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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. |
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144 | |
145 | @item | |
146 | @cindex syntax tables in modes | |
147 | The mode may have its own syntax table or may share one with other | |
148 | related modes. If it has its own syntax table, it should store this in | |
de9f0bd9 | 149 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax |
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150 | Tables}. |
151 | ||
152 | @item | |
153 | @cindex abbrev tables in modes | |
154 | The mode may have its own abbrev table or may share one with other | |
155 | related modes. If it has its own abbrev table, it should store this in | |
156 | a variable named @code{@var{modename}-mode-abbrev-table}. @xref{Abbrev | |
157 | Tables}. | |
158 | ||
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159 | @item |
160 | Use @code{defvar} to set mode-related variables, so that they are not | |
161 | reinitialized if they already have a value. (Such reinitialization | |
162 | could discard customizations made by the user.) | |
163 | ||
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164 | @item |
165 | @cindex buffer-local variables in modes | |
166 | To make a buffer-local binding for an Emacs customization variable, use | |
167 | @code{make-local-variable} in the major mode command, not | |
168 | @code{make-variable-buffer-local}. The latter function would make the | |
169 | variable local to every buffer in which it is subsequently set, which | |
170 | would affect buffers that do not use this mode. It is undesirable for a | |
171 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
172 | ||
173 | It's ok to use @code{make-variable-buffer-local}, if you wish, for a | |
174 | variable used only within a single Lisp package. | |
175 | ||
176 | @item | |
177 | @cindex mode hook | |
178 | @cindex major mode hook | |
179 | Each major mode should have a @dfn{mode hook} named | |
180 | @code{@var{modename}-mode-hook}. The major mode command should run that | |
181 | hook, with @code{run-hooks}, as the very last thing it | |
182 | does. @xref{Hooks}. | |
183 | ||
184 | @item | |
185 | The major mode command may also run the hooks of some more basic modes. | |
186 | For example, @code{indented-text-mode} runs @code{text-mode-hook} as | |
187 | well as @code{indented-text-mode-hook}. It may run these other hooks | |
188 | immediately before the mode's own hook (that is, after everything else), | |
189 | or it may run them earlier. | |
190 | ||
191 | @item | |
192 | If something special should be done if the user switches a buffer from | |
193 | this mode to any other major mode, the mode can set a local value for | |
194 | @code{change-major-mode-hook}. | |
195 | ||
196 | @item | |
197 | If this mode is appropriate only for specially-prepared text, then the | |
198 | major mode command symbol should have a property named @code{mode-class} | |
199 | with value @code{special}, put on as follows: | |
200 | ||
201 | @cindex @code{mode-class} property | |
202 | @cindex @code{special} | |
203 | @example | |
204 | (put 'funny-mode 'mode-class 'special) | |
205 | @end example | |
206 | ||
207 | @noindent | |
208 | This tells Emacs that new buffers created while the current buffer has | |
209 | Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, | |
210 | and Buffer List use this feature. | |
211 | ||
212 | @item | |
213 | If you want to make the new mode the default for files with certain | |
214 | recognizable names, add an element to @code{auto-mode-alist} to select | |
215 | the mode for those file names. If you define the mode command to | |
216 | autoload, you should add this element in the same file that calls | |
217 | @code{autoload}. Otherwise, it is sufficient to add the element in the | |
218 | file that contains the mode definition. @xref{Auto Major Mode}. | |
219 | ||
220 | @item | |
221 | @cindex @file{.emacs} customization | |
222 | In the documentation, you should provide a sample @code{autoload} form | |
223 | and an example of how to add to @code{auto-mode-alist}, that users can | |
224 | include in their @file{.emacs} files. | |
225 | ||
226 | @item | |
227 | @cindex mode loading | |
de9f0bd9 | 228 | The top-level forms in the file defining the mode should be written so |
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229 | that they may be evaluated more than once without adverse consequences. |
230 | Even if you never load the file more than once, someone else will. | |
231 | @end itemize | |
232 | ||
233 | @defvar change-major-mode-hook | |
234 | This normal hook is run by @code{kill-all-local-variables} before it | |
235 | does anything else. This gives major modes a way to arrange for | |
236 | something special to be done if the user switches to a different major | |
237 | mode. For best results, make this variable buffer-local, so that it | |
238 | will disappear after doing its job and will not interfere with the | |
de9f0bd9 | 239 | subsequent major mode. @xref{Hooks}. |
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240 | @end defvar |
241 | ||
242 | @node Example Major Modes | |
243 | @subsection Major Mode Examples | |
244 | ||
245 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
246 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
247 | the conventions listed above: | |
248 | ||
249 | @smallexample | |
250 | @group | |
251 | ;; @r{Create mode-specific tables.} | |
252 | (defvar text-mode-syntax-table nil | |
253 | "Syntax table used while in text mode.") | |
254 | @end group | |
255 | ||
256 | @group | |
257 | (if text-mode-syntax-table | |
258 | () ; @r{Do not change the table if it is already set up.} | |
259 | (setq text-mode-syntax-table (make-syntax-table)) | |
260 | (modify-syntax-entry ?\" ". " text-mode-syntax-table) | |
261 | (modify-syntax-entry ?\\ ". " text-mode-syntax-table) | |
262 | (modify-syntax-entry ?' "w " text-mode-syntax-table)) | |
263 | @end group | |
264 | ||
265 | @group | |
266 | (defvar text-mode-abbrev-table nil | |
267 | "Abbrev table used while in text mode.") | |
268 | (define-abbrev-table 'text-mode-abbrev-table ()) | |
269 | @end group | |
270 | ||
271 | @group | |
272 | (defvar text-mode-map nil) ; @r{Create a mode-specific keymap.} | |
273 | ||
274 | (if text-mode-map | |
275 | () ; @r{Do not change the keymap if it is already set up.} | |
276 | (setq text-mode-map (make-sparse-keymap)) | |
277 | (define-key text-mode-map "\t" 'tab-to-tab-stop) | |
278 | (define-key text-mode-map "\es" 'center-line) | |
279 | (define-key text-mode-map "\eS" 'center-paragraph)) | |
280 | @end group | |
281 | @end smallexample | |
282 | ||
283 | Here is the complete major mode function definition for Text mode: | |
284 | ||
285 | @smallexample | |
286 | @group | |
287 | (defun text-mode () | |
288 | "Major mode for editing text intended for humans to read. | |
289 | Special commands: \\@{text-mode-map@} | |
290 | @end group | |
291 | @group | |
292 | Turning on text-mode runs the hook `text-mode-hook'." | |
