector:
See ``Functions for Vectors''.
makehash:
See ``Creating Hash Tables''.
makunbound:
See ``When a Variable is "Void"''.
map-char-table:
See ``Char-Tables''.
map-y-or-n-p:
See ``Asking Multiple Y-or-N Questions''.
mapatoms:
See ``Creating and Interning Symbols''.
mapc:
See ``Mapping Functions''.
mapcar:
See ``Mapping Functions''.
mapconcat:
See ``Mapping Functions''.
maphash:
See ``Hash Table Access''.
mapping functions:
See ``Mapping Functions''.
margins, display:
See ``Displaying in the Margins''.
mark:
See ``The Mark''.
mark excursion:
See ``Excursions''.
mark ring:
See ``The Mark''.
mark, the:
See ``The Mark''.
mark-active:
See ``The Mark''.
mark-diary-entries-hook:
See ``Fancy Diary Display''.
mark-diary-entries-in-calendar:
See ``Customizing the Calendar''.
mark-even-if-inactive:
See ``The Mark''.
mark-hebrew-diary-entries:
See ``Hebrew- and Islamic-Date Diary Entries''.
mark-holidays-in-calendar:
See ``Customizing the Calendar''.
mark-included-diary-files:
See ``Fancy Diary Display''.
mark-islamic-diary-entries:
See ``Hebrew- and Islamic-Date Diary Entries''.
mark-marker:
See ``The Mark''.
mark-ring:
See ``The Mark''.
mark-ring-max:
See ``The Mark''.
marker argument:
See ``Code Characters for `interactive'''.
marker garbage collection:
See ``Overview of Markers''.
marker input stream:
See ``Input Streams''.
marker output stream:
See ``Output Streams''.
marker relocation:
See ``Overview of Markers''.
marker-buffer:
See ``Information from Markers''.
marker-insertion-type:
See ``Marker Insertion Types''.
marker-position:
See ``Information from Markers''.
markerp:
See ``Predicates on Markers''.
markers:
See ``Markers''.
markers as numbers:
See ``Overview of Markers''.
match data:
See ``The Match Data''.
match-beginning:
See ``Simple Match Data Access''.
match-data:
See ``Accessing the Entire Match Data''.
match-end:
See ``Simple Match Data Access''.
match-string:
See ``Simple Match Data Access''.
match-string-no-properties:
See ``Simple Match Data Access''.
mathematical functions:
See ``Standard Mathematical Functions''.
max:
See ``Comparison of Numbers''.
max-lisp-eval-depth:
See ``Eval''.
max-specpdl-size:
See ``Local Variables''.
md5:
See ``MD5 Checksum''.
MD5 checksum:
See ``MD5 Checksum''.
member:
See ``Using Lists as Sets''.
member-ignore-case:
See ``Using Lists as Sets''.
membership in a list:
See ``Using Lists as Sets''.
memory allocation:
See ``Garbage Collection''.
memory-limit:
See ``Garbage Collection''.
memq:
See ``Using Lists as Sets''.
menu bar:
See ``The Menu Bar''.
menu definition example:
See ``Menu Example''.
menu keymaps:
See ``Menu Keymaps''.
menu prompt string:
See ``Defining Menus''.
menu separators:
See ``Menu Separators''.
menu-bar prefix key:
See ``Key Sequence Input''.
menu-bar-edit-menu:
See ``Standard Keymaps''.
menu-bar-files-menu:
See ``Standard Keymaps''.
menu-bar-final-items:
See ``The Menu Bar''.
menu-bar-help-menu:
See ``Standard Keymaps''.
menu-bar-mule-menu:
See ``Standard Keymaps''.
menu-bar-search-menu:
See ``Standard Keymaps''.
menu-bar-tools-menu:
See ``Standard Keymaps''.
menu-bar-update-hook:
See ``The Menu Bar''.
menu-item:
See ``Extended Menu Items''.
menu-prompt-more-char:
See ``Menus and the Keyboard''.
message:
See ``The Echo Area''.
message digest computation:
See ``MD5 Checksum''.
message-box:
See ``The Echo Area''.
message-log-max:
See ``The Echo Area''.
message-or-box:
See ``The Echo Area''.
message-truncate-lines:
See ``The Echo Area''.
meta character key constants:
See ``Changing Key Bindings''.
meta character printing:
See ``Describing Characters for Help Messages''.
meta characters:
See ``Character Type''.
meta characters lookup:
See ``Format of Keymaps''.
meta-prefix-char:
See ``Functions for Key Lookup''.
min:
See ``Comparison of Numbers''.
minibuffer:
See ``Minibuffers''.
minibuffer history:
See ``Minibuffer History''.
minibuffer input:
See ``Recursive Editing''.
minibuffer window:
See ``Cyclic Ordering of Windows''.
minibuffer-allow-text-properties:
See ``Reading Text Strings with the Minibuffer''.
minibuffer-auto-raise:
See ``Raising and Lowering Frames''.
minibuffer-complete:
See ``Minibuffer Commands that Do Completion''.
minibuffer-complete-and-exit:
See ``Minibuffer Commands that Do Completion''.
minibuffer-complete-word:
See ``Minibuffer Commands that Do Completion''.
minibuffer-completion-confirm:
See ``Minibuffer Commands that Do Completion''.
minibuffer-completion-help:
See ``Minibuffer Commands that Do Completion''.
minibuffer-completion-predicate:
See ``Minibuffer Commands that Do Completion''.
minibuffer-completion-table:
See ``Minibuffer Commands that Do Completion''.
minibuffer-contents:
See ``Minibuffer Miscellany''.
minibuffer-contents-no-properties:
See ``Minibuffer Miscellany''.
minibuffer-depth:
See ``Minibuffer Miscellany''.
minibuffer-exit-hook:
See ``Minibuffer Miscellany''.
minibuffer-frame-alist:
See ``Initial Frame Parameters''.
minibuffer-help-form:
See ``Minibuffer Miscellany''.
minibuffer-history:
See ``Minibuffer History''.
minibuffer-local-completion-map:
See ``Minibuffer Commands that Do Completion''.
minibuffer-local-map:
See ``Reading Text Strings with the Minibuffer''.
minibuffer-local-must-match-map:
See ``Minibuffer Commands that Do Completion''.
minibuffer-local-ns-map:
See ``Reading Text Strings with the Minibuffer''.
minibuffer-prompt:
See ``Minibuffer Miscellany''.
minibuffer-prompt-end:
See ``Minibuffer Miscellany''.
minibuffer-scroll-window:
See ``Minibuffer Miscellany''.
minibuffer-setup-hook:
See ``Minibuffer Miscellany''.
minibuffer-window:
See ``Minibuffer Miscellany''.
minibuffer-window-active-p:
See ``Minibuffer Miscellany''.
minimum window size:
See ``Changing the Size of a Window''.
minor mode:
See ``Minor Modes''.
minor mode conventions:
See ``Conventions for Writing Minor Modes''.
minor-mode-alist:
See ``Variables Used in the Mode Line''.
minor-mode-key-binding:
See ``Functions for Key Lookup''.
minor-mode-map-alist:
See ``Active Keymaps''.
minor-mode-overriding-map-alist:
See ``Active Keymaps''.
minubuffer-prompt-width:
See ``Minibuffer Miscellany''.
misc-objects-consed:
See ``Memory Usage''.
mod:
See ``Arithmetic Operations''.
mode:
See ``Major and Minor Modes''.
mode help:
See ``Getting Help about a Major Mode''.
mode hook:
See ``Major Mode Conventions''.
mode line:
See ``Mode Line Format''.
mode line construct:
See ``The Data Structure of the Mode Line''.
mode loading:
See ``Major Mode Conventions''.
mode variable:
See ``Conventions for Writing Minor Modes''.
mode-class property:
See ``Major Mode Conventions''.
mode-line (face name):
See ``Standard Faces''.
mode-line prefix key:
See ``Key Sequence Input''.
mode-line-buffer-identification:
See ``Variables Used in the Mode Line''.
mode-line-format:
See ``The Data Structure of the Mode Line''.
mode-line-frame-identification:
See ``Variables Used in the Mode Line''.
mode-line-inverse-video:
See ``Inverse Video''.
mode-line-modified:
See ``Variables Used in the Mode Line''.
mode-line-mule-info:
See ``Variables Used in the Mode Line''.
mode-line-process:
See ``Variables Used in the Mode Line''.
mode-name:
See ``Variables Used in the Mode Line''.
mode-specific-map:
See ``Prefix Keys''.
modeline (face name):
See ``Standard Faces''.
modification flag (of buffer):
See ``Buffer Modification''.
modification of lists:
See ``Functions that Rearrange Lists''.
modification time, comparison of:
See ``Comparison of Modification Time''.
modification-hooks (overlay property):
See ``Overlay Properties''.
modification-hooks (text property):
See ``Properties with Special Meanings''.
modifier bits (of input character):
See ``Keyboard Events''.
modify-category-entry:
See ``Categories''.
modify-frame-parameters:
See ``Access to Frame Parameters''.
modify-syntax-entry:
See ``Syntax Table Functions''.
modulus:
See ``Arithmetic Operations''.
momentary-string-display:
See ``Temporary Displays''.
motion event:
See ``Motion Events''.
mouse click event:
See ``Click Events''.
mouse drag event:
See ``Drag Events''.
mouse event, timestamp:
See ``Accessing Events''.
mouse events, accessing the data:
See ``Accessing Events''.
mouse events, in special parts of frame:
See ``Key Sequence Input''.
mouse events, repeated:
See ``Repeat Events''.
mouse motion events:
See ``Motion Events''.
mouse pointer shape:
See ``Pointer Shapes''.
mouse position:
See ``Mouse Position''.
mouse position list, accessing:
See ``Accessing Events''.
mouse tracking:
See ``Mouse Tracking''.
mouse, availability:
See ``Display Feature Testing''.
mouse-2:
See ``Emacs Lisp Coding Conventions''.
mouse-face (overlay property):
See ``Overlay Properties''.
mouse-face (text property):
See ``Properties with Special Meanings''.
mouse-movement-p:
See ``Classifying Events''.
mouse-pixel-position:
See ``Mouse Position''.
mouse-position:
See ``Mouse Position''.
mouse-position-function:
See ``Mouse Position''.
mouse-wheel event:
See ``Miscellaneous Window System Events''.
move-marker:
See ``Moving Marker Positions''.
move-overlay:
See ``Managing Overlays''.
move-to-column:
See ``Counting Columns''.
move-to-left-margin:
See ``Margins for Filling''.
move-to-window-line:
See ``Motion by Screen Lines''.
movemail:
See ``Functions that Create Subprocesses''.
