Commit | Line | Data |
---|---|---|
b8d4c8d0 GM |
1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
73b0cd50 | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2011 Free Software Foundation, Inc. |
b8d4c8d0 | 4 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 5 | @setfilename ../../info/modes |
b8d4c8d0 GM |
6 | @node Modes, Documentation, Keymaps, Top |
7 | @chapter Major and Minor Modes | |
8 | @cindex mode | |
9 | ||
10 | A @dfn{mode} is a set of definitions that customize Emacs and can be | |
11 | turned on and off while you edit. There are two varieties of modes: | |
12 | @dfn{major modes}, which are mutually exclusive and used for editing | |
13 | particular kinds of text, and @dfn{minor modes}, which provide features | |
14 | that users can enable individually. | |
15 | ||
16 | This chapter describes how to write both major and minor modes, how to | |
17 | indicate them in the mode line, and how they run hooks supplied by the | |
18 | user. For related topics such as keymaps and syntax tables, see | |
19 | @ref{Keymaps}, and @ref{Syntax Tables}. | |
20 | ||
21 | @menu | |
769741e3 SM |
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. | |
5dcb4c4e | 26 | * Imenu:: How a mode can provide a menu |
b8d4c8d0 | 27 | of definitions in the buffer. |
5dcb4c4e SM |
28 | * Font Lock Mode:: How modes can highlight text according to syntax. |
29 | * Auto-Indentation:: How to teach Emacs to indent for a major mode. | |
30 | * Desktop Save Mode:: How modes can have buffer state saved between | |
b8d4c8d0 GM |
31 | Emacs sessions. |
32 | @end menu | |
33 | ||
34 | @node Hooks | |
35 | @section Hooks | |
36 | @cindex hooks | |
37 | ||
38 | A @dfn{hook} is a variable where you can store a function or functions | |
39 | to be called on a particular occasion by an existing program. Emacs | |
40 | provides hooks for the sake of customization. Most often, hooks are set | |
41 | up in the init file (@pxref{Init File}), but Lisp programs can set them also. | |
42 | @xref{Standard Hooks}, for a list of standard hook variables. | |
43 | ||
44 | @cindex normal hook | |
45 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
46 | contain lists of functions to be called with no arguments. By | |
47 | convention, whenever the hook name ends in @samp{-hook}, that tells | |
48 | you it is normal. We try to make all hooks normal, as much as | |
49 | possible, so that you can use them in a uniform way. | |
50 | ||
51 | Every major mode function is supposed to run a normal hook called | |
52 | the @dfn{mode hook} as the one of the last steps of initialization. | |
53 | This makes it easy for a user to customize the behavior of the mode, | |
54 | by overriding the buffer-local variable assignments already made by | |
55 | the mode. Most minor mode functions also run a mode hook at the end. | |
56 | But hooks are used in other contexts too. For example, the hook | |
57 | @code{suspend-hook} runs just before Emacs suspends itself | |
58 | (@pxref{Suspending Emacs}). | |
59 | ||
60 | The recommended way to add a hook function to a normal hook is by | |
61 | calling @code{add-hook} (see below). The hook functions may be any of | |
62 | the valid kinds of functions that @code{funcall} accepts (@pxref{What | |
63 | Is a Function}). Most normal hook variables are initially void; | |
64 | @code{add-hook} knows how to deal with this. You can add hooks either | |
65 | globally or buffer-locally with @code{add-hook}. | |
66 | ||
67 | @cindex abnormal hook | |
68 | If the hook variable's name does not end with @samp{-hook}, that | |
69 | indicates it is probably an @dfn{abnormal hook}. That means the hook | |
70 | functions are called with arguments, or their return values are used | |
71 | in some way. The hook's documentation says how the functions are | |
72 | called. You can use @code{add-hook} to add a function to an abnormal | |
73 | hook, but you must write the function to follow the hook's calling | |
74 | convention. | |
75 | ||
76 | By convention, abnormal hook names end in @samp{-functions} or | |
77 | @samp{-hooks}. If the variable's name ends in @samp{-function}, then | |
78 | its value is just a single function, not a list of functions. | |
79 | ||
fd9a7a58 | 80 | @menu |
769741e3 SM |
81 | * Running Hooks:: How to run a hook. |
82 | * Setting Hooks:: How to put functions on a hook, or remove them. | |
fd9a7a58 | 83 | @end menu |
b8d4c8d0 | 84 | |
fd9a7a58 RS |
85 | @node Running Hooks |
86 | @subsection Running Hooks | |
b8d4c8d0 | 87 | |
fd9a7a58 RS |
88 | At the appropriate times, Emacs uses the @code{run-hooks} function |
89 | and the other functions below to run particular hooks. | |
b8d4c8d0 GM |
90 | |
91 | @defun run-hooks &rest hookvars | |
92 | This function takes one or more normal hook variable names as | |
93 | arguments, and runs each hook in turn. Each argument should be a | |
94 | symbol that is a normal hook variable. These arguments are processed | |
95 | in the order specified. | |
96 | ||
97 | If a hook variable has a non-@code{nil} value, that value should be a | |
98 | list of functions. @code{run-hooks} calls all the functions, one by | |
99 | one, with no arguments. | |
100 | ||
101 | The hook variable's value can also be a single function---either a | |
102 | lambda expression or a symbol with a function definition---which | |
103 | @code{run-hooks} calls. But this usage is obsolete. | |
104 | @end defun | |
105 | ||
106 | @defun run-hook-with-args hook &rest args | |
107 | This function is the way to run an abnormal hook and always call all | |
108 | of the hook functions. It calls each of the hook functions one by | |
109 | one, passing each of them the arguments @var{args}. | |
110 | @end defun | |
111 | ||
112 | @defun run-hook-with-args-until-failure hook &rest args | |
113 | This function is the way to run an abnormal hook until one of the hook | |
114 | functions fails. It calls each of the hook functions, passing each of | |
115 | them the arguments @var{args}, until some hook function returns | |
116 | @code{nil}. It then stops and returns @code{nil}. If none of the | |
117 | hook functions return @code{nil}, it returns a non-@code{nil} value. | |
118 | @end defun | |
119 | ||
120 | @defun run-hook-with-args-until-success hook &rest args | |
121 | This function is the way to run an abnormal hook until a hook function | |
122 | succeeds. It calls each of the hook functions, passing each of them | |
123 | the arguments @var{args}, until some hook function returns | |
124 | non-@code{nil}. Then it stops, and returns whatever was returned by | |
125 | the last hook function that was called. If all hook functions return | |
126 | @code{nil}, it returns @code{nil} as well. | |
127 | @end defun | |
128 | ||
fd9a7a58 RS |
129 | @node Setting Hooks |
130 | @subsection Setting Hooks | |
131 | ||
132 | Here's an example that uses a mode hook to turn on Auto Fill mode when | |
133 | in Lisp Interaction mode: | |
134 | ||
135 | @example | |
136 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
137 | @end example | |
138 | ||
b8d4c8d0 GM |
139 | @defun add-hook hook function &optional append local |
140 | This function is the handy way to add function @var{function} to hook | |
141 | variable @var{hook}. You can use it for abnormal hooks as well as for | |
142 | normal hooks. @var{function} can be any Lisp function that can accept | |
143 | the proper number of arguments for @var{hook}. For example, | |
144 | ||
145 | @example | |
146 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
147 | @end example | |
148 | ||
149 | @noindent | |
150 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
151 | ||
152 | If @var{function} is already present in @var{hook} (comparing using | |
153 | @code{equal}), then @code{add-hook} does not add it a second time. | |
154 | ||
fd9a7a58 RS |
155 | If @var{function} has a non-@code{nil} property |
156 | @code{permanent-local-hook}, then @code{kill-all-local-variables} (or | |
157 | changing major modes) won't delete it from the hook variable's local | |
158 | value. | |
159 | ||
41633740 CY |
160 | It is best to design your hook functions so that the order in which |
161 | they are executed does not matter. Any dependence on the order is | |
162 | asking for trouble. However, the order is predictable: normally, | |
b8d4c8d0 | 163 | @var{function} goes at the front of the hook list, so it will be |
41633740 CY |
164 | executed first (barring another @code{add-hook} call). If the |
165 | optional argument @var{append} is non-@code{nil}, the new hook | |
166 | function goes at the end of the hook list and will be executed last. | |
b8d4c8d0 GM |
167 | |
168 | @code{add-hook} can handle the cases where @var{hook} is void or its | |
169 | value is a single function; it sets or changes the value to a list of | |
170 | functions. | |
171 | ||
172 | If @var{local} is non-@code{nil}, that says to add @var{function} to | |
173 | the buffer-local hook list instead of to the global hook list. If | |
174 | needed, this makes the hook buffer-local and adds @code{t} to the | |
175 | buffer-local value. The latter acts as a flag to run the hook | |
176 | functions in the default value as well as in the local value. | |
177 | @end defun | |
178 | ||
179 | @defun remove-hook hook function &optional local | |
180 | This function removes @var{function} from the hook variable | |
181 | @var{hook}. It compares @var{function} with elements of @var{hook} | |
182 | using @code{equal}, so it works for both symbols and lambda | |
183 | expressions. | |
184 | ||
185 | If @var{local} is non-@code{nil}, that says to remove @var{function} | |
186 | from the buffer-local hook list instead of from the global hook list. | |
187 | @end defun | |
188 | ||
189 | @node Major Modes | |
190 | @section Major Modes | |
191 | @cindex major mode | |
192 | ||
193 | Major modes specialize Emacs for editing particular kinds of text. | |
194 | Each buffer has only one major mode at a time. For each major mode | |
195 | there is a function to switch to that mode in the current buffer; its | |
196 | name should end in @samp{-mode}. These functions work by setting | |
197 | buffer-local variable bindings and other data associated with the | |
198 | buffer, such as a local keymap. The effect lasts until you switch | |
199 | to another major mode in the same buffer. | |
200 | ||
201 | @menu | |
769741e3 SM |
202 | * Major Mode Basics:: |
203 | * Major Mode Conventions:: Coding conventions for keymaps, etc. | |
204 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
205 | * Mode Help:: Finding out how to use a mode. | |
206 | * Derived Modes:: Defining a new major mode based on another major | |
b8d4c8d0 | 207 | mode. |
769741e3 | 208 | * Generic Modes:: Defining a simple major mode that supports |
b8d4c8d0 | 209 | comment syntax and Font Lock mode. |
769741e3 SM |
210 | * Mode Hooks:: Hooks run at the end of major mode functions. |
211 | * Example Major Modes:: Text mode and Lisp modes. | |
b8d4c8d0 GM |
212 | @end menu |
213 | ||
214 | @node Major Mode Basics | |
215 | @subsection Major Mode Basics | |
216 | @cindex Fundamental mode | |
217 | ||
218 | The least specialized major mode is called @dfn{Fundamental mode}. | |
219 | This mode has no mode-specific definitions or variable settings, so each | |
220 | Emacs command behaves in its default manner, and each option is in its | |
221 | default state. All other major modes redefine various keys and options. | |
222 | For example, Lisp Interaction mode provides special key bindings for | |
223 | @kbd{C-j} (@code{eval-print-last-sexp}), @key{TAB} | |
224 | (@code{lisp-indent-line}), and other keys. | |
225 | ||
226 | When you need to write several editing commands to help you perform a | |
227 | specialized editing task, creating a new major mode is usually a good | |
228 | idea. In practice, writing a major mode is easy (in contrast to | |
229 | writing a minor mode, which is often difficult). | |
230 | ||
231 | If the new mode is similar to an old one, it is often unwise to | |
232 | modify the old one to serve two purposes, since it may become harder | |
233 | to use and maintain. Instead, copy and rename an existing major mode | |
41633740 CY |
234 | definition and alter the copy---or use the @code{define-derived-mode} |
235 | macro to define a @dfn{derived mode} (@pxref{Derived Modes}). For | |
236 | example, Rmail Edit mode is a major mode that is very similar to Text | |
237 | mode except that it provides two additional commands. Its definition | |
238 | is distinct from that of Text mode, but uses that of Text mode. | |
b8d4c8d0 GM |
239 | |
240 | Even if the new mode is not an obvious derivative of any other mode, | |
769741e3 SM |
241 | we recommend to use @code{define-derived-mode}, since it automatically |
242 | enforces the most important coding conventions for you. | |
b8d4c8d0 GM |
243 | |
244 | For a very simple programming language major mode that handles | |
245 | comments and fontification, you can use @code{define-generic-mode}. | |
246 | @xref{Generic Modes}. | |
247 | ||
248 | Rmail Edit mode offers an example of changing the major mode | |
249 | temporarily for a buffer, so it can be edited in a different way (with | |
250 | ordinary Emacs commands rather than Rmail commands). In such cases, the | |
251 | temporary major mode usually provides a command to switch back to the | |
252 | buffer's usual mode (Rmail mode, in this case). You might be tempted to | |
253 | present the temporary redefinitions inside a recursive edit and restore | |
254 | the usual ones when the user exits; but this is a bad idea because it | |
255 | constrains the user's options when it is done in more than one buffer: | |
256 | recursive edits must be exited most-recently-entered first. Using an | |
257 | alternative major mode avoids this limitation. @xref{Recursive | |
258 | Editing}. | |
259 | ||
260 | The standard GNU Emacs Lisp library directory tree contains the code | |
261 | for several major modes, in files such as @file{text-mode.el}, | |
262 | @file{texinfo.el}, @file{lisp-mode.el}, @file{c-mode.el}, and | |
263 | @file{rmail.el}. They are found in various subdirectories of the | |
264 | @file{lisp} directory. You can study these libraries to see how modes | |
265 | are written. Text mode is perhaps the simplest major mode aside from | |
266 | Fundamental mode. Rmail mode is a complicated and specialized mode. | |
267 | ||
268 | @node Major Mode Conventions | |
269 | @subsection Major Mode Conventions | |
270 | @cindex major mode conventions | |
271 | @cindex conventions for writing major modes | |
272 | ||
273 | The code for existing major modes follows various coding conventions, | |
274 | including conventions for local keymap and syntax table initialization, | |
275 | global names, and hooks. Please follow these conventions when you | |
276 | define a new major mode. (Fundamental mode is an exception to many | |
277 | of these conventions, because its definition is to present the global | |
278 | state of Emacs.) | |
279 | ||
280 | This list of conventions is only partial, because each major mode | |
281 | should aim for consistency in general with other Emacs major modes. | |
282 | This makes Emacs as a whole more coherent. It is impossible to list | |
283 | here all the possible points where this issue might come up; if the | |
284 | Emacs developers point out an area where your major mode deviates from | |
285 | the usual conventions, please make it compatible. | |
286 | ||
287 | @itemize @bullet | |
288 | @item | |
289 | Define a command whose name ends in @samp{-mode}, with no arguments, | |
290 | that switches to the new mode in the current buffer. This command | |
291 | should set up the keymap, syntax table, and buffer-local variables in an | |
292 | existing buffer, without changing the buffer's contents. | |
293 | ||
294 | @item | |
295 | Write a documentation string for this command that describes the | |
296 | special commands available in this mode. @kbd{C-h m} | |
297 | (@code{describe-mode}) in your mode will display this string. | |
298 | ||
299 | The documentation string may include the special documentation | |
300 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
301 | @samp{\<@var{keymap}>}, which enable the documentation to adapt | |
302 | automatically to the user's own key bindings. @xref{Keys in | |
303 | Documentation}. | |
304 | ||
305 | @item | |
306 | The major mode command should start by calling | |
307 | @code{kill-all-local-variables}. This runs the normal hook | |
308 | @code{change-major-mode-hook}, then gets rid of the buffer-local | |
309 | variables of the major mode previously in effect. @xref{Creating | |
310 | Buffer-Local}. | |
311 | ||
312 | @item | |
313 | The major mode command should set the variable @code{major-mode} to the | |
314 | major mode command symbol. This is how @code{describe-mode} discovers | |
315 | which documentation to print. | |
316 | ||
317 | @item | |
318 | The major mode command should set the variable @code{mode-name} to the | |
9cf52b11 EZ |
319 | ``pretty'' name of the mode, usually a string (but see @ref{Mode Line |
320 | Data}, for other possible forms). The name of the mode appears | |
321 | in the mode line. | |
b8d4c8d0 GM |
322 | |
323 | @item | |
324 | @cindex functions in modes | |
325 | Since all global names are in the same name space, all the global | |
326 | variables, constants, and functions that are part of the mode should | |
327 | have names that start with the major mode name (or with an abbreviation | |
328 | of it if the name is long). @xref{Coding Conventions}. | |
329 | ||
330 | @item | |
331 | In a major mode for editing some kind of structured text, such as a | |
332 | programming language, indentation of text according to structure is | |
333 | probably useful. So the mode should set @code{indent-line-function} | |
334 | to a suitable function, and probably customize other variables | |
5dcb4c4e | 335 | for indentation. @xref{Auto-Indentation}. |
b8d4c8d0 GM |
336 | |
337 | @item | |
338 | @cindex keymaps in modes | |
339 | The major mode should usually have its own keymap, which is used as the | |
340 | local keymap in all buffers in that mode. The major mode command should | |
341 | call @code{use-local-map} to install this local map. @xref{Active | |
342 | Keymaps}, for more information. | |
343 | ||
344 | This keymap should be stored permanently in a global variable named | |
345 | @code{@var{modename}-mode-map}. Normally the library that defines the | |
346 | mode sets this variable. | |
347 | ||
348 | @xref{Tips for Defining}, for advice about how to write the code to set | |
349 | up the mode's keymap variable. | |
350 | ||
351 | @item | |
352 | The key sequences bound in a major mode keymap should usually start with | |
353 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, | |
354 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation | |
355 | characters are reserved for minor modes, and ordinary letters are | |
356 | reserved for users. | |
357 | ||
358 | A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and | |
359 | @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally | |
360 | be some kind of ``moving forward and backward,'' but this does not | |
361 | necessarily mean cursor motion. | |
362 | ||
363 | It is legitimate for a major mode to rebind a standard key sequence if | |
364 | it provides a command that does ``the same job'' in a way better | |
365 | suited to the text this mode is used for. For example, a major mode | |
366 | for editing a programming language might redefine @kbd{C-M-a} to | |
367 | ``move to the beginning of a function'' in a way that works better for | |
368 | that language. | |
369 | ||
370 | It is also legitimate for a major mode to rebind a standard key | |
371 | sequence whose standard meaning is rarely useful in that mode. For | |
372 | instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is | |
373 | rarely of any use in the minibuffer. Major modes such as Dired or | |
374 | Rmail that do not allow self-insertion of text can reasonably redefine | |
375 | letters and other printing characters as special commands. | |
376 | ||
377 | @item | |
867d4bb3 | 378 | Major modes for editing text should not define @key{RET} to do |
b8d4c8d0 GM |
379 | anything other than insert a newline. However, it is ok for |
380 | specialized modes for text that users don't directly edit, such as | |
381 | Dired and Info modes, to redefine @key{RET} to do something entirely | |
382 | different. | |
383 | ||
384 | @item | |
385 | Major modes should not alter options that are primarily a matter of user | |
386 | preference, such as whether Auto-Fill mode is enabled. Leave this to | |
387 | each user to decide. However, a major mode should customize other | |
388 | variables so that Auto-Fill mode will work usefully @emph{if} the user | |
389 | decides to use it. | |
390 | ||
391 | @item | |
392 | @cindex syntax tables in modes | |
393 | The mode may have its own syntax table or may share one with other | |
394 | related modes. If it has its own syntax table, it should store this in | |
395 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax | |
396 | Tables}. | |
397 | ||
398 | @item | |
399 | If the mode handles a language that has a syntax for comments, it should | |
400 | set the variables that define the comment syntax. @xref{Options for | |
401 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. | |
402 | ||
403 | @item | |
404 | @cindex abbrev tables in modes | |
405 | The mode may have its own abbrev table or may share one with other | |
406 | related modes. If it has its own abbrev table, it should store this | |
407 | in a variable named @code{@var{modename}-mode-abbrev-table}. If the | |
408 | major mode command defines any abbrevs itself, it should pass @code{t} | |
409 | for the @var{system-flag} argument to @code{define-abbrev}. | |
410 | @xref{Defining Abbrevs}. | |
411 | ||
412 | @item | |
413 | The mode should specify how to do highlighting for Font Lock mode, by | |
414 | setting up a buffer-local value for the variable | |
415 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). | |
416 | ||
e0dd6837 CY |
417 | @item |
418 | Each face that the mode defines should, if possible, inherit from an | |
419 | existing Emacs face. This reduces the chance of conflicting with a | |
420 | user's face customizations. Useful faces include: | |
421 | ||
422 | @table @asis | |
423 | @item @code{highlight} | |
424 | for stretches of text that should temporarily stand out. | |
425 | ||
426 | @item @code{match} | |
427 | for text matching a search command. | |
428 | ||
429 | @item @code{link} and @code{link-visited} | |
430 | for clickable text buttons that send the user to a different buffer or | |
431 | ``location''. | |
432 | ||
433 | @item @code{button} | |
434 | for clickable text buttons that perform other actions. | |
435 | ||
436 | @item @asis{Font Lock faces} | |
437 | for other kinds of syntactic highlighting, if highlighting is not | |
438 | handled by Font Lock mode or some Font Lock faces are not in use. | |
439 | @xref{Faces for Font Lock}, for how to assign Font Lock faces. | |
440 | @end table | |
441 | ||
b8d4c8d0 GM |
442 | @item |
443 | The mode should specify how Imenu should find the definitions or | |
444 | sections of a buffer, by setting up a buffer-local value for the | |
445 | variable @code{imenu-generic-expression}, for the two variables | |
446 | @code{imenu-prev-index-position-function} and | |
447 | @code{imenu-extract-index-name-function}, or for the variable | |
448 | @code{imenu-create-index-function} (@pxref{Imenu}). | |
449 | ||
450 | @item | |
451 | The mode can specify a local value for | |
452 | @code{eldoc-documentation-function} to tell ElDoc mode how to handle | |
453 | this mode. | |
454 | ||
769741e3 SM |
455 | @item |
456 | The mode can specify how to complete various keywords by adding | |
457 | to the special hook @code{completion-at-point-functions}. | |
458 | ||
b8d4c8d0 GM |
459 | @item |
460 | Use @code{defvar} or @code{defcustom} to set mode-related variables, so | |
461 | that they are not reinitialized if they already have a value. (Such | |
462 | reinitialization could discard customizations made by the user.) | |
463 | ||
464 | @item | |
465 | @cindex buffer-local variables in modes | |
466 | To make a buffer-local binding for an Emacs customization variable, use | |
467 | @code{make-local-variable} in the major mode command, not | |
468 | @code{make-variable-buffer-local}. The latter function would make the | |
469 | variable local to every buffer in which it is subsequently set, which | |
470 | would affect buffers that do not use this mode. It is undesirable for a | |
471 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
472 | ||
473 | With rare exceptions, the only reasonable way to use | |
474 | @code{make-variable-buffer-local} in a Lisp package is for a variable | |
