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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/modes | |
6 | @node Modes, Documentation, Keymaps, Top | |
7 | @chapter Major and Minor Modes | |
8 | @cindex mode | |
9 | ||
10 | A @dfn{mode} is a set of definitions that customize Emacs and can be | |
11 | turned on and off while you edit. There are two varieties of modes: | |
12 | @dfn{major modes}, which are mutually exclusive and used for editing | |
13 | particular kinds of text, and @dfn{minor modes}, which provide features | |
14 | that users can enable individually. | |
15 | ||
16 | This chapter describes how to write both major and minor modes, how to | |
17 | indicate them in the mode line, and how they run hooks supplied by the | |
18 | user. For related topics such as keymaps and syntax tables, see | |
19 | @ref{Keymaps}, and @ref{Syntax Tables}. | |
20 | ||
21 | @menu | |
22 | * Major Modes:: Defining major modes. | |
23 | * Minor Modes:: Defining minor modes. | |
24 | * Mode Line Format:: Customizing the text that appears in the mode line. | |
25 | * Hooks:: How to use hooks; how to write code that provides hooks. | |
26 | @end menu | |
27 | ||
28 | @node Major Modes | |
29 | @section Major Modes | |
30 | @cindex major mode | |
31 | @cindex Fundamental mode | |
32 | ||
33 | Major modes specialize Emacs for editing particular kinds of text. | |
34 | Each buffer has only one major mode at a time. | |
35 | ||
36 | The least specialized major mode is called @dfn{Fundamental mode}. | |
37 | This mode has no mode-specific definitions or variable settings, so each | |
38 | Emacs command behaves in its default manner, and each option is in its | |
39 | default state. All other major modes redefine various keys and options. | |
40 | For example, Lisp Interaction mode provides special key bindings for | |
41 | @key{LFD} (@code{eval-print-last-sexp}), @key{TAB} | |
42 | (@code{lisp-indent-line}), and other keys. | |
43 | ||
44 | When you need to write several editing commands to help you perform a | |
45 | specialized editing task, creating a new major mode is usually a good | |
46 | idea. In practice, writing a major mode is easy (in contrast to | |
47 | writing a minor mode, which is often difficult). | |
48 | ||
49 | If the new mode is similar to an old one, it is often unwise to modify | |
50 | the old one to serve two purposes, since it may become harder to use and | |
51 | maintain. Instead, copy and rename an existing major mode definition | |
52 | and alter the copy---or define a @dfn{derived mode} (@pxref{Derived | |
53 | Modes}). For example, Rmail Edit mode, which is in | |
54 | @file{emacs/lisp/rmailedit.el}, is a major mode that is very similar to | |
55 | Text mode except that it provides three additional commands. Its | |
56 | definition is distinct from that of Text mode, but was derived from it. | |
57 | ||
58 | Rmail Edit mode is an example of a case where one piece of text is put | |
59 | temporarily into a different major mode so it can be edited in a | |
60 | different way (with ordinary Emacs commands rather than Rmail). In such | |
61 | cases, the temporary major mode usually has a command to switch back to | |
62 | the buffer's usual mode (Rmail mode, in this case). You might be | |
63 | tempted to present the temporary redefinitions inside a recursive edit | |
64 | and restore the usual ones when the user exits; but this is a bad idea | |
65 | because it constrains the user's options when it is done in more than | |
66 | one buffer: recursive edits must be exited most-recently-entered first. | |
67 | Using alternative major modes avoids this limitation. @xref{Recursive | |
68 | Editing}. | |
69 | ||
70 | The standard GNU Emacs Lisp library directory contains the code for | |
71 | several major modes, in files including @file{text-mode.el}, | |
72 | @file{texinfo.el}, @file{lisp-mode.el}, @file{c-mode.el}, and | |
73 | @file{rmail.el}. You can look at these libraries to see how modes are | |
74 | written. Text mode is perhaps the simplest major mode aside from | |
75 | Fundamental mode. Rmail mode is a complicated and specialized mode. | |
76 | ||
77 | @menu | |
78 | * Major Mode Conventions:: Coding conventions for keymaps, etc. | |
79 | * Example Major Modes:: Text mode and Lisp modes. | |
80 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
81 | * Mode Help:: Finding out how to use a mode. | |
82 | * Derived Modes:: Defining a new major mode based on another major | |
83 | mode. | |
84 | @end menu | |
85 | ||
86 | @node Major Mode Conventions | |
87 | @subsection Major Mode Conventions | |
88 | ||
89 | The code for existing major modes follows various coding conventions, | |
90 | including conventions for local keymap and syntax table initialization, | |
91 | global names, and hooks. Please follow these conventions when you | |
92 | define a new major mode: | |
93 | ||
94 | @itemize @bullet | |
95 | @item | |
96 | Define a command whose name ends in @samp{-mode}, with no arguments, | |
97 | that switches to the new mode in the current buffer. This command | |
98 | should set up the keymap, syntax table, and local variables in an | |
99 | existing buffer without changing the buffer's text. | |
100 | ||
101 | @item | |
de9f0bd9 | 102 | Write a documentation string for this command that describes the |
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103 | special commands available in this mode. @kbd{C-h m} |
104 | (@code{describe-mode}) in your mode will display this string. | |
105 | ||
106 | The documentation string may include the special documentation | |
107 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
108 | @samp{\<@var{keymap}>}, that enable the documentation to adapt | |
109 | automatically to the user's own key bindings. @xref{Keys in | |
110 | Documentation}. | |
111 | ||
112 | @item | |
113 | The major mode command should start by calling | |
114 | @code{kill-all-local-variables}. This is what gets rid of the local | |
115 | variables of the major mode previously in effect. | |
116 | ||
117 | @item | |
118 | The major mode command should set the variable @code{major-mode} to the | |
119 | major mode command symbol. This is how @code{describe-mode} discovers | |
120 | which documentation to print. | |
121 | ||
122 | @item | |
123 | The major mode command should set the variable @code{mode-name} to the | |
124 | ``pretty'' name of the mode, as a string. This appears in the mode | |
125 | line. | |
126 | ||
127 | @item | |
128 | @cindex functions in modes | |
129 | Since all global names are in the same name space, all the global | |
130 | variables, constants, and functions that are part of the mode should | |
131 | have names that start with the major mode name (or with an abbreviation | |
132 | of it if the name is long). @xref{Style Tips}. | |
133 | ||
134 | @item | |
135 | @cindex keymaps in modes | |
136 | The major mode should usually have its own keymap, which is used as the | |
137 | local keymap in all buffers in that mode. The major mode function | |
138 | should call @code{use-local-map} to install this local map. | |
139 | @xref{Active Keymaps}, for more information. | |
140 | ||
141 | This keymap should be kept in a global variable named | |
142 | @code{@var{modename}-mode-map}. Normally the library that defines the | |
de9f0bd9 | 143 | mode sets this variable. |
a44af9f2 | 144 | |
23ce41fc RS |
145 | @xref{Tips for Defining}, for advice about how to write the code to set |
146 | up the mode's keymap variable. | |
147 | ||
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148 | @item |
149 | @cindex syntax tables in modes | |
150 | The mode may have its own syntax table or may share one with other | |
151 | related modes. If it has its own syntax table, it should store this in | |
de9f0bd9 | 152 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax |
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153 | Tables}. |
154 | ||
155 | @item | |
156 | @cindex abbrev tables in modes | |
157 | The mode may have its own abbrev table or may share one with other | |
158 | related modes. If it has its own abbrev table, it should store this in | |
159 | a variable named @code{@var{modename}-mode-abbrev-table}. @xref{Abbrev | |
160 | Tables}. | |
161 | ||
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162 | @item |
163 | Use @code{defvar} to set mode-related variables, so that they are not | |
164 | reinitialized if they already have a value. (Such reinitialization | |
