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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
ba318903 | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software |
ab422c4d | 4 | @c Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 6 | @node Modes |
b8d4c8d0 GM |
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 | |
3fd50d5c CY |
22 | * Hooks:: How to use hooks; how to write code that provides hooks. |
23 | * Major Modes:: Defining major modes. | |
24 | * Minor Modes:: Defining minor modes. | |
25 | * Mode Line Format:: Customizing the text that appears in the mode line. | |
26 | * Imenu:: Providing a menu of definitions made in a buffer. | |
27 | * Font Lock Mode:: How modes can highlight text according to syntax. | |
28 | * Auto-Indentation:: How to teach Emacs to indent for a major mode. | |
29 | * Desktop Save Mode:: How modes can have buffer state saved between | |
30 | Emacs sessions. | |
b8d4c8d0 GM |
31 | @end menu |
32 | ||
33 | @node Hooks | |
34 | @section Hooks | |
35 | @cindex hooks | |
36 | ||
37 | A @dfn{hook} is a variable where you can store a function or functions | |
38 | to be called on a particular occasion by an existing program. Emacs | |
39 | provides hooks for the sake of customization. Most often, hooks are set | |
40 | up in the init file (@pxref{Init File}), but Lisp programs can set them also. | |
2064cc6a | 41 | @xref{Standard Hooks}, for a list of some standard hook variables. |
b8d4c8d0 GM |
42 | |
43 | @cindex normal hook | |
44 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
45 | contain lists of functions to be called with no arguments. By | |
46 | convention, whenever the hook name ends in @samp{-hook}, that tells | |
47 | you it is normal. We try to make all hooks normal, as much as | |
48 | possible, so that you can use them in a uniform way. | |
49 | ||
3fd50d5c | 50 | Every major mode command is supposed to run a normal hook called the |
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51 | @dfn{mode hook} as one of the last steps of initialization. This makes |
52 | it easy for a user to customize the behavior of the mode, by overriding | |
53 | the buffer-local variable assignments already made by the mode. Most | |
54 | minor mode functions also run a mode hook at the end. But hooks are | |
55 | used in other contexts too. For example, the hook @code{suspend-hook} | |
56 | runs just before Emacs suspends itself (@pxref{Suspending Emacs}). | |
57 | ||
58 | The recommended way to add a hook function to a hook is by calling | |
59 | @code{add-hook} (@pxref{Setting Hooks}). The hook functions may be any | |
60 | of the valid kinds of functions that @code{funcall} accepts (@pxref{What | |
b8d4c8d0 GM |
61 | Is a Function}). Most normal hook variables are initially void; |
62 | @code{add-hook} knows how to deal with this. You can add hooks either | |
63 | globally or buffer-locally with @code{add-hook}. | |
64 | ||
65 | @cindex abnormal hook | |
66 | If the hook variable's name does not end with @samp{-hook}, that | |
67 | indicates it is probably an @dfn{abnormal hook}. That means the hook | |
68 | functions are called with arguments, or their return values are used | |
69 | in some way. The hook's documentation says how the functions are | |
70 | called. You can use @code{add-hook} to add a function to an abnormal | |
71 | hook, but you must write the function to follow the hook's calling | |
72 | convention. | |
73 | ||
d1069532 SM |
74 | By convention, abnormal hook names end in @samp{-functions}. If the |
75 | variable's name ends in @samp{-function}, then its value is just a single | |
76 | function, not a list of functions. | |
b8d4c8d0 | 77 | |
fd9a7a58 | 78 | @menu |
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79 | * Running Hooks:: How to run a hook. |
80 | * Setting Hooks:: How to put functions on a hook, or remove them. | |
fd9a7a58 | 81 | @end menu |
b8d4c8d0 | 82 | |
fd9a7a58 RS |
83 | @node Running Hooks |
84 | @subsection Running Hooks | |
b8d4c8d0 | 85 | |
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86 | In this section, we document the @code{run-hooks} function, which is |
87 | used to run a normal hook. We also document the functions for running | |
88 | various kinds of abnormal hooks. | |
b8d4c8d0 GM |
89 | |
90 | @defun run-hooks &rest hookvars | |
91 | This function takes one or more normal hook variable names as | |
92 | arguments, and runs each hook in turn. Each argument should be a | |
93 | symbol that is a normal hook variable. These arguments are processed | |
94 | in the order specified. | |
95 | ||
96 | If a hook variable has a non-@code{nil} value, that value should be a | |
97 | list of functions. @code{run-hooks} calls all the functions, one by | |
98 | one, with no arguments. | |
99 | ||
100 | The hook variable's value can also be a single function---either a | |
101 | lambda expression or a symbol with a function definition---which | |
102 | @code{run-hooks} calls. But this usage is obsolete. | |
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103 | |
104 | If the hook variable is buffer-local, the buffer-local variable will | |
105 | be used instead of the global variable. However, if the buffer-local | |
106 | variable contains the element @code{t}, the global hook variable will | |
107 | be run as well. | |
b8d4c8d0 GM |
108 | @end defun |
109 | ||
110 | @defun run-hook-with-args hook &rest args | |
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111 | This function runs an abnormal hook by calling all the hook functions in |
112 | @var{hook}, passing each one the arguments @var{args}. | |
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113 | @end defun |
114 | ||
115 | @defun run-hook-with-args-until-failure hook &rest args | |
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116 | This function runs an abnormal hook by calling each hook function in |
117 | turn, stopping if one of them ``fails'' by returning @code{nil}. Each | |
118 | hook function is passed the arguments @var{args}. If this function | |
119 | stops because one of the hook functions fails, it returns @code{nil}; | |
120 | otherwise it returns a non-@code{nil} value. | |
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121 | @end defun |
122 | ||
123 | @defun run-hook-with-args-until-success hook &rest args | |
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124 | This function runs an abnormal hook by calling each hook function, |
125 | stopping if one of them ``succeeds'' by returning a non-@code{nil} | |
126 | value. Each hook function is passed the arguments @var{args}. If this | |
127 | function stops because one of the hook functions returns a | |
128 | non-@code{nil} value, it returns that value; otherwise it returns | |
129 | @code{nil}. | |
b8d4c8d0 GM |
130 | @end defun |
131 | ||
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132 | @defmac with-wrapper-hook hook args &rest body |
133 | This macro runs the abnormal hook @code{hook} as a series of nested | |
134 | ``wrapper functions'' around the @var{body} forms. The effect is | |
135 | similar to nested @code{around} advices (@pxref{Around-Advice}). | |
136 | ||
c7291ad9 | 137 | Each hook function should accept an argument list consisting of a function |
60754666 | 138 | @var{fun}, followed by the additional arguments listed in @var{args}. |
c7291ad9 GM |
139 | The first hook function is passed a function @var{fun} that, if it is |
140 | called with arguments @var{args}, performs @var{body} (i.e., the default | |
141 | operation). The @var{fun} passed to each successive hook function is | |
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142 | constructed from all the preceding hook functions (and @var{body}); if |
143 | this @var{fun} is called with arguments @var{args}, it does what the | |
144 | @code{with-wrapper-hook} call would if the preceding hook functions were | |
145 | the only ones in @var{hook}. | |
146 | ||
c7291ad9 GM |
147 | Each hook function may call its @var{fun} argument as many times as it |
148 | wishes, including never. In that case, such a hook function acts to | |
149 | replace the default definition altogether, and any preceding hook | |
150 | functions. Of course, a subsequent hook function may do the same thing. | |
151 | ||
152 | Each hook function definition is used to construct the @var{fun} passed | |
153 | to the next hook function in @var{hook}, if any. The last or | |
154 | ``outermost'' @var{fun} is called once to produce the overall effect. | |
155 | ||
156 | When might you want to use a wrapper hook? The function | |
157 | @code{filter-buffer-substring} illustrates a common case. There is a | |
158 | basic functionality, performed by @var{body}---in this case, to extract | |
159 | a buffer-substring. Then any number of hook functions can act in | |
160 | sequence to modify that string, before returning the final result. | |
161 | A wrapper-hook also allows for a hook function to completely replace the | |
162 | default definition (by not calling @var{fun}). | |
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163 | @end defmac |
164 | ||
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165 | @defun run-hook-wrapped hook wrap-function &rest args |
166 | This function is similar to @code{run-hook-with-args-until-success}. | |
167 | Like that function, it runs the functions on the abnormal hook | |
168 | @code{hook}, stopping at the first one that returns non-@code{nil}. | |
169 | Instead of calling the hook functions directly, though, it actually | |
170 | calls @code{wrap-function} with arguments @code{fun} and @code{args}. | |
171 | @end defun | |
172 | ||
fd9a7a58 RS |
173 | @node Setting Hooks |
174 | @subsection Setting Hooks | |
175 | ||
176 | Here's an example that uses a mode hook to turn on Auto Fill mode when | |
177 | in Lisp Interaction mode: | |
178 | ||
179 | @example | |
60236b0d | 180 | (add-hook 'lisp-interaction-mode-hook 'auto-fill-mode) |
fd9a7a58 RS |
181 | @end example |
182 | ||
b8d4c8d0 GM |
183 | @defun add-hook hook function &optional append local |
184 | This function is the handy way to add function @var{function} to hook | |
185 | variable @var{hook}. You can use it for abnormal hooks as well as for | |
186 | normal hooks. @var{function} can be any Lisp function that can accept | |
187 | the proper number of arguments for @var{hook}. For example, | |
188 | ||
189 | @example | |
190 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
191 | @end example | |
192 | ||
193 | @noindent | |
194 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
195 | ||
196 | If @var{function} is already present in @var{hook} (comparing using | |
197 | @code{equal}), then @code{add-hook} does not add it a second time. | |
198 | ||
fd9a7a58 RS |
199 | If @var{function} has a non-@code{nil} property |
200 | @code{permanent-local-hook}, then @code{kill-all-local-variables} (or | |
201 | changing major modes) won't delete it from the hook variable's local | |
202 | value. | |
203 | ||
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204 | For a normal hook, hook functions should be designed so that the order |
205 | in which they are executed does not matter. Any dependence on the order | |
206 | is asking for trouble. However, the order is predictable: normally, | |
207 | @var{function} goes at the front of the hook list, so it is executed | |
208 | first (barring another @code{add-hook} call). If the optional argument | |
209 | @var{append} is non-@code{nil}, the new hook function goes at the end of | |
210 | the hook list and is executed last. | |
b8d4c8d0 GM |
211 | |
212 | @code{add-hook} can handle the cases where @var{hook} is void or its | |
213 | value is a single function; it sets or changes the value to a list of | |
214 | functions. | |
215 | ||
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216 | If @var{local} is non-@code{nil}, that says to add @var{function} to the |
217 | buffer-local hook list instead of to the global hook list. This makes | |
218 | the hook buffer-local and adds @code{t} to the buffer-local value. The | |
219 | latter acts as a flag to run the hook functions in the default value as | |
220 | well as in the local value. | |
b8d4c8d0 GM |
221 | @end defun |
222 | ||
223 | @defun remove-hook hook function &optional local | |
224 | This function removes @var{function} from the hook variable | |
225 | @var{hook}. It compares @var{function} with elements of @var{hook} | |
226 | using @code{equal}, so it works for both symbols and lambda | |
227 | expressions. | |
228 | ||
229 | If @var{local} is non-@code{nil}, that says to remove @var{function} | |
230 | from the buffer-local hook list instead of from the global hook list. | |
231 | @end defun | |
232 | ||
233 | @node Major Modes | |
234 | @section Major Modes | |
235 | @cindex major mode | |
236 | ||
3fd50d5c | 237 | @cindex major mode command |
b8d4c8d0 | 238 | Major modes specialize Emacs for editing particular kinds of text. |
3fd50d5c CY |
239 | Each buffer has one major mode at a time. Every major mode is |
240 | associated with a @dfn{major mode command}, whose name should end in | |
241 | @samp{-mode}. This command takes care of switching to that mode in the | |
242 | current buffer, by setting various buffer-local variables such as a | |
243 | local keymap. @xref{Major Mode Conventions}. | |
244 | ||
245 | The least specialized major mode is called @dfn{Fundamental mode}, | |
246 | which has no mode-specific definitions or variable settings. | |
247 | ||
248 | @deffn Command fundamental-mode | |
249 | This is the major mode command for Fundamental mode. Unlike other mode | |
250 | commands, it does @emph{not} run any mode hooks (@pxref{Major Mode | |
251 | Conventions}), since you are not supposed to customize this mode. | |
252 | @end deffn | |
253 | ||
254 | The easiest way to write a major mode is to use the macro | |
255 | @code{define-derived-mode}, which sets up the new mode as a variant of | |
256 | an existing major mode. @xref{Derived Modes}. We recommend using | |
257 | @code{define-derived-mode} even if the new mode is not an obvious | |
258 | derivative of another mode, as it automatically enforces many coding | |
259 | conventions for you. @xref{Basic Major Modes}, for common modes to | |
260 | derive from. | |
261 | ||
262 | The standard GNU Emacs Lisp directory tree contains the code for | |
263 | several major modes, in files such as @file{text-mode.el}, | |
264 | @file{texinfo.el}, @file{lisp-mode.el}, and @file{rmail.el}. You can | |
265 | study these libraries to see how modes are written. | |
266 | ||
267 | @defopt major-mode | |
35137ed3 CY |
268 | The buffer-local value of this variable holds the symbol for the current |
269 | major mode. Its default value holds the default major mode for new | |
270 | buffers. The standard default value is @code{fundamental-mode}. | |
3fd50d5c CY |
271 | |
272 | If the default value is @code{nil}, then whenever Emacs creates a new | |
273 | buffer via a command such as @kbd{C-x b} (@code{switch-to-buffer}), the | |
274 | new buffer is put in the major mode of the previously current buffer. | |
275 | As an exception, if the major mode of the previous buffer has a | |
276 | @code{mode-class} symbol property with value @code{special}, the new | |
277 | buffer is put in Fundamental mode (@pxref{Major Mode Conventions}). | |
278 | @end defopt | |
b8d4c8d0 GM |
279 | |
280 | @menu | |
3fd50d5c CY |
281 | * Major Mode Conventions:: Coding conventions for keymaps, etc. |
282 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
283 | * Mode Help:: Finding out how to use a mode. | |
284 | * Derived Modes:: Defining a new major mode based on another major | |
b8d4c8d0 | 285 | mode. |
3fd50d5c | 286 | * Basic Major Modes:: Modes that other modes are often derived from. |
cf988578 | 287 | * Mode Hooks:: Hooks run at the end of major mode functions. |
82233bea | 288 | * Tabulated List Mode:: Parent mode for buffers containing tabulated data. |
3fd50d5c | 289 | * Generic Modes:: Defining a simple major mode that supports |
b8d4c8d0 | 290 | comment syntax and Font Lock mode. |
3fd50d5c | 291 | * Example Major Modes:: Text mode and Lisp modes. |
b8d4c8d0 GM |
292 | @end menu |
293 | ||
b8d4c8d0 GM |
294 | @node Major Mode Conventions |
295 | @subsection Major Mode Conventions | |
296 | @cindex major mode conventions | |
297 | @cindex conventions for writing major modes | |
298 | ||
3fd50d5c CY |
299 | The code for every major mode should follow various coding |
300 | conventions, including conventions for local keymap and syntax table | |
301 | initialization, function and variable names, and hooks. | |
302 | ||
303 | If you use the @code{define-derived-mode} macro, it will take care of | |
304 | many of these conventions automatically. @xref{Derived Modes}. Note | |
60236b0d CY |
305 | also that Fundamental mode is an exception to many of these conventions, |
306 | because it represents the default state of Emacs. | |
b8d4c8d0 | 307 | |
3fd50d5c CY |
308 | The following list of conventions is only partial. Each major mode |
309 | should aim for consistency in general with other Emacs major modes, as | |
310 | this makes Emacs as a whole more coherent. It is impossible to list | |
b8d4c8d0 GM |
311 | here all the possible points where this issue might come up; if the |
312 | Emacs developers point out an area where your major mode deviates from | |
313 | the usual conventions, please make it compatible. | |
314 | ||
315 | @itemize @bullet | |
316 | @item | |
3fd50d5c CY |
317 | Define a major mode command whose name ends in @samp{-mode}. When |
318 | called with no arguments, this command should switch to the new mode in | |
319 | the current buffer by setting up the keymap, syntax table, and | |
320 | buffer-local variables in an existing buffer. It should not change the | |
321 | buffer's contents. | |
b8d4c8d0 GM |
322 | |
323 | @item | |
3fd50d5c CY |
324 | Write a documentation string for this command that describes the special |
325 | commands available in this mode. @xref{Mode Help}. | |
b8d4c8d0 GM |
326 | |
327 | The documentation string may include the special documentation | |
328 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
3fd50d5c | 329 | @samp{\<@var{keymap}>}, which allow the help display to adapt |
b8d4c8d0 GM |
330 | automatically to the user's own key bindings. @xref{Keys in |
331 | Documentation}. | |
332 | ||
333 | @item | |
334 | The major mode command should start by calling | |
335 | @code{kill-all-local-variables}. This runs the normal hook | |
336 | @code{change-major-mode-hook}, then gets rid of the buffer-local | |
337 | variables of the major mode previously in effect. @xref{Creating | |
338 | Buffer-Local}. | |
339 | ||
340 | @item | |
341 | The major mode command should set the variable @code{major-mode} to the | |
342 | major mode command symbol. This is how @code{describe-mode} discovers | |
343 | which documentation to print. | |
344 | ||
345 | @item | |
346 | The major mode command should set the variable @code{mode-name} to the | |
9cf52b11 EZ |
347 | ``pretty'' name of the mode, usually a string (but see @ref{Mode Line |
348 | Data}, for other possible forms). The name of the mode appears | |
349 | in the mode line. | |
b8d4c8d0 GM |
350 | |
351 | @item | |
352 | @cindex functions in modes | |
353 | Since all global names are in the same name space, all the global | |
354 | variables, constants, and functions that are part of the mode should | |
355 | have names that start with the major mode name (or with an abbreviation | |
356 | of it if the name is long). @xref{Coding Conventions}. | |
357 | ||
358 | @item | |
359 | In a major mode for editing some kind of structured text, such as a | |
360 | programming language, indentation of text according to structure is | |
361 | probably useful. So the mode should set @code{indent-line-function} | |
362 | to a suitable function, and probably customize other variables | |
5dcb4c4e | 363 | for indentation. @xref{Auto-Indentation}. |
b8d4c8d0 GM |
364 | |
365 | @item | |
366 | @cindex keymaps in modes | |
367 | The major mode should usually have its own keymap, which is used as the | |
368 | local keymap in all buffers in that mode. The major mode command should | |
369 | call @code{use-local-map} to install this local map. @xref{Active | |
370 | Keymaps}, for more information. | |
371 | ||
372 | This keymap should be stored permanently in a global variable named | |
373 | @code{@var{modename}-mode-map}. Normally the library that defines the | |
374 | mode sets this variable. | |
375 | ||
376 | @xref{Tips for Defining}, for advice about how to write the code to set | |
377 | up the mode's keymap variable. | |
378 | ||
379 | @item | |
380 | The key sequences bound in a major mode keymap should usually start with | |
381 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, | |
382 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation | |
383 | characters are reserved for minor modes, and ordinary letters are | |
384 | reserved for users. | |
385 | ||
386 | A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and | |
387 | @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally | |
16152b76 | 388 | be some kind of ``moving forward and backward'', but this does not |
b8d4c8d0 GM |
389 | necessarily mean cursor motion. |
390 | ||
391 | It is legitimate for a major mode to rebind a standard key sequence if | |
392 | it provides a command that does ``the same job'' in a way better | |
393 | suited to the text this mode is used for. For example, a major mode | |
394 | for editing a programming language might redefine @kbd{C-M-a} to | |
395 | ``move to the beginning of a function'' in a way that works better for | |
396 | that language. | |
397 | ||
398 | It is also legitimate for a major mode to rebind a standard key | |
399 | sequence whose standard meaning is rarely useful in that mode. For | |
400 | instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is | |
401 | rarely of any use in the minibuffer. Major modes such as Dired or | |
402 | Rmail that do not allow self-insertion of text can reasonably redefine | |
403 | letters and other printing characters as special commands. | |
404 | ||
405 | @item | |
867d4bb3 | 406 | Major modes for editing text should not define @key{RET} to do |
b8d4c8d0 GM |
407 | anything other than insert a newline. However, it is ok for |
408 | specialized modes for text that users don't directly edit, such as | |
409 | Dired and Info modes, to redefine @key{RET} to do something entirely | |
410 | different. | |
411 | ||
412 | @item | |
413 | Major modes should not alter options that are primarily a matter of user | |
414 | preference, such as whether Auto-Fill mode is enabled. Leave this to | |
415 | each user to decide. However, a major mode should customize other | |
416 | variables so that Auto-Fill mode will work usefully @emph{if} the user | |
417 | decides to use it. | |
418 | ||
419 | @item | |
420 | @cindex syntax tables in modes | |
421 | The mode may have its own syntax table or may share one with other | |
422 | related modes. If it has its own syntax table, it should store this in | |
423 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax | |
424 | Tables}. | |
425 | ||
426 | @item | |
427 | If the mode handles a language that has a syntax for comments, it should | |
428 | set the variables that define the comment syntax. @xref{Options for | |
429 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. | |
430 | ||
431 | @item | |
432 | @cindex abbrev tables in modes | |
433 | The mode may have its own abbrev table or may share one with other | |
434 | related modes. If it has its own abbrev table, it should store this | |
435 | in a variable named @code{@var{modename}-mode-abbrev-table}. If the | |
436 | major mode command defines any abbrevs itself, it should pass @code{t} | |
437 | for the @var{system-flag} argument to @code{define-abbrev}. | |
438 | @xref{Defining Abbrevs}. | |
439 | ||
440 | @item | |
441 | The mode should specify how to do highlighting for Font Lock mode, by | |
442 | setting up a buffer-local value for the variable | |
443 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). | |
444 | ||
e0dd6837 CY |
445 | @item |
446 | Each face that the mode defines should, if possible, inherit from an | |
35137ed3 | 447 | existing Emacs face. @xref{Basic Faces}, and @ref{Faces for Font Lock}. |
e0dd6837 | 448 | |
b8d4c8d0 GM |
449 | @item |
450 | The mode should specify how Imenu should find the definitions or | |
451 | sections of a buffer, by setting up a buffer-local value for the | |
452 | variable @code{imenu-generic-expression}, for the two variables | |
453 | @code{imenu-prev-index-position-function} and | |
454 | @code{imenu-extract-index-name-function}, or for the variable | |
455 | @code{imenu-create-index-function} (@pxref{Imenu}). | |
456 | ||
457 | @item | |
458 | The mode can specify a local value for | |
459 | @code{eldoc-documentation-function} to tell ElDoc mode how to handle | |
460 | this mode. | |
461 | ||
769741e3 | 462 | @item |
60236b0d CY |
463 | The mode can specify how to complete various keywords by adding one or |
464 | more buffer-local entries to the special hook | |
465 | @code{completion-at-point-functions}. @xref{Completion in Buffers}. | |
769741e3 | 466 | |
b8d4c8d0 GM |
467 | @item |
468 | @cindex buffer-local variables in modes | |
469 | To make a buffer-local binding for an Emacs customization variable, use | |
470 | @code{make-local-variable} in the major mode command, not | |
471 | @code{make-variable-buffer-local}. The latter function would make the | |
472 | variable local to every buffer in which it is subsequently set, which | |
473 | would affect buffers that do not use this mode. It is undesirable for a | |
474 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
475 | ||
476 | With rare exceptions, the only reasonable way to use | |
477 | @code{make-variable-buffer-local} in a Lisp package is for a variable | |
478 | which is used only within that package. Using it on a variable used by | |
479 | other packages would interfere with them. | |
480 | ||
481 | @item | |
482 | @cindex mode hook | |
483 | @cindex major mode hook | |
484 | Each major mode should have a normal @dfn{mode hook} named | |
