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This is Info file elisp, produced by Makeinfo-1.55 from the input file
elisp.texi.
This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 19.
Published by the Free Software Foundation, 675 Massachusetts Avenue,
Cambridge, MA 02139 USA
Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
File: elisp, Node: Major Mode Conventions, Next: Example Major Modes, Prev: Major Modes, Up: Major Modes
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 keep these conventions in mind when you
create a new major mode:
* 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 local variables in an
existing buffer without changing the buffer's text.
* Write a documentation string for this command which describes the
special commands available in this mode. `C-h m'
(`describe-mode') will print this.
The documentation string may include the special documentation
substrings, `\[COMMAND]', `\{KEYMAP}', and `\<KEYMAP>', that
enable the documentation to adapt automatically to the user's own
key bindings. *Note Keys in Documentation::. The `describe-mode'
function replaces these special documentation substrings with
their current meanings. *Note Accessing Documentation::.
* 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 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 Style Tips::.
* 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
function should call `use-local-map' to install this local map.
*Note Active Keymaps::, for more information.
This keymap should be kept in a global variable named
`MODENAME-mode-map'. Normally the library that defines the mode
sets this variable. Use `defvar' to set the variable, so that it
is not reinitialized if it already has a value. (Such
reinitialization could discard customizations made by the user.)
* 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'. The reasons
for this are the same as for using a keymap variable. *Note
Syntax Tables::.
* 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::.
* To give a variable a buffer-local binding, 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::.
* If hooks are appropriate for the mode, the major mode command
should run the hooks after completing all other initialization so
the user may further customize any of the settings. *Note Hooks::.
* 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
has Funny mode should not inherit Funny mode. Modes such as
Dired, Rmail, and Buffer List use this feature.
* If it is desirable that Emacs use the new mode by default after
visiting 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 `.emacs' files.
* 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.
File: elisp, Node: Example Major Modes, Next: Auto Major Mode, Prev: Major Mode Conventions, Up: Major Modes
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.
(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 "\t" 'tab-to-tab-stop)
(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) ; This provides the local keymap.
(setq mode-name "Text") ; This name goes into the mode line.
(setq major-mode 'text-mode) ; This is how `describe-mode'
; finds the doc string to print.
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(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)
;; The `lisp-syntax' argument is `nil' in Emacs Lisp mode,
;; and `t' in the other two Lisp modes.
(cond (lisp-syntax
(if (not lisp-mode-syntax-table)
;; The Emacs Lisp mode syntax table always exists, but
;; the Lisp Mode syntax table is created the first time a
;; mode that needs it is called. This is to save space.
(progn (setq lisp-mode-syntax-table
(copy-syntax-table emacs-lisp-mode-syntax-table))
;; Change some entries for Lisp mode.
(modify-syntax-entry ?\| "\" "
lisp-mode-syntax-table)
(modify-syntax-entry ?\[ "_ "
lisp-mode-syntax-table)
(modify-syntax-entry ?\] "_ "
lisp-mode-syntax-table)))
(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 '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-l' to `run-lisp', but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following function adds these common commands to a given
keymap.
(defun lisp-mode-commands (map)
(define-key map "\e\C-q" 'indent-sexp)
(define-key map "\177" 'backward-delete-char-untabify)
(define-key map "\t" 'lisp-indent-line))
Here is an example of using `lisp-mode-commands' to initialize a
keymap, as part of the code for Emacs Lisp mode. First we declare a
variable with `defvar' to hold the mode-specific keymap. When this
`defvar' executes, it sets the variable to `nil' if it was void. Then
we set up the keymap if the variable is `nil'.
This code avoids changing the keymap or the variable if it is already
set up. This lets the user customize the keymap if he or she so wishes.
(defvar emacs-lisp-mode-map () "")
(if emacs-lisp-mode-map
()
(setq emacs-lisp-mode-map (make-sparse-keymap))
(define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun)
(lisp-mode-commands emacs-lisp-mode-map))
Finally, here is the complete major mode function definition for
Emacs Lisp mode.
(defun emacs-lisp-mode ()
"Major mode for editing Lisp code to run in Emacs.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{emacs-lisp-mode-map}
Entry to this mode runs the hook `emacs-lisp-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map emacs-lisp-mode-map) ; This provides the local keymap.
(set-syntax-table emacs-lisp-mode-syntax-table)
(setq major-mode 'emacs-lisp-mode) ; This is how `describe-mode'
; finds out what to describe.
(setq mode-name "Emacs-Lisp") ; This goes into the mode line.
(lisp-mode-variables nil) ; This define various variables.