293 | (interactive) | |
294 | (kill-all-local-variables) | |
295 | @end group | |
296 | @group | |
297 | (use-local-map text-mode-map) ; @r{This provides the local keymap.} | |
298 | (setq mode-name "Text") ; @r{This name goes into the mode line.} | |
299 | (setq major-mode 'text-mode) ; @r{This is how @code{describe-mode}} | |
300 | ; @r{finds the doc string to print.} | |
301 | (setq local-abbrev-table text-mode-abbrev-table) | |
302 | (set-syntax-table text-mode-syntax-table) | |
303 | (run-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} | |
304 | ; @r{customize the mode with a hook.} | |
305 | @end group | |
306 | @end smallexample | |
307 | ||
308 | @cindex @file{lisp-mode.el} | |
309 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
310 | Interaction mode) have more features than Text mode and the code is | |
311 | correspondingly more complicated. Here are excerpts from | |
312 | @file{lisp-mode.el} that illustrate how these modes are written. | |
313 | ||
314 | @cindex syntax table example | |
315 | @smallexample | |
316 | @group | |
317 | ;; @r{Create mode-specific table variables.} | |
318 | (defvar lisp-mode-syntax-table nil "") | |
319 | (defvar emacs-lisp-mode-syntax-table nil "") | |
320 | (defvar lisp-mode-abbrev-table nil "") | |
321 | @end group | |
322 | ||
323 | @group | |
324 | (if (not emacs-lisp-mode-syntax-table) ; @r{Do not change the table} | |
325 | ; @r{if it is already set.} | |
326 | (let ((i 0)) | |
327 | (setq emacs-lisp-mode-syntax-table (make-syntax-table)) | |
328 | @end group | |
329 | ||
330 | @group | |
331 | ;; @r{Set syntax of chars up to 0 to class of chars that are} | |
332 | ;; @r{part of symbol names but not words.} | |
333 | ;; @r{(The number 0 is @code{48} in the @sc{ASCII} character set.)} | |
334 | (while (< i ?0) | |
335 | (modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table) | |
336 | (setq i (1+ i))) | |
337 | @dots{} | |
338 | @end group | |
339 | @group | |
340 | ;; @r{Set the syntax for other characters.} | |
341 | (modify-syntax-entry ? " " emacs-lisp-mode-syntax-table) | |
342 | (modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table) | |
343 | @dots{} | |
344 | @end group | |
345 | @group | |
346 | (modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table) | |
347 | (modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table) | |
348 | @dots{})) | |
349 | ;; @r{Create an abbrev table for lisp-mode.} | |
350 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
351 | @end group | |
352 | @end smallexample | |
353 | ||
354 | Much code is shared among the three Lisp modes. The following | |
355 | function sets various variables; it is called by each of the major Lisp | |
356 | mode functions: | |
357 | ||
358 | @smallexample | |
359 | @group | |
360 | (defun lisp-mode-variables (lisp-syntax) | |
361 | ;; @r{The @code{lisp-syntax} argument is @code{nil} in Emacs Lisp mode,} | |
362 | ;; @r{and @code{t} in the other two Lisp modes.} | |
363 | (cond (lisp-syntax | |
364 | (if (not lisp-mode-syntax-table) | |
365 | ;; @r{The Emacs Lisp mode syntax table always exists, but} | |
366 | ;; @r{the Lisp Mode syntax table is created the first time a} | |
367 | ;; @r{mode that needs it is called. This is to save space.} | |
368 | @end group | |
369 | @group | |
370 | (progn (setq lisp-mode-syntax-table | |
371 | (copy-syntax-table emacs-lisp-mode-syntax-table)) | |
372 | ;; @r{Change some entries for Lisp mode.} | |
373 | (modify-syntax-entry ?\| "\" " | |
374 | lisp-mode-syntax-table) | |
375 | (modify-syntax-entry ?\[ "_ " | |
376 | lisp-mode-syntax-table) | |
377 | (modify-syntax-entry ?\] "_ " | |
378 | lisp-mode-syntax-table))) | |
379 | @end group | |
380 | @group | |
381 | (set-syntax-table lisp-mode-syntax-table))) | |
382 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
383 | @dots{}) | |
384 | @end group | |
385 | @end smallexample | |
386 | ||
387 | Functions such as @code{forward-paragraph} use the value of the | |
388 | @code{paragraph-start} variable. Since Lisp code is different from | |
389 | ordinary text, the @code{paragraph-start} variable needs to be set | |
390 | specially to handle Lisp. Also, comments are indented in a special | |
391 | fashion in Lisp and the Lisp modes need their own mode-specific | |
392 | @code{comment-indent-function}. The code to set these variables is the | |
393 | rest of @code{lisp-mode-variables}. | |
394 | ||
395 | @smallexample | |
396 | @group | |
397 | (make-local-variable 'paragraph-start) | |
398 | (setq paragraph-start (concat "^$\\|" page-delimiter)) | |
399 | @dots{} | |
400 | @end group | |
401 | @group | |
402 | (make-local-variable 'comment-indent-function) | |
403 | (setq comment-indent-function 'lisp-comment-indent)) | |
404 | @end group | |
405 | @end smallexample | |
406 | ||
407 | Each of the different Lisp modes has a slightly different keymap. For | |
408 | example, Lisp mode binds @kbd{C-c C-l} to @code{run-lisp}, but the other | |
409 | Lisp modes do not. However, all Lisp modes have some commands in | |
410 | common. The following function adds these common commands to a given | |
411 | keymap. | |
412 | ||
413 | @smallexample | |
414 | @group | |
415 | (defun lisp-mode-commands (map) | |
416 | (define-key map "\e\C-q" 'indent-sexp) | |
417 | (define-key map "\177" 'backward-delete-char-untabify) | |
418 | (define-key map "\t" 'lisp-indent-line)) | |
419 | @end group | |
420 | @end smallexample | |
421 | ||
422 | Here is an example of using @code{lisp-mode-commands} to initialize a | |
423 | keymap, as part of the code for Emacs Lisp mode. First we declare a | |
424 | variable with @code{defvar} to hold the mode-specific keymap. When this | |
425 | @code{defvar} executes, it sets the variable to @code{nil} if it was | |
426 | void. Then we set up the keymap if the variable is @code{nil}. | |
427 | ||
428 | This code avoids changing the keymap or the variable if it is already | |
de9f0bd9 | 429 | set up. This lets the user customize the keymap. |
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430 | |
431 | @smallexample | |
432 | @group | |
433 | (defvar emacs-lisp-mode-map () "") | |
434 | (if emacs-lisp-mode-map | |
435 | () | |
436 | (setq emacs-lisp-mode-map (make-sparse-keymap)) | |
437 | (define-key emacs-lisp-mode-map "\e\C-x" 'eval-defun) | |
438 | (lisp-mode-commands emacs-lisp-mode-map)) | |
439 | @end group | |
440 | @end smallexample | |
441 | ||
442 | Finally, here is the complete major mode function definition for | |
443 | Emacs Lisp mode. | |
444 | ||
445 | @smallexample | |
446 | @group | |
447 | (defun emacs-lisp-mode () | |
448 | "Major mode for editing Lisp code to run in Emacs. | |
449 | Commands: | |
450 | Delete converts tabs to spaces as it moves back. | |
451 | Blank lines separate paragraphs. Semicolons start comments. | |
452 | \\@{emacs-lisp-mode-map@} | |
453 | @end group | |
454 | @group | |
455 | Entry to this mode runs the hook `emacs-lisp-mode-hook'." | |
456 | (interactive) | |
457 | (kill-all-local-variables) | |
458 | (use-local-map emacs-lisp-mode-map) ; @r{This provides the local keymap.} | |