485 | @code{@var{modename}-mode-hook}. The very last thing the major mode command | |
12f381b7 GM |
486 | should do is to call @code{run-mode-hooks}. This runs the normal |
487 | hook @code{change-major-mode-after-body-hook}, the mode hook, | |
488 | and then the normal hook @code{after-change-major-mode-hook}. | |
b8d4c8d0 GM |
489 | @xref{Mode Hooks}. |
490 | ||
491 | @item | |
492 | The major mode command may start by calling some other major mode | |
493 | command (called the @dfn{parent mode}) and then alter some of its | |
494 | settings. A mode that does this is called a @dfn{derived mode}. The | |
41633740 CY |
495 | recommended way to define one is to use the @code{define-derived-mode} |
496 | macro, but this is not required. Such a mode should call the parent | |
497 | mode command inside a @code{delay-mode-hooks} form. (Using | |
b8d4c8d0 GM |
498 | @code{define-derived-mode} does this automatically.) @xref{Derived |
499 | Modes}, and @ref{Mode Hooks}. | |
500 | ||
501 | @item | |
502 | If something special should be done if the user switches a buffer from | |
503 | this mode to any other major mode, this mode can set up a buffer-local | |
504 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). | |
505 | ||
506 | @item | |
9adfcd0b EZ |
507 | If this mode is appropriate only for specially-prepared text produced by |
508 | the mode itself (rather than by the user typing at the keyboard or by an | |
509 | external file), then the major mode command symbol should have a | |
510 | property named @code{mode-class} with value @code{special}, put on as | |
511 | follows: | |
b8d4c8d0 GM |
512 | |
513 | @kindex mode-class @r{(property)} | |
9adfcd0b | 514 | @cindex @code{special} modes |
b8d4c8d0 GM |
515 | @example |
516 | (put 'funny-mode 'mode-class 'special) | |
517 | @end example | |
518 | ||
519 | @noindent | |
9adfcd0b EZ |
520 | This tells Emacs that new buffers created while the current buffer is in |
521 | Funny mode should not be put in Funny mode, even though the default | |
522 | value of @code{major-mode} is @code{nil}. By default, the value of | |
523 | @code{nil} for @code{major-mode} means to use the current buffer's major | |
524 | mode when creating new buffers (@pxref{Auto Major Mode}), but with such | |
525 | @code{special} modes, Fundamental mode is used instead. Modes such as | |
526 | Dired, Rmail, and Buffer List use this feature. | |
b8d4c8d0 | 527 | |
da986230 GM |
528 | The function @code{view-buffer} does not enable View mode in buffers |
529 | whose mode-class is special, because such modes usually provide their | |
530 | own View-like bindings. | |
531 | ||
41633740 | 532 | The @code{define-derived-mode} macro automatically marks the derived |
3fd50d5c CY |
533 | mode as special if the parent mode is special. Special mode is a |
534 | convenient parent for such modes to inherit from; @xref{Basic Major | |
535 | Modes}. | |
41633740 | 536 | |
b8d4c8d0 GM |
537 | @item |
538 | If you want to make the new mode the default for files with certain | |
539 | recognizable names, add an element to @code{auto-mode-alist} to select | |
540 | the mode for those file names (@pxref{Auto Major Mode}). If you | |
541 | define the mode command to autoload, you should add this element in | |
542 | the same file that calls @code{autoload}. If you use an autoload | |
543 | cookie for the mode command, you can also use an autoload cookie for | |
544 | the form that adds the element (@pxref{autoload cookie}). If you do | |
545 | not autoload the mode command, it is sufficient to add the element in | |
546 | the file that contains the mode definition. | |
547 | ||
b8d4c8d0 GM |
548 | @item |
549 | @cindex mode loading | |
550 | The top-level forms in the file defining the mode should be written so | |
551 | that they may be evaluated more than once without adverse consequences. | |
f700caa3 CY |
552 | For instance, use @code{defvar} or @code{defcustom} to set mode-related |
553 | variables, so that they are not reinitialized if they already have a | |
554 | value (@pxref{Defining Variables}). | |
555 | ||
b8d4c8d0 GM |
556 | @end itemize |
557 | ||
558 | @node Auto Major Mode | |
559 | @subsection How Emacs Chooses a Major Mode | |
560 | @cindex major mode, automatic selection | |
561 | ||
60236b0d CY |
562 | When Emacs visits a file, it automatically selects a major mode for |
563 | the buffer based on information in the file name or in the file itself. | |
564 | It also processes local variables specified in the file text. | |
b8d4c8d0 | 565 | |
b8d4c8d0 GM |
566 | @deffn Command normal-mode &optional find-file |
567 | This function establishes the proper major mode and buffer-local variable | |
568 | bindings for the current buffer. First it calls @code{set-auto-mode} | |
569 | (see below), then it runs @code{hack-local-variables} to parse, and | |
570 | bind or evaluate as appropriate, the file's local variables | |
571 | (@pxref{File Local Variables}). | |
572 | ||
573 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, | |
574 | @code{normal-mode} assumes that the @code{find-file} function is calling | |
575 | it. In this case, it may process local variables in the @samp{-*-} | |
576 | line or at the end of the file. The variable | |
577 | @code{enable-local-variables} controls whether to do so. @xref{File | |
578 | Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, | |
579 | for the syntax of the local variables section of a file. | |
580 | ||
581 | If you run @code{normal-mode} interactively, the argument | |
582 | @var{find-file} is normally @code{nil}. In this case, | |
583 | @code{normal-mode} unconditionally processes any file local variables. | |
584 | ||
95459571 | 585 | The function calls @code{set-auto-mode} to choose a major mode. If this |
e145f188 GM |
586 | does not specify a mode, the buffer stays in the major mode determined |
587 | by the default value of @code{major-mode} (see below). | |
b8d4c8d0 GM |
588 | |
589 | @cindex file mode specification error | |
590 | @code{normal-mode} uses @code{condition-case} around the call to the | |
3fd50d5c CY |
591 | major mode command, so errors are caught and reported as a @samp{File |
592 | mode specification error}, followed by the original error message. | |
b8d4c8d0 GM |
593 | @end deffn |
594 | ||
595 | @defun set-auto-mode &optional keep-mode-if-same | |
596 | @cindex visited file mode | |
597 | This function selects the major mode that is appropriate for the | |
3fd50d5c CY |
598 | current buffer. It bases its decision (in order of precedence) on the |
599 | @w{@samp{-*-}} line, on any @samp{mode:} local variable near the end of | |
600 | a file, on the @w{@samp{#!}} line (using @code{interpreter-mode-alist}), | |
601 | on the text at the beginning of the buffer (using | |
602 | @code{magic-mode-alist}), and finally on the visited file name (using | |
603 | @code{auto-mode-alist}). @xref{Choosing Modes, , How Major Modes are | |
604 | Chosen, emacs, The GNU Emacs Manual}. If @code{enable-local-variables} | |
605 | is @code{nil}, @code{set-auto-mode} does not check the @w{@samp{-*-}} | |
606 | line, or near the end of the file, for any mode tag. | |
b8d4c8d0 | 607 | |
61086eb6 GM |
608 | @vindex inhibit-local-variables-regexps |
609 | There are some file types where it is not appropriate to scan the file | |
610 | contents for a mode specifier. For example, a tar archive may happen to | |
611 | contain, near the end of the file, a member file that has a local | |
612 | variables section specifying a mode for that particular file. This | |
613 | should not be applied to the containing tar file. Similarly, a tiff | |
614 | image file might just happen to contain a first line that seems to | |
615 | match the @w{@samp{-*-}} pattern. For these reasons, both these file | |
07b9c0be | 616 | extensions are members of the list @code{inhibit-local-variables-regexps}. |
61086eb6 GM |
617 | Add patterns to this list to prevent Emacs searching them for local |
618 | variables of any kind (not just mode specifiers). | |
619 | ||
b8d4c8d0 GM |
620 | If @var{keep-mode-if-same} is non-@code{nil}, this function does not |
621 | call the mode command if the buffer is already in the proper major | |
622 | mode. For instance, @code{set-visited-file-name} sets this to | |
623 | @code{t} to avoid killing buffer local variables that the user may | |
624 | have set. | |
625 | @end defun | |
626 | ||
b8d4c8d0 | 627 | @defun set-buffer-major-mode buffer |
4e3b4528 SM |
628 | This function sets the major mode of @var{buffer} to the default value of |
629 | @code{major-mode}; if that is @code{nil}, it uses the | |
b8d4c8d0 | 630 | current buffer's major mode (if that is suitable). As an exception, |
2bb0eca1 | 631 | if @var{buffer}'s name is @file{*scratch*}, it sets the mode to |
b8d4c8d0 GM |
632 | @code{initial-major-mode}. |
633 | ||
634 | The low-level primitives for creating buffers do not use this function, | |
635 | but medium-level commands such as @code{switch-to-buffer} and | |
636 | @code{find-file-noselect} use it whenever they create buffers. | |
637 | @end defun | |
638 | ||
639 | @defopt initial-major-mode | |
2bb0eca1 | 640 | @cindex @file{*scratch*} |
b8d4c8d0 | 641 | The value of this variable determines the major mode of the initial |
2bb0eca1 | 642 | @file{*scratch*} buffer. The value should be a symbol that is a major |
b8d4c8d0 GM |
643 | mode command. The default value is @code{lisp-interaction-mode}. |
644 | @end defopt | |
645 | ||
646 | @defvar interpreter-mode-alist | |
647 | This variable specifies major modes to use for scripts that specify a | |
648 | command interpreter in a @samp{#!} line. Its value is an alist with | |
4364185f CY |
649 | elements of the form @code{(@var{regexp} . @var{mode})}; this says to |
650 | use mode @var{mode} if the file specifies an interpreter which matches | |
651 | @code{\\`@var{regexp}\\'}. For example, one of the default elements | |
652 | is @code{("python[0-9.]*" . python-mode)}. | |
b8d4c8d0 GM |
653 | @end defvar |
654 | ||
655 | @defvar magic-mode-alist | |
656 | This variable's value is an alist with elements of the form | |
657 | @code{(@var{regexp} . @var{function})}, where @var{regexp} is a | |
658 | regular expression and @var{function} is a function or @code{nil}. | |
659 | After visiting a file, @code{set-auto-mode} calls @var{function} if | |
660 | the text at the beginning of the buffer matches @var{regexp} and | |
661 | @var{function} is non-@code{nil}; if @var{function} is @code{nil}, | |
662 | @code{auto-mode-alist} gets to decide the mode. | |
663 | @end defvar | |
664 | ||
665 | @defvar magic-fallback-mode-alist | |
666 | This works like @code{magic-mode-alist}, except that it is handled | |
667 | only if @code{auto-mode-alist} does not specify a mode for this file. | |
668 | @end defvar | |
669 | ||
670 | @defvar auto-mode-alist | |
671 | This variable contains an association list of file name patterns | |
672 | (regular expressions) and corresponding major mode commands. Usually, | |
673 | the file name patterns test for suffixes, such as @samp{.el} and | |
674 | @samp{.c}, but this need not be the case. An ordinary element of the | |
675 | alist looks like @code{(@var{regexp} . @var{mode-function})}. | |
676 | ||
677 | For example, | |
678 | ||
679 | @smallexample | |
680 | @group | |
681 | (("\\`/tmp/fol/" . text-mode) | |
682 | ("\\.texinfo\\'" . texinfo-mode) | |
683 | ("\\.texi\\'" . texinfo-mode) | |
684 | @end group | |
685 | @group | |
686 | ("\\.el\\'" . emacs-lisp-mode) | |
687 | ("\\.c\\'" . c-mode) | |
688 | ("\\.h\\'" . c-mode) | |
689 | @dots{}) | |
690 | @end group | |
691 | @end smallexample | |
692 | ||
693 | When you visit a file whose expanded file name (@pxref{File Name | |
694 | Expansion}), with version numbers and backup suffixes removed using | |
695 | @code{file-name-sans-versions} (@pxref{File Name Components}), matches | |
696 | a @var{regexp}, @code{set-auto-mode} calls the corresponding | |
697 | @var{mode-function}. This feature enables Emacs to select the proper | |
698 | major mode for most files. | |
699 | ||
700 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
701 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
702 | @code{auto-mode-alist} again for a match against the portion of the file | |
703 | name that did not match before. This feature is useful for | |
704 | uncompression packages: an entry of the form @code{("\\.gz\\'" | |
705 | @var{function} t)} can uncompress the file and then put the uncompressed | |
706 | file in the proper mode according to the name sans @samp{.gz}. | |
707 | ||
708 | Here is an example of how to prepend several pattern pairs to | |
709 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
710 | init file.) | |
711 | ||
712 | @smallexample | |
713 | @group | |
714 | (setq auto-mode-alist | |
715 | (append | |
716 | ;; @r{File name (within directory) starts with a dot.} | |
717 | '(("/\\.[^/]*\\'" . fundamental-mode) | |
718 | ;; @r{File name has no dot.} | |
2674569b | 719 | ("/[^\\./]*\\'" . fundamental-mode) |
b8d4c8d0 GM |
720 | ;; @r{File name ends in @samp{.C}.} |
721 | ("\\.C\\'" . c++-mode)) | |
722 | auto-mode-alist)) | |
723 | @end group | |
724 | @end smallexample | |
725 | @end defvar | |
726 | ||
727 | @node Mode Help | |
728 | @subsection Getting Help about a Major Mode | |
729 | @cindex mode help | |
730 | @cindex help for major mode | |
731 | @cindex documentation for major mode | |
732 | ||
db7ab02f | 733 | The @code{describe-mode} function provides information about major |
3fd50d5c | 734 | modes. It is normally bound to @kbd{C-h m}. It uses the value of the |
35137ed3 CY |
735 | variable @code{major-mode} (@pxref{Major Modes}), which is why every |
736 | major mode command needs to set that variable. | |
b8d4c8d0 | 737 | |
27d1f87a CY |
738 | @deffn Command describe-mode &optional buffer |
739 | This command displays the documentation of the current buffer's major | |
740 | mode and minor modes. It uses the @code{documentation} function to | |
741 | retrieve the documentation strings of the major and minor mode | |
742 | commands (@pxref{Accessing Documentation}). | |
743 | ||
744 | If called from Lisp with a non-nil @var{buffer} argument, this | |
745 | function displays the documentation for that buffer's major and minor | |
746 | modes, rather than those of the current buffer. | |
b8d4c8d0 GM |
747 | @end deffn |
748 | ||
b8d4c8d0 GM |
749 | @node Derived Modes |
750 | @subsection Defining Derived Modes | |
751 | @cindex derived mode | |
752 | ||
3fd50d5c CY |
753 | The recommended way to define a new major mode is to derive it from an |
754 | existing one using @code{define-derived-mode}. If there is no closely | |
755 | related mode, you should inherit from either @code{text-mode}, | |
756 | @code{special-mode}, or @code{prog-mode}. @xref{Basic Major Modes}. If | |
757 | none of these are suitable, you can inherit from @code{fundamental-mode} | |
758 | (@pxref{Major Modes}). | |
b8d4c8d0 GM |
759 | |
760 | @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{} | |
c986813b | 761 | This macro defines @var{variant} as a major mode command, using |
b8d4c8d0 GM |
762 | @var{name} as the string form of the mode name. @var{variant} and |
763 | @var{parent} should be unquoted symbols. | |
764 | ||
765 | The new command @var{variant} is defined to call the function | |
766 | @var{parent}, then override certain aspects of that parent mode: | |
767 | ||
768 | @itemize @bullet | |
769 | @item | |
770 | The new mode has its own sparse keymap, named | |
771 | @code{@var{variant}-map}. @code{define-derived-mode} | |
772 | makes the parent mode's keymap the parent of the new map, unless | |
773 | @code{@var{variant}-map} is already set and already has a parent. | |
774 | ||
775 | @item | |
776 | The new mode has its own syntax table, kept in the variable | |
777 | @code{@var{variant}-syntax-table}, unless you override this using the | |
778 | @code{:syntax-table} keyword (see below). @code{define-derived-mode} | |
779 | makes the parent mode's syntax-table the parent of | |
780 | @code{@var{variant}-syntax-table}, unless the latter is already set | |
781 | and already has a parent different from the standard syntax table. | |
782 | ||
783 | @item | |
784 | The new mode has its own abbrev table, kept in the variable | |
785 | @code{@var{variant}-abbrev-table}, unless you override this using the | |
786 | @code{:abbrev-table} keyword (see below). | |
787 | ||
788 | @item | |
789 | The new mode has its own mode hook, @code{@var{variant}-hook}. It | |
790 | runs this hook, after running the hooks of its ancestor modes, with | |
791 | @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}. | |
792 | @end itemize | |
793 | ||
794 | In addition, you can specify how to override other aspects of | |
795 | @var{parent} with @var{body}. The command @var{variant} | |
796 | evaluates the forms in @var{body} after setting up all its usual | |
797 | overrides, just before running the mode hooks. | |
798 | ||
c986813b CY |
799 | If @var{parent} has a non-@code{nil} @code{mode-class} symbol |
800 | property, then @code{define-derived-mode} sets the @code{mode-class} | |
801 | property of @var{variant} to the same value. This ensures, for | |
802 | example, that if @var{parent} is a special mode, then @var{variant} is | |
803 | also a special mode (@pxref{Major Mode Conventions}). | |
804 | ||
b8d4c8d0 GM |
805 | You can also specify @code{nil} for @var{parent}. This gives the new |
806 | mode no parent. Then @code{define-derived-mode} behaves as described | |
807 | above, but, of course, omits all actions connected with @var{parent}. | |
808 | ||
8376d7c2 CY |
809 | The argument @var{docstring} specifies the documentation string for the |
810 | new mode. @code{define-derived-mode} adds some general information | |
811 | about the mode's hook, followed by the mode's keymap, at the end of this | |
812 | documentation string. If you omit @var{docstring}, | |
b8d4c8d0 GM |
813 | @code{define-derived-mode} generates a documentation string. |
814 | ||
815 | The @var{keyword-args} are pairs of keywords and values. The values | |
816 | are evaluated. The following keywords are currently supported: | |
817 | ||
818 | @table @code | |
819 | @item :syntax-table | |
820 | You can use this to explicitly specify a syntax table for the new | |
821 | mode. If you specify a @code{nil} value, the new mode uses the same | |
822 | syntax table as @var{parent}, or the standard syntax table if | |
823 | @var{parent} is @code{nil}. (Note that this does @emph{not} follow | |
824 | the convention used for non-keyword arguments that a @code{nil} value | |
825 | is equivalent with not specifying the argument.) | |
826 | ||
827 | @item :abbrev-table | |
828 | You can use this to explicitly specify an abbrev table for the new | |
829 | mode. If you specify a @code{nil} value, the new mode uses the same | |
830 | abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table} | |
831 | if @var{parent} is @code{nil}. (Again, a @code{nil} value is | |
832 | @emph{not} equivalent to not specifying this keyword.) | |
833 | ||
834 | @item :group | |
835 | If this is specified, the value should be the customization group for | |
836 | this mode. (Not all major modes have one.) Only the (still | |
837 | experimental and unadvertised) command @code{customize-mode} currently | |
838 | uses this. @code{define-derived-mode} does @emph{not} automatically | |
839 | define the specified customization group. | |
840 | @end table | |
841 | ||
842 | Here is a hypothetical example: | |
843 | ||
844 | @example | |
845 | (define-derived-mode hypertext-mode | |
846 | text-mode "Hypertext" | |
847 | "Major mode for hypertext. | |
848 | \\@{hypertext-mode-map@}" | |
849 | (setq case-fold-search nil)) | |
850 | ||
851 | (define-key hypertext-mode-map | |
852 | [down-mouse-3] 'do-hyper-link) | |
853 | @end example | |
854 | ||
855 | Do not write an @code{interactive} spec in the definition; | |
856 | @code{define-derived-mode} does that automatically. | |
857 | @end defmac | |
858 | ||
3fd50d5c CY |
859 | @defun derived-mode-p &rest modes |
860 | This function returns non-@code{nil} if the current major mode is | |
861 | derived from any of the major modes given by the symbols @var{modes}. | |
862 | @end defun | |
863 | ||
864 | @node Basic Major Modes | |
865 | @subsection Basic Major Modes | |
866 | ||
867 | Apart from Fundamental mode, there are three major modes that other | |
868 | major modes commonly derive from: Text mode, Prog mode, and Special | |
1df7defd | 869 | mode. While Text mode is useful in its own right (e.g., for editing |
3fd50d5c CY |
870 | files ending in @file{.txt}), Prog mode and Special mode exist mainly to |
871 | let other modes derive from them. | |
872 | ||
873 | @vindex prog-mode-hook | |
874 | As far as possible, new major modes should be derived, either directly | |
875 | or indirectly, from one of these three modes. One reason is that this | |
876 | allows users to customize a single mode hook | |
1df7defd PE |
877 | (e.g., @code{prog-mode-hook}) for an entire family of relevant modes |
878 | (e.g., all programming language modes). | |
3fd50d5c CY |
879 | |
880 | @deffn Command text-mode | |
881 | Text mode is a major mode for editing human languages. It defines the | |
882 | @samp{"} and @samp{\} characters as having punctuation syntax | |
883 | (@pxref{Syntax Class Table}), and binds @kbd{M-@key{TAB}} to | |
884 | @code{ispell-complete-word} (@pxref{Spelling,,, emacs, The GNU Emacs | |
885 | Manual}). | |
886 | ||
887 | An example of a major mode derived from Text mode is HTML mode. | |
888 | @xref{HTML Mode,,SGML and HTML Modes, emacs, The GNU Emacs Manual}. | |
889 | @end deffn | |
890 | ||
891 | @deffn Command prog-mode | |
892 | Prog mode is a basic major mode for buffers containing programming | |
893 | language source code. Most of the programming language major modes | |
894 | built into Emacs are derived from it. | |
895 | ||
896 | Prog mode binds @code{parse-sexp-ignore-comments} to @code{t} | |
897 | (@pxref{Motion via Parsing}) and @code{bidi-paragraph-direction} to | |
898 | @code{left-to-right} (@pxref{Bidirectional Display}). | |
899 | @end deffn | |
900 | ||
901 | @deffn Command special-mode | |
902 | Special mode is a basic major mode for buffers containing text that is | |
82233bea CY |
903 | produced specially by Emacs, rather than directly from a file. Major |
904 | modes derived from Special mode are given a @code{mode-class} property | |
905 | of @code{special} (@pxref{Major Mode Conventions}). | |
3fd50d5c CY |
906 | |
907 | Special mode sets the buffer to read-only. Its keymap defines several | |
df1af142 GM |
908 | common bindings, including @kbd{q} for @code{quit-window} and @kbd{g} |
909 | for @code{revert-buffer} (@pxref{Reverting}). | |
3fd50d5c CY |
910 | |
911 | An example of a major mode derived from Special mode is Buffer Menu | |
2bb0eca1 | 912 | mode, which is used by the @file{*Buffer List*} buffer. @xref{List |
3fd50d5c CY |
913 | Buffers,,Listing Existing Buffers, emacs, The GNU Emacs Manual}. |
914 | @end deffn | |
915 | ||
82233bea CY |
916 | In addition, modes for buffers of tabulated data can inherit from |
917 | Tabulated List mode, which is in turn derived from Special mode. | |
918 | @xref{Tabulated List Mode}. | |
b8d4c8d0 GM |
919 | |
920 | @node Mode Hooks | |
921 | @subsection Mode Hooks | |
922 | ||
12f381b7 GM |
923 | Every major mode command should finish by running the mode-independent |
924 | normal hook @code{change-major-mode-after-body-hook}, its mode hook, | |
925 | and the normal hook @code{after-change-major-mode-hook}. | |
b8d4c8d0 GM |
926 | It does this by calling @code{run-mode-hooks}. If the major mode is a |
927 | derived mode, that is if it calls another major mode (the parent mode) | |
928 | in its body, it should do this inside @code{delay-mode-hooks} so that | |
929 | the parent won't run these hooks itself. Instead, the derived mode's | |
930 | call to @code{run-mode-hooks} runs the parent's mode hook too. | |
931 | @xref{Major Mode Conventions}. | |
932 | ||
933 | Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}. | |
12f381b7 GM |
934 | Versions before 24 did not have @code{change-major-mode-after-body-hook}. |
935 | When user-implemented major modes do not use @code{run-mode-hooks} and | |
936 | have not been updated to use these newer features, they won't entirely | |
937 | follow these conventions: they may run the parent's mode hook too early, | |
938 | or fail to run @code{after-change-major-mode-hook}. If you encounter | |
939 | such a major mode, please correct it to follow these conventions. | |
b8d4c8d0 GM |
940 | |
941 | When you defined a major mode using @code{define-derived-mode}, it | |
942 | automatically makes sure these conventions are followed. If you | |
16152b76 | 943 | define a major mode ``by hand'', not using @code{define-derived-mode}, |
b8d4c8d0 GM |
944 | use the following functions to handle these conventions automatically. |
945 | ||
946 | @defun run-mode-hooks &rest hookvars | |
947 | Major modes should run their mode hook using this function. It is | |
948 | similar to @code{run-hooks} (@pxref{Hooks}), but it also runs | |
12f381b7 | 949 | @code{change-major-mode-after-body-hook} and |
b8d4c8d0 GM |
950 | @code{after-change-major-mode-hook}. |
951 | ||
952 | When this function is called during the execution of a | |
953 | @code{delay-mode-hooks} form, it does not run the hooks immediately. | |
954 | Instead, it arranges for the next call to @code{run-mode-hooks} to run | |
955 | them. | |
956 | @end defun | |
957 | ||
958 | @defmac delay-mode-hooks body@dots{} | |
959 | When one major mode command calls another, it should do so inside of | |
960 | @code{delay-mode-hooks}. | |
961 | ||
962 | This macro executes @var{body}, but tells all @code{run-mode-hooks} | |
963 | calls during the execution of @var{body} to delay running their hooks. | |
964 | The hooks will actually run during the next call to | |
965 | @code{run-mode-hooks} after the end of the @code{delay-mode-hooks} | |
966 | construct. | |
967 | @end defmac | |
968 | ||
12f381b7 GM |
969 | @defvar change-major-mode-after-body-hook |
970 | This is a normal hook run by @code{run-mode-hooks}. It is run before | |
971 | the mode hooks. | |