MS-DOS and file modes:
See ``Changing File Names and Attributes''.
MS-DOS file types:
See ``MS-DOS File Types''.
mule-keymap:
See ``Prefix Keys''.
multibyte characters:
See ``Non-ASCII Characters''.
multibyte text:
See ``Text Representations''.
multibyte-string-p:
See ``Text Representations''.
multibyte-syntax-as-symbol:
See ``Parsing Balanced Expressions''.
multiple windows:
See ``Basic Concepts of Emacs Windows''.
multiple X displays:
See ``Multiple Displays''.
multiple-frames:
See ``Frame Titles''.
named function:
See ``Naming a Function''.
NaN:
See ``Floating Point Basics''.
narrow-to-page:
See ``Narrowing''.
narrow-to-region:
See ``Narrowing''.
narrowing:
See ``Narrowing''.
natnump:
See ``Type Predicates for Numbers''.
natural numbers:
See ``Type Predicates for Numbers''.
nbutlast:
See ``Accessing Elements of Lists''.
nconc:
See ``Functions that Rearrange Lists''.
negative infinity:
See ``Floating Point Basics''.
negative-argument:
See ``Prefix Command Arguments''.
network connection:
See ``Network Connections''.
network-coding-system-alist:
See ``Default Coding Systems''.
new file message:
See ``Subroutines of Visiting''.
newline <1>:
See ``User-Level Insertion Commands''.
newline:
See ``Character Type''.
newline and Auto Fill mode:
See ``User-Level Insertion Commands''.
newline in print:
See ``Output Functions''.
newline in strings:
See ``Syntax for Strings''.
newline-and-indent:
See ``Indentation Controlled by Major Mode''.
next input:
See ``Miscellaneous Event Input Features''.
next-char-property-change:
See ``Text Property Search Functions''.
next-frame:
See ``Finding All Frames''.
next-history-element:
See ``Minibuffer Miscellany''.
next-matching-history-element:
See ``Minibuffer Miscellany''.
next-overlay-change:
See ``Searching for Overlays''.
next-property-change:
See ``Text Property Search Functions''.
next-screen-context-lines:
See ``Textual Scrolling''.
next-single-char-property-change:
See ``Text Property Search Functions''.
next-single-property-change:
See ``Text Property Search Functions''.
next-window:
See ``Cyclic Ordering of Windows''.
nil:
See ``Variables that Never Change''.
nil and lists:
See ``Lists and Cons Cells''.
nil in keymap:
See ``Key Lookup''.
nil in lists:
See ``Cons Cell and List Types''.
nil input stream:
See ``Input Streams''.
nil output stream:
See ``Output Streams''.
nil, uses of:
See ```nil' and `t'''.
nlistp:
See ``Predicates on Lists''.
no-catch:
See ``Explicit Nonlocal Exits: `catch' and `throw'''.
no-redraw-on-reenter:
See ``Refreshing the Screen''.
non-ASCII characters:
See ``Non-ASCII Characters''.
non-ASCII text in keybindings:
See ``Commands for Binding Keys''.
nonascii-insert-offset:
See ``Converting Text Representations''.
nonascii-translation-table:
See ``Converting Text Representations''.
nondirectory part (of file name):
See ``File Name Components''.
nongregorian-diary-listing-hook:
See ``Hebrew- and Islamic-Date Diary Entries''.
nongregorian-diary-marking-hook:
See ``Hebrew- and Islamic-Date Diary Entries''.
noninteractive:
See ``Batch Mode''.
noninteractive use:
See ``Batch Mode''.
nonlocal exits:
See ``Nonlocal Exits''.
nonprinting characters, reading:
See ``Quoted Character Input''.
normal hook:
See ``Hooks''.
normal-auto-fill-function:
See ``Auto Filling''.
normal-backup-enable-predicate:
See ``Making Backup Files''.
normal-mode:
See ``How Emacs Chooses a Major Mode''.
not:
See ``Constructs for Combining Conditions''.
not-modified:
See ``Buffer Modification''.
nreverse:
See ``Functions that Rearrange Lists''.
nth:
See ``Accessing Elements of Lists''.
nthcdr:
See ``Accessing Elements of Lists''.
null:
See ``Predicates on Lists''.
num-input-keys:
See ``Key Sequence Input''.
num-nonmacro-input-events:
See ``Key Sequence Input''.
number equality:
See ``Comparison of Numbers''.
number-of-diary-entries:
See ``Customizing the Diary''.
number-or-marker-p:
See ``Predicates on Markers''.
number-to-string:
See ``Conversion of Characters and Strings''.
numberp:
See ``Type Predicates for Numbers''.
numbers:
See ``Numbers''.
numeric prefix:
See ``Formatting Strings''.
numeric prefix argument:
See ``Prefix Command Arguments''.
numeric prefix argument usage:
See ``Code Characters for `interactive'''.
obarray:
See ``Creating and Interning Symbols''.
obarray in completion:
See ``Basic Completion Functions''.
object:
See ``Lisp Data Types''.
object internals:
See ``Object Internals''.
object to string:
See ``Output Functions''.
obsolete buffer:
See ``Comparison of Modification Time''.
occur-mode-map:
See ``Standard Keymaps''.
octal character code:
See ``Character Type''.
octal character input:
See ``Quoted Character Input''.
omer count:
See ``Sexp Entries and the Fancy Diary Display''.
one-window-p:
See ``Splitting Windows''.
only-global-abbrevs:
See ``Defining Abbrevs''.
open-dribble-file:
See ``Recording Input''.
open-network-stream:
See ``Network Connections''.
open-paren-in-column-0-is-defun-start:
See ``Moving over Balanced Expressions''.
open-termscript:
See ``Terminal Output''.
open parenthesis character:
See ``Table of Syntax Classes''.
operating system environment:
See ``Operating System Environment''.
option descriptions:
See ``A Sample Variable Description''.
optional arguments:
See ``Other Features of Argument Lists''.
options on command line:
See ``Command-Line Arguments''.
or:
See ``Constructs for Combining Conditions''.
ordering of windows, cyclic:
See ``Cyclic Ordering of Windows''.
other-buffer:
See ``The Buffer List''.
other-holidays:
See ``Customizing the Holidays''.
other-window:
See ``Cyclic Ordering of Windows''.
other-window-scroll-buffer:
See ``Textual Scrolling''.
output from processes:
See ``Receiving Output from Processes''.
output stream:
See ``Output Streams''.
overall prompt string:
See ``Format of Keymaps''.
overflow:
See ``Integer Basics''.
overlay arrow:
See ``The Overlay Arrow''.
overlay-arrow-position:
See ``The Overlay Arrow''.
overlay-arrow-string:
See ``The Overlay Arrow''.
overlay-buffer:
See ``Managing Overlays''.
overlay-end:
See ``Managing Overlays''.
overlay-get:
See ``Overlay Properties''.
overlay-put:
See ``Overlay Properties''.
overlay-start:
See ``Managing Overlays''.
overlays:
See ``Overlays''.
overlays-at:
See ``Searching for Overlays''.
overlays-in:
See ``Searching for Overlays''.
overriding-local-map:
See ``Active Keymaps''.
overriding-local-map-menu-flag:
See ``Active Keymaps''.
overriding-terminal-local-map:
See ``Active Keymaps''.
overwrite-mode:
See ``User-Level Insertion Commands''.
padding:
See ``Formatting Strings''.
page-delimiter:
See ``Standard Regular Expressions Used in Editing''.
paired delimiter:
See ``Table of Syntax Classes''.
paragraph-separate:
See ``Standard Regular Expressions Used in Editing''.
paragraph-start:
See ``Standard Regular Expressions Used in Editing''.
parasha, weekly:
See ``Sexp Entries and the Fancy Diary Display''.
parent of char-table:
See ``Char-Tables''.
parent process:
See ``Processes''.
parenthesis:
See ``Cons Cell and List Types''.
parenthesis depth:
See ``Parsing Balanced Expressions''.
parenthesis matching:
See ``Blinking Parentheses''.
parenthesis syntax:
See ``Table of Syntax Classes''.
parse state:
See ``Parsing Balanced Expressions''.
parse-colon-path:
See ``Operating System Environment''.
parse-partial-sexp:
See ``Parsing Balanced Expressions''.
parse-sexp-ignore-comments:
See ``Parsing Balanced Expressions''.
parse-sexp-lookup-properties:
See ``Syntax Properties''.
parsing:
See ``Syntax Tables''.
passwords, reading:
See ``Reading a Password''.
PATH environment variable:
See ``Functions that Create Subprocesses''.
path-separator:
See ``Operating System Environment''.
pausing:
See ``Waiting for Elapsed Time or Input''.