165 | could discard customizations made by the user.) | |
166 | ||
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167 | @item |
168 | @cindex buffer-local variables in modes | |
169 | To make a buffer-local binding for an Emacs customization variable, use | |
170 | @code{make-local-variable} in the major mode command, not | |
171 | @code{make-variable-buffer-local}. The latter function would make the | |
172 | variable local to every buffer in which it is subsequently set, which | |
173 | would affect buffers that do not use this mode. It is undesirable for a | |
174 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
175 | ||
176 | It's ok to use @code{make-variable-buffer-local}, if you wish, for a | |
177 | variable used only within a single Lisp package. | |
178 | ||
179 | @item | |
180 | @cindex mode hook | |
181 | @cindex major mode hook | |
182 | Each major mode should have a @dfn{mode hook} named | |
183 | @code{@var{modename}-mode-hook}. The major mode command should run that | |
184 | hook, with @code{run-hooks}, as the very last thing it | |
185 | does. @xref{Hooks}. | |
186 | ||
187 | @item | |
188 | The major mode command may also run the hooks of some more basic modes. | |
189 | For example, @code{indented-text-mode} runs @code{text-mode-hook} as | |
190 | well as @code{indented-text-mode-hook}. It may run these other hooks | |
191 | immediately before the mode's own hook (that is, after everything else), | |
192 | or it may run them earlier. | |
193 | ||
194 | @item | |
195 | If something special should be done if the user switches a buffer from | |
196 | this mode to any other major mode, the mode can set a local value for | |
197 | @code{change-major-mode-hook}. | |
198 | ||
199 | @item | |
200 | If this mode is appropriate only for specially-prepared text, then the | |
201 | major mode command symbol should have a property named @code{mode-class} | |
202 | with value @code{special}, put on as follows: | |
203 | ||
204 | @cindex @code{mode-class} property | |
205 | @cindex @code{special} | |
206 | @example | |
207 | (put 'funny-mode 'mode-class 'special) | |
208 | @end example | |
209 | ||
210 | @noindent | |
211 | This tells Emacs that new buffers created while the current buffer has | |
212 | Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, | |
213 | and Buffer List use this feature. | |
214 | ||
215 | @item | |
216 | If you want to make the new mode the default for files with certain | |
217 | recognizable names, add an element to @code{auto-mode-alist} to select | |
218 | the mode for those file names. If you define the mode command to | |
219 | autoload, you should add this element in the same file that calls | |
220 | @code{autoload}. Otherwise, it is sufficient to add the element in the | |
221 | file that contains the mode definition. @xref{Auto Major Mode}. | |
222 | ||
223 | @item | |
224 | @cindex @file{.emacs} customization | |
225 | In the documentation, you should provide a sample @code{autoload} form | |
226 | and an example of how to add to @code{auto-mode-alist}, that users can | |
227 | include in their @file{.emacs} files. | |
228 | ||
229 | @item | |
230 | @cindex mode loading | |
de9f0bd9 | 231 | The top-level forms in the file defining the mode should be written so |
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232 | that they may be evaluated more than once without adverse consequences. |
233 | Even if you never load the file more than once, someone else will. | |
234 | @end itemize | |
235 | ||
236 | @defvar change-major-mode-hook | |
237 | This normal hook is run by @code{kill-all-local-variables} before it | |
238 | does anything else. This gives major modes a way to arrange for | |
239 | something special to be done if the user switches to a different major | |
240 | mode. For best results, make this variable buffer-local, so that it | |
241 | will disappear after doing its job and will not interfere with the | |
de9f0bd9 | 242 | subsequent major mode. @xref{Hooks}. |
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243 | @end defvar |
244 | ||
245 | @node Example Major Modes | |
246 | @subsection Major Mode Examples | |
247 | ||
248 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
249 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
250 | the conventions listed above: | |
251 | ||
252 | @smallexample | |
253 | @group | |
254 | ;; @r{Create mode-specific tables.} | |
255 | (defvar text-mode-syntax-table nil | |
256 | "Syntax table used while in text mode.") | |
257 | @end group | |
258 | ||
259 | @group | |
260 | (if text-mode-syntax-table | |
261 | () ; @r{Do not change the table if it is already set up.} | |
262 | (setq text-mode-syntax-table (make-syntax-table)) | |
263 | (modify-syntax-entry ?\" ". " text-mode-syntax-table) | |
264 | (modify-syntax-entry ?\\ ". " text-mode-syntax-table) | |
265 | (modify-syntax-entry ?' "w " text-mode-syntax-table)) | |
266 | @end group | |
267 | ||
268 | @group | |
269 | (defvar text-mode-abbrev-table nil | |
270 | "Abbrev table used while in text mode.") | |
271 | (define-abbrev-table 'text-mode-abbrev-table ()) | |
272 | @end group | |
273 | ||
274 | @group | |
275 | (defvar text-mode-map nil) ; @r{Create a mode-specific keymap.} | |
276 | ||
277 | (if text-mode-map | |
278 | () ; @r{Do not change the keymap if it is already set up.} | |
279 | (setq text-mode-map (make-sparse-keymap)) | |
280 | (define-key text-mode-map "\t" 'tab-to-tab-stop) | |
281 | (define-key text-mode-map "\es" 'center-line) | |
282 | (define-key text-mode-map "\eS" 'center-paragraph)) | |
283 | @end group | |
284 | @end smallexample | |
285 | ||
286 | Here is the complete major mode function definition for Text mode: | |
287 | ||
288 | @smallexample | |
289 | @group | |
290 | (defun text-mode () | |
291 | "Major mode for editing text intended for humans to read. | |
292 | Special commands: \\@{text-mode-map@} | |
293 | @end group | |
294 | @group | |
295 | Turning on text-mode runs the hook `text-mode-hook'." | |
296 | (interactive) | |
297 | (kill-all-local-variables) | |
298 | @end group | |
299 | @group | |
300 | (use-local-map text-mode-map) ; @r{This provides the local keymap.} | |
301 | (setq mode-name "Text") ; @r{This name goes into the mode line.} | |
302 | (setq major-mode 'text-mode) ; @r{This is how @code{describe-mode}} | |
303 | ; @r{finds the doc string to print.} | |
304 | (setq local-abbrev-table text-mode-abbrev-table) | |
305 | (set-syntax-table text-mode-syntax-table) | |
306 | (run-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} | |
307 | ; @r{customize the mode with a hook.} | |
308 | @end group | |
309 | @end smallexample | |
310 | ||
311 | @cindex @file{lisp-mode.el} | |
312 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
313 | Interaction mode) have more features than Text mode and the code is | |
314 | correspondingly more complicated. Here are excerpts from | |
315 | @file{lisp-mode.el} that illustrate how these modes are written. | |
316 | ||
317 | @cindex syntax table example | |
318 | @smallexample | |
319 | @group | |
320 | ;; @r{Create mode-specific table variables.} | |
321 | (defvar lisp-mode-syntax-table nil "") | |
322 | (defvar emacs-lisp-mode-syntax-table nil "") | |
323 | (defvar lisp-mode-abbrev-table nil "") | |
324 | @end group | |
325 | ||
326 | @group | |
327 | (if (not emacs-lisp-mode-syntax-table) ; @r{Do not change the table} | |
328 | ; @r{if it is already set.} | |
329 | (let ((i 0)) | |
330 | (setq emacs-lisp-mode-syntax-table (make-syntax-table)) | |
331 | @end group | |
332 | ||
333 | @group | |
334 | ;; @r{Set syntax of chars up to 0 to class of chars that are} | |
335 | ;; @r{part of symbol names but not words.} | |
336 | ;; @r{(The number 0 is @code{48} in the @sc{ASCII} character set.)} | |
337 | (while (< i ?0) | |
338 | (modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table) | |
339 | (setq i (1+ i))) | |
340 | @dots{} | |
341 | @end group | |
342 | @group | |
343 | ;; @r{Set the syntax for other characters.} | |
344 | (modify-syntax-entry ? " " emacs-lisp-mode-syntax-table) | |
345 | (modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table) | |
346 | @dots{} | |
347 | @end group | |
348 | @group | |
349 | (modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table) | |
350 | (modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table) | |
351 | @dots{})) | |
352 | ;; @r{Create an abbrev table for lisp-mode.} | |