475 | which is used only within that package. Using it on a variable used by | |
476 | other packages would interfere with them. | |
477 | ||
478 | @item | |
479 | @cindex mode hook | |
480 | @cindex major mode hook | |
481 | Each major mode should have a normal @dfn{mode hook} named | |
482 | @code{@var{modename}-mode-hook}. The very last thing the major mode command | |
483 | should do is to call @code{run-mode-hooks}. This runs the mode hook, | |
484 | and then runs the normal hook @code{after-change-major-mode-hook}. | |
485 | @xref{Mode Hooks}. | |
486 | ||
487 | @item | |
488 | The major mode command may start by calling some other major mode | |
489 | command (called the @dfn{parent mode}) and then alter some of its | |
490 | settings. A mode that does this is called a @dfn{derived mode}. The | |
41633740 CY |
491 | recommended way to define one is to use the @code{define-derived-mode} |
492 | macro, but this is not required. Such a mode should call the parent | |
493 | mode command inside a @code{delay-mode-hooks} form. (Using | |
b8d4c8d0 GM |
494 | @code{define-derived-mode} does this automatically.) @xref{Derived |
495 | Modes}, and @ref{Mode Hooks}. | |
496 | ||
497 | @item | |
498 | If something special should be done if the user switches a buffer from | |
499 | this mode to any other major mode, this mode can set up a buffer-local | |
500 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). | |
501 | ||
502 | @item | |
503 | If this mode is appropriate only for specially-prepared text, then the | |
504 | major mode command symbol should have a property named @code{mode-class} | |
505 | with value @code{special}, put on as follows: | |
506 | ||
507 | @kindex mode-class @r{(property)} | |
508 | @cindex @code{special} | |
509 | @example | |
510 | (put 'funny-mode 'mode-class 'special) | |
511 | @end example | |
512 | ||
513 | @noindent | |
514 | This tells Emacs that new buffers created while the current buffer is | |
4e3b4528 SM |
515 | in Funny mode should not inherit Funny mode, in case the default value |
516 | of @code{major-mode} is @code{nil}. Modes such as Dired, Rmail, | |
b8d4c8d0 GM |
517 | and Buffer List use this feature. |
518 | ||
41633740 CY |
519 | The @code{define-derived-mode} macro automatically marks the derived |
520 | mode as special if the parent mode is special. The special mode | |
521 | @code{special-mode} provides a convenient parent for other special | |
522 | modes to inherit from; it sets @code{buffer-read-only} to @code{t}, | |
769741e3 | 523 | and does little else. |
41633740 | 524 | |
b8d4c8d0 GM |
525 | @item |
526 | If you want to make the new mode the default for files with certain | |
527 | recognizable names, add an element to @code{auto-mode-alist} to select | |
528 | the mode for those file names (@pxref{Auto Major Mode}). If you | |
529 | define the mode command to autoload, you should add this element in | |
530 | the same file that calls @code{autoload}. If you use an autoload | |
531 | cookie for the mode command, you can also use an autoload cookie for | |
532 | the form that adds the element (@pxref{autoload cookie}). If you do | |
533 | not autoload the mode command, it is sufficient to add the element in | |
534 | the file that contains the mode definition. | |
535 | ||
536 | @item | |
537 | In the comments that document the file, you should provide a sample | |
538 | @code{autoload} form and an example of how to add to | |
539 | @code{auto-mode-alist}, that users can include in their init files | |
540 | (@pxref{Init File}). | |
541 | ||
542 | @item | |
543 | @cindex mode loading | |
544 | The top-level forms in the file defining the mode should be written so | |
545 | that they may be evaluated more than once without adverse consequences. | |
546 | Even if you never load the file more than once, someone else will. | |
547 | @end itemize | |
548 | ||
549 | @node Auto Major Mode | |
550 | @subsection How Emacs Chooses a Major Mode | |
551 | @cindex major mode, automatic selection | |
552 | ||
553 | Based on information in the file name or in the file itself, Emacs | |
554 | automatically selects a major mode for the new buffer when a file is | |
555 | visited. It also processes local variables specified in the file text. | |
556 | ||
557 | @deffn Command fundamental-mode | |
558 | Fundamental mode is a major mode that is not specialized for anything | |
559 | in particular. Other major modes are defined in effect by comparison | |
560 | with this one---their definitions say what to change, starting from | |
561 | Fundamental mode. The @code{fundamental-mode} function does @emph{not} | |
562 | run any mode hooks; you're not supposed to customize it. (If you want Emacs | |
563 | to behave differently in Fundamental mode, change the @emph{global} | |
564 | state of Emacs.) | |
565 | @end deffn | |
566 | ||
567 | @deffn Command normal-mode &optional find-file | |
568 | This function establishes the proper major mode and buffer-local variable | |
569 | bindings for the current buffer. First it calls @code{set-auto-mode} | |
570 | (see below), then it runs @code{hack-local-variables} to parse, and | |
571 | bind or evaluate as appropriate, the file's local variables | |
572 | (@pxref{File Local Variables}). | |
573 | ||
574 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, | |
575 | @code{normal-mode} assumes that the @code{find-file} function is calling | |
576 | it. In this case, it may process local variables in the @samp{-*-} | |
577 | line or at the end of the file. The variable | |
578 | @code{enable-local-variables} controls whether to do so. @xref{File | |
579 | Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, | |
580 | for the syntax of the local variables section of a file. | |
581 | ||
582 | If you run @code{normal-mode} interactively, the argument | |
583 | @var{find-file} is normally @code{nil}. In this case, | |
584 | @code{normal-mode} unconditionally processes any file local variables. | |
585 | ||
95459571 | 586 | The function calls @code{set-auto-mode} to choose a major mode. If this |
e145f188 GM |
587 | does not specify a mode, the buffer stays in the major mode determined |
588 | by the default value of @code{major-mode} (see below). | |
b8d4c8d0 GM |
589 | |
590 | @cindex file mode specification error | |
591 | @code{normal-mode} uses @code{condition-case} around the call to the | |
592 | major mode function, so errors are caught and reported as a @samp{File | |
593 | mode specification error}, followed by the original error message. | |
594 | @end deffn | |
595 | ||
596 | @defun set-auto-mode &optional keep-mode-if-same | |
597 | @cindex visited file mode | |
598 | This function selects the major mode that is appropriate for the | |
599 | current buffer. It bases its decision (in order of precedence) on | |
e145f188 GM |
600 | the @w{@samp{-*-}} line, on any @samp{mode:} local variable near the |
601 | end of a file, on the @w{@samp{#!}} line (using | |
b8d4c8d0 GM |
602 | @code{interpreter-mode-alist}), on the text at the beginning of the |
603 | buffer (using @code{magic-mode-alist}), and finally on the visited | |
604 | file name (using @code{auto-mode-alist}). @xref{Choosing Modes, , How | |
e145f188 | 605 | Major Modes are Chosen, emacs, The GNU Emacs Manual}. |
b8d4c8d0 | 606 | If @code{enable-local-variables} is @code{nil}, @code{set-auto-mode} |
e145f188 GM |
607 | does not check the @w{@samp{-*-}} line, or near the end of the file, |
608 | for any mode tag. | |
b8d4c8d0 GM |
609 | |
610 | If @var{keep-mode-if-same} is non-@code{nil}, this function does not | |
611 | call the mode command if the buffer is already in the proper major | |
612 | mode. For instance, @code{set-visited-file-name} sets this to | |
613 | @code{t} to avoid killing buffer local variables that the user may | |
614 | have set. | |
615 | @end defun | |
616 | ||
4e3b4528 SM |
617 | @defopt major-mode |
618 | The buffer-local value of this variable holds the major mode | |
619 | currently active. The default value of this variable holds the | |
620 | default major mode for new buffers. The standard default value is | |
621 | @code{fundamental-mode}. | |
b8d4c8d0 | 622 | |
4e3b4528 | 623 | If the default value of @code{major-mode} is @code{nil}, Emacs uses |
b8d4c8d0 GM |
624 | the (previously) current buffer's major mode as the default major mode |
625 | of a new buffer. However, if that major mode symbol has a @code{mode-class} | |
626 | property with value @code{special}, then it is not used for new buffers; | |
627 | Fundamental mode is used instead. The modes that have this property are | |
628 | those such as Dired and Rmail that are useful only with text that has | |
629 | been specially prepared. | |
630 | @end defopt | |
631 | ||
632 | @defun set-buffer-major-mode buffer | |
4e3b4528 SM |
633 | This function sets the major mode of @var{buffer} to the default value of |
634 | @code{major-mode}; if that is @code{nil}, it uses the | |
b8d4c8d0 GM |
635 | current buffer's major mode (if that is suitable). As an exception, |
636 | if @var{buffer}'s name is @samp{*scratch*}, it sets the mode to | |
637 | @code{initial-major-mode}. | |
638 | ||
639 | The low-level primitives for creating buffers do not use this function, | |
640 | but medium-level commands such as @code{switch-to-buffer} and | |
641 | @code{find-file-noselect} use it whenever they create buffers. | |
642 | @end defun | |
643 | ||
644 | @defopt initial-major-mode | |
645 | @cindex @samp{*scratch*} | |
646 | The value of this variable determines the major mode of the initial | |
647 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
648 | mode command. The default value is @code{lisp-interaction-mode}. | |
649 | @end defopt | |
650 | ||
651 | @defvar interpreter-mode-alist | |
652 | This variable specifies major modes to use for scripts that specify a | |
653 | command interpreter in a @samp{#!} line. Its value is an alist with | |
654 | elements of the form @code{(@var{interpreter} . @var{mode})}; for | |
655 | example, @code{("perl" . perl-mode)} is one element present by | |
656 | default. The element says to use mode @var{mode} if the file | |
657 | specifies an interpreter which matches @var{interpreter}. | |
658 | @end defvar | |
659 | ||
660 | @defvar magic-mode-alist | |
661 | This variable's value is an alist with elements of the form | |
662 | @code{(@var{regexp} . @var{function})}, where @var{regexp} is a | |
663 | regular expression and @var{function} is a function or @code{nil}. | |
664 | After visiting a file, @code{set-auto-mode} calls @var{function} if | |
665 | the text at the beginning of the buffer matches @var{regexp} and | |
666 | @var{function} is non-@code{nil}; if @var{function} is @code{nil}, | |
667 | @code{auto-mode-alist} gets to decide the mode. | |
668 | @end defvar | |
669 | ||
670 | @defvar magic-fallback-mode-alist | |
671 | This works like @code{magic-mode-alist}, except that it is handled | |
672 | only if @code{auto-mode-alist} does not specify a mode for this file. | |
673 | @end defvar | |
674 | ||
675 | @defvar auto-mode-alist | |
676 | This variable contains an association list of file name patterns | |
677 | (regular expressions) and corresponding major mode commands. Usually, | |
678 | the file name patterns test for suffixes, such as @samp{.el} and | |
679 | @samp{.c}, but this need not be the case. An ordinary element of the | |
680 | alist looks like @code{(@var{regexp} . @var{mode-function})}. | |
681 | ||
682 | For example, | |
683 | ||
684 | @smallexample | |
685 | @group | |
686 | (("\\`/tmp/fol/" . text-mode) | |
687 | ("\\.texinfo\\'" . texinfo-mode) | |
688 | ("\\.texi\\'" . texinfo-mode) | |
689 | @end group | |
690 | @group | |
691 | ("\\.el\\'" . emacs-lisp-mode) | |
692 | ("\\.c\\'" . c-mode) | |
693 | ("\\.h\\'" . c-mode) | |
694 | @dots{}) | |
695 | @end group | |
696 | @end smallexample | |
697 | ||
698 | When you visit a file whose expanded file name (@pxref{File Name | |
699 | Expansion}), with version numbers and backup suffixes removed using | |
700 | @code{file-name-sans-versions} (@pxref{File Name Components}), matches | |
701 | a @var{regexp}, @code{set-auto-mode} calls the corresponding | |
702 | @var{mode-function}. This feature enables Emacs to select the proper | |
703 | major mode for most files. | |
704 | ||
705 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
706 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
707 | @code{auto-mode-alist} again for a match against the portion of the file | |
708 | name that did not match before. This feature is useful for | |
709 | uncompression packages: an entry of the form @code{("\\.gz\\'" | |
710 | @var{function} t)} can uncompress the file and then put the uncompressed | |
711 | file in the proper mode according to the name sans @samp{.gz}. | |
712 | ||
713 | Here is an example of how to prepend several pattern pairs to | |
714 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
715 | init file.) | |
716 | ||
717 | @smallexample | |
718 | @group | |
719 | (setq auto-mode-alist | |
720 | (append | |
721 | ;; @r{File name (within directory) starts with a dot.} | |
722 | '(("/\\.[^/]*\\'" . fundamental-mode) | |
723 | ;; @r{File name has no dot.} | |
2674569b | 724 | ("/[^\\./]*\\'" . fundamental-mode) |
b8d4c8d0 GM |
725 | ;; @r{File name ends in @samp{.C}.} |
726 | ("\\.C\\'" . c++-mode)) | |
727 | auto-mode-alist)) | |
728 | @end group | |
729 | @end smallexample | |
730 | @end defvar | |
731 | ||
732 | @node Mode Help | |
733 | @subsection Getting Help about a Major Mode | |
734 | @cindex mode help | |
735 | @cindex help for major mode | |
736 | @cindex documentation for major mode | |
737 | ||
738 | The @code{describe-mode} function is used to provide information | |
739 | about major modes. It is normally called with @kbd{C-h m}. The | |
740 | @code{describe-mode} function uses the value of @code{major-mode}, | |
741 | which is why every major mode function needs to set the | |
742 | @code{major-mode} variable. | |
743 | ||
744 | @deffn Command describe-mode | |
745 | This function displays the documentation of the current major mode. | |
746 | ||
747 | The @code{describe-mode} function calls the @code{documentation} | |
748 | function using the value of @code{major-mode} as an argument. Thus, it | |
749 | displays the documentation string of the major mode function. | |
750 | (@xref{Accessing Documentation}.) | |
751 | @end deffn | |
752 | ||
753 | @defvar major-mode | |
754 | This buffer-local variable holds the symbol for the current buffer's | |
755 | major mode. This symbol should have a function definition that is the | |
756 | command to switch to that major mode. The @code{describe-mode} | |
757 | function uses the documentation string of the function as the | |
758 | documentation of the major mode. | |
759 | @end defvar | |
760 | ||
761 | @node Derived Modes | |
762 | @subsection Defining Derived Modes | |
763 | @cindex derived mode | |
764 | ||
769741e3 SM |
765 | The recommended way to define a new major mode is to derive it |
766 | from an existing one using @code{define-derived-mode}. If there is no | |
767 | closely related mode, you can inherit from @code{text-mode}, | |
80b33766 SM |
768 | @code{special-mode}, @code{prog-mode}, or in the worst case |
769 | @code{fundamental-mode}. | |
b8d4c8d0 GM |
770 | |
771 | @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{} | |
c986813b | 772 | This macro defines @var{variant} as a major mode command, using |
b8d4c8d0 GM |
773 | @var{name} as the string form of the mode name. @var{variant} and |
774 | @var{parent} should be unquoted symbols. | |
775 | ||
776 | The new command @var{variant} is defined to call the function | |
777 | @var{parent}, then override certain aspects of that parent mode: | |
778 | ||
779 | @itemize @bullet | |
780 | @item | |
781 | The new mode has its own sparse keymap, named | |
782 | @code{@var{variant}-map}. @code{define-derived-mode} | |
783 | makes the parent mode's keymap the parent of the new map, unless | |
784 | @code{@var{variant}-map} is already set and already has a parent. | |
785 | ||
786 | @item | |
787 | The new mode has its own syntax table, kept in the variable | |
788 | @code{@var{variant}-syntax-table}, unless you override this using the | |
789 | @code{:syntax-table} keyword (see below). @code{define-derived-mode} | |
790 | makes the parent mode's syntax-table the parent of | |
791 | @code{@var{variant}-syntax-table}, unless the latter is already set | |
792 | and already has a parent different from the standard syntax table. | |
793 | ||
794 | @item | |
795 | The new mode has its own abbrev table, kept in the variable | |
796 | @code{@var{variant}-abbrev-table}, unless you override this using the | |
797 | @code{:abbrev-table} keyword (see below). | |
798 | ||
799 | @item | |
800 | The new mode has its own mode hook, @code{@var{variant}-hook}. It | |
801 | runs this hook, after running the hooks of its ancestor modes, with | |
802 | @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}. | |
803 | @end itemize | |
804 | ||
805 | In addition, you can specify how to override other aspects of | |
806 | @var{parent} with @var{body}. The command @var{variant} | |
807 | evaluates the forms in @var{body} after setting up all its usual | |
808 | overrides, just before running the mode hooks. | |
809 | ||
c986813b CY |
810 | If @var{parent} has a non-@code{nil} @code{mode-class} symbol |
811 | property, then @code{define-derived-mode} sets the @code{mode-class} | |
812 | property of @var{variant} to the same value. This ensures, for | |
813 | example, that if @var{parent} is a special mode, then @var{variant} is | |
814 | also a special mode (@pxref{Major Mode Conventions}). | |
815 | ||
b8d4c8d0 GM |
816 | You can also specify @code{nil} for @var{parent}. This gives the new |
817 | mode no parent. Then @code{define-derived-mode} behaves as described | |
818 | above, but, of course, omits all actions connected with @var{parent}. | |
819 | ||
820 | The argument @var{docstring} specifies the documentation string for | |
821 | the new mode. @code{define-derived-mode} adds some general | |
822 | information about the mode's hook, followed by the mode's keymap, at | |
823 | the end of this docstring. If you omit @var{docstring}, | |
824 | @code{define-derived-mode} generates a documentation string. | |
825 | ||
826 | The @var{keyword-args} are pairs of keywords and values. The values | |
827 | are evaluated. The following keywords are currently supported: | |
828 | ||
829 | @table @code | |
830 | @item :syntax-table | |
831 | You can use this to explicitly specify a syntax table for the new | |
832 | mode. If you specify a @code{nil} value, the new mode uses the same | |
833 | syntax table as @var{parent}, or the standard syntax table if | |
834 | @var{parent} is @code{nil}. (Note that this does @emph{not} follow | |
835 | the convention used for non-keyword arguments that a @code{nil} value | |
836 | is equivalent with not specifying the argument.) | |
837 | ||
838 | @item :abbrev-table | |
839 | You can use this to explicitly specify an abbrev table for the new | |
840 | mode. If you specify a @code{nil} value, the new mode uses the same | |
841 | abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table} | |
842 | if @var{parent} is @code{nil}. (Again, a @code{nil} value is | |
843 | @emph{not} equivalent to not specifying this keyword.) | |
844 | ||
845 | @item :group | |
846 | If this is specified, the value should be the customization group for | |
847 | this mode. (Not all major modes have one.) Only the (still | |
848 | experimental and unadvertised) command @code{customize-mode} currently | |
849 | uses this. @code{define-derived-mode} does @emph{not} automatically | |
850 | define the specified customization group. | |
851 | @end table | |
852 | ||
853 | Here is a hypothetical example: | |
854 | ||
855 | @example | |
856 | (define-derived-mode hypertext-mode | |
857 | text-mode "Hypertext" | |
858 | "Major mode for hypertext. | |
859 | \\@{hypertext-mode-map@}" | |
860 | (setq case-fold-search nil)) | |
861 | ||
862 | (define-key hypertext-mode-map | |
863 | [down-mouse-3] 'do-hyper-link) | |
864 | @end example | |
865 | ||
866 | Do not write an @code{interactive} spec in the definition; | |
867 | @code{define-derived-mode} does that automatically. | |
868 | @end defmac | |
869 | ||
870 | @node Generic Modes | |
871 | @subsection Generic Modes | |
872 | @cindex generic mode | |
873 | ||
874 | @dfn{Generic modes} are simple major modes with basic support for | |
875 | comment syntax and Font Lock mode. To define a generic mode, use the | |
876 | macro @code{define-generic-mode}. See the file @file{generic-x.el} | |
877 | for some examples of the use of @code{define-generic-mode}. | |
878 | ||
879 | @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring | |
880 | This macro defines a generic mode command named @var{mode} (a symbol, | |
881 | not quoted). The optional argument @var{docstring} is the | |
882 | documentation for the mode command. If you do not supply it, | |
883 | @code{define-generic-mode} generates one by default. | |
884 | ||
885 | The argument @var{comment-list} is a list in which each element is | |
886 | either a character, a string of one or two characters, or a cons cell. | |
887 | A character or a string is set up in the mode's syntax table as a | |
888 | ``comment starter.'' If the entry is a cons cell, the @sc{car} is set | |
889 | up as a ``comment starter'' and the @sc{cdr} as a ``comment ender.'' | |
890 | (Use @code{nil} for the latter if you want comments to end at the end | |
891 | of the line.) Note that the syntax table mechanism has limitations | |
892 | about what comment starters and enders are actually possible. | |
893 | @xref{Syntax Tables}. | |
894 | ||
895 | The argument @var{keyword-list} is a list of keywords to highlight | |
896 | with @code{font-lock-keyword-face}. Each keyword should be a string. | |
897 | Meanwhile, @var{font-lock-list} is a list of additional expressions to | |
898 | highlight. Each element of this list should have the same form as an | |
899 | element of @code{font-lock-keywords}. @xref{Search-based | |
900 | Fontification}. | |
901 | ||
902 | The argument @var{auto-mode-list} is a list of regular expressions to | |
903 | add to the variable @code{auto-mode-alist}. They are added by the execution | |
904 | of the @code{define-generic-mode} form, not by expanding the macro call. | |
905 | ||
906 | Finally, @var{function-list} is a list of functions for the mode | |
907 | command to call for additional setup. It calls these functions just | |
908 | before it runs the mode hook variable @code{@var{mode}-hook}. | |
909 | @end defmac | |
910 | ||
911 | @node Mode Hooks | |
912 | @subsection Mode Hooks | |
913 | ||
914 | Every major mode function should finish by running its mode hook and | |
915 | the mode-independent normal hook @code{after-change-major-mode-hook}. | |
916 | It does this by calling @code{run-mode-hooks}. If the major mode is a | |
917 | derived mode, that is if it calls another major mode (the parent mode) | |
918 | in its body, it should do this inside @code{delay-mode-hooks} so that | |
919 | the parent won't run these hooks itself. Instead, the derived mode's | |
920 | call to @code{run-mode-hooks} runs the parent's mode hook too. | |
921 | @xref{Major Mode Conventions}. | |
922 | ||
923 | Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}. | |
924 | When user-implemented major modes have not been updated to use it, | |
925 | they won't entirely follow these conventions: they may run the | |
926 | parent's mode hook too early, or fail to run | |
927 | @code{after-change-major-mode-hook}. If you encounter such a major | |
928 | mode, please correct it to follow these conventions. | |
929 | ||
930 | When you defined a major mode using @code{define-derived-mode}, it | |
931 | automatically makes sure these conventions are followed. If you | |
932 | define a major mode ``by hand,'' not using @code{define-derived-mode}, | |
933 | use the following functions to handle these conventions automatically. | |
934 | ||
935 | @defun run-mode-hooks &rest hookvars | |
936 | Major modes should run their mode hook using this function. It is | |
937 | similar to @code{run-hooks} (@pxref{Hooks}), but it also runs | |
938 | @code{after-change-major-mode-hook}. | |
939 | ||
940 | When this function is called during the execution of a | |
941 | @code{delay-mode-hooks} form, it does not run the hooks immediately. | |
942 | Instead, it arranges for the next call to @code{run-mode-hooks} to run | |
943 | them. | |
944 | @end defun | |
945 | ||
946 | @defmac delay-mode-hooks body@dots{} | |
947 | When one major mode command calls another, it should do so inside of | |
948 | @code{delay-mode-hooks}. | |
949 | ||
950 | This macro executes @var{body}, but tells all @code{run-mode-hooks} | |
951 | calls during the execution of @var{body} to delay running their hooks. | |
