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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
acaf905b | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 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 | |
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22 | * Hooks:: How to use hooks; how to write code that provides hooks. |
23 | * Major Modes:: Defining major modes. | |
24 | * Minor Modes:: Defining minor modes. | |
25 | * Mode Line Format:: Customizing the text that appears in the mode line. | |
26 | * Imenu:: Providing a menu of definitions made in a buffer. | |
27 | * Font Lock Mode:: How modes can highlight text according to syntax. | |
28 | * Auto-Indentation:: How to teach Emacs to indent for a major mode. | |
29 | * Desktop Save Mode:: How modes can have buffer state saved between | |
30 | Emacs sessions. | |
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31 | @end menu |
32 | ||
33 | @node Hooks | |
34 | @section Hooks | |
35 | @cindex hooks | |
36 | ||
37 | A @dfn{hook} is a variable where you can store a function or functions | |
38 | to be called on a particular occasion by an existing program. Emacs | |
39 | provides hooks for the sake of customization. Most often, hooks are set | |
40 | up in the init file (@pxref{Init File}), but Lisp programs can set them also. | |
41 | @xref{Standard Hooks}, for a list of standard hook variables. | |
42 | ||
43 | @cindex normal hook | |
44 | Most of the hooks in Emacs are @dfn{normal hooks}. These variables | |
45 | contain lists of functions to be called with no arguments. By | |
46 | convention, whenever the hook name ends in @samp{-hook}, that tells | |
47 | you it is normal. We try to make all hooks normal, as much as | |
48 | possible, so that you can use them in a uniform way. | |
49 | ||
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50 | Every major mode command is supposed to run a normal hook called the |
51 | @dfn{mode hook} as the one of the last steps of initialization. This | |
52 | makes it easy for a user to customize the behavior of the mode, by | |
53 | overriding the buffer-local variable assignments already made by the | |
54 | mode. Most minor mode functions also run a mode hook at the end. But | |
55 | hooks are used in other contexts too. For example, the hook | |
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56 | @code{suspend-hook} runs just before Emacs suspends itself |
57 | (@pxref{Suspending Emacs}). | |
58 | ||
59 | The recommended way to add a hook function to a normal hook is by | |
60 | calling @code{add-hook} (see below). The hook functions may be any of | |
61 | the valid kinds of functions that @code{funcall} accepts (@pxref{What | |
62 | Is a Function}). Most normal hook variables are initially void; | |
63 | @code{add-hook} knows how to deal with this. You can add hooks either | |
64 | globally or buffer-locally with @code{add-hook}. | |
65 | ||
66 | @cindex abnormal hook | |
67 | If the hook variable's name does not end with @samp{-hook}, that | |
68 | indicates it is probably an @dfn{abnormal hook}. That means the hook | |
69 | functions are called with arguments, or their return values are used | |
70 | in some way. The hook's documentation says how the functions are | |
71 | called. You can use @code{add-hook} to add a function to an abnormal | |
72 | hook, but you must write the function to follow the hook's calling | |
73 | convention. | |
74 | ||
75 | By convention, abnormal hook names end in @samp{-functions} or | |
76 | @samp{-hooks}. If the variable's name ends in @samp{-function}, then | |
77 | its value is just a single function, not a list of functions. | |
78 | ||
fd9a7a58 | 79 | @menu |
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80 | * Running Hooks:: How to run a hook. |
81 | * Setting Hooks:: How to put functions on a hook, or remove them. | |
fd9a7a58 | 82 | @end menu |
b8d4c8d0 | 83 | |
fd9a7a58 RS |
84 | @node Running Hooks |
85 | @subsection Running Hooks | |
b8d4c8d0 | 86 | |
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87 | In this section, we document the @code{run-hooks} function, which is |
88 | used to run a normal hook. We also document the functions for running | |
89 | various kinds of abnormal hooks. | |
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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. | |
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104 | |
105 | If the hook variable is buffer-local, the buffer-local variable will | |
106 | be used instead of the global variable. However, if the buffer-local | |
107 | variable contains the element @code{t}, the global hook variable will | |
108 | be run as well. | |
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109 | @end defun |
110 | ||
111 | @defun run-hook-with-args hook &rest args | |
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112 | This function runs an abnormal hook by calling all the hook functions in |
113 | @var{hook}, passing each one the arguments @var{args}. | |
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114 | @end defun |
115 | ||
116 | @defun run-hook-with-args-until-failure hook &rest args | |
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117 | This function runs an abnormal hook by calling each hook function in |
118 | turn, stopping if one of them ``fails'' by returning @code{nil}. Each | |
119 | hook function is passed the arguments @var{args}. If this function | |
120 | stops because one of the hook functions fails, it returns @code{nil}; | |
121 | otherwise it returns a non-@code{nil} value. | |
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122 | @end defun |
123 | ||
124 | @defun run-hook-with-args-until-success hook &rest args | |
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125 | This function runs an abnormal hook by calling each hook function, |