972 | @end defvar | |
973 | ||
b8d4c8d0 GM |
974 | @defvar after-change-major-mode-hook |
975 | This is a normal hook run by @code{run-mode-hooks}. It is run at the | |
3fd50d5c | 976 | very end of every properly-written major mode command. |
b8d4c8d0 | 977 | @end defvar |
82233bea CY |
978 | |
979 | @node Tabulated List Mode | |
980 | @subsection Tabulated List mode | |
981 | @cindex Tabulated List mode | |
982 | ||
983 | Tabulated List mode is a major mode for displaying tabulated data, | |
1df7defd | 984 | i.e., data consisting of @dfn{entries}, each entry occupying one row of |
82233bea CY |
985 | text with its contents divided into columns. Tabulated List mode |
986 | provides facilities for pretty-printing rows and columns, and sorting | |
987 | the rows according to the values in each column. It is derived from | |
988 | Special mode (@pxref{Basic Major Modes}). | |
989 | ||
990 | Tabulated List mode is intended to be used as a parent mode by a more | |
991 | specialized major mode. Examples include Process Menu mode | |
992 | (@pxref{Process Information}) and Package Menu mode (@pxref{Package | |
993 | Menu,,, emacs, The GNU Emacs Manual}). | |
994 | ||
995 | @findex tabulated-list-mode | |
996 | Such a derived mode should use @code{define-derived-mode} in the usual | |
997 | way, specifying @code{tabulated-list-mode} as the second argument | |
998 | (@pxref{Derived Modes}). The body of the @code{define-derived-mode} | |
999 | form should specify the format of the tabulated data, by assigning | |
1000 | values to the variables documented below; then, it should call the | |
1001 | function @code{tabulated-list-init-header} to initialize the header | |
1002 | line. | |
1003 | ||
1004 | The derived mode should also define a @dfn{listing command}. This, | |
1df7defd | 1005 | not the mode command, is what the user calls (e.g., @kbd{M-x |
82233bea CY |
1006 | list-processes}). The listing command should create or switch to a |
1007 | buffer, turn on the derived mode, specify the tabulated data, and | |
1008 | finally call @code{tabulated-list-print} to populate the buffer. | |
1009 | ||
1010 | @defvar tabulated-list-format | |
1011 | This buffer-local variable specifies the format of the Tabulated List | |
1012 | data. Its value should be a vector. Each element of the vector | |
1013 | represents a data column, and should be a list @code{(@var{name} | |
1014 | @var{width} @var{sort})}, where | |
1015 | ||
1016 | @itemize | |
1017 | @item | |
1018 | @var{name} is the column's name (a string). | |
1019 | ||
1020 | @item | |
1021 | @var{width} is the width to reserve for the column (an integer). This | |
1022 | is meaningless for the last column, which runs to the end of each line. | |
1023 | ||
1024 | @item | |
1025 | @var{sort} specifies how to sort entries by the column. If @code{nil}, | |
1026 | the column cannot be used for sorting. If @code{t}, the column is | |
1027 | sorted by comparing string values. Otherwise, this should be a | |
1028 | predicate function for @code{sort} (@pxref{Rearrangement}), which | |
1029 | accepts two arguments with the same form as the elements of | |
1030 | @code{tabulated-list-entries} (see below). | |
1031 | @end itemize | |
1032 | @end defvar | |
1033 | ||
1034 | @defvar tabulated-list-entries | |
1035 | This buffer-local variable specifies the entries displayed in the | |
1036 | Tabulated List buffer. Its value should be either a list, or a | |
1037 | function. | |
1038 | ||
1039 | If the value is a list, each list element corresponds to one entry, and | |
1040 | should have the form @w{@code{(@var{id} @var{contents})}}, where | |
1041 | ||
1042 | @itemize | |
1043 | @item | |
1044 | @var{id} is either @code{nil}, or a Lisp object that identifies the | |
1045 | entry. If the latter, the cursor stays on the ``same'' entry when | |
1046 | re-sorting entries. Comparison is done with @code{equal}. | |
1047 | ||
1048 | @item | |
1049 | @var{contents} is a vector with the same number of elements as | |
1050 | @code{tabulated-list-format}. Each vector element is either a string, | |
1051 | which is inserted into the buffer as-is, or a list @code{(@var{label} | |
1052 | . @var{properties})}, which means to insert a text button by calling | |
1053 | @code{insert-text-button} with @var{label} and @var{properties} as | |
1054 | arguments (@pxref{Making Buttons}). | |
1055 | ||
1056 | There should be no newlines in any of these strings. | |
1057 | @end itemize | |
1058 | ||
1059 | Otherwise, the value should be a function which returns a list of the | |
1060 | above form when called with no arguments. | |
1061 | @end defvar | |
1062 | ||
1063 | @defvar tabulated-list-revert-hook | |
1064 | This normal hook is run prior to reverting a Tabulated List buffer. A | |
1065 | derived mode can add a function to this hook to recompute | |
1066 | @code{tabulated-list-entries}. | |
1067 | @end defvar | |
1068 | ||
1069 | @defvar tabulated-list-printer | |
1070 | The value of this variable is the function called to insert an entry at | |
1071 | point, including its terminating newline. The function should accept | |
1072 | two arguments, @var{id} and @var{contents}, having the same meanings as | |
1073 | in @code{tabulated-list-entries}. The default value is a function which | |
1074 | inserts an entry in a straightforward way; a mode which uses Tabulated | |
1075 | List mode in a more complex way can specify another function. | |
1076 | @end defvar | |
1077 | ||
1078 | @defvar tabulated-list-sort-key | |
1079 | The value of this variable specifies the current sort key for the | |
1080 | Tabulated List buffer. If it is @code{nil}, no sorting is done. | |
1081 | Otherwise, it should have the form @code{(@var{name} . @var{flip})}, | |
1082 | where @var{name} is a string matching one of the column names in | |
1083 | @code{tabulated-list-format}, and @var{flip}, if non-@code{nil}, means | |
1084 | to invert the sort order. | |
1085 | @end defvar | |
1086 | ||
1087 | @defun tabulated-list-init-header | |
1088 | This function computes and sets @code{header-line-format} for the | |
1089 | Tabulated List buffer (@pxref{Header Lines}), and assigns a keymap to | |
1090 | the header line to allow sort entries by clicking on column headers. | |
1091 | ||
1092 | Modes derived from Tabulated List mode should call this after setting | |
1093 | the above variables (in particular, only after setting | |
1094 | @code{tabulated-list-format}). | |
1095 | @end defun | |
1096 | ||
1097 | @defun tabulated-list-print &optional remember-pos | |
1098 | This function populates the current buffer with entries. It should be | |
1099 | called by the listing command. It erases the buffer, sorts the entries | |
1100 | specified by @code{tabulated-list-entries} according to | |
1101 | @code{tabulated-list-sort-key}, then calls the function specified by | |
1102 | @code{tabulated-list-printer} to insert each entry. | |
1103 | ||
1104 | If the optional argument @var{remember-pos} is non-@code{nil}, this | |
1105 | function looks for the @var{id} element on the current line, if any, and | |
1106 | tries to move to that entry after all the entries are (re)inserted. | |
1107 | @end defun | |
1108 | ||
1109 | @node Generic Modes | |
1110 | @subsection Generic Modes | |
1111 | @cindex generic mode | |
1112 | ||
1113 | @dfn{Generic modes} are simple major modes with basic support for | |
1114 | comment syntax and Font Lock mode. To define a generic mode, use the | |
1115 | macro @code{define-generic-mode}. See the file @file{generic-x.el} | |
1116 | for some examples of the use of @code{define-generic-mode}. | |
1117 | ||
1118 | @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring | |
1119 | This macro defines a generic mode command named @var{mode} (a symbol, | |
1120 | not quoted). The optional argument @var{docstring} is the | |
1121 | documentation for the mode command. If you do not supply it, | |
1122 | @code{define-generic-mode} generates one by default. | |
1123 | ||
1124 | The argument @var{comment-list} is a list in which each element is | |
1125 | either a character, a string of one or two characters, or a cons cell. | |
1126 | A character or a string is set up in the mode's syntax table as a | |
16152b76 GM |
1127 | ``comment starter''. If the entry is a cons cell, the @sc{car} is set |
1128 | up as a ``comment starter'' and the @sc{cdr} as a ``comment ender''. | |
82233bea CY |
1129 | (Use @code{nil} for the latter if you want comments to end at the end |
1130 | of the line.) Note that the syntax table mechanism has limitations | |
1131 | about what comment starters and enders are actually possible. | |
1132 | @xref{Syntax Tables}. | |
1133 | ||
1134 | The argument @var{keyword-list} is a list of keywords to highlight | |
1135 | with @code{font-lock-keyword-face}. Each keyword should be a string. | |
1136 | Meanwhile, @var{font-lock-list} is a list of additional expressions to | |
1137 | highlight. Each element of this list should have the same form as an | |
1138 | element of @code{font-lock-keywords}. @xref{Search-based | |
1139 | Fontification}. | |
1140 | ||
1141 | The argument @var{auto-mode-list} is a list of regular expressions to | |
1142 | add to the variable @code{auto-mode-alist}. They are added by the execution | |
1143 | of the @code{define-generic-mode} form, not by expanding the macro call. | |
1144 | ||
1145 | Finally, @var{function-list} is a list of functions for the mode | |
1146 | command to call for additional setup. It calls these functions just | |
1147 | before it runs the mode hook variable @code{@var{mode}-hook}. | |
1148 | @end defmac | |
b8d4c8d0 GM |
1149 | |
1150 | @node Example Major Modes | |
1151 | @subsection Major Mode Examples | |
1152 | ||
1153 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
1154 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
1155 | the conventions listed above: | |
1156 | ||
1157 | @smallexample | |
1158 | @group | |
1159 | ;; @r{Create the syntax table for this mode.} | |
1160 | (defvar text-mode-syntax-table | |
1161 | (let ((st (make-syntax-table))) | |
1162 | (modify-syntax-entry ?\" ". " st) | |
1163 | (modify-syntax-entry ?\\ ". " st) | |
1164 | ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. | |
1165 | (modify-syntax-entry ?' "w p" st) | |
1166 | st) | |
1167 | "Syntax table used while in `text-mode'.") | |
1168 | @end group | |
1169 | ||
1170 | ;; @r{Create the keymap for this mode.} | |
1171 | @group | |
1172 | (defvar text-mode-map | |
1173 | (let ((map (make-sparse-keymap))) | |
1174 | (define-key map "\e\t" 'ispell-complete-word) | |
b8d4c8d0 GM |
1175 | map) |
1176 | "Keymap for `text-mode'. | |
9962192e CY |
1177 | Many other modes, such as `mail-mode', `outline-mode' and |
1178 | `indented-text-mode', inherit all the commands defined in this map.") | |
b8d4c8d0 GM |
1179 | @end group |
1180 | @end smallexample | |
1181 | ||
1182 | Here is how the actual mode command is defined now: | |
1183 | ||
1184 | @smallexample | |
1185 | @group | |
1186 | (define-derived-mode text-mode nil "Text" | |
1187 | "Major mode for editing text written for humans to read. | |
1188 | In this mode, paragraphs are delimited only by blank or white lines. | |
1189 | You can thus get the full benefit of adaptive filling | |
1190 | (see the variable `adaptive-fill-mode'). | |
1191 | \\@{text-mode-map@} | |
1192 | Turning on Text mode runs the normal hook `text-mode-hook'." | |
1193 | @end group | |
1194 | @group | |
769741e3 | 1195 | (set (make-local-variable 'text-mode-variant) t) |
b8d4c8d0 GM |
1196 | (set (make-local-variable 'require-final-newline) |
1197 | mode-require-final-newline) | |
1198 | (set (make-local-variable 'indent-line-function) 'indent-relative)) | |
1199 | @end group | |
1200 | @end smallexample | |
1201 | ||
1202 | @noindent | |
1203 | (The last line is redundant nowadays, since @code{indent-relative} is | |
1204 | the default value, and we'll delete it in a future version.) | |
1205 | ||
b8d4c8d0 | 1206 | @cindex @file{lisp-mode.el} |
9962192e CY |
1207 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction |
1208 | mode) have more features than Text mode and the code is correspondingly | |
1209 | more complicated. Here are excerpts from @file{lisp-mode.el} that | |
1210 | illustrate how these modes are written. | |
1211 | ||
1212 | Here is how the Lisp mode syntax and abbrev tables are defined: | |
b8d4c8d0 GM |
1213 | |
1214 | @cindex syntax table example | |
1215 | @smallexample | |
1216 | @group | |
1217 | ;; @r{Create mode-specific table variables.} | |
9962192e | 1218 | (defvar lisp-mode-abbrev-table nil) |
b8d4c8d0 | 1219 | (define-abbrev-table 'lisp-mode-abbrev-table ()) |
9962192e CY |
1220 | |
1221 | (defvar lisp-mode-syntax-table | |
1222 | (let ((table (copy-syntax-table emacs-lisp-mode-syntax-table))) | |
1223 | (modify-syntax-entry ?\[ "_ " table) | |
1224 | (modify-syntax-entry ?\] "_ " table) | |
1225 | (modify-syntax-entry ?# "' 14" table) | |
1226 | (modify-syntax-entry ?| "\" 23bn" table) | |
1227 | table) | |
1228 | "Syntax table used in `lisp-mode'.") | |
b8d4c8d0 GM |
1229 | @end group |
1230 | @end smallexample | |
1231 | ||
1232 | The three modes for Lisp share much of their code. For instance, | |
1233 | each calls the following function to set various variables: | |
1234 | ||
1235 | @smallexample | |
1236 | @group | |
84f4a531 CY |
1237 | (defun lisp-mode-variables (&optional syntax keywords-case-insensitive) |
1238 | (when syntax | |
b8d4c8d0 GM |
1239 | (set-syntax-table lisp-mode-syntax-table)) |
1240 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
1241 | @dots{} | |
1242 | @end group | |
1243 | @end smallexample | |
1244 | ||
9962192e CY |
1245 | @noindent |
1246 | Amongst other things, this function sets up the @code{comment-start} | |
1247 | variable to handle Lisp comments: | |
b8d4c8d0 GM |
1248 | |
1249 | @smallexample | |
1250 | @group | |
9962192e CY |
1251 | (make-local-variable 'comment-start) |
1252 | (setq comment-start ";") | |
b8d4c8d0 GM |
1253 | @dots{} |
1254 | @end group | |
1255 | @end smallexample | |
1256 | ||
1257 | Each of the different Lisp modes has a slightly different keymap. For | |
1258 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other | |
1259 | Lisp modes do not. However, all Lisp modes have some commands in | |
1260 | common. The following code sets up the common commands: | |
1261 | ||
1262 | @smallexample | |
1263 | @group | |
9962192e | 1264 | (defvar lisp-mode-shared-map |
769741e3 | 1265 | (let ((map (make-sparse-keymap))) |
9962192e CY |
1266 | (define-key map "\e\C-q" 'indent-sexp) |
1267 | (define-key map "\177" 'backward-delete-char-untabify) | |
769741e3 | 1268 | map) |
b8d4c8d0 | 1269 | "Keymap for commands shared by all sorts of Lisp modes.") |
b8d4c8d0 GM |
1270 | @end group |
1271 | @end smallexample | |
1272 | ||
1273 | @noindent | |
1274 | And here is the code to set up the keymap for Lisp mode: | |
1275 | ||
1276 | @smallexample | |
1277 | @group | |
769741e3 | 1278 | (defvar lisp-mode-map |
9962192e CY |
1279 | (let ((map (make-sparse-keymap)) |
1280 | (menu-map (make-sparse-keymap "Lisp"))) | |
1281 | (set-keymap-parent map lisp-mode-shared-map) | |
769741e3 SM |
1282 | (define-key map "\e\C-x" 'lisp-eval-defun) |
1283 | (define-key map "\C-c\C-z" 'run-lisp) | |
9962192e | 1284 | @dots{} |
769741e3 | 1285 | map) |
9962192e CY |
1286 | "Keymap for ordinary Lisp mode. |
1287 | All commands in `lisp-mode-shared-map' are inherited by this map.") | |
b8d4c8d0 GM |
1288 | @end group |
1289 | @end smallexample | |
1290 | ||
9962192e CY |
1291 | @noindent |
1292 | Finally, here is the major mode command for Lisp mode: | |
b8d4c8d0 GM |
1293 | |
1294 | @smallexample | |
1295 | @group | |
9962192e | 1296 | (define-derived-mode lisp-mode prog-mode "Lisp" |
b8d4c8d0 GM |
1297 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. |
1298 | Commands: | |
1299 | Delete converts tabs to spaces as it moves back. | |
1300 | Blank lines separate paragraphs. Semicolons start comments. | |
9962192e | 1301 | |
b8d4c8d0 GM |
1302 | \\@{lisp-mode-map@} |
1303 | Note that `run-lisp' may be used either to start an inferior Lisp job | |
1304 | or to switch back to an existing one. | |
1305 | @end group | |
1306 | ||
1307 | @group | |
1308 | Entry to this mode calls the value of `lisp-mode-hook' | |
1309 | if that value is non-nil." | |
9962192e | 1310 | (lisp-mode-variables nil t) |
84f4a531 CY |
1311 | (set (make-local-variable 'find-tag-default-function) |
1312 | 'lisp-find-tag-default) | |
1313 | (set (make-local-variable 'comment-start-skip) | |
769741e3 | 1314 | "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") |
9962192e | 1315 | (setq imenu-case-fold-search t)) |
b8d4c8d0 GM |
1316 | @end group |
1317 | @end smallexample | |
1318 | ||
1319 | @node Minor Modes | |
1320 | @section Minor Modes | |
1321 | @cindex minor mode | |
1322 | ||
f700caa3 CY |
1323 | A @dfn{minor mode} provides optional features that users may enable or |
1324 | disable independently of the choice of major mode. Minor modes can be | |
1325 | enabled individually or in combination. | |
b8d4c8d0 | 1326 | |
f700caa3 CY |
1327 | Most minor modes implement features that are independent of the major |
1328 | mode, and can thus be used with most major modes. For example, Auto | |
1329 | Fill mode works with any major mode that permits text insertion. A few | |
1330 | minor modes, however, are specific to a particular major mode. For | |
1331 | example, Diff Auto Refine mode is a minor mode that is intended to be | |
1332 | used only with Diff mode. | |
b8d4c8d0 | 1333 | |
f700caa3 CY |
1334 | Ideally, a minor mode should have its desired effect regardless of the |
1335 | other minor modes in effect. It should be possible to activate and | |
1336 | deactivate minor modes in any order. | |
b8d4c8d0 GM |
1337 | |
1338 | @defvar minor-mode-list | |
1339 | The value of this variable is a list of all minor mode commands. | |
1340 | @end defvar | |
1341 | ||
1342 | @menu | |
1343 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
1344 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
1345 | * Defining Minor Modes:: A convenient facility for defining minor modes. | |
1346 | @end menu | |
1347 | ||
1348 | @node Minor Mode Conventions | |
1349 | @subsection Conventions for Writing Minor Modes | |
1350 | @cindex minor mode conventions | |
1351 | @cindex conventions for writing minor modes | |
1352 | ||
1353 | There are conventions for writing minor modes just as there are for | |
f700caa3 CY |
1354 | major modes. These conventions are described below. The easiest way to |
1355 | follow them is to use the macro @code{define-minor-mode}. | |
1356 | @xref{Defining Minor Modes}. | |
b8d4c8d0 GM |
1357 | |
1358 | @itemize @bullet | |
1359 | @item | |
1360 | @cindex mode variable | |
f700caa3 CY |
1361 | Define a variable whose name ends in @samp{-mode}. We call this the |
1362 | @dfn{mode variable}. The minor mode command should set this variable. | |
b5ca9d53 | 1363 | The value will be @code{nil} if the mode is disabled, and non-@code{nil} |
f700caa3 CY |
1364 | if the mode is enabled. The variable should be buffer-local if the |
1365 | minor mode is buffer-local. | |
b8d4c8d0 GM |
1366 | |
1367 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
f700caa3 CY |
1368 | display the minor mode name in the mode line. It also determines |
1369 | whether the minor mode keymap is active, via @code{minor-mode-map-alist} | |
1370 | (@pxref{Controlling Active Maps}). Individual commands or hooks can | |
1371 | also check its value. | |
b8d4c8d0 GM |
1372 | |
1373 | @item | |
f700caa3 CY |
1374 | Define a command, called the @dfn{mode command}, whose name is the same |
1375 | as the mode variable. Its job is to set the value of the mode variable, | |
1376 | plus anything else that needs to be done to actually enable or disable | |
1377 | the mode's features. | |
1378 | ||
1379 | The mode command should accept one optional argument. If called | |
1380 | interactively with no prefix argument, it should toggle the mode | |
1df7defd | 1381 | (i.e., enable if it is disabled, and disable if it is enabled). If |
f700caa3 CY |
1382 | called interactively with a prefix argument, it should enable the mode |
1383 | if the argument is positive and disable it otherwise. | |
1384 | ||
1df7defd | 1385 | If the mode command is called from Lisp (i.e., non-interactively), it |
f700caa3 CY |
1386 | should enable the mode if the argument is omitted or @code{nil}; it |
1387 | should toggle the mode if the argument is the symbol @code{toggle}; | |
1388 | otherwise it should treat the argument in the same way as for an | |
1389 | interactive call with a numeric prefix argument, as described above. | |
1390 | ||
1391 | The following example shows how to implement this behavior (it is | |
1392 | similar to the code generated by the @code{define-minor-mode} macro): | |
b8d4c8d0 | 1393 | |
f700caa3 CY |
1394 | @example |
1395 | (interactive (list (or current-prefix-arg 'toggle))) | |
1396 | (let ((enable (if (eq arg 'toggle) | |
1397 | (not foo-mode) ; @r{this mode's mode variable} | |
1398 | (> (prefix-numeric-value arg) 0)))) | |
1399 | (if enable | |
1400 | @var{do-enable} | |
1401 | @var{do-disable})) | |
1402 | @end example | |
1403 | ||
1404 | The reason for this somewhat complex behavior is that it lets users | |
1405 | easily toggle the minor mode interactively, and also lets the minor mode | |
1406 | be easily enabled in a mode hook, like this: | |
1407 | ||
1408 | @example | |
1409 | (add-hook 'text-mode-hook 'foo-mode) | |
1410 | @end example | |
1411 | ||
1412 | @noindent | |
1413 | This behaves correctly whether or not @code{foo-mode} was already | |
1414 | enabled, since the @code{foo-mode} mode command unconditionally enables | |
1415 | the minor mode when it is called from Lisp with no argument. Disabling | |
1416 | a minor mode in a mode hook is a little uglier: | |
1417 | ||
1418 | @example | |
1419 | (add-hook 'text-mode-hook (lambda () (foo-mode -1))) | |
1420 | @end example | |
1421 | ||
1422 | @noindent | |
1423 | However, this is not very commonly done. | |
b8d4c8d0 GM |
1424 | |
1425 | @item | |
1426 | Add an element to @code{minor-mode-alist} for each minor mode | |
1427 | (@pxref{Definition of minor-mode-alist}), if you want to indicate the | |
1428 | minor mode in the mode line. This element should be a list of the | |
1429 | following form: | |
1430 | ||
1431 | @smallexample | |
1432 | (@var{mode-variable} @var{string}) | |
1433 | @end smallexample | |
1434 | ||
1435 | Here @var{mode-variable} is the variable that controls enabling of the | |
1436 | minor mode, and @var{string} is a short string, starting with a space, | |
1437 | to represent the mode in the mode line. These strings must be short so | |
1438 | that there is room for several of them at once. | |
1439 | ||
1440 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
1441 | check for an existing element, to avoid duplication. For example: | |
1442 | ||
1443 | @smallexample | |
1444 | @group | |
1445 | (unless (assq 'leif-mode minor-mode-alist) | |
f700caa3 | 1446 | (push '(leif-mode " Leif") minor-mode-alist)) |
b8d4c8d0 GM |
1447 | @end group |
1448 | @end smallexample | |
1449 | ||
1450 | @noindent | |
1451 | or like this, using @code{add-to-list} (@pxref{List Variables}): | |
1452 | ||
1453 | @smallexample | |
1454 | @group | |
1455 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) | |
1456 | @end group | |
1457 | @end smallexample | |
1458 | @end itemize | |
1459 | ||
f700caa3 CY |
1460 | In addition, several major mode conventions apply to minor modes as |
1461 | well: those regarding the names of global symbols, the use of a hook at | |
1462 | the end of the initialization function, and the use of keymaps and other | |
1463 | tables. | |
b8d4c8d0 | 1464 | |
f700caa3 CY |
1465 | The minor mode should, if possible, support enabling and disabling via |
1466 | Custom (@pxref{Customization}). To do this, the mode variable should be | |
1467 | defined with @code{defcustom}, usually with @code{:type 'boolean}. If | |
1468 | just setting the variable is not sufficient to enable the mode, you | |
b8d4c8d0 | 1469 | should also specify a @code{:set} method which enables the mode by |
f700caa3 CY |
1470 | invoking the mode command. Note in the variable's documentation string |
1471 | that setting the variable other than via Custom may not take effect. | |
1472 | Also, mark the definition with an autoload cookie (@pxref{autoload | |
1473 | cookie}), and specify a @code{:require} so that customizing the variable | |
1474 | will load the library that defines the mode. For example: | |
b8d4c8d0 GM |
1475 | |
1476 | @smallexample | |
1477 | @group | |
b8d4c8d0 GM |
1478 | ;;;###autoload |
1479 | (defcustom msb-mode nil | |
1480 | "Toggle msb-mode. | |
1481 | Setting this variable directly does not take effect; | |
1482 | use either \\[customize] or the function `msb-mode'." | |
1483 | :set 'custom-set-minor-mode | |
1484 | :initialize 'custom-initialize-default | |
1485 | :version "20.4" | |
1486 | :type 'boolean | |
1487 | :group 'msb | |
1488 | :require 'msb) | |
1489 | @end group | |
1490 | @end smallexample | |
1491 | ||
1492 | @node Keymaps and Minor Modes | |
1493 | @subsection Keymaps and Minor Modes | |
1494 | ||
1495 | Each minor mode can have its own keymap, which is active when the mode | |
1496 | is enabled. To set up a keymap for a minor mode, add an element to the | |
1497 | alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}. | |
1498 | ||
1499 | @cindex @code{self-insert-command}, minor modes | |
1500 | One use of minor mode keymaps is to modify the behavior of certain | |
1501 | self-inserting characters so that they do something else as well as | |
f58b9822 GM |
1502 | self-insert. (Another way to customize @code{self-insert-command} is |
1503 | through @code{post-self-insert-hook}. Apart from this, the facilities | |
1504 | for customizing @code{self-insert-command} are limited to special cases, | |
1505 | designed for abbrevs and Auto Fill mode. Do not try substituting your | |
1506 | own definition of @code{self-insert-command} for the standard one. The | |
1507 | editor command loop handles this function specially.) | |
b8d4c8d0 | 1508 | |
fb891cc8 CY |