952 | The hooks will actually run during the next call to | |
953 | @code{run-mode-hooks} after the end of the @code{delay-mode-hooks} | |
954 | construct. | |
955 | @end defmac | |
956 | ||
957 | @defvar after-change-major-mode-hook | |
958 | This is a normal hook run by @code{run-mode-hooks}. It is run at the | |
959 | very end of every properly-written major mode function. | |
960 | @end defvar | |
961 | ||
962 | @node Example Major Modes | |
963 | @subsection Major Mode Examples | |
964 | ||
965 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
966 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
967 | the conventions listed above: | |
968 | ||
969 | @smallexample | |
970 | @group | |
971 | ;; @r{Create the syntax table for this mode.} | |
972 | (defvar text-mode-syntax-table | |
973 | (let ((st (make-syntax-table))) | |
974 | (modify-syntax-entry ?\" ". " st) | |
975 | (modify-syntax-entry ?\\ ". " st) | |
976 | ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. | |
977 | (modify-syntax-entry ?' "w p" st) | |
978 | st) | |
979 | "Syntax table used while in `text-mode'.") | |
980 | @end group | |
981 | ||
982 | ;; @r{Create the keymap for this mode.} | |
983 | @group | |
984 | (defvar text-mode-map | |
985 | (let ((map (make-sparse-keymap))) | |
986 | (define-key map "\e\t" 'ispell-complete-word) | |
987 | (define-key map "\es" 'center-line) | |
988 | (define-key map "\eS" 'center-paragraph) | |
989 | map) | |
990 | "Keymap for `text-mode'. | |
991 | Many other modes, such as Mail mode, Outline mode | |
992 | and Indented Text mode, inherit all the commands | |
993 | defined in this map.") | |
994 | @end group | |
995 | @end smallexample | |
996 | ||
997 | Here is how the actual mode command is defined now: | |
998 | ||
999 | @smallexample | |
1000 | @group | |
1001 | (define-derived-mode text-mode nil "Text" | |
1002 | "Major mode for editing text written for humans to read. | |
1003 | In this mode, paragraphs are delimited only by blank or white lines. | |
1004 | You can thus get the full benefit of adaptive filling | |
1005 | (see the variable `adaptive-fill-mode'). | |
1006 | \\@{text-mode-map@} | |
1007 | Turning on Text mode runs the normal hook `text-mode-hook'." | |
1008 | @end group | |
1009 | @group | |
769741e3 | 1010 | (set (make-local-variable 'text-mode-variant) t) |
b8d4c8d0 GM |
1011 | ;; @r{These two lines are a feature added recently.} |
1012 | (set (make-local-variable 'require-final-newline) | |
1013 | mode-require-final-newline) | |
1014 | (set (make-local-variable 'indent-line-function) 'indent-relative)) | |
1015 | @end group | |
1016 | @end smallexample | |
1017 | ||
1018 | @noindent | |
1019 | (The last line is redundant nowadays, since @code{indent-relative} is | |
1020 | the default value, and we'll delete it in a future version.) | |
1021 | ||
1022 | Here is how it was defined formerly, before | |
1023 | @code{define-derived-mode} existed: | |
1024 | ||
1025 | @smallexample | |
1026 | @group | |
1027 | ;; @r{This isn't needed nowadays, since @code{define-derived-mode} does it.} | |
769741e3 | 1028 | (define-abbrev-table 'text-mode-abbrev-table () |
b8d4c8d0 | 1029 | "Abbrev table used while in text mode.") |
b8d4c8d0 GM |
1030 | @end group |
1031 | ||
1032 | @group | |
1033 | (defun text-mode () | |
1034 | "Major mode for editing text intended for humans to read... | |
1035 | Special commands: \\@{text-mode-map@} | |
1036 | @end group | |
1037 | @group | |
1038 | Turning on text-mode runs the hook `text-mode-hook'." | |
1039 | (interactive) | |
1040 | (kill-all-local-variables) | |
1041 | (use-local-map text-mode-map) | |
1042 | @end group | |
1043 | @group | |
1044 | (setq local-abbrev-table text-mode-abbrev-table) | |
1045 | (set-syntax-table text-mode-syntax-table) | |
1046 | @end group | |
1047 | @group | |
1048 | ;; @r{These four lines are absent from the current version} | |
049bcbcb CY |
1049 | ;; @r{not because this is done some other way, but because} |
1050 | ;; @r{nowadays Text mode uses the normal definition of paragraphs.} | |
769741e3 SM |
1051 | (set (make-local-variable 'paragraph-start) |
1052 | (concat "[ \t]*$\\|" page-delimiter)) | |
1053 | (set (make-local-variable 'paragraph-separate) paragraph-start) | |
1054 | (set (make-local-variable 'indent-line-function) 'indent-relative-maybe) | |
b8d4c8d0 GM |
1055 | @end group |
1056 | @group | |
1057 | (setq mode-name "Text") | |
1058 | (setq major-mode 'text-mode) | |
1059 | (run-mode-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} | |
1060 | ; @r{customize the mode with a hook.} | |
1061 | @end group | |
1062 | @end smallexample | |
1063 | ||
1064 | @cindex @file{lisp-mode.el} | |
1065 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
1066 | Interaction mode) have more features than Text mode and the code is | |
1067 | correspondingly more complicated. Here are excerpts from | |
1068 | @file{lisp-mode.el} that illustrate how these modes are written. | |
1069 | ||
1070 | @cindex syntax table example | |
1071 | @smallexample | |
1072 | @group | |
1073 | ;; @r{Create mode-specific table variables.} | |
1074 | (defvar lisp-mode-syntax-table nil "") | |
1075 | (defvar lisp-mode-abbrev-table nil "") | |
1076 | @end group | |
1077 | ||
1078 | @group | |
1079 | (defvar emacs-lisp-mode-syntax-table | |
1080 | (let ((table (make-syntax-table))) | |
1081 | (let ((i 0)) | |
1082 | @end group | |
1083 | ||
1084 | @group | |
1085 | ;; @r{Set syntax of chars up to @samp{0} to say they are} | |
1086 | ;; @r{part of symbol names but not words.} | |
1087 | ;; @r{(The digit @samp{0} is @code{48} in the @acronym{ASCII} character set.)} | |
1088 | (while (< i ?0) | |
2f3725cd EZ |
1089 | (modify-syntax-entry i "_ " table) |
1090 | (setq i (1+ i))) | |
b8d4c8d0 GM |
1091 | ;; @r{@dots{} similar code follows for other character ranges.} |
1092 | @end group | |
1093 | @group | |
1094 | ;; @r{Then set the syntax codes for characters that are special in Lisp.} | |
1095 | (modify-syntax-entry ? " " table) | |
1096 | (modify-syntax-entry ?\t " " table) | |
1097 | (modify-syntax-entry ?\f " " table) | |
1098 | (modify-syntax-entry ?\n "> " table) | |
1099 | @end group | |
1100 | @group | |
1101 | ;; @r{Give CR the same syntax as newline, for selective-display.} | |
1102 | (modify-syntax-entry ?\^m "> " table) | |
1103 | (modify-syntax-entry ?\; "< " table) | |
1104 | (modify-syntax-entry ?` "' " table) | |
1105 | (modify-syntax-entry ?' "' " table) | |
1106 | (modify-syntax-entry ?, "' " table) | |
1107 | @end group | |
1108 | @group | |
1109 | ;; @r{@dots{}likewise for many other characters@dots{}} | |
1110 | (modify-syntax-entry ?\( "() " table) | |
1111 | (modify-syntax-entry ?\) ")( " table) | |
1112 | (modify-syntax-entry ?\[ "(] " table) | |
1113 | (modify-syntax-entry ?\] ")[ " table)) | |
1114 | table)) | |
1115 | @end group | |
1116 | @group | |
1117 | ;; @r{Create an abbrev table for lisp-mode.} | |
1118 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
1119 | @end group | |
1120 | @end smallexample | |
1121 | ||
1122 | The three modes for Lisp share much of their code. For instance, | |
1123 | each calls the following function to set various variables: | |
1124 | ||
1125 | @smallexample | |
1126 | @group | |
1127 | (defun lisp-mode-variables (lisp-syntax) | |
1128 | (when lisp-syntax | |
1129 | (set-syntax-table lisp-mode-syntax-table)) | |
1130 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
1131 | @dots{} | |
1132 | @end group | |
1133 | @end smallexample | |
1134 | ||
1135 | In Lisp and most programming languages, we want the paragraph | |
1136 | commands to treat only blank lines as paragraph separators. And the | |
1137 | modes should understand the Lisp conventions for comments. The rest of | |
1138 | @code{lisp-mode-variables} sets this up: | |
1139 | ||
1140 | @smallexample | |
1141 | @group | |
049bcbcb CY |
1142 | (set (make-local-variable 'paragraph-start) |
1143 | (concat page-delimiter "\\|$" )) | |
1144 | (set (make-local-variable 'paragraph-separate) | |
1145 | paragraph-start) | |
b8d4c8d0 GM |
1146 | @dots{} |
1147 | @end group | |
1148 | @group | |
049bcbcb CY |
1149 | (set (make-local-variable 'comment-indent-function) |
1150 | 'lisp-comment-indent)) | |
b8d4c8d0 GM |
1151 | @dots{} |
1152 | @end group | |
1153 | @end smallexample | |
1154 | ||
1155 | Each of the different Lisp modes has a slightly different keymap. For | |
1156 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other | |
1157 | Lisp modes do not. However, all Lisp modes have some commands in | |
1158 | common. The following code sets up the common commands: | |
1159 | ||
1160 | @smallexample | |
1161 | @group | |
769741e3 SM |
1162 | (defvar shared-lisp-mode-map |
1163 | (let ((map (make-sparse-keymap))) | |
1164 | (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) | |
1165 | (define-key shared-lisp-mode-map "\177" | |
1166 | 'backward-delete-char-untabify) | |
1167 | map) | |
b8d4c8d0 | 1168 | "Keymap for commands shared by all sorts of Lisp modes.") |
b8d4c8d0 GM |
1169 | @end group |
1170 | @end smallexample | |
1171 | ||
1172 | @noindent | |
1173 | And here is the code to set up the keymap for Lisp mode: | |
1174 | ||
1175 | @smallexample | |
1176 | @group | |
769741e3 SM |
1177 | (defvar lisp-mode-map |
1178 | (let ((map (make-sparse-keymap))) | |
1179 | (set-keymap-parent map shared-lisp-mode-map) | |
1180 | (define-key map "\e\C-x" 'lisp-eval-defun) | |
1181 | (define-key map "\C-c\C-z" 'run-lisp) | |
1182 | map) | |
b8d4c8d0 | 1183 | "Keymap for ordinary Lisp mode...") |
b8d4c8d0 GM |
1184 | @end group |
1185 | @end smallexample | |
1186 | ||
1187 | Finally, here is the complete major mode function definition for | |
1188 | Lisp mode. | |
1189 | ||
1190 | @smallexample | |
1191 | @group | |
1192 | (defun lisp-mode () | |
1193 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. | |
1194 | Commands: | |
1195 | Delete converts tabs to spaces as it moves back. | |
1196 | Blank lines separate paragraphs. Semicolons start comments. | |
1197 | \\@{lisp-mode-map@} | |
1198 | Note that `run-lisp' may be used either to start an inferior Lisp job | |
1199 | or to switch back to an existing one. | |
1200 | @end group | |
1201 | ||
1202 | @group | |
1203 | Entry to this mode calls the value of `lisp-mode-hook' | |
1204 | if that value is non-nil." | |
1205 | (interactive) | |
1206 | (kill-all-local-variables) | |
1207 | @end group | |
1208 | @group | |
1209 | (use-local-map lisp-mode-map) ; @r{Select the mode's keymap.} | |
1210 | (setq major-mode 'lisp-mode) ; @r{This is how @code{describe-mode}} | |
1211 | ; @r{finds out what to describe.} | |
1212 | (setq mode-name "Lisp") ; @r{This goes into the mode line.} | |
1213 | (lisp-mode-variables t) ; @r{This defines various variables.} | |
769741e3 SM |
1214 | (set (make-local-variable 'comment-start-skip) |
1215 | "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") | |
1216 | (set (make-local-variable 'font-lock-keywords-case-fold-search) t) | |
b8d4c8d0 GM |
1217 | @end group |
1218 | @group | |
1219 | (setq imenu-case-fold-search t) | |
1220 | (set-syntax-table lisp-mode-syntax-table) | |
1221 | (run-mode-hooks 'lisp-mode-hook)) ; @r{This permits the user to use a} | |
1222 | ; @r{hook to customize the mode.} | |
1223 | @end group | |
1224 | @end smallexample | |
1225 | ||
1226 | @node Minor Modes | |
1227 | @section Minor Modes | |
1228 | @cindex minor mode | |
1229 | ||
1230 | A @dfn{minor mode} provides features that users may enable or disable | |
1231 | independently of the choice of major mode. Minor modes can be enabled | |
1232 | individually or in combination. Minor modes would be better named | |
1233 | ``generally available, optional feature modes,'' except that such a name | |
1234 | would be unwieldy. | |
1235 | ||
1236 | A minor mode is not usually meant as a variation of a single major mode. | |
1237 | Usually they are general and can apply to many major modes. For | |
1238 | example, Auto Fill mode works with any major mode that permits text | |
1239 | insertion. To be general, a minor mode must be effectively independent | |
1240 | of the things major modes do. | |
1241 | ||
1242 | A minor mode is often much more difficult to implement than a major | |
1243 | mode. One reason is that you should be able to activate and deactivate | |
1244 | minor modes in any order. A minor mode should be able to have its | |
1245 | desired effect regardless of the major mode and regardless of the other | |
1246 | minor modes in effect. | |
1247 | ||
1248 | Often the biggest problem in implementing a minor mode is finding a | |
1249 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
1250 | keymaps make this easier than it used to be. | |
1251 | ||
1252 | @defvar minor-mode-list | |
1253 | The value of this variable is a list of all minor mode commands. | |
1254 | @end defvar | |
1255 | ||
1256 | @menu | |
1257 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
1258 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
1259 | * Defining Minor Modes:: A convenient facility for defining minor modes. | |
1260 | @end menu | |
1261 | ||
1262 | @node Minor Mode Conventions | |
1263 | @subsection Conventions for Writing Minor Modes | |
1264 | @cindex minor mode conventions | |
1265 | @cindex conventions for writing minor modes | |
1266 | ||
1267 | There are conventions for writing minor modes just as there are for | |
1268 | major modes. Several of the major mode conventions apply to minor | |
1269 | modes as well: those regarding the name of the mode initialization | |
1270 | function, the names of global symbols, the use of a hook at the end of | |
1271 | the initialization function, and the use of keymaps and other tables. | |
1272 | ||
1273 | In addition, there are several conventions that are specific to | |
1274 | minor modes. (The easiest way to follow all the conventions is to use | |
1275 | the macro @code{define-minor-mode}; @ref{Defining Minor Modes}.) | |
1276 | ||
1277 | @itemize @bullet | |
1278 | @item | |
1279 | @cindex mode variable | |
1280 | Make a variable whose name ends in @samp{-mode} to control the minor | |
1281 | mode. We call this the @dfn{mode variable}. The minor mode command | |
1282 | should set this variable (@code{nil} to disable; anything else to | |
1283 | enable). | |
1284 | ||
1285 | If possible, implement the mode so that setting the variable | |
1286 | automatically enables or disables the mode. Then the minor mode command | |
1287 | does not need to do anything except set the variable. | |
1288 | ||
1289 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
1290 | display the minor mode name in the mode line. It can also enable | |
1291 | or disable a minor mode keymap. Individual commands or hooks can also | |
1292 | check the variable's value. | |
1293 | ||
1294 | If you want the minor mode to be enabled separately in each buffer, | |
1295 | make the variable buffer-local. | |
1296 | ||
1297 | @item | |
1298 | Define a command whose name is the same as the mode variable. | |
1299 | Its job is to enable and disable the mode by setting the variable. | |
1300 | ||
1301 | The command should accept one optional argument. If the argument is | |
1302 | @code{nil}, it should toggle the mode (turn it on if it is off, and | |
1303 | off if it is on). It should turn the mode on if the argument is a | |
1304 | positive integer, the symbol @code{t}, or a list whose @sc{car} is one | |
1305 | of those. It should turn the mode off if the argument is a negative | |
1306 | integer or zero, the symbol @code{-}, or a list whose @sc{car} is a | |
1307 | negative integer or zero. The meaning of other arguments is not | |
1308 | specified. | |
1309 | ||
1310 | Here is an example taken from the definition of @code{transient-mark-mode}. | |
1311 | It shows the use of @code{transient-mark-mode} as a variable that enables or | |
1312 | disables the mode's behavior, and also shows the proper way to toggle, | |
1313 | enable or disable the minor mode based on the raw prefix argument value. | |
1314 | ||
1315 | @smallexample | |
1316 | @group | |
1317 | (setq transient-mark-mode | |
1318 | (if (null arg) (not transient-mark-mode) | |
1319 | (> (prefix-numeric-value arg) 0))) | |
1320 | @end group | |
1321 | @end smallexample | |
1322 | ||
1323 | @item | |
1324 | Add an element to @code{minor-mode-alist} for each minor mode | |
1325 | (@pxref{Definition of minor-mode-alist}), if you want to indicate the | |
1326 | minor mode in the mode line. This element should be a list of the | |
1327 | following form: | |
1328 | ||
1329 | @smallexample | |
1330 | (@var{mode-variable} @var{string}) | |
1331 | @end smallexample | |
1332 | ||
1333 | Here @var{mode-variable} is the variable that controls enabling of the | |
1334 | minor mode, and @var{string} is a short string, starting with a space, | |
1335 | to represent the mode in the mode line. These strings must be short so | |
1336 | that there is room for several of them at once. | |
1337 | ||
1338 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
1339 | check for an existing element, to avoid duplication. For example: | |
1340 | ||
1341 | @smallexample | |
1342 | @group | |
1343 | (unless (assq 'leif-mode minor-mode-alist) | |
1344 | (setq minor-mode-alist | |
1345 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
1346 | @end group | |
1347 | @end smallexample | |
1348 | ||
1349 | @noindent | |
1350 | or like this, using @code{add-to-list} (@pxref{List Variables}): | |
1351 | ||
1352 | @smallexample | |
1353 | @group | |
1354 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) | |
1355 | @end group | |
1356 | @end smallexample | |
1357 | @end itemize | |
1358 | ||
1359 | Global minor modes distributed with Emacs should if possible support | |
1360 | enabling and disabling via Custom (@pxref{Customization}). To do this, | |
1361 | the first step is to define the mode variable with @code{defcustom}, and | |
0fc76035 | 1362 | specify @code{:type 'boolean}. |
b8d4c8d0 GM |
1363 | |
1364 | If just setting the variable is not sufficient to enable the mode, you | |
1365 | should also specify a @code{:set} method which enables the mode by | |
1366 | invoking the mode command. Note in the variable's documentation string that | |
1367 | setting the variable other than via Custom may not take effect. | |
1368 | ||
1369 | Also mark the definition with an autoload cookie (@pxref{autoload cookie}), | |
1370 | and specify a @code{:require} so that customizing the variable will load | |
1371 | the library that defines the mode. This will copy suitable definitions | |
1372 | into @file{loaddefs.el} so that users can use @code{customize-option} to | |
1373 | enable the mode. For example: | |
1374 | ||
1375 | @smallexample | |
1376 | @group | |
1377 | ||
1378 | ;;;###autoload | |
1379 | (defcustom msb-mode nil | |
1380 | "Toggle msb-mode. | |
1381 | Setting this variable directly does not take effect; | |
1382 | use either \\[customize] or the function `msb-mode'." | |
1383 | :set 'custom-set-minor-mode | |
1384 | :initialize 'custom-initialize-default | |
1385 | :version "20.4" | |
1386 | :type 'boolean | |
1387 | :group 'msb | |
1388 | :require 'msb) | |
1389 | @end group | |
1390 | @end smallexample | |
1391 | ||
1392 | @node Keymaps and Minor Modes | |
1393 | @subsection Keymaps and Minor Modes | |
1394 | ||
1395 | Each minor mode can have its own keymap, which is active when the mode | |
1396 | is enabled. To set up a keymap for a minor mode, add an element to the | |
1397 | alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}. | |
1398 | ||
1399 | @cindex @code{self-insert-command}, minor modes | |
1400 | One use of minor mode keymaps is to modify the behavior of certain | |
1401 | self-inserting characters so that they do something else as well as | |
1402 | self-insert. In general, this is the only way to do that, since the | |
1403 | facilities for customizing @code{self-insert-command} are limited to | |
1404 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
1405 | substituting your own definition of @code{self-insert-command} for the | |
1406 | standard one. The editor command loop handles this function specially.) | |
1407 | ||
1408 | The key sequences bound in a minor mode should consist of @kbd{C-c} | |
1409 | followed by one of @kbd{.,/?`'"[]\|~!#$%^&*()-_+=}. (The other | |
1410 | punctuation characters are reserved for major modes.) | |
1411 | ||
1412 | @node Defining Minor Modes | |
1413 | @subsection Defining Minor Modes | |
1414 | ||
1415 | The macro @code{define-minor-mode} offers a convenient way of | |
1416 | implementing a mode in one self-contained definition. | |
1417 | ||
1418 | @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{} | |
1419 | This macro defines a new minor mode whose name is @var{mode} (a | |
1420 | symbol). It defines a command named @var{mode} to toggle the minor | |
1421 | mode, with @var{doc} as its documentation string. It also defines a | |
1422 | variable named @var{mode}, which is set to @code{t} or @code{nil} by | |
1423 | enabling or disabling the mode. The variable is initialized to | |
1424 | @var{init-value}. Except in unusual circumstances (see below), this | |
1425 | value must be @code{nil}. | |
1426 | ||
1427 | The string @var{lighter} says what to display in the mode line | |
1428 | when the mode is enabled; if it is @code{nil}, the mode is not displayed | |
1429 | in the mode line. | |
1430 | ||
bc7d7ea6 CY |
1431 | The optional argument @var{keymap} specifies the keymap for the minor |
1432 | mode. If non-@code{nil}, it should be a variable name (whose value is | |
1433 | a keymap), a keymap, or an alist of the form | |
b8d4c8d0 GM |
1434 | |
1435 | @example | |
1436 | (@var{key-sequence} . @var{definition}) | |
1437 | @end example | |
1438 | ||
bc7d7ea6 CY |
1439 | @noindent |
1440 | where each @var{key-sequence} and @var{definition} are arguments | |
1441 | suitable for passing to @code{define-key} (@pxref{Changing Key | |
1442 | Bindings}). If @var{keymap} is a keymap or an alist, this also | |
1443 | defines the variable @code{@var{mode}-map}. | |
1444 | ||
b8d4c8d0 GM |
1445 | The above three arguments @var{init-value}, @var{lighter}, and |
1446 | @var{keymap} can be (partially) omitted when @var{keyword-args} are | |
1447 | used. The @var{keyword-args} consist of keywords followed by | |
1448 | corresponding values. A few keywords have special meanings: | |
1449 | ||
1450 | @table @code | |
1451 | @item :group @var{group} | |
1452 | Custom group name to use in all generated @code{defcustom} forms. | |
1453 | Defaults to @var{mode} without the possible trailing @samp{-mode}. | |
1454 | @strong{Warning:} don't use this default group name unless you have | |
1455 | written a @code{defgroup} to define that group properly. @xref{Group | |
1456 | Definitions}. | |
1457 | ||
1458 | @item :global @var{global} | |
1459 | If non-@code{nil}, this specifies that the minor mode should be global | |
1460 | rather than buffer-local. It defaults to @code{nil}. | |
1461 | ||
1462 | One of the effects of making a minor mode global is that the | |
1463 | @var{mode} variable becomes a customization variable. Toggling it | |
1464 | through the Custom interface turns the mode on and off, and its value | |
1465 | can be saved for future Emacs sessions (@pxref{Saving | |
1466 | Customizations,,, emacs, The GNU Emacs Manual}. For the saved | |
1467 | variable to work, you should ensure that the @code{define-minor-mode} | |
1468 | form is evaluated each time Emacs starts; for packages that are not | |
1469 | part of Emacs, the easiest way to do this is to specify a | |
1470 | @code{:require} keyword. | |
1471 | ||
1472 | @item :init-value @var{init-value} | |
1473 | This is equivalent to specifying @var{init-value} positionally. | |
1474 | ||
1475 | @item :lighter @var{lighter} | |
1476 | This is equivalent to specifying @var{lighter} positionally. | |
1477 | ||
1478 | @item :keymap @var{keymap} | |
1479 | This is equivalent to specifying @var{keymap} positionally. | |
1480 | @end table | |
1481 | ||
1482 | Any other keyword arguments are passed directly to the | |
1483 | @code{defcustom} generated for the variable @var{mode}. | |
1484 | ||
1485 | The command named @var{mode} first performs the standard actions such | |
1486 | as setting the variable named @var{mode} and then executes the | |
1487 | @var{body} forms, if any. It finishes by running the mode hook | |
1488 | variable @code{@var{mode}-hook}. | |
1489 | @end defmac | |
1490 | ||
1491 | The initial value must be @code{nil} except in cases where (1) the | |
1492 | mode is preloaded in Emacs, or (2) it is painless for loading to | |
1493 | enable the mode even though the user did not request it. For | |
1494 | instance, if the mode has no effect unless something else is enabled, | |
1495 | and will always be loaded by that time, enabling it by default is | |
1496 | harmless. But these are unusual circumstances. Normally, the | |