459 | (set-syntax-table emacs-lisp-mode-syntax-table) | |
460 | @end group | |
461 | @group | |
462 | (setq major-mode 'emacs-lisp-mode) ; @r{This is how @code{describe-mode}} | |
463 | ; @r{finds out what to describe.} | |
464 | (setq mode-name "Emacs-Lisp") ; @r{This goes into the mode line.} | |
de9f0bd9 | 465 | (lisp-mode-variables nil) ; @r{This defines various variables.} |
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466 | (run-hooks 'emacs-lisp-mode-hook)) ; @r{This permits the user to use a} |
467 | ; @r{hook to customize the mode.} | |
468 | @end group | |
469 | @end smallexample | |
470 | ||
471 | @node Auto Major Mode | |
472 | @subsection How Emacs Chooses a Major Mode | |
473 | ||
474 | Based on information in the file name or in the file itself, Emacs | |
475 | automatically selects a major mode for the new buffer when a file is | |
476 | visited. | |
477 | ||
478 | @deffn Command fundamental-mode | |
479 | Fundamental mode is a major mode that is not specialized for anything | |
480 | in particular. Other major modes are defined in effect by comparison | |
481 | with this one---their definitions say what to change, starting from | |
482 | Fundamental mode. The @code{fundamental-mode} function does @emph{not} | |
483 | run any hooks; you're not supposed to customize it. (If you want Emacs | |
484 | to behave differently in Fundamental mode, change the @emph{global} | |
485 | state of Emacs.) | |
486 | @end deffn | |
487 | ||
488 | @deffn Command normal-mode &optional find-file | |
489 | This function establishes the proper major mode and local variable | |
490 | bindings for the current buffer. First it calls @code{set-auto-mode}, | |
491 | then it runs @code{hack-local-variables} to parse, and bind or | |
492 | evaluate as appropriate, any local variables. | |
493 | ||
494 | If the @var{find-file} argument to @code{normal-mode} is | |
495 | non-@code{nil}, @code{normal-mode} assumes that the @code{find-file} | |
496 | function is calling it. In this case, it may process a local variables | |
497 | list at the end of the file. The variable @code{enable-local-variables} | |
498 | controls whether to do so. | |
499 | ||
500 | If you run @code{normal-mode} interactively, the argument | |
501 | @var{find-file} is normally @code{nil}. In this case, | |
502 | @code{normal-mode} unconditionally processes any local variables list. | |
503 | @xref{File variables, , Local Variables in Files, emacs, The GNU Emacs | |
504 | Manual}, for the syntax of the local variables section of a file. | |
505 | ||
506 | @cindex file mode specification error | |
507 | @code{normal-mode} uses @code{condition-case} around the call to the | |
508 | major mode function, so errors are caught and reported as a @samp{File | |
509 | mode specification error}, followed by the original error message. | |
510 | @end deffn | |
511 | ||
512 | @defopt enable-local-variables | |
513 | This variable controls processing of local variables lists in files | |
514 | being visited. A value of @code{t} means process the local variables | |
515 | lists unconditionally; @code{nil} means ignore them; anything else means | |
516 | ask the user what to do for each file. The default value is @code{t}. | |
517 | @end defopt | |
518 | ||
519 | @defopt enable-local-eval | |
520 | This variable controls processing of @samp{Eval:} in local variables | |
521 | lists in files being visited. A value of @code{t} means process them | |
522 | unconditionally; @code{nil} means ignore them; anything else means ask | |
523 | the user what to do for each file. The default value is @code{maybe}. | |
524 | @end defopt | |
525 | ||
526 | @defun set-auto-mode | |
527 | @cindex visited file mode | |
528 | This function selects the major mode that is appropriate for the | |
529 | current buffer. It may base its decision on the value of the @w{@samp{-*-}} | |
530 | line, on the visited file name (using @code{auto-mode-alist}), or on the | |
de9f0bd9 | 531 | value of a local variable. However, this function does not look for |
a44af9f2 RS |
532 | the @samp{mode:} local variable near the end of a file; the |
533 | @code{hack-local-variables} function does that. @xref{Choosing Modes, , | |
534 | How Major Modes are Chosen, emacs, The GNU Emacs Manual}. | |
535 | @end defun | |
536 | ||
537 | @defopt default-major-mode | |
538 | This variable holds the default major mode for new buffers. The | |
539 | standard value is @code{fundamental-mode}. | |
540 | ||
541 | If the value of @code{default-major-mode} is @code{nil}, Emacs uses | |
542 | the (previously) current buffer's major mode for the major mode of a new | |
543 | buffer. However, if the major mode symbol has a @code{mode-class} | |
544 | property with value @code{special}, then it is not used for new buffers; | |
545 | Fundamental mode is used instead. The modes that have this property are | |
546 | those such as Dired and Rmail that are useful only with text that has | |
547 | been specially prepared. | |
548 | @end defopt | |
549 | ||
550 | @defvar initial-major-mode | |
551 | @cindex @samp{*scratch*} | |
552 | The value of this variable determines the major mode of the initial | |
553 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
554 | mode command name. The default value is @code{lisp-interaction-mode}. | |
555 | @end defvar | |
556 | ||
557 | @defvar auto-mode-alist | |
558 | This variable contains an association list of file name patterns | |
559 | (regular expressions; @pxref{Regular Expressions}) and corresponding | |
560 | major mode functions. Usually, the file name patterns test for | |
561 | suffixes, such as @samp{.el} and @samp{.c}, but this need not be the | |
562 | case. An ordinary element of the alist looks like @code{(@var{regexp} . | |
563 | @var{mode-function})}. | |
564 | ||
565 | For example, | |
566 | ||
567 | @smallexample | |
568 | @group | |
569 | (("^/tmp/fol/" . text-mode) | |
24675e99 RS |
570 | ("\\.texinfo\\'" . texinfo-mode) |
571 | ("\\.texi\\'" . texinfo-mode) | |
a44af9f2 RS |
572 | @end group |
573 | @group | |
24675e99 RS |
574 | ("\\.el\\'" . emacs-lisp-mode) |
575 | ("\\.c\\'" . c-mode) | |
576 | ("\\.h\\'" . c-mode) | |
a44af9f2 RS |
577 | @dots{}) |
578 | @end group | |
579 | @end smallexample | |
580 | ||
581 | When you visit a file whose expanded file name (@pxref{File Name | |
582 | Expansion}) matches a @var{regexp}, @code{set-auto-mode} calls the | |
583 | corresponding @var{mode-function}. This feature enables Emacs to select | |
584 | the proper major mode for most files. | |
585 | ||
586 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
587 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
588 | @code{auto-mode-alist} again for a match against the portion of the file | |
589 | name that did not match before. | |
590 | ||
591 | This match-again feature is useful for uncompression packages: an entry | |
592 | of the form @code{("\\.gz\\'" . @var{function})} can uncompress the file | |
593 | and then put the uncompressed file in the proper mode according to the | |
594 | name sans @samp{.gz}. | |
595 | ||