(run-hooks 'emacs-lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
File: elisp, Node: Auto Major Mode, Next: Mode Help, Prev: Example Major Modes, Up: Major Modes
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.
- 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, so it is not readily customizable.
- Command: normal-mode &optional FIND-FILE
This function establishes the proper major mode and 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, any 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. The variable `enable-local-variables' controls whether
to do so.
If you run `normal-mode' yourself, the argument FIND-FILE is
normally `nil'. In this case, `normal-mode' unconditionally
processes any local variables list. *Note Local Variables in
Files: (emacs)File variables, for the syntax of the local
variables section of a file.
`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.
- User Option: enable-local-variables
This variable controls processing of local variables lists in files
being visited. 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'.
- 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'.
- 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'), or on the
value of a local variable). 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 the 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.
- 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 name. 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 functions. Usually, the file name
patterns test for suffixes, such as `.el' and `.c', but this need
not be the case. Each 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.
Here is an example of how to prepend several pattern pairs to
`auto-mode-alist'. (You might use this sort of expression in your
`.emacs' file.)
(setq auto-mode-alist
(append
;; Filename starts with a dot.
'(("/\\.[^/]*$" . fundamental-mode)
;; Filename has no dot.
("[^\\./]*$" . fundamental-mode)
("\\.C$" . c++-mode))
auto-mode-alist))
- Function: hack-local-variables &optional FORCE
This function parses, and binds or evaluates as appropriate, any
local variables for the current buffer.
The handling of `enable-local-variables' documented for
`normal-mode' actually takes place here. The argument FORCE
reflects the argument FIND-FILE given to `normal-mode'.
File: elisp, Node: Mode Help, Prev: Auto Major Mode, Up: Major Modes
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 be the name of the function that is
called to initialize the mode. The `describe-mode' function uses
the documentation string of this symbol as the documentation of
the major mode.
File: elisp, Node: Minor Modes, Next: Mode Line Format, Prev: Major Modes, Up: Modes
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 is
unwieldy.
A minor mode is not usually a modification of single major mode. For
example, Auto Fill mode may be used in 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 deactivate a minor mode
and restore the environment of the major mode to the state it was in
before the minor mode was activated.
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.
* Menu:
* Minor Mode Conventions:: Tips for writing a minor mode.
* Keymaps and Minor Modes:: How a minor mode can have its own keymap.
File: elisp, Node: Minor Mode Conventions, Next: Keymaps and Minor Modes, Up: Minor Modes
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 represent the minor
mode. Its value should enable or disable the mode (`nil' to
disable; anything else to enable.) We call this the "mode
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 `overwrite-mode'.
It shows the use of `overwrite-mode' as a variable which enables or
disables the mode's behavior.
(setq overwrite-mode
(if (null arg) (not overwrite-mode)
(> (prefix-numeric-value arg) 0)))
* Add an element to `minor-mode-alist' for each minor mode (*note
Mode Line Variables::.). This element should be a list of the
following form:
(MODE-VARIABLE STRING)
Here MODE-VARIABLE is the variable that controls enablement 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:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
File: elisp, Node: Keymaps and Minor Modes, Prev: Minor Mode Conventions, Up: Minor Modes
Keymaps and Minor Modes
-----------------------
As of Emacs version 19, each minor mode can have its own keymap
which is active when the mode is enabled. *Note Active Keymaps::. To
set up a keymap for a minor mode, add an element to the alist
`minor-mode-map-alist'.
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. This is the only way to accomplish this in general, since
there is no way to customize what `self-insert-command' does except in
certain 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.)
- Variable: minor-mode-map-alist
This variable is an alist of elements element that look like this:
(VARIABLE . KEYMAP)
where VARIABLE is the variable which indicates whether the minor
mode is enabled, and KEYMAP is the keymap. The keymap KEYMAP is
active whenever VARIABLE has a non-`nil' value.
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.
What's more, the keymap itself must appear in the CDR. It does not
work to store a variable in the CDR and make the map the value of
that variable.
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.
File: elisp, Node: Mode Line Format, Next: Hooks, Prev: Minor Modes, Up: Modes
Mode Line Format
================
Each Emacs window (aside from minibuffer windows) includes a mode
line 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 the major and
minor modes of the buffer.
This section describes how the contents of the mode line are
controlled. It is in the chapter on modes 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' and the mode lines will
appear the same (except perhaps for the percentage of the file scrolled
off the top).
The mode line of a window is 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', you may want to force an
update of the mode line so as to display the new information.
- Function: force-mode-line-update
Force redisplay of the current buffer's mode line.