1497 | initial value must be @code{nil}. | |
1498 | ||
1499 | @findex easy-mmode-define-minor-mode | |
1500 | The name @code{easy-mmode-define-minor-mode} is an alias | |
1501 | for this macro. | |
1502 | ||
1503 | Here is an example of using @code{define-minor-mode}: | |
1504 | ||
1505 | @smallexample | |
1506 | (define-minor-mode hungry-mode | |
1507 | "Toggle Hungry mode. | |
1508 | With no argument, this command toggles the mode. | |
1509 | Non-null prefix argument turns on the mode. | |
1510 | Null prefix argument turns off the mode. | |
1511 | ||
1512 | When Hungry mode is enabled, the control delete key | |
1513 | gobbles all preceding whitespace except the last. | |
1514 | See the command \\[hungry-electric-delete]." | |
1515 | ;; The initial value. | |
1516 | nil | |
1517 | ;; The indicator for the mode line. | |
1518 | " Hungry" | |
1519 | ;; The minor mode bindings. | |
e8bf5266 | 1520 | '(([C-backspace] . hungry-electric-delete)) |
b8d4c8d0 GM |
1521 | :group 'hunger) |
1522 | @end smallexample | |
1523 | ||
1524 | @noindent | |
1525 | This defines a minor mode named ``Hungry mode,'' a command named | |
1526 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} | |
1527 | which indicates whether the mode is enabled, and a variable named | |
1528 | @code{hungry-mode-map} which holds the keymap that is active when the | |
1529 | mode is enabled. It initializes the keymap with a key binding for | |
1530 | @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into | |
1531 | custom group @code{hunger}. There are no @var{body} forms---many | |
1532 | minor modes don't need any. | |
1533 | ||
1534 | Here's an equivalent way to write it: | |
1535 | ||
1536 | @smallexample | |
1537 | (define-minor-mode hungry-mode | |
1538 | "Toggle Hungry mode. | |
1539 | With no argument, this command toggles the mode. | |
1540 | Non-null prefix argument turns on the mode. | |
1541 | Null prefix argument turns off the mode. | |
1542 | ||
1543 | When Hungry mode is enabled, the control delete key | |
1544 | gobbles all preceding whitespace except the last. | |
1545 | See the command \\[hungry-electric-delete]." | |
1546 | ;; The initial value. | |
1547 | :init-value nil | |
1548 | ;; The indicator for the mode line. | |
1549 | :lighter " Hungry" | |
1550 | ;; The minor mode bindings. | |
1551 | :keymap | |
e8bf5266 JB |
1552 | '(([C-backspace] . hungry-electric-delete) |
1553 | ([C-M-backspace] | |
b8d4c8d0 GM |
1554 | . (lambda () |
1555 | (interactive) | |
1556 | (hungry-electric-delete t)))) | |
1557 | :group 'hunger) | |
1558 | @end smallexample | |
1559 | ||
1560 | @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{} | |
1561 | This defines a global toggle named @var{global-mode} whose meaning is | |
1562 | to enable or disable the buffer-local minor mode @var{mode} in all | |
1563 | buffers. To turn on the minor mode in a buffer, it uses the function | |
1564 | @var{turn-on}; to turn off the minor mode, it calls @code{mode} with | |
1565 | @minus{}1 as argument. | |
1566 | ||
1567 | Globally enabling the mode also affects buffers subsequently created | |
1568 | by visiting files, and buffers that use a major mode other than | |
1569 | Fundamental mode; but it does not detect the creation of a new buffer | |
1570 | in Fundamental mode. | |
1571 | ||
1572 | This defines the customization option @var{global-mode} (@pxref{Customization}), | |
1573 | which can be toggled in the Custom interface to turn the minor mode on | |
1574 | and off. As with @code{define-minor-mode}, you should ensure that the | |
1575 | @code{define-globalized-minor-mode} form is evaluated each time Emacs | |
1576 | starts, for example by providing a @code{:require} keyword. | |
1577 | ||
1578 | Use @code{:group @var{group}} in @var{keyword-args} to specify the | |
1579 | custom group for the mode variable of the global minor mode. | |
1580 | @end defmac | |
1581 | ||
1582 | @node Mode Line Format | |
1583 | @section Mode-Line Format | |
1584 | @cindex mode line | |
1585 | ||
1586 | Each Emacs window (aside from minibuffer windows) typically has a mode | |
1587 | line at the bottom, which displays status information about the buffer | |
1588 | displayed in the window. The mode line contains information about the | |
1589 | buffer, such as its name, associated file, depth of recursive editing, | |
1590 | and major and minor modes. A window can also have a @dfn{header | |
1591 | line}, which is much like the mode line but appears at the top of the | |
1592 | window. | |
1593 | ||
1594 | This section describes how to control the contents of the mode line | |
1595 | and header line. We include it in this chapter because much of the | |
1596 | information displayed in the mode line relates to the enabled major and | |
1597 | minor modes. | |
1598 | ||
1599 | @menu | |
769741e3 SM |
1600 | * Base: Mode Line Basics. Basic ideas of mode line control. |
1601 | * Data: Mode Line Data. The data structure that controls the mode line. | |
1602 | * Top: Mode Line Top. The top level variable, mode-line-format. | |
1603 | * Mode Line Variables:: Variables used in that data structure. | |
1604 | * %-Constructs:: Putting information into a mode line. | |
1605 | * Properties in Mode:: Using text properties in the mode line. | |
1606 | * Header Lines:: Like a mode line, but at the top. | |
1607 | * Emulating Mode Line:: Formatting text as the mode line would. | |
b8d4c8d0 GM |
1608 | @end menu |
1609 | ||
1610 | @node Mode Line Basics | |
1611 | @subsection Mode Line Basics | |
1612 | ||
1613 | @code{mode-line-format} is a buffer-local variable that holds a | |
1614 | @dfn{mode line construct}, a kind of template, which controls what is | |
1615 | displayed on the mode line of the current buffer. The value of | |
1616 | @code{header-line-format} specifies the buffer's header line in the | |
1617 | same way. All windows for the same buffer use the same | |
1618 | @code{mode-line-format} and @code{header-line-format}. | |
1619 | ||
1620 | For efficiency, Emacs does not continuously recompute the mode | |
1621 | line and header line of a window. It does so when circumstances | |
1622 | appear to call for it---for instance, if you change the window | |
1623 | configuration, switch buffers, narrow or widen the buffer, scroll, or | |
1624 | change the buffer's modification status. If you modify any of the | |
1625 | variables referenced by @code{mode-line-format} (@pxref{Mode Line | |
1626 | Variables}), or any other variables and data structures that affect | |
1627 | how text is displayed (@pxref{Display}), you may want to force an | |
1628 | update of the mode line so as to display the new information or | |
1629 | display it in the new way. | |
1630 | ||
1631 | @defun force-mode-line-update &optional all | |
1632 | Force redisplay of the current buffer's mode line and header line. | |
1633 | The next redisplay will update the mode line and header line based on | |
1634 | the latest values of all relevant variables. With optional | |
1635 | non-@code{nil} @var{all}, force redisplay of all mode lines and header | |
1636 | lines. | |
1637 | ||
1638 | This function also forces recomputation of the menu bar menus | |
1639 | and the frame title. | |
1640 | @end defun | |
1641 | ||
1642 | The selected window's mode line is usually displayed in a different | |
1643 | color using the face @code{mode-line}. Other windows' mode lines | |
1644 | appear in the face @code{mode-line-inactive} instead. @xref{Faces}. | |
1645 | ||
1646 | @node Mode Line Data | |
1647 | @subsection The Data Structure of the Mode Line | |
1648 | @cindex mode-line construct | |
1649 | ||
1650 | The mode-line contents are controlled by a data structure called a | |
1651 | @dfn{mode-line construct}, made up of lists, strings, symbols, and | |
1652 | numbers kept in buffer-local variables. Each data type has a specific | |
1653 | meaning for the mode-line appearance, as described below. The same | |
1654 | data structure is used for constructing frame titles (@pxref{Frame | |
1655 | Titles}) and header lines (@pxref{Header Lines}). | |
1656 | ||
1657 | A mode-line construct may be as simple as a fixed string of text, | |
1658 | but it usually specifies how to combine fixed strings with variables' | |
1659 | values to construct the text. Many of these variables are themselves | |
1660 | defined to have mode-line constructs as their values. | |
1661 | ||
1662 | Here are the meanings of various data types as mode-line constructs: | |
1663 | ||
1664 | @table @code | |
1665 | @cindex percent symbol in mode line | |
1666 | @item @var{string} | |
1667 | A string as a mode-line construct appears verbatim except for | |
1668 | @dfn{@code{%}-constructs} in it. These stand for substitution of | |
1669 | other data; see @ref{%-Constructs}. | |
1670 | ||
1671 | If parts of the string have @code{face} properties, they control | |
1672 | display of the text just as they would text in the buffer. Any | |
1673 | characters which have no @code{face} properties are displayed, by | |
1674 | default, in the face @code{mode-line} or @code{mode-line-inactive} | |
1675 | (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The | |
1676 | @code{help-echo} and @code{local-map} properties in @var{string} have | |
1677 | special meanings. @xref{Properties in Mode}. | |
1678 | ||
1679 | @item @var{symbol} | |
1680 | A symbol as a mode-line construct stands for its value. The value of | |
1681 | @var{symbol} is used as a mode-line construct, in place of @var{symbol}. | |
1682 | However, the symbols @code{t} and @code{nil} are ignored, as is any | |
1683 | symbol whose value is void. | |
1684 | ||
1685 | There is one exception: if the value of @var{symbol} is a string, it is | |
1686 | displayed verbatim: the @code{%}-constructs are not recognized. | |
1687 | ||
1688 | Unless @var{symbol} is marked as ``risky'' (i.e., it has a | |
1689 | non-@code{nil} @code{risky-local-variable} property), all text | |
1690 | properties specified in @var{symbol}'s value are ignored. This | |
1691 | includes the text properties of strings in @var{symbol}'s value, as | |
1692 | well as all @code{:eval} and @code{:propertize} forms in it. (The | |
1693 | reason for this is security: non-risky variables could be set | |
1694 | automatically from file variables without prompting the user.) | |
1695 | ||
1696 | @item (@var{string} @var{rest}@dots{}) | |
1697 | @itemx (@var{list} @var{rest}@dots{}) | |
1698 | A list whose first element is a string or list means to process all the | |
1699 | elements recursively and concatenate the results. This is the most | |
1700 | common form of mode-line construct. | |
1701 | ||
1702 | @item (:eval @var{form}) | |
1703 | A list whose first element is the symbol @code{:eval} says to evaluate | |
1704 | @var{form}, and use the result as a string to display. Make sure this | |
1705 | evaluation cannot load any files, as doing so could cause infinite | |
1706 | recursion. | |
1707 | ||
1708 | @item (:propertize @var{elt} @var{props}@dots{}) | |
1709 | A list whose first element is the symbol @code{:propertize} says to | |
1710 | process the mode-line construct @var{elt} recursively, then add the text | |
1711 | properties specified by @var{props} to the result. The argument | |
1712 | @var{props} should consist of zero or more pairs @var{text-property} | |
1713 | @var{value}. (This feature is new as of Emacs 22.1.) | |
1714 | ||
1715 | @item (@var{symbol} @var{then} @var{else}) | |
1716 | A list whose first element is a symbol that is not a keyword specifies | |
1717 | a conditional. Its meaning depends on the value of @var{symbol}. If | |
1718 | @var{symbol} has a non-@code{nil} value, the second element, | |
1719 | @var{then}, is processed recursively as a mode-line element. | |
1720 | Otherwise, the third element, @var{else}, is processed recursively. | |
1721 | You may omit @var{else}; then the mode-line element displays nothing | |
1722 | if the value of @var{symbol} is @code{nil} or void. | |
1723 | ||
1724 | @item (@var{width} @var{rest}@dots{}) | |
1725 | A list whose first element is an integer specifies truncation or | |
1726 | padding of the results of @var{rest}. The remaining elements | |
1727 | @var{rest} are processed recursively as mode-line constructs and | |
1728 | concatenated together. When @var{width} is positive, the result is | |
1729 | space filled on the right if its width is less than @var{width}. When | |
1730 | @var{width} is negative, the result is truncated on the right to | |
1731 | @minus{}@var{width} columns if its width exceeds @minus{}@var{width}. | |
1732 | ||
1733 | For example, the usual way to show what percentage of a buffer is above | |
1734 | the top of the window is to use a list like this: @code{(-3 "%p")}. | |
1735 | @end table | |
1736 | ||
1737 | @node Mode Line Top | |
1738 | @subsection The Top Level of Mode Line Control | |
1739 | ||
1740 | The variable in overall control of the mode line is | |
1741 | @code{mode-line-format}. | |
1742 | ||
01f17ae2 | 1743 | @defopt mode-line-format |
b8d4c8d0 GM |
1744 | The value of this variable is a mode-line construct that controls the |
1745 | contents of the mode-line. It is always buffer-local in all buffers. | |
1746 | ||
1747 | If you set this variable to @code{nil} in a buffer, that buffer does | |
1748 | not have a mode line. (A window that is just one line tall never | |
1749 | displays a mode line.) | |
01f17ae2 | 1750 | @end defopt |
b8d4c8d0 GM |
1751 | |
1752 | The default value of @code{mode-line-format} is designed to use the | |
1753 | values of other variables such as @code{mode-line-position} and | |
1754 | @code{mode-line-modes} (which in turn incorporates the values of the | |
1755 | variables @code{mode-name} and @code{minor-mode-alist}). Very few | |
1756 | modes need to alter @code{mode-line-format} itself. For most | |
1757 | purposes, it is sufficient to alter some of the variables that | |
1758 | @code{mode-line-format} either directly or indirectly refers to. | |
1759 | ||
1760 | If you do alter @code{mode-line-format} itself, the new value should | |
1761 | use the same variables that appear in the default value (@pxref{Mode | |
1762 | Line Variables}), rather than duplicating their contents or displaying | |
1763 | the information in another fashion. This way, customizations made by | |
1764 | the user or by Lisp programs (such as @code{display-time} and major | |
1765 | modes) via changes to those variables remain effective. | |
1766 | ||
1767 | Here is an example of a @code{mode-line-format} that might be | |
1768 | useful for @code{shell-mode}, since it contains the host name and default | |
1769 | directory. | |
1770 | ||
1771 | @example | |
1772 | @group | |
1773 | (setq mode-line-format | |
1774 | (list "-" | |
1775 | 'mode-line-mule-info | |
1776 | 'mode-line-modified | |
1777 | 'mode-line-frame-identification | |
1778 | "%b--" | |
1779 | @end group | |
1780 | @group | |
1781 | ;; @r{Note that this is evaluated while making the list.} | |
1782 | ;; @r{It makes a mode-line construct which is just a string.} | |
1783 | (getenv "HOST") | |
1784 | @end group | |
1785 | ":" | |
1786 | 'default-directory | |
1787 | " " | |
1788 | 'global-mode-string | |
1789 | " %[(" | |
1790 | '(:eval (mode-line-mode-name)) | |
1791 | 'mode-line-process | |
1792 | 'minor-mode-alist | |
1793 | "%n" | |
1794 | ")%]--" | |
1795 | @group | |
1796 | '(which-func-mode ("" which-func-format "--")) | |
1797 | '(line-number-mode "L%l--") | |
1798 | '(column-number-mode "C%c--") | |
1799 | '(-3 "%p") | |
1800 | "-%-")) | |
1801 | @end group | |
1802 | @end example | |
1803 | ||
1804 | @noindent | |
1805 | (The variables @code{line-number-mode}, @code{column-number-mode} | |
1806 | and @code{which-func-mode} enable particular minor modes; as usual, | |
1807 | these variable names are also the minor mode command names.) | |
1808 | ||
1809 | @node Mode Line Variables | |
1810 | @subsection Variables Used in the Mode Line | |
1811 | ||
1812 | This section describes variables incorporated by the standard value | |
1813 | of @code{mode-line-format} into the text of the mode line. There is | |
1814 | nothing inherently special about these variables; any other variables | |
1815 | could have the same effects on the mode line if | |
1816 | @code{mode-line-format}'s value were changed to use them. However, | |
1817 | various parts of Emacs set these variables on the understanding that | |
1818 | they will control parts of the mode line; therefore, practically | |
1819 | speaking, it is essential for the mode line to use them. | |
1820 | ||
1821 | @defvar mode-line-mule-info | |
1822 | This variable holds the value of the mode-line construct that displays | |
1823 | information about the language environment, buffer coding system, and | |
1824 | current input method. @xref{Non-ASCII Characters}. | |
1825 | @end defvar | |
1826 | ||
1827 | @defvar mode-line-modified | |
1828 | This variable holds the value of the mode-line construct that displays | |
2079438a CY |
1829 | whether the current buffer is modified. Its default value displays |
1830 | @samp{**} if the buffer is modified, @samp{--} if the buffer is not | |
1831 | modified, @samp{%%} if the buffer is read only, and @samp{%*} if the | |
1832 | buffer is read only and modified. | |
b8d4c8d0 GM |
1833 | |
1834 | Changing this variable does not force an update of the mode line. | |
1835 | @end defvar | |
1836 | ||
1837 | @defvar mode-line-frame-identification | |
2079438a CY |
1838 | This variable identifies the current frame. Its default value |
1839 | displays @code{" "} if you are using a window system which can show | |
1840 | multiple frames, or @code{"-%F "} on an ordinary terminal which shows | |
1841 | only one frame at a time. | |
b8d4c8d0 GM |
1842 | @end defvar |
1843 | ||
1844 | @defvar mode-line-buffer-identification | |
2079438a CY |
1845 | This variable identifies the buffer being displayed in the window. |
1846 | Its default value displays the buffer name, padded with spaces to at | |
1847 | least 12 columns. | |
b8d4c8d0 GM |
1848 | @end defvar |
1849 | ||
01f17ae2 | 1850 | @defopt mode-line-position |
2079438a CY |
1851 | This variable indicates the position in the buffer. Its default value |
1852 | displays the buffer percentage and, optionally, the buffer size, the | |
1853 | line number and the column number. | |
01f17ae2 | 1854 | @end defopt |
b8d4c8d0 GM |
1855 | |
1856 | @defvar vc-mode | |
1857 | The variable @code{vc-mode}, buffer-local in each buffer, records | |
1858 | whether the buffer's visited file is maintained with version control, | |
1859 | and, if so, which kind. Its value is a string that appears in the mode | |
1860 | line, or @code{nil} for no version control. | |
1861 | @end defvar | |
1862 | ||
01f17ae2 | 1863 | @defopt mode-line-modes |
2079438a CY |
1864 | This variable displays the buffer's major and minor modes. Its |
1865 | default value also displays the recursive editing level, information | |
1866 | on the process status, and whether narrowing is in effect. | |
18d59e29 LMI |
1867 | @end defopt |
1868 | ||
1869 | @defopt mode-line-remote | |
1870 | This variable is used to show whether @code{default-directory} for the | |
1871 | current buffer is remote. | |
1872 | @end defopt | |
1873 | ||
1874 | @defopt mode-line-client | |
1875 | This variable is used to identify @code{emacsclient} frames. | |
01f17ae2 | 1876 | @end defopt |
b8d4c8d0 GM |
1877 | |
1878 | The following three variables are used in @code{mode-line-modes}: | |
1879 | ||
1880 | @defvar mode-name | |
1881 | This buffer-local variable holds the ``pretty'' name of the current | |
9cf52b11 EZ |
1882 | buffer's major mode. Each major mode should set this variable so that |
1883 | the mode name will appear in the mode line. The value does not have | |
1884 | to be a string, but can use any of the data types valid in a mode-line | |
1885 | construct (@pxref{Mode Line Data}). To compute the string that will | |
1886 | identify the mode name in the mode line, use @code{format-mode-line} | |
1887 | (@pxref{Emulating Mode Line}). | |
b8d4c8d0 GM |
1888 | @end defvar |
1889 | ||
1890 | @defvar mode-line-process | |
1891 | This buffer-local variable contains the mode-line information on process | |
1892 | status in modes used for communicating with subprocesses. It is | |
1893 | displayed immediately following the major mode name, with no intervening | |
1894 | space. For example, its value in the @samp{*shell*} buffer is | |
1895 | @code{(":%s")}, which allows the shell to display its status along | |
1896 | with the major mode as: @samp{(Shell:run)}. Normally this variable | |
1897 | is @code{nil}. | |
1898 | @end defvar | |
1899 | ||
1900 | @defvar minor-mode-alist | |
1901 | @anchor{Definition of minor-mode-alist} | |
1902 | This variable holds an association list whose elements specify how the | |
1903 | mode line should indicate that a minor mode is active. Each element of | |
1904 | the @code{minor-mode-alist} should be a two-element list: | |
1905 | ||
1906 | @example | |
1907 | (@var{minor-mode-variable} @var{mode-line-string}) | |
1908 | @end example | |
1909 | ||
1910 | More generally, @var{mode-line-string} can be any mode-line spec. It | |
1911 | appears in the mode line when the value of @var{minor-mode-variable} | |
1912 | is non-@code{nil}, and not otherwise. These strings should begin with | |
1913 | spaces so that they don't run together. Conventionally, the | |
1914 | @var{minor-mode-variable} for a specific mode is set to a | |
1915 | non-@code{nil} value when that minor mode is activated. | |
1916 | ||
1917 | @code{minor-mode-alist} itself is not buffer-local. Each variable | |
1918 | mentioned in the alist should be buffer-local if its minor mode can be | |
1919 | enabled separately in each buffer. | |
1920 | @end defvar | |
1921 | ||
1922 | @defvar global-mode-string | |
1923 | This variable holds a mode-line spec that, by default, appears in the | |
1924 | mode line just after the @code{which-func-mode} minor mode if set, | |
1925 | else after @code{mode-line-modes}. The command @code{display-time} | |
1926 | sets @code{global-mode-string} to refer to the variable | |
1927 | @code{display-time-string}, which holds a string containing the time | |
1928 | and load information. | |
1929 | ||
1930 | The @samp{%M} construct substitutes the value of | |
1931 | @code{global-mode-string}, but that is obsolete, since the variable is | |
1932 | included in the mode line from @code{mode-line-format}. | |
1933 | @end defvar | |
1934 | ||
b8d4c8d0 | 1935 | Here is a simplified version of the default value of |
4e3b4528 | 1936 | @code{mode-line-format}. The real default value also |
b8d4c8d0 GM |
1937 | specifies addition of text properties. |
1938 | ||
1939 | @example | |
1940 | @group | |
1941 | ("-" | |
1942 | mode-line-mule-info | |
1943 | mode-line-modified | |
1944 | mode-line-frame-identification | |
1945 | mode-line-buffer-identification | |
1946 | @end group | |
1947 | " " | |
1948 | mode-line-position | |
1949 | (vc-mode vc-mode) | |
1950 | " " | |
1951 | @group | |
1952 | mode-line-modes | |
1953 | (which-func-mode ("" which-func-format "--")) | |
1954 | (global-mode-string ("--" global-mode-string)) | |
1955 | "-%-") | |
1956 | @end group | |
1957 | @end example | |
b8d4c8d0 GM |
1958 | |
1959 | @node %-Constructs | |
1960 | @subsection @code{%}-Constructs in the Mode Line | |
1961 | ||
1962 | Strings used as mode-line constructs can use certain | |
1963 | @code{%}-constructs to substitute various kinds of data. Here is a | |
1964 | list of the defined @code{%}-constructs, and what they mean. In any | |
1965 | construct except @samp{%%}, you can add a decimal integer after the | |
1966 | @samp{%} to specify a minimum field width. If the width is less, the | |
1967 | field is padded with spaces to the right. | |
1968 | ||
1969 | @table @code | |
1970 | @item %b | |
1971 | The current buffer name, obtained with the @code{buffer-name} function. | |
1972 | @xref{Buffer Names}. | |
1973 | ||
1974 | @item %c | |
1975 | The current column number of point. | |
1976 | ||
1977 | @item %e | |
1978 | When Emacs is nearly out of memory for Lisp objects, a brief message | |
1979 | saying so. Otherwise, this is empty. | |
1980 | ||
1981 | @item %f | |
1982 | The visited file name, obtained with the @code{buffer-file-name} | |
1983 | function. @xref{Buffer File Name}. | |
1984 | ||
1985 | @item %F | |
1986 | The title (only on a window system) or the name of the selected frame. | |
1987 | @xref{Basic Parameters}. | |
1988 | ||
1989 | @item %i | |
1990 | The size of the accessible part of the current buffer; basically | |
1991 | @code{(- (point-max) (point-min))}. | |
1992 | ||
1993 | @item %I | |
1994 | Like @samp{%i}, but the size is printed in a more readable way by using | |
1995 | @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to | |
1996 | abbreviate. | |
1997 | ||
1998 | @item %l | |