1509 | Minor modes may bind commands to key sequences consisting of @kbd{C-c} |
1510 | followed by a punctuation character. However, sequences consisting of | |
1511 | @kbd{C-c} followed by one of @kbd{@{@}<>:;}, or a control character or | |
1512 | digit, are reserved for major modes. Also, @kbd{C-c @var{letter}} is | |
1513 | reserved for users. @xref{Key Binding Conventions}. | |
b8d4c8d0 GM |
1514 | |
1515 | @node Defining Minor Modes | |
1516 | @subsection Defining Minor Modes | |
1517 | ||
1518 | The macro @code{define-minor-mode} offers a convenient way of | |
1519 | implementing a mode in one self-contained definition. | |
1520 | ||
1521 | @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{} | |
1522 | This macro defines a new minor mode whose name is @var{mode} (a | |
1523 | symbol). It defines a command named @var{mode} to toggle the minor | |
60d47423 GM |
1524 | mode, with @var{doc} as its documentation string. |
1525 | ||
1526 | The toggle command takes one optional (prefix) argument. | |
1527 | If called interactively with no argument it toggles the mode on or off. | |
1528 | A positive prefix argument enables the mode, any other prefix argument | |
1529 | disables it. From Lisp, an argument of @code{toggle} toggles the mode, | |
1530 | whereas an omitted or @code{nil} argument enables the mode. | |
1531 | This makes it easy to enable the minor mode in a major mode hook, for example. | |
1532 | If @var{doc} is nil, the macro supplies a default documentation string | |
1533 | explaining the above. | |
1534 | ||
1535 | By default, it also defines a variable named @var{mode}, which is set to | |
1536 | @code{t} or @code{nil} by enabling or disabling the mode. The variable | |
1537 | is initialized to @var{init-value}. Except in unusual circumstances | |
1538 | (see below), this value must be @code{nil}. | |
b8d4c8d0 GM |
1539 | |
1540 | The string @var{lighter} says what to display in the mode line | |
1541 | when the mode is enabled; if it is @code{nil}, the mode is not displayed | |
1542 | in the mode line. | |
1543 | ||
bc7d7ea6 CY |
1544 | The optional argument @var{keymap} specifies the keymap for the minor |
1545 | mode. If non-@code{nil}, it should be a variable name (whose value is | |
1546 | a keymap), a keymap, or an alist of the form | |
b8d4c8d0 GM |
1547 | |
1548 | @example | |
1549 | (@var{key-sequence} . @var{definition}) | |
1550 | @end example | |
1551 | ||
bc7d7ea6 CY |
1552 | @noindent |
1553 | where each @var{key-sequence} and @var{definition} are arguments | |
1554 | suitable for passing to @code{define-key} (@pxref{Changing Key | |
1555 | Bindings}). If @var{keymap} is a keymap or an alist, this also | |
1556 | defines the variable @code{@var{mode}-map}. | |
1557 | ||
b8d4c8d0 GM |
1558 | The above three arguments @var{init-value}, @var{lighter}, and |
1559 | @var{keymap} can be (partially) omitted when @var{keyword-args} are | |
1560 | used. The @var{keyword-args} consist of keywords followed by | |
1561 | corresponding values. A few keywords have special meanings: | |
1562 | ||
1563 | @table @code | |
1564 | @item :group @var{group} | |
1565 | Custom group name to use in all generated @code{defcustom} forms. | |
1566 | Defaults to @var{mode} without the possible trailing @samp{-mode}. | |
1567 | @strong{Warning:} don't use this default group name unless you have | |
1568 | written a @code{defgroup} to define that group properly. @xref{Group | |
1569 | Definitions}. | |
1570 | ||
1571 | @item :global @var{global} | |
1572 | If non-@code{nil}, this specifies that the minor mode should be global | |
1573 | rather than buffer-local. It defaults to @code{nil}. | |
1574 | ||
1575 | One of the effects of making a minor mode global is that the | |
1576 | @var{mode} variable becomes a customization variable. Toggling it | |
81927dd2 CY |
1577 | through the Customize interface turns the mode on and off, and its |
1578 | value can be saved for future Emacs sessions (@pxref{Saving | |
b8d4c8d0 GM |
1579 | Customizations,,, emacs, The GNU Emacs Manual}. For the saved |
1580 | variable to work, you should ensure that the @code{define-minor-mode} | |
1581 | form is evaluated each time Emacs starts; for packages that are not | |
1582 | part of Emacs, the easiest way to do this is to specify a | |
1583 | @code{:require} keyword. | |
1584 | ||
1585 | @item :init-value @var{init-value} | |
1586 | This is equivalent to specifying @var{init-value} positionally. | |
1587 | ||
1588 | @item :lighter @var{lighter} | |
1589 | This is equivalent to specifying @var{lighter} positionally. | |
1590 | ||
1591 | @item :keymap @var{keymap} | |
1592 | This is equivalent to specifying @var{keymap} positionally. | |
56afad3a GM |
1593 | |
1594 | @item :variable @var{place} | |
1595 | This replaces the default variable @var{mode}, used to store the state | |
1596 | of the mode. If you specify this, the @var{mode} variable is not | |
1597 | defined, and any @var{init-value} argument is unused. @var{place} | |
1598 | can be a different named variable (which you must define yourself), or | |
1599 | anything that can be used with the @code{setf} function | |
5241598a | 1600 | (@pxref{Generalized Variables}). |
56afad3a GM |
1601 | @var{place} can also be a cons @code{(@var{get} . @var{set})}, |
1602 | where @var{get} is an expression that returns the current state, | |
1603 | and @var{set} is a function of one argument (a state) that sets it. | |
2cb228f7 AM |
1604 | |
1605 | @item :after-hook @var{after-hook} | |
9a4888c0 | 1606 | This defines a single Lisp form which is evaluated after the mode hooks |
2cb228f7 | 1607 | have run. It should not be quoted. |
b8d4c8d0 GM |
1608 | @end table |
1609 | ||
1610 | Any other keyword arguments are passed directly to the | |
1611 | @code{defcustom} generated for the variable @var{mode}. | |
1612 | ||
2cb228f7 AM |
1613 | The command named @var{mode} first performs the standard actions such as |
1614 | setting the variable named @var{mode} and then executes the @var{body} | |
1615 | forms, if any. It then runs the mode hook variable | |
1616 | @code{@var{mode}-hook} and finishes by evaluating any form in | |
1617 | @code{:after-hook}. | |
b8d4c8d0 GM |
1618 | @end defmac |
1619 | ||
1620 | The initial value must be @code{nil} except in cases where (1) the | |
1621 | mode is preloaded in Emacs, or (2) it is painless for loading to | |
1622 | enable the mode even though the user did not request it. For | |
1623 | instance, if the mode has no effect unless something else is enabled, | |
1624 | and will always be loaded by that time, enabling it by default is | |
1625 | harmless. But these are unusual circumstances. Normally, the | |
1626 | initial value must be @code{nil}. | |
1627 | ||
1628 | @findex easy-mmode-define-minor-mode | |
1629 | The name @code{easy-mmode-define-minor-mode} is an alias | |
1630 | for this macro. | |
1631 | ||
1632 | Here is an example of using @code{define-minor-mode}: | |
1633 | ||
1634 | @smallexample | |
1635 | (define-minor-mode hungry-mode | |
1636 | "Toggle Hungry mode. | |
60d47423 GM |
1637 | Interactively with no argument, this command toggles the mode. |
1638 | A positive prefix argument enables the mode, any other prefix | |
1639 | argument disables it. From Lisp, argument omitted or nil enables | |
1640 | the mode, `toggle' toggles the state. | |
b8d4c8d0 GM |
1641 | |
1642 | When Hungry mode is enabled, the control delete key | |
1643 | gobbles all preceding whitespace except the last. | |
1644 | See the command \\[hungry-electric-delete]." | |
1645 | ;; The initial value. | |
1646 | nil | |
1647 | ;; The indicator for the mode line. | |
1648 | " Hungry" | |
1649 | ;; The minor mode bindings. | |
e8bf5266 | 1650 | '(([C-backspace] . hungry-electric-delete)) |
b8d4c8d0 GM |
1651 | :group 'hunger) |
1652 | @end smallexample | |
1653 | ||
1654 | @noindent | |
16152b76 | 1655 | This defines a minor mode named ``Hungry mode'', a command named |
b8d4c8d0 GM |
1656 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} |
1657 | which indicates whether the mode is enabled, and a variable named | |
1658 | @code{hungry-mode-map} which holds the keymap that is active when the | |
1659 | mode is enabled. It initializes the keymap with a key binding for | |
1660 | @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into | |
1661 | custom group @code{hunger}. There are no @var{body} forms---many | |
1662 | minor modes don't need any. | |
1663 | ||
1664 | Here's an equivalent way to write it: | |
1665 | ||
1666 | @smallexample | |
1667 | (define-minor-mode hungry-mode | |
1668 | "Toggle Hungry mode. | |
60d47423 | 1669 | ...rest of documentation as before..." |
b8d4c8d0 GM |
1670 | ;; The initial value. |
1671 | :init-value nil | |
1672 | ;; The indicator for the mode line. | |
1673 | :lighter " Hungry" | |
1674 | ;; The minor mode bindings. | |
1675 | :keymap | |
e8bf5266 JB |
1676 | '(([C-backspace] . hungry-electric-delete) |
1677 | ([C-M-backspace] | |
b8d4c8d0 GM |
1678 | . (lambda () |
1679 | (interactive) | |
1680 | (hungry-electric-delete t)))) | |
1681 | :group 'hunger) | |
1682 | @end smallexample | |
1683 | ||
1684 | @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{} | |
1685 | This defines a global toggle named @var{global-mode} whose meaning is | |
1686 | to enable or disable the buffer-local minor mode @var{mode} in all | |
1687 | buffers. To turn on the minor mode in a buffer, it uses the function | |
fb891cc8 | 1688 | @var{turn-on}; to turn off the minor mode, it calls @var{mode} with |
b8d4c8d0 GM |
1689 | @minus{}1 as argument. |
1690 | ||
1691 | Globally enabling the mode also affects buffers subsequently created | |
1692 | by visiting files, and buffers that use a major mode other than | |
1693 | Fundamental mode; but it does not detect the creation of a new buffer | |
1694 | in Fundamental mode. | |
1695 | ||
1696 | This defines the customization option @var{global-mode} (@pxref{Customization}), | |
81927dd2 | 1697 | which can be toggled in the Customize interface to turn the minor mode on |
b8d4c8d0 GM |
1698 | and off. As with @code{define-minor-mode}, you should ensure that the |
1699 | @code{define-globalized-minor-mode} form is evaluated each time Emacs | |
1700 | starts, for example by providing a @code{:require} keyword. | |
1701 | ||
1702 | Use @code{:group @var{group}} in @var{keyword-args} to specify the | |
1703 | custom group for the mode variable of the global minor mode. | |
7a9a2fc6 | 1704 | |
cf46a8ff GM |
1705 | Generally speaking, when you define a globalized minor mode, you should |
1706 | also define a non-globalized version, so that people can use (or | |
1707 | disable) it in individual buffers. This also allows them to disable a | |
1708 | globally enabled minor mode in a specific major mode, by using that | |
1709 | mode's hook. | |
b8d4c8d0 GM |
1710 | @end defmac |
1711 | ||
7a9a2fc6 | 1712 | |
b8d4c8d0 | 1713 | @node Mode Line Format |
f700caa3 | 1714 | @section Mode Line Format |
b8d4c8d0 GM |
1715 | @cindex mode line |
1716 | ||
1717 | Each Emacs window (aside from minibuffer windows) typically has a mode | |
1718 | line at the bottom, which displays status information about the buffer | |
1719 | displayed in the window. The mode line contains information about the | |
1720 | buffer, such as its name, associated file, depth of recursive editing, | |
1721 | and major and minor modes. A window can also have a @dfn{header | |
1722 | line}, which is much like the mode line but appears at the top of the | |
1723 | window. | |
1724 | ||
1725 | This section describes how to control the contents of the mode line | |
1726 | and header line. We include it in this chapter because much of the | |
1727 | information displayed in the mode line relates to the enabled major and | |
1728 | minor modes. | |
1729 | ||
1730 | @menu | |
769741e3 SM |
1731 | * Base: Mode Line Basics. Basic ideas of mode line control. |
1732 | * Data: Mode Line Data. The data structure that controls the mode line. | |
1733 | * Top: Mode Line Top. The top level variable, mode-line-format. | |
1734 | * Mode Line Variables:: Variables used in that data structure. | |
1735 | * %-Constructs:: Putting information into a mode line. | |
1736 | * Properties in Mode:: Using text properties in the mode line. | |
1737 | * Header Lines:: Like a mode line, but at the top. | |
1738 | * Emulating Mode Line:: Formatting text as the mode line would. | |
b8d4c8d0 GM |
1739 | @end menu |
1740 | ||
1741 | @node Mode Line Basics | |
1742 | @subsection Mode Line Basics | |
1743 | ||
f700caa3 CY |
1744 | The contents of each mode line are specified by the buffer-local |
1745 | variable @code{mode-line-format} (@pxref{Mode Line Top}). This variable | |
1746 | holds a @dfn{mode line construct}: a template that controls what is | |
1747 | displayed on the buffer's mode line. The value of | |
1748 | @code{header-line-format} specifies the buffer's header line in the same | |
1749 | way. All windows for the same buffer use the same | |
b8d4c8d0 GM |
1750 | @code{mode-line-format} and @code{header-line-format}. |
1751 | ||
f700caa3 CY |
1752 | For efficiency, Emacs does not continuously recompute each window's |
1753 | mode line and header line. It does so when circumstances appear to call | |
1754 | for it---for instance, if you change the window configuration, switch | |
1755 | buffers, narrow or widen the buffer, scroll, or modify the buffer. If | |
1756 | you alter any of the variables referenced by @code{mode-line-format} or | |
1757 | @code{header-line-format} (@pxref{Mode Line Variables}), or any other | |
1758 | data structures that affect how text is displayed (@pxref{Display}), you | |
1759 | should use the function @code{force-mode-line-update} to update the | |
1760 | display. | |
b8d4c8d0 GM |
1761 | |
1762 | @defun force-mode-line-update &optional all | |
f700caa3 CY |
1763 | This function forces Emacs to update the current buffer's mode line and |
1764 | header line, based on the latest values of all relevant variables, | |
1765 | during its next redisplay cycle. If the optional argument @var{all} is | |
1766 | non-@code{nil}, it forces an update for all mode lines and header lines. | |
1767 | ||
1768 | This function also forces an update of the menu bar and frame title. | |
b8d4c8d0 GM |
1769 | @end defun |
1770 | ||
1771 | The selected window's mode line is usually displayed in a different | |
f700caa3 CY |
1772 | color using the face @code{mode-line}. Other windows' mode lines appear |
1773 | in the face @code{mode-line-inactive} instead. @xref{Faces}. | |
b8d4c8d0 GM |
1774 | |
1775 | @node Mode Line Data | |
1776 | @subsection The Data Structure of the Mode Line | |
f700caa3 | 1777 | @cindex mode line construct |
b8d4c8d0 | 1778 | |
f700caa3 CY |
1779 | The mode line contents are controlled by a data structure called a |
1780 | @dfn{mode line construct}, made up of lists, strings, symbols, and | |
b8d4c8d0 | 1781 | numbers kept in buffer-local variables. Each data type has a specific |
f700caa3 CY |
1782 | meaning for the mode line appearance, as described below. The same data |
1783 | structure is used for constructing frame titles (@pxref{Frame Titles}) | |
1784 | and header lines (@pxref{Header Lines}). | |
b8d4c8d0 | 1785 | |
f700caa3 | 1786 | A mode line construct may be as simple as a fixed string of text, |
b8d4c8d0 GM |
1787 | but it usually specifies how to combine fixed strings with variables' |
1788 | values to construct the text. Many of these variables are themselves | |
f700caa3 | 1789 | defined to have mode line constructs as their values. |
b8d4c8d0 | 1790 | |
f700caa3 | 1791 | Here are the meanings of various data types as mode line constructs: |
b8d4c8d0 GM |
1792 | |
1793 | @table @code | |
1794 | @cindex percent symbol in mode line | |
1795 | @item @var{string} | |
f700caa3 | 1796 | A string as a mode line construct appears verbatim except for |
b8d4c8d0 GM |
1797 | @dfn{@code{%}-constructs} in it. These stand for substitution of |
1798 | other data; see @ref{%-Constructs}. | |
1799 | ||
1800 | If parts of the string have @code{face} properties, they control | |
1801 | display of the text just as they would text in the buffer. Any | |
1802 | characters which have no @code{face} properties are displayed, by | |
1803 | default, in the face @code{mode-line} or @code{mode-line-inactive} | |
1804 | (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The | |
9716fedb | 1805 | @code{help-echo} and @code{keymap} properties in @var{string} have |
b8d4c8d0 GM |
1806 | special meanings. @xref{Properties in Mode}. |
1807 | ||
1808 | @item @var{symbol} | |
f700caa3 CY |
1809 | A symbol as a mode line construct stands for its value. The value of |
1810 | @var{symbol} is used as a mode line construct, in place of @var{symbol}. | |
b8d4c8d0 GM |
1811 | However, the symbols @code{t} and @code{nil} are ignored, as is any |
1812 | symbol whose value is void. | |
1813 | ||
1814 | There is one exception: if the value of @var{symbol} is a string, it is | |
1815 | displayed verbatim: the @code{%}-constructs are not recognized. | |
1816 | ||
1817 | Unless @var{symbol} is marked as ``risky'' (i.e., it has a | |
1818 | non-@code{nil} @code{risky-local-variable} property), all text | |
f700caa3 CY |
1819 | properties specified in @var{symbol}'s value are ignored. This includes |
1820 | the text properties of strings in @var{symbol}'s value, as well as all | |
1821 | @code{:eval} and @code{:propertize} forms in it. (The reason for this | |
1822 | is security: non-risky variables could be set automatically from file | |
1823 | variables without prompting the user.) | |
b8d4c8d0 GM |
1824 | |
1825 | @item (@var{string} @var{rest}@dots{}) | |
1826 | @itemx (@var{list} @var{rest}@dots{}) | |
1827 | A list whose first element is a string or list means to process all the | |
1828 | elements recursively and concatenate the results. This is the most | |
f700caa3 | 1829 | common form of mode line construct. |
b8d4c8d0 GM |
1830 | |
1831 | @item (:eval @var{form}) | |
1832 | A list whose first element is the symbol @code{:eval} says to evaluate | |
1833 | @var{form}, and use the result as a string to display. Make sure this | |
1834 | evaluation cannot load any files, as doing so could cause infinite | |
1835 | recursion. | |
1836 | ||
1837 | @item (:propertize @var{elt} @var{props}@dots{}) | |
1838 | A list whose first element is the symbol @code{:propertize} says to | |
f700caa3 | 1839 | process the mode line construct @var{elt} recursively, then add the text |
b8d4c8d0 GM |
1840 | properties specified by @var{props} to the result. The argument |
1841 | @var{props} should consist of zero or more pairs @var{text-property} | |
f700caa3 | 1842 | @var{value}. |
b8d4c8d0 GM |
1843 | |
1844 | @item (@var{symbol} @var{then} @var{else}) | |
1845 | A list whose first element is a symbol that is not a keyword specifies | |
1846 | a conditional. Its meaning depends on the value of @var{symbol}. If | |
1847 | @var{symbol} has a non-@code{nil} value, the second element, | |
5f2c76c6 | 1848 | @var{then}, is processed recursively as a mode line construct. |
b8d4c8d0 | 1849 | Otherwise, the third element, @var{else}, is processed recursively. |
5f2c76c6 | 1850 | You may omit @var{else}; then the mode line construct displays nothing |
b8d4c8d0 GM |
1851 | if the value of @var{symbol} is @code{nil} or void. |
1852 | ||
1853 | @item (@var{width} @var{rest}@dots{}) | |
1854 | A list whose first element is an integer specifies truncation or | |
1855 | padding of the results of @var{rest}. The remaining elements | |
f700caa3 | 1856 | @var{rest} are processed recursively as mode line constructs and |
b8d4c8d0 GM |
1857 | concatenated together. When @var{width} is positive, the result is |
1858 | space filled on the right if its width is less than @var{width}. When | |
1859 | @var{width} is negative, the result is truncated on the right to | |
1860 | @minus{}@var{width} columns if its width exceeds @minus{}@var{width}. | |
1861 | ||
1862 | For example, the usual way to show what percentage of a buffer is above | |
1863 | the top of the window is to use a list like this: @code{(-3 "%p")}. | |
1864 | @end table | |
1865 | ||
1866 | @node Mode Line Top | |
1867 | @subsection The Top Level of Mode Line Control | |
1868 | ||
1869 | The variable in overall control of the mode line is | |
1870 | @code{mode-line-format}. | |
1871 | ||
01f17ae2 | 1872 | @defopt mode-line-format |
f700caa3 | 1873 | The value of this variable is a mode line construct that controls the |
b8d4c8d0 GM |
1874 | contents of the mode-line. It is always buffer-local in all buffers. |
1875 | ||
f700caa3 CY |
1876 | If you set this variable to @code{nil} in a buffer, that buffer does not |
1877 | have a mode line. (A window that is just one line tall also does not | |
1878 | display a mode line.) | |
01f17ae2 | 1879 | @end defopt |
b8d4c8d0 GM |
1880 | |
1881 | The default value of @code{mode-line-format} is designed to use the | |
1882 | values of other variables such as @code{mode-line-position} and | |
1883 | @code{mode-line-modes} (which in turn incorporates the values of the | |
1884 | variables @code{mode-name} and @code{minor-mode-alist}). Very few | |
1885 | modes need to alter @code{mode-line-format} itself. For most | |
1886 | purposes, it is sufficient to alter some of the variables that | |
1887 | @code{mode-line-format} either directly or indirectly refers to. | |
1888 | ||
1889 | If you do alter @code{mode-line-format} itself, the new value should | |
1890 | use the same variables that appear in the default value (@pxref{Mode | |
1891 | Line Variables}), rather than duplicating their contents or displaying | |
1892 | the information in another fashion. This way, customizations made by | |
1893 | the user or by Lisp programs (such as @code{display-time} and major | |
1894 | modes) via changes to those variables remain effective. | |
1895 | ||
f700caa3 CY |
1896 | Here is a hypothetical example of a @code{mode-line-format} that might |
1897 | be useful for Shell mode (in reality, Shell mode does not set | |
1898 | @code{mode-line-format}): | |
b8d4c8d0 GM |
1899 | |
1900 | @example | |
1901 | @group | |
1902 | (setq mode-line-format | |
1903 | (list "-" | |
1904 | 'mode-line-mule-info | |
1905 | 'mode-line-modified | |
1906 | 'mode-line-frame-identification | |
1907 | "%b--" | |
1908 | @end group | |
1909 | @group | |
1910 | ;; @r{Note that this is evaluated while making the list.} | |
f700caa3 | 1911 | ;; @r{It makes a mode line construct which is just a string.} |
b8d4c8d0 GM |
1912 | (getenv "HOST") |
1913 | @end group | |
1914 | ":" | |
1915 | 'default-directory | |
1916 | " " | |
1917 | 'global-mode-string | |
1918 | " %[(" | |
1919 | '(:eval (mode-line-mode-name)) | |
1920 | 'mode-line-process | |
1921 | 'minor-mode-alist | |
1922 | "%n" | |
1923 | ")%]--" | |
1924 | @group | |
1925 | '(which-func-mode ("" which-func-format "--")) | |
1926 | '(line-number-mode "L%l--") | |
1927 | '(column-number-mode "C%c--") | |
f700caa3 | 1928 | '(-3 "%p"))) |
b8d4c8d0 GM |
1929 | @end group |
1930 | @end example | |
1931 | ||
1932 | @noindent | |
1933 | (The variables @code{line-number-mode}, @code{column-number-mode} | |
1934 | and @code{which-func-mode} enable particular minor modes; as usual, | |
1935 | these variable names are also the minor mode command names.) | |
1936 | ||
1937 | @node Mode Line Variables | |
1938 | @subsection Variables Used in the Mode Line | |
1939 | ||
f700caa3 CY |
1940 | This section describes variables incorporated by the standard value of |
1941 | @code{mode-line-format} into the text of the mode line. There is | |
b8d4c8d0 | 1942 | nothing inherently special about these variables; any other variables |
f700caa3 CY |
1943 | could have the same effects on the mode line if the value of |
1944 | @code{mode-line-format} is changed to use them. However, various parts | |
1945 | of Emacs set these variables on the understanding that they will control | |
1946 | parts of the mode line; therefore, practically speaking, it is essential | |
1947 | for the mode line to use them. | |
b8d4c8d0 GM |
1948 | |
1949 | @defvar mode-line-mule-info | |
f700caa3 | 1950 | This variable holds the value of the mode line construct that displays |
b8d4c8d0 GM |
1951 | information about the language environment, buffer coding system, and |
1952 | current input method. @xref{Non-ASCII Characters}. | |
1953 | @end defvar | |
1954 | ||
1955 | @defvar mode-line-modified | |
f700caa3 | 1956 | This variable holds the value of the mode line construct that displays |
2079438a CY |
1957 | whether the current buffer is modified. Its default value displays |
1958 | @samp{**} if the buffer is modified, @samp{--} if the buffer is not | |
1959 | modified, @samp{%%} if the buffer is read only, and @samp{%*} if the | |
1960 | buffer is read only and modified. | |
b8d4c8d0 GM |
1961 | |
1962 | Changing this variable does not force an update of the mode line. | |
1963 | @end defvar | |
1964 | ||
1965 | @defvar mode-line-frame-identification | |
2079438a CY |
1966 | This variable identifies the current frame. Its default value |
1967 | displays @code{" "} if you are using a window system which can show | |
1968 | multiple frames, or @code{"-%F "} on an ordinary terminal which shows | |
1969 | only one frame at a time. | |
b8d4c8d0 GM |
1970 | @end defvar |
1971 | ||
1972 | @defvar mode-line-buffer-identification | |
2079438a CY |
1973 | This variable identifies the buffer being displayed in the window. |
1974 | Its default value displays the buffer name, padded with spaces to at | |
1975 | least 12 columns. | |
b8d4c8d0 GM |
1976 | @end defvar |
1977 | ||
01f17ae2 | 1978 | @defopt mode-line-position |
2079438a CY |
1979 | This variable indicates the position in the buffer. Its default value |
1980 | displays the buffer percentage and, optionally, the buffer size, the | |
1981 | line number and the column number. | |
01f17ae2 | 1982 | @end defopt |
b8d4c8d0 GM |
1983 | |
1984 | @defvar vc-mode | |
1985 | The variable @code{vc-mode}, buffer-local in each buffer, records | |
1986 | whether the buffer's visited file is maintained with version control, | |
1987 | and, if so, which kind. Its value is a string that appears in the mode | |
1988 | line, or @code{nil} for no version control. | |
1989 | @end defvar | |
1990 | ||