353 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
354 | @end group | |
355 | @end smallexample | |
356 | ||
357 | Much code is shared among the three Lisp modes. The following | |
358 | function sets various variables; it is called by each of the major Lisp | |
359 | mode functions: | |
360 | ||
361 | @smallexample | |
362 | @group | |
363 | (defun lisp-mode-variables (lisp-syntax) | |
364 | ;; @r{The @code{lisp-syntax} argument is @code{nil} in Emacs Lisp mode,} | |
365 | ;; @r{and @code{t} in the other two Lisp modes.} | |
366 | (cond (lisp-syntax | |
367 | (if (not lisp-mode-syntax-table) | |
368 | ;; @r{The Emacs Lisp mode syntax table always exists, but} | |
369 | ;; @r{the Lisp Mode syntax table is created the first time a} | |
370 | ;; @r{mode that needs it is called. This is to save space.} | |
371 | @end group | |
372 | @group | |
373 | (progn (setq lisp-mode-syntax-table | |
374 | (copy-syntax-table emacs-lisp-mode-syntax-table)) | |
375 | ;; @r{Change some entries for Lisp mode.} | |
376 | (modify-syntax-entry ?\| "\" " | |
377 | lisp-mode-syntax-table) | |
378 | (modify-syntax-entry ?\[ "_ " | |
379 | lisp-mode-syntax-table) | |
380 | (modify-syntax-entry ?\] "_ " | |
381 | lisp-mode-syntax-table))) | |
382 | @end group | |
383 | @group | |
384 | (set-syntax-table lisp-mode-syntax-table))) | |
385 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
386 | @dots{}) | |
387 | @end group | |
388 | @end smallexample | |
389 | ||
390 | Functions such as @code{forward-paragraph} use the value of the | |
391 | @code{paragraph-start} variable. Since Lisp code is different from | |
392 | ordinary text, the @code{paragraph-start} variable needs to be set | |
393 | specially to handle Lisp. Also, comments are indented in a special | |
394 | fashion in Lisp and the Lisp modes need their own mode-specific | |
395 | @code{comment-indent-function}. The code to set these variables is the | |
396 | rest of @code{lisp-mode-variables}. | |
397 | ||
398 | @smallexample | |
399 | @group | |
400 | (make-local-variable 'paragraph-start) | |
bfe721d1 KH |
401 | ;; @r{Having @samp{^} is not clean, but @code{page-delimiter}} |
402 | ;; @r{has them too, and removing those is a pain.} | |
a44af9f2 RS |
403 | (setq paragraph-start (concat "^$\\|" page-delimiter)) |
404 | @dots{} | |
405 | @end group | |
406 | @group | |
407 | (make-local-variable 'comment-indent-function) | |
408 | (setq comment-indent-function 'lisp-comment-indent)) | |
409 | @end group | |
410 | @end smallexample | |
411 | ||
412 | Each of the different Lisp modes has a slightly different keymap. For | |
413 | example, Lisp mode binds @kbd{C-c C-l} to @code{run-lisp}, but the other | |
414 | Lisp modes do not. However, all Lisp modes have some commands in | |
415 | common. The following function adds these common commands to a given | |
416 | keymap. | |
417 | ||
418 | @smallexample | |
419 | @group | |
420 | (defun lisp-mode-commands (map) | |
421 | (define-key map "\e\C-q" 'indent-sexp) | |
422 | (define-key map "\177" 'backward-delete-char-untabify) | |
423 | (define-key map "\t" 'lisp-indent-line)) | |
424 | @end group | |
425 | @end smallexample | |
426 | ||
427 | Here is an example of using @code{lisp-mode-commands} to initialize a | |
428 | keymap, as part of the code for Emacs Lisp mode. First we declare a | |
429 | variable with @code{defvar} to hold the mode-specific keymap. When this | |
430 | @code{defvar} executes, it sets the variable to @code{nil} if it was | |
431 | void. Then we set up the keymap if the variable is @code{nil}. | |
432 | ||
433 | This code avoids changing the keymap or the variable if it is already | |
de9f0bd9 | 434 | set up. This lets the user customize the keymap. |
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435 | |
436 | @smallexample | |
437 | @group | |
438 | (defvar emacs-lisp-mode-map () "") | |
439 | (if emacs-lisp-mode-map | |
440 | () | |
441 | (setq emacs-lisp-mode-map (make-sparse-keymap)) | |
442 | (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun) | |
443 | (lisp-mode-commands emacs-lisp-mode-map)) | |
444 | @end group | |
445 | @end smallexample | |
446 | ||
447 | Finally, here is the complete major mode function definition for | |
448 | Emacs Lisp mode. | |
449 | ||
450 | @smallexample | |
451 | @group | |
452 | (defun emacs-lisp-mode () | |
453 | "Major mode for editing Lisp code to run in Emacs. | |
454 | Commands: | |
455 | Delete converts tabs to spaces as it moves back. | |
456 | Blank lines separate paragraphs. Semicolons start comments. | |
457 | \\@{emacs-lisp-mode-map@} | |
458 | @end group | |
459 | @group | |
460 | Entry to this mode runs the hook `emacs-lisp-mode-hook'." | |
461 | (interactive) | |
462 | (kill-all-local-variables) | |
463 | (use-local-map emacs-lisp-mode-map) ; @r{This provides the local keymap.} | |
464 | (set-syntax-table emacs-lisp-mode-syntax-table) | |
465 | @end group | |
466 | @group | |
467 | (setq major-mode 'emacs-lisp-mode) ; @r{This is how @code{describe-mode}} | |
468 | ; @r{finds out what to describe.} | |
469 | (setq mode-name "Emacs-Lisp") ; @r{This goes into the mode line.} | |
de9f0bd9 | 470 | (lisp-mode-variables nil) ; @r{This defines various variables.} |
a44af9f2 RS |
471 | (run-hooks 'emacs-lisp-mode-hook)) ; @r{This permits the user to use a} |
472 | ; @r{hook to customize the mode.} | |
473 | @end group | |
474 | @end smallexample | |
475 | ||
476 | @node Auto Major Mode | |
477 | @subsection How Emacs Chooses a Major Mode | |
478 | ||
479 | Based on information in the file name or in the file itself, Emacs | |
480 | automatically selects a major mode for the new buffer when a file is | |
481 | visited. | |
482 | ||
483 | @deffn Command fundamental-mode | |
484 | Fundamental mode is a major mode that is not specialized for anything | |
485 | in particular. Other major modes are defined in effect by comparison | |
486 | with this one---their definitions say what to change, starting from | |
487 | Fundamental mode. The @code{fundamental-mode} function does @emph{not} | |
488 | run any hooks; you're not supposed to customize it. (If you want Emacs | |
489 | to behave differently in Fundamental mode, change the @emph{global} | |
490 | state of Emacs.) | |
491 | @end deffn | |
492 | ||
493 | @deffn Command normal-mode &optional find-file | |
bfe721d1 | 494 | This function establishes the proper major mode and local variable |
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495 | bindings for the current buffer. First it calls @code{set-auto-mode}, |
496 | then it runs @code{hack-local-variables} to parse, and bind or | |
497 | evaluate as appropriate, any local variables. | |
498 | ||
bfe721d1 | 499 | If the @var{find-file} argument to @code{normal-mode} is |
a44af9f2 RS |
500 | non-@code{nil}, @code{normal-mode} assumes that the @code{find-file} |
501 | function is calling it. In this case, it may process a local variables | |
bfe721d1 KH |
502 | list at the end of the file and in the @samp{-*-} line. The variable |
503 | @code{enable-local-variables} controls whether to do so. | |
a44af9f2 | 504 | |
bfe721d1 | 505 | If you run @code{normal-mode} interactively, the argument |
a44af9f2 RS |
506 | @var{find-file} is normally @code{nil}. In this case, |
507 | @code{normal-mode} unconditionally processes any local variables list. | |
508 | @xref{File variables, , Local Variables in Files, emacs, The GNU Emacs | |
509 | Manual}, for the syntax of the local variables section of a file. | |
510 | ||
511 | @cindex file mode specification error | |
bfe721d1 | 512 | @code{normal-mode} uses @code{condition-case} around the call to the |
a44af9f2 RS |
513 | major mode function, so errors are caught and reported as a @samp{File |
514 | mode specification error}, followed by the original error message. | |
515 | @end deffn | |
516 | ||
517 | @defopt enable-local-variables | |
518 | This variable controls processing of local variables lists in files | |
519 | being visited. A value of @code{t} means process the local variables | |
520 | lists unconditionally; @code{nil} means ignore them; anything else means | |
521 | ask the user what to do for each file. The default value is @code{t}. | |
522 | @end defopt | |
523 | ||
bfe721d1 KH |
524 | @defvar ignored-local-variables |
525 | This variable holds a list of variables that should not be | |
526 | set by a local variables list. Any value specified | |
527 | for one of these variables is ignored. | |
528 | @end defvar | |
529 | ||