1999 | The current line number of point, counting within the accessible portion | |
2000 | of the buffer. | |
2001 | ||
2002 | @item %n | |
2003 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
2004 | @code{narrow-to-region} in @ref{Narrowing}). | |
2005 | ||
2006 | @item %p | |
2007 | The percentage of the buffer text above the @strong{top} of window, or | |
2008 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default | |
2009 | mode-line specification truncates this to three characters. | |
2010 | ||
2011 | @item %P | |
2012 | The percentage of the buffer text that is above the @strong{bottom} of | |
2013 | the window (which includes the text visible in the window, as well as | |
2014 | the text above the top), plus @samp{Top} if the top of the buffer is | |
2015 | visible on screen; or @samp{Bottom} or @samp{All}. | |
2016 | ||
2017 | @item %s | |
2018 | The status of the subprocess belonging to the current buffer, obtained with | |
2019 | @code{process-status}. @xref{Process Information}. | |
2020 | ||
2021 | @item %t | |
2022 | Whether the visited file is a text file or a binary file. This is a | |
2023 | meaningful distinction only on certain operating systems (@pxref{MS-DOS | |
2024 | File Types}). | |
2025 | ||
2026 | @item %z | |
2027 | The mnemonics of keyboard, terminal, and buffer coding systems. | |
2028 | ||
2029 | @item %Z | |
2030 | Like @samp{%z}, but including the end-of-line format. | |
2031 | ||
2032 | @item %* | |
2033 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2034 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2035 | @samp{-} otherwise. @xref{Buffer Modification}. | |
2036 | ||
2037 | @item %+ | |
2038 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2039 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2040 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
2041 | read-only buffer. @xref{Buffer Modification}. | |
2042 | ||
2043 | @item %& | |
2044 | @samp{*} if the buffer is modified, and @samp{-} otherwise. | |
2045 | ||
2046 | @item %[ | |
2047 | An indication of the depth of recursive editing levels (not counting | |
2048 | minibuffer levels): one @samp{[} for each editing level. | |
2049 | @xref{Recursive Editing}. | |
2050 | ||
2051 | @item %] | |
2052 | One @samp{]} for each recursive editing level (not counting minibuffer | |
2053 | levels). | |
2054 | ||
2055 | @item %- | |
2056 | Dashes sufficient to fill the remainder of the mode line. | |
2057 | ||
2058 | @item %% | |
2059 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
2060 | string in which @code{%}-constructs are allowed. | |
2061 | @end table | |
2062 | ||
2063 | The following two @code{%}-constructs are still supported, but they are | |
2064 | obsolete, since you can get the same results with the variables | |
2065 | @code{mode-name} and @code{global-mode-string}. | |
2066 | ||
2067 | @table @code | |
2068 | @item %m | |
2069 | The value of @code{mode-name}. | |
2070 | ||
2071 | @item %M | |
2072 | The value of @code{global-mode-string}. | |
2073 | @end table | |
2074 | ||
2075 | @node Properties in Mode | |
2076 | @subsection Properties in the Mode Line | |
2077 | @cindex text properties in the mode line | |
2078 | ||
2079 | Certain text properties are meaningful in the | |
2080 | mode line. The @code{face} property affects the appearance of text; the | |
2081 | @code{help-echo} property associates help strings with the text, and | |
2082 | @code{local-map} can make the text mouse-sensitive. | |
2083 | ||
2084 | There are four ways to specify text properties for text in the mode | |
2085 | line: | |
2086 | ||
2087 | @enumerate | |
2088 | @item | |
2089 | Put a string with a text property directly into the mode-line data | |
2090 | structure. | |
2091 | ||
2092 | @item | |
2093 | Put a text property on a mode-line %-construct such as @samp{%12b}; then | |
2094 | the expansion of the %-construct will have that same text property. | |
2095 | ||
2096 | @item | |
2097 | Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to | |
2098 | give @var{elt} a text property specified by @var{props}. | |
2099 | ||
2100 | @item | |
2101 | Use a list containing @code{:eval @var{form}} in the mode-line data | |
2102 | structure, and make @var{form} evaluate to a string that has a text | |
2103 | property. | |
2104 | @end enumerate | |
2105 | ||
2106 | You can use the @code{local-map} property to specify a keymap. This | |
2107 | keymap only takes real effect for mouse clicks; binding character keys | |
2108 | and function keys to it has no effect, since it is impossible to move | |
2109 | point into the mode line. | |
2110 | ||
2111 | When the mode line refers to a variable which does not have a | |
2112 | non-@code{nil} @code{risky-local-variable} property, any text | |
2113 | properties given or specified within that variable's values are | |
2114 | ignored. This is because such properties could otherwise specify | |
2115 | functions to be called, and those functions could come from file | |
2116 | local variables. | |
2117 | ||
2118 | @node Header Lines | |
2119 | @subsection Window Header Lines | |
2120 | @cindex header line (of a window) | |
2121 | @cindex window header line | |
2122 | ||
2123 | A window can have a @dfn{header line} at the | |
2124 | top, just as it can have a mode line at the bottom. The header line | |
2125 | feature works just like the mode-line feature, except that it's | |
2126 | controlled by different variables. | |
2127 | ||
2128 | @defvar header-line-format | |
2129 | This variable, local in every buffer, specifies how to display the | |
2130 | header line, for windows displaying the buffer. The format of the value | |
2131 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). | |
b8d4c8d0 GM |
2132 | It is normally @code{nil}, so that ordinary buffers have no header line. |
2133 | @end defvar | |
2134 | ||
2135 | A window that is just one line tall never displays a header line. A | |
2136 | window that is two lines tall cannot display both a mode line and a | |
2137 | header line at once; if it has a mode line, then it does not display a | |
2138 | header line. | |
2139 | ||
2140 | @node Emulating Mode Line | |
2141 | @subsection Emulating Mode-Line Formatting | |
2142 | ||
2143 | You can use the function @code{format-mode-line} to compute | |
2144 | the text that would appear in a mode line or header line | |
2145 | based on a certain mode-line specification. | |
2146 | ||
2147 | @defun format-mode-line format &optional face window buffer | |
287e63bb EZ |
2148 | This function formats a line of text according to @var{format} as if it |
2149 | were generating the mode line for @var{window}, but it also returns the | |
2150 | text as a string. The argument @var{window} defaults to the selected | |
2151 | window. If @var{buffer} is non-@code{nil}, all the information used is | |
2152 | taken from @var{buffer}; by default, it comes from @var{window}'s | |
2153 | buffer. | |
b8d4c8d0 GM |
2154 | |
2155 | The value string normally has text properties that correspond to the | |
2e4ab211 EZ |
2156 | faces, keymaps, etc., that the mode line would have. Any character for |
2157 | which no @code{face} property is specified by @var{format} gets a | |
2158 | default value determined by @var{face}. If @var{face} is @code{t}, that | |
2159 | stands for either @code{mode-line} if @var{window} is selected, | |
b8d4c8d0 | 2160 | otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or |
2e4ab211 EZ |
2161 | omitted, that stands for the default face. If @var{face} is an integer, |
2162 | the value returned by this function will have no text properties. | |
b8d4c8d0 | 2163 | |
287e63bb | 2164 | You can also specify other valid faces as the value of @var{face}. |
2e4ab211 EZ |
2165 | If specified, that face provides the @code{face} property for characters |
2166 | whose face is not specified by @var{format}. | |
287e63bb EZ |
2167 | |
2168 | Note that using @code{mode-line}, @code{mode-line-inactive}, or | |
2169 | @code{header-line} as @var{face} will actually redisplay the mode line | |
2170 | or the header line, respectively, using the current definitions of the | |
2171 | corresponding face, in addition to returning the formatted string. | |
2172 | (Other faces do not cause redisplay.) | |
b8d4c8d0 GM |
2173 | |
2174 | For example, @code{(format-mode-line header-line-format)} returns the | |
2175 | text that would appear in the selected window's header line (@code{""} | |
2176 | if it has no header line). @code{(format-mode-line header-line-format | |
2177 | 'header-line)} returns the same text, with each character | |
287e63bb EZ |
2178 | carrying the face that it will have in the header line itself, and also |
2179 | redraws the header line. | |
b8d4c8d0 GM |
2180 | @end defun |
2181 | ||
2182 | @node Imenu | |
2183 | @section Imenu | |
2184 | ||
2185 | @cindex Imenu | |
2186 | @dfn{Imenu} is a feature that lets users select a definition or | |
2187 | section in the buffer, from a menu which lists all of them, to go | |
2188 | directly to that location in the buffer. Imenu works by constructing | |
2189 | a buffer index which lists the names and buffer positions of the | |
2190 | definitions, or other named portions of the buffer; then the user can | |
2191 | choose one of them and move point to it. Major modes can add a menu | |
2192 | bar item to use Imenu using @code{imenu-add-to-menubar}. | |
2193 | ||
2194 | @defun imenu-add-to-menubar name | |
2195 | This function defines a local menu bar item named @var{name} | |
2196 | to run Imenu. | |
2197 | @end defun | |
2198 | ||
2199 | The user-level commands for using Imenu are described in the Emacs | |
2200 | Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section | |
2201 | explains how to customize Imenu's method of finding definitions or | |
2202 | buffer portions for a particular major mode. | |
2203 | ||
2204 | The usual and simplest way is to set the variable | |
2205 | @code{imenu-generic-expression}: | |
2206 | ||
2207 | @defvar imenu-generic-expression | |
2208 | This variable, if non-@code{nil}, is a list that specifies regular | |
2209 | expressions for finding definitions for Imenu. Simple elements of | |
2210 | @code{imenu-generic-expression} look like this: | |
2211 | ||
2212 | @example | |
2213 | (@var{menu-title} @var{regexp} @var{index}) | |
2214 | @end example | |
2215 | ||
2216 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches | |
2217 | for this element should go in a submenu of the buffer index; | |
2218 | @var{menu-title} itself specifies the name for the submenu. If | |
2219 | @var{menu-title} is @code{nil}, the matches for this element go directly | |
2220 | in the top level of the buffer index. | |
2221 | ||
2222 | The second item in the list, @var{regexp}, is a regular expression | |
2223 | (@pxref{Regular Expressions}); anything in the buffer that it matches | |
2224 | is considered a definition, something to mention in the buffer index. | |
2225 | The third item, @var{index}, is a non-negative integer that indicates | |
2226 | which subexpression in @var{regexp} matches the definition's name. | |
2227 | ||
2228 | An element can also look like this: | |
2229 | ||
2230 | @example | |
2231 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) | |
2232 | @end example | |
2233 | ||
2234 | Each match for this element creates an index item, and when the index | |
2235 | item is selected by the user, it calls @var{function} with arguments | |
2236 | consisting of the item name, the buffer position, and @var{arguments}. | |
2237 | ||
2238 | For Emacs Lisp mode, @code{imenu-generic-expression} could look like | |
2239 | this: | |
2240 | ||
2241 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] | |
2242 | @example | |
2243 | @group | |
2244 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ | |
2245 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2246 | @end group | |
2247 | @group | |
2248 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ | |
2249 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2250 | @end group | |
2251 | @group | |
2252 | ("*Types*" | |
2253 | "^\\s-*\ | |
2254 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ | |
2255 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) | |
2256 | @end group | |
2257 | @end example | |
2258 | ||
2259 | Setting this variable makes it buffer-local in the current buffer. | |
2260 | @end defvar | |
2261 | ||
2262 | @defvar imenu-case-fold-search | |
2263 | This variable controls whether matching against the regular | |
2264 | expressions in the value of @code{imenu-generic-expression} is | |
2265 | case-sensitive: @code{t}, the default, means matching should ignore | |
2266 | case. | |
2267 | ||
2268 | Setting this variable makes it buffer-local in the current buffer. | |
2269 | @end defvar | |
2270 | ||
2271 | @defvar imenu-syntax-alist | |
2272 | This variable is an alist of syntax table modifiers to use while | |
2273 | processing @code{imenu-generic-expression}, to override the syntax table | |
2274 | of the current buffer. Each element should have this form: | |
2275 | ||
2276 | @example | |
2277 | (@var{characters} . @var{syntax-description}) | |
2278 | @end example | |
2279 | ||
2280 | The @sc{car}, @var{characters}, can be either a character or a string. | |
2281 | The element says to give that character or characters the syntax | |
2282 | specified by @var{syntax-description}, which is passed to | |
2283 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). | |
2284 | ||
2285 | This feature is typically used to give word syntax to characters which | |
2286 | normally have symbol syntax, and thus to simplify | |
2287 | @code{imenu-generic-expression} and speed up matching. | |
2288 | For example, Fortran mode uses it this way: | |
2289 | ||
2290 | @example | |
2291 | (setq imenu-syntax-alist '(("_$" . "w"))) | |
2292 | @end example | |
2293 | ||
2294 | The @code{imenu-generic-expression} regular expressions can then use | |
2295 | @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this | |
2296 | technique may be inconvenient when the mode needs to limit the initial | |
2297 | character of a name to a smaller set of characters than are allowed in | |
2298 | the rest of a name. | |
2299 | ||
2300 | Setting this variable makes it buffer-local in the current buffer. | |
2301 | @end defvar | |
2302 | ||
2303 | Another way to customize Imenu for a major mode is to set the | |
2304 | variables @code{imenu-prev-index-position-function} and | |
2305 | @code{imenu-extract-index-name-function}: | |
2306 | ||
2307 | @defvar imenu-prev-index-position-function | |
2308 | If this variable is non-@code{nil}, its value should be a function that | |
2309 | finds the next ``definition'' to put in the buffer index, scanning | |
2310 | backward in the buffer from point. It should return @code{nil} if it | |
2311 | doesn't find another ``definition'' before point. Otherwise it should | |
2312 | leave point at the place it finds a ``definition'' and return any | |
2313 | non-@code{nil} value. | |
2314 | ||
2315 | Setting this variable makes it buffer-local in the current buffer. | |
2316 | @end defvar | |
2317 | ||
2318 | @defvar imenu-extract-index-name-function | |
2319 | If this variable is non-@code{nil}, its value should be a function to | |
2320 | return the name for a definition, assuming point is in that definition | |
2321 | as the @code{imenu-prev-index-position-function} function would leave | |
2322 | it. | |
2323 | ||
2324 | Setting this variable makes it buffer-local in the current buffer. | |
2325 | @end defvar | |
2326 | ||
2327 | The last way to customize Imenu for a major mode is to set the | |
2328 | variable @code{imenu-create-index-function}: | |
2329 | ||
2330 | @defvar imenu-create-index-function | |
2331 | This variable specifies the function to use for creating a buffer | |
2332 | index. The function should take no arguments, and return an index | |
2333 | alist for the current buffer. It is called within | |
2334 | @code{save-excursion}, so where it leaves point makes no difference. | |
2335 | ||
2336 | The index alist can have three types of elements. Simple elements | |
2337 | look like this: | |
2338 | ||
2339 | @example | |
2340 | (@var{index-name} . @var{index-position}) | |
2341 | @end example | |
2342 | ||
2343 | Selecting a simple element has the effect of moving to position | |
2344 | @var{index-position} in the buffer. Special elements look like this: | |
2345 | ||
2346 | @example | |
2347 | (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{}) | |
2348 | @end example | |
2349 | ||
2350 | Selecting a special element performs: | |
2351 | ||
2352 | @example | |
2353 | (funcall @var{function} | |
2354 | @var{index-name} @var{index-position} @var{arguments}@dots{}) | |
2355 | @end example | |
2356 | ||
2357 | A nested sub-alist element looks like this: | |
2358 | ||
2359 | @example | |
2360 | (@var{menu-title} @var{sub-alist}) | |
2361 | @end example | |
2362 | ||
2363 | It creates the submenu @var{menu-title} specified by @var{sub-alist}. | |
2364 | ||
2365 | The default value of @code{imenu-create-index-function} is | |
2366 | @code{imenu-default-create-index-function}. This function calls the | |
2367 | value of @code{imenu-prev-index-position-function} and the value of | |
2368 | @code{imenu-extract-index-name-function} to produce the index alist. | |
2369 | However, if either of these two variables is @code{nil}, the default | |
2370 | function uses @code{imenu-generic-expression} instead. | |
2371 | ||
2372 | Setting this variable makes it buffer-local in the current buffer. | |
2373 | @end defvar | |
2374 | ||
2375 | @node Font Lock Mode | |
2376 | @section Font Lock Mode | |
2377 | @cindex Font Lock mode | |
2378 | ||
2379 | @dfn{Font Lock mode} is a feature that automatically attaches | |
2380 | @code{face} properties to certain parts of the buffer based on their | |
2381 | syntactic role. How it parses the buffer depends on the major mode; | |
2382 | most major modes define syntactic criteria for which faces to use in | |
2383 | which contexts. This section explains how to customize Font Lock for a | |
2384 | particular major mode. | |
2385 | ||
2386 | Font Lock mode finds text to highlight in two ways: through | |
2387 | syntactic parsing based on the syntax table, and through searching | |
2388 | (usually for regular expressions). Syntactic fontification happens | |
2389 | first; it finds comments and string constants and highlights them. | |
2390 | Search-based fontification happens second. | |
2391 | ||
2392 | @menu | |
2393 | * Font Lock Basics:: Overview of customizing Font Lock. | |
2394 | * Search-based Fontification:: Fontification based on regexps. | |
2395 | * Customizing Keywords:: Customizing search-based fontification. | |
2396 | * Other Font Lock Variables:: Additional customization facilities. | |
2397 | * Levels of Font Lock:: Each mode can define alternative levels | |
2398 | so that the user can select more or less. | |
769741e3 | 2399 | * Precalculated Fontification:: How Lisp programs that produce the buffer |
b8d4c8d0 GM |
2400 | contents can also specify how to fontify it. |
2401 | * Faces for Font Lock:: Special faces specifically for Font Lock. | |
2402 | * Syntactic Font Lock:: Fontification based on syntax tables. | |
2403 | * Setting Syntax Properties:: Defining character syntax based on context | |
2404 | using the Font Lock mechanism. | |
2405 | * Multiline Font Lock:: How to coerce Font Lock into properly | |
2406 | highlighting multiline constructs. | |
2407 | @end menu | |
2408 | ||
2409 | @node Font Lock Basics | |
2410 | @subsection Font Lock Basics | |
2411 | ||
2412 | There are several variables that control how Font Lock mode highlights | |
2413 | text. But major modes should not set any of these variables directly. | |
2414 | Instead, they should set @code{font-lock-defaults} as a buffer-local | |
2415 | variable. The value assigned to this variable is used, if and when Font | |
2416 | Lock mode is enabled, to set all the other variables. | |
2417 | ||
2418 | @defvar font-lock-defaults | |
2419 | This variable is set by major modes, as a buffer-local variable, to | |
2420 | specify how to fontify text in that mode. It automatically becomes | |
2421 | buffer-local when you set it. If its value is @code{nil}, Font-Lock | |
2422 | mode does no highlighting, and you can use the @samp{Faces} menu | |
2423 | (under @samp{Edit} and then @samp{Text Properties} in the menu bar) to | |
2424 | assign faces explicitly to text in the buffer. | |
2425 | ||
2426 | If non-@code{nil}, the value should look like this: | |
2427 | ||
2428 | @example | |
2429 | (@var{keywords} [@var{keywords-only} [@var{case-fold} | |
2430 | [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]]) | |
2431 | @end example | |
2432 | ||
2433 | The first element, @var{keywords}, indirectly specifies the value of | |
2434 | @code{font-lock-keywords} which directs search-based fontification. | |
2435 | It can be a symbol, a variable or a function whose value is the list | |
2436 | to use for @code{font-lock-keywords}. It can also be a list of | |
2437 | several such symbols, one for each possible level of fontification. | |
caef3ed2 GM |
2438 | The first symbol specifies the @samp{mode default} level of |
2439 | fontification, the next symbol level 1 fontification, the next level 2, | |
2440 | and so on. The @samp{mode default} level is normally the same as level | |
2441 | 1. It is used when @code{font-lock-maximum-decoration} has a @code{nil} | |
2442 | value. @xref{Levels of Font Lock}. | |
b8d4c8d0 GM |
2443 | |
2444 | The second element, @var{keywords-only}, specifies the value of the | |
2445 | variable @code{font-lock-keywords-only}. If this is omitted or | |
2446 | @code{nil}, syntactic fontification (of strings and comments) is also | |
2447 | performed. If this is non-@code{nil}, such fontification is not | |
2448 | performed. @xref{Syntactic Font Lock}. | |
2449 | ||
2450 | The third element, @var{case-fold}, specifies the value of | |
2451 | @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, | |
2452 | Font Lock mode ignores case when searching as directed by | |
2453 | @code{font-lock-keywords}. | |
2454 | ||
2455 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it | |
2456 | should be a list of cons cells of the form @code{(@var{char-or-string} | |
2457 | . @var{string})}. These are used to set up a syntax table for | |
2458 | syntactic fontification (@pxref{Syntax Table Functions}). The | |
2459 | resulting syntax table is stored in @code{font-lock-syntax-table}. | |
2460 | ||
2461 | The fifth element, @var{syntax-begin}, specifies the value of | |
2462 | @code{font-lock-beginning-of-syntax-function}. We recommend setting | |
2463 | this variable to @code{nil} and using @code{syntax-begin-function} | |
2464 | instead. | |
2465 | ||
2466 | All the remaining elements (if any) are collectively called | |
2467 | @var{other-vars}. Each of these elements should have the form | |
2468 | @code{(@var{variable} . @var{value})}---which means, make | |
2469 | @var{variable} buffer-local and then set it to @var{value}. You can | |
2470 | use these @var{other-vars} to set other variables that affect | |
2471 | fontification, aside from those you can control with the first five | |
2472 | elements. @xref{Other Font Lock Variables}. | |
2473 | @end defvar | |
2474 | ||
2475 | If your mode fontifies text explicitly by adding | |
2476 | @code{font-lock-face} properties, it can specify @code{(nil t)} for | |
2477 | @code{font-lock-defaults} to turn off all automatic fontification. | |
2478 | However, this is not required; it is possible to fontify some things | |
2479 | using @code{font-lock-face} properties and set up automatic | |
2480 | fontification for other parts of the text. | |
2481 | ||
2482 | @node Search-based Fontification | |
2483 | @subsection Search-based Fontification | |
2484 | ||
2485 | The most important variable for customizing Font Lock mode is | |
2486 | @code{font-lock-keywords}. It specifies the search criteria for | |
2487 | search-based fontification. You should specify the value of this | |
2488 | variable with @var{keywords} in @code{font-lock-defaults}. | |
2489 | ||
2490 | @defvar font-lock-keywords | |
2491 | This variable's value is a list of the keywords to highlight. Be | |
2492 | careful when composing regular expressions for this list; a poorly | |
2493 | written pattern can dramatically slow things down! | |
2494 | @end defvar | |
2495 | ||
2496 | Each element of @code{font-lock-keywords} specifies how to find | |
2497 | certain cases of text, and how to highlight those cases. Font Lock mode | |
2498 | processes the elements of @code{font-lock-keywords} one by one, and for | |
2499 | each element, it finds and handles all matches. Ordinarily, once | |
2500 | part of the text has been fontified already, this cannot be overridden | |
2501 | by a subsequent match in the same text; but you can specify different | |