01f17ae2 | 1991 | @defopt mode-line-modes |
2079438a CY |
1992 | This variable displays the buffer's major and minor modes. Its |
1993 | default value also displays the recursive editing level, information | |
1994 | on the process status, and whether narrowing is in effect. | |
18d59e29 LMI |
1995 | @end defopt |
1996 | ||
0b128ac4 | 1997 | @defvar mode-line-remote |
18d59e29 LMI |
1998 | This variable is used to show whether @code{default-directory} for the |
1999 | current buffer is remote. | |
0b128ac4 | 2000 | @end defvar |
18d59e29 | 2001 | |
0b128ac4 | 2002 | @defvar mode-line-client |
18d59e29 | 2003 | This variable is used to identify @code{emacsclient} frames. |
0b128ac4 | 2004 | @end defvar |
b8d4c8d0 GM |
2005 | |
2006 | The following three variables are used in @code{mode-line-modes}: | |
2007 | ||
2008 | @defvar mode-name | |
2009 | This buffer-local variable holds the ``pretty'' name of the current | |
9cf52b11 EZ |
2010 | buffer's major mode. Each major mode should set this variable so that |
2011 | the mode name will appear in the mode line. The value does not have | |
2012 | to be a string, but can use any of the data types valid in a mode-line | |
2013 | construct (@pxref{Mode Line Data}). To compute the string that will | |
2014 | identify the mode name in the mode line, use @code{format-mode-line} | |
2015 | (@pxref{Emulating Mode Line}). | |
b8d4c8d0 GM |
2016 | @end defvar |
2017 | ||
2018 | @defvar mode-line-process | |
f700caa3 | 2019 | This buffer-local variable contains the mode line information on process |
b8d4c8d0 GM |
2020 | status in modes used for communicating with subprocesses. It is |
2021 | displayed immediately following the major mode name, with no intervening | |
2bb0eca1 | 2022 | space. For example, its value in the @file{*shell*} buffer is |
b8d4c8d0 GM |
2023 | @code{(":%s")}, which allows the shell to display its status along |
2024 | with the major mode as: @samp{(Shell:run)}. Normally this variable | |
2025 | is @code{nil}. | |
2026 | @end defvar | |
2027 | ||
2028 | @defvar minor-mode-alist | |
2029 | @anchor{Definition of minor-mode-alist} | |
2030 | This variable holds an association list whose elements specify how the | |
2031 | mode line should indicate that a minor mode is active. Each element of | |
2032 | the @code{minor-mode-alist} should be a two-element list: | |
2033 | ||
2034 | @example | |
2035 | (@var{minor-mode-variable} @var{mode-line-string}) | |
2036 | @end example | |
2037 | ||
f700caa3 CY |
2038 | More generally, @var{mode-line-string} can be any mode line construct. |
2039 | It appears in the mode line when the value of @var{minor-mode-variable} | |
b8d4c8d0 GM |
2040 | is non-@code{nil}, and not otherwise. These strings should begin with |
2041 | spaces so that they don't run together. Conventionally, the | |
f700caa3 CY |
2042 | @var{minor-mode-variable} for a specific mode is set to a non-@code{nil} |
2043 | value when that minor mode is activated. | |
b8d4c8d0 GM |
2044 | |
2045 | @code{minor-mode-alist} itself is not buffer-local. Each variable | |
2046 | mentioned in the alist should be buffer-local if its minor mode can be | |
2047 | enabled separately in each buffer. | |
2048 | @end defvar | |
2049 | ||
2050 | @defvar global-mode-string | |
f700caa3 CY |
2051 | This variable holds a mode line construct that, by default, appears in |
2052 | the mode line just after the @code{which-func-mode} minor mode if set, | |
2053 | else after @code{mode-line-modes}. The command @code{display-time} sets | |
2054 | @code{global-mode-string} to refer to the variable | |
2055 | @code{display-time-string}, which holds a string containing the time and | |
2056 | load information. | |
b8d4c8d0 GM |
2057 | |
2058 | The @samp{%M} construct substitutes the value of | |
2059 | @code{global-mode-string}, but that is obsolete, since the variable is | |
2060 | included in the mode line from @code{mode-line-format}. | |
2061 | @end defvar | |
2062 | ||
b8d4c8d0 | 2063 | Here is a simplified version of the default value of |
4e3b4528 | 2064 | @code{mode-line-format}. The real default value also |
b8d4c8d0 GM |
2065 | specifies addition of text properties. |
2066 | ||
2067 | @example | |
2068 | @group | |
2069 | ("-" | |
2070 | mode-line-mule-info | |
2071 | mode-line-modified | |
2072 | mode-line-frame-identification | |
2073 | mode-line-buffer-identification | |
2074 | @end group | |
2075 | " " | |
2076 | mode-line-position | |
2077 | (vc-mode vc-mode) | |
2078 | " " | |
2079 | @group | |
2080 | mode-line-modes | |
2081 | (which-func-mode ("" which-func-format "--")) | |
2082 | (global-mode-string ("--" global-mode-string)) | |
2083 | "-%-") | |
2084 | @end group | |
2085 | @end example | |
b8d4c8d0 GM |
2086 | |
2087 | @node %-Constructs | |
2088 | @subsection @code{%}-Constructs in the Mode Line | |
2089 | ||
f700caa3 | 2090 | Strings used as mode line constructs can use certain |
90d99fdf CY |
2091 | @code{%}-constructs to substitute various kinds of data. The |
2092 | following is a list of the defined @code{%}-constructs, and what they | |
2093 | mean. | |
2094 | ||
2095 | In any construct except @samp{%%}, you can add a decimal integer | |
2096 | after the @samp{%} to specify a minimum field width. If the width is | |
2097 | less, the field is padded to that width. Purely numeric constructs | |
2098 | (@samp{c}, @samp{i}, @samp{I}, and @samp{l}) are padded by inserting | |
2099 | spaces to the left, and others are padded by inserting spaces to the | |
2100 | right. | |
b8d4c8d0 GM |
2101 | |
2102 | @table @code | |
2103 | @item %b | |
2104 | The current buffer name, obtained with the @code{buffer-name} function. | |
2105 | @xref{Buffer Names}. | |
2106 | ||
2107 | @item %c | |
2108 | The current column number of point. | |
2109 | ||
2110 | @item %e | |
2111 | When Emacs is nearly out of memory for Lisp objects, a brief message | |
2112 | saying so. Otherwise, this is empty. | |
2113 | ||
2114 | @item %f | |
2115 | The visited file name, obtained with the @code{buffer-file-name} | |
2116 | function. @xref{Buffer File Name}. | |
2117 | ||
2118 | @item %F | |
2119 | The title (only on a window system) or the name of the selected frame. | |
2120 | @xref{Basic Parameters}. | |
2121 | ||
2122 | @item %i | |
2123 | The size of the accessible part of the current buffer; basically | |
2124 | @code{(- (point-max) (point-min))}. | |
2125 | ||
2126 | @item %I | |
2127 | Like @samp{%i}, but the size is printed in a more readable way by using | |
2128 | @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to | |
2129 | abbreviate. | |
2130 | ||
2131 | @item %l | |
2132 | The current line number of point, counting within the accessible portion | |
2133 | of the buffer. | |
2134 | ||
2135 | @item %n | |
2136 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
2137 | @code{narrow-to-region} in @ref{Narrowing}). | |
2138 | ||
2139 | @item %p | |
2140 | The percentage of the buffer text above the @strong{top} of window, or | |
f700caa3 CY |
2141 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default mode |
2142 | line construct truncates this to three characters. | |
b8d4c8d0 GM |
2143 | |
2144 | @item %P | |
2145 | The percentage of the buffer text that is above the @strong{bottom} of | |
2146 | the window (which includes the text visible in the window, as well as | |
2147 | the text above the top), plus @samp{Top} if the top of the buffer is | |
2148 | visible on screen; or @samp{Bottom} or @samp{All}. | |
2149 | ||
2150 | @item %s | |
2151 | The status of the subprocess belonging to the current buffer, obtained with | |
2152 | @code{process-status}. @xref{Process Information}. | |
2153 | ||
b8d4c8d0 GM |
2154 | @item %z |
2155 | The mnemonics of keyboard, terminal, and buffer coding systems. | |
2156 | ||
2157 | @item %Z | |
2158 | Like @samp{%z}, but including the end-of-line format. | |
2159 | ||
2160 | @item %* | |
2161 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2162 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2163 | @samp{-} otherwise. @xref{Buffer Modification}. | |
2164 | ||
2165 | @item %+ | |
2166 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2167 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2168 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
2169 | read-only buffer. @xref{Buffer Modification}. | |
2170 | ||
2171 | @item %& | |
2172 | @samp{*} if the buffer is modified, and @samp{-} otherwise. | |
2173 | ||
2174 | @item %[ | |
2175 | An indication of the depth of recursive editing levels (not counting | |
2176 | minibuffer levels): one @samp{[} for each editing level. | |
2177 | @xref{Recursive Editing}. | |
2178 | ||
2179 | @item %] | |
2180 | One @samp{]} for each recursive editing level (not counting minibuffer | |
2181 | levels). | |
2182 | ||
2183 | @item %- | |
2184 | Dashes sufficient to fill the remainder of the mode line. | |
2185 | ||
2186 | @item %% | |
2187 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
2188 | string in which @code{%}-constructs are allowed. | |
2189 | @end table | |
2190 | ||
2191 | The following two @code{%}-constructs are still supported, but they are | |
2192 | obsolete, since you can get the same results with the variables | |
2193 | @code{mode-name} and @code{global-mode-string}. | |
2194 | ||
2195 | @table @code | |
2196 | @item %m | |
2197 | The value of @code{mode-name}. | |
2198 | ||
2199 | @item %M | |
2200 | The value of @code{global-mode-string}. | |
2201 | @end table | |
2202 | ||
2203 | @node Properties in Mode | |
2204 | @subsection Properties in the Mode Line | |
2205 | @cindex text properties in the mode line | |
2206 | ||
2207 | Certain text properties are meaningful in the | |
2208 | mode line. The @code{face} property affects the appearance of text; the | |
2209 | @code{help-echo} property associates help strings with the text, and | |
9716fedb | 2210 | @code{keymap} can make the text mouse-sensitive. |
b8d4c8d0 GM |
2211 | |
2212 | There are four ways to specify text properties for text in the mode | |
2213 | line: | |
2214 | ||
2215 | @enumerate | |
2216 | @item | |
f700caa3 | 2217 | Put a string with a text property directly into the mode line data |
b8d4c8d0 GM |
2218 | structure. |
2219 | ||
2220 | @item | |
f700caa3 | 2221 | Put a text property on a mode line %-construct such as @samp{%12b}; then |
b8d4c8d0 GM |
2222 | the expansion of the %-construct will have that same text property. |
2223 | ||
2224 | @item | |
2225 | Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to | |
2226 | give @var{elt} a text property specified by @var{props}. | |
2227 | ||
2228 | @item | |
f700caa3 | 2229 | Use a list containing @code{:eval @var{form}} in the mode line data |
b8d4c8d0 GM |
2230 | structure, and make @var{form} evaluate to a string that has a text |
2231 | property. | |
2232 | @end enumerate | |
2233 | ||
9716fedb | 2234 | You can use the @code{keymap} property to specify a keymap. This |
b8d4c8d0 GM |
2235 | keymap only takes real effect for mouse clicks; binding character keys |
2236 | and function keys to it has no effect, since it is impossible to move | |
2237 | point into the mode line. | |
2238 | ||
2239 | When the mode line refers to a variable which does not have a | |
2240 | non-@code{nil} @code{risky-local-variable} property, any text | |
2241 | properties given or specified within that variable's values are | |
2242 | ignored. This is because such properties could otherwise specify | |
2243 | functions to be called, and those functions could come from file | |
2244 | local variables. | |
2245 | ||
2246 | @node Header Lines | |
2247 | @subsection Window Header Lines | |
2248 | @cindex header line (of a window) | |
2249 | @cindex window header line | |
2250 | ||
f700caa3 CY |
2251 | A window can have a @dfn{header line} at the top, just as it can have |
2252 | a mode line at the bottom. The header line feature works just like the | |
2253 | mode line feature, except that it's controlled by | |
2254 | @code{header-line-format}: | |
b8d4c8d0 GM |
2255 | |
2256 | @defvar header-line-format | |
2257 | This variable, local in every buffer, specifies how to display the | |
2258 | header line, for windows displaying the buffer. The format of the value | |
2259 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). | |
b8d4c8d0 GM |
2260 | It is normally @code{nil}, so that ordinary buffers have no header line. |
2261 | @end defvar | |
2262 | ||
2263 | A window that is just one line tall never displays a header line. A | |
2264 | window that is two lines tall cannot display both a mode line and a | |
2265 | header line at once; if it has a mode line, then it does not display a | |
2266 | header line. | |
2267 | ||
2268 | @node Emulating Mode Line | |
f700caa3 | 2269 | @subsection Emulating Mode Line Formatting |
b8d4c8d0 | 2270 | |
f700caa3 CY |
2271 | You can use the function @code{format-mode-line} to compute the text |
2272 | that would appear in a mode line or header line based on a certain | |
2273 | mode line construct. | |
b8d4c8d0 GM |
2274 | |
2275 | @defun format-mode-line format &optional face window buffer | |
287e63bb EZ |
2276 | This function formats a line of text according to @var{format} as if it |
2277 | were generating the mode line for @var{window}, but it also returns the | |
2278 | text as a string. The argument @var{window} defaults to the selected | |
2279 | window. If @var{buffer} is non-@code{nil}, all the information used is | |
2280 | taken from @var{buffer}; by default, it comes from @var{window}'s | |
2281 | buffer. | |
b8d4c8d0 GM |
2282 | |
2283 | The value string normally has text properties that correspond to the | |
2e4ab211 EZ |
2284 | faces, keymaps, etc., that the mode line would have. Any character for |
2285 | which no @code{face} property is specified by @var{format} gets a | |
2286 | default value determined by @var{face}. If @var{face} is @code{t}, that | |
2287 | stands for either @code{mode-line} if @var{window} is selected, | |
b8d4c8d0 | 2288 | otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or |
2e4ab211 EZ |
2289 | omitted, that stands for the default face. If @var{face} is an integer, |
2290 | the value returned by this function will have no text properties. | |
b8d4c8d0 | 2291 | |
287e63bb | 2292 | You can also specify other valid faces as the value of @var{face}. |
2e4ab211 EZ |
2293 | If specified, that face provides the @code{face} property for characters |
2294 | whose face is not specified by @var{format}. | |
287e63bb EZ |
2295 | |
2296 | Note that using @code{mode-line}, @code{mode-line-inactive}, or | |
2297 | @code{header-line} as @var{face} will actually redisplay the mode line | |
2298 | or the header line, respectively, using the current definitions of the | |
2299 | corresponding face, in addition to returning the formatted string. | |
2300 | (Other faces do not cause redisplay.) | |
b8d4c8d0 GM |
2301 | |
2302 | For example, @code{(format-mode-line header-line-format)} returns the | |
2303 | text that would appear in the selected window's header line (@code{""} | |
2304 | if it has no header line). @code{(format-mode-line header-line-format | |
2305 | 'header-line)} returns the same text, with each character | |
287e63bb EZ |
2306 | carrying the face that it will have in the header line itself, and also |
2307 | redraws the header line. | |
b8d4c8d0 GM |
2308 | @end defun |
2309 | ||
2310 | @node Imenu | |
2311 | @section Imenu | |
2312 | ||
2313 | @cindex Imenu | |
2314 | @dfn{Imenu} is a feature that lets users select a definition or | |
2315 | section in the buffer, from a menu which lists all of them, to go | |
2316 | directly to that location in the buffer. Imenu works by constructing | |
2317 | a buffer index which lists the names and buffer positions of the | |
2318 | definitions, or other named portions of the buffer; then the user can | |
2319 | choose one of them and move point to it. Major modes can add a menu | |
2320 | bar item to use Imenu using @code{imenu-add-to-menubar}. | |
2321 | ||
0b128ac4 | 2322 | @deffn Command imenu-add-to-menubar name |
b8d4c8d0 GM |
2323 | This function defines a local menu bar item named @var{name} |
2324 | to run Imenu. | |
0b128ac4 | 2325 | @end deffn |
b8d4c8d0 GM |
2326 | |
2327 | The user-level commands for using Imenu are described in the Emacs | |
2328 | Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section | |
2329 | explains how to customize Imenu's method of finding definitions or | |
2330 | buffer portions for a particular major mode. | |
2331 | ||
2332 | The usual and simplest way is to set the variable | |
2333 | @code{imenu-generic-expression}: | |
2334 | ||
2335 | @defvar imenu-generic-expression | |
2336 | This variable, if non-@code{nil}, is a list that specifies regular | |
2337 | expressions for finding definitions for Imenu. Simple elements of | |
2338 | @code{imenu-generic-expression} look like this: | |
2339 | ||
2340 | @example | |
2341 | (@var{menu-title} @var{regexp} @var{index}) | |
2342 | @end example | |
2343 | ||
2344 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches | |
2345 | for this element should go in a submenu of the buffer index; | |
2346 | @var{menu-title} itself specifies the name for the submenu. If | |
2347 | @var{menu-title} is @code{nil}, the matches for this element go directly | |
2348 | in the top level of the buffer index. | |
2349 | ||
2350 | The second item in the list, @var{regexp}, is a regular expression | |
2351 | (@pxref{Regular Expressions}); anything in the buffer that it matches | |
2352 | is considered a definition, something to mention in the buffer index. | |
2353 | The third item, @var{index}, is a non-negative integer that indicates | |
2354 | which subexpression in @var{regexp} matches the definition's name. | |
2355 | ||
2356 | An element can also look like this: | |
2357 | ||
2358 | @example | |
2359 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) | |
2360 | @end example | |
2361 | ||
2362 | Each match for this element creates an index item, and when the index | |
2363 | item is selected by the user, it calls @var{function} with arguments | |
2364 | consisting of the item name, the buffer position, and @var{arguments}. | |
2365 | ||
2366 | For Emacs Lisp mode, @code{imenu-generic-expression} could look like | |
2367 | this: | |
2368 | ||
2369 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] | |
2370 | @example | |
2371 | @group | |
2372 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ | |
2373 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2374 | @end group | |
2375 | @group | |
2376 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ | |
2377 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2378 | @end group | |
2379 | @group | |
2380 | ("*Types*" | |
2381 | "^\\s-*\ | |
2382 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ | |
2383 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) | |
2384 | @end group | |
2385 | @end example | |
2386 | ||
2387 | Setting this variable makes it buffer-local in the current buffer. | |
2388 | @end defvar | |
2389 | ||
2390 | @defvar imenu-case-fold-search | |
2391 | This variable controls whether matching against the regular | |
2392 | expressions in the value of @code{imenu-generic-expression} is | |
2393 | case-sensitive: @code{t}, the default, means matching should ignore | |
2394 | case. | |
2395 | ||
2396 | Setting this variable makes it buffer-local in the current buffer. | |
2397 | @end defvar | |
2398 | ||
2399 | @defvar imenu-syntax-alist | |
2400 | This variable is an alist of syntax table modifiers to use while | |
2401 | processing @code{imenu-generic-expression}, to override the syntax table | |
2402 | of the current buffer. Each element should have this form: | |
2403 | ||
2404 | @example | |
2405 | (@var{characters} . @var{syntax-description}) | |
2406 | @end example | |
2407 | ||
2408 | The @sc{car}, @var{characters}, can be either a character or a string. | |
2409 | The element says to give that character or characters the syntax | |
2410 | specified by @var{syntax-description}, which is passed to | |
2411 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). | |
2412 | ||
2413 | This feature is typically used to give word syntax to characters which | |
2414 | normally have symbol syntax, and thus to simplify | |
2415 | @code{imenu-generic-expression} and speed up matching. | |
2416 | For example, Fortran mode uses it this way: | |
2417 | ||
2418 | @example | |
2419 | (setq imenu-syntax-alist '(("_$" . "w"))) | |
2420 | @end example | |
2421 | ||
2422 | The @code{imenu-generic-expression} regular expressions can then use | |
2423 | @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this | |
2424 | technique may be inconvenient when the mode needs to limit the initial | |
2425 | character of a name to a smaller set of characters than are allowed in | |
2426 | the rest of a name. | |
2427 | ||
2428 | Setting this variable makes it buffer-local in the current buffer. | |
2429 | @end defvar | |
2430 | ||
2431 | Another way to customize Imenu for a major mode is to set the | |
2432 | variables @code{imenu-prev-index-position-function} and | |
2433 | @code{imenu-extract-index-name-function}: | |
2434 | ||
2435 | @defvar imenu-prev-index-position-function | |
2436 | If this variable is non-@code{nil}, its value should be a function that | |
2437 | finds the next ``definition'' to put in the buffer index, scanning | |
2438 | backward in the buffer from point. It should return @code{nil} if it | |
2439 | doesn't find another ``definition'' before point. Otherwise it should | |
2440 | leave point at the place it finds a ``definition'' and return any | |
2441 | non-@code{nil} value. | |
2442 | ||
2443 | Setting this variable makes it buffer-local in the current buffer. | |
2444 | @end defvar | |
2445 | ||
2446 | @defvar imenu-extract-index-name-function | |
2447 | If this variable is non-@code{nil}, its value should be a function to | |
2448 | return the name for a definition, assuming point is in that definition | |
2449 | as the @code{imenu-prev-index-position-function} function would leave | |
2450 | it. | |
2451 | ||
2452 | Setting this variable makes it buffer-local in the current buffer. | |
2453 | @end defvar | |
2454 | ||
2455 | The last way to customize Imenu for a major mode is to set the | |
2456 | variable @code{imenu-create-index-function}: | |
2457 | ||
2458 | @defvar imenu-create-index-function | |
2459 | This variable specifies the function to use for creating a buffer | |
2460 | index. The function should take no arguments, and return an index | |
2461 | alist for the current buffer. It is called within | |
2462 | @code{save-excursion}, so where it leaves point makes no difference. | |
2463 | ||
2464 | The index alist can have three types of elements. Simple elements | |
2465 | look like this: | |
2466 | ||
2467 | @example | |
2468 | (@var{index-name} . @var{index-position}) | |
2469 | @end example | |
2470 | ||
2471 | Selecting a simple element has the effect of moving to position | |
2472 | @var{index-position} in the buffer. Special elements look like this: | |
2473 | ||
2474 | @example | |
2475 | (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{}) | |
2476 | @end example | |
2477 | ||
2478 | Selecting a special element performs: | |
2479 | ||
2480 | @example | |
2481 | (funcall @var{function} | |
2482 | @var{index-name} @var{index-position} @var{arguments}@dots{}) | |
2483 | @end example | |
2484 | ||
2485 | A nested sub-alist element looks like this: | |
2486 | ||
2487 | @example | |
c8f0efc2 | 2488 | (@var{menu-title} . @var{sub-alist}) |
b8d4c8d0 GM |
2489 | @end example |
2490 | ||
2491 | It creates the submenu @var{menu-title} specified by @var{sub-alist}. | |
2492 | ||
2493 | The default value of @code{imenu-create-index-function} is | |
2494 | @code{imenu-default-create-index-function}. This function calls the | |
2495 | value of @code{imenu-prev-index-position-function} and the value of | |
2496 | @code{imenu-extract-index-name-function} to produce the index alist. | |
2497 | However, if either of these two variables is @code{nil}, the default | |
2498 | function uses @code{imenu-generic-expression} instead. | |
2499 | ||
2500 | Setting this variable makes it buffer-local in the current buffer. | |
2501 | @end defvar | |
2502 | ||
2503 | @node Font Lock Mode | |
2504 | @section Font Lock Mode | |
2505 | @cindex Font Lock mode | |
2506 | ||
f700caa3 CY |
2507 | @dfn{Font Lock mode} is a buffer-local minor mode that automatically |
2508 | attaches @code{face} properties to certain parts of the buffer based on | |
2509 | their syntactic role. How it parses the buffer depends on the major | |
2510 | mode; most major modes define syntactic criteria for which faces to use | |
2511 | in which contexts. This section explains how to customize Font Lock for | |
2512 | a particular major mode. | |
b8d4c8d0 GM |
2513 | |
2514 | Font Lock mode finds text to highlight in two ways: through | |
2515 | syntactic parsing based on the syntax table, and through searching | |
2516 | (usually for regular expressions). Syntactic fontification happens | |
2517 | first; it finds comments and string constants and highlights them. | |
2518 | Search-based fontification happens second. | |
2519 | ||
2520 | @menu | |
2521 | * Font Lock Basics:: Overview of customizing Font Lock. | |
2522 | * Search-based Fontification:: Fontification based on regexps. | |
2523 | * Customizing Keywords:: Customizing search-based fontification. | |
2524 | * Other Font Lock Variables:: Additional customization facilities. | |
2525 | * Levels of Font Lock:: Each mode can define alternative levels | |
2526 | so that the user can select more or less. | |
769741e3 | 2527 | * Precalculated Fontification:: How Lisp programs that produce the buffer |
b8d4c8d0 GM |
2528 | contents can also specify how to fontify it. |
2529 | * Faces for Font Lock:: Special faces specifically for Font Lock. | |
2530 | * Syntactic Font Lock:: Fontification based on syntax tables. | |
b8d4c8d0 GM |
2531 | * Multiline Font Lock:: How to coerce Font Lock into properly |
2532 | highlighting multiline constructs. | |
2533 | @end menu | |
2534 | ||
2535 | @node Font Lock Basics | |
2536 | @subsection Font Lock Basics | |
2537 | ||
2538 | There are several variables that control how Font Lock mode highlights | |