596 | Here is an example of how to prepend several pattern pairs to | |
597 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
598 | @file{.emacs} file.) | |
599 | ||
600 | @smallexample | |
601 | @group | |
602 | (setq auto-mode-alist | |
603 | (append | |
de9f0bd9 | 604 | ;; @r{File name starts with a dot.} |
24675e99 | 605 | '(("/\\.[^/]*\\'" . fundamental-mode) |
de9f0bd9 | 606 | ;; @r{File name has no dot.} |
24675e99 | 607 | ("[^\\./]*\\'" . fundamental-mode) |
de9f0bd9 | 608 | ;; @r{File name ends in @samp{.C}.} |
24675e99 | 609 | ("\\.C\\'" . c++-mode)) |
a44af9f2 RS |
610 | auto-mode-alist)) |
611 | @end group | |
612 | @end smallexample | |
613 | @end defvar | |
614 | ||
615 | @defvar interpreter-mode-alist | |
616 | This variable specifes major modes to use for scripts that specify a | |
617 | command interpreter in an @samp{!#} line. Its value is a list of | |
618 | elements of the form @code{(@var{interpreter} . @var{mode})}; for | |
619 | example, @code{("perl" . perl-mode)} is one element present by default. | |
620 | The element says to use mode @var{mode} if the file specifies | |
621 | @var{interpreter}. | |
622 | ||
de9f0bd9 RS |
623 | This variable is applicable only when the @code{auto-mode-alist} does |
624 | not indicate which major mode to use. | |
a44af9f2 RS |
625 | @end defvar |
626 | ||
627 | @defun hack-local-variables &optional force | |
628 | This function parses, and binds or evaluates as appropriate, any local | |
629 | variables for the current buffer. | |
630 | ||
631 | The handling of @code{enable-local-variables} documented for | |
632 | @code{normal-mode} actually takes place here. The argument @var{force} | |
de9f0bd9 RS |
633 | usually comes from the argument @var{find-file} given to |
634 | @code{normal-mode}. | |
a44af9f2 RS |
635 | @end defun |
636 | ||
637 | @node Mode Help | |
638 | @subsection Getting Help about a Major Mode | |
639 | @cindex mode help | |
640 | @cindex help for major mode | |
641 | @cindex documentation for major mode | |
642 | ||
643 | The @code{describe-mode} function is used to provide information | |
644 | about major modes. It is normally called with @kbd{C-h m}. The | |
645 | @code{describe-mode} function uses the value of @code{major-mode}, | |
646 | which is why every major mode function needs to set the | |
647 | @code{major-mode} variable. | |
648 | ||
649 | @deffn Command describe-mode | |
650 | This function displays the documentation of the current major mode. | |
651 | ||
652 | The @code{describe-mode} function calls the @code{documentation} | |
653 | function using the value of @code{major-mode} as an argument. Thus, it | |
654 | displays the documentation string of the major mode function. | |
655 | (@xref{Accessing Documentation}.) | |
656 | @end deffn | |
657 | ||
658 | @defvar major-mode | |
659 | This variable holds the symbol for the current buffer's major mode. | |
de9f0bd9 | 660 | This symbol should have a function definition that is the command to |
a44af9f2 | 661 | switch to that major mode. The @code{describe-mode} function uses the |
de9f0bd9 | 662 | documentation string of the function as the documentation of the major |
a44af9f2 RS |
663 | mode. |
664 | @end defvar | |
665 | ||
666 | @node Derived Modes | |
667 | @subsection Defining Derived Modes | |
668 | ||
669 | It's often useful to define a new major mode in terms of an existing | |
670 | one. An easy way to do this is to use @code{define-derived-mode}. | |
671 | ||
de9f0bd9 | 672 | @defmac define-derived-mode variant parent name docstring body@dots{} |
a44af9f2 | 673 | This construct defines @var{variant} as a major mode command, using |
de9f0bd9 | 674 | @var{name} as the string form of the mode name. |
a44af9f2 | 675 | |
de9f0bd9 RS |
676 | The new command @var{variant} is defined to call the function |
677 | @var{parent}, then override certain aspects of that parent mode: | |
a44af9f2 RS |
678 | |
679 | @itemize @bullet | |
680 | @item | |
681 | The new mode has its own keymap, named @code{@var{variant}-map}. | |
682 | @code{define-derived-mode} initializes this map to inherit from | |
683 | @code{@var{parent}-map}, if it is not already set. | |
684 | ||
685 | @item | |
de9f0bd9 | 686 | The new mode has its own syntax table, kept in the variable |
a44af9f2 RS |
687 | @code{@var{variant}-syntax-table}. |
688 | @code{define-derived-mode} initializes this variable by copying | |
689 | @code{@var{parent}-syntax-table}, if it is not already set. | |
690 | ||
691 | @item | |
de9f0bd9 | 692 | The new mode has its own abbrev table, kept in the variable |
a44af9f2 RS |
693 | @code{@var{variant}-abbrev-table}. |
694 | @code{define-derived-mode} initializes this variable by copying | |
695 | @code{@var{parent}-abbrev-table}, if it is not already set. | |
696 | ||
697 | @item | |
698 | The new mode has its own mode hook, @code{@var{variant}-hook}, | |
699 | which it runs in standard fashion as the very last thing that it does. | |
700 | (The new mode also runs the mode hook of @var{parent} as part | |
701 | of calling @var{parent}.) | |
702 | @end itemize | |
703 | ||
704 | In addition, you can specify how to override other aspects of | |
de9f0bd9 | 705 | @var{parent} with @var{body}. The command @var{variant} |
a44af9f2 RS |
706 | evaluates the forms in @var{body} after setting up all its usual |
707 | overrides, just before running @code{@var{variant}-hook}. | |
708 | ||
709 | The argument @var{docstring} specifies the documentation string for the | |
710 | new mode. If you omit @var{docstring}, @code{define-derived-mode} | |
711 | generates a documentation string. | |
712 | ||
713 | Here is a hypothetical example: | |
714 | ||
715 | @example | |
716 | (define-derived-mode hypertext-mode | |
717 | text-mode "Hypertext" | |
718 | "Major mode for hypertext. | |
719 | \\@{hypertext-mode-map@}" | |
720 | (setq case-fold-search nil)) | |
721 | ||
722 | (define-key hypertext-mode-map | |
723 | [down-mouse-3] 'do-hyper-link) | |
724 | @end example | |
725 | @end defmac | |
726 | ||
727 | @node Minor Modes | |
728 | @section Minor Modes | |
729 | @cindex minor mode | |
730 | ||
731 | A @dfn{minor mode} provides features that users may enable or disable | |
732 | independently of the choice of major mode. Minor modes can be enabled | |
733 | individually or in combination. Minor modes would be better named | |
734 | ``Generally available, optional feature modes'' except that such a name is | |
735 | unwieldy. | |
736 | ||
737 | A minor mode is not usually a modification of single major mode. For | |
738 | example, Auto Fill mode may be used in any major mode that permits text | |
739 | insertion. To be general, a minor mode must be effectively independent | |
740 | of the things major modes do. | |
741 | ||
742 | A minor mode is often much more difficult to implement than a major | |
743 | mode. One reason is that you should be able to activate and deactivate | |
de9f0bd9 RS |
744 | minor modes in any order. A minor mode should be able to have its |
745 | desired effect regardless of the major mode and regardless of the other | |
746 | minor modes in effect. | |