2502 | behavior using the @var{override} element of a @var{subexp-highlighter}. | |
2503 | ||
2504 | Each element of @code{font-lock-keywords} should have one of these | |
2505 | forms: | |
2506 | ||
2507 | @table @code | |
2508 | @item @var{regexp} | |
2509 | Highlight all matches for @var{regexp} using | |
2510 | @code{font-lock-keyword-face}. For example, | |
2511 | ||
2512 | @example | |
2513 | ;; @r{Highlight occurrences of the word @samp{foo}} | |
2514 | ;; @r{using @code{font-lock-keyword-face}.} | |
2515 | "\\<foo\\>" | |
2516 | @end example | |
2517 | ||
2518 | The function @code{regexp-opt} (@pxref{Regexp Functions}) is useful | |
2519 | for calculating optimal regular expressions to match a number of | |
2520 | different keywords. | |
2521 | ||
2522 | @item @var{function} | |
2523 | Find text by calling @var{function}, and highlight the matches | |
2524 | it finds using @code{font-lock-keyword-face}. | |
2525 | ||
2526 | When @var{function} is called, it receives one argument, the limit of | |
2527 | the search; it should begin searching at point, and not search beyond the | |
2528 | limit. It should return non-@code{nil} if it succeeds, and set the | |
2529 | match data to describe the match that was found. Returning @code{nil} | |
2530 | indicates failure of the search. | |
2531 | ||
2532 | Fontification will call @var{function} repeatedly with the same limit, | |
2533 | and with point where the previous invocation left it, until | |
2534 | @var{function} fails. On failure, @var{function} need not reset point | |
2535 | in any particular way. | |
2536 | ||
2537 | @item (@var{matcher} . @var{subexp}) | |
2538 | In this kind of element, @var{matcher} is either a regular | |
2539 | expression or a function, as described above. The @sc{cdr}, | |
2540 | @var{subexp}, specifies which subexpression of @var{matcher} should be | |
2541 | highlighted (instead of the entire text that @var{matcher} matched). | |
2542 | ||
2543 | @example | |
2544 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} | |
2545 | ;; @r{using @code{font-lock-keyword-face}.} | |
2546 | ("fu\\(bar\\)" . 1) | |
2547 | @end example | |
2548 | ||
2549 | If you use @code{regexp-opt} to produce the regular expression | |
2550 | @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp | |
2551 | Functions}) to calculate the value for @var{subexp}. | |
2552 | ||
2553 | @item (@var{matcher} . @var{facespec}) | |
2554 | In this kind of element, @var{facespec} is an expression whose value | |
2555 | specifies the face to use for highlighting. In the simplest case, | |
2556 | @var{facespec} is a Lisp variable (a symbol) whose value is a face | |
2557 | name. | |
2558 | ||
2559 | @example | |
2560 | ;; @r{Highlight occurrences of @samp{fubar},} | |
2561 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2562 | ("fubar" . fubar-face) | |
2563 | @end example | |
2564 | ||
2565 | However, @var{facespec} can also evaluate to a list of this form: | |
2566 | ||
2567 | @example | |
2568 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) | |
2569 | @end example | |
2570 | ||
2571 | @noindent | |
2572 | to specify the face @var{face} and various additional text properties | |
2573 | to put on the text that matches. If you do this, be sure to add the | |
2574 | other text property names that you set in this way to the value of | |
2575 | @code{font-lock-extra-managed-props} so that the properties will also | |
2576 | be cleared out when they are no longer appropriate. Alternatively, | |
2577 | you can set the variable @code{font-lock-unfontify-region-function} to | |
2578 | a function that clears these properties. @xref{Other Font Lock | |
2579 | Variables}. | |
2580 | ||
2581 | @item (@var{matcher} . @var{subexp-highlighter}) | |
2582 | In this kind of element, @var{subexp-highlighter} is a list | |
2583 | which specifies how to highlight matches found by @var{matcher}. | |
2584 | It has the form: | |
2585 | ||
2586 | @example | |
e6c815ae | 2587 | (@var{subexp} @var{facespec} [@var{override} [@var{laxmatch}]]) |
b8d4c8d0 GM |
2588 | @end example |
2589 | ||
2590 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression | |
2591 | of the match to fontify (0 means the entire matching text). The second | |
2592 | subelement, @var{facespec}, is an expression whose value specifies the | |
2593 | face, as described above. | |
2594 | ||
2595 | The last two values in @var{subexp-highlighter}, @var{override} and | |
2596 | @var{laxmatch}, are optional flags. If @var{override} is @code{t}, | |
2597 | this element can override existing fontification made by previous | |
2598 | elements of @code{font-lock-keywords}. If it is @code{keep}, then | |
2599 | each character is fontified if it has not been fontified already by | |
2600 | some other element. If it is @code{prepend}, the face specified by | |
2601 | @var{facespec} is added to the beginning of the @code{font-lock-face} | |
2602 | property. If it is @code{append}, the face is added to the end of the | |
2603 | @code{font-lock-face} property. | |
2604 | ||
2605 | If @var{laxmatch} is non-@code{nil}, it means there should be no error | |
2606 | if there is no subexpression numbered @var{subexp} in @var{matcher}. | |
2607 | Obviously, fontification of the subexpression numbered @var{subexp} will | |
2608 | not occur. However, fontification of other subexpressions (and other | |
2609 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the | |
2610 | specified subexpression is missing, then an error is signaled which | |
2611 | terminates search-based fontification. | |
2612 | ||
2613 | Here are some examples of elements of this kind, and what they do: | |
2614 | ||
2615 | @smallexample | |
2616 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using} | |
2617 | ;; @r{@code{foo-bar-face}, even if they have already been highlighted.} | |
2618 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} | |
2619 | ("foo\\|bar" 0 foo-bar-face t) | |
2620 | ||
2621 | ;; @r{Highlight the first subexpression within each occurrence} | |
2622 | ;; @r{that the function @code{fubar-match} finds,} | |
2623 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2624 | (fubar-match 1 fubar-face) | |
2625 | @end smallexample | |
2626 | ||
2627 | @item (@var{matcher} . @var{anchored-highlighter}) | |
2628 | In this kind of element, @var{anchored-highlighter} specifies how to | |
2629 | highlight text that follows a match found by @var{matcher}. So a | |
2630 | match found by @var{matcher} acts as the anchor for further searches | |
2631 | specified by @var{anchored-highlighter}. @var{anchored-highlighter} | |
2632 | is a list of the following form: | |
2633 | ||
2634 | @example | |
2635 | (@var{anchored-matcher} @var{pre-form} @var{post-form} | |
2636 | @var{subexp-highlighters}@dots{}) | |
2637 | @end example | |
2638 | ||
2639 | Here, @var{anchored-matcher}, like @var{matcher}, is either a regular | |
2640 | expression or a function. After a match of @var{matcher} is found, | |
2641 | point is at the end of the match. Now, Font Lock evaluates the form | |
2642 | @var{pre-form}. Then it searches for matches of | |
2643 | @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight | |
2644 | these. A @var{subexp-highlighter} is as described above. Finally, | |
2645 | Font Lock evaluates @var{post-form}. | |
2646 | ||
2647 | The forms @var{pre-form} and @var{post-form} can be used to initialize | |
2648 | before, and cleanup after, @var{anchored-matcher} is used. Typically, | |
2649 | @var{pre-form} is used to move point to some position relative to the | |
2650 | match of @var{matcher}, before starting with @var{anchored-matcher}. | |
2651 | @var{post-form} might be used to move back, before resuming with | |
2652 | @var{matcher}. | |
2653 | ||
2654 | After Font Lock evaluates @var{pre-form}, it does not search for | |
2655 | @var{anchored-matcher} beyond the end of the line. However, if | |
2656 | @var{pre-form} returns a buffer position that is greater than the | |
2657 | position of point after @var{pre-form} is evaluated, then the position | |
2658 | returned by @var{pre-form} is used as the limit of the search instead. | |
2659 | It is generally a bad idea to return a position greater than the end | |
2660 | of the line; in other words, the @var{anchored-matcher} search should | |
2661 | not span lines. | |
2662 | ||
2663 | For example, | |
2664 | ||
2665 | @smallexample | |
2666 | ;; @r{Highlight occurrences of the word @samp{item} following} | |
2667 | ;; @r{an occurrence of the word @samp{anchor} (on the same line)} | |
2668 | ;; @r{in the value of @code{item-face}.} | |
2669 | ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) | |
2670 | @end smallexample | |
2671 | ||
2672 | Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore | |
2673 | searching for @samp{item} starts at the end of the match of | |
2674 | @samp{anchor}, and searching for subsequent instances of @samp{anchor} | |
2675 | resumes from where searching for @samp{item} concluded. | |
2676 | ||
2677 | @item (@var{matcher} @var{highlighters}@dots{}) | |
2678 | This sort of element specifies several @var{highlighter} lists for a | |
2679 | single @var{matcher}. A @var{highlighter} list can be of the type | |
2680 | @var{subexp-highlighter} or @var{anchored-highlighter} as described | |
2681 | above. | |
2682 | ||
2683 | For example, | |
2684 | ||
2685 | @smallexample | |
2686 | ;; @r{Highlight occurrences of the word @samp{anchor} in the value} | |
2687 | ;; @r{of @code{anchor-face}, and subsequent occurrences of the word} | |
2688 | ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.} | |
2689 | ("\\<anchor\\>" (0 anchor-face) | |
2690 | ("\\<item\\>" nil nil (0 item-face))) | |
2691 | @end smallexample | |
2692 | ||
2693 | @item (eval . @var{form}) | |
2694 | Here @var{form} is an expression to be evaluated the first time | |
2695 | this value of @code{font-lock-keywords} is used in a buffer. | |
2696 | Its value should have one of the forms described in this table. | |
2697 | @end table | |
2698 | ||
2699 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} | |
2700 | to match text which spans lines; this does not work reliably. | |
2701 | For details, see @xref{Multiline Font Lock}. | |
2702 | ||
2703 | You can use @var{case-fold} in @code{font-lock-defaults} to specify | |
2704 | the value of @code{font-lock-keywords-case-fold-search} which says | |
2705 | whether search-based fontification should be case-insensitive. | |
2706 | ||
2707 | @defvar font-lock-keywords-case-fold-search | |
2708 | Non-@code{nil} means that regular expression matching for the sake of | |
2709 | @code{font-lock-keywords} should be case-insensitive. | |
2710 | @end defvar | |
2711 | ||
2712 | @node Customizing Keywords | |
2713 | @subsection Customizing Search-Based Fontification | |
2714 | ||
2715 | You can use @code{font-lock-add-keywords} to add additional | |
2716 | search-based fontification rules to a major mode, and | |
867d4bb3 | 2717 | @code{font-lock-remove-keywords} to remove rules. |
b8d4c8d0 GM |
2718 | |
2719 | @defun font-lock-add-keywords mode keywords &optional how | |
2720 | This function adds highlighting @var{keywords}, for the current buffer | |
2721 | or for major mode @var{mode}. The argument @var{keywords} should be a | |
2722 | list with the same format as the variable @code{font-lock-keywords}. | |
2723 | ||
2724 | If @var{mode} is a symbol which is a major mode command name, such as | |
2725 | @code{c-mode}, the effect is that enabling Font Lock mode in | |
2726 | @var{mode} will add @var{keywords} to @code{font-lock-keywords}. | |
2727 | Calling with a non-@code{nil} value of @var{mode} is correct only in | |
2728 | your @file{~/.emacs} file. | |
2729 | ||
2730 | If @var{mode} is @code{nil}, this function adds @var{keywords} to | |
2731 | @code{font-lock-keywords} in the current buffer. This way of calling | |
2732 | @code{font-lock-add-keywords} is usually used in mode hook functions. | |
2733 | ||
2734 | By default, @var{keywords} are added at the beginning of | |
2735 | @code{font-lock-keywords}. If the optional argument @var{how} is | |
2736 | @code{set}, they are used to replace the value of | |
2737 | @code{font-lock-keywords}. If @var{how} is any other non-@code{nil} | |
2738 | value, they are added at the end of @code{font-lock-keywords}. | |
2739 | ||
2740 | Some modes provide specialized support you can use in additional | |
2741 | highlighting patterns. See the variables | |
2742 | @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types}, | |
2743 | and @code{java-font-lock-extra-types}, for example. | |
2744 | ||
2745 | @strong{Warning:} major mode functions must not call | |
2746 | @code{font-lock-add-keywords} under any circumstances, either directly | |
2747 | or indirectly, except through their mode hooks. (Doing so would lead | |
2748 | to incorrect behavior for some minor modes.) They should set up their | |
2749 | rules for search-based fontification by setting | |
2750 | @code{font-lock-keywords}. | |
2751 | @end defun | |
2752 | ||
2753 | @defun font-lock-remove-keywords mode keywords | |
2754 | This function removes @var{keywords} from @code{font-lock-keywords} | |
2755 | for the current buffer or for major mode @var{mode}. As in | |
2756 | @code{font-lock-add-keywords}, @var{mode} should be a major mode | |
2757 | command name or @code{nil}. All the caveats and requirements for | |
2758 | @code{font-lock-add-keywords} apply here too. | |
2759 | @end defun | |
2760 | ||
2761 | For example, this code | |
2762 | ||
2763 | @smallexample | |
2764 | (font-lock-add-keywords 'c-mode | |
2765 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2766 | ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) | |
2767 | @end smallexample | |
2768 | ||
2769 | @noindent | |
2770 | adds two fontification patterns for C mode: one to fontify the word | |
2771 | @samp{FIXME}, even in comments, and another to fontify the words | |
2772 | @samp{and}, @samp{or} and @samp{not} as keywords. | |
2773 | ||
2774 | @noindent | |
2775 | That example affects only C mode proper. To add the same patterns to | |
2776 | C mode @emph{and} all modes derived from it, do this instead: | |
2777 | ||
2778 | @smallexample | |
2779 | (add-hook 'c-mode-hook | |
2780 | (lambda () | |
2781 | (font-lock-add-keywords nil | |
2782 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2783 | ("\\<\\(and\\|or\\|not\\)\\>" . | |
2784 | font-lock-keyword-face))))) | |
2785 | @end smallexample | |
2786 | ||
2787 | @node Other Font Lock Variables | |
2788 | @subsection Other Font Lock Variables | |
2789 | ||
2790 | This section describes additional variables that a major mode can | |
2791 | set by means of @var{other-vars} in @code{font-lock-defaults} | |
2792 | (@pxref{Font Lock Basics}). | |
2793 | ||
2794 | @defvar font-lock-mark-block-function | |
2795 | If this variable is non-@code{nil}, it should be a function that is | |
2796 | called with no arguments, to choose an enclosing range of text for | |
2797 | refontification for the command @kbd{M-o M-o} | |
2798 | (@code{font-lock-fontify-block}). | |
2799 | ||
2800 | The function should report its choice by placing the region around it. | |
2801 | A good choice is a range of text large enough to give proper results, | |
2802 | but not too large so that refontification becomes slow. Typical values | |
2803 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for | |
2804 | textual modes. | |
2805 | @end defvar | |
2806 | ||
2807 | @defvar font-lock-extra-managed-props | |
2808 | This variable specifies additional properties (other than | |
2809 | @code{font-lock-face}) that are being managed by Font Lock mode. It | |
2810 | is used by @code{font-lock-default-unfontify-region}, which normally | |
2811 | only manages the @code{font-lock-face} property. If you want Font | |
2812 | Lock to manage other properties as well, you must specify them in a | |
2813 | @var{facespec} in @code{font-lock-keywords} as well as add them to | |
2814 | this list. @xref{Search-based Fontification}. | |
2815 | @end defvar | |
2816 | ||
2817 | @defvar font-lock-fontify-buffer-function | |
2818 | Function to use for fontifying the buffer. The default value is | |
2819 | @code{font-lock-default-fontify-buffer}. | |
2820 | @end defvar | |
2821 | ||
2822 | @defvar font-lock-unfontify-buffer-function | |
2823 | Function to use for unfontifying the buffer. This is used when | |
2824 | turning off Font Lock mode. The default value is | |
2825 | @code{font-lock-default-unfontify-buffer}. | |
2826 | @end defvar | |
2827 | ||
2828 | @defvar font-lock-fontify-region-function | |
2829 | Function to use for fontifying a region. It should take two | |
2830 | arguments, the beginning and end of the region, and an optional third | |
2831 | argument @var{verbose}. If @var{verbose} is non-@code{nil}, the | |
2832 | function should print status messages. The default value is | |
2833 | @code{font-lock-default-fontify-region}. | |
2834 | @end defvar | |
2835 | ||
2836 | @defvar font-lock-unfontify-region-function | |
2837 | Function to use for unfontifying a region. It should take two | |
2838 | arguments, the beginning and end of the region. The default value is | |
2839 | @code{font-lock-default-unfontify-region}. | |
2840 | @end defvar | |
2841 | ||
e070558d CY |
2842 | @defun jit-lock-register function &optional contextual |
2843 | This function tells Font Lock mode to run the Lisp function | |
2844 | @var{function} any time it has to fontify or refontify part of the | |
2845 | current buffer. It calls @var{function} before calling the default | |
2846 | fontification functions, and gives it two arguments, @var{start} and | |
2847 | @var{end}, which specify the region to be fontified or refontified. | |
2848 | ||
2849 | The optional argument @var{contextual}, if non-@code{nil}, forces Font | |
2850 | Lock mode to always refontify a syntactically relevant part of the | |
2851 | buffer, and not just the modified lines. This argument can usually be | |
2852 | omitted. | |
2853 | @end defun | |
2854 | ||
2855 | @defun jit-lock-unregister function | |
2856 | If @var{function} was previously registered as a fontification | |
2857 | function using @code{jit-lock-register}, this function unregisters it. | |
2858 | @end defun | |
b8d4c8d0 GM |
2859 | |
2860 | @node Levels of Font Lock | |
2861 | @subsection Levels of Font Lock | |
2862 | ||
2863 | Many major modes offer three different levels of fontification. You | |
2864 | can define multiple levels by using a list of symbols for @var{keywords} | |
2865 | in @code{font-lock-defaults}. Each symbol specifies one level of | |
caef3ed2 GM |
2866 | fontification; it is up to the user to choose one of these levels, |
2867 | normally by setting @code{font-lock-maximum-decoration} (@pxref{Font | |
2868 | Lock,,, emacs, the GNU Emacs Manual}). The chosen level's symbol | |
2869 | value is used to initialize @code{font-lock-keywords}. | |
b8d4c8d0 GM |
2870 | |
2871 | Here are the conventions for how to define the levels of | |
2872 | fontification: | |
2873 | ||
2874 | @itemize @bullet | |
2875 | @item | |
2876 | Level 1: highlight function declarations, file directives (such as include or | |
2877 | import directives), strings and comments. The idea is speed, so only | |
2878 | the most important and top-level components are fontified. | |
2879 | ||
2880 | @item | |
2881 | Level 2: in addition to level 1, highlight all language keywords, | |
2882 | including type names that act like keywords, as well as named constant | |
2883 | values. The idea is that all keywords (either syntactic or semantic) | |
2884 | should be fontified appropriately. | |
2885 | ||
2886 | @item | |
2887 | Level 3: in addition to level 2, highlight the symbols being defined in | |
2888 | function and variable declarations, and all builtin function names, | |
2889 | wherever they appear. | |
2890 | @end itemize | |
2891 | ||
2892 | @node Precalculated Fontification | |
2893 | @subsection Precalculated Fontification | |
2894 | ||
eae7d8f8 RS |
2895 | Some major modes such as @code{list-buffers} and @code{occur} |
2896 | construct the buffer text programmatically. The easiest way for them | |
2897 | to support Font Lock mode is to specify the faces of text when they | |
2898 | insert the text in the buffer. | |
2899 | ||
2900 | The way to do this is to specify the faces in the text with the | |
2901 | special text property @code{font-lock-face} (@pxref{Special | |
2902 | Properties}). When Font Lock mode is enabled, this property controls | |
2903 | the display, just like the @code{face} property. When Font Lock mode | |
2904 | is disabled, @code{font-lock-face} has no effect on the display. | |
2905 | ||
2906 | It is ok for a mode to use @code{font-lock-face} for some text and | |
2907 | also use the normal Font Lock machinery. But if the mode does not use | |
2908 | the normal Font Lock machinery, it should not set the variable | |
2909 | @code{font-lock-defaults}. | |
b8d4c8d0 GM |
2910 | |
2911 | @node Faces for Font Lock | |
2912 | @subsection Faces for Font Lock | |
2913 | @cindex faces for font lock | |
2914 | @cindex font lock faces | |
2915 | ||
e0dd6837 CY |
2916 | Font Lock mode can highlight using any face, but Emacs defines several |
2917 | faces specifically for syntactic highlighting. These @dfn{Font Lock | |
2918 | faces} are listed below. They can also be used by major modes for | |
2919 | syntactic highlighting outside of Font Lock mode (@pxref{Major Mode | |
2920 | Conventions}). | |
b8d4c8d0 | 2921 | |
e0dd6837 CY |
2922 | Each of these symbols is both a face name, and a variable whose |
2923 | default value is the symbol itself. Thus, the default value of | |
2924 | @code{font-lock-comment-face} is @code{font-lock-comment-face}. | |
b8d4c8d0 | 2925 | |
e0dd6837 CY |
2926 | The faces are listed with descriptions of their typical usage, and in |
2927 | order of greater to lesser ``prominence''. If a mode's syntactic | |
2928 | categories do not fit well with the usage descriptions, the faces can be | |
2929 | assigned using the ordering as a guide. | |
b8d4c8d0 | 2930 | |
e0dd6837 CY |
2931 | @table @code |
2932 | @item font-lock-warning-face | |
2933 | @vindex font-lock-warning-face | |
2934 | for a construct that is peculiar, or that greatly changes the meaning of | |
2935 | other text, like @samp{;;;###autoload} in Emacs Lisp and @samp{#error} | |
2936 | in C. | |
b8d4c8d0 GM |
2937 | |
2938 | @item font-lock-function-name-face | |
2939 | @vindex font-lock-function-name-face | |
e0dd6837 | 2940 | for the name of a function being defined or declared. |
b8d4c8d0 GM |
2941 | |
2942 | @item font-lock-variable-name-face | |
2943 | @vindex font-lock-variable-name-face | |
e0dd6837 CY |
2944 | for the name of a variable being defined or declared. |
2945 | ||
2946 | @item font-lock-keyword-face | |
2947 | @vindex font-lock-keyword-face | |
2948 | for a keyword with special syntactic significance, like @samp{for} and | |
2949 | @samp{if} in C. | |
2950 | ||
2951 | @item font-lock-comment-face | |
2952 | @vindex font-lock-comment-face | |
2953 | for comments. | |
2954 | ||
2955 | @item font-lock-comment-delimiter-face | |
2956 | @vindex font-lock-comment-delimiter-face | |
2957 | for comments delimiters, like @samp{/*} and @samp{*/} in C. On most | |
2958 | terminals, this inherits from @code{font-lock-comment-face}. | |
b8d4c8d0 GM |
2959 | |
2960 | @item font-lock-type-face | |
2961 | @vindex font-lock-type-face | |
e0dd6837 | 2962 | for the names of user-defined data types. |
b8d4c8d0 GM |
2963 | |
2964 | @item font-lock-constant-face | |
2965 | @vindex font-lock-constant-face | |
e0dd6837 CY |
2966 | for the names of constants, like @samp{NULL} in C. |
2967 | ||
2968 | @item font-lock-builtin-face | |
2969 | @vindex font-lock-builtin-face | |
2970 | for the names of built-in functions. | |
b8d4c8d0 GM |
2971 | |
2972 | @item font-lock-preprocessor-face | |
2973 | @vindex font-lock-preprocessor-face | |
e0dd6837 CY |
2974 | for preprocessor commands. This inherits, by default, from |
2975 | @code{font-lock-builtin-face}. | |
2976 | ||
2977 | @item font-lock-string-face | |
2978 | @vindex font-lock-string-face | |
2979 | for string constants. | |
2980 | ||
2981 | @item font-lock-doc-face | |
2982 | @vindex font-lock-doc-face | |
2983 | for documentation strings in the code. This inherits, by default, from | |
2984 | @code{font-lock-string-face}. | |
b8d4c8d0 GM |
2985 | |
2986 | @item font-lock-negation-char-face | |
2987 | @vindex font-lock-negation-char-face | |
e0dd6837 | 2988 | for easily-overlooked negation characters. |
b8d4c8d0 GM |
2989 | @end table |
2990 | ||
2991 | @node Syntactic Font Lock | |
2992 | @subsection Syntactic Font Lock | |
2993 | @cindex syntactic font lock | |
2994 | ||
2995 | Syntactic fontification uses the syntax table to find comments and | |
2996 | string constants (@pxref{Syntax Tables}). It highlights them using | |