PBM:
See ``Other Image Types''.
peculiar error:
See ``Error Symbols and Condition Names''.
peeking at input:
See ``Miscellaneous Event Input Features''.
percent symbol in mode line:
See ``The Data Structure of the Mode Line''.
perform-replace:
See ``Search and Replace''.
performance analysis:
See ``Coverage Testing''.
permanent local variable:
See ``Creating and Deleting Buffer-Local Bindings''.
permission:
See ``Other Information about Files''.
piece of advice:
See ``Advising Emacs Lisp Functions''.
pipes:
See ``Creating an Asynchronous Process''.
play-sound:
See ``Sound Output''.
play-sound-file:
See ``Sound Output''.
play-sound-functions:
See ``Sound Output''.
plist:
See ``Property Lists''.
plist-get:
See ``Property Lists Outside Symbols''.
plist-member:
See ``Property Lists Outside Symbols''.
plist-put:
See ``Property Lists Outside Symbols''.
point:
See ``Point''.
point excursion:
See ``Excursions''.
point in window:
See ``Windows and Point''.
point with narrowing:
See ``Point''.
point-entered (text property):
See ``Properties with Special Meanings''.
point-left (text property):
See ``Properties with Special Meanings''.
point-marker:
See ``Functions that Create Markers''.
point-max:
See ``Point''.
point-max-marker:
See ``Functions that Create Markers''.
point-min:
See ``Point''.
point-min-marker:
See ``Functions that Create Markers''.
pointer shape:
See ``Pointer Shapes''.
pointers:
See ``Cons Cell and List Types''.
pop:
See ``Accessing Elements of Lists''.
pop-mark:
See ``The Mark''.
pop-to-buffer:
See ``Displaying Buffers in Windows''.
pop-up-frame-alist:
See ``Choosing a Window for Display''.
pop-up-frame-function:
See ``Choosing a Window for Display''.
pop-up-frames:
See ``Choosing a Window for Display''.
pop-up-windows:
See ``Choosing a Window for Display''.
pos-visible-in-window-p:
See ``The Window Start Position''.
position (in buffer):
See ``Positions''.
position argument:
See ``Code Characters for `interactive'''.
position in window:
See ``Windows and Point''.
position of mouse:
See ``Mouse Position''.
position-bytes:
See ``Text Representations''.
positive infinity:
See ``Floating Point Basics''.
posix-looking-at:
See ``POSIX Regular Expression Searching''.
posix-search-backward:
See ``POSIX Regular Expression Searching''.
posix-search-forward:
See ``POSIX Regular Expression Searching''.
posix-string-match:
See ``POSIX Regular Expression Searching''.
posn-col-row:
See ``Accessing Events''.
posn-point:
See ``Accessing Events''.
posn-timestamp:
See ``Accessing Events''.
posn-window:
See ``Accessing Events''.
posn-x-y:
See ``Accessing Events''.
post-command-hook:
See ``Command Loop Overview''.
Postscript images:
See ``Postscript Images''.
pre-abbrev-expand-hook:
See ``Looking Up and Expanding Abbreviations''.
pre-command-hook:
See ``Command Loop Overview''.
preactivating advice:
See ``Preactivation''.
preceding-char:
See ``Examining Text Near Point''.
predicates:
See ``Type Predicates''.
prefix argument:
See ``Prefix Command Arguments''.
prefix argument unreading:
See ``Miscellaneous Event Input Features''.
prefix command:
See ``Prefix Keys''.
prefix key:
See ``Prefix Keys''.
prefix-arg:
See ``Prefix Command Arguments''.
prefix-help-command:
See ``Help Functions''.
prefix-numeric-value:
See ``Prefix Command Arguments''.
preventing backtracking:
See ``Specification List''.
preventing prefix key:
See ``Key Lookup''.
previous complete subexpression:
See ``Parsing Balanced Expressions''.
previous-char-property-change:
See ``Text Property Search Functions''.
previous-frame:
See ``Finding All Frames''.
previous-history-element:
See ``Minibuffer Miscellany''.
previous-matching-history-element:
See ``Minibuffer Miscellany''.
previous-overlay-change:
See ``Searching for Overlays''.
previous-property-change:
See ``Text Property Search Functions''.
previous-single-char-property-change:
See ``Text Property Search Functions''.
previous-single-property-change:
See ``Text Property Search Functions''.
previous-window:
See ``Cyclic Ordering of Windows''.
primitive:
See ``What Is a Function?''.
primitive function internals:
See ``Writing Emacs Primitives''.
primitive type:
See ``Lisp Data Types''.
primitive-undo:
See ``Undo''.
prin1:
See ``Output Functions''.
prin1-to-string:
See ``Output Functions''.
princ:
See ``Output Functions''.
print:
See ``Output Functions''.
print example:
See ``Output Streams''.
print name cell:
See ``Symbol Components''.
print-circle:
See ``Variables Affecting Output''.
print-diary-entries:
See ``Customizing the Diary''.
print-diary-entries-hook:
See ``Customizing the Diary''.
print-escape-multibyte:
See ``Variables Affecting Output''.
print-escape-newlines:
See ``Variables Affecting Output''.
print-escape-nonascii:
See ``Variables Affecting Output''.
print-gensym:
See ``Variables Affecting Output''.
print-help-return-message:
See ``Help Functions''.
print-length:
See ``Variables Affecting Output''.
print-level:
See ``Variables Affecting Output''.
printed representation:
See ``Printed Representation and Read Syntax''.
printed representation for characters:
See ``Character Type''.
printing:
See ``Introduction to Reading and Printing''.
printing (Edebug):
See ``Printing in Edebug''.
printing circular structures:
See ``Printing in Edebug''.
printing limits:
See ``Variables Affecting Output''.
printing notation:
See ``Printing Notation''.
priority (overlay property):
See ``Overlay Properties''.
process:
See ``Processes''.
process filter:
See ``Process Filter Functions''.
process input:
See ``Sending Input to Processes''.
process internals:
See ``Process Internals''.
process output:
See ``Receiving Output from Processes''.
process sentinel:
See ``Sentinels: Detecting Process Status Changes''.
process signals:
See ``Sending Signals to Processes''.
process-buffer:
See ``Process Buffers''.
process-coding-system:
See ``Process Information''.
process-coding-system-alist:
See ``Default Coding Systems''.
process-command:
See ``Process Information''.
process-connection-type:
See ``Creating an Asynchronous Process''.
process-contact:
See ``Process Information''.
process-environment:
See ``Operating System Environment''.
process-exit-status:
See ``Process Information''.
process-filter:
See ``Process Filter Functions''.
process-id:
See ``Process Information''.
process-kill-without-query:
See ``Deleting Processes''.
process-list:
See ``Process Information''.
process-mark:
See ``Process Buffers''.
process-name:
See ``Process Information''.
process-running-child-p:
See ``Sending Input to Processes''.
process-send-eof:
See ``Sending Input to Processes''.
process-send-region:
See ``Sending Input to Processes''.
process-send-string:
See ``Sending Input to Processes''.
process-sentinel:
See ``Sentinels: Detecting Process Status Changes''.
process-status:
See ``Process Information''.
process-tty-name:
See ``Process Information''.
processp:
See ``Processes''.
profile.el:
See ``Tips for Making Compiled Code Fast''.
profiling:
See ``Tips for Making Compiled Code Fast''.
prog1:
See ``Sequencing''.
prog2:
See ``Sequencing''.
progn:
See ``Sequencing''.
program arguments:
See ``Functions that Create Subprocesses''.
program directories:
See ``Functions that Create Subprocesses''.
programmed completion:
See ``Programmed Completion''.
programming types:
See ``Programming Types''.
prompt string (of menu):
See ``Defining Menus''.
prompt string of keymap:
See ``Format of Keymaps''.
properties of text:
See ``Text Properties''.
propertize:
See ``Changing Text Properties''.
property list:
See ``Property Lists''.
property list cell:
See ``Symbol Components''.
property lists vs association lists:
See ``Property Lists and Association Lists''.
protected forms:
See ``Cleaning Up from Nonlocal Exits''.
provide:
See ``Features''.
providing features:
See ``Features''.
PTYs:
See ``Creating an Asynchronous Process''.
punctuation character:
See ``Table of Syntax Classes''.
pure storage:
See ``Pure Storage''.
pure-bytes-used:
See ``Pure Storage''.
purecopy:
See ``Pure Storage''.
purify-flag:
See ``Pure Storage''.
push:
See ``Building Cons Cells and Lists''.
push-mark:
See ``The Mark''.
put:
See ``Property List Functions for Symbols''.
put-image:
See ``Showing Images''.
put-text-property:
See ``Changing Text Properties''.
puthash:
See ``Hash Table Access''.
query-replace-history:
See ``Minibuffer History''.
query-replace-map:
See ``Search and Replace''.
querying the user:
See ``Yes-or-No Queries''.
question mark in character constant:
See ``Character Type''.
quietly-read-abbrev-file:
See ``Saving Abbrevs in Files''.
quit-flag:
See ``Quitting''.
quit-process:
See ``Sending Signals to Processes''.
quitting:
See ``Quitting''.
quitting from infinite loop:
See ``Debugging Infinite Loops''.
quote:
See ``Quoting''.
quote character:
See ``Parsing Balanced Expressions''.
quoted character input:
See ``Quoted Character Input''.
quoted-insert suppression:
See ``Changing Key Bindings''.
quoting:
See ``Quoting''.
quoting characters in printing:
See ``Output Functions''.
quoting using apostrophe:
See ``Quoting''.
radix for reading an integer:
See ``Integer Basics''.
raise-frame:
See ``Raising and Lowering Frames''.
raising a frame:
See ``Raising and Lowering Frames''.
random:
See ``Random Numbers''.
random numbers:
See ``Random Numbers''.
rassoc:
See ``Association Lists''.
rassq:
See ``Association Lists''.
raw prefix argument:
See ``Prefix Command Arguments''.
raw prefix argument usage:
See ``Code Characters for `interactive'''.
re-search-backward:
See ``Regular Expression Searching''.
re-search-forward:
See ``Regular Expression Searching''.
reactivating advice:
See ``Activation of Advice''.
read:
See ``Input Functions''.
read command name:
See ``Interactive Call''.
read syntax:
See ``Printed Representation and Read Syntax''.
read syntax for characters:
See ``Character Type''.
read-buffer:
See ``High-Level Completion Functions''.
read-buffer-function:
See ``High-Level Completion Functions''.
read-char:
See ``Reading One Event''.
read-char-exclusive:
See ``Reading One Event''.
read-coding-system:
See ``User-Chosen Coding Systems''.
read-command:
See ``High-Level Completion Functions''.
read-event:
See ``Reading One Event''.
read-expression-history:
See ``Minibuffer History''.
read-file-name:
See ``Reading File Names''.
read-from-minibuffer:
See ``Reading Text Strings with the Minibuffer''.
read-from-string:
See ``Input Functions''.
read-input-method-name:
See ``Input Methods''.
read-kbd-macro:
See ``Describing Characters for Help Messages''.
read-key-sequence:
See ``Key Sequence Input''.
read-key-sequence-vector:
See ``Key Sequence Input''.
read-minibuffer:
See ``Reading Lisp Objects with the Minibuffer''.
read-no-blanks-input:
See ``Reading Text Strings with the Minibuffer''.
read-non-nil-coding-system:
See ``User-Chosen Coding Systems''.
read-only (text property):
See ``Properties with Special Meanings''.
read-only buffer:
See ``Read-Only Buffers''.
read-only buffers in interactive:
See ``Using `interactive'''.