a44af9f2 RS |
747 | |
748 | Often the biggest problem in implementing a minor mode is finding a | |
749 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
750 | keymaps make this easier in Emacs 19 than it used to be. | |
751 | ||
752 | @menu | |
753 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
754 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
755 | @end menu | |
756 | ||
757 | @node Minor Mode Conventions | |
758 | @subsection Conventions for Writing Minor Modes | |
759 | @cindex minor mode conventions | |
760 | @cindex conventions for writing minor modes | |
761 | ||
762 | There are conventions for writing minor modes just as there are for | |
763 | major modes. Several of the major mode conventions apply to minor | |
764 | modes as well: those regarding the name of the mode initialization | |
765 | function, the names of global symbols, and the use of keymaps and | |
766 | other tables. | |
767 | ||
768 | In addition, there are several conventions that are specific to | |
769 | minor modes. | |
770 | ||
771 | @itemize @bullet | |
772 | @item | |
773 | @cindex mode variable | |
774 | Make a variable whose name ends in @samp{-mode} to represent the minor | |
775 | mode. Its value should enable or disable the mode (@code{nil} to | |
776 | disable; anything else to enable.) We call this the @dfn{mode | |
777 | variable}. | |
778 | ||
779 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
780 | display the minor mode name in the mode line. It can also enable | |
781 | or disable a minor mode keymap. Individual commands or hooks can also | |
782 | check the variable's value. | |
783 | ||
784 | If you want the minor mode to be enabled separately in each buffer, | |
785 | make the variable buffer-local. | |
786 | ||
787 | @item | |
788 | Define a command whose name is the same as the mode variable. | |
789 | Its job is to enable and disable the mode by setting the variable. | |
790 | ||
791 | The command should accept one optional argument. If the argument is | |
792 | @code{nil}, it should toggle the mode (turn it on if it is off, and off | |
793 | if it is on). Otherwise, it should turn the mode on if the argument is | |
794 | a positive integer, a symbol other than @code{nil} or @code{-}, or a | |
795 | list whose @sc{car} is such an integer or symbol; it should turn the | |
796 | mode off otherwise. | |
797 | ||
798 | Here is an example taken from the definition of @code{overwrite-mode}. | |
de9f0bd9 RS |
799 | It shows the use of @code{overwrite-mode} as a variable that enables or |
800 | disables the mode's behavior, and also shows the proper way to toggle, | |
801 | enable or disable the minor mode based on the raw prefix argument value. | |
a44af9f2 RS |
802 | |
803 | @smallexample | |
804 | @group | |
805 | (setq overwrite-mode | |
806 | (if (null arg) (not overwrite-mode) | |
807 | (> (prefix-numeric-value arg) 0))) | |
808 | @end group | |
809 | @end smallexample | |
810 | ||
811 | @item | |
812 | Add an element to @code{minor-mode-alist} for each minor mode | |
813 | (@pxref{Mode Line Variables}). This element should be a list of the | |
814 | following form: | |
815 | ||
816 | @smallexample | |
817 | (@var{mode-variable} @var{string}) | |
818 | @end smallexample | |
819 | ||
de9f0bd9 | 820 | Here @var{mode-variable} is the variable that controls enabling of the |
a44af9f2 RS |
821 | minor mode, and @var{string} is a short string, starting with a space, |
822 | to represent the mode in the mode line. These strings must be short so | |
823 | that there is room for several of them at once. | |
824 | ||
825 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
826 | check for an existing element, to avoid duplication. For example: | |
827 | ||
828 | @smallexample | |
829 | @group | |
830 | (or (assq 'leif-mode minor-mode-alist) | |
831 | (setq minor-mode-alist | |
832 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
833 | @end group | |
834 | @end smallexample | |
835 | @end itemize | |
836 | ||
837 | @node Keymaps and Minor Modes | |
838 | @subsection Keymaps and Minor Modes | |
839 | ||
de9f0bd9 | 840 | As of Emacs version 19, each minor mode can have its own keymap, which is |
a44af9f2 RS |
841 | active when the mode is enabled. @xref{Active Keymaps}. To set up a |
842 | keymap for a minor mode, add an element to the alist | |
843 | @code{minor-mode-map-alist}. | |
844 | ||
845 | @cindex @code{self-insert-command}, minor modes | |
846 | One use of minor mode keymaps is to modify the behavior of certain | |
847 | self-inserting characters so that they do something else as well as | |
848 | self-insert. In general, this is the only way to do that, since the | |
849 | facilities for customizing @code{self-insert-command} are limited to | |
850 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
851 | substituting your own definition of @code{self-insert-command} for the | |
852 | standard one. The editor command loop handles this function specially.) | |
853 | ||
854 | @defvar minor-mode-map-alist | |
855 | This variable is an alist of elements that look like this: | |
856 | ||
857 | @example | |
858 | (@var{variable} . @var{keymap}) | |
859 | @end example | |
860 | ||
861 | @noindent | |
de9f0bd9 | 862 | where @var{variable} is the variable that indicates whether the minor |
a44af9f2 RS |
863 | mode is enabled, and @var{keymap} is the keymap. The keymap |
864 | @var{keymap} is active whenever @var{variable} has a non-@code{nil} | |
865 | value. | |
866 | ||
867 | Note that elements of @code{minor-mode-map-alist} do not have the same | |
868 | structure as elements of @code{minor-mode-alist}. The map must be the | |
869 | @sc{cdr} of the element; a list with the map as the second element will | |
870 | not do. | |
871 | ||
872 | What's more, the keymap itself must appear in the @sc{cdr}. It does not | |
873 | work to store a variable in the @sc{cdr} and make the map the value of | |
874 | that variable. | |
875 | ||
876 | When more than one minor mode keymap is active, their order of priority | |
877 | is the order of @code{minor-mode-map-alist}. But you should design | |
878 | minor modes so that they don't interfere with each other. If you do | |
879 | this properly, the order will not matter. | |
880 | @end defvar | |
881 | ||
882 | @node Mode Line Format | |
883 | @section Mode Line Format | |
884 | @cindex mode line | |
885 | ||
de9f0bd9 | 886 | Each Emacs window (aside from minibuffer windows) includes a mode line, |
a44af9f2 | 887 | which displays status information about the buffer displayed in the |
de9f0bd9 | 888 | window. The mode line contains information about the buffer, such as its |
a44af9f2 | 889 | name, associated file, depth of recursive editing, and the major and |
de9f0bd9 | 890 | minor modes. |
a44af9f2 RS |
891 | |
892 | This section describes how the contents of the mode line are | |
893 | controlled. It is in the chapter on modes because much of the | |
894 | information displayed in the mode line relates to the enabled major and | |
895 | minor modes. | |
896 | ||
897 | @code{mode-line-format} is a buffer-local variable that holds a | |