2997 | @code{font-lock-comment-face} and @code{font-lock-string-face} | |
2998 | (@pxref{Faces for Font Lock}), or whatever | |
2999 | @code{font-lock-syntactic-face-function} chooses. There are several | |
3000 | variables that affect syntactic fontification; you should set them by | |
3001 | means of @code{font-lock-defaults} (@pxref{Font Lock Basics}). | |
3002 | ||
3003 | @defvar font-lock-keywords-only | |
3004 | Non-@code{nil} means Font Lock should not do syntactic fontification; | |
3005 | it should only fontify based on @code{font-lock-keywords}. The normal | |
3006 | way for a mode to set this variable to @code{t} is with | |
3007 | @var{keywords-only} in @code{font-lock-defaults}. | |
3008 | @end defvar | |
3009 | ||
3010 | @defvar font-lock-syntax-table | |
3011 | This variable holds the syntax table to use for fontification of | |
3012 | comments and strings. Specify it using @var{syntax-alist} in | |
3013 | @code{font-lock-defaults}. If this is @code{nil}, fontification uses | |
3014 | the buffer's syntax table. | |
3015 | @end defvar | |
3016 | ||
3017 | @defvar font-lock-beginning-of-syntax-function | |
3018 | If this variable is non-@code{nil}, it should be a function to move | |
3019 | point back to a position that is syntactically at ``top level'' and | |
3020 | outside of strings or comments. Font Lock uses this when necessary | |
3021 | to get the right results for syntactic fontification. | |
3022 | ||
3023 | This function is called with no arguments. It should leave point at | |
3024 | the beginning of any enclosing syntactic block. Typical values are | |
3025 | @code{beginning-of-line} (used when the start of the line is known to | |
3026 | be outside a syntactic block), or @code{beginning-of-defun} for | |
3027 | programming modes, or @code{backward-paragraph} for textual modes. | |
3028 | ||
3029 | If the value is @code{nil}, Font Lock uses | |
3030 | @code{syntax-begin-function} to move back outside of any comment, | |
3031 | string, or sexp. This variable is semi-obsolete; we recommend setting | |
3032 | @code{syntax-begin-function} instead. | |
3033 | ||
3034 | Specify this variable using @var{syntax-begin} in | |
3035 | @code{font-lock-defaults}. | |
3036 | @end defvar | |
3037 | ||
3038 | @defvar font-lock-syntactic-face-function | |
3039 | A function to determine which face to use for a given syntactic | |
3040 | element (a string or a comment). The function is called with one | |
3041 | argument, the parse state at point returned by | |
3042 | @code{parse-partial-sexp}, and should return a face. The default | |
3043 | value returns @code{font-lock-comment-face} for comments and | |
3044 | @code{font-lock-string-face} for strings. | |
3045 | ||
3046 | This can be used to highlighting different kinds of strings or | |
3047 | comments differently. It is also sometimes abused together with | |
3048 | @code{font-lock-syntactic-keywords} to highlight constructs that span | |
3049 | multiple lines, but this is too esoteric to document here. | |
3050 | ||
3051 | Specify this variable using @var{other-vars} in | |
3052 | @code{font-lock-defaults}. | |
3053 | @end defvar | |
3054 | ||
3055 | @node Setting Syntax Properties | |
3056 | @subsection Setting Syntax Properties | |
3057 | ||
3058 | Font Lock mode can be used to update @code{syntax-table} properties | |
3059 | automatically (@pxref{Syntax Properties}). This is useful in | |
3060 | languages for which a single syntax table by itself is not sufficient. | |
3061 | ||
3062 | @defvar font-lock-syntactic-keywords | |
3063 | This variable enables and controls updating @code{syntax-table} | |
3064 | properties by Font Lock. Its value should be a list of elements of | |
3065 | this form: | |
3066 | ||
3067 | @example | |
3068 | (@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch}) | |
3069 | @end example | |
3070 | ||
3071 | The parts of this element have the same meanings as in the corresponding | |
3072 | sort of element of @code{font-lock-keywords}, | |
3073 | ||
3074 | @example | |
3075 | (@var{matcher} @var{subexp} @var{facespec} @var{override} @var{laxmatch}) | |
3076 | @end example | |
3077 | ||
3078 | However, instead of specifying the value @var{facespec} to use for the | |
3079 | @code{face} property, it specifies the value @var{syntax} to use for | |
3080 | the @code{syntax-table} property. Here, @var{syntax} can be a string | |
3081 | (as taken by @code{modify-syntax-entry}), a syntax table, a cons cell | |
3082 | (as returned by @code{string-to-syntax}), or an expression whose value | |
3083 | is one of those two types. @var{override} cannot be @code{prepend} or | |
3084 | @code{append}. | |
3085 | ||
3086 | For example, an element of the form: | |
3087 | ||
3088 | @example | |
3089 | ("\\$\\(#\\)" 1 ".") | |
3090 | @end example | |
3091 | ||
3092 | highlights syntactically a hash character when following a dollar | |
3093 | character, with a SYNTAX of @code{"."} (meaning punctuation syntax). | |
3094 | Assuming that the buffer syntax table specifies hash characters to | |
3095 | have comment start syntax, the element will only highlight hash | |
3096 | characters that do not follow dollar characters as comments | |
3097 | syntactically. | |
3098 | ||
3099 | An element of the form: | |
3100 | ||
3101 | @example | |
3102 | ("\\('\\).\\('\\)" | |
3103 | (1 "\"") | |
3104 | (2 "\"")) | |
3105 | @end example | |
3106 | ||
3107 | highlights syntactically both single quotes which surround a single | |
3108 | character, with a SYNTAX of @code{"\""} (meaning string quote syntax). | |
3109 | Assuming that the buffer syntax table does not specify single quotes | |
3110 | to have quote syntax, the element will only highlight single quotes of | |
3111 | the form @samp{'@var{c}'} as strings syntactically. Other forms, such | |
3112 | as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as | |
3113 | strings. | |
3114 | ||
3115 | Major modes normally set this variable with @var{other-vars} in | |
3116 | @code{font-lock-defaults}. | |
3117 | @end defvar | |
3118 | ||
3119 | @node Multiline Font Lock | |
3120 | @subsection Multiline Font Lock Constructs | |
3121 | @cindex multiline font lock | |
3122 | ||
3123 | Normally, elements of @code{font-lock-keywords} should not match | |
3124 | across multiple lines; that doesn't work reliably, because Font Lock | |
3125 | usually scans just part of the buffer, and it can miss a multi-line | |
3126 | construct that crosses the line boundary where the scan starts. (The | |
3127 | scan normally starts at the beginning of a line.) | |
3128 | ||
3129 | Making elements that match multiline constructs work properly has | |
3130 | two aspects: correct @emph{identification} and correct | |
3131 | @emph{rehighlighting}. The first means that Font Lock finds all | |
3132 | multiline constructs. The second means that Font Lock will correctly | |
3133 | rehighlight all the relevant text when a multiline construct is | |
3134 | changed---for example, if some of the text that was previously part of | |
3135 | a multiline construct ceases to be part of it. The two aspects are | |
3136 | closely related, and often getting one of them to work will appear to | |
3137 | make the other also work. However, for reliable results you must | |
3138 | attend explicitly to both aspects. | |
3139 | ||
3140 | There are three ways to ensure correct identification of multiline | |
3141 | constructs: | |
3142 | ||
3143 | @itemize | |
3144 | @item | |
3145 | Add a function to @code{font-lock-extend-region-functions} that does | |
3146 | the @emph{identification} and extends the scan so that the scanned | |
3147 | text never starts or ends in the middle of a multiline construct. | |
3148 | @item | |
3149 | Use the @code{font-lock-fontify-region-function} hook similarly to | |
3150 | extend the scan so that the scanned text never starts or ends in the | |
3151 | middle of a multiline construct. | |
3152 | @item | |
3153 | Somehow identify the multiline construct right when it gets inserted | |
3154 | into the buffer (or at any point after that but before font-lock | |
3155 | tries to highlight it), and mark it with a @code{font-lock-multiline} | |
3156 | which will instruct font-lock not to start or end the scan in the | |
3157 | middle of the construct. | |
3158 | @end itemize | |
3159 | ||
3160 | There are three ways to do rehighlighting of multiline constructs: | |
3161 | ||
3162 | @itemize | |
3163 | @item | |
3164 | Place a @code{font-lock-multiline} property on the construct. This | |
3165 | will rehighlight the whole construct if any part of it is changed. In | |
3166 | some cases you can do this automatically by setting the | |
3167 | @code{font-lock-multiline} variable, which see. | |
3168 | @item | |
3169 | Make sure @code{jit-lock-contextually} is set and rely on it doing its | |
3170 | job. This will only rehighlight the part of the construct that | |
3171 | follows the actual change, and will do it after a short delay. | |
3172 | This only works if the highlighting of the various parts of your | |
3173 | multiline construct never depends on text in subsequent lines. | |
3174 | Since @code{jit-lock-contextually} is activated by default, this can | |
3175 | be an attractive solution. | |
3176 | @item | |
3177 | Place a @code{jit-lock-defer-multiline} property on the construct. | |
3178 | This works only if @code{jit-lock-contextually} is used, and with the | |
3179 | same delay before rehighlighting, but like @code{font-lock-multiline}, | |
3180 | it also handles the case where highlighting depends on | |
3181 | subsequent lines. | |
3182 | @end itemize | |
3183 | ||
3184 | @menu | |
fe42c16a | 3185 | * Font Lock Multiline:: Marking multiline chunks with a text property. |
bc3bea9c | 3186 | * Region to Refontify:: Controlling which region gets refontified |
b8d4c8d0 GM |
3187 | after a buffer change. |
3188 | @end menu | |
3189 | ||
3190 | @node Font Lock Multiline | |
3191 | @subsubsection Font Lock Multiline | |
3192 | ||
3193 | One way to ensure reliable rehighlighting of multiline Font Lock | |
3194 | constructs is to put on them the text property @code{font-lock-multiline}. | |
3195 | It should be present and non-@code{nil} for text that is part of a | |
3196 | multiline construct. | |
3197 | ||
3198 | When Font Lock is about to highlight a range of text, it first | |
3199 | extends the boundaries of the range as necessary so that they do not | |
3200 | fall within text marked with the @code{font-lock-multiline} property. | |
3201 | Then it removes any @code{font-lock-multiline} properties from the | |
3202 | range, and highlights it. The highlighting specification (mostly | |
3203 | @code{font-lock-keywords}) must reinstall this property each time, | |
3204 | whenever it is appropriate. | |
3205 | ||
3206 | @strong{Warning:} don't use the @code{font-lock-multiline} property | |
3207 | on large ranges of text, because that will make rehighlighting slow. | |
3208 | ||
3209 | @defvar font-lock-multiline | |
3210 | If the @code{font-lock-multiline} variable is set to @code{t}, Font | |
3211 | Lock will try to add the @code{font-lock-multiline} property | |
3212 | automatically on multiline constructs. This is not a universal | |
3213 | solution, however, since it slows down Font Lock somewhat. It can | |
3214 | miss some multiline constructs, or make the property larger or smaller | |
3215 | than necessary. | |
3216 | ||
3217 | For elements whose @var{matcher} is a function, the function should | |
3218 | ensure that submatch 0 covers the whole relevant multiline construct, | |
3219 | even if only a small subpart will be highlighted. It is often just as | |
3220 | easy to add the @code{font-lock-multiline} property by hand. | |
3221 | @end defvar | |
3222 | ||
3223 | The @code{font-lock-multiline} property is meant to ensure proper | |
3224 | refontification; it does not automatically identify new multiline | |
3225 | constructs. Identifying the requires that Font-Lock operate on large | |
3226 | enough chunks at a time. This will happen by accident on many cases, | |
3227 | which may give the impression that multiline constructs magically work. | |
3228 | If you set the @code{font-lock-multiline} variable non-@code{nil}, | |
3229 | this impression will be even stronger, since the highlighting of those | |
3230 | constructs which are found will be properly updated from then on. | |
3231 | But that does not work reliably. | |
3232 | ||
3233 | To find multiline constructs reliably, you must either manually | |
3234 | place the @code{font-lock-multiline} property on the text before | |
3235 | Font-Lock looks at it, or use | |
3236 | @code{font-lock-fontify-region-function}. | |
3237 | ||
bc3bea9c | 3238 | @node Region to Refontify |
b8d4c8d0 GM |
3239 | @subsubsection Region to Fontify after a Buffer Change |
3240 | ||
3241 | When a buffer is changed, the region that Font Lock refontifies is | |
3242 | by default the smallest sequence of whole lines that spans the change. | |
3243 | While this works well most of the time, sometimes it doesn't---for | |
3244 | example, when a change alters the syntactic meaning of text on an | |
3245 | earlier line. | |
3246 | ||
bc3bea9c | 3247 | You can enlarge (or even reduce) the region to refontify by setting |
e6dc6206 | 3248 | the following variable: |
b8d4c8d0 GM |
3249 | |
3250 | @defvar font-lock-extend-after-change-region-function | |
3251 | This buffer-local variable is either @code{nil} or a function for | |
3252 | Font-Lock to call to determine the region to scan and fontify. | |
3253 | ||
3254 | The function is given three parameters, the standard @var{beg}, | |
bc3bea9c | 3255 | @var{end}, and @var{old-len} from @code{after-change-functions} |
b8d4c8d0 GM |
3256 | (@pxref{Change Hooks}). It should return either a cons of the |
3257 | beginning and end buffer positions (in that order) of the region to | |
3258 | fontify, or @code{nil} (which means choose the region in the standard | |
3259 | way). This function needs to preserve point, the match-data, and the | |
3260 | current restriction. The region it returns may start or end in the | |
3261 | middle of a line. | |
3262 | ||
3263 | Since this function is called after every buffer change, it should be | |
3264 | reasonably fast. | |
3265 | @end defvar | |
3266 | ||
5dcb4c4e | 3267 | @node Auto-Indentation |
35a30759 | 3268 | @section Auto-indentation of code |
5dcb4c4e SM |
3269 | |
3270 | For programming languages, an important feature of a major mode is to | |
3271 | provide automatic indentation. This is controlled in Emacs by | |
3272 | @code{indent-line-function} (@pxref{Mode-Specific Indent}). | |
3273 | Writing a good indentation function can be difficult and to a large | |
3274 | extent it is still a black art. | |
3275 | ||
3276 | Many major mode authors will start by writing a simple indentation | |
3277 | function that works for simple cases, for example by comparing with the | |
3278 | indentation of the previous text line. For most programming languages | |
3279 | that are not really line-based, this tends to scale very poorly: | |
3280 | improving such a function to let it handle more diverse situations tends | |
3281 | to become more and more difficult, resulting in the end with a large, | |
3282 | complex, unmaintainable indentation function which nobody dares to touch. | |
3283 | ||
3284 | A good indentation function will usually need to actually parse the | |
3285 | text, according to the syntax of the language. Luckily, it is not | |
3286 | necessary to parse the text in as much detail as would be needed | |
3287 | for a compiler, but on the other hand, the parser embedded in the | |
3288 | indentation code will want to be somewhat friendly to syntactically | |
3289 | incorrect code. | |
3290 | ||
3291 | Good maintainable indentation functions usually fall into 2 categories: | |
3292 | either parsing forward from some ``safe'' starting point until the | |
3293 | position of interest, or parsing backward from the position of interest. | |
3294 | Neither of the two is a clearly better choice than the other: parsing | |
3295 | backward is often more difficult than parsing forward because | |
3296 | programming languages are designed to be parsed forward, but for the | |
3297 | purpose of indentation it has the advantage of not needing to | |
3298 | guess a ``safe'' starting point, and it generally enjoys the property | |
3299 | that only a minimum of text will be analyzed to decide the indentation | |
3300 | of a line, so indentation will tend to be unaffected by syntax errors in | |
3301 | some earlier unrelated piece of code. Parsing forward on the other hand | |
3302 | is usually easier and has the advantage of making it possible to | |
3303 | reindent efficiently a whole region at a time, with a single parse. | |
3304 | ||
3305 | Rather than write your own indentation function from scratch, it is | |
3306 | often preferable to try and reuse some existing ones or to rely | |
3307 | on a generic indentation engine. There are sadly few such | |
3308 | engines. The CC-mode indentation code (used with C, C++, Java, Awk | |
3309 | and a few other such modes) has been made more generic over the years, | |
3310 | so if your language seems somewhat similar to one of those languages, | |
3311 | you might try to use that engine. @c FIXME: documentation? | |
3312 | Another one is SMIE which takes an approach in the spirit | |
3313 | of Lisp sexps and adapts it to non-Lisp languages. | |
3314 | ||
3315 | @menu | |
3316 | * SMIE:: A simple minded indentation engine | |
3317 | @end menu | |
3318 | ||
3319 | @node SMIE | |
3320 | @subsection Simple Minded Indentation Engine | |
3321 | ||
3322 | SMIE is a package that provides a generic navigation and indentation | |
3323 | engine. Based on a very simple parser using an ``operator precedence | |
3324 | grammar'', it lets major modes extend the sexp-based navigation of Lisp | |
3325 | to non-Lisp languages as well as provide a simple to use but reliable | |
3326 | auto-indentation. | |
3327 | ||
3328 | Operator precedence grammar is a very primitive technology for parsing | |
3329 | compared to some of the more common techniques used in compilers. | |
3330 | It has the following characteristics: its parsing power is very limited, | |
3331 | and it is largely unable to detect syntax errors, but it has the | |
3332 | advantage of being algorithmically efficient and able to parse forward | |
3333 | just as well as backward. In practice that means that SMIE can use it | |
3334 | for indentation based on backward parsing, that it can provide both | |
3335 | @code{forward-sexp} and @code{backward-sexp} functionality, and that it | |
3336 | will naturally work on syntactically incorrect code without any extra | |
3337 | effort. The downside is that it also means that most programming | |
3338 | languages cannot be parsed correctly using SMIE, at least not without | |
3339 | resorting to some special tricks (@pxref{SMIE Tricks}). | |
3340 | ||
3341 | @menu | |
3342 | * SMIE setup:: SMIE setup and features | |
3343 | * Operator Precedence Grammars:: A very simple parsing technique | |
3344 | * SMIE Grammar:: Defining the grammar of a language | |
3345 | * SMIE Lexer:: Defining tokens | |
3346 | * SMIE Tricks:: Working around the parser's limitations | |
3347 | * SMIE Indentation:: Specifying indentation rules | |
3348 | * SMIE Indentation Helpers:: Helper functions for indentation rules | |
3349 | * SMIE Indentation Example:: Sample indentation rules | |
3350 | @end menu | |
3351 | ||
3352 | @node SMIE setup | |
3353 | @subsubsection SMIE Setup and Features | |
3354 | ||
3355 | SMIE is meant to be a one-stop shop for structural navigation and | |
3356 | various other features which rely on the syntactic structure of code, in | |
3357 | particular automatic indentation. The main entry point is | |
3358 | @code{smie-setup} which is a function typically called while setting | |
3359 | up a major mode. | |
3360 | ||
3361 | @defun smie-setup grammar rules-function &rest keywords | |
3362 | Setup SMIE navigation and indentation. | |
3363 | @var{grammar} is a grammar table generated by @code{smie-prec2->grammar}. | |
3364 | @var{rules-function} is a set of indentation rules for use on | |
3365 | @code{smie-rules-function}. | |
3366 | @var{keywords} are additional arguments, which can include the following | |
3367 | keywords: | |
3368 | @itemize | |
3369 | @item | |
3370 | @code{:forward-token} @var{fun}: Specify the forward lexer to use. | |
3371 | @item | |
3372 | @code{:backward-token} @var{fun}: Specify the backward lexer to use. | |
3373 | @end itemize | |
3374 | @end defun | |
3375 | ||
3376 | Calling this function is sufficient to make commands such as | |
3377 | @code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be | |
3378 | able to properly handle structural elements other than just the paired | |
3379 | parentheses already handled by syntax tables. For example, if the | |
3380 | provided grammar is precise enough, @code{transpose-sexps} can correctly | |
3381 | transpose the two arguments of a @code{+} operator, taking into account | |
3382 | the precedence rules of the language. | |
3383 | ||
3384 | Calling `smie-setup' is also sufficient to make TAB indentation work in | |
f49d1f52 SM |
3385 | the expected way, extends @code{blink-matching-paren} to apply to |
3386 | elements like @code{begin...end}, and provides some commands that you | |
3387 | can bind in the major mode keymap. | |
5dcb4c4e SM |
3388 | |
3389 | @deffn Command smie-close-block | |
3390 | This command closes the most recently opened (and not yet closed) block. | |
3391 | @end deffn | |
3392 | ||
3393 | @deffn Command smie-down-list &optional arg | |
3394 | This command is like @code{down-list} but it also pays attention to | |
3395 | nesting of tokens other than parentheses, such as @code{begin...end}. | |
3396 | @end deffn | |
3397 | ||
3398 | @node Operator Precedence Grammars | |
3399 | @subsubsection Operator Precedence Grammars | |
3400 | ||
3401 | SMIE's precedence grammars simply give to each token a pair of | |
3402 | precedences: the left-precedence and the right-precedence. We say | |
3403 | @code{T1 < T2} if the right-precedence of token @code{T1} is less than | |
3404 | the left-precedence of token @code{T2}. A good way to read this | |
3405 | @code{<} is as a kind of parenthesis: if we find @code{... T1 something | |
3406 | T2 ...} then that should be parsed as @code{... T1 (something T2 ...} | |
3407 | rather than as @code{... T1 something) T2 ...}. The latter | |
3408 | interpretation would be the case if we had @code{T1 > T2}. If we have | |
3409 | @code{T1 = T2}, it means that token T2 follows token T1 in the same | |
3410 | syntactic construction, so typically we have @code{"begin" = "end"}. | |
3411 | Such pairs of precedences are sufficient to express left-associativity | |
3412 | or right-associativity of infix operators, nesting of tokens like | |
3413 | parentheses and many other cases. | |
3414 | ||
62d94509 | 3415 | @c Let's leave this undocumented to leave it more open for change! |
5dcb4c4e SM |
3416 | @c @defvar smie-grammar |
3417 | @c The value of this variable is an alist specifying the left and right | |
3418 | @c precedence of each token. It is meant to be initialized by using one of | |
3419 | @c the functions below. | |
3420 | @c @end defvar | |
3421 | ||
3422 | @defun smie-prec2->grammar table | |
3423 | This function takes a @emph{prec2} grammar @var{table} and returns an | |
3424 | alist suitable for use in @code{smie-setup}. The @emph{prec2} | |
3425 | @var{table} is itself meant to be built by one of the functions below. | |
3426 | @end defun | |
3427 | ||
3428 | @defun smie-merge-prec2s &rest tables | |
3429 | This function takes several @emph{prec2} @var{tables} and merges them | |
3430 | into a new @emph{prec2} table. | |
3431 | @end defun | |
3432 | ||
3433 | @defun smie-precs->prec2 precs | |
3434 | This function builds a @emph{prec2} table from a table of precedences | |
3435 | @var{precs}. @var{precs} should be a list, sorted by precedence (for | |
3436 | example @code{"+"} will come before @code{"*"}), of elements of the form | |
3437 | @code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that | |
3438 | acts as an operator; @var{assoc} is their associativity, which can be | |
3439 | either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}. | |
3440 | All operators in a given element share the same precedence level | |
3441 | and associativity. | |
3442 | @end defun | |
3443 | ||
3444 | @defun smie-bnf->prec2 bnf &rest resolvers | |
3445 | This function lets you specify the grammar using a BNF notation. | |
3446 | It accepts a @var{bnf} description of the grammar along with a set of | |
3447 | conflict resolution rules @var{resolvers}, and | |
3448 | returns a @emph{prec2} table. | |
3449 | ||
3450 | @var{bnf} is a list of nonterminal definitions of the form | |