530 | In addition to this list, any variable whose name has a non-@code{nil} | |
531 | @code{risky-local-variable} property is also ignored. | |
532 | ||
a44af9f2 RS |
533 | @defopt enable-local-eval |
534 | This variable controls processing of @samp{Eval:} in local variables | |
535 | lists in files being visited. A value of @code{t} means process them | |
536 | unconditionally; @code{nil} means ignore them; anything else means ask | |
537 | the user what to do for each file. The default value is @code{maybe}. | |
538 | @end defopt | |
539 | ||
540 | @defun set-auto-mode | |
541 | @cindex visited file mode | |
542 | This function selects the major mode that is appropriate for the | |
543 | current buffer. It may base its decision on the value of the @w{@samp{-*-}} | |
76352dc1 RS |
544 | line, on the visited file name (using @code{auto-mode-alist}), on the |
545 | @w{@samp{#!}} line (using @code{interpreter-mode-alist}), or on the | |
de9f0bd9 | 546 | value of a local variable. However, this function does not look for |
a44af9f2 RS |
547 | the @samp{mode:} local variable near the end of a file; the |
548 | @code{hack-local-variables} function does that. @xref{Choosing Modes, , | |
549 | How Major Modes are Chosen, emacs, The GNU Emacs Manual}. | |
550 | @end defun | |
551 | ||
552 | @defopt default-major-mode | |
553 | This variable holds the default major mode for new buffers. The | |
554 | standard value is @code{fundamental-mode}. | |
555 | ||
556 | If the value of @code{default-major-mode} is @code{nil}, Emacs uses | |
557 | the (previously) current buffer's major mode for the major mode of a new | |
558 | buffer. However, if the major mode symbol has a @code{mode-class} | |
559 | property with value @code{special}, then it is not used for new buffers; | |
560 | Fundamental mode is used instead. The modes that have this property are | |
561 | those such as Dired and Rmail that are useful only with text that has | |
562 | been specially prepared. | |
563 | @end defopt | |
564 | ||
22697dac KH |
565 | @defun set-buffer-major-mode buffer |
566 | This function sets the major mode of @var{buffer} to the value of | |
567 | @code{default-major-mode}. If that variable is @code{nil}, it uses | |
568 | the current buffer's major mode (if that is suitable). | |
569 | ||
570 | The low-level primitives for creating buffers do not use this function, | |
bfe721d1 KH |
571 | but medium-level commands such as @code{switch-to-buffer} and |
572 | @code{find-file-noselect} use it whenever they create buffers. | |
22697dac KH |
573 | @end defun |
574 | ||
a44af9f2 RS |
575 | @defvar initial-major-mode |
576 | @cindex @samp{*scratch*} | |
577 | The value of this variable determines the major mode of the initial | |
578 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
579 | mode command name. The default value is @code{lisp-interaction-mode}. | |
580 | @end defvar | |
581 | ||
582 | @defvar auto-mode-alist | |
583 | This variable contains an association list of file name patterns | |
584 | (regular expressions; @pxref{Regular Expressions}) and corresponding | |
585 | major mode functions. Usually, the file name patterns test for | |
586 | suffixes, such as @samp{.el} and @samp{.c}, but this need not be the | |
587 | case. An ordinary element of the alist looks like @code{(@var{regexp} . | |
588 | @var{mode-function})}. | |
589 | ||
590 | For example, | |
591 | ||
592 | @smallexample | |
593 | @group | |
594 | (("^/tmp/fol/" . text-mode) | |
24675e99 RS |
595 | ("\\.texinfo\\'" . texinfo-mode) |
596 | ("\\.texi\\'" . texinfo-mode) | |
a44af9f2 RS |
597 | @end group |
598 | @group | |
24675e99 RS |
599 | ("\\.el\\'" . emacs-lisp-mode) |
600 | ("\\.c\\'" . c-mode) | |
601 | ("\\.h\\'" . c-mode) | |
a44af9f2 RS |
602 | @dots{}) |
603 | @end group | |
604 | @end smallexample | |
605 | ||
606 | When you visit a file whose expanded file name (@pxref{File Name | |
607 | Expansion}) matches a @var{regexp}, @code{set-auto-mode} calls the | |
608 | corresponding @var{mode-function}. This feature enables Emacs to select | |
609 | the proper major mode for most files. | |
610 | ||
611 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
612 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
613 | @code{auto-mode-alist} again for a match against the portion of the file | |
614 | name that did not match before. | |
615 | ||
616 | This match-again feature is useful for uncompression packages: an entry | |
617 | of the form @code{("\\.gz\\'" . @var{function})} can uncompress the file | |
618 | and then put the uncompressed file in the proper mode according to the | |
619 | name sans @samp{.gz}. | |
620 | ||
621 | Here is an example of how to prepend several pattern pairs to | |
622 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
623 | @file{.emacs} file.) | |
624 | ||
625 | @smallexample | |
626 | @group | |
627 | (setq auto-mode-alist | |
628 | (append | |
de9f0bd9 | 629 | ;; @r{File name starts with a dot.} |
24675e99 | 630 | '(("/\\.[^/]*\\'" . fundamental-mode) |
de9f0bd9 | 631 | ;; @r{File name has no dot.} |
24675e99 | 632 | ("[^\\./]*\\'" . fundamental-mode) |
de9f0bd9 | 633 | ;; @r{File name ends in @samp{.C}.} |
24675e99 | 634 | ("\\.C\\'" . c++-mode)) |
a44af9f2 RS |
635 | auto-mode-alist)) |
636 | @end group | |
637 | @end smallexample | |
638 | @end defvar | |
639 | ||
640 | @defvar interpreter-mode-alist | |
641 | This variable specifes major modes to use for scripts that specify a | |
76352dc1 | 642 | command interpreter in an @samp{#!} line. Its value is a list of |
a44af9f2 RS |
643 | elements of the form @code{(@var{interpreter} . @var{mode})}; for |
644 | example, @code{("perl" . perl-mode)} is one element present by default. | |
645 | The element says to use mode @var{mode} if the file specifies | |
646 | @var{interpreter}. | |
647 | ||
de9f0bd9 RS |
648 | This variable is applicable only when the @code{auto-mode-alist} does |
649 | not indicate which major mode to use. | |
a44af9f2 RS |
650 | @end defvar |
651 | ||
652 | @defun hack-local-variables &optional force | |
653 | This function parses, and binds or evaluates as appropriate, any local | |
654 | variables for the current buffer. | |
655 | ||
656 | The handling of @code{enable-local-variables} documented for | |
657 | @code{normal-mode} actually takes place here. The argument @var{force} | |
de9f0bd9 RS |
658 | usually comes from the argument @var{find-file} given to |
659 | @code{normal-mode}. | |
a44af9f2 RS |
660 | @end defun |
661 | ||
662 | @node Mode Help | |
663 | @subsection Getting Help about a Major Mode | |
664 | @cindex mode help | |
665 | @cindex help for major mode | |
666 | @cindex documentation for major mode | |
667 | ||
668 | The @code{describe-mode} function is used to provide information | |
669 | about major modes. It is normally called with @kbd{C-h m}. The | |
670 | @code{describe-mode} function uses the value of @code{major-mode}, | |
671 | which is why every major mode function needs to set the | |
672 | @code{major-mode} variable. | |
673 | ||
674 | @deffn Command describe-mode | |
675 | This function displays the documentation of the current major mode. | |
676 | ||
677 | The @code{describe-mode} function calls the @code{documentation} | |
678 | function using the value of @code{major-mode} as an argument. Thus, it | |
679 | displays the documentation string of the major mode function. | |
680 | (@xref{Accessing Documentation}.) | |
681 | @end deffn | |
682 | ||
683 | @defvar major-mode | |
684 | This variable holds the symbol for the current buffer's major mode. | |
de9f0bd9 | 685 | This symbol should have a function definition that is the command to |
a44af9f2 | 686 | switch to that major mode. The @code{describe-mode} function uses the |
de9f0bd9 | 687 | documentation string of the function as the documentation of the major |
a44af9f2 RS |
688 | mode. |
689 | @end defvar | |
690 | ||
691 | @node Derived Modes | |
692 | @subsection Defining Derived Modes | |
693 | ||
694 | It's often useful to define a new major mode in terms of an existing | |
695 | one. An easy way to do this is to use @code{define-derived-mode}. | |
696 | ||
de9f0bd9 | 697 | @defmac define-derived-mode variant parent name docstring body@dots{} |
a44af9f2 | 698 | This construct defines @var{variant} as a major mode command, using |
de9f0bd9 | 699 | @var{name} as the string form of the mode name. |
a44af9f2 | 700 | |
de9f0bd9 RS |
701 | The new command @var{variant} is defined to call the function |