126 | stopping if one of them ``succeeds'' by returning a non-@code{nil} | |
127 | value. Each hook function is passed the arguments @var{args}. If this | |
128 | function stops because one of the hook functions returns a | |
129 | non-@code{nil} value, it returns that value; otherwise it returns | |
130 | @code{nil}. | |
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131 | @end defun |
132 | ||
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133 | @defmac with-wrapper-hook hook args &rest body |
134 | This macro runs the abnormal hook @code{hook} as a series of nested | |
135 | ``wrapper functions'' around the @var{body} forms. The effect is | |
136 | similar to nested @code{around} advices (@pxref{Around-Advice}). | |
137 | ||
138 | Each hook function must accept an argument list consisting of a function | |
139 | @var{fun}, followed by the additional arguments listed in @var{args}. | |
140 | The function @var{fun} passed to the very first hook function in | |
141 | @var{hook} does the same as @var{body}, if it is called with arguments | |
142 | @var{args}. The @var{fun} passed to each successive hook function is | |
143 | constructed from all the preceding hook functions (and @var{body}); if | |
144 | this @var{fun} is called with arguments @var{args}, it does what the | |
145 | @code{with-wrapper-hook} call would if the preceding hook functions were | |
146 | the only ones in @var{hook}. | |
147 | ||
148 | In the function definition of the hook function, @var{fun} can be called | |
149 | any number of times (including not calling it at all). This function | |
150 | definition is then used to construct the @var{fun} passed to the next | |
151 | hook function in @var{hook}, if any. The last or ``outermost'' | |
152 | @var{fun} is called once to produce the effect. | |
153 | @end defmac | |
154 | ||
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155 | @node Setting Hooks |
156 | @subsection Setting Hooks | |
157 | ||
158 | Here's an example that uses a mode hook to turn on Auto Fill mode when | |
159 | in Lisp Interaction mode: | |
160 | ||
161 | @example | |
162 | (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) | |
163 | @end example | |
164 | ||
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165 | @defun add-hook hook function &optional append local |
166 | This function is the handy way to add function @var{function} to hook | |
167 | variable @var{hook}. You can use it for abnormal hooks as well as for | |
168 | normal hooks. @var{function} can be any Lisp function that can accept | |
169 | the proper number of arguments for @var{hook}. For example, | |
170 | ||
171 | @example | |
172 | (add-hook 'text-mode-hook 'my-text-hook-function) | |
173 | @end example | |
174 | ||
175 | @noindent | |
176 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. | |
177 | ||
178 | If @var{function} is already present in @var{hook} (comparing using | |
179 | @code{equal}), then @code{add-hook} does not add it a second time. | |
180 | ||
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181 | If @var{function} has a non-@code{nil} property |
182 | @code{permanent-local-hook}, then @code{kill-all-local-variables} (or | |
183 | changing major modes) won't delete it from the hook variable's local | |
184 | value. | |
185 | ||
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186 | It is best to design your hook functions so that the order in which |
187 | they are executed does not matter. Any dependence on the order is | |
188 | asking for trouble. However, the order is predictable: normally, | |
b8d4c8d0 | 189 | @var{function} goes at the front of the hook list, so it will be |
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190 | executed first (barring another @code{add-hook} call). If the |
191 | optional argument @var{append} is non-@code{nil}, the new hook | |
192 | function goes at the end of the hook list and will be executed last. | |
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193 | |
194 | @code{add-hook} can handle the cases where @var{hook} is void or its | |
195 | value is a single function; it sets or changes the value to a list of | |
196 | functions. | |
197 | ||
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198 | If @var{local} is non-@code{nil}, that says to add @var{function} to the |
199 | buffer-local hook list instead of to the global hook list. This makes | |
200 | the hook buffer-local and adds @code{t} to the buffer-local value. The | |
201 | latter acts as a flag to run the hook functions in the default value as | |
202 | well as in the local value. | |
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203 | @end defun |
204 | ||
205 | @defun remove-hook hook function &optional local | |
206 | This function removes @var{function} from the hook variable | |
207 | @var{hook}. It compares @var{function} with elements of @var{hook} | |
208 | using @code{equal}, so it works for both symbols and lambda | |
209 | expressions. | |
210 | ||
211 | If @var{local} is non-@code{nil}, that says to remove @var{function} | |
212 | from the buffer-local hook list instead of from the global hook list. | |
213 | @end defun | |
214 | ||
215 | @node Major Modes | |
216 | @section Major Modes | |
217 | @cindex major mode | |
218 | ||
3fd50d5c | 219 | @cindex major mode command |
b8d4c8d0 | 220 | Major modes specialize Emacs for editing particular kinds of text. |
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221 | Each buffer has one major mode at a time. Every major mode is |
222 | associated with a @dfn{major mode command}, whose name should end in | |
223 | @samp{-mode}. This command takes care of switching to that mode in the | |
224 | current buffer, by setting various buffer-local variables such as a | |
225 | local keymap. @xref{Major Mode Conventions}. | |
226 | ||
227 | The least specialized major mode is called @dfn{Fundamental mode}, | |