2539 | text. But major modes should not set any of these variables directly. | |
2540 | Instead, they should set @code{font-lock-defaults} as a buffer-local | |
2541 | variable. The value assigned to this variable is used, if and when Font | |
2542 | Lock mode is enabled, to set all the other variables. | |
2543 | ||
2544 | @defvar font-lock-defaults | |
f700caa3 CY |
2545 | This variable is set by major modes to specify how to fontify text in |
2546 | that mode. It automatically becomes buffer-local when set. If its | |
2547 | value is @code{nil}, Font Lock mode does no highlighting, and you can | |
2548 | use the @samp{Faces} menu (under @samp{Edit} and then @samp{Text | |
2549 | Properties} in the menu bar) to assign faces explicitly to text in the | |
2550 | buffer. | |
b8d4c8d0 GM |
2551 | |
2552 | If non-@code{nil}, the value should look like this: | |
2553 | ||
2554 | @example | |
2555 | (@var{keywords} [@var{keywords-only} [@var{case-fold} | |
2556 | [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]]) | |
2557 | @end example | |
2558 | ||
2559 | The first element, @var{keywords}, indirectly specifies the value of | |
2560 | @code{font-lock-keywords} which directs search-based fontification. | |
2561 | It can be a symbol, a variable or a function whose value is the list | |
2562 | to use for @code{font-lock-keywords}. It can also be a list of | |
2563 | several such symbols, one for each possible level of fontification. | |
caef3ed2 GM |
2564 | The first symbol specifies the @samp{mode default} level of |
2565 | fontification, the next symbol level 1 fontification, the next level 2, | |
2566 | and so on. The @samp{mode default} level is normally the same as level | |
2567 | 1. It is used when @code{font-lock-maximum-decoration} has a @code{nil} | |
2568 | value. @xref{Levels of Font Lock}. | |
b8d4c8d0 GM |
2569 | |
2570 | The second element, @var{keywords-only}, specifies the value of the | |
2571 | variable @code{font-lock-keywords-only}. If this is omitted or | |
2572 | @code{nil}, syntactic fontification (of strings and comments) is also | |
f700caa3 | 2573 | performed. If this is non-@code{nil}, syntactic fontification is not |
b8d4c8d0 GM |
2574 | performed. @xref{Syntactic Font Lock}. |
2575 | ||
2576 | The third element, @var{case-fold}, specifies the value of | |
2577 | @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, | |
f700caa3 | 2578 | Font Lock mode ignores case during search-based fontification. |
b8d4c8d0 | 2579 | |
f700caa3 CY |
2580 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it should |
2581 | be a list of cons cells of the form @code{(@var{char-or-string} | |
2582 | . @var{string})}. These are used to set up a syntax table for syntactic | |
2583 | fontification; the resulting syntax table is stored in | |
2584 | @code{font-lock-syntax-table}. If @var{syntax-alist} is omitted or | |
2585 | @code{nil}, syntactic fontification uses the syntax table returned by | |
2586 | the @code{syntax-table} function. @xref{Syntax Table Functions}. | |
b8d4c8d0 GM |
2587 | |
2588 | The fifth element, @var{syntax-begin}, specifies the value of | |
2589 | @code{font-lock-beginning-of-syntax-function}. We recommend setting | |
2590 | this variable to @code{nil} and using @code{syntax-begin-function} | |
2591 | instead. | |
2592 | ||
2593 | All the remaining elements (if any) are collectively called | |
2594 | @var{other-vars}. Each of these elements should have the form | |
2595 | @code{(@var{variable} . @var{value})}---which means, make | |
2596 | @var{variable} buffer-local and then set it to @var{value}. You can | |
2597 | use these @var{other-vars} to set other variables that affect | |
2598 | fontification, aside from those you can control with the first five | |
2599 | elements. @xref{Other Font Lock Variables}. | |
2600 | @end defvar | |
2601 | ||
2602 | If your mode fontifies text explicitly by adding | |
2603 | @code{font-lock-face} properties, it can specify @code{(nil t)} for | |
2604 | @code{font-lock-defaults} to turn off all automatic fontification. | |
2605 | However, this is not required; it is possible to fontify some things | |
2606 | using @code{font-lock-face} properties and set up automatic | |
2607 | fontification for other parts of the text. | |
2608 | ||
2609 | @node Search-based Fontification | |
2610 | @subsection Search-based Fontification | |
2611 | ||
f700caa3 CY |
2612 | The variable which directly controls search-based fontification is |
2613 | @code{font-lock-keywords}, which is typically specified via the | |
2614 | @var{keywords} element in @code{font-lock-defaults}. | |
b8d4c8d0 GM |
2615 | |
2616 | @defvar font-lock-keywords | |
f700caa3 CY |
2617 | The value of this variable is a list of the keywords to highlight. Lisp |
2618 | programs should not set this variable directly. Normally, the value is | |
2619 | automatically set by Font Lock mode, using the @var{keywords} element in | |
2620 | @code{font-lock-defaults}. The value can also be altered using the | |
2621 | functions @code{font-lock-add-keywords} and | |
2622 | @code{font-lock-remove-keywords} (@pxref{Customizing Keywords}). | |
b8d4c8d0 GM |
2623 | @end defvar |
2624 | ||
2625 | Each element of @code{font-lock-keywords} specifies how to find | |
2626 | certain cases of text, and how to highlight those cases. Font Lock mode | |
2627 | processes the elements of @code{font-lock-keywords} one by one, and for | |
2628 | each element, it finds and handles all matches. Ordinarily, once | |
2629 | part of the text has been fontified already, this cannot be overridden | |
2630 | by a subsequent match in the same text; but you can specify different | |
2631 | behavior using the @var{override} element of a @var{subexp-highlighter}. | |
2632 | ||
2633 | Each element of @code{font-lock-keywords} should have one of these | |
2634 | forms: | |
2635 | ||
2636 | @table @code | |
2637 | @item @var{regexp} | |
2638 | Highlight all matches for @var{regexp} using | |
2639 | @code{font-lock-keyword-face}. For example, | |
2640 | ||
2641 | @example | |
2642 | ;; @r{Highlight occurrences of the word @samp{foo}} | |
2643 | ;; @r{using @code{font-lock-keyword-face}.} | |
2644 | "\\<foo\\>" | |
2645 | @end example | |
2646 | ||
f700caa3 CY |
2647 | Be careful when composing these regular expressions; a poorly written |
2648 | pattern can dramatically slow things down! The function | |
2649 | @code{regexp-opt} (@pxref{Regexp Functions}) is useful for calculating | |
2650 | optimal regular expressions to match several keywords. | |
b8d4c8d0 GM |
2651 | |
2652 | @item @var{function} | |
2653 | Find text by calling @var{function}, and highlight the matches | |
2654 | it finds using @code{font-lock-keyword-face}. | |
2655 | ||
2656 | When @var{function} is called, it receives one argument, the limit of | |
2657 | the search; it should begin searching at point, and not search beyond the | |
2658 | limit. It should return non-@code{nil} if it succeeds, and set the | |
2659 | match data to describe the match that was found. Returning @code{nil} | |
2660 | indicates failure of the search. | |
2661 | ||
2662 | Fontification will call @var{function} repeatedly with the same limit, | |
2663 | and with point where the previous invocation left it, until | |
2664 | @var{function} fails. On failure, @var{function} need not reset point | |
2665 | in any particular way. | |
2666 | ||
2667 | @item (@var{matcher} . @var{subexp}) | |
2668 | In this kind of element, @var{matcher} is either a regular | |
2669 | expression or a function, as described above. The @sc{cdr}, | |
2670 | @var{subexp}, specifies which subexpression of @var{matcher} should be | |
2671 | highlighted (instead of the entire text that @var{matcher} matched). | |
2672 | ||
2673 | @example | |
2674 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} | |
2675 | ;; @r{using @code{font-lock-keyword-face}.} | |
2676 | ("fu\\(bar\\)" . 1) | |
2677 | @end example | |
2678 | ||
2679 | If you use @code{regexp-opt} to produce the regular expression | |
2680 | @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp | |
2681 | Functions}) to calculate the value for @var{subexp}. | |
2682 | ||
2683 | @item (@var{matcher} . @var{facespec}) | |
2684 | In this kind of element, @var{facespec} is an expression whose value | |
2685 | specifies the face to use for highlighting. In the simplest case, | |
2686 | @var{facespec} is a Lisp variable (a symbol) whose value is a face | |
2687 | name. | |
2688 | ||
2689 | @example | |
2690 | ;; @r{Highlight occurrences of @samp{fubar},} | |
2691 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2692 | ("fubar" . fubar-face) | |
2693 | @end example | |
2694 | ||
2695 | However, @var{facespec} can also evaluate to a list of this form: | |
2696 | ||
2697 | @example | |
2698 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) | |
2699 | @end example | |
2700 | ||
2701 | @noindent | |
2702 | to specify the face @var{face} and various additional text properties | |
2703 | to put on the text that matches. If you do this, be sure to add the | |
2704 | other text property names that you set in this way to the value of | |
2705 | @code{font-lock-extra-managed-props} so that the properties will also | |
2706 | be cleared out when they are no longer appropriate. Alternatively, | |
2707 | you can set the variable @code{font-lock-unfontify-region-function} to | |
2708 | a function that clears these properties. @xref{Other Font Lock | |
2709 | Variables}. | |
2710 | ||
2711 | @item (@var{matcher} . @var{subexp-highlighter}) | |
2712 | In this kind of element, @var{subexp-highlighter} is a list | |
2713 | which specifies how to highlight matches found by @var{matcher}. | |
2714 | It has the form: | |
2715 | ||
2716 | @example | |
e6c815ae | 2717 | (@var{subexp} @var{facespec} [@var{override} [@var{laxmatch}]]) |
b8d4c8d0 GM |
2718 | @end example |
2719 | ||
2720 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression | |
2721 | of the match to fontify (0 means the entire matching text). The second | |
2722 | subelement, @var{facespec}, is an expression whose value specifies the | |
2723 | face, as described above. | |
2724 | ||
2725 | The last two values in @var{subexp-highlighter}, @var{override} and | |
2726 | @var{laxmatch}, are optional flags. If @var{override} is @code{t}, | |
2727 | this element can override existing fontification made by previous | |
2728 | elements of @code{font-lock-keywords}. If it is @code{keep}, then | |
2729 | each character is fontified if it has not been fontified already by | |
2730 | some other element. If it is @code{prepend}, the face specified by | |
2731 | @var{facespec} is added to the beginning of the @code{font-lock-face} | |
2732 | property. If it is @code{append}, the face is added to the end of the | |
2733 | @code{font-lock-face} property. | |
2734 | ||
2735 | If @var{laxmatch} is non-@code{nil}, it means there should be no error | |
2736 | if there is no subexpression numbered @var{subexp} in @var{matcher}. | |
2737 | Obviously, fontification of the subexpression numbered @var{subexp} will | |
2738 | not occur. However, fontification of other subexpressions (and other | |
2739 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the | |
2740 | specified subexpression is missing, then an error is signaled which | |
2741 | terminates search-based fontification. | |
2742 | ||
2743 | Here are some examples of elements of this kind, and what they do: | |
2744 | ||
2745 | @smallexample | |
2746 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using} | |
2747 | ;; @r{@code{foo-bar-face}, even if they have already been highlighted.} | |
2748 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} | |
2749 | ("foo\\|bar" 0 foo-bar-face t) | |
2750 | ||
2751 | ;; @r{Highlight the first subexpression within each occurrence} | |
2752 | ;; @r{that the function @code{fubar-match} finds,} | |
2753 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2754 | (fubar-match 1 fubar-face) | |
2755 | @end smallexample | |
2756 | ||
2757 | @item (@var{matcher} . @var{anchored-highlighter}) | |
2758 | In this kind of element, @var{anchored-highlighter} specifies how to | |
2759 | highlight text that follows a match found by @var{matcher}. So a | |
2760 | match found by @var{matcher} acts as the anchor for further searches | |
2761 | specified by @var{anchored-highlighter}. @var{anchored-highlighter} | |
2762 | is a list of the following form: | |
2763 | ||
2764 | @example | |
2765 | (@var{anchored-matcher} @var{pre-form} @var{post-form} | |
2766 | @var{subexp-highlighters}@dots{}) | |
2767 | @end example | |
2768 | ||
2769 | Here, @var{anchored-matcher}, like @var{matcher}, is either a regular | |
2770 | expression or a function. After a match of @var{matcher} is found, | |
2771 | point is at the end of the match. Now, Font Lock evaluates the form | |
2772 | @var{pre-form}. Then it searches for matches of | |
2773 | @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight | |
2774 | these. A @var{subexp-highlighter} is as described above. Finally, | |
2775 | Font Lock evaluates @var{post-form}. | |
2776 | ||
2777 | The forms @var{pre-form} and @var{post-form} can be used to initialize | |
2778 | before, and cleanup after, @var{anchored-matcher} is used. Typically, | |
2779 | @var{pre-form} is used to move point to some position relative to the | |
2780 | match of @var{matcher}, before starting with @var{anchored-matcher}. | |
2781 | @var{post-form} might be used to move back, before resuming with | |
2782 | @var{matcher}. | |
2783 | ||
2784 | After Font Lock evaluates @var{pre-form}, it does not search for | |
2785 | @var{anchored-matcher} beyond the end of the line. However, if | |
2786 | @var{pre-form} returns a buffer position that is greater than the | |
2787 | position of point after @var{pre-form} is evaluated, then the position | |
2788 | returned by @var{pre-form} is used as the limit of the search instead. | |
2789 | It is generally a bad idea to return a position greater than the end | |
2790 | of the line; in other words, the @var{anchored-matcher} search should | |
2791 | not span lines. | |
2792 | ||
2793 | For example, | |
2794 | ||
2795 | @smallexample | |
2796 | ;; @r{Highlight occurrences of the word @samp{item} following} | |
2797 | ;; @r{an occurrence of the word @samp{anchor} (on the same line)} | |
2798 | ;; @r{in the value of @code{item-face}.} | |
2799 | ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) | |
2800 | @end smallexample | |
2801 | ||
2802 | Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore | |
2803 | searching for @samp{item} starts at the end of the match of | |
2804 | @samp{anchor}, and searching for subsequent instances of @samp{anchor} | |
2805 | resumes from where searching for @samp{item} concluded. | |
2806 | ||
2807 | @item (@var{matcher} @var{highlighters}@dots{}) | |
2808 | This sort of element specifies several @var{highlighter} lists for a | |
2809 | single @var{matcher}. A @var{highlighter} list can be of the type | |
2810 | @var{subexp-highlighter} or @var{anchored-highlighter} as described | |
2811 | above. | |
2812 | ||
2813 | For example, | |
2814 | ||
2815 | @smallexample | |
2816 | ;; @r{Highlight occurrences of the word @samp{anchor} in the value} | |
2817 | ;; @r{of @code{anchor-face}, and subsequent occurrences of the word} | |
2818 | ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.} | |
2819 | ("\\<anchor\\>" (0 anchor-face) | |
2820 | ("\\<item\\>" nil nil (0 item-face))) | |
2821 | @end smallexample | |
2822 | ||
2823 | @item (eval . @var{form}) | |
2824 | Here @var{form} is an expression to be evaluated the first time | |
2825 | this value of @code{font-lock-keywords} is used in a buffer. | |
2826 | Its value should have one of the forms described in this table. | |
2827 | @end table | |
2828 | ||
2829 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} | |
2830 | to match text which spans lines; this does not work reliably. | |
2831 | For details, see @xref{Multiline Font Lock}. | |
2832 | ||
2833 | You can use @var{case-fold} in @code{font-lock-defaults} to specify | |
2834 | the value of @code{font-lock-keywords-case-fold-search} which says | |
2835 | whether search-based fontification should be case-insensitive. | |
2836 | ||
2837 | @defvar font-lock-keywords-case-fold-search | |
2838 | Non-@code{nil} means that regular expression matching for the sake of | |
2839 | @code{font-lock-keywords} should be case-insensitive. | |
2840 | @end defvar | |
2841 | ||
2842 | @node Customizing Keywords | |
2843 | @subsection Customizing Search-Based Fontification | |
2844 | ||
2845 | You can use @code{font-lock-add-keywords} to add additional | |
2846 | search-based fontification rules to a major mode, and | |
867d4bb3 | 2847 | @code{font-lock-remove-keywords} to remove rules. |
b8d4c8d0 GM |
2848 | |
2849 | @defun font-lock-add-keywords mode keywords &optional how | |
2850 | This function adds highlighting @var{keywords}, for the current buffer | |
2851 | or for major mode @var{mode}. The argument @var{keywords} should be a | |
2852 | list with the same format as the variable @code{font-lock-keywords}. | |
2853 | ||
2854 | If @var{mode} is a symbol which is a major mode command name, such as | |
2855 | @code{c-mode}, the effect is that enabling Font Lock mode in | |
2856 | @var{mode} will add @var{keywords} to @code{font-lock-keywords}. | |
2857 | Calling with a non-@code{nil} value of @var{mode} is correct only in | |
2858 | your @file{~/.emacs} file. | |
2859 | ||
2860 | If @var{mode} is @code{nil}, this function adds @var{keywords} to | |
2861 | @code{font-lock-keywords} in the current buffer. This way of calling | |
2862 | @code{font-lock-add-keywords} is usually used in mode hook functions. | |
2863 | ||
2864 | By default, @var{keywords} are added at the beginning of | |
2865 | @code{font-lock-keywords}. If the optional argument @var{how} is | |
2866 | @code{set}, they are used to replace the value of | |
2867 | @code{font-lock-keywords}. If @var{how} is any other non-@code{nil} | |
2868 | value, they are added at the end of @code{font-lock-keywords}. | |
2869 | ||
2870 | Some modes provide specialized support you can use in additional | |
2871 | highlighting patterns. See the variables | |
2872 | @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types}, | |
2873 | and @code{java-font-lock-extra-types}, for example. | |
2874 | ||
f700caa3 | 2875 | @strong{Warning:} Major mode commands must not call |
b8d4c8d0 | 2876 | @code{font-lock-add-keywords} under any circumstances, either directly |
3fd50d5c CY |
2877 | or indirectly, except through their mode hooks. (Doing so would lead to |
2878 | incorrect behavior for some minor modes.) They should set up their | |
b8d4c8d0 GM |
2879 | rules for search-based fontification by setting |
2880 | @code{font-lock-keywords}. | |
2881 | @end defun | |
2882 | ||
2883 | @defun font-lock-remove-keywords mode keywords | |
2884 | This function removes @var{keywords} from @code{font-lock-keywords} | |
2885 | for the current buffer or for major mode @var{mode}. As in | |
2886 | @code{font-lock-add-keywords}, @var{mode} should be a major mode | |
2887 | command name or @code{nil}. All the caveats and requirements for | |
2888 | @code{font-lock-add-keywords} apply here too. | |
2889 | @end defun | |
2890 | ||
f700caa3 CY |
2891 | For example, the following code adds two fontification patterns for C |
2892 | mode: one to fontify the word @samp{FIXME}, even in comments, and | |
2893 | another to fontify the words @samp{and}, @samp{or} and @samp{not} as | |
2894 | keywords. | |
b8d4c8d0 GM |
2895 | |
2896 | @smallexample | |
2897 | (font-lock-add-keywords 'c-mode | |
2898 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2899 | ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) | |
2900 | @end smallexample | |
2901 | ||
2902 | @noindent | |
f700caa3 CY |
2903 | This example affects only C mode proper. To add the same patterns to C |
2904 | mode @emph{and} all modes derived from it, do this instead: | |
b8d4c8d0 GM |
2905 | |
2906 | @smallexample | |
2907 | (add-hook 'c-mode-hook | |
2908 | (lambda () | |
2909 | (font-lock-add-keywords nil | |
2910 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2911 | ("\\<\\(and\\|or\\|not\\)\\>" . | |
2912 | font-lock-keyword-face))))) | |
2913 | @end smallexample | |
2914 | ||
2915 | @node Other Font Lock Variables | |
2916 | @subsection Other Font Lock Variables | |
2917 | ||
2918 | This section describes additional variables that a major mode can | |
2919 | set by means of @var{other-vars} in @code{font-lock-defaults} | |
2920 | (@pxref{Font Lock Basics}). | |
2921 | ||
2922 | @defvar font-lock-mark-block-function | |
2923 | If this variable is non-@code{nil}, it should be a function that is | |
2924 | called with no arguments, to choose an enclosing range of text for | |
2925 | refontification for the command @kbd{M-o M-o} | |
2926 | (@code{font-lock-fontify-block}). | |
2927 | ||
2928 | The function should report its choice by placing the region around it. | |
2929 | A good choice is a range of text large enough to give proper results, | |
2930 | but not too large so that refontification becomes slow. Typical values | |
2931 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for | |
2932 | textual modes. | |
2933 | @end defvar | |
2934 | ||
2935 | @defvar font-lock-extra-managed-props | |
2936 | This variable specifies additional properties (other than | |
2937 | @code{font-lock-face}) that are being managed by Font Lock mode. It | |
2938 | is used by @code{font-lock-default-unfontify-region}, which normally | |
2939 | only manages the @code{font-lock-face} property. If you want Font | |
2940 | Lock to manage other properties as well, you must specify them in a | |
2941 | @var{facespec} in @code{font-lock-keywords} as well as add them to | |
2942 | this list. @xref{Search-based Fontification}. | |
2943 | @end defvar | |
2944 | ||
2945 | @defvar font-lock-fontify-buffer-function | |
2946 | Function to use for fontifying the buffer. The default value is | |
2947 | @code{font-lock-default-fontify-buffer}. | |
2948 | @end defvar | |
2949 | ||
2950 | @defvar font-lock-unfontify-buffer-function | |
2951 | Function to use for unfontifying the buffer. This is used when | |
2952 | turning off Font Lock mode. The default value is | |
2953 | @code{font-lock-default-unfontify-buffer}. | |
2954 | @end defvar | |
2955 | ||
2956 | @defvar font-lock-fontify-region-function | |
2957 | Function to use for fontifying a region. It should take two | |
2958 | arguments, the beginning and end of the region, and an optional third | |
2959 | argument @var{verbose}. If @var{verbose} is non-@code{nil}, the | |
2960 | function should print status messages. The default value is | |
2961 | @code{font-lock-default-fontify-region}. | |
2962 | @end defvar | |
2963 | ||
2964 | @defvar font-lock-unfontify-region-function | |
2965 | Function to use for unfontifying a region. It should take two | |
2966 | arguments, the beginning and end of the region. The default value is | |
2967 | @code{font-lock-default-unfontify-region}. | |
2968 | @end defvar | |
2969 | ||
e070558d CY |
2970 | @defun jit-lock-register function &optional contextual |
2971 | This function tells Font Lock mode to run the Lisp function | |
2972 | @var{function} any time it has to fontify or refontify part of the | |
2973 | current buffer. It calls @var{function} before calling the default | |
2974 | fontification functions, and gives it two arguments, @var{start} and | |
2975 | @var{end}, which specify the region to be fontified or refontified. | |
2976 | ||
2977 | The optional argument @var{contextual}, if non-@code{nil}, forces Font | |
2978 | Lock mode to always refontify a syntactically relevant part of the | |
2979 | buffer, and not just the modified lines. This argument can usually be | |
2980 | omitted. | |
2981 | @end defun | |
2982 | ||
2983 | @defun jit-lock-unregister function | |
2984 | If @var{function} was previously registered as a fontification | |
2985 | function using @code{jit-lock-register}, this function unregisters it. | |
2986 | @end defun | |
b8d4c8d0 GM |
2987 | |
2988 | @node Levels of Font Lock | |
2989 | @subsection Levels of Font Lock | |
2990 | ||
f700caa3 | 2991 | Some major modes offer three different levels of fontification. You |
b8d4c8d0 GM |
2992 | can define multiple levels by using a list of symbols for @var{keywords} |
2993 | in @code{font-lock-defaults}. Each symbol specifies one level of | |
caef3ed2 GM |
2994 | fontification; it is up to the user to choose one of these levels, |
2995 | normally by setting @code{font-lock-maximum-decoration} (@pxref{Font | |
f700caa3 CY |
2996 | Lock,,, emacs, the GNU Emacs Manual}). The chosen level's symbol value |
2997 | is used to initialize @code{font-lock-keywords}. | |
b8d4c8d0 GM |
2998 | |
2999 | Here are the conventions for how to define the levels of | |
3000 | fontification: | |
3001 | ||
3002 | @itemize @bullet | |
3003 | @item | |
3004 | Level 1: highlight function declarations, file directives (such as include or | |
3005 | import directives), strings and comments. The idea is speed, so only | |
3006 | the most important and top-level components are fontified. | |
3007 | ||
3008 | @item | |
3009 | Level 2: in addition to level 1, highlight all language keywords, | |
3010 | including type names that act like keywords, as well as named constant | |
3011 | values. The idea is that all keywords (either syntactic or semantic) | |
3012 | should be fontified appropriately. | |
3013 | ||
3014 | @item | |
3015 | Level 3: in addition to level 2, highlight the symbols being defined in | |
3016 | function and variable declarations, and all builtin function names, | |
3017 | wherever they appear. | |
3018 | @end itemize | |
3019 | ||
3020 | @node Precalculated Fontification | |
3021 | @subsection Precalculated Fontification | |
3022 | ||
eae7d8f8 RS |
3023 | Some major modes such as @code{list-buffers} and @code{occur} |
3024 | construct the buffer text programmatically. The easiest way for them | |
3025 | to support Font Lock mode is to specify the faces of text when they | |
3026 | insert the text in the buffer. | |
3027 | ||
3028 | The way to do this is to specify the faces in the text with the | |