The mode line is usually displayed in inverse video; see
`mode-line-inverse-video' in *Note Inverse Video::.
* Menu:
* Mode Line Data:: The data structure that controls the mode line.
* Mode Line Variables:: Variables used in that data structure.
* %-Constructs:: Putting information into a mode line.
File: elisp, Node: Mode Line Data, Next: Mode Line Variables, Prev: Mode Line Format, Up: Mode Line Format
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 the buffer-local variable
`mode-line-format'. The data structure is called a "mode line
construct", and it is built in recursive fashion out of simpler mode
line constructs.
- 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.
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'. For most purposes, it
is sufficient to alter the variables referenced by `mode-line-format'.
A mode line construct may be a list, cons cell, symbol, or string.
If the value is a list, each element may be a list, a cons cell, a
symbol, or a string.
`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 in place of SYMBOL unless SYMBOL is `t' or
`nil', or is void, in which case SYMBOL is ignored.
There is one exception: if the value of SYMBOL is a string, it is
processed verbatim in that the `%'-constructs are not recognized.
`(STRING REST...) or (LIST REST...)'
A list whose first element is a string or list, means to
concatenate all the elements. This is the most common form of
mode line construct.
`(SYMBOL THEN ELSE)'
A list whose first element is a symbol is a conditional. Its
meaning depends on the value of SYMBOL. If the value is non-`nil',
the second element of the list (THEN) is processed recursively as
a mode line element. But if the value of SYMBOL is `nil', the
third element of the list (if there is one) is processed
recursively.
`(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
all the same variables that are used by the default value, rather than
duplicating their contents or displaying the information in another
fashion. This permits customizations made by the user, by libraries
(such as `display-time') or by 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 hostname and default directory.
(setq mode-line-format
(list ""
'mode-line-modified
"%b--"
(getenv "HOST") ; One element is not constant.
":"
'default-directory
" "
'global-mode-string
" %[(" 'mode-name
'minor-mode-alist
"%n"
'mode-line-process
")%]----"
'(-3 . "%p")
"-%-"))
File: elisp, Node: Mode Line Variables, Next: %-Constructs, Prev: Mode Line Data, Up: Mode Line Format
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-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, and `--%%-' if
the buffer is read only.
Changing this variable does not force an update of the mode line.
- Variable: mode-line-buffer-identification
This variable identifies the buffer being displayed in the window.
Its default value is `Emacs: %17b', which means that it displays
`Emacs:' followed by the buffer name. You may want to change this
in modes such as Rmail that do not behave like a "normal" Emacs.
- Variable: global-mode-string
This variable holds a string that is displayed in the mode line.
The command `display-time' puts the time and load in this variable.
The `%M' construct substitutes the value of `global-mode-string',
but this is obsolete, since the variable is included directly in
the mode line.
- 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)
The string MODE-LINE-STRING is included 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
=> ((abbrev-mode " Abbrev")
(overwrite-mode " Ovwrt")
(auto-fill-function " Fill")
(defining-kbd-macro " Def"))
(In earlier Emacs versions, `auto-fill-function' was called
`auto-fill-hook'.)
`minor-mode-alist' is not buffer-local. The variables mentioned
in the alist should be buffer-local if the 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'.
- 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:
(""
mode-line-modified
mode-line-buffer-identification
" "
global-mode-string
" %[("
mode-name
minor-mode-alist
"%n"
mode-line-process
")%]----"
(-3 . "%p")
"-%-")
File: elisp, Node: %-Constructs, Prev: Mode Line Variables, Up: Mode Line Format
`%'-Constructs in the Mode Line
-------------------------------
The following table lists the recognized `%'-constructs and what
they mean.
the current buffer name, using the `buffer-name' function.
the visited file name, using the `buffer-file-name' function.
`%' if the buffer is read only (see `buffer-read-only');
`*' if the buffer is modified (see `buffer-modified-p');
`-' otherwise.
the status of the subprocess belonging to the current buffer, using
`process-status'.
the percent of the buffer above the top of window, or `Top',
`Bottom' or `All'.
`Narrow' when narrowing is in effect; nothing otherwise (see
`narrow-to-region' in *Note Narrowing::).
an indication of the depth of recursive editing levels (not
counting minibuffer levels): one `[' for each editing level.
one `]' for each recursive editing level (not counting minibuffer
levels).
the character `%'--this is how to include a literal `%' in a
string in which `%'-constructs are allowed.
dashes sufficient to fill the remainder of the mode line.
The following two `%'-constructs are still supported but are
obsolete since use of the `mode-name' and `global-mode-string'
variables will produce the same results.
the value of `mode-name'.
the value of `global-mode-string'. Currently, only `display-time'
modifies the value of `global-mode-string'.