898 | template used to display the mode line of the current buffer. All | |
899 | windows for the same buffer use the same @code{mode-line-format} and the | |
900 | mode lines will appear the same (except for scrolling percentages and | |
901 | line numbers). | |
902 | ||
903 | The mode line of a window is normally updated whenever a different | |
904 | buffer is shown in the window, or when the buffer's modified-status | |
905 | changes from @code{nil} to @code{t} or vice-versa. If you modify any of | |
de9f0bd9 RS |
906 | the variables referenced by @code{mode-line-format} (@pxref{Mode Line |
907 | Variables}), you may want to force an update of the mode line so as to | |
908 | display the new information. | |
a44af9f2 RS |
909 | |
910 | @c Emacs 19 feature | |
911 | @defun force-mode-line-update | |
912 | Force redisplay of the current buffer's mode line. | |
913 | @end defun | |
914 | ||
915 | The mode line is usually displayed in inverse video; see | |
916 | @code{mode-line-inverse-video} in @ref{Inverse Video}. | |
917 | ||
918 | @menu | |
919 | * Mode Line Data:: The data structure that controls the mode line. | |
920 | * Mode Line Variables:: Variables used in that data structure. | |
921 | * %-Constructs:: Putting information into a mode line. | |
922 | @end menu | |
923 | ||
924 | @node Mode Line Data | |
925 | @subsection The Data Structure of the Mode Line | |
926 | @cindex mode line construct | |
927 | ||
928 | The mode line contents are controlled by a data structure of lists, | |
de9f0bd9 | 929 | strings, symbols, and numbers kept in the buffer-local variable |
a44af9f2 RS |
930 | @code{mode-line-format}. The data structure is called a @dfn{mode line |
931 | construct}, and it is built in recursive fashion out of simpler mode line | |
932 | constructs. | |
933 | ||
934 | @defvar mode-line-format | |
935 | The value of this variable is a mode line construct with overall | |
936 | responsibility for the mode line format. The value of this variable | |
937 | controls which other variables are used to form the mode line text, and | |
938 | where they appear. | |
939 | @end defvar | |
940 | ||
941 | A mode line construct may be as simple as a fixed string of text, but | |
942 | it usually specifies how to use other variables to construct the text. | |
943 | Many of these variables are themselves defined to have mode line | |
944 | constructs as their values. | |
945 | ||
946 | The default value of @code{mode-line-format} incorporates the values | |
947 | of variables such as @code{mode-name} and @code{minor-mode-alist}. | |
948 | Because of this, very few modes need to alter @code{mode-line-format}. | |
949 | For most purposes, it is sufficient to alter the variables referenced by | |
950 | @code{mode-line-format}. | |
951 | ||
de9f0bd9 RS |
952 | A mode line construct may be a list, a symbol, or a string. If the |
953 | value is a list, each element may be a list, a symbol, or a string. | |
a44af9f2 RS |
954 | |
955 | @table @code | |
956 | @cindex percent symbol in mode line | |
957 | @item @var{string} | |
958 | A string as a mode line construct is displayed verbatim in the mode line | |
959 | except for @dfn{@code{%}-constructs}. Decimal digits after the @code{%} | |
960 | specify the field width for space filling on the right (i.e., the data | |
961 | is left justified). @xref{%-Constructs}. | |
962 | ||
963 | @item @var{symbol} | |
964 | A symbol as a mode line construct stands for its value. The value of | |
de9f0bd9 RS |
965 | @var{symbol} is used as a mode line construct, in place of @var{symbol}. |
966 | However, the symbols @code{t} and @code{nil} are ignored; so is any | |
967 | symbol whose value is void. | |
a44af9f2 RS |
968 | |
969 | There is one exception: if the value of @var{symbol} is a string, it is | |
de9f0bd9 | 970 | displayed verbatim: the @code{%}-constructs are not recognized. |
a44af9f2 RS |
971 | |
972 | @item (@var{string} @var{rest}@dots{}) @r{or} (@var{list} @var{rest}@dots{}) | |
de9f0bd9 RS |
973 | A list whose first element is a string or list means to process all the |
974 | elements recursively and concatenate the results. This is the most | |
975 | common form of mode line construct. | |
a44af9f2 RS |
976 | |
977 | @item (@var{symbol} @var{then} @var{else}) | |
978 | A list whose first element is a symbol is a conditional. Its meaning | |
979 | depends on the value of @var{symbol}. If the value is non-@code{nil}, | |
de9f0bd9 RS |
980 | the second element, @var{then}, is processed recursively as a mode line |
981 | element. But if the value of @var{symbol} is @code{nil}, the third | |
982 | element, @var{else}, is processed recursively. You may omit @var{else}; | |
983 | then the mode line element displays nothing if the value of @var{symbol} | |
984 | is @code{nil}. | |
a44af9f2 RS |
985 | |
986 | @item (@var{width} @var{rest}@dots{}) | |
987 | A list whose first element is an integer specifies truncation or | |
988 | padding of the results of @var{rest}. The remaining elements | |
989 | @var{rest} are processed recursively as mode line constructs and | |
990 | concatenated together. Then the result is space filled (if | |
991 | @var{width} is positive) or truncated (to @minus{}@var{width} columns, | |
992 | if @var{width} is negative) on the right. | |
993 | ||
994 | For example, the usual way to show what percentage of a buffer is above | |
de9f0bd9 | 995 | the top of the window is to use a list like this: @code{(-3 "%p")}. |
a44af9f2 RS |
996 | @end table |
997 | ||
998 | If you do alter @code{mode-line-format} itself, the new value should | |
de9f0bd9 RS |
999 | use the same variables that appear in the default value (@pxref{Mode |
1000 | Line Variables}), rather than duplicating their contents or displaying | |
1001 | the information in another fashion. This way, customizations made by | |
1002 | the user, by libraries (such as @code{display-time}) and by major modes | |
1003 | via changes to those variables remain effective. | |
a44af9f2 RS |
1004 | |
1005 | @cindex Shell mode @code{mode-line-format} | |
1006 | Here is an example of a @code{mode-line-format} that might be | |
de9f0bd9 | 1007 | useful for @code{shell-mode}, since it contains the hostname and default |
a44af9f2 RS |
1008 | directory. |
1009 | ||
1010 | @example | |
1011 | @group | |
1012 | (setq mode-line-format | |
1013 | (list "" | |
1014 | 'mode-line-modified | |
1015 | "%b--" | |
1016 | @end group | |
1017 | (getenv "HOST") ; @r{One element is not constant.} | |
1018 | ":" | |
1019 | 'default-directory | |
1020 | " " | |
1021 | 'global-mode-string | |
de9f0bd9 RS |
1022 | " %[(" |
1023 | 'mode-name | |
1024 | 'mode-line-process | |
a44af9f2 RS |
1025 | 'minor-mode-alist |
1026 | "%n" | |
a44af9f2 RS |
1027 | ")%]----" |
1028 | @group | |
1029 | (line-number-mode "L%l--") | |
1030 | '(-3 . "%p") | |
1031 | "-%-")) | |
1032 | @end group | |
1033 | @end example | |
1034 | ||
1035 | @node Mode Line Variables | |
1036 | @subsection Variables Used in the Mode Line | |
1037 | ||
1038 | This section describes variables incorporated by the | |