3029 | special text property @code{font-lock-face} (@pxref{Special | |
3030 | Properties}). When Font Lock mode is enabled, this property controls | |
3031 | the display, just like the @code{face} property. When Font Lock mode | |
3032 | is disabled, @code{font-lock-face} has no effect on the display. | |
3033 | ||
3034 | It is ok for a mode to use @code{font-lock-face} for some text and | |
3035 | also use the normal Font Lock machinery. But if the mode does not use | |
3036 | the normal Font Lock machinery, it should not set the variable | |
3037 | @code{font-lock-defaults}. | |
b8d4c8d0 GM |
3038 | |
3039 | @node Faces for Font Lock | |
3040 | @subsection Faces for Font Lock | |
3041 | @cindex faces for font lock | |
3042 | @cindex font lock faces | |
3043 | ||
e0dd6837 | 3044 | Font Lock mode can highlight using any face, but Emacs defines several |
f700caa3 CY |
3045 | faces specifically for Font Lock to use to highlight text. These |
3046 | @dfn{Font Lock faces} are listed below. They can also be used by major | |
3047 | modes for syntactic highlighting outside of Font Lock mode (@pxref{Major | |
3048 | Mode Conventions}). | |
b8d4c8d0 | 3049 | |
e0dd6837 CY |
3050 | Each of these symbols is both a face name, and a variable whose |
3051 | default value is the symbol itself. Thus, the default value of | |
3052 | @code{font-lock-comment-face} is @code{font-lock-comment-face}. | |
b8d4c8d0 | 3053 | |
e0dd6837 CY |
3054 | The faces are listed with descriptions of their typical usage, and in |
3055 | order of greater to lesser ``prominence''. If a mode's syntactic | |
3056 | categories do not fit well with the usage descriptions, the faces can be | |
3057 | assigned using the ordering as a guide. | |
b8d4c8d0 | 3058 | |
e0dd6837 CY |
3059 | @table @code |
3060 | @item font-lock-warning-face | |
3061 | @vindex font-lock-warning-face | |
3062 | for a construct that is peculiar, or that greatly changes the meaning of | |
3063 | other text, like @samp{;;;###autoload} in Emacs Lisp and @samp{#error} | |
3064 | in C. | |
b8d4c8d0 GM |
3065 | |
3066 | @item font-lock-function-name-face | |
3067 | @vindex font-lock-function-name-face | |
e0dd6837 | 3068 | for the name of a function being defined or declared. |
b8d4c8d0 GM |
3069 | |
3070 | @item font-lock-variable-name-face | |
3071 | @vindex font-lock-variable-name-face | |
e0dd6837 CY |
3072 | for the name of a variable being defined or declared. |
3073 | ||
3074 | @item font-lock-keyword-face | |
3075 | @vindex font-lock-keyword-face | |
3076 | for a keyword with special syntactic significance, like @samp{for} and | |
3077 | @samp{if} in C. | |
3078 | ||
3079 | @item font-lock-comment-face | |
3080 | @vindex font-lock-comment-face | |
3081 | for comments. | |
3082 | ||
3083 | @item font-lock-comment-delimiter-face | |
3084 | @vindex font-lock-comment-delimiter-face | |
1df7defd | 3085 | for comments delimiters, like @samp{/*} and @samp{*/} in C@. On most |
e0dd6837 | 3086 | terminals, this inherits from @code{font-lock-comment-face}. |
b8d4c8d0 GM |
3087 | |
3088 | @item font-lock-type-face | |
3089 | @vindex font-lock-type-face | |
e0dd6837 | 3090 | for the names of user-defined data types. |
b8d4c8d0 GM |
3091 | |
3092 | @item font-lock-constant-face | |
3093 | @vindex font-lock-constant-face | |
e0dd6837 CY |
3094 | for the names of constants, like @samp{NULL} in C. |
3095 | ||
3096 | @item font-lock-builtin-face | |
3097 | @vindex font-lock-builtin-face | |
3098 | for the names of built-in functions. | |
b8d4c8d0 GM |
3099 | |
3100 | @item font-lock-preprocessor-face | |
3101 | @vindex font-lock-preprocessor-face | |
e0dd6837 CY |
3102 | for preprocessor commands. This inherits, by default, from |
3103 | @code{font-lock-builtin-face}. | |
3104 | ||
3105 | @item font-lock-string-face | |
3106 | @vindex font-lock-string-face | |
3107 | for string constants. | |
3108 | ||
3109 | @item font-lock-doc-face | |
3110 | @vindex font-lock-doc-face | |
3111 | for documentation strings in the code. This inherits, by default, from | |
3112 | @code{font-lock-string-face}. | |
b8d4c8d0 GM |
3113 | |
3114 | @item font-lock-negation-char-face | |
3115 | @vindex font-lock-negation-char-face | |
e0dd6837 | 3116 | for easily-overlooked negation characters. |
b8d4c8d0 GM |
3117 | @end table |
3118 | ||
3119 | @node Syntactic Font Lock | |
3120 | @subsection Syntactic Font Lock | |
3121 | @cindex syntactic font lock | |
3122 | ||
f700caa3 CY |
3123 | Syntactic fontification uses a syntax table (@pxref{Syntax Tables}) to |
3124 | find and highlight syntactically relevant text. If enabled, it runs | |
3125 | prior to search-based fontification. The variable | |
3126 | @code{font-lock-syntactic-face-function}, documented below, determines | |
3127 | which syntactic constructs to highlight. There are several variables | |
3128 | that affect syntactic fontification; you should set them by means of | |
3129 | @code{font-lock-defaults} (@pxref{Font Lock Basics}). | |
b8d4c8d0 | 3130 | |
4230351b CY |
3131 | Whenever Font Lock mode performs syntactic fontification on a stretch |
3132 | of text, it first calls the function specified by | |
3133 | @code{syntax-propertize-function}. Major modes can use this to apply | |
3134 | @code{syntax-table} text properties to override the buffer's syntax | |
3135 | table in special cases. @xref{Syntax Properties}. | |
3136 | ||
b8d4c8d0 | 3137 | @defvar font-lock-keywords-only |
f700caa3 CY |
3138 | If the value of this variable is non-@code{nil}, Font Lock does not do |
3139 | syntactic fontification, only search-based fontification based on | |
3140 | @code{font-lock-keywords}. It is normally set by Font Lock mode based | |
3141 | on the @var{keywords-only} element in @code{font-lock-defaults}. | |
b8d4c8d0 GM |
3142 | @end defvar |
3143 | ||
3144 | @defvar font-lock-syntax-table | |
3145 | This variable holds the syntax table to use for fontification of | |
f700caa3 CY |
3146 | comments and strings. It is normally set by Font Lock mode based on the |
3147 | @var{syntax-alist} element in @code{font-lock-defaults}. If this value | |
3148 | is @code{nil}, syntactic fontification uses the buffer's syntax table | |
3149 | (the value returned by the function @code{syntax-table}; @pxref{Syntax | |
3150 | Table Functions}). | |
b8d4c8d0 GM |
3151 | @end defvar |
3152 | ||
3153 | @defvar font-lock-beginning-of-syntax-function | |
3154 | If this variable is non-@code{nil}, it should be a function to move | |
3155 | point back to a position that is syntactically at ``top level'' and | |
f700caa3 CY |
3156 | outside of strings or comments. The value is normally set through an |
3157 | @var{other-vars} element in @code{font-lock-defaults}. If it is | |
3158 | @code{nil}, Font Lock uses @code{syntax-begin-function} to move back | |
3159 | outside of any comment, string, or sexp (@pxref{Position Parse}). | |
3160 | ||
3161 | This variable is semi-obsolete; we usually recommend setting | |
3162 | @code{syntax-begin-function} instead. One of its uses is to tune the | |
1df7defd | 3163 | behavior of syntactic fontification, e.g., to ensure that different |
f700caa3 CY |
3164 | kinds of strings or comments are highlighted differently. |
3165 | ||
3166 | The specified function is called with no arguments. It should leave | |
3167 | point at the beginning of any enclosing syntactic block. Typical values | |
3168 | are @code{beginning-of-line} (used when the start of the line is known | |
3169 | to be outside a syntactic block), or @code{beginning-of-defun} for | |
b8d4c8d0 | 3170 | programming modes, or @code{backward-paragraph} for textual modes. |
b8d4c8d0 GM |
3171 | @end defvar |
3172 | ||
3173 | @defvar font-lock-syntactic-face-function | |
f700caa3 CY |
3174 | If this variable is non-@code{nil}, it should be a function to determine |
3175 | which face to use for a given syntactic element (a string or a comment). | |
3176 | The value is normally set through an @var{other-vars} element in | |
b8d4c8d0 | 3177 | @code{font-lock-defaults}. |
b8d4c8d0 | 3178 | |
f700caa3 CY |
3179 | The function is called with one argument, the parse state at point |
3180 | returned by @code{parse-partial-sexp}, and should return a face. The | |
3181 | default value returns @code{font-lock-comment-face} for comments and | |
3182 | @code{font-lock-string-face} for strings (@pxref{Faces for Font Lock}). | |
b8d4c8d0 GM |
3183 | @end defvar |
3184 | ||
3185 | @node Multiline Font Lock | |
3186 | @subsection Multiline Font Lock Constructs | |
3187 | @cindex multiline font lock | |
3188 | ||
3189 | Normally, elements of @code{font-lock-keywords} should not match | |
3190 | across multiple lines; that doesn't work reliably, because Font Lock | |
3191 | usually scans just part of the buffer, and it can miss a multi-line | |
3192 | construct that crosses the line boundary where the scan starts. (The | |
3193 | scan normally starts at the beginning of a line.) | |
3194 | ||
3195 | Making elements that match multiline constructs work properly has | |
3196 | two aspects: correct @emph{identification} and correct | |
3197 | @emph{rehighlighting}. The first means that Font Lock finds all | |
3198 | multiline constructs. The second means that Font Lock will correctly | |
3199 | rehighlight all the relevant text when a multiline construct is | |
3200 | changed---for example, if some of the text that was previously part of | |
3201 | a multiline construct ceases to be part of it. The two aspects are | |
3202 | closely related, and often getting one of them to work will appear to | |
3203 | make the other also work. However, for reliable results you must | |
3204 | attend explicitly to both aspects. | |
3205 | ||
3206 | There are three ways to ensure correct identification of multiline | |
3207 | constructs: | |
3208 | ||
3209 | @itemize | |
3210 | @item | |
3211 | Add a function to @code{font-lock-extend-region-functions} that does | |
3212 | the @emph{identification} and extends the scan so that the scanned | |
3213 | text never starts or ends in the middle of a multiline construct. | |
3214 | @item | |
3215 | Use the @code{font-lock-fontify-region-function} hook similarly to | |
3216 | extend the scan so that the scanned text never starts or ends in the | |
3217 | middle of a multiline construct. | |
3218 | @item | |
3219 | Somehow identify the multiline construct right when it gets inserted | |
3220 | into the buffer (or at any point after that but before font-lock | |
3221 | tries to highlight it), and mark it with a @code{font-lock-multiline} | |
3222 | which will instruct font-lock not to start or end the scan in the | |
3223 | middle of the construct. | |
3224 | @end itemize | |
3225 | ||
3226 | There are three ways to do rehighlighting of multiline constructs: | |
3227 | ||
3228 | @itemize | |
3229 | @item | |
3230 | Place a @code{font-lock-multiline} property on the construct. This | |
3231 | will rehighlight the whole construct if any part of it is changed. In | |
3232 | some cases you can do this automatically by setting the | |
3233 | @code{font-lock-multiline} variable, which see. | |
3234 | @item | |
3235 | Make sure @code{jit-lock-contextually} is set and rely on it doing its | |
3236 | job. This will only rehighlight the part of the construct that | |
3237 | follows the actual change, and will do it after a short delay. | |
3238 | This only works if the highlighting of the various parts of your | |
3239 | multiline construct never depends on text in subsequent lines. | |
3240 | Since @code{jit-lock-contextually} is activated by default, this can | |
3241 | be an attractive solution. | |
3242 | @item | |
3243 | Place a @code{jit-lock-defer-multiline} property on the construct. | |
3244 | This works only if @code{jit-lock-contextually} is used, and with the | |
3245 | same delay before rehighlighting, but like @code{font-lock-multiline}, | |
3246 | it also handles the case where highlighting depends on | |
3247 | subsequent lines. | |
3248 | @end itemize | |
3249 | ||
3250 | @menu | |
fe42c16a | 3251 | * Font Lock Multiline:: Marking multiline chunks with a text property. |
bc3bea9c | 3252 | * Region to Refontify:: Controlling which region gets refontified |
b8d4c8d0 GM |
3253 | after a buffer change. |
3254 | @end menu | |
3255 | ||
3256 | @node Font Lock Multiline | |
3257 | @subsubsection Font Lock Multiline | |
3258 | ||
3259 | One way to ensure reliable rehighlighting of multiline Font Lock | |
3260 | constructs is to put on them the text property @code{font-lock-multiline}. | |
3261 | It should be present and non-@code{nil} for text that is part of a | |
3262 | multiline construct. | |
3263 | ||
3264 | When Font Lock is about to highlight a range of text, it first | |
3265 | extends the boundaries of the range as necessary so that they do not | |
3266 | fall within text marked with the @code{font-lock-multiline} property. | |
3267 | Then it removes any @code{font-lock-multiline} properties from the | |
3268 | range, and highlights it. The highlighting specification (mostly | |
3269 | @code{font-lock-keywords}) must reinstall this property each time, | |
3270 | whenever it is appropriate. | |
3271 | ||
3272 | @strong{Warning:} don't use the @code{font-lock-multiline} property | |
3273 | on large ranges of text, because that will make rehighlighting slow. | |
3274 | ||
3275 | @defvar font-lock-multiline | |
3276 | If the @code{font-lock-multiline} variable is set to @code{t}, Font | |
3277 | Lock will try to add the @code{font-lock-multiline} property | |
3278 | automatically on multiline constructs. This is not a universal | |
3279 | solution, however, since it slows down Font Lock somewhat. It can | |
3280 | miss some multiline constructs, or make the property larger or smaller | |
3281 | than necessary. | |
3282 | ||
3283 | For elements whose @var{matcher} is a function, the function should | |
3284 | ensure that submatch 0 covers the whole relevant multiline construct, | |
3285 | even if only a small subpart will be highlighted. It is often just as | |
3286 | easy to add the @code{font-lock-multiline} property by hand. | |
3287 | @end defvar | |
3288 | ||
3289 | The @code{font-lock-multiline} property is meant to ensure proper | |
3290 | refontification; it does not automatically identify new multiline | |
f700caa3 CY |
3291 | constructs. Identifying the requires that Font Lock mode operate on |
3292 | large enough chunks at a time. This will happen by accident on many | |
3293 | cases, which may give the impression that multiline constructs magically | |
3294 | work. If you set the @code{font-lock-multiline} variable | |
3295 | non-@code{nil}, this impression will be even stronger, since the | |
3296 | highlighting of those constructs which are found will be properly | |
3297 | updated from then on. But that does not work reliably. | |
3298 | ||
3299 | To find multiline constructs reliably, you must either manually place | |
3300 | the @code{font-lock-multiline} property on the text before Font Lock | |
3301 | mode looks at it, or use @code{font-lock-fontify-region-function}. | |
b8d4c8d0 | 3302 | |
bc3bea9c | 3303 | @node Region to Refontify |
b8d4c8d0 GM |
3304 | @subsubsection Region to Fontify after a Buffer Change |
3305 | ||
3306 | When a buffer is changed, the region that Font Lock refontifies is | |
3307 | by default the smallest sequence of whole lines that spans the change. | |
3308 | While this works well most of the time, sometimes it doesn't---for | |
3309 | example, when a change alters the syntactic meaning of text on an | |
3310 | earlier line. | |
3311 | ||
bc3bea9c | 3312 | You can enlarge (or even reduce) the region to refontify by setting |
e6dc6206 | 3313 | the following variable: |
b8d4c8d0 GM |
3314 | |
3315 | @defvar font-lock-extend-after-change-region-function | |
f700caa3 CY |
3316 | This buffer-local variable is either @code{nil} or a function for Font |
3317 | Lock mode to call to determine the region to scan and fontify. | |
b8d4c8d0 GM |
3318 | |
3319 | The function is given three parameters, the standard @var{beg}, | |
bc3bea9c | 3320 | @var{end}, and @var{old-len} from @code{after-change-functions} |
b8d4c8d0 GM |
3321 | (@pxref{Change Hooks}). It should return either a cons of the |
3322 | beginning and end buffer positions (in that order) of the region to | |
3323 | fontify, or @code{nil} (which means choose the region in the standard | |
3324 | way). This function needs to preserve point, the match-data, and the | |
3325 | current restriction. The region it returns may start or end in the | |
3326 | middle of a line. | |
3327 | ||
3328 | Since this function is called after every buffer change, it should be | |
3329 | reasonably fast. | |
3330 | @end defvar | |
3331 | ||
5dcb4c4e | 3332 | @node Auto-Indentation |
4230351b | 3333 | @section Automatic Indentation of code |
5dcb4c4e SM |
3334 | |
3335 | For programming languages, an important feature of a major mode is to | |
3336 | provide automatic indentation. This is controlled in Emacs by | |
3337 | @code{indent-line-function} (@pxref{Mode-Specific Indent}). | |
3338 | Writing a good indentation function can be difficult and to a large | |
3339 | extent it is still a black art. | |
3340 | ||
3341 | Many major mode authors will start by writing a simple indentation | |
3342 | function that works for simple cases, for example by comparing with the | |
3343 | indentation of the previous text line. For most programming languages | |
3344 | that are not really line-based, this tends to scale very poorly: | |
3345 | improving such a function to let it handle more diverse situations tends | |
3346 | to become more and more difficult, resulting in the end with a large, | |
3347 | complex, unmaintainable indentation function which nobody dares to touch. | |
3348 | ||
3349 | A good indentation function will usually need to actually parse the | |
3350 | text, according to the syntax of the language. Luckily, it is not | |
3351 | necessary to parse the text in as much detail as would be needed | |
3352 | for a compiler, but on the other hand, the parser embedded in the | |
3353 | indentation code will want to be somewhat friendly to syntactically | |
3354 | incorrect code. | |
3355 | ||
4230351b | 3356 | Good maintainable indentation functions usually fall into two categories: |
5dcb4c4e SM |
3357 | either parsing forward from some ``safe'' starting point until the |
3358 | position of interest, or parsing backward from the position of interest. | |
3359 | Neither of the two is a clearly better choice than the other: parsing | |
3360 | backward is often more difficult than parsing forward because | |
3361 | programming languages are designed to be parsed forward, but for the | |
3362 | purpose of indentation it has the advantage of not needing to | |
3363 | guess a ``safe'' starting point, and it generally enjoys the property | |
3364 | that only a minimum of text will be analyzed to decide the indentation | |
3365 | of a line, so indentation will tend to be unaffected by syntax errors in | |
3366 | some earlier unrelated piece of code. Parsing forward on the other hand | |
3367 | is usually easier and has the advantage of making it possible to | |
3368 | reindent efficiently a whole region at a time, with a single parse. | |
3369 | ||
3370 | Rather than write your own indentation function from scratch, it is | |
3371 | often preferable to try and reuse some existing ones or to rely | |
3372 | on a generic indentation engine. There are sadly few such | |
3373 | engines. The CC-mode indentation code (used with C, C++, Java, Awk | |
3374 | and a few other such modes) has been made more generic over the years, | |
3375 | so if your language seems somewhat similar to one of those languages, | |
3376 | you might try to use that engine. @c FIXME: documentation? | |
3377 | Another one is SMIE which takes an approach in the spirit | |
3378 | of Lisp sexps and adapts it to non-Lisp languages. | |
3379 | ||
3380 | @menu | |
cf988578 | 3381 | * SMIE:: A simple minded indentation engine. |
5dcb4c4e SM |
3382 | @end menu |
3383 | ||
3384 | @node SMIE | |
3385 | @subsection Simple Minded Indentation Engine | |
ab100635 | 3386 | @cindex SMIE |
5dcb4c4e SM |
3387 | |
3388 | SMIE is a package that provides a generic navigation and indentation | |
3389 | engine. Based on a very simple parser using an ``operator precedence | |
3390 | grammar'', it lets major modes extend the sexp-based navigation of Lisp | |
3391 | to non-Lisp languages as well as provide a simple to use but reliable | |
3392 | auto-indentation. | |
3393 | ||
3394 | Operator precedence grammar is a very primitive technology for parsing | |
3395 | compared to some of the more common techniques used in compilers. | |
3396 | It has the following characteristics: its parsing power is very limited, | |
3397 | and it is largely unable to detect syntax errors, but it has the | |
3398 | advantage of being algorithmically efficient and able to parse forward | |
3399 | just as well as backward. In practice that means that SMIE can use it | |
3400 | for indentation based on backward parsing, that it can provide both | |
3401 | @code{forward-sexp} and @code{backward-sexp} functionality, and that it | |
3402 | will naturally work on syntactically incorrect code without any extra | |
3403 | effort. The downside is that it also means that most programming | |
3404 | languages cannot be parsed correctly using SMIE, at least not without | |
3405 | resorting to some special tricks (@pxref{SMIE Tricks}). | |
3406 | ||
3407 | @menu | |
cf988578 GM |
3408 | * SMIE setup:: SMIE setup and features. |
3409 | * Operator Precedence Grammars:: A very simple parsing technique. | |
3410 | * SMIE Grammar:: Defining the grammar of a language. | |
3411 | * SMIE Lexer:: Defining tokens. | |
3412 | * SMIE Tricks:: Working around the parser's limitations. | |
3413 | * SMIE Indentation:: Specifying indentation rules. | |
3414 | * SMIE Indentation Helpers:: Helper functions for indentation rules. | |
3415 | * SMIE Indentation Example:: Sample indentation rules. | |
5dcb4c4e SM |
3416 | @end menu |
3417 | ||
3418 | @node SMIE setup | |
3419 | @subsubsection SMIE Setup and Features | |
3420 | ||
3421 | SMIE is meant to be a one-stop shop for structural navigation and | |
3422 | various other features which rely on the syntactic structure of code, in | |
3423 | particular automatic indentation. The main entry point is | |
3424 | @code{smie-setup} which is a function typically called while setting | |
3425 | up a major mode. | |
3426 | ||
3427 | @defun smie-setup grammar rules-function &rest keywords | |
3428 | Setup SMIE navigation and indentation. | |
3429 | @var{grammar} is a grammar table generated by @code{smie-prec2->grammar}. | |
3430 | @var{rules-function} is a set of indentation rules for use on | |
3431 | @code{smie-rules-function}. | |
3432 | @var{keywords} are additional arguments, which can include the following | |
3433 | keywords: | |
3434 | @itemize | |
3435 | @item | |
3436 | @code{:forward-token} @var{fun}: Specify the forward lexer to use. | |
3437 | @item | |
3438 | @code{:backward-token} @var{fun}: Specify the backward lexer to use. | |
3439 | @end itemize | |
3440 | @end defun | |
3441 | ||
3442 | Calling this function is sufficient to make commands such as | |
3443 | @code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be | |
3444 | able to properly handle structural elements other than just the paired | |
3445 | parentheses already handled by syntax tables. For example, if the | |
3446 | provided grammar is precise enough, @code{transpose-sexps} can correctly | |
3447 | transpose the two arguments of a @code{+} operator, taking into account | |
3448 | the precedence rules of the language. | |
3449 | ||
3450 | Calling `smie-setup' is also sufficient to make TAB indentation work in | |
f49d1f52 SM |
3451 | the expected way, extends @code{blink-matching-paren} to apply to |
3452 | elements like @code{begin...end}, and provides some commands that you | |
3453 | can bind in the major mode keymap. | |
5dcb4c4e SM |
3454 | |
3455 | @deffn Command smie-close-block | |
3456 | This command closes the most recently opened (and not yet closed) block. | |
3457 | @end deffn | |
3458 | ||
3459 | @deffn Command smie-down-list &optional arg | |
3460 | This command is like @code{down-list} but it also pays attention to | |
3461 | nesting of tokens other than parentheses, such as @code{begin...end}. | |
3462 | @end deffn | |
3463 | ||
3464 | @node Operator Precedence Grammars | |
3465 | @subsubsection Operator Precedence Grammars | |
3466 | ||
3467 | SMIE's precedence grammars simply give to each token a pair of | |
3468 | precedences: the left-precedence and the right-precedence. We say | |
3469 | @code{T1 < T2} if the right-precedence of token @code{T1} is less than | |
3470 | the left-precedence of token @code{T2}. A good way to read this | |
3471 | @code{<} is as a kind of parenthesis: if we find @code{... T1 something | |
3472 | T2 ...} then that should be parsed as @code{... T1 (something T2 ...} | |
3473 | rather than as @code{... T1 something) T2 ...}. The latter | |
3474 | interpretation would be the case if we had @code{T1 > T2}. If we have | |
3475 | @code{T1 = T2}, it means that token T2 follows token T1 in the same | |
3476 | syntactic construction, so typically we have @code{"begin" = "end"}. | |
3477 | Such pairs of precedences are sufficient to express left-associativity | |
3478 | or right-associativity of infix operators, nesting of tokens like | |
3479 | parentheses and many other cases. | |
3480 | ||
62d94509 | 3481 | @c Let's leave this undocumented to leave it more open for change! |
5dcb4c4e SM |
3482 | @c @defvar smie-grammar |
3483 | @c The value of this variable is an alist specifying the left and right | |
3484 | @c precedence of each token. It is meant to be initialized by using one of | |
3485 | @c the functions below. | |
3486 | @c @end defvar | |
3487 | ||
3488 | @defun smie-prec2->grammar table | |
3489 | This function takes a @emph{prec2} grammar @var{table} and returns an | |
3490 | alist suitable for use in @code{smie-setup}. The @emph{prec2} | |
3491 | @var{table} is itself meant to be built by one of the functions below. | |
3492 | @end defun | |
3493 | ||
3494 | @defun smie-merge-prec2s &rest tables | |
3495 | This function takes several @emph{prec2} @var{tables} and merges them | |