File: elisp, Node: Hooks, Prev: Mode Line Format, Up: Modes
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 lots of hooks for the sake of customization. Most often, hooks
are set up in the `.emacs' 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. The reason
most hooks are normal hooks is so that you can use them in a uniform
way. You can always tell when a hook is a normal hook, because its
name ends in `-hook'.
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.
As for abnormal hooks, those whose names end in `-function' have a
value which is a single function. Those whose names end in `-hooks'
have a value which is a list of functions. Any hook which is abnormal
is abnormal because a normal hook won't do the job; either the
functions are called with arguments, or their values are meaningful.
The name shows you that the hook is abnormal and you need to look up
how to use it properly.
Most major modes run hooks as the last step of initialization. This
makes it easy for a user to customize the behavior of the mode, by
overriding the local variable assignments already made by the mode. But
hooks may also be used in other contexts. For example, the hook
`suspend-hook' runs just before Emacs suspends itself (*note Suspending
Emacs::.).
For example, you can put the following expression in your `.emacs'
file if you want to turn on Auto Fill mode when in Lisp Interaction
mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
The next example shows how to use a hook to customize the way Emacs
formats C code. (People often have strong personal preferences for one
format compared to another.) Here the hook function is an anonymous
lambda expression.
(add-hook 'c-mode-hook
(function (lambda ()
(setq c-indent-level 4
c-argdecl-indent 0
c-label-offset -4
c-continued-statement-indent 0
c-brace-offset 0
comment-column 40))))
(setq c++-mode-hook c-mode-hook)
Finally, here is an example of how to use the Text mode hook to
provide a customized mode line for buffers in Text mode, displaying the
default directory in addition to the standard components of the mode
line. (This may cause the mode line to run out of space if you have
very long file names or display the time and load.)
(add-hook 'text-mode-hook
(function (lambda ()
(setq mode-line-format
'(mode-line-modified
"Emacs: %14b"
" "
default-directory
" "
global-mode-string
"%[("
mode-name
minor-mode-alist
"%n"
mode-line-process
") %]---"
(-3 . "%p")
"-%-")))))
At the appropriate time, Emacs uses the `run-hooks' function to run
particular hooks. This function calls the hook functions you have
added with `add-hooks'.
- Function: run-hooks &rest HOOKVAR
This function takes one or more hook names as arguments and runs
each one in turn. Each HOOKVAR 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.
For example:
(run-hooks 'emacs-lisp-mode-hook)
Major mode functions use this function to call any hooks defined
by the user.
- Function: add-hook HOOK FUNCTION &optional APPEND
This function is the handy way to add function FUNCTION to hook
variable HOOK. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)
adds `my-text-hook-function' to the hook called `text-mode-hook'.
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.
File: elisp, Node: Documentation, Next: Files, Prev: Modes, Up: Top
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.
* Menu:
* Documentation Basics:: Good style for doc strings.
Where to put them. How Emacs stores them.
* Accessing Documentation:: How Lisp programs can access doc strings.
* Keys in Documentation:: Substituting current key bindings.
* Describing Characters:: Making printable descriptions of
non-printing characters and key sequences.
* Help Functions:: Subroutines used by Emacs help facilities.
File: elisp, Node: Documentation Basics, Next: Accessing Documentation, Prev: Documentation, Up: Documentation
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', print only the first line of a multi-line documentation
string. Also, you should not indent the second line of a documentation
string, if you have one, because that looks odd when you use `C-h f'
(`describe-function') or `C-h v' (`describe-variable').
Documentation strings may 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::.)
Within the Lisp world, a documentation string is kept with 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 on the variable's
property list under the property name `variable-documentation'.
The function `documentation-property' knows how to extract it.
However, to save space, the documentation for preloaded functions and
variables (including primitive functions and autoloaded functions) are
stored in the `emacs/etc/DOC-VERSION' file. Both the `documentation'
and the `documentation-property' functions know how to access
`emacs/etc/DOC-VERSION', and the process is transparent to the user.
In this case, the documentation string is replaced with an integer
offset into the `emacs/etc/DOC-VERSION' file. Keeping the documentation
strings out of the Emacs core image saves a significant amount of space.
*Note Building Emacs::.
For information on the uses of documentation strings, see *Note
Help: (emacs)Help.
The `emacs/etc' directory contains two utilities that you can use to
print nice-looking hardcopy for the file `emacs/etc/DOC-VERSION'.
These are `sorted-doc.c' and `digest-doc.c'.