1039 | standard value of @code{mode-line-format} into the text of the mode | |
1040 | line. There is nothing inherently special about these variables; any | |
1041 | other variables could have the same effects on the mode line if | |
1042 | @code{mode-line-format} were changed to use them. | |
1043 | ||
1044 | @defvar mode-line-modified | |
de9f0bd9 | 1045 | This variable holds the value of the mode-line construct that displays |
a44af9f2 RS |
1046 | whether the current buffer is modified. |
1047 | ||
de9f0bd9 | 1048 | The default value of @code{mode-line-modified} is |
a44af9f2 RS |
1049 | @code{("--%1*%1*-")}. This means that the mode line displays |
1050 | @samp{--**-} if the buffer is modified, @samp{-----} if the buffer is | |
1051 | not modified, and @samp{--%%-} if the buffer is read only. | |
1052 | ||
1053 | Changing this variable does not force an update of the mode line. | |
1054 | @end defvar | |
1055 | ||
1056 | @defvar mode-line-buffer-identification | |
de9f0bd9 | 1057 | This variable identifies the buffer being displayed in the window. Its |
8dd7abfc | 1058 | default value is @code{("Emacs: %17b")}, which means that it displays |
de9f0bd9 RS |
1059 | @samp{Emacs:} followed by seventeen characters of the buffer name. You |
1060 | may want to change this in modes such as Rmail that do not behave like a | |
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 | |
1103 | @result{} ((abbrev-mode " Abbrev") | |
1104 | (overwrite-mode " Ovwrt") | |
1105 | (auto-fill-function " Fill") | |
1106 | (defining-kbd-macro " Def")) | |
1107 | @end group | |
1108 | @end example | |
1109 | ||
1110 | @noindent | |
1111 | (In earlier Emacs versions, @code{auto-fill-function} was called | |
1112 | @code{auto-fill-hook}.) | |
1113 | ||
1114 | @code{minor-mode-alist} is not buffer-local. The variables mentioned | |
1115 | in the alist should be buffer-local if the minor mode can be enabled | |
1116 | separately in each buffer. | |
1117 | @end defvar | |
1118 | ||
1119 | @defvar mode-line-process | |
1120 | This buffer-local variable contains the mode line information on process | |
1121 | status in modes used for communicating with subprocesses. It is | |
1122 | displayed immediately following the major mode name, with no intervening | |
1123 | space. For example, its value in the @samp{*shell*} buffer is | |
1124 | @code{(":@: %s")}, which allows the shell to display its status along | |
1125 | with the major mode as: @samp{(Shell:@: run)}. Normally this variable | |
1126 | is @code{nil}. | |
1127 | @end defvar | |
1128 | ||
1129 | @defvar default-mode-line-format | |
de9f0bd9 | 1130 | This variable holds the default @code{mode-line-format} for buffers |
a44af9f2 RS |
1131 | that do not override it. This is the same as @code{(default-value |
1132 | 'mode-line-format)}. | |
1133 | ||
de9f0bd9 | 1134 | The default value of @code{default-mode-line-format} is: |
a44af9f2 RS |
1135 | |
1136 | @example | |
1137 | @group | |
1138 | ("" | |
1139 | mode-line-modified | |
1140 | mode-line-buffer-identification | |
1141 | " " | |
1142 | global-mode-string | |
1143 | " %[(" | |
1144 | mode-name | |
1145 | @end group | |
1146 | @group | |
1147 | minor-mode-alist | |
1148 | "%n" | |
1149 | mode-line-process | |
1150 | ")%]----" | |
1151 | (-3 . "%p") | |
1152 | "-%-") | |
1153 | @end group | |
1154 | @end example | |
1155 | @end defvar | |
1156 | ||
de9f0bd9 RS |
1157 | @defvar vc-mode |
1158 | The variable @code{vc-mode}, local in each buffer, records whether the | |
1159 | buffer's visited file is maintained with version control, and, if so, | |
1160 | which kind. Its value is @code{nil} for no version control, or a string | |
1161 | that appears in the mode line. | |
1162 | @end defvar | |
1163 | ||
a44af9f2 RS |
1164 | @node %-Constructs |
1165 | @subsection @code{%}-Constructs in the Mode Line | |
1166 | ||
1167 | The following table lists the recognized @code{%}-constructs and what | |
de9f0bd9 RS |
1168 | they mean. In any construct except @samp{%%}, you can add a decimal |
1169 | integer after the @samp{%} to specify how many characters to display. | |
a44af9f2 RS |
1170 | |
1171 | @table @code | |
1172 | @item %b | |
1173 | The current buffer name, obtained with the @code{buffer-name} function. | |
1174 | @xref{Buffer Names}. | |
1175 | ||
1176 | @item %f | |
1177 | The visited file name, obtained with the @code{buffer-file-name} | |
1178 | function. @xref{Buffer File Name}. | |
1179 | ||
1180 | @item %* | |
1181 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
1182 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
1183 | @samp{-} otherwise. @xref{Buffer Modification}. | |
1184 | ||
1185 | @item %+ | |
de9f0bd9 | 1186 | @samp{*} if the buffer is modified, and @samp{-} otherwise. |
a44af9f2 RS |
1187 | |
1188 | @item %s | |
1189 | The status of the subprocess belonging to the current buffer, obtained with | |
1190 | @code{process-status}. @xref{Process Information}. | |
1191 | ||
1192 | @item %p | |
1193 | The percent of the buffer above the @strong{top} of window, or | |
1194 | @samp{Top}, @samp{Bottom} or @samp{All}. | |
1195 | ||
1196 | @item %P | |
1197 | The percentage of the buffer text that is above the @strong{bottom} of | |
1198 | the window (which includes the text visible in the window, as well as | |
1199 | the text above the top), plus @samp{Top} if the top of the buffer is | |
1200 | visible on screen; or @samp{Bottom} or @samp{All}. | |
1201 | ||
1202 | @item %n | |
1203 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
1204 | @code{narrow-to-region} in @ref{Narrowing}). | |
1205 | ||
1206 | @item %[ | |
1207 | An indication of the depth of recursive editing levels (not counting | |
1208 | minibuffer levels): one @samp{[} for each editing level. | |
1209 | @xref{Recursive Editing}. | |
1210 | ||
1211 | @item %] | |
1212 | One @samp{]} for each recursive editing level (not counting minibuffer | |
1213 | levels). | |
1214 | ||
1215 | @item %% | |
1216 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
1217 | string in which @code{%}-constructs are allowed. | |
1218 | ||
1219 | @item %- | |
1220 | Dashes sufficient to fill the remainder of the mode line. | |
1221 | @end table | |
1222 | ||
1223 | The following two @code{%}-constructs are still supported, but they are | |
1224 | obsolete, since you can get the same results with the variables | |
1225 | @code{mode-name} and @code{global-mode-string}. | |
1226 | ||
1227 | @table @code | |
1228 | @item %m | |
1229 | The value of @code{mode-name}. | |
1230 | ||
1231 | @item %M | |
1232 | The value of @code{global-mode-string}. Currently, only | |
1233 | @code{display-time} modifies the value of @code{global-mode-string}. | |
1234 | @end table | |
1235 | ||
1236 | @node Hooks | |
1237 | @section Hooks | |
1238 | @cindex hooks | |
1239 | ||
1240 | A @dfn{hook} is a variable where you can store a function or functions | |
1241 | to be called on a particular occasion by an existing program. Emacs | |
1242 | provides hooks for the sake of customization. Most often, hooks are set | |
1243 | up in the @file{.emacs} file, but Lisp programs can set them also. | |