3496 | into a new @emph{prec2} table. | |
3497 | @end defun | |
3498 | ||
3499 | @defun smie-precs->prec2 precs | |
3500 | This function builds a @emph{prec2} table from a table of precedences | |
3501 | @var{precs}. @var{precs} should be a list, sorted by precedence (for | |
3502 | example @code{"+"} will come before @code{"*"}), of elements of the form | |
3503 | @code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that | |
3504 | acts as an operator; @var{assoc} is their associativity, which can be | |
3505 | either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}. | |
3506 | All operators in a given element share the same precedence level | |
3507 | and associativity. | |
3508 | @end defun | |
3509 | ||
3510 | @defun smie-bnf->prec2 bnf &rest resolvers | |
3511 | This function lets you specify the grammar using a BNF notation. | |
3512 | It accepts a @var{bnf} description of the grammar along with a set of | |
3513 | conflict resolution rules @var{resolvers}, and | |
3514 | returns a @emph{prec2} table. | |
3515 | ||
3516 | @var{bnf} is a list of nonterminal definitions of the form | |
3517 | @code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs} | |
3518 | is a (non-empty) list of terminals (aka tokens) or non-terminals. | |
3519 | ||
3520 | Not all grammars are accepted: | |
3521 | @itemize | |
3522 | @item | |
3523 | An @var{rhs} cannot be an empty list (an empty list is never needed, | |
3524 | since SMIE allows all non-terminals to match the empty string anyway). | |
3525 | @item | |
3526 | An @var{rhs} cannot have 2 consecutive non-terminals: each pair of | |
3527 | non-terminals needs to be separated by a terminal (aka token). | |
3528 | This is a fundamental limitation of operator precedence grammars. | |
3529 | @end itemize | |
3530 | ||
3531 | Additionally, conflicts can occur: | |
3532 | @itemize | |
3533 | @item | |
3534 | The returned @emph{prec2} table holds constraints between pairs of tokens, and | |
3535 | for any given pair only one constraint can be present: T1 < T2, | |
3536 | T1 = T2, or T1 > T2. | |
3537 | @item | |
3538 | A token can be an @code{opener} (something similar to an open-paren), | |
3539 | a @code{closer} (like a close-paren), or @code{neither} of the two | |
1df7defd | 3540 | (e.g., an infix operator, or an inner token like @code{"else"}). |
5dcb4c4e SM |
3541 | @end itemize |
3542 | ||
3543 | Precedence conflicts can be resolved via @var{resolvers}, which | |
3544 | is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for | |
3545 | each precedence conflict, if those @code{precs} tables | |
3546 | specify a particular constraint, then the conflict is resolved by using | |
3547 | this constraint instead, else a conflict is reported and one of the | |
3548 | conflicting constraints is picked arbitrarily and the others are | |
3549 | simply ignored. | |
3550 | @end defun | |
3551 | ||
3552 | @node SMIE Grammar | |
3553 | @subsubsection Defining the Grammar of a Language | |
ab100635 XF |
3554 | @cindex SMIE grammar |
3555 | @cindex grammar, SMIE | |
5dcb4c4e SM |
3556 | |
3557 | The usual way to define the SMIE grammar of a language is by | |
3558 | defining a new global variable that holds the precedence table by | |
3559 | giving a set of BNF rules. | |
3560 | For example, the grammar definition for a small Pascal-like language | |
3561 | could look like: | |
3562 | @example | |
3563 | @group | |
3564 | (require 'smie) | |
3565 | (defvar sample-smie-grammar | |
3566 | (smie-prec2->grammar | |
3567 | (smie-bnf->prec2 | |
3568 | @end group | |
3569 | @group | |
3570 | '((id) | |
3571 | (inst ("begin" insts "end") | |
3572 | ("if" exp "then" inst "else" inst) | |
3573 | (id ":=" exp) | |
3574 | (exp)) | |
3575 | (insts (insts ";" insts) (inst)) | |
3576 | (exp (exp "+" exp) | |
3577 | (exp "*" exp) | |
3578 | ("(" exps ")")) | |
3579 | (exps (exps "," exps) (exp))) | |
3580 | @end group | |
3581 | @group | |
3582 | '((assoc ";")) | |
3583 | '((assoc ",")) | |
3584 | '((assoc "+") (assoc "*"))))) | |
3585 | @end group | |
3586 | @end example | |
3587 | ||
3588 | @noindent | |
3589 | A few things to note: | |
3590 | ||
3591 | @itemize | |
3592 | @item | |
3593 | The above grammar does not explicitly mention the syntax of function | |
3594 | calls: SMIE will automatically allow any sequence of sexps, such as | |
3595 | identifiers, balanced parentheses, or @code{begin ... end} blocks | |
3596 | to appear anywhere anyway. | |
3597 | @item | |
3598 | The grammar category @code{id} has no right hand side: this does not | |
3599 | mean that it can match only the empty string, since as mentioned any | |
3600 | sequence of sexps can appear anywhere anyway. | |
3601 | @item | |
3602 | Because non terminals cannot appear consecutively in the BNF grammar, it | |
3603 | is difficult to correctly handle tokens that act as terminators, so the | |
3604 | above grammar treats @code{";"} as a statement @emph{separator} instead, | |
3605 | which SMIE can handle very well. | |
3606 | @item | |
3607 | Separators used in sequences (such as @code{","} and @code{";"} above) | |
3608 | are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)} | |
3609 | which generate precedence conflicts which are then resolved by giving | |
3610 | them an explicit @code{(assoc "separator")}. | |
3611 | @item | |
3612 | The @code{("(" exps ")")} rule was not needed to pair up parens, since | |
3613 | SMIE will pair up any characters that are marked as having paren syntax | |
3614 | in the syntax table. What this rule does instead (together with the | |
3615 | definition of @code{exps}) is to make it clear that @code{","} should | |
3616 | not appear outside of parentheses. | |
3617 | @item | |
3618 | Rather than have a single @emph{precs} table to resolve conflicts, it is | |
3619 | preferable to have several tables, so as to let the BNF part of the | |
3620 | grammar specify relative precedences where possible. | |
3621 | @item | |
3622 | Unless there is a very good reason to prefer @code{left} or | |
3623 | @code{right}, it is usually preferable to mark operators as associative, | |
3624 | using @code{assoc}. For that reason @code{"+"} and @code{"*"} are | |
3625 | defined above as @code{assoc}, although the language defines them | |
3626 | formally as left associative. | |
3627 | @end itemize | |
3628 | ||
3629 | @node SMIE Lexer | |
3630 | @subsubsection Defining Tokens | |
ab100635 XF |
3631 | @cindex SMIE lexer |
3632 | @cindex defining tokens, SMIE | |
5dcb4c4e SM |
3633 | |
3634 | SMIE comes with a predefined lexical analyzer which uses syntax tables | |
3635 | in the following way: any sequence of characters that have word or | |
3636 | symbol syntax is considered a token, and so is any sequence of | |
3637 | characters that have punctuation syntax. This default lexer is | |
3638 | often a good starting point but is rarely actually correct for any given | |
3639 | language. For example, it will consider @code{"2,+3"} to be composed | |
3640 | of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}. | |
3641 | ||
3642 | To describe the lexing rules of your language to SMIE, you need | |
3643 | 2 functions, one to fetch the next token, and another to fetch the | |
3644 | previous token. Those functions will usually first skip whitespace and | |
3645 | comments and then look at the next chunk of text to see if it | |
3646 | is a special token. If so it should skip the token and | |
3647 | return a description of this token. Usually this is simply the string | |
3648 | extracted from the buffer, but it can be anything you want. | |
3649 | For example: | |
3650 | @example | |
3651 | @group | |
3652 | (defvar sample-keywords-regexp | |
3653 | (regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "="))) | |
3654 | @end group | |
3655 | @group | |
3656 | (defun sample-smie-forward-token () | |
3657 | (forward-comment (point-max)) | |
3658 | (cond | |
3659 | ((looking-at sample-keywords-regexp) | |
3660 | (goto-char (match-end 0)) | |
3661 | (match-string-no-properties 0)) | |
3662 | (t (buffer-substring-no-properties | |
3663 | (point) | |
3664 | (progn (skip-syntax-forward "w_") | |
3665 | (point)))))) | |
3666 | @end group | |
3667 | @group | |
3668 | (defun sample-smie-backward-token () | |
3669 | (forward-comment (- (point))) | |
3670 | (cond | |
3671 | ((looking-back sample-keywords-regexp (- (point) 2) t) | |
3672 | (goto-char (match-beginning 0)) | |
3673 | (match-string-no-properties 0)) | |
3674 | (t (buffer-substring-no-properties | |
3675 | (point) | |
3676 | (progn (skip-syntax-backward "w_") | |
3677 | (point)))))) | |
3678 | @end group | |
3679 | @end example | |
3680 | ||
3681 | Notice how those lexers return the empty string when in front of | |
3682 | parentheses. This is because SMIE automatically takes care of the | |
3683 | parentheses defined in the syntax table. More specifically if the lexer | |
3684 | returns nil or an empty string, SMIE tries to handle the corresponding | |
3685 | text as a sexp according to syntax tables. | |
3686 | ||
3687 | @node SMIE Tricks | |
3688 | @subsubsection Living With a Weak Parser | |
3689 | ||
3690 | The parsing technique used by SMIE does not allow tokens to behave | |
3691 | differently in different contexts. For most programming languages, this | |
3692 | manifests itself by precedence conflicts when converting the | |
3693 | BNF grammar. | |
3694 | ||
3695 | Sometimes, those conflicts can be worked around by expressing the | |
3696 | grammar slightly differently. For example, for Modula-2 it might seem | |
3697 | natural to have a BNF grammar that looks like this: | |
3698 | ||
3699 | @example | |
3700 | ... | |
3701 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3702 | ("CASE" exp "OF" cases "END") | |
3703 | ...) | |
049bcbcb CY |
3704 | (cases (cases "|" cases) |
3705 | (caselabel ":" insts) | |
3706 | ("ELSE" insts)) | |
5dcb4c4e SM |
3707 | ... |
3708 | @end example | |
3709 | ||
3710 | But this will create conflicts for @code{"ELSE"}: on the one hand, the | |
3711 | IF rule implies (among many other things) that @code{"ELSE" = "END"}; | |
3712 | but on the other hand, since @code{"ELSE"} appears within @code{cases}, | |
3713 | which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}. | |
3714 | We can solve the conflict either by using: | |
3715 | @example | |
3716 | ... | |
3717 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3718 | ("CASE" exp "OF" cases "END") | |
3719 | ("CASE" exp "OF" cases "ELSE" insts "END") | |
3720 | ...) | |
3721 | (cases (cases "|" cases) (caselabel ":" insts)) | |
3722 | ... | |
3723 | @end example | |
3724 | or | |
3725 | @example | |
3726 | ... | |
3727 | (inst ("IF" exp "THEN" else "END") | |
3728 | ("CASE" exp "OF" cases "END") | |
3729 | ...) | |
3730 | (else (insts "ELSE" insts)) | |
3731 | (cases (cases "|" cases) (caselabel ":" insts) (else)) | |
3732 | ... | |
3733 | @end example | |
3734 | ||
3735 | Reworking the grammar to try and solve conflicts has its downsides, tho, | |
3736 | because SMIE assumes that the grammar reflects the logical structure of | |
3737 | the code, so it is preferable to keep the BNF closer to the intended | |
3738 | abstract syntax tree. | |
3739 | ||
3740 | Other times, after careful consideration you may conclude that those | |
3741 | conflicts are not serious and simply resolve them via the | |
3742 | @var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is | |
3743 | because the grammar is simply ambiguous: the conflict does not affect | |
3744 | the set of programs described by the grammar, but only the way those | |
3745 | programs are parsed. This is typically the case for separators and | |
3746 | associative infix operators, where you want to add a resolver like | |
3747 | @code{'((assoc "|"))}. Another case where this can happen is for the | |
3748 | classic @emph{dangling else} problem, where you will use @code{'((assoc | |
3749 | "else" "then"))}. It can also happen for cases where the conflict is | |
3750 | real and cannot really be resolved, but it is unlikely to pose a problem | |
3751 | in practice. | |
3752 | ||
3753 | Finally, in many cases some conflicts will remain despite all efforts to | |
3754 | restructure the grammar. Do not despair: while the parser cannot be | |
3755 | made more clever, you can make the lexer as smart as you want. So, the | |
3756 | solution is then to look at the tokens involved in the conflict and to | |
1df7defd | 3757 | split one of those tokens into 2 (or more) different tokens. E.g., if |
5dcb4c4e SM |
3758 | the grammar needs to distinguish between two incompatible uses of the |
3759 | token @code{"begin"}, make the lexer return different tokens (say | |
3760 | @code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of | |
3761 | @code{"begin"} it finds. This pushes the work of distinguishing the | |
3762 | different cases to the lexer, which will thus have to look at the | |
3763 | surrounding text to find ad-hoc clues. | |
3764 | ||
3765 | @node SMIE Indentation | |
3766 | @subsubsection Specifying Indentation Rules | |
ab100635 | 3767 | @cindex indentation rules, SMIE |
5dcb4c4e SM |
3768 | |
3769 | Based on the provided grammar, SMIE will be able to provide automatic | |
3770 | indentation without any extra effort. But in practice, this default | |
3771 | indentation style will probably not be good enough. You will want to | |
3772 | tweak it in many different cases. | |
3773 | ||
3774 | SMIE indentation is based on the idea that indentation rules should be | |
3775 | as local as possible. To this end, it relies on the idea of | |
3776 | @emph{virtual} indentation, which is the indentation that a particular | |
3777 | program point would have if it were at the beginning of a line. | |
3778 | Of course, if that program point is indeed at the beginning of a line, | |
3779 | its virtual indentation is its current indentation. But if not, then | |
3780 | SMIE uses the indentation algorithm to compute the virtual indentation | |
3781 | of that point. Now in practice, the virtual indentation of a program | |
3782 | point does not have to be identical to the indentation it would have if | |
3783 | we inserted a newline before it. To see how this works, the SMIE rule | |
3784 | for indentation after a @code{@{} in C does not care whether the | |
3785 | @code{@{} is standing on a line of its own or is at the end of the | |
3786 | preceding line. Instead, these different cases are handled in the | |
3787 | indentation rule that decides how to indent before a @code{@{}. | |
3788 | ||
3789 | Another important concept is the notion of @emph{parent}: The | |
3790 | @emph{parent} of a token, is the head token of the nearest enclosing | |
3791 | syntactic construct. For example, the parent of an @code{else} is the | |
3792 | @code{if} to which it belongs, and the parent of an @code{if}, in turn, | |
3793 | is the lead token of the surrounding construct. The command | |
3794 | @code{backward-sexp} jumps from a token to its parent, but there are | |
3795 | some caveats: for @emph{openers} (tokens which start a construct, like | |
3796 | @code{if}), you need to start with point before the token, while for | |
3797 | others you need to start with point after the token. | |
3798 | @code{backward-sexp} stops with point before the parent token if that is | |
3799 | the @emph{opener} of the token of interest, and otherwise it stops with | |
3800 | point after the parent token. | |
3801 | ||
3802 | SMIE indentation rules are specified using a function that takes two | |
3803 | arguments @var{method} and @var{arg} where the meaning of @var{arg} and the | |
3804 | expected return value depend on @var{method}. | |
3805 | ||
3806 | @var{method} can be: | |
3807 | @itemize | |
3808 | @item | |
3809 | @code{:after}, in which case @var{arg} is a token and the function | |
3810 | should return the @var{offset} to use for indentation after @var{arg}. | |
3811 | @item | |
3812 | @code{:before}, in which case @var{arg} is a token and the function | |
3813 | should return the @var{offset} to use to indent @var{arg} itself. | |
3814 | @item | |
3815 | @code{:elem}, in which case the function should return either the offset | |
3816 | to use to indent function arguments (if @var{arg} is the symbol | |
3817 | @code{arg}) or the basic indentation step (if @var{arg} is the symbol | |
3818 | @code{basic}). | |
3819 | @item | |
3820 | @code{:list-intro}, in which case @var{arg} is a token and the function | |
3821 | should return non-@code{nil} if the token is followed by a list of | |
3822 | expressions (not separated by any token) rather than an expression. | |
3823 | @end itemize | |
3824 | ||
3825 | When @var{arg} is a token, the function is called with point just before | |
3826 | that token. A return value of nil always means to fallback on the | |
3827 | default behavior, so the function should return nil for arguments it | |
3828 | does not expect. | |
3829 | ||
3830 | @var{offset} can be: | |
3831 | @itemize | |
3832 | @item | |
3833 | @code{nil}: use the default indentation rule. | |
3834 | @item | |
3835 | @code{(column . @var{column})}: indent to column @var{column}. | |
3836 | @item | |
3837 | @var{number}: offset by @var{number}, relative to a base token which is | |
3838 | the current token for @code{:after} and its parent for @code{:before}. | |
3839 | @end itemize | |
3840 | ||
3841 | @node SMIE Indentation Helpers | |
3842 | @subsubsection Helper Functions for Indentation Rules | |
3843 | ||
3844 | SMIE provides various functions designed specifically for use in the | |
3845 | indentation rules function (several of those functions break if used in | |
3846 | another context). These functions all start with the prefix | |
3847 | @code{smie-rule-}. | |
3848 | ||
3849 | @defun smie-rule-bolp | |
3850 | Return non-@code{nil} if the current token is the first on the line. | |
3851 | @end defun | |
3852 | ||
3853 | @defun smie-rule-hanging-p | |
3854 | Return non-@code{nil} if the current token is @emph{hanging}. | |
3855 | A token is @emph{hanging} if it is the last token on the line | |
3856 | and if it is preceded by other tokens: a lone token on a line is not | |
3857 | hanging. | |
3858 | @end defun | |
3859 | ||
3860 | @defun smie-rule-next-p &rest tokens | |
3861 | Return non-@code{nil} if the next token is among @var{tokens}. | |
3862 | @end defun | |
3863 | ||
3864 | @defun smie-rule-prev-p &rest tokens | |
3865 | Return non-@code{nil} if the previous token is among @var{tokens}. | |
3866 | @end defun | |
3867 | ||
3868 | @defun smie-rule-parent-p &rest parents | |
3869 | Return non-@code{nil} if the current token's parent is among @var{parents}. | |
3870 | @end defun | |
3871 | ||
3872 | @defun smie-rule-sibling-p | |
0b128ac4 MR |
3873 | Return non-@code{nil} if the current token's parent is actually a |
3874 | sibling. This is the case for example when the parent of a @code{","} | |
3875 | is just the previous @code{","}. | |
5dcb4c4e SM |
3876 | @end defun |
3877 | ||
3878 | @defun smie-rule-parent &optional offset | |
3879 | Return the proper offset to align the current token with the parent. | |
3880 | If non-@code{nil}, @var{offset} should be an integer giving an | |
3881 | additional offset to apply. | |
3882 | @end defun | |
3883 | ||
3884 | @defun smie-rule-separator method | |
3885 | Indent current token as a @emph{separator}. | |
3886 | ||
3887 | By @emph{separator}, we mean here a token whose sole purpose is to | |
3888 | separate various elements within some enclosing syntactic construct, and | |
1df7defd | 3889 | which does not have any semantic significance in itself (i.e., it would |
5dcb4c4e SM |
3890 | typically not exist as a node in an abstract syntax tree). |
3891 | ||
3892 | Such a token is expected to have an associative syntax and be closely | |
3893 | tied to its syntactic parent. Typical examples are @code{","} in lists | |
3894 | of arguments (enclosed inside parentheses), or @code{";"} in sequences | |
3895 | of instructions (enclosed in a @code{@{...@}} or @code{begin...end} | |
3896 | block). | |
3897 | ||
3898 | @var{method} should be the method name that was passed to | |
3899 | `smie-rules-function'. | |
3900 | @end defun | |
3901 | ||
3902 | @node SMIE Indentation Example | |
3903 | @subsubsection Sample Indentation Rules | |
3904 | ||
3905 | Here is an example of an indentation function: | |
3906 | ||
3907 | @example | |
5dcb4c4e | 3908 | (defun sample-smie-rules (kind token) |
f49d1f52 SM |
3909 | (pcase (cons kind token) |
3910 | (`(:elem . basic) sample-indent-basic) | |
3911 | (`(,_ . ",") (smie-rule-separator kind)) | |
3912 | (`(:after . ":=") sample-indent-basic) | |
3913 | (`(:before . ,(or `"begin" `"(" `"@{"))) | |
3914 | (if (smie-rule-hanging-p) (smie-rule-parent))) | |
3915 | (`(:before . "if") | |
3916 | (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") | |
3917 | (smie-rule-parent))))) | |
5dcb4c4e SM |
3918 | @end example |
3919 | ||
3920 | @noindent | |
3921 | A few things to note: | |
3922 | ||
3923 | @itemize | |
3924 | @item | |
3925 | The first case indicates the basic indentation increment to use. | |
3926 | If @code{sample-indent-basic} is nil, then SMIE uses the global | |
3927 | setting @code{smie-indent-basic}. The major mode could have set | |
3928 | @code{smie-indent-basic} buffer-locally instead, but that | |
3929 | is discouraged. | |
3930 | ||
3931 | @item | |
f49d1f52 SM |
3932 | The rule for the token @code{","} make SMIE try to be more clever when |
3933 | the comma separator is placed at the beginning of lines. It tries to | |
3934 | outdent the separator so as to align the code after the comma; for | |
3935 | example: | |
5dcb4c4e SM |
3936 | |
3937 | @example | |
3938 | x = longfunctionname ( | |
3939 | arg1 | |
3940 | , arg2 | |
3941 | ); | |
3942 | @end example | |
3943 | ||
3944 | @item | |
3945 | The rule for indentation after @code{":="} exists because otherwise | |
3946 | SMIE would treat @code{":="} as an infix operator and would align the | |
3947 | right argument with the left one. | |
3948 | ||
3949 | @item | |
3950 | The rule for indentation before @code{"begin"} is an example of the use | |
3951 | of virtual indentation: This rule is used only when @code{"begin"} is | |
3952 | hanging, which can happen only when @code{"begin"} is not at the | |
3953 | beginning of a line. So this is not used when indenting | |
3954 | @code{"begin"} itself but only when indenting something relative to this | |
3955 | @code{"begin"}. Concretely, this rule changes the indentation from: | |
3956 | ||
3957 | @example | |
3958 | if x > 0 then begin | |
3959 | dosomething(x); | |
3960 | end | |
3961 | @end example | |
3962 | to | |
3963 | @example | |
3964 | if x > 0 then begin | |
3965 | dosomething(x); | |
3966 | end | |
3967 | @end example | |
3968 | ||
3969 | @item | |
3970 | The rule for indentation before @code{"if"} is similar to the one for | |
3971 | @code{"begin"}, but where the purpose is to treat @code{"else if"} | |
3972 | as a single unit, so as to align a sequence of tests rather than indent | |
3973 | each test further to the right. This function does this only in the | |
3974 | case where the @code{"if"} is not placed on a separate line, hence the | |
3975 | @code{smie-rule-bolp} test. | |
3976 | ||
3977 | If we know that the @code{"else"} is always aligned with its @code{"if"} | |
3978 | and is always at the beginning of a line, we can use a more efficient | |
3979 | rule: | |
3980 | @example | |
3981 | ((equal token "if") | |
049bcbcb CY |
3982 | (and (not (smie-rule-bolp)) |
3983 | (smie-rule-prev-p "else") | |
5dcb4c4e | 3984 | (save-excursion |
049bcbcb | 3985 | (sample-smie-backward-token) |
5dcb4c4e SM |
3986 | (cons 'column (current-column))))) |
3987 | @end example | |
3988 | ||
3989 | The advantage of this formulation is that it reuses the indentation of | |
3990 | the previous @code{"else"}, rather than going all the way back to the | |
3991 | first @code{"if"} of the sequence. | |
3992 | @end itemize | |
3993 | ||
b8d4c8d0 GM |
3994 | @node Desktop Save Mode |
3995 | @section Desktop Save Mode | |
3996 | @cindex desktop save mode | |
3997 | ||
3998 | @dfn{Desktop Save Mode} is a feature to save the state of Emacs from | |
3999 | one session to another. The user-level commands for using Desktop | |
4000 | Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs | |
4001 | Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit | |
4002 | a file, don't have to do anything to use this feature. | |
4003 | ||
4004 | For buffers not visiting a file to have their state saved, the major | |
4005 | mode must bind the buffer local variable @code{desktop-save-buffer} to | |
4006 | a non-@code{nil} value. | |
4007 | ||
4008 | @defvar desktop-save-buffer | |
4009 | If this buffer-local variable is non-@code{nil}, the buffer will have | |
4010 | its state saved in the desktop file at desktop save. If the value is | |
4011 | a function, it is called at desktop save with argument | |
4012 | @var{desktop-dirname}, and its value is saved in the desktop file along | |
4013 | with the state of the buffer for which it was called. When file names | |
4014 | are returned as part of the auxiliary information, they should be | |
4015 | formatted using the call | |
4016 | ||
4017 | @example | |
4018 | (desktop-file-name @var{file-name} @var{desktop-dirname}) | |
4019 | @end example | |
4020 | ||
4021 | @end defvar | |
4022 | ||
4023 | For buffers not visiting a file to be restored, the major mode must | |
4024 | define a function to do the job, and that function must be listed in | |
4025 | the alist @code{desktop-buffer-mode-handlers}. | |
4026 | ||
4027 | @defvar desktop-buffer-mode-handlers | |
4028 | Alist with elements | |
4029 | ||
4030 | @example | |
4031 | (@var{major-mode} . @var{restore-buffer-function}) | |
4032 | @end example | |
4033 | ||
4034 | The function @var{restore-buffer-function} will be called with | |
4035 | argument list | |
4036 | ||
4037 | @example | |
4038 | (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc}) | |
4039 | @end example | |
4040 | ||
4041 | and it should return the restored buffer. | |
4042 | Here @var{desktop-buffer-misc} is the value returned by the function | |
4043 | optionally bound to @code{desktop-save-buffer}. | |
4044 | @end defvar |