3451 | @code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs} | |
3452 | is a (non-empty) list of terminals (aka tokens) or non-terminals. | |
3453 | ||
3454 | Not all grammars are accepted: | |
3455 | @itemize | |
3456 | @item | |
3457 | An @var{rhs} cannot be an empty list (an empty list is never needed, | |
3458 | since SMIE allows all non-terminals to match the empty string anyway). | |
3459 | @item | |
3460 | An @var{rhs} cannot have 2 consecutive non-terminals: each pair of | |
3461 | non-terminals needs to be separated by a terminal (aka token). | |
3462 | This is a fundamental limitation of operator precedence grammars. | |
3463 | @end itemize | |
3464 | ||
3465 | Additionally, conflicts can occur: | |
3466 | @itemize | |
3467 | @item | |
3468 | The returned @emph{prec2} table holds constraints between pairs of tokens, and | |
3469 | for any given pair only one constraint can be present: T1 < T2, | |
3470 | T1 = T2, or T1 > T2. | |
3471 | @item | |
3472 | A token can be an @code{opener} (something similar to an open-paren), | |
3473 | a @code{closer} (like a close-paren), or @code{neither} of the two | |
3474 | (e.g. an infix operator, or an inner token like @code{"else"}). | |
3475 | @end itemize | |
3476 | ||
3477 | Precedence conflicts can be resolved via @var{resolvers}, which | |
3478 | is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for | |
3479 | each precedence conflict, if those @code{precs} tables | |
3480 | specify a particular constraint, then the conflict is resolved by using | |
3481 | this constraint instead, else a conflict is reported and one of the | |
3482 | conflicting constraints is picked arbitrarily and the others are | |
3483 | simply ignored. | |
3484 | @end defun | |
3485 | ||
3486 | @node SMIE Grammar | |
3487 | @subsubsection Defining the Grammar of a Language | |
3488 | ||
3489 | The usual way to define the SMIE grammar of a language is by | |
3490 | defining a new global variable that holds the precedence table by | |
3491 | giving a set of BNF rules. | |
3492 | For example, the grammar definition for a small Pascal-like language | |
3493 | could look like: | |
3494 | @example | |
3495 | @group | |
3496 | (require 'smie) | |
3497 | (defvar sample-smie-grammar | |
3498 | (smie-prec2->grammar | |
3499 | (smie-bnf->prec2 | |
3500 | @end group | |
3501 | @group | |
3502 | '((id) | |
3503 | (inst ("begin" insts "end") | |
3504 | ("if" exp "then" inst "else" inst) | |
3505 | (id ":=" exp) | |
3506 | (exp)) | |
3507 | (insts (insts ";" insts) (inst)) | |
3508 | (exp (exp "+" exp) | |
3509 | (exp "*" exp) | |
3510 | ("(" exps ")")) | |
3511 | (exps (exps "," exps) (exp))) | |
3512 | @end group | |
3513 | @group | |
3514 | '((assoc ";")) | |
3515 | '((assoc ",")) | |
3516 | '((assoc "+") (assoc "*"))))) | |
3517 | @end group | |
3518 | @end example | |
3519 | ||
3520 | @noindent | |
3521 | A few things to note: | |
3522 | ||
3523 | @itemize | |
3524 | @item | |
3525 | The above grammar does not explicitly mention the syntax of function | |
3526 | calls: SMIE will automatically allow any sequence of sexps, such as | |
3527 | identifiers, balanced parentheses, or @code{begin ... end} blocks | |
3528 | to appear anywhere anyway. | |
3529 | @item | |
3530 | The grammar category @code{id} has no right hand side: this does not | |
3531 | mean that it can match only the empty string, since as mentioned any | |
3532 | sequence of sexps can appear anywhere anyway. | |
3533 | @item | |
3534 | Because non terminals cannot appear consecutively in the BNF grammar, it | |
3535 | is difficult to correctly handle tokens that act as terminators, so the | |
3536 | above grammar treats @code{";"} as a statement @emph{separator} instead, | |
3537 | which SMIE can handle very well. | |
3538 | @item | |
3539 | Separators used in sequences (such as @code{","} and @code{";"} above) | |
3540 | are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)} | |
3541 | which generate precedence conflicts which are then resolved by giving | |
3542 | them an explicit @code{(assoc "separator")}. | |
3543 | @item | |
3544 | The @code{("(" exps ")")} rule was not needed to pair up parens, since | |
3545 | SMIE will pair up any characters that are marked as having paren syntax | |
3546 | in the syntax table. What this rule does instead (together with the | |
3547 | definition of @code{exps}) is to make it clear that @code{","} should | |
3548 | not appear outside of parentheses. | |
3549 | @item | |
3550 | Rather than have a single @emph{precs} table to resolve conflicts, it is | |
3551 | preferable to have several tables, so as to let the BNF part of the | |
3552 | grammar specify relative precedences where possible. | |
3553 | @item | |
3554 | Unless there is a very good reason to prefer @code{left} or | |
3555 | @code{right}, it is usually preferable to mark operators as associative, | |
3556 | using @code{assoc}. For that reason @code{"+"} and @code{"*"} are | |
3557 | defined above as @code{assoc}, although the language defines them | |
3558 | formally as left associative. | |
3559 | @end itemize | |
3560 | ||
3561 | @node SMIE Lexer | |
3562 | @subsubsection Defining Tokens | |
3563 | ||
3564 | SMIE comes with a predefined lexical analyzer which uses syntax tables | |
3565 | in the following way: any sequence of characters that have word or | |
3566 | symbol syntax is considered a token, and so is any sequence of | |
3567 | characters that have punctuation syntax. This default lexer is | |
3568 | often a good starting point but is rarely actually correct for any given | |
3569 | language. For example, it will consider @code{"2,+3"} to be composed | |
3570 | of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}. | |
3571 | ||
3572 | To describe the lexing rules of your language to SMIE, you need | |
3573 | 2 functions, one to fetch the next token, and another to fetch the | |
3574 | previous token. Those functions will usually first skip whitespace and | |
3575 | comments and then look at the next chunk of text to see if it | |
3576 | is a special token. If so it should skip the token and | |
3577 | return a description of this token. Usually this is simply the string | |
3578 | extracted from the buffer, but it can be anything you want. | |
3579 | For example: | |
3580 | @example | |
3581 | @group | |
3582 | (defvar sample-keywords-regexp | |
3583 | (regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "="))) | |
3584 | @end group | |
3585 | @group | |
3586 | (defun sample-smie-forward-token () | |
3587 | (forward-comment (point-max)) | |
3588 | (cond | |
3589 | ((looking-at sample-keywords-regexp) | |
3590 | (goto-char (match-end 0)) | |
3591 | (match-string-no-properties 0)) | |
3592 | (t (buffer-substring-no-properties | |
3593 | (point) | |
3594 | (progn (skip-syntax-forward "w_") | |
3595 | (point)))))) | |
3596 | @end group | |
3597 | @group | |
3598 | (defun sample-smie-backward-token () | |
3599 | (forward-comment (- (point))) | |
3600 | (cond | |
3601 | ((looking-back sample-keywords-regexp (- (point) 2) t) | |
3602 | (goto-char (match-beginning 0)) | |
3603 | (match-string-no-properties 0)) | |
3604 | (t (buffer-substring-no-properties | |
3605 | (point) | |
3606 | (progn (skip-syntax-backward "w_") | |
3607 | (point)))))) | |
3608 | @end group | |
3609 | @end example | |
3610 | ||
3611 | Notice how those lexers return the empty string when in front of | |
3612 | parentheses. This is because SMIE automatically takes care of the | |
3613 | parentheses defined in the syntax table. More specifically if the lexer | |
3614 | returns nil or an empty string, SMIE tries to handle the corresponding | |
3615 | text as a sexp according to syntax tables. | |
3616 | ||
3617 | @node SMIE Tricks | |
3618 | @subsubsection Living With a Weak Parser | |
3619 | ||
3620 | The parsing technique used by SMIE does not allow tokens to behave | |
3621 | differently in different contexts. For most programming languages, this | |
3622 | manifests itself by precedence conflicts when converting the | |
3623 | BNF grammar. | |
3624 | ||
3625 | Sometimes, those conflicts can be worked around by expressing the | |
3626 | grammar slightly differently. For example, for Modula-2 it might seem | |
3627 | natural to have a BNF grammar that looks like this: | |
3628 | ||
3629 | @example | |
3630 | ... | |
3631 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3632 | ("CASE" exp "OF" cases "END") | |
3633 | ...) | |
049bcbcb CY |
3634 | (cases (cases "|" cases) |
3635 | (caselabel ":" insts) | |
3636 | ("ELSE" insts)) | |
5dcb4c4e SM |
3637 | ... |
3638 | @end example | |
3639 | ||
3640 | But this will create conflicts for @code{"ELSE"}: on the one hand, the | |
3641 | IF rule implies (among many other things) that @code{"ELSE" = "END"}; | |
3642 | but on the other hand, since @code{"ELSE"} appears within @code{cases}, | |
3643 | which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}. | |
3644 | We can solve the conflict either by using: | |
3645 | @example | |
3646 | ... | |
3647 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3648 | ("CASE" exp "OF" cases "END") | |
3649 | ("CASE" exp "OF" cases "ELSE" insts "END") | |
3650 | ...) | |
3651 | (cases (cases "|" cases) (caselabel ":" insts)) | |
3652 | ... | |
3653 | @end example | |
3654 | or | |
3655 | @example | |
3656 | ... | |
3657 | (inst ("IF" exp "THEN" else "END") | |
3658 | ("CASE" exp "OF" cases "END") | |
3659 | ...) | |
3660 | (else (insts "ELSE" insts)) | |
3661 | (cases (cases "|" cases) (caselabel ":" insts) (else)) | |
3662 | ... | |
3663 | @end example | |
3664 | ||
3665 | Reworking the grammar to try and solve conflicts has its downsides, tho, | |
3666 | because SMIE assumes that the grammar reflects the logical structure of | |
3667 | the code, so it is preferable to keep the BNF closer to the intended | |
3668 | abstract syntax tree. | |
3669 | ||
3670 | Other times, after careful consideration you may conclude that those | |
3671 | conflicts are not serious and simply resolve them via the | |
3672 | @var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is | |
3673 | because the grammar is simply ambiguous: the conflict does not affect | |
3674 | the set of programs described by the grammar, but only the way those | |
3675 | programs are parsed. This is typically the case for separators and | |
3676 | associative infix operators, where you want to add a resolver like | |
3677 | @code{'((assoc "|"))}. Another case where this can happen is for the | |
3678 | classic @emph{dangling else} problem, where you will use @code{'((assoc | |
3679 | "else" "then"))}. It can also happen for cases where the conflict is | |
3680 | real and cannot really be resolved, but it is unlikely to pose a problem | |
3681 | in practice. | |
3682 | ||
3683 | Finally, in many cases some conflicts will remain despite all efforts to | |
3684 | restructure the grammar. Do not despair: while the parser cannot be | |
3685 | made more clever, you can make the lexer as smart as you want. So, the | |
3686 | solution is then to look at the tokens involved in the conflict and to | |
3687 | split one of those tokens into 2 (or more) different tokens. E.g. if | |
3688 | the grammar needs to distinguish between two incompatible uses of the | |
3689 | token @code{"begin"}, make the lexer return different tokens (say | |
3690 | @code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of | |
3691 | @code{"begin"} it finds. This pushes the work of distinguishing the | |
3692 | different cases to the lexer, which will thus have to look at the | |
3693 | surrounding text to find ad-hoc clues. | |
3694 | ||
3695 | @node SMIE Indentation | |
3696 | @subsubsection Specifying Indentation Rules | |
3697 | ||
3698 | Based on the provided grammar, SMIE will be able to provide automatic | |
3699 | indentation without any extra effort. But in practice, this default | |
3700 | indentation style will probably not be good enough. You will want to | |
3701 | tweak it in many different cases. | |
3702 | ||
3703 | SMIE indentation is based on the idea that indentation rules should be | |
3704 | as local as possible. To this end, it relies on the idea of | |
3705 | @emph{virtual} indentation, which is the indentation that a particular | |
3706 | program point would have if it were at the beginning of a line. | |
3707 | Of course, if that program point is indeed at the beginning of a line, | |
3708 | its virtual indentation is its current indentation. But if not, then | |
3709 | SMIE uses the indentation algorithm to compute the virtual indentation | |
3710 | of that point. Now in practice, the virtual indentation of a program | |
3711 | point does not have to be identical to the indentation it would have if | |
3712 | we inserted a newline before it. To see how this works, the SMIE rule | |
3713 | for indentation after a @code{@{} in C does not care whether the | |
3714 | @code{@{} is standing on a line of its own or is at the end of the | |
3715 | preceding line. Instead, these different cases are handled in the | |
3716 | indentation rule that decides how to indent before a @code{@{}. | |
3717 | ||
3718 | Another important concept is the notion of @emph{parent}: The | |
3719 | @emph{parent} of a token, is the head token of the nearest enclosing | |
3720 | syntactic construct. For example, the parent of an @code{else} is the | |
3721 | @code{if} to which it belongs, and the parent of an @code{if}, in turn, | |
3722 | is the lead token of the surrounding construct. The command | |
3723 | @code{backward-sexp} jumps from a token to its parent, but there are | |
3724 | some caveats: for @emph{openers} (tokens which start a construct, like | |
3725 | @code{if}), you need to start with point before the token, while for | |
3726 | others you need to start with point after the token. | |
3727 | @code{backward-sexp} stops with point before the parent token if that is | |
3728 | the @emph{opener} of the token of interest, and otherwise it stops with | |
3729 | point after the parent token. | |
3730 | ||
3731 | SMIE indentation rules are specified using a function that takes two | |
3732 | arguments @var{method} and @var{arg} where the meaning of @var{arg} and the | |
3733 | expected return value depend on @var{method}. | |
3734 | ||
3735 | @var{method} can be: | |
3736 | @itemize | |
3737 | @item | |
3738 | @code{:after}, in which case @var{arg} is a token and the function | |
3739 | should return the @var{offset} to use for indentation after @var{arg}. | |
3740 | @item | |
3741 | @code{:before}, in which case @var{arg} is a token and the function | |
3742 | should return the @var{offset} to use to indent @var{arg} itself. | |
3743 | @item | |
3744 | @code{:elem}, in which case the function should return either the offset | |
3745 | to use to indent function arguments (if @var{arg} is the symbol | |
3746 | @code{arg}) or the basic indentation step (if @var{arg} is the symbol | |
3747 | @code{basic}). | |
3748 | @item | |
3749 | @code{:list-intro}, in which case @var{arg} is a token and the function | |
3750 | should return non-@code{nil} if the token is followed by a list of | |
3751 | expressions (not separated by any token) rather than an expression. | |
3752 | @end itemize | |
3753 | ||
3754 | When @var{arg} is a token, the function is called with point just before | |
3755 | that token. A return value of nil always means to fallback on the | |
3756 | default behavior, so the function should return nil for arguments it | |
3757 | does not expect. | |
3758 | ||
3759 | @var{offset} can be: | |
3760 | @itemize | |
3761 | @item | |
3762 | @code{nil}: use the default indentation rule. | |
3763 | @item | |
3764 | @code{(column . @var{column})}: indent to column @var{column}. | |
3765 | @item | |
3766 | @var{number}: offset by @var{number}, relative to a base token which is | |
3767 | the current token for @code{:after} and its parent for @code{:before}. | |
3768 | @end itemize | |
3769 | ||
3770 | @node SMIE Indentation Helpers | |
3771 | @subsubsection Helper Functions for Indentation Rules | |
3772 | ||
3773 | SMIE provides various functions designed specifically for use in the | |
3774 | indentation rules function (several of those functions break if used in | |
3775 | another context). These functions all start with the prefix | |
3776 | @code{smie-rule-}. | |
3777 | ||
3778 | @defun smie-rule-bolp | |
3779 | Return non-@code{nil} if the current token is the first on the line. | |
3780 | @end defun | |
3781 | ||
3782 | @defun smie-rule-hanging-p | |
3783 | Return non-@code{nil} if the current token is @emph{hanging}. | |
3784 | A token is @emph{hanging} if it is the last token on the line | |
3785 | and if it is preceded by other tokens: a lone token on a line is not | |
3786 | hanging. | |
3787 | @end defun | |
3788 | ||
3789 | @defun smie-rule-next-p &rest tokens | |
3790 | Return non-@code{nil} if the next token is among @var{tokens}. | |
3791 | @end defun | |
3792 | ||
3793 | @defun smie-rule-prev-p &rest tokens | |
3794 | Return non-@code{nil} if the previous token is among @var{tokens}. | |
3795 | @end defun | |
3796 | ||
3797 | @defun smie-rule-parent-p &rest parents | |
3798 | Return non-@code{nil} if the current token's parent is among @var{parents}. | |
3799 | @end defun | |
3800 | ||
3801 | @defun smie-rule-sibling-p | |
3802 | Return non-nil if the current token's parent is actually a sibling. | |
3803 | This is the case for example when the parent of a @code{","} is just the | |
3804 | previous @code{","}. | |
3805 | @end defun | |
3806 | ||
3807 | @defun smie-rule-parent &optional offset | |
3808 | Return the proper offset to align the current token with the parent. | |
3809 | If non-@code{nil}, @var{offset} should be an integer giving an | |
3810 | additional offset to apply. | |
3811 | @end defun | |
3812 | ||
3813 | @defun smie-rule-separator method | |
3814 | Indent current token as a @emph{separator}. | |
3815 | ||
3816 | By @emph{separator}, we mean here a token whose sole purpose is to | |
3817 | separate various elements within some enclosing syntactic construct, and | |
3818 | which does not have any semantic significance in itself (i.e. it would | |
3819 | typically not exist as a node in an abstract syntax tree). | |
3820 | ||
3821 | Such a token is expected to have an associative syntax and be closely | |
3822 | tied to its syntactic parent. Typical examples are @code{","} in lists | |
3823 | of arguments (enclosed inside parentheses), or @code{";"} in sequences | |
3824 | of instructions (enclosed in a @code{@{...@}} or @code{begin...end} | |
3825 | block). | |
3826 | ||
3827 | @var{method} should be the method name that was passed to | |
3828 | `smie-rules-function'. | |
3829 | @end defun | |
3830 | ||
3831 | @node SMIE Indentation Example | |
3832 | @subsubsection Sample Indentation Rules | |
3833 | ||
3834 | Here is an example of an indentation function: | |
3835 | ||
3836 | @example | |
5dcb4c4e | 3837 | (defun sample-smie-rules (kind token) |
f49d1f52 SM |
3838 | (pcase (cons kind token) |
3839 | (`(:elem . basic) sample-indent-basic) | |
3840 | (`(,_ . ",") (smie-rule-separator kind)) | |
3841 | (`(:after . ":=") sample-indent-basic) | |
3842 | (`(:before . ,(or `"begin" `"(" `"@{"))) | |
3843 | (if (smie-rule-hanging-p) (smie-rule-parent))) | |
3844 | (`(:before . "if") | |
3845 | (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") | |
3846 | (smie-rule-parent))))) | |
5dcb4c4e SM |
3847 | @end example |
3848 | ||
3849 | @noindent | |
3850 | A few things to note: | |
3851 | ||
3852 | @itemize | |
3853 | @item | |
3854 | The first case indicates the basic indentation increment to use. | |
3855 | If @code{sample-indent-basic} is nil, then SMIE uses the global | |
3856 | setting @code{smie-indent-basic}. The major mode could have set | |
3857 | @code{smie-indent-basic} buffer-locally instead, but that | |
3858 | is discouraged. | |
3859 | ||
3860 | @item | |
f49d1f52 SM |
3861 | The rule for the token @code{","} make SMIE try to be more clever when |
3862 | the comma separator is placed at the beginning of lines. It tries to | |
3863 | outdent the separator so as to align the code after the comma; for | |
3864 | example: | |
5dcb4c4e SM |
3865 | |
3866 | @example | |
3867 | x = longfunctionname ( | |
3868 | arg1 | |
3869 | , arg2 | |
3870 | ); | |
3871 | @end example | |
3872 | ||
3873 | @item | |
3874 | The rule for indentation after @code{":="} exists because otherwise | |
3875 | SMIE would treat @code{":="} as an infix operator and would align the | |
3876 | right argument with the left one. | |
3877 | ||
3878 | @item | |
3879 | The rule for indentation before @code{"begin"} is an example of the use | |
3880 | of virtual indentation: This rule is used only when @code{"begin"} is | |
3881 | hanging, which can happen only when @code{"begin"} is not at the | |
3882 | beginning of a line. So this is not used when indenting | |
3883 | @code{"begin"} itself but only when indenting something relative to this | |
3884 | @code{"begin"}. Concretely, this rule changes the indentation from: | |
3885 | ||
3886 | @example | |
3887 | if x > 0 then begin | |
3888 | dosomething(x); | |
3889 | end | |
3890 | @end example | |
3891 | to | |
3892 | @example | |
3893 | if x > 0 then begin | |
3894 | dosomething(x); | |
3895 | end | |
3896 | @end example | |
3897 | ||
3898 | @item | |
3899 | The rule for indentation before @code{"if"} is similar to the one for | |
3900 | @code{"begin"}, but where the purpose is to treat @code{"else if"} | |
3901 | as a single unit, so as to align a sequence of tests rather than indent | |
3902 | each test further to the right. This function does this only in the | |
3903 | case where the @code{"if"} is not placed on a separate line, hence the | |
3904 | @code{smie-rule-bolp} test. | |
3905 | ||
3906 | If we know that the @code{"else"} is always aligned with its @code{"if"} | |
3907 | and is always at the beginning of a line, we can use a more efficient | |
3908 | rule: | |
3909 | @example | |
3910 | ((equal token "if") | |
049bcbcb CY |
3911 | (and (not (smie-rule-bolp)) |
3912 | (smie-rule-prev-p "else") | |
5dcb4c4e | 3913 | (save-excursion |
049bcbcb | 3914 | (sample-smie-backward-token) |
5dcb4c4e SM |
3915 | (cons 'column (current-column))))) |
3916 | @end example | |
3917 | ||
3918 | The advantage of this formulation is that it reuses the indentation of | |
3919 | the previous @code{"else"}, rather than going all the way back to the | |
3920 | first @code{"if"} of the sequence. | |
3921 | @end itemize | |
3922 | ||
b8d4c8d0 GM |
3923 | @node Desktop Save Mode |
3924 | @section Desktop Save Mode | |
3925 | @cindex desktop save mode | |
3926 | ||
3927 | @dfn{Desktop Save Mode} is a feature to save the state of Emacs from | |
3928 | one session to another. The user-level commands for using Desktop | |
3929 | Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs | |
3930 | Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit | |
3931 | a file, don't have to do anything to use this feature. | |
3932 | ||
3933 | For buffers not visiting a file to have their state saved, the major | |
3934 | mode must bind the buffer local variable @code{desktop-save-buffer} to | |
3935 | a non-@code{nil} value. | |
3936 | ||
3937 | @defvar desktop-save-buffer | |
3938 | If this buffer-local variable is non-@code{nil}, the buffer will have | |
3939 | its state saved in the desktop file at desktop save. If the value is | |
3940 | a function, it is called at desktop save with argument | |
3941 | @var{desktop-dirname}, and its value is saved in the desktop file along | |
3942 | with the state of the buffer for which it was called. When file names | |
3943 | are returned as part of the auxiliary information, they should be | |
3944 | formatted using the call | |
3945 | ||
3946 | @example | |
3947 | (desktop-file-name @var{file-name} @var{desktop-dirname}) | |
3948 | @end example | |
3949 | ||
3950 | @end defvar | |
3951 | ||
3952 | For buffers not visiting a file to be restored, the major mode must | |
3953 | define a function to do the job, and that function must be listed in | |
3954 | the alist @code{desktop-buffer-mode-handlers}. | |
3955 | ||
3956 | @defvar desktop-buffer-mode-handlers | |
3957 | Alist with elements | |
3958 | ||
3959 | @example | |
3960 | (@var{major-mode} . @var{restore-buffer-function}) | |
3961 | @end example | |
3962 | ||
3963 | The function @var{restore-buffer-function} will be called with | |
3964 | argument list | |
3965 | ||
3966 | @example | |
3967 | (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc}) | |
3968 | @end example | |
3969 | ||
3970 | and it should return the restored buffer. | |
3971 | Here @var{desktop-buffer-misc} is the value returned by the function | |
3972 | optionally bound to @code{desktop-save-buffer}. | |
3973 | @end defvar | |
3974 | ||
3975 | @ignore | |
769741e3 SM |
3976 | Local Variables: |
3977 | fill-column: 72 | |
3978 | End: | |
b8d4c8d0 | 3979 | @end ignore |