read-only character:
See ``Properties with Special Meanings''.
read-passwd:
See ``Reading a Password''.
read-quoted-char:
See ``Quoted Character Input''.
read-quoted-char quitting:
See ``Quitting''.
read-string:
See ``Reading Text Strings with the Minibuffer''.
read-variable:
See ``High-Level Completion Functions''.
reading:
See ``Introduction to Reading and Printing''.
reading a single event:
See ``Reading One Event''.
reading interactive arguments:
See ``Code Characters for `interactive'''.
reading symbols:
See ``Creating and Interning Symbols''.
real-last-command:
See ``Information from the Command Loop''.
rearrangement of lists:
See ``Functions that Rearrange Lists''.
rebinding:
See ``Changing Key Bindings''.
recent-auto-save-p:
See ``Auto-Saving''.
recent-keys:
See ``Recording Input''.
recenter:
See ``Textual Scrolling''.
record command history:
See ``Interactive Call''.
recursion:
See ``Iteration''.
recursion-depth:
See ``Recursive Editing''.
recursive command loop:
See ``Recursive Editing''.
recursive editing level:
See ``Recursive Editing''.
recursive evaluation:
See ``Introduction to Evaluation''.
recursive-edit:
See ``Recursive Editing''.
redirect-frame-focus:
See ``Input Focus''.
redisplay-dont-pause:
See ``Forcing Redisplay''.
redisplay-end-trigger-functions:
See ``Hooks for Window Scrolling and Changes''.
redo:
See ``Undo''.
redraw-display:
See ``Refreshing the Screen''.
redraw-frame:
See ``Refreshing the Screen''.
references, following:
See ``Emacs Lisp Coding Conventions''.
regexp:
See ``Regular Expressions''.
regexp alternative:
See ``Backslash Constructs in Regular Expressions''.
regexp grouping:
See ``Backslash Constructs in Regular Expressions''.
regexp searching:
See ``Regular Expression Searching''.
regexp-history:
See ``Minibuffer History''.
regexp-opt:
See ``Regular Expression Functions''.
regexp-opt-depth:
See ``Regular Expression Functions''.
regexp-quote:
See ``Regular Expression Functions''.
regexps used standardly in editing:
See ``Standard Regular Expressions Used in Editing''.
region (face name):
See ``Standard Faces''.
region argument:
See ``Code Characters for `interactive'''.
region, the:
See ``The Region''.
region-beginning:
See ``The Region''.
region-end:
See ``The Region''.
register-alist:
See ``Registers''.
registers:
See ``Registers''.
regular expression:
See ``Regular Expressions''.
regular expression searching:
See ``Regular Expression Searching''.
reindent-then-newline-and-indent:
See ``Indentation Controlled by Major Mode''.
relative file name:
See ``Absolute and Relative File Names''.
remainder:
See ``Arithmetic Operations''.
remhash:
See ``Hash Table Access''.
remove:
See ``Using Lists as Sets''.
remove-from-invisibility-spec:
See ``Invisible Text''.
remove-hook:
See ``Hooks''.
remove-images:
See ``Showing Images''.
remove-text-properties:
See ``Changing Text Properties''.
remq:
See ``Building Cons Cells and Lists''.
rename-auto-save-file:
See ``Auto-Saving''.
rename-buffer:
See ``Buffer Names''.
rename-file:
See ``Changing File Names and Attributes''.
renaming files:
See ``Changing File Names and Attributes''.
repeat events:
See ``Repeat Events''.
repeated loading:
See ``Repeated Loading''.
replace bindings:
See ``Changing Key Bindings''.
replace characters:
See ``Substituting for a Character Code''.
replace-buffer-in-windows:
See ``Displaying Buffers in Windows''.
replace-match:
See ``Replacing the Text that Matched''.
replacement:
See ``Search and Replace''.
require:
See ``Features''.
require-final-newline:
See ``Saving Buffers''.
requiring features:
See ``Features''.
reserved keys:
See ``Emacs Lisp Coding Conventions''.
resize frame:
See ``Frame Size And Position''.
rest arguments:
See ``Other Features of Argument Lists''.
restriction (in a buffer):
See ``Narrowing''.
resume (cf. no-redraw-on-reenter):
See ``Refreshing the Screen''.
return:
See ``Character Type''.
reverse:
See ``Building Cons Cells and Lists''.
reversing a list:
See ``Functions that Rearrange Lists''.
revert-buffer:
See ``Reverting''.
revert-buffer-function:
See ``Reverting''.
revert-buffer-insert-file-contents-function:
See ``Reverting''.
revert-without-query:
See ``Reverting''.
rgb value:
See ``Text Terminal Colors''.
right-margin-width:
See ``Displaying in the Margins''.
ring-bell-function:
See ``Beeping''.
rm:
See ``Changing File Names and Attributes''.
rosh hodesh:
See ``Sexp Entries and the Fancy Diary Display''.
round:
See ``Numeric Conversions''.
rounding in conversions:
See ``Numeric Conversions''.
rounding without conversion:
See ``Rounding Operations''.
rplaca:
See ``Modifying Existing List Structure''.
rplacd:
See ``Modifying Existing List Structure''.
run time stack:
See ``Internals of the Debugger''.
run-at-time:
See ``Timers for Delayed Execution''.
run-hook-with-args:
See ``Hooks''.
run-hook-with-args-until-failure:
See ``Hooks''.
run-hook-with-args-until-success:
See ``Hooks''.
run-hooks:
See ``Hooks''.
run-with-idle-timer:
See ``Timers for Delayed Execution''.
safe-length:
See ``Accessing Elements of Lists''.
same-window-buffer-names:
See ``Choosing a Window for Display''.
same-window-regexps:
See ``Choosing a Window for Display''.
save-abbrevs:
See ``Saving Abbrevs in Files''.
save-buffer:
See ``Saving Buffers''.
save-buffer-coding-system:
See ``Encoding and I/O''.
save-current-buffer:
See ``The Current Buffer''.
save-excursion:
See ``Excursions''.
save-match-data:
See ``Saving and Restoring the Match Data''.
save-restriction:
See ``Narrowing''.
save-selected-window:
See ``Selecting Windows''.
save-some-buffers:
See ``Saving Buffers''.
save-window-excursion:
See ``Window Configurations''.
saving text properties:
See ``Saving Text Properties in Files''.
saving window information:
See ``Window Configurations''.
scalable-fonts-allowed:
See ``Font Selection''.
scan-lists:
See ``Parsing Balanced Expressions''.
scan-sexps:
See ``Parsing Balanced Expressions''.
scope:
See ``Scoping Rules for Variable Bindings''.
screen layout <1>:
See ``Frame Configuration Type''.
screen layout:
See ``Window Configuration Type''.
screen of terminal:
See ``Basic Concepts of Emacs Windows''.
screen size:
See ``Frame Size And Position''.
screen-height:
See ``Frame Size And Position''.
screen-width:
See ``Frame Size And Position''.
scroll-bar (face name):
See ``Standard Faces''.
scroll-bar-event-ratio:
See ``Accessing Events''.
scroll-bar-scale:
See ``Accessing Events''.
scroll-conservatively:
See ``Textual Scrolling''.
scroll-down:
See ``Textual Scrolling''.
scroll-down-aggressively:
See ``Textual Scrolling''.
scroll-left:
See ``Horizontal Scrolling''.
scroll-margin:
See ``Textual Scrolling''.
scroll-other-window:
See ``Textual Scrolling''.
scroll-preserve-screen-position:
See ``Textual Scrolling''.
scroll-right:
See ``Horizontal Scrolling''.
scroll-step:
See ``Textual Scrolling''.
scroll-up:
See ``Textual Scrolling''.
scroll-up-aggressively:
See ``Textual Scrolling''.
scrolling textually:
See ``Textual Scrolling''.
search-backward:
See ``Searching for Strings''.
search-failed:
See ``Searching for Strings''.
search-forward:
See ``Searching for Strings''.
searching:
See ``Searching and Matching''.
searching and case:
See ``Searching and Case''.
searching for regexp:
See ``Regular Expression Searching''.
secondary-selection (face name):
See ``Standard Faces''.
select-frame:
See ``Input Focus''.
select-safe-coding-system:
See ``User-Chosen Coding Systems''.
select-safe-coding-system-accept-default-p:
See ``User-Chosen Coding Systems''.
select-window:
See ``Selecting Windows''.
selected frame:
See ``Input Focus''.
selected window:
See ``Basic Concepts of Emacs Windows''.
selected-frame:
See ``Input Focus''.
selected-window:
See ``Selecting Windows''.
selecting a buffer:
See ``The Current Buffer''.
selecting windows:
See ``Selecting Windows''.
selection (for window systems):
See ``Window System Selections''.
selection-coding-system:
See ``Window System Selections''.
selective display:
See ``Selective Display''.
selective-display:
See ``Selective Display''.
selective-display-ellipses:
See ``Selective Display''.
self-evaluating form:
See ``Self-Evaluating Forms''.
self-insert-and-exit:
See ``Minibuffer Miscellany''.
self-insert-command:
See ``User-Level Insertion Commands''.
self-insert-command override:
See ``Changing Key Bindings''.
self-insert-command, minor modes:
See ``Keymaps and Minor Modes''.
self-insertion:
See ``User-Level Insertion Commands''.
send-string-to-terminal:
See ``Terminal Output''.
sending signals:
See ``Sending Signals to Processes''.
sentence-end:
See ``Standard Regular Expressions Used in Editing''.
sentence-end-double-space:
See ``Filling''.
sentinel:
See ``Sentinels: Detecting Process Status Changes''.
sequence:
See ``Sequences, Arrays, and Vectors''.
sequence length:
See ``Sequences''.
sequencep:
See ``Sequences''.
set:
See ``How to Alter a Variable Value''.
set-auto-mode:
See ``How Emacs Chooses a Major Mode''.
set-buffer:
See ``The Current Buffer''.
set-buffer-auto-saved:
See ``Auto-Saving''.
set-buffer-major-mode:
See ``How Emacs Chooses a Major Mode''.
set-buffer-modified-p:
See ``Buffer Modification''.
set-buffer-multibyte:
See ``Selecting a Representation''.
set-case-syntax:
See ``The Case Table''.
set-case-syntax-delims:
See ``The Case Table''.