702 | @var{parent}, then override certain aspects of that parent mode: | |
a44af9f2 RS |
703 | |
704 | @itemize @bullet | |
705 | @item | |
706 | The new mode has its own keymap, named @code{@var{variant}-map}. | |
707 | @code{define-derived-mode} initializes this map to inherit from | |
708 | @code{@var{parent}-map}, if it is not already set. | |
709 | ||
710 | @item | |
de9f0bd9 | 711 | The new mode has its own syntax table, kept in the variable |
a44af9f2 RS |
712 | @code{@var{variant}-syntax-table}. |
713 | @code{define-derived-mode} initializes this variable by copying | |
714 | @code{@var{parent}-syntax-table}, if it is not already set. | |
715 | ||
716 | @item | |
de9f0bd9 | 717 | The new mode has its own abbrev table, kept in the variable |
a44af9f2 RS |
718 | @code{@var{variant}-abbrev-table}. |
719 | @code{define-derived-mode} initializes this variable by copying | |
720 | @code{@var{parent}-abbrev-table}, if it is not already set. | |
721 | ||
722 | @item | |
723 | The new mode has its own mode hook, @code{@var{variant}-hook}, | |
724 | which it runs in standard fashion as the very last thing that it does. | |
725 | (The new mode also runs the mode hook of @var{parent} as part | |
726 | of calling @var{parent}.) | |
727 | @end itemize | |
728 | ||
729 | In addition, you can specify how to override other aspects of | |
de9f0bd9 | 730 | @var{parent} with @var{body}. The command @var{variant} |
a44af9f2 RS |
731 | evaluates the forms in @var{body} after setting up all its usual |
732 | overrides, just before running @code{@var{variant}-hook}. | |
733 | ||
734 | The argument @var{docstring} specifies the documentation string for the | |
735 | new mode. If you omit @var{docstring}, @code{define-derived-mode} | |
736 | generates a documentation string. | |
737 | ||
738 | Here is a hypothetical example: | |
739 | ||
740 | @example | |
741 | (define-derived-mode hypertext-mode | |
742 | text-mode "Hypertext" | |
743 | "Major mode for hypertext. | |
744 | \\@{hypertext-mode-map@}" | |
745 | (setq case-fold-search nil)) | |
746 | ||
747 | (define-key hypertext-mode-map | |
748 | [down-mouse-3] 'do-hyper-link) | |
749 | @end example | |
750 | @end defmac | |
751 | ||
752 | @node Minor Modes | |
753 | @section Minor Modes | |
754 | @cindex minor mode | |
755 | ||
756 | A @dfn{minor mode} provides features that users may enable or disable | |
757 | independently of the choice of major mode. Minor modes can be enabled | |
758 | individually or in combination. Minor modes would be better named | |
759 | ``Generally available, optional feature modes'' except that such a name is | |
760 | unwieldy. | |
761 | ||
762 | A minor mode is not usually a modification of single major mode. For | |
763 | example, Auto Fill mode may be used in any major mode that permits text | |
764 | insertion. To be general, a minor mode must be effectively independent | |
765 | of the things major modes do. | |
766 | ||
767 | A minor mode is often much more difficult to implement than a major | |
768 | mode. One reason is that you should be able to activate and deactivate | |
de9f0bd9 RS |
769 | minor modes in any order. A minor mode should be able to have its |
770 | desired effect regardless of the major mode and regardless of the other | |
771 | minor modes in effect. | |
a44af9f2 RS |
772 | |
773 | Often the biggest problem in implementing a minor mode is finding a | |
774 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
bfe721d1 | 775 | keymaps make this easier than it used to be. |
a44af9f2 RS |
776 | |
777 | @menu | |
778 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
779 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
780 | @end menu | |
781 | ||
782 | @node Minor Mode Conventions | |
783 | @subsection Conventions for Writing Minor Modes | |
784 | @cindex minor mode conventions | |
785 | @cindex conventions for writing minor modes | |
786 | ||
787 | There are conventions for writing minor modes just as there are for | |
788 | major modes. Several of the major mode conventions apply to minor | |
789 | modes as well: those regarding the name of the mode initialization | |
790 | function, the names of global symbols, and the use of keymaps and | |
791 | other tables. | |
792 | ||
793 | In addition, there are several conventions that are specific to | |
794 | minor modes. | |
795 | ||
796 | @itemize @bullet | |
797 | @item | |
798 | @cindex mode variable | |
799 | Make a variable whose name ends in @samp{-mode} to represent the minor | |
800 | mode. Its value should enable or disable the mode (@code{nil} to | |
801 | disable; anything else to enable.) We call this the @dfn{mode | |
802 | variable}. | |
803 | ||
804 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
805 | display the minor mode name in the mode line. It can also enable | |
806 | or disable a minor mode keymap. Individual commands or hooks can also | |
807 | check the variable's value. | |
808 | ||
809 | If you want the minor mode to be enabled separately in each buffer, | |
810 | make the variable buffer-local. | |
811 | ||
812 | @item | |
813 | Define a command whose name is the same as the mode variable. | |
814 | Its job is to enable and disable the mode by setting the variable. | |
815 | ||
816 | The command should accept one optional argument. If the argument is | |
817 | @code{nil}, it should toggle the mode (turn it on if it is off, and off | |
818 | if it is on). Otherwise, it should turn the mode on if the argument is | |
819 | a positive integer, a symbol other than @code{nil} or @code{-}, or a | |
820 | list whose @sc{car} is such an integer or symbol; it should turn the | |
821 | mode off otherwise. | |
822 | ||
bfe721d1 KH |
823 | Here is an example taken from the definition of @code{transient-mark-mode}. |
824 | It shows the use of @code{transient-mark-mode} as a variable that enables or | |
de9f0bd9 RS |
825 | disables the mode's behavior, and also shows the proper way to toggle, |
826 | enable or disable the minor mode based on the raw prefix argument value. | |
a44af9f2 RS |
827 | |
828 | @smallexample | |
829 | @group | |
bfe721d1 KH |
830 | (setq transient-mark-mode |
831 | (if (null arg) (not transient-mark-mode) | |
a44af9f2 RS |
832 | (> (prefix-numeric-value arg) 0))) |
833 | @end group | |
834 | @end smallexample | |
835 | ||
836 | @item | |
837 | Add an element to @code{minor-mode-alist} for each minor mode | |
838 | (@pxref{Mode Line Variables}). This element should be a list of the | |
839 | following form: | |
840 | ||
841 | @smallexample | |
842 | (@var{mode-variable} @var{string}) | |
843 | @end smallexample | |
844 | ||
de9f0bd9 | 845 | Here @var{mode-variable} is the variable that controls enabling of the |
a44af9f2 RS |
846 | minor mode, and @var{string} is a short string, starting with a space, |
847 | to represent the mode in the mode line. These strings must be short so | |
848 | that there is room for several of them at once. | |
849 | ||
850 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
851 | check for an existing element, to avoid duplication. For example: | |
852 | ||
853 | @smallexample | |
854 | @group | |
855 | (or (assq 'leif-mode minor-mode-alist) | |
856 | (setq minor-mode-alist | |
857 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
858 | @end group | |
859 | @end smallexample | |
860 | @end itemize | |
861 | ||
862 | @node Keymaps and Minor Modes | |
863 | @subsection Keymaps and Minor Modes | |
864 | ||
bfe721d1 KH |
865 | Each minor mode can have its own keymap, which is active when the mode |
866 | is enabled. To set up a keymap for a minor mode, add an element to the | |
867 | alist @code{minor-mode-map-alist}. @xref{Active Keymaps}. | |
a44af9f2 RS |
868 | |
869 | @cindex @code{self-insert-command}, minor modes | |
870 | One use of minor mode keymaps is to modify the behavior of certain | |
871 | self-inserting characters so that they do something else as well as | |
872 | self-insert. In general, this is the only way to do that, since the | |
873 | facilities for customizing @code{self-insert-command} are limited to | |
874 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
875 | substituting your own definition of @code{self-insert-command} for the | |
876 | standard one. The editor command loop handles this function specially.) | |
877 | ||
a44af9f2 RS |
878 | @node Mode Line Format |
879 | @section Mode Line Format | |
880 | @cindex mode line | |
881 | ||