1244 | @xref{Standard Hooks}, for a list of standard hook variables. | |
1245 | ||
1246 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
1247 | contain lists of functions to be called with no arguments. The reason | |
1248 | most hooks are normal hooks is so that you can use them in a uniform | |
1249 | way. You can always tell when a hook is a normal hook, because its | |
1250 | name ends in @samp{-hook}. | |
1251 | ||
1252 | The recommended way to add a hook function to a normal hook is by | |
1253 | calling @code{add-hook} (see below). The hook functions may be any of | |
1254 | the valid kinds of functions that @code{funcall} accepts (@pxref{What Is | |
1255 | a Function}). Most normal hook variables are initially void; | |
1256 | @code{add-hook} knows how to deal with this. | |
1257 | ||
1258 | As for abnormal hooks, those whose names end in @samp{-function} have | |
de9f0bd9 RS |
1259 | a value that is a single function. Those whose names end in |
1260 | @samp{-hooks} have a value that is a list of functions. Any hook that | |
a44af9f2 RS |
1261 | is abnormal is abnormal because a normal hook won't do the job; either |
1262 | the functions are called with arguments, or their values are meaningful. | |
1263 | The name shows you that the hook is abnormal and that you should look at | |
1264 | its documentation string to see how to use it properly. | |
1265 | ||
1266 | Most major modes run hooks as the last step of initialization. This | |
1267 | makes it easy for a user to customize the behavior of the mode, by | |
1268 | overriding the local variable assignments already made by the mode. But | |
1269 | hooks are used in other contexts too. For example, the hook | |
1270 | @code{suspend-hook} runs just before Emacs suspends itself | |
1271 | (@pxref{Suspending Emacs}). | |
1272 | ||
1273 | Here's an expression you can put in your @file{.emacs} file to turn on | |
1274 | Auto Fill mode when in Lisp Interaction mode: | |
1275 | ||
1276 | @example | |
1277 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
1278 | @end example | |
1279 | ||
1280 | The next example shows how to use a hook to customize the way Emacs | |
1281 | formats C code. (People often have strong personal preferences for one | |
1282 | format or another.) Here the hook function is an anonymous lambda | |
1283 | expression. | |
1284 | ||
1285 | @cindex lambda expression in hook | |
1286 | @example | |
1287 | @group | |
1288 | (add-hook 'c-mode-hook | |
1289 | (function (lambda () | |
1290 | (setq c-indent-level 4 | |
1291 | c-argdecl-indent 0 | |
1292 | c-label-offset -4 | |
1293 | @end group | |
1294 | @group | |
1295 | c-continued-statement-indent 0 | |
1296 | c-brace-offset 0 | |
1297 | comment-column 40)))) | |
1298 | ||
1299 | (setq c++-mode-hook c-mode-hook) | |
1300 | @end group | |
1301 | @end example | |
1302 | ||
1303 | Finally, here is an example of how to use the Text mode hook to | |
1304 | provide a customized mode line for buffers in Text mode, displaying the | |
1305 | default directory in addition to the standard components of the | |
1306 | mode line. (This may cause the mode line to run out of space if you | |
1307 | have very long file names or display the time and load.) | |
1308 | ||
1309 | @example | |
1310 | @group | |
1311 | (add-hook 'text-mode-hook | |
1312 | (function (lambda () | |
1313 | (setq mode-line-format | |
b22f3a19 | 1314 | @end group |
a44af9f2 RS |
1315 | '(mode-line-modified |
1316 | "Emacs: %14b" | |
1317 | " " | |
a44af9f2 RS |
1318 | default-directory |
1319 | " " | |
1320 | global-mode-string | |
1321 | "%[(" | |
1322 | mode-name | |
1323 | minor-mode-alist | |
1324 | @group | |
1325 | "%n" | |
1326 | mode-line-process | |
1327 | ") %]---" | |
1328 | (-3 . "%p") | |
1329 | "-%-"))))) | |
1330 | @end group | |
1331 | @end example | |
1332 | ||
1333 | At the appropriate time, Emacs uses the @code{run-hooks} function to | |
1334 | run particular hooks. This function calls the hook functions you have | |
1335 | added with @code{add-hooks}. | |
1336 | ||
1337 | @defun run-hooks &rest hookvar | |
1338 | This function takes one or more hook variable names as arguments, and | |
1339 | runs each hook in turn. Each @var{hookvar} argument should be a symbol | |
1340 | that is a hook variable. These arguments are processed in the order | |
1341 | specified. | |
1342 | ||
1343 | If a hook variable has a non-@code{nil} value, that value may be a | |
1344 | function or a list of functions. If the value is a function (either a | |
1345 | lambda expression or a symbol with a function definition), it is | |
1346 | called. If it is a list, the elements are called, in order. | |
1347 | The hook functions are called with no arguments. | |
1348 | ||
1349 | For example, here's how @code{emacs-lisp-hooks} runs its mode hook: | |
1350 | ||
1351 | @example | |
1352 | (run-hooks 'emacs-lisp-mode-hook) | |
1353 | @end example | |
1354 | @end defun | |
1355 | ||
1356 | @defun add-hook hook function &optional append | |
1357 | This function is the handy way to add function @var{function} to hook | |
de9f0bd9 RS |
1358 | variable @var{hook}. The argument @var{function} may be any valid Lisp |
1359 | function with the proper number of arguments. For example, | |
a44af9f2 RS |
1360 | |
1361 | @example | |
1362 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
1363 | @end example | |
1364 | ||
1365 | @noindent | |
1366 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
1367 | ||
de9f0bd9 RS |
1368 | You can use @code{add-hook} for abnormal hooks as well as for normal |
1369 | hooks. | |
1370 | ||
a44af9f2 RS |
1371 | It is best to design your hook functions so that the order in which they |
1372 | are executed does not matter. Any dependence on the order is ``asking | |
1373 | for trouble.'' However, the order is predictable: normally, | |
1374 | @var{function} goes at the front of the hook list, so it will be | |
1375 | executed first (barring another @code{add-hook} call). | |
1376 | ||
1377 | If the optional argument @var{append} is non-@code{nil}, the new hook | |
1378 | function goes at the end of the hook list and will be executed last. | |
1379 | @end defun | |
1380 | ||
1381 | @defun remove-hook hook function | |
1382 | This function removes @var{function} from the hook variable @var{hook}. | |
1383 | @end defun | |
c44d2ced | 1384 | |
a8a642a4 | 1385 | @ignore @c Should no longer be necessary |
c44d2ced RS |
1386 | If you make a hook variable buffer-local, copy its value before you use |
1387 | @code{add-hook} or @code{remove-hook} to change it. For example, | |
1388 | ||
1389 | @example | |
1390 | (defun my-major-mode () | |
1391 | @dots{} | |
1392 | (make-local-variable 'foo-hook) | |
1393 | (if (boundp 'foo-hook) | |
1394 | (setq foo-hook (copy-sequence foo-hook))) | |
1395 | (add-hook 'foo-hook 'my-foo-function)" | |
1396 | @dots{} | |
1397 | ) | |
1398 | @end example | |
1399 | ||
1400 | Otherwise you may accidentally alter the list structure that forms part | |
1401 | of the global value of the hook variable. | |
a8a642a4 | 1402 | @end ignore |