set-case-syntax-pair:
See ``The Case Table''.
set-case-table:
See ``The Case Table''.
set-category-table:
See ``Categories''.
set-char-table-default:
See ``Char-Tables''.
set-char-table-extra-slot:
See ``Char-Tables''.
set-char-table-parent:
See ``Char-Tables''.
set-char-table-range:
See ``Char-Tables''.
set-default:
See ``The Default Value of a Buffer-Local Variable''.
set-default-file-modes:
See ``Changing File Names and Attributes''.
set-display-table-slot:
See ``Display Table Format''.
set-face-attribute:
See ``Face Attribute Functions''.
set-face-background:
See ``Face Attribute Functions''.
set-face-bold-p:
See ``Face Attribute Functions''.
set-face-font:
See ``Face Attribute Functions''.
set-face-foreground:
See ``Face Attribute Functions''.
set-face-italic-p:
See ``Face Attribute Functions''.
set-face-stipple:
See ``Face Attribute Functions''.
set-face-underline-p:
See ``Face Attribute Functions''.
set-file-modes:
See ``Changing File Names and Attributes''.
set-frame-configuration:
See ``Frame Configurations''.
set-frame-height:
See ``Frame Size And Position''.
set-frame-position:
See ``Frame Size And Position''.
set-frame-size:
See ``Frame Size And Position''.
set-frame-width:
See ``Frame Size And Position''.
set-input-method:
See ``Input Methods''.
set-input-mode:
See ``Input Modes''.
set-keyboard-coding-system:
See ``Terminal I/O Encoding''.
set-keymap-parent:
See ``Inheritance and Keymaps''.
set-left-margin:
See ``Margins for Filling''.
set-mark:
See ``The Mark''.
set-marker:
See ``Moving Marker Positions''.
set-marker-insertion-type:
See ``Marker Insertion Types''.
set-match-data:
See ``Accessing the Entire Match Data''.
set-mouse-pixel-position:
See ``Mouse Position''.
set-mouse-position:
See ``Mouse Position''.
set-process-buffer:
See ``Process Buffers''.
set-process-coding-system:
See ``Process Information''.
set-process-filter:
See ``Process Filter Functions''.
set-process-sentinel:
See ``Sentinels: Detecting Process Status Changes''.
set-register:
See ``Registers''.
set-right-margin:
See ``Margins for Filling''.
set-screen-height:
See ``Frame Size And Position''.
set-screen-width:
See ``Frame Size And Position''.
set-standard-case-table:
See ``The Case Table''.
set-syntax-table:
See ``Syntax Table Functions''.
set-terminal-coding-system:
See ``Terminal I/O Encoding''.
set-text-properties:
See ``Changing Text Properties''.
set-visited-file-modtime:
See ``Comparison of Modification Time''.
set-visited-file-name:
See ``Buffer File Name''.
set-window-buffer:
See ``Buffers and Windows''.
set-window-configuration:
See ``Window Configurations''.
set-window-dedicated-p:
See ``Choosing a Window for Display''.
set-window-display-table:
See ``Active Display Table''.
set-window-hscroll:
See ``Horizontal Scrolling''.
set-window-margins:
See ``Displaying in the Margins''.
set-window-point:
See ``Windows and Point''.
set-window-redisplay-end-trigger:
See ``Hooks for Window Scrolling and Changes''.
set-window-start:
See ``The Window Start Position''.
set-window-vscroll:
See ``Vertical Fractional Scrolling''.
setcar:
See ``Altering List Elements with `setcar'''.
setcdr:
See ``Altering the CDR of a List''.
setenv:
See ``Operating System Environment''.
setplist:
See ``Property List Functions for Symbols''.
setprv:
See ``Operating System Environment''.
setq:
See ``How to Alter a Variable Value''.
setq-default:
See ``The Default Value of a Buffer-Local Variable''.
sets:
See ``Using Lists as Sets''.
setting modes of files:
See ``Changing File Names and Attributes''.
setting-constant:
See ``Variables that Never Change''.
sexp diary entries:
See ``Sexp Entries and the Fancy Diary Display''.
sexp motion:
See ``Moving over Balanced Expressions''.
shadowing of variables:
See ``Local Variables''.
shallow binding:
See ``Implementation of Dynamic Scoping''.
shared structure, read syntax:
See ``Read Syntax for Circular Objects''.
Shell mode mode-line-format:
See ``The Data Structure of the Mode Line''.
shell-command-history:
See ``Minibuffer History''.
shell-command-to-string:
See ``Creating a Synchronous Process''.
shell-quote-argument:
See ``Shell Arguments''.
show-help-function:
See ``Properties with Special Meanings''.
show-trailing-whitespace:
See ``Standard Faces''.
shrink-window:
See ``Changing the Size of a Window''.
shrink-window-horizontally:
See ``Changing the Size of a Window''.
shrink-window-if-larger-than-buffer:
See ``Changing the Size of a Window''.
side effect:
See ``Introduction to Evaluation''.
signal:
See ``How to Signal an Error''.
signal-process:
See ``Sending Signals to Processes''.
signaling errors:
See ``How to Signal an Error''.
signals:
See ``Sending Signals to Processes''.
simple-diary-display:
See ``Fancy Diary Display''.
sin:
See ``Standard Mathematical Functions''.
single-key-description:
See ``Describing Characters for Help Messages''.
sit-for:
See ``Waiting for Elapsed Time or Input''.
site-init.el:
See ``Building Emacs''.
site-load.el:
See ``Building Emacs''.
site-run-file:
See ``The Init File, `.emacs'''.
site-start.el:
See ``Summary: Sequence of Actions at Startup''.
size of frame:
See ``Frame Size And Position''.
size of window:
See ``The Size of a Window''.
skip-chars-backward:
See ``Skipping Characters''.
skip-chars-forward:
See ``Skipping Characters''.
skip-syntax-backward:
See ``Motion and Syntax''.
skip-syntax-forward:
See ``Motion and Syntax''.
skipping characters:
See ``Skipping Characters''.
skipping comments:
See ``Parsing Balanced Expressions''.
sleep-for:
See ``Waiting for Elapsed Time or Input''.
small-temporary-file-directory:
See ``Generating Unique File Names''.
Snarf-documentation:
See ``Access to Documentation Strings''.
sort:
See ``Functions that Rearrange Lists''.
sort-columns:
See ``Sorting Text''.
sort-diary-entries:
See ``Fancy Diary Display''.
sort-fields:
See ``Sorting Text''.
sort-fold-case:
See ``Sorting Text''.
sort-lines:
See ``Sorting Text''.
sort-numeric-fields:
See ``Sorting Text''.
sort-pages:
See ``Sorting Text''.
sort-paragraphs:
See ``Sorting Text''.
sort-regexp-fields:
See ``Sorting Text''.
sort-subr:
See ``Sorting Text''.
sorting diary entries:
See ``Fancy Diary Display''.
sorting lists:
See ``Functions that Rearrange Lists''.
sorting text:
See ``Sorting Text''.
sound:
See ``Sound Output''.
source breakpoints:
See ``Source Breakpoints''.
spaces, specified height or width:
See ``Specified Spaces''.
sparse keymap:
See ``Format of Keymaps''.
special:
See ``Major Mode Conventions''.
special events:
See ``Special Events''.
special form descriptions:
See ``A Sample Function Description''.
special form evaluation:
See ``Special Forms''.
special forms:
See ``Primitive Function Type''.
special forms (Edebug):
See ``Instrumenting for Edebug''.
special forms for control structures:
See ``Control Structures''.
special-display-buffer-names:
See ``Choosing a Window for Display''.
special-display-frame-alist:
See ``Choosing a Window for Display''.
special-display-function:
See ``Choosing a Window for Display''.
special-display-popup-frame:
See ``Choosing a Window for Display''.
special-display-regexps:
See ``Choosing a Window for Display''.
special-event-map:
See ``Active Keymaps''.
specified spaces:
See ``Specified Spaces''.
speedups:
See ``Tips for Making Compiled Code Fast''.
splicing (with backquote):
See ``Backquote''.
split-char:
See ``Splitting Characters''.
split-height-threshold:
See ``Choosing a Window for Display''.
split-line:
See ``User-Level Insertion Commands''.
split-string:
See ``Creating Strings''.
split-window:
See ``Splitting Windows''.
split-window-horizontally:
See ``Splitting Windows''.
split-window-vertically:
See ``Splitting Windows''.
splitting windows:
See ``Splitting Windows''.
sqrt:
See ``Standard Mathematical Functions''.
stable sort:
See ``Functions that Rearrange Lists''.
standard regexps used in editing:
See ``Standard Regular Expressions Used in Editing''.
standard-case-table:
See ``The Case Table''.
standard-category-table:
See ``Categories''.
standard-display-table:
See ``Active Display Table''.
standard-input:
See ``Input Functions''.
standard-output:
See ``Variables Affecting Output''.
standard-syntax-table:
See ``Some Standard Syntax Tables''.
standard-translation-table-for-decode:
See ``Translation of Characters''.
standard-translation-table-for-encode:
See ``Translation of Characters''.
standards of coding style:
See ``Tips and Conventions''.
start-process:
See ``Creating an Asynchronous Process''.
start-process-shell-command:
See ``Creating an Asynchronous Process''.
startup of Emacs:
See ``Summary: Sequence of Actions at Startup''.
startup.el:
See ``Summary: Sequence of Actions at Startup''.
sticky text properties:
See ``Stickiness of Text Properties''.
stop points:
See ``Using Edebug''.
stop-process:
See ``Sending Signals to Processes''.
stopping an infinite loop:
See ``Debugging Infinite Loops''.
stopping on events:
See ``Global Break Condition''.
store-match-data:
See ``Accessing the Entire Match Data''.
store-substring:
See ``Modifying Strings''.
stream (for printing):
See ``Output Streams''.
stream (for reading):
See ``Input Streams''.
string:
See ``Creating Strings''.
string equality:
See ``Comparison of Characters and Strings''.
string in keymap:
See ``Key Lookup''.
string input stream:
See ``Input Streams''.
string length:
See ``Sequences''.
string search:
See ``Searching for Strings''.
string to character:
See ``Conversion of Characters and Strings''.
string to number:
See ``Conversion of Characters and Strings''.
string to object:
See ``Input Functions''.