de9f0bd9 | 882 | Each Emacs window (aside from minibuffer windows) includes a mode line, |
a44af9f2 | 883 | which displays status information about the buffer displayed in the |
de9f0bd9 | 884 | window. The mode line contains information about the buffer, such as its |
a44af9f2 | 885 | name, associated file, depth of recursive editing, and the major and |
de9f0bd9 | 886 | minor modes. |
a44af9f2 RS |
887 | |
888 | This section describes how the contents of the mode line are | |
889 | controlled. It is in the chapter on modes because much of the | |
890 | information displayed in the mode line relates to the enabled major and | |
891 | minor modes. | |
892 | ||
893 | @code{mode-line-format} is a buffer-local variable that holds a | |
894 | template used to display the mode line of the current buffer. All | |
bfe721d1 KH |
895 | windows for the same buffer use the same @code{mode-line-format} and |
896 | their mode lines appear the same (except for scrolling percentages and | |
a44af9f2 RS |
897 | line numbers). |
898 | ||
899 | The mode line of a window is normally updated whenever a different | |
900 | buffer is shown in the window, or when the buffer's modified-status | |
901 | changes from @code{nil} to @code{t} or vice-versa. If you modify any of | |
de9f0bd9 RS |
902 | the variables referenced by @code{mode-line-format} (@pxref{Mode Line |
903 | Variables}), you may want to force an update of the mode line so as to | |
904 | display the new information. | |
a44af9f2 RS |
905 | |
906 | @c Emacs 19 feature | |
907 | @defun force-mode-line-update | |
908 | Force redisplay of the current buffer's mode line. | |
909 | @end defun | |
910 | ||
911 | The mode line is usually displayed in inverse video; see | |
912 | @code{mode-line-inverse-video} in @ref{Inverse Video}. | |
913 | ||
914 | @menu | |
915 | * Mode Line Data:: The data structure that controls the mode line. | |
916 | * Mode Line Variables:: Variables used in that data structure. | |
917 | * %-Constructs:: Putting information into a mode line. | |
918 | @end menu | |
919 | ||
920 | @node Mode Line Data | |
921 | @subsection The Data Structure of the Mode Line | |
922 | @cindex mode line construct | |
923 | ||
924 | The mode line contents are controlled by a data structure of lists, | |
de9f0bd9 | 925 | strings, symbols, and numbers kept in the buffer-local variable |
a44af9f2 RS |
926 | @code{mode-line-format}. The data structure is called a @dfn{mode line |
927 | construct}, and it is built in recursive fashion out of simpler mode line | |
22697dac | 928 | constructs. The same data structure is used for constructing |
bfe721d1 | 929 | frame titles (@pxref{Frame Titles}). |
a44af9f2 RS |
930 | |
931 | @defvar mode-line-format | |
932 | The value of this variable is a mode line construct with overall | |
933 | responsibility for the mode line format. The value of this variable | |
934 | controls which other variables are used to form the mode line text, and | |
935 | where they appear. | |
936 | @end defvar | |
937 | ||
938 | A mode line construct may be as simple as a fixed string of text, but | |
939 | it usually specifies how to use other variables to construct the text. | |
940 | Many of these variables are themselves defined to have mode line | |
941 | constructs as their values. | |
942 | ||
943 | The default value of @code{mode-line-format} incorporates the values | |
944 | of variables such as @code{mode-name} and @code{minor-mode-alist}. | |
945 | Because of this, very few modes need to alter @code{mode-line-format}. | |
946 | For most purposes, it is sufficient to alter the variables referenced by | |
947 | @code{mode-line-format}. | |
948 | ||
de9f0bd9 RS |
949 | A mode line construct may be a list, a symbol, or a string. If the |
950 | value is a list, each element may be a list, a symbol, or a string. | |
a44af9f2 RS |
951 | |
952 | @table @code | |
953 | @cindex percent symbol in mode line | |
954 | @item @var{string} | |
955 | A string as a mode line construct is displayed verbatim in the mode line | |
bfe721d1 | 956 | except for @dfn{@code{%}-constructs}. Decimal digits after the @samp{%} |
a44af9f2 RS |
957 | specify the field width for space filling on the right (i.e., the data |
958 | is left justified). @xref{%-Constructs}. | |
959 | ||
960 | @item @var{symbol} | |
961 | A symbol as a mode line construct stands for its value. The value of | |
de9f0bd9 RS |
962 | @var{symbol} is used as a mode line construct, in place of @var{symbol}. |
963 | However, the symbols @code{t} and @code{nil} are ignored; so is any | |
964 | symbol whose value is void. | |
a44af9f2 RS |
965 | |
966 | There is one exception: if the value of @var{symbol} is a string, it is | |
de9f0bd9 | 967 | displayed verbatim: the @code{%}-constructs are not recognized. |
a44af9f2 RS |
968 | |
969 | @item (@var{string} @var{rest}@dots{}) @r{or} (@var{list} @var{rest}@dots{}) | |
de9f0bd9 RS |
970 | A list whose first element is a string or list means to process all the |
971 | elements recursively and concatenate the results. This is the most | |
972 | common form of mode line construct. | |
a44af9f2 RS |
973 | |
974 | @item (@var{symbol} @var{then} @var{else}) | |
975 | A list whose first element is a symbol is a conditional. Its meaning | |
976 | depends on the value of @var{symbol}. If the value is non-@code{nil}, | |
de9f0bd9 RS |
977 | the second element, @var{then}, is processed recursively as a mode line |
978 | element. But if the value of @var{symbol} is @code{nil}, the third | |
979 | element, @var{else}, is processed recursively. You may omit @var{else}; | |
980 | then the mode line element displays nothing if the value of @var{symbol} | |
981 | is @code{nil}. | |
a44af9f2 RS |
982 | |
983 | @item (@var{width} @var{rest}@dots{}) | |
984 | A list whose first element is an integer specifies truncation or | |
985 | padding of the results of @var{rest}. The remaining elements | |
986 | @var{rest} are processed recursively as mode line constructs and | |
987 | concatenated together. Then the result is space filled (if | |
988 | @var{width} is positive) or truncated (to @minus{}@var{width} columns, | |
989 | if @var{width} is negative) on the right. | |
990 | ||
991 | For example, the usual way to show what percentage of a buffer is above | |
de9f0bd9 | 992 | the top of the window is to use a list like this: @code{(-3 "%p")}. |
a44af9f2 RS |
993 | @end table |
994 | ||
995 | If you do alter @code{mode-line-format} itself, the new value should | |
de9f0bd9 RS |
996 | use the same variables that appear in the default value (@pxref{Mode |
997 | Line Variables}), rather than duplicating their contents or displaying | |
998 | the information in another fashion. This way, customizations made by | |
bfe721d1 KH |
999 | the user or by Lisp programs (such as @code{display-time} and major |
1000 | modes) via changes to those variables remain effective. | |
a44af9f2 RS |
1001 | |
1002 | @cindex Shell mode @code{mode-line-format} | |
1003 | Here is an example of a @code{mode-line-format} that might be | |
de9f0bd9 | 1004 | useful for @code{shell-mode}, since it contains the hostname and default |
a44af9f2 RS |
1005 | directory. |
1006 | ||
1007 | @example | |
1008 | @group | |
1009 | (setq mode-line-format | |
1010 | (list "" | |
1011 | 'mode-line-modified | |
1012 | "%b--" | |
1013 | @end group | |
1014 | (getenv "HOST") ; @r{One element is not constant.} | |
1015 | ":" | |
1016 | 'default-directory | |
1017 | " " | |
1018 | 'global-mode-string | |
de9f0bd9 RS |
1019 | " %[(" |
1020 | 'mode-name | |
1021 | 'mode-line-process | |
a44af9f2 RS |
1022 | 'minor-mode-alist |
1023 | "%n" | |
a44af9f2 RS |
1024 | ")%]----" |
1025 | @group | |
bfe721d1 | 1026 | '(line-number-mode "L%l--") |
a44af9f2 RS |
1027 | '(-3 . "%p") |
1028 | "-%-")) | |
1029 | @end group | |
1030 | @end example | |
1031 | ||
1032 | @node Mode Line Variables | |
1033 | @subsection Variables Used in the Mode Line | |
1034 | ||
1035 | This section describes variables incorporated by the | |
1036 | standard value of @code{mode-line-format} into the text of the mode | |
1037 | line. There is nothing inherently special about these variables; any | |
1038 | other variables could have the same effects on the mode line if | |
1039 | @code{mode-line-format} were changed to use them. | |
1040 | ||
1041 | @defvar mode-line-modified | |
de9f0bd9 | 1042 | This variable holds the value of the mode-line construct that displays |
a44af9f2 RS |
1043 | whether the current buffer is modified. |
1044 | ||
bfe721d1 KH |
1045 | The default value of @code{mode-line-modified} is @code{("--%1*%1+-")}. |
1046 | This means that the mode line displays @samp{--**-} if the buffer is | |
1047 | modified, @samp{-----} if the buffer is not modified, @samp{--%%-} if | |
1048 | the buffer is read only, and @samp{--%*--} if the buffer is read only | |
1049 | and modified. | |
a44af9f2 RS |
1050 | |
1051 | Changing this variable does not force an update of the mode line. | |
1052 | @end defvar | |
1053 | ||
1054 | @defvar mode-line-buffer-identification | |
de9f0bd9 | 1055 | This variable identifies the buffer being displayed in the window. Its |
bfe721d1 KH |
1056 | default value is @code{("%F: %17b")}, which means that it usually |
1057 | displays @samp{Emacs:} followed by seventeen characters of the buffer | |
1058 | name. (In a terminal frame, it displays the frame name instead of | |
1059 | @samp{Emacs}; this has the effect of showing the frame number.) You may | |
1060 | want to change this in modes such as Rmail that do not behave like a | |
de9f0bd9 | 1061 | ``normal'' Emacs. |
a44af9f2 RS |
1062 | @end defvar |
1063 | ||
1064 | @defvar global-mode-string | |
1065 | This variable holds a mode line spec that appears in the mode line by | |
1066 | default, just after the buffer name. The command @code{display-time} | |
1067 | sets @code{global-mode-string} to refer to the variable | |
1068 | @code{display-time-string}, which holds a string containing the time and | |
1069 | load information. | |
1070 | ||
1071 | The @samp{%M} construct substitutes the value of | |
1072 | @code{global-mode-string}, but this is obsolete, since the variable is | |
1073 | included directly in the mode line. | |
1074 | @end defvar | |
1075 | ||
1076 | @defvar mode-name | |
de9f0bd9 | 1077 | This buffer-local variable holds the ``pretty'' name of the current |
a44af9f2 RS |
1078 | buffer's major mode. Each major mode should set this variable so that the |
1079 | mode name will appear in the mode line. | |
1080 | @end defvar | |
1081 | ||
1082 | @defvar minor-mode-alist | |
de9f0bd9 | 1083 | This variable holds an association list whose elements specify how the |
a44af9f2 RS |
1084 | mode line should indicate that a minor mode is active. Each element of |
1085 | the @code{minor-mode-alist} should be a two-element list: | |
1086 | ||
1087 | @example | |
1088 | (@var{minor-mode-variable} @var{mode-line-string}) | |
1089 | @end example | |
1090 | ||
1091 | More generally, @var{mode-line-string} can be any mode line spec. It | |
1092 | appears in the mode line when the value of @var{minor-mode-variable} is | |
1093 | non-@code{nil}, and not otherwise. These strings should begin with | |
1094 | spaces so that they don't run together. Conventionally, the | |
1095 | @var{minor-mode-variable} for a specific mode is set to a non-@code{nil} | |
1096 | value when that minor mode is activated. | |
1097 | ||
1098 | The default value of @code{minor-mode-alist} is: | |
1099 | ||
1100 | @example | |
1101 | @group | |
1102 | minor-mode-alist | |
bfe721d1 KH |
1103 | @result{} ((vc-mode vc-mode) |
1104 | (abbrev-mode " Abbrev") | |
1105 | (overwrite-mode overwrite-mode) | |
a44af9f2 | 1106 | (auto-fill-function " Fill") |
bfe721d1 KH |
1107 | (defining-kbd-macro " Def") |
1108 | (isearch-mode isearch-mode)) | |
a44af9f2 RS |
1109 | @end group |
1110 | @end example | |
1111 | ||
bfe721d1 | 1112 | @code{minor-mode-alist} is not buffer-local. The variables mentioned |
a44af9f2 RS |
1113 | in the alist should be buffer-local if the minor mode can be enabled |
1114 | separately in each buffer. | |
1115 | @end defvar | |
1116 | ||
1117 | @defvar mode-line-process | |
1118 | This buffer-local variable contains the mode line information on process | |
1119 | status in modes used for communicating with subprocesses. It is | |
1120 | displayed immediately following the major mode name, with no intervening | |
1121 | space. For example, its value in the @samp{*shell*} buffer is | |
1122 | @code{(":@: %s")}, which allows the shell to display its status along | |
1123 | with the major mode as: @samp{(Shell:@: run)}. Normally this variable | |
1124 | is @code{nil}. | |
1125 | @end defvar | |
1126 | ||
1127 | @defvar default-mode-line-format | |
de9f0bd9 | 1128 | This variable holds the default @code{mode-line-format} for buffers |
a44af9f2 RS |
1129 | that do not override it. This is the same as @code{(default-value |
1130 | 'mode-line-format)}. | |
1131 | ||
de9f0bd9 | 1132 | The default value of @code{default-mode-line-format} is: |
a44af9f2 RS |
1133 | |
1134 | @example | |
1135 | @group | |
1136 | ("" | |
1137 | mode-line-modified | |
1138 | mode-line-buffer-identification | |
1139 | " " | |
1140 | global-mode-string | |
1141 | " %[(" | |
1142 | mode-name | |
1143 | @end group | |
1144 | @group | |
bfe721d1 | 1145 | mode-line-process |
a44af9f2 RS |
1146 | minor-mode-alist |
1147 | "%n" | |
a44af9f2 | 1148 | ")%]----" |
bfe721d1 | 1149 | (line-number-mode "L%l--") |
a44af9f2 RS |
1150 | (-3 . "%p") |
1151 | "-%-") | |
1152 | @end group | |
1153 | @end example | |
1154 | @end defvar | |
1155 | ||
de9f0bd9 RS |
1156 | @defvar vc-mode |
1157 | The variable @code{vc-mode}, local in each buffer, records whether the | |
1158 | buffer's visited file is maintained with version control, and, if so, | |
1159 | which kind. Its value is @code{nil} for no version control, or a string | |
1160 | that appears in the mode line. | |
1161 | @end defvar | |
1162 | ||
a44af9f2 RS |
1163 | @node %-Constructs |
1164 | @subsection @code{%}-Constructs in the Mode Line | |
1165 | ||
1166 | The following table lists the recognized @code{%}-constructs and what | |
de9f0bd9 RS |
1167 | they mean. In any construct except @samp{%%}, you can add a decimal |
1168 | integer after the @samp{%} to specify how many characters to display. | |
a44af9f2 RS |
1169 | |
1170 | @table @code | |
1171 | @item %b | |
1172 | The current buffer name, obtained with the @code{buffer-name} function. | |
1173 | @xref{Buffer Names}. | |
1174 | ||
1175 | @item %f | |
1176 | The visited file name, obtained with the @code{buffer-file-name} | |
1177 | function. @xref{Buffer File Name}. | |
1178 | ||
22697dac KH |
1179 | @item %F |
1180 | The name of the selected frame. | |
1181 | ||
1182 | @item %c | |
1183 | The current column number of point. | |
1184 | ||
1185 | @item %l | |
1186 | The current line number of point. | |
1187 | ||
a44af9f2 RS |
1188 | @item %* |
1189 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
1190 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
1191 | @samp{-} otherwise. @xref{Buffer Modification}. | |
1192 | ||
1193 | @item %+ | |
22697dac KH |
1194 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* |
1195 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
1196 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
1197 | read-only buffer. @xref{Buffer Modification}. | |
1198 | ||
1199 | @item %& | |
de9f0bd9 | 1200 | @samp{*} if the buffer is modified, and @samp{-} otherwise. |
a44af9f2 RS |
1201 | |
1202 | @item %s | |
1203 | The status of the subprocess belonging to the current buffer, obtained with | |
1204 | @code{process-status}. @xref{Process Information}. | |
1205 | ||
22697dac KH |
1206 | @item %t |
1207 | Whether the visited file is a text file or a binary file. (This is a | |
1208 | meaningful distinction only on certain operating systems.) | |
1209 | ||
a44af9f2 | 1210 | @item %p |
22697dac | 1211 | The percentage of the buffer text above the @strong{top} of window, or |
a44af9f2 RS |
1212 | @samp{Top}, @samp{Bottom} or @samp{All}. |
1213 | ||
1214 | @item %P | |
1215 | The percentage of the buffer text that is above the @strong{bottom} of | |
1216 | the window (which includes the text visible in the window, as well as | |
1217 | the text above the top), plus @samp{Top} if the top of the buffer is | |
1218 | visible on screen; or @samp{Bottom} or @samp{All}. | |
1219 | ||
1220 | @item %n | |
1221 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
1222 | @code{narrow-to-region} in @ref{Narrowing}). | |
1223 | ||
1224 | @item %[ | |
1225 | An indication of the depth of recursive editing levels (not counting | |
1226 | minibuffer levels): one @samp{[} for each editing level. | |
1227 | @xref{Recursive Editing}. | |
1228 | ||
1229 | @item %] | |
1230 | One @samp{]} for each recursive editing level (not counting minibuffer | |
1231 | levels). | |
1232 | ||