string, writing a doc string:
See ``Documentation Basics''.
string-as-multibyte:
See ``Selecting a Representation''.
string-as-unibyte:
See ``Selecting a Representation''.
string-chars-consed:
See ``Memory Usage''.
string-equal:
See ``Comparison of Characters and Strings''.
string-lessp:
See ``Comparison of Characters and Strings''.
string-make-multibyte:
See ``Converting Text Representations''.
string-make-unibyte:
See ``Converting Text Representations''.
string-match:
See ``Regular Expression Searching''.
string-to-char:
See ``Conversion of Characters and Strings''.
string-to-int:
See ``Conversion of Characters and Strings''.
string-to-number:
See ``Conversion of Characters and Strings''.
string-to-syntax:
See ``Syntax Table Internals''.
string-width:
See ``Width''.
string<:
See ``Comparison of Characters and Strings''.
string=:
See ``Comparison of Characters and Strings''.
stringp:
See ``The Predicates for Strings''.
strings:
See ``Strings and Characters''.
strings with keyboard events:
See ``Putting Keyboard Events in Strings''.
strings, formatting them:
See ``Formatting Strings''.
strings-consed:
See ``Memory Usage''.
string quote:
See ``Table of Syntax Classes''.
subprocess:
See ``Processes''.
subr:
See ``What Is a Function?''.
subr-arity:
See ``What Is a Function?''.
subrp:
See ``What Is a Function?''.
subst-char-in-region:
See ``Substituting for a Character Code''.
substitute-command-keys:
See ``Substituting Key Bindings in Documentation''.
substitute-in-file-name:
See ``Functions that Expand Filenames''.
substitute-key-definition:
See ``Changing Key Bindings''.
substituting keys in documentation:
See ``Substituting Key Bindings in Documentation''.
substring:
See ``Creating Strings''.
subtype of char-table:
See ``Char-Tables''.
super characters:
See ``Character Type''.
suppress-keymap:
See ``Changing Key Bindings''.
suspend (cf. no-redraw-on-reenter):
See ``Refreshing the Screen''.
suspend evaluation:
See ``Recursive Editing''.
suspend-emacs:
See ``Suspending Emacs''.
suspend-hook:
See ``Suspending Emacs''.
suspend-resume-hook:
See ``Suspending Emacs''.
suspending Emacs:
See ``Suspending Emacs''.
switch-to-buffer:
See ``Displaying Buffers in Windows''.
switch-to-buffer-other-window:
See ``Displaying Buffers in Windows''.
switches on command line:
See ``Command-Line Arguments''.
switching to a buffer:
See ``Displaying Buffers in Windows''.
sxhash:
See ``Defining Hash Comparisons''.
symbol:
See ``Symbols''.
symbol components:
See ``Symbol Components''.
symbol equality:
See ``Creating and Interning Symbols''.
symbol evaluation:
See ``Symbol Forms''.
symbol function indirection:
See ``Symbol Function Indirection''.
symbol in keymap:
See ``Key Lookup''.
symbol name hashing:
See ``Creating and Interning Symbols''.
symbol-file:
See ``Unloading''.
symbol-function:
See ``Accessing Function Cell Contents''.
symbol-name:
See ``Creating and Interning Symbols''.
symbol-plist:
See ``Property List Functions for Symbols''.
symbol-value:
See ``Accessing Variable Values''.
symbolp:
See ``Symbols''.
symbols-consed:
See ``Memory Usage''.
symbol constituent:
See ``Table of Syntax Classes''.
synchronous subprocess:
See ``Creating a Synchronous Process''.
syntax classes:
See ``Syntax Descriptors''.
syntax descriptor:
See ``Syntax Descriptors''.
syntax error (Edebug):
See ``Backtracking in Specifications''.
syntax flags:
See ``Syntax Flags''.
syntax for characters:
See ``Character Type''.
syntax table:
See ``Syntax Tables''.
syntax table example:
See ``Major Mode Examples''.
syntax table internals:
See ``Syntax Table Internals''.
syntax tables in modes:
See ``Major Mode Conventions''.
syntax-table:
See ``Syntax Table Functions''.
syntax-table (text property):
See ``Syntax Properties''.
syntax-table-p:
See ``Syntax Table Concepts''.
system-configuration:
See ``Operating System Environment''.
system-key-alist:
See ``System-Specific X11 Keysyms''.
system-messages-locale:
See ``Locales''.
system-name:
See ``Operating System Environment''.
system-time-locale:
See ``Locales''.
system-type:
See ``Operating System Environment''.
t:
See ``Variables that Never Change''.
t and truth:
See ```nil' and `t'''.
t input stream:
See ``Input Streams''.
t output stream:
See ``Output Streams''.
tab:
See ``Character Type''.
tab deletion:
See ``Deleting Text''.
tab-stop-list:
See ``Adjustable "Tab Stops"''.
tab-to-tab-stop:
See ``Adjustable "Tab Stops"''.
tab-width:
See ``Usual Display Conventions''.
tabs stops for indentation:
See ``Adjustable "Tab Stops"''.
tag on run time stack:
See ``Explicit Nonlocal Exits: `catch' and `throw'''.
tan:
See ``Standard Mathematical Functions''.
TCP:
See ``Network Connections''.
temacs:
See ``Building Emacs''.
TEMP environment variable:
See ``Generating Unique File Names''.
temp-buffer-setup-hook:
See ``Temporary Displays''.
temp-buffer-show-function:
See ``Temporary Displays''.
temp-buffer-show-hook:
See ``Temporary Displays''.
temporary-file-directory:
See ``Generating Unique File Names''.
TERM environment variable:
See ``Terminal-Specific Initialization''.
term-file-prefix:
See ``Terminal-Specific Initialization''.
term-setup-hook:
See ``Terminal-Specific Initialization''.
Termcap:
See ``Terminal-Specific Initialization''.
terminal frame:
See ``Frames''.
terminal input:
See ``Terminal Input''.
terminal input modes:
See ``Input Modes''.
terminal output:
See ``Terminal Output''.
terminal screen:
See ``Basic Concepts of Emacs Windows''.
terminal-coding-system:
See ``Terminal I/O Encoding''.
terminal-specific initialization:
See ``Terminal-Specific Initialization''.
terminate keyboard macro:
See ``Miscellaneous Event Input Features''.
termscript file:
See ``Terminal Output''.
terpri:
See ``Output Functions''.
testing types:
See ``Type Predicates''.
text:
See ``Text''.
text files and binary files:
See ``MS-DOS File Types''.
text insertion:
See ``Inserting Text''.
text parsing:
See ``Syntax Tables''.
text properties:
See ``Text Properties''.
text properties in files:
See ``Saving Text Properties in Files''.
text representations:
See ``Text Representations''.
text-char-description:
See ``Describing Characters for Help Messages''.
text-mode-abbrev-table:
See ``Standard Abbrev Tables''.
text-mode-map:
See ``Standard Keymaps''.
text-mode-syntax-table:
See ``Some Standard Syntax Tables''.
text-properties-at:
See ``Examining Text Properties''.
text-property-any:
See ``Text Property Search Functions''.
text-property-default-nonsticky:
See ``Stickiness of Text Properties''.
text-property-not-all:
See ``Text Property Search Functions''.
textual scrolling:
See ``Textual Scrolling''.
thing-at-point:
See ``Examining Buffer Contents''.
this-command:
See ``Information from the Command Loop''.
this-command-keys:
See ``Information from the Command Loop''.
this-command-keys-vector:
See ``Information from the Command Loop''.
three-step-help:
See ``Help Functions''.
throw:
See ``Explicit Nonlocal Exits: `catch' and `throw'''.
throw example:
See ``Recursive Editing''.
tiled windows:
See ``Basic Concepts of Emacs Windows''.
timer:
See ``Timers for Delayed Execution''.
timestamp of a mouse event:
See ``Accessing Events''.
timing programs:
See ``Tips for Making Compiled Code Fast''.
tips:
See ``Tips and Conventions''.
TMP environment variable:
See ``Generating Unique File Names''.
TMPDIR environment variable:
See ``Generating Unique File Names''.
today-invisible-calendar-hook:
See ``Customizing the Calendar''.
today-visible-calendar-hook:
See ``Customizing the Calendar''.
toggle-read-only:
See ``Read-Only Buffers''.
tool bar:
See ``Tool bars''.
tool-bar (face name):
See ``Standard Faces''.
tool-bar-add-item:
See ``Tool bars''.
tool-bar-add-item-from-menu:
See ``Tool bars''.
tool-bar-item-margin:
See ``Tool bars''.
tool-bar-item-relief:
See ``Tool bars''.
tool-bar-map:
See ``Tool bars''.
top-level:
See ``Recursive Editing''.
top-level form:
See ``Loading''.
tq-close:
See ``Transaction Queues''.
tq-create:
See ``Transaction Queues''.
tq-enqueue:
See ``Transaction Queues''.
trace buffer:
See ``Trace Buffer''.
track-mouse:
See ``Mouse Tracking''.
tracking the mouse:
See ``Mouse Tracking''.
trailing codes:
See ``Text Representations''.
trailing-whitespace (face name):
See ``Standard Faces''.
transaction queue:
See ``Transaction Queues''.
transcendental functions:
See ``Standard Mathematical Functions''.