1233 | @item %% | |
1234 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
1235 | string in which @code{%}-constructs are allowed. | |
1236 | ||
1237 | @item %- | |
1238 | Dashes sufficient to fill the remainder of the mode line. | |
1239 | @end table | |
1240 | ||
1241 | The following two @code{%}-constructs are still supported, but they are | |
1242 | obsolete, since you can get the same results with the variables | |
1243 | @code{mode-name} and @code{global-mode-string}. | |
1244 | ||
1245 | @table @code | |
1246 | @item %m | |
1247 | The value of @code{mode-name}. | |
1248 | ||
1249 | @item %M | |
1250 | The value of @code{global-mode-string}. Currently, only | |
1251 | @code{display-time} modifies the value of @code{global-mode-string}. | |
1252 | @end table | |
1253 | ||
1254 | @node Hooks | |
1255 | @section Hooks | |
1256 | @cindex hooks | |
1257 | ||
1258 | A @dfn{hook} is a variable where you can store a function or functions | |
1259 | to be called on a particular occasion by an existing program. Emacs | |
1260 | provides hooks for the sake of customization. Most often, hooks are set | |
1261 | up in the @file{.emacs} file, but Lisp programs can set them also. | |
1262 | @xref{Standard Hooks}, for a list of standard hook variables. | |
1263 | ||
1264 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
1265 | contain lists of functions to be called with no arguments. The reason | |
1266 | most hooks are normal hooks is so that you can use them in a uniform | |
1267 | way. You can always tell when a hook is a normal hook, because its | |
1268 | name ends in @samp{-hook}. | |
1269 | ||
1270 | The recommended way to add a hook function to a normal hook is by | |
1271 | calling @code{add-hook} (see below). The hook functions may be any of | |
1272 | the valid kinds of functions that @code{funcall} accepts (@pxref{What Is | |
1273 | a Function}). Most normal hook variables are initially void; | |
1274 | @code{add-hook} knows how to deal with this. | |
1275 | ||
1276 | As for abnormal hooks, those whose names end in @samp{-function} have | |
de9f0bd9 RS |
1277 | a value that is a single function. Those whose names end in |
1278 | @samp{-hooks} have a value that is a list of functions. Any hook that | |
a44af9f2 RS |
1279 | is abnormal is abnormal because a normal hook won't do the job; either |
1280 | the functions are called with arguments, or their values are meaningful. | |
1281 | The name shows you that the hook is abnormal and that you should look at | |
1282 | its documentation string to see how to use it properly. | |
1283 | ||
bfe721d1 KH |
1284 | Major mode functions are supposed to run a hook called the @dfn{mode |
1285 | hook} as the last step of initialization. This makes it easy for a user | |
1286 | to customize the behavior of the mode, by overriding the local variable | |
1287 | assignments already made by the mode. But hooks are used in other | |
1288 | contexts too. For example, the hook @code{suspend-hook} runs just | |
1289 | before Emacs suspends itself (@pxref{Suspending Emacs}). | |
a44af9f2 | 1290 | |
bfe721d1 KH |
1291 | Here's an expression that uses a mode hook to turn on Auto Fill mode |
1292 | when in Lisp Interaction mode: | |
a44af9f2 RS |
1293 | |
1294 | @example | |
1295 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
1296 | @end example | |
1297 | ||
1298 | The next example shows how to use a hook to customize the way Emacs | |
1299 | formats C code. (People often have strong personal preferences for one | |
1300 | format or another.) Here the hook function is an anonymous lambda | |
1301 | expression. | |
1302 | ||
1303 | @cindex lambda expression in hook | |
1304 | @example | |
1305 | @group | |
1306 | (add-hook 'c-mode-hook | |
1307 | (function (lambda () | |
1308 | (setq c-indent-level 4 | |
1309 | c-argdecl-indent 0 | |
1310 | c-label-offset -4 | |
1311 | @end group | |
1312 | @group | |
1313 | c-continued-statement-indent 0 | |
1314 | c-brace-offset 0 | |
1315 | comment-column 40)))) | |
1316 | ||
1317 | (setq c++-mode-hook c-mode-hook) | |
1318 | @end group | |
a44af9f2 RS |
1319 | @end example |
1320 | ||
1321 | At the appropriate time, Emacs uses the @code{run-hooks} function to | |
bfe721d1 KH |
1322 | run particular hooks. This function calls the hook functions that have |
1323 | been added with @code{add-hook}. | |
a44af9f2 RS |
1324 | |
1325 | @defun run-hooks &rest hookvar | |
1326 | This function takes one or more hook variable names as arguments, and | |
1327 | runs each hook in turn. Each @var{hookvar} argument should be a symbol | |
1328 | that is a hook variable. These arguments are processed in the order | |
1329 | specified. | |
1330 | ||
1331 | If a hook variable has a non-@code{nil} value, that value may be a | |
1332 | function or a list of functions. If the value is a function (either a | |
1333 | lambda expression or a symbol with a function definition), it is | |
1334 | called. If it is a list, the elements are called, in order. | |
1335 | The hook functions are called with no arguments. | |
1336 | ||
bfe721d1 | 1337 | For example, here's how @code{emacs-lisp-mode} runs its mode hook: |
a44af9f2 RS |
1338 | |
1339 | @example | |
1340 | (run-hooks 'emacs-lisp-mode-hook) | |
1341 | @end example | |
1342 | @end defun | |
1343 | ||
22697dac | 1344 | @defun add-hook hook function &optional append local |
a44af9f2 | 1345 | This function is the handy way to add function @var{function} to hook |
de9f0bd9 RS |
1346 | variable @var{hook}. The argument @var{function} may be any valid Lisp |
1347 | function with the proper number of arguments. For example, | |
a44af9f2 RS |
1348 | |
1349 | @example | |
1350 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
1351 | @end example | |
1352 | ||
1353 | @noindent | |
1354 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
1355 | ||
de9f0bd9 RS |
1356 | You can use @code{add-hook} for abnormal hooks as well as for normal |
1357 | hooks. | |
1358 | ||
a44af9f2 RS |
1359 | It is best to design your hook functions so that the order in which they |
1360 | are executed does not matter. Any dependence on the order is ``asking | |
1361 | for trouble.'' However, the order is predictable: normally, | |
1362 | @var{function} goes at the front of the hook list, so it will be | |
1363 | executed first (barring another @code{add-hook} call). | |
1364 | ||
1365 | If the optional argument @var{append} is non-@code{nil}, the new hook | |
1366 | function goes at the end of the hook list and will be executed last. | |
22697dac KH |
1367 | |
1368 | If @var{local} is non-@code{nil}, that says to make the new hook | |
1369 | function local to the current buffer. Before you can do this, you must | |
1370 | make the hook itself buffer-local by calling @code{make-local-hook} | |
1371 | (@strong{not} @code{make-local-variable}). If the hook itself is not | |
1372 | buffer-local, then the value of @var{local} makes no difference---the | |
1373 | hook function is always global. | |
a44af9f2 RS |
1374 | @end defun |
1375 | ||
22697dac | 1376 | @defun remove-hook hook function &optional local |
a44af9f2 | 1377 | This function removes @var{function} from the hook variable @var{hook}. |
c44d2ced | 1378 | |
22697dac KH |
1379 | If @var{local} is non-@code{nil}, that says to remove @var{function} |
1380 | from the local hook list instead of from the global hook list. If the | |
1381 | hook itself is not buffer-local, then the value of @var{local} makes no | |
1382 | difference. | |
1383 | @end defun | |
c44d2ced | 1384 | |
22697dac KH |
1385 | @defun make-local-hook hook |
1386 | This function makes the hook variable @code{hook} local to the current | |
1387 | buffer. When a hook variable is local, it can have local and global | |
1388 | hook functions, and @code{run-hooks} runs all of them. | |
c44d2ced | 1389 | |
fc0cb073 RS |
1390 | This function works by making @code{t} an element of the buffer-local |
1391 | value. That serves as a flag to use the hook functions in the default | |
1392 | value of the hook variable as well as those in the local value. Since | |
1393 | @code{run-hooks} understands this flag, @code{make-local-hook} works | |
1394 | with all normal hooks. It works for only some non-normal hooks---those | |
1395 | whose callers have been updated to understand this meaning of @code{t}. | |
1396 | ||
22697dac KH |
1397 | Do not use @code{make-local-variable} directly for hook variables; it is |
1398 | not sufficient. | |
1399 | @end defun |