Transient Mark mode:
See ``The Mark''.
transient-mark-mode:
See ``The Mark''.
translate-region:
See ``Substituting for a Character Code''.
translating input events:
See ``Translating Input Events''.
translation tables:
See ``Translation of Characters''.
transpose-regions:
See ``Transposition of Text''.
triple-click events:
See ``Repeat Events''.
true:
See ```nil' and `t'''.
truename (of file):
See ``Truenames''.
truncate:
See ``Numeric Conversions''.
truncate-lines:
See ``Truncation''.
truncate-partial-width-windows:
See ``Truncation''.
truncate-string-to-width:
See ``Width''.
truth value:
See ```nil' and `t'''.
try-completion:
See ``Basic Completion Functions''.
tty-color-alist:
See ``Text Terminal Colors''.
tty-color-approximate:
See ``Text Terminal Colors''.
tty-color-clear:
See ``Text Terminal Colors''.
tty-color-define:
See ``Text Terminal Colors''.
tty-color-translate:
See ``Text Terminal Colors''.
tty-erase-char:
See ``Operating System Environment''.
two's complement:
See ``Integer Basics''.
type:
See ``Lisp Data Types''.
type checking:
See ``Type Predicates''.
type checking internals:
See ``Object Internals''.
type predicates:
See ``Type Predicates''.
type-of:
See ``Type Predicates''.
unbinding keys:
See ``Commands for Binding Keys''.
undefined:
See ``Functions for Key Lookup''.
undefined in keymap:
See ``Key Lookup''.
undefined key:
See ``Keymap Terminology''.
underline (face name):
See ``Standard Faces''.
undo avoidance:
See ``Substituting for a Character Code''.
undo-boundary:
See ``Undo''.
undo-limit:
See ``Maintaining Undo Lists''.
undo-strong-limit:
See ``Maintaining Undo Lists''.
unexec:
See ``Building Emacs''.
unhandled-file-name-directory:
See ``Making Certain File Names "Magic"''.
unibyte text:
See ``Text Representations''.
unintern:
See ``Creating and Interning Symbols''.
uninterned symbol:
See ``Creating and Interning Symbols''.
universal-argument:
See ``Prefix Command Arguments''.
unless:
See ``Conditionals''.
unload-feature:
See ``Unloading''.
unloading:
See ``Unloading''.
unlock-buffer:
See ``File Locks''.
unread-command-char:
See ``Miscellaneous Event Input Features''.
unread-command-events:
See ``Miscellaneous Event Input Features''.
unwind-protect:
See ``Cleaning Up from Nonlocal Exits''.
unwinding:
See ``Cleaning Up from Nonlocal Exits''.
up-list:
See ``Moving over Balanced Expressions''.
upcase:
See ``Case Conversion in Lisp''.
upcase-initials:
See ``Case Conversion in Lisp''.
upcase-region:
See ``Case Changes''.
upcase-word:
See ``Case Changes''.
update-directory-autoloads:
See ``Autoload''.
update-file-autoloads:
See ``Autoload''.
upper case:
See ``Case Conversion in Lisp''.
upper case key sequence:
See ``Key Sequence Input''.
use-global-map:
See ``Active Keymaps''.
use-hard-newlines:
See ``Filling''.
use-local-map:
See ``Active Keymaps''.
user option:
See ``Defining Global Variables''.
user-defined error:
See ``Error Symbols and Condition Names''.
user-full-name:
See ``User Identification''.
user-init-file:
See ``The Init File, `.emacs'''.
user-login-name:
See ``User Identification''.
user-mail-address:
See ``User Identification''.
user-real-login-name:
See ``User Identification''.
user-real-uid:
See ``User Identification''.
user-uid:
See ``User Identification''.
user-variable-p:
See ``Defining Global Variables''.
user-variable-p example:
See ``High-Level Completion Functions''.
value cell:
See ``Symbol Components''.
value of expression:
See ``Evaluation''.
values:
See ``Eval''.
variable:
See ``Variables''.
variable definition:
See ``Defining Global Variables''.
variable descriptions:
See ``A Sample Variable Description''.
variable limit error:
See ``Local Variables''.
variable-documentation:
See ``Documentation Basics''.
variable-interactive:
See ``Defining Global Variables''.
variable-pitch (face name):
See ``Standard Faces''.
variable-width spaces:
See ``Specified Spaces''.
variables, buffer-local:
See ``Buffer-Local Variables''.
variant coding system:
See ``Basic Concepts of Coding Systems''.
vc-mode:
See ``Variables Used in the Mode Line''.
vc-prefix-map:
See ``Prefix Keys''.
vconcat:
See ``Functions for Vectors''.
vector <1>:
See ``Functions for Vectors''.
vector:
See ``Vectors''.
vector evaluation:
See ``Self-Evaluating Forms''.
vector length:
See ``Sequences''.
vector-cells-consed:
See ``Memory Usage''.
vectorp:
See ``Functions for Vectors''.
verify-visited-file-modtime:
See ``Comparison of Modification Time''.
version number (in file name):
See ``File Name Components''.
version-control:
See ``Making and Deleting Numbered Backup Files''.
Vertical Fractional Scrolling:
See ``Vertical Fractional Scrolling''.
vertical tab:
See ``Character Type''.
vertical-line prefix key:
See ``Key Sequence Input''.
vertical-motion:
See ``Motion by Screen Lines''.
vertical-scroll-bar prefix key:
See ``Key Sequence Input''.
view-calendar-holidays-initially:
See ``Customizing the Calendar''.
view-diary-entries-initially:
See ``Customizing the Calendar''.
view-file:
See ``Functions for Visiting Files''.
view-mode-map:
See ``Standard Keymaps''.
view-register:
See ``Registers''.
visible frame:
See ``Visibility of Frames''.
visible-bell:
See ``Beeping''.
visible-frame-list:
See ``Finding All Frames''.
visited file:
See ``Buffer File Name''.
visited file mode:
See ``How Emacs Chooses a Major Mode''.
visited-file-modtime:
See ``Comparison of Modification Time''.
visiting files:
See ``Visiting Files''.
void function:
See ``Symbol Function Indirection''.
void function cell:
See ``Accessing Function Cell Contents''.
void variable:
See ``When a Variable is "Void"''.
void-function:
See ``Accessing Function Cell Contents''.
void-variable:
See ``When a Variable is "Void"''.
waiting:
See ``Waiting for Elapsed Time or Input''.
waiting for command key input:
See ``Miscellaneous Event Input Features''.
waiting-for-user-input-p:
See ``Sentinels: Detecting Process Status Changes''.
walk-windows:
See ``Cyclic Ordering of Windows''.
when:
See ``Conditionals''.
where-is-internal:
See ``Scanning Keymaps''.
while:
See ``Iteration''.
whitespace:
See ``Character Type''.
whitespace character:
See ``Table of Syntax Classes''.
wholenump:
See ``Type Predicates for Numbers''.
widen:
See ``Narrowing''.
widening:
See ``Narrowing''.
window:
See ``Basic Concepts of Emacs Windows''.
window (overlay property):
See ``Overlay Properties''.
window configuration (Edebug):
See ``Edebug Display Update''.
window configurations:
See ``Window Configurations''.
window excursions:
See ``Excursions''.
window frame:
See ``Frames''.
window header line:
See ``Window Header Lines''.
window internals:
See ``Window Internals''.
window ordering, cyclic:
See ``Cyclic Ordering of Windows''.
window point:
See ``Windows and Point''.
window point internals:
See ``Window Internals''.
window position:
See ``Windows and Point''.
window resizing:
See ``Changing the Size of a Window''.
window size:
See ``The Size of a Window''.
window size, changing:
See ``Changing the Size of a Window''.
window splitting:
See ``Splitting Windows''.
window that satisfies a predicate:
See ``Selecting Windows''.
window top line:
See ``The Window Start Position''.
window-at:
See ``Coordinates and Windows''.
window-buffer:
See ``Buffers and Windows''.
window-configuration-change-hook:
See ``Hooks for Window Scrolling and Changes''.
window-configuration-p:
See ``Window Configurations''.
window-dedicated-p:
See ``Choosing a Window for Display''.
window-display-table:
See ``Active Display Table''.
window-edges:
See ``The Size of a Window''.
window-end:
See ``The Window Start Position''.
window-frame:
See ``Frames and Windows''.
window-height:
See ``The Size of a Window''.
window-hscroll:
See ``Horizontal Scrolling''.
window-list:
See ``Cyclic Ordering of Windows''.
window-live-p:
See ``Deleting Windows''.
window-margins:
See ``Displaying in the Margins''.
window-min-height:
See ``Changing the Size of a Window''.
window-min-width:
See ``Changing the Size of a Window''.
window-minibuffer-p:
See ``Minibuffer Miscellany''.
window-point:
See ``Windows and Point''.
window-redisplay-end-trigger:
See ``Hooks for Window Scrolling and Changes''.
window-scroll-functions:
See ``Hooks for Window Scrolling and Changes''.
window-setup-hook:
See ``Window Systems''.
window-size-change-functions:
See ``Hooks for Window Scrolling and Changes''.
window-size-fixed:
See ``Changing the Size of a Window''.
window-start:
See ``The Window Start Position''.
window-system:
See ``Window Systems''.
window-vscroll:
See ``Vertical Fractional Scrolling''.
window-width:
See ``The Size of a Window''.
windowp:
See ``Basic Concepts of Emacs Windows''.
Windows file types:
See ``MS-DOS File Types''.
windows, controlling precisely:
See ``Buffers and Windows''.
with-current-buffer:
See ``The Current Buffer''.
with-output-to-string:
See ``Output Functions''.
with-output-to-temp-buffer:
See ``Temporary Displays''.
with-syntax-table:
See ``Syntax Table Functions''.
with-temp-buffer:
See ``The Current Buffer''.
with-temp-file:
See ``Writing to Files''.
with-temp-message:
See ``The Echo Area''.
with-timeout:
See ``Timers for Delayed Execution''.
word search:
See ``Searching for Strings''.
word-search-backward:
See ``Searching for Strings''.
word-search-forward:
See ``Searching for Strings''.
words-include-escapes:
See ``Motion by Words''.
word constituent:
See ``Table of Syntax Classes''.
write-abbrev-file:
See ``Saving Abbrevs in Files''.
write-char:
See ``Output Functions''.
write-contents-hooks:
See ``Saving Buffers''.
write-file:
See ``Saving Buffers''.
write-file-hooks:
See ``Saving Buffers''.
write-region:
See ``Writing to Files''.
write-region-annotate-functions:
See ``Saving Text Properties in Files''.
writing a documentation string:
See ``Documentation Basics''.
wrong-number-of-arguments:
See ``Other Features of Argument Lists''.
wrong-type-argument:
See ``Type Predicates''.
X Window System:
See ``Window Systems''.
x-bitmap-file-path:
See ``Face Attributes''.
x-close-connection:
See ``Multiple Displays''.
x-color-defined-p:
See ``Color Names''.
x-color-values:
See ``Color Names''.
x-defined-colors:
See ``Color Names''.
x-display-color-p:
See ``Display Feature Testing''.
x-display-list:
See ``Multiple Displays''.
x-family-fonts:
See ``Looking Up Fonts''.
x-font-family-list:
See ``Looking Up Fonts''.
x-get-cut-buffer:
See ``Window System Selections''.
x-get-resource:
See ``X Resources''.
x-get-selection:
See ``Window System Selections''.
x-list-fonts:
See ``Looking Up Fonts''.
x-open-connection:
See ``Multiple Displays''.
x-parse-geometry:
See ``Frame Size And Position''.
x-pointer-shape:
See ``Pointer Shapes''.
x-popup-dialog:
See ``Dialog Boxes''.
x-popup-menu:
See ``Pop-Up Menus''.
x-resource-class:
See ``X Resources''.
x-select-enable-clipboard:
See ``Window System Selections''.
x-sensitive-text-pointer-shape:
See ``Pointer Shapes''.
x-server-vendor:
See ``Display Feature Testing''.
x-server-version:
See ``Display Feature Testing''.
x-set-cut-buffer:
See ``Window System Selections''.
x-set-selection:
See ``Window System Selections''.
XBM:
See ``XBM Images''.
XPM:
See ``XPM Images''.
y-or-n-p:
See ``Yes-or-No Queries''.
y-or-n-p-with-timeout:
See ``Yes-or-No Queries''.
yahrzeits:
See ``Sexp Entries and the Fancy Diary Display''.
yank:
See ``Functions for Yanking''.
yank suppression:
See ``Changing Key Bindings''.
yank-pop:
See ``Functions for Yanking''.
yes-or-no questions:
See ``Yes-or-No Queries''.
yes-or-no-p:
See ``Yes-or-No Queries''.
zerop:
See ``Type Predicates for Numbers''.
| in regexp:
See ``Backslash Constructs in Regular Expressions''.
New Symbols Since the Previous Edition
**************************************
after-make-frame-functions:
See ``Creating Frames''.
assq-delete-all:
See ``Association Lists''.
auto-raise-tool-bar-items:
See ``Tool bars''.
auto-resize-tool-bar:
See ``Tool bars''.
auto-save-list-file-prefix:
See ``Auto-Saving''.
backup-directory-alist:
See ``Making Backup Files''.
base64-decode-region:
See ``Base 64 Encoding''.
base64-decode-string:
See ``Base 64 Encoding''.
base64-encode-region:
See ``Base 64 Encoding''.
base64-encode-string:
See ``Base 64 Encoding''.
beginning-of-defun-function:
See ``Moving over Balanced Expressions''.
buffer-has-markers-at:
See ``Information from Markers''.
byte-to-position:
See ``Text Representations''.
charset-bytes:
See ``Characters and Bytes''.
charset-plist:
See ``Character Sets''.
clear-face-cache:
See ``Font Selection''.
clear-image-cache:
See ``Image Cache''.
clear-this-command-keys:
See ``Information from the Command Loop''.
clrhash:
See ``Hash Table Access''.
color-defined-p:
See ``Color Names''.
color-gray-p:
See ``Color Names''.
color-supported-p:
See ``Color Names''.
color-values:
See ``Color Names''.
constrain-to-field:
See ``Defining and Using Fields''.
copy-hash-table:
See ``Other Hash Table Functions''.
create-glyph:
See ``Glyphs''.
create-image:
See ``Defining Images''.
default-header-line-format:
See ``Window Header Lines''.
defimage:
See ``Defining Images''.
define-hash-table-test:
See ``Defining Hash Comparisons''.
define-minor-mode:
See ``Defining Minor Modes''.
defined-colors:
See ``Color Names''.
delete-and-extract-region:
See ``Deleting Text''.
delete-field:
See ``Defining and Using Fields''.
delete-minibuffer-contents:
See ``Minibuffer Miscellany''.
describe-current-display-table:
See ``Display Table Format''.
describe-display-table:
See ``Display Table Format''.
disable-point-adjustment:
See ``Adjusting Point After Commands''.
display-backing-store:
See ``Display Feature Testing''.
display-color-cells:
See ``Display Feature Testing''.
display-color-p:
See ``Display Feature Testing''.
display-graphic-p:
See ``Display Feature Testing''.
display-grayscale-p:
See ``Display Feature Testing''.
display-message-or-buffer:
See ``The Echo Area''.
display-mm-height:
See ``Display Feature Testing''.
display-mm-width:
See ``Display Feature Testing''.
display-mouse-p:
See ``Display Feature Testing''.
display-pixel-height:
See ``Display Feature Testing''.
display-pixel-width:
See ``Display Feature Testing''.
display-planes:
See ``Display Feature Testing''.
display-popup-menus-p:
See ``Display Feature Testing''.
display-save-under:
See ``Display Feature Testing''.
display-screens:
See ``Display Feature Testing''.
display-selections-p:
See ``Display Feature Testing''.
display-visual-class:
See ``Display Feature Testing''.
dolist:
See ``Iteration''.
dotimes:
See ``Iteration''.
emacs-startup-hook:
See ``The Init File, `.emacs'''.
end-of-defun-function:
See ``Moving over Balanced Expressions''.
face-attribute:
See ``Face Attribute Functions''.
face-font-family-alternatives:
See ``Font Selection''.
face-font-registry-alternatives:
See ``Font Selection''.
face-font-selection-order:
See ``Font Selection''.
field-beginning:
See ``Defining and Using Fields''.
field-end:
See ``Defining and Using Fields''.
field-string:
See ``Defining and Using Fields''.
field-string-no-properties:
See ``Defining and Using Fields''.
file-expand-wildcards:
See ``Contents of Directories''.
find-file-wildcards:
See ``Functions for Visiting Files''.
find-image:
See ``Defining Images''.
font-list-limit:
See ``Looking Up Fonts''.
fontification-functions:
See ``Automatic Face Assignment''.
frame-parameter:
See ``Access to Frame Parameters''.
gethash:
See ``Hash Table Access''.
global-disable-point-adjustment:
See ``Adjusting Point After Commands''.
hash-table-count:
See ``Other Hash Table Functions''.
hash-table-p:
See ``Other Hash Table Functions''.
hash-table-rehash-size:
See ``Other Hash Table Functions''.
hash-table-rehash-threshold:
See ``Other Hash Table Functions''.
hash-table-size:
See ``Other Hash Table Functions''.
hash-table-test:
See ``Other Hash Table Functions''.
hash-table-weakness:
See ``Other Hash Table Functions''.
header-line-format:
See ``Window Header Lines''.
image-cache-eviction-delay:
See ``Image Cache''.
image-mask-p:
See ``Image Descriptors''.
image-size:
See ``Showing Images''.
indicate-empty-lines:
See ``Usual Display Conventions''.
inhibit-field-text-motion:
See ``Motion by Words''.
inhibit-modification-hooks:
See ``Change Hooks''.
keywordp:
See ``Variables that Never Change''.
left-margin-width:
See ``Displaying in the Margins''.
line-beginning-position:
See ``Motion by Text Lines''.
line-end-position:
See ``Motion by Text Lines''.
locale-coding-system:
See ``Locales''.
make-backup-file-name-function:
See ``Making Backup Files''.
make-category-table:
See ``Categories''.
make-hash-table:
See ``Creating Hash Tables''.
make-temp-file:
See ``Generating Unique File Names''.
makehash:
See ``Creating Hash Tables''.
mapc:
See ``Mapping Functions''.
maphash:
See ``Hash Table Access''.
minibuffer-contents:
See ``Minibuffer Miscellany''.
minibuffer-contents-no-properties:
See ``Minibuffer Miscellany''.
minibuffer-prompt-end:
See ``Minibuffer Miscellany''.
multibyte-syntax-as-symbol:
See ``Parsing Balanced Expressions''.
next-single-char-property-change:
See ``Text Property Search Functions''.
parse-colon-path:
See ``Operating System Environment''.
play-sound:
See ``Sound Output''.
play-sound-file:
See ``Sound Output''.
play-sound-functions:
See ``Sound Output''.
plist-member:
See ``Property Lists Outside Symbols''.
pop:
See ``Accessing Elements of Lists''.
position-bytes:
See ``Text Representations''.
previous-single-char-property-change:
See ``Text Property Search Functions''.
print-circle:
See ``Variables Affecting Output''.
print-gensym:
See ``Variables Affecting Output''.
process-running-child-p process:
See ``Sending Input to Processes''.
propertize:
See ``Changing Text Properties''.
push:
See ``Building Cons Cells and Lists''.
puthash:
See ``Hash Table Access''.
redisplay-dont-pause:
See ``Forcing Redisplay''.
remhash:
See ``Hash Table Access''.
right-margin-width:
See ``Displaying in the Margins''.
scalable-fonts-allowed:
See ``Font Selection''.
scroll-down-aggressively:
See ``Textual Scrolling''.
scroll-up-aggressively:
See ``Textual Scrolling''.
set-face-attribute:
See ``Face Attribute Functions''.
set-window-margins:
See ``Displaying in the Margins''.
show-help-function:
See ``Properties with Special Meanings''.
show-trailing-whitespace:
See ``Standard Faces''.
small-temporary-file-directory:
See ``Generating Unique File Names''.
subr-arity:
See ``What Is a Function?''.
sxhash:
See ``Defining Hash Comparisons''.
system-messages-locale:
See ``Locales''.
system-time-locale:
See ``Locales''.
temp-buffer-setup-hook:
See ``Temporary Displays''.
text-property-default-nonsticky:
See ``Stickiness of Text Properties''.
tool-bar-add-item:
See ``Tool bars''.
tool-bar-add-item-from-menu:
See ``Tool bars''.
tool-bar-item-margin:
See ``Tool bars''.
tool-bar-item-relief:
See ``Tool bars''.
tool-bar-map:
See ``Tool bars''.
tty-color-alist:
See ``Text Terminal Colors''.
tty-color-approximate:
See ``Text Terminal Colors''.
tty-color-clear:
See ``Text Terminal Colors''.
tty-color-define:
See ``Text Terminal Colors''.
tty-color-translate:
See ``Text Terminal Colors''.
user-init-file:
See ``The Init File, `.emacs'''.
window-margins:
See ``Displaying in the Margins''.
window-size-fixed:
See ``Changing the Size of a Window''.
with-syntax-table:
See ``Syntax Table Functions''.
with-temp-message:
See ``The Echo Area''.
x-family-fonts:
See ``Looking Up Fonts''.
x-font-family-list:
See ``Looking Up Fonts''.
...Short Contents...
...Table of Contents...