228 | which has no mode-specific definitions or variable settings. | |
229 | ||
230 | @deffn Command fundamental-mode | |
231 | This is the major mode command for Fundamental mode. Unlike other mode | |
232 | commands, it does @emph{not} run any mode hooks (@pxref{Major Mode | |
233 | Conventions}), since you are not supposed to customize this mode. | |
234 | @end deffn | |
235 | ||
236 | The easiest way to write a major mode is to use the macro | |
237 | @code{define-derived-mode}, which sets up the new mode as a variant of | |
238 | an existing major mode. @xref{Derived Modes}. We recommend using | |
239 | @code{define-derived-mode} even if the new mode is not an obvious | |
240 | derivative of another mode, as it automatically enforces many coding | |
241 | conventions for you. @xref{Basic Major Modes}, for common modes to | |
242 | derive from. | |
243 | ||
244 | The standard GNU Emacs Lisp directory tree contains the code for | |
245 | several major modes, in files such as @file{text-mode.el}, | |
246 | @file{texinfo.el}, @file{lisp-mode.el}, and @file{rmail.el}. You can | |
247 | study these libraries to see how modes are written. | |
248 | ||
249 | @defopt major-mode | |
35137ed3 CY |
250 | The buffer-local value of this variable holds the symbol for the current |
251 | major mode. Its default value holds the default major mode for new | |
252 | buffers. The standard default value is @code{fundamental-mode}. | |
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253 | |
254 | If the default value is @code{nil}, then whenever Emacs creates a new | |
255 | buffer via a command such as @kbd{C-x b} (@code{switch-to-buffer}), the | |
256 | new buffer is put in the major mode of the previously current buffer. | |
257 | As an exception, if the major mode of the previous buffer has a | |
258 | @code{mode-class} symbol property with value @code{special}, the new | |
259 | buffer is put in Fundamental mode (@pxref{Major Mode Conventions}). | |
260 | @end defopt | |
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261 | |
262 | @menu | |
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263 | * Major Mode Conventions:: Coding conventions for keymaps, etc. |
264 | * Auto Major Mode:: How Emacs chooses the major mode automatically. | |
265 | * Mode Help:: Finding out how to use a mode. | |
266 | * Derived Modes:: Defining a new major mode based on another major | |
b8d4c8d0 | 267 | mode. |
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268 | * Basic Major Modes:: Modes that other modes are often derived from. |
269 | * Generic Modes:: Defining a simple major mode that supports | |
b8d4c8d0 | 270 | comment syntax and Font Lock mode. |
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271 | * Mode Hooks:: Hooks run at the end of major mode commands. |
272 | * Example Major Modes:: Text mode and Lisp modes. | |
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273 | @end menu |
274 | ||
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275 | @node Major Mode Conventions |
276 | @subsection Major Mode Conventions | |
277 | @cindex major mode conventions | |
278 | @cindex conventions for writing major modes | |
279 | ||
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280 | The code for every major mode should follow various coding |
281 | conventions, including conventions for local keymap and syntax table | |
282 | initialization, function and variable names, and hooks. | |
283 | ||
284 | If you use the @code{define-derived-mode} macro, it will take care of | |
285 | many of these conventions automatically. @xref{Derived Modes}. Note | |
286 | also that fundamental mode is an exception to many of these conventions, | |
287 | because its definition is to present the global state of Emacs. | |
b8d4c8d0 | 288 | |
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289 | The following list of conventions is only partial. Each major mode |
290 | should aim for consistency in general with other Emacs major modes, as | |
291 | this makes Emacs as a whole more coherent. It is impossible to list | |
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292 | here all the possible points where this issue might come up; if the |
293 | Emacs developers point out an area where your major mode deviates from | |
294 | the usual conventions, please make it compatible. | |
295 | ||
296 | @itemize @bullet | |
297 | @item | |
3fd50d5c CY |
298 | Define a major mode command whose name ends in @samp{-mode}. When |
299 | called with no arguments, this command should switch to the new mode in | |
300 | the current buffer by setting up the keymap, syntax table, and | |
301 | buffer-local variables in an existing buffer. It should not change the | |
302 | buffer's contents. | |
b8d4c8d0 GM |
303 | |
304 | @item | |
3fd50d5c CY |
305 | Write a documentation string for this command that describes the special |
306 | commands available in this mode. @xref{Mode Help}. | |
b8d4c8d0 GM |
307 | |
308 | The documentation string may include the special documentation | |
309 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and | |
3fd50d5c | 310 | @samp{\<@var{keymap}>}, which allow the help display to adapt |
b8d4c8d0 GM |
311 | automatically to the user's own key bindings. @xref{Keys in |
312 | Documentation}. | |
313 | ||
314 | @item | |
315 | The major mode command should start by calling | |
316 | @code{kill-all-local-variables}. This runs the normal hook | |
317 | @code{change-major-mode-hook}, then gets rid of the buffer-local | |
318 | variables of the major mode previously in effect. @xref{Creating | |
319 | Buffer-Local}. | |
320 | ||
321 | @item | |
322 | The major mode command should set the variable @code{major-mode} to the | |
323 | major mode command symbol. This is how @code{describe-mode} discovers | |
324 | which documentation to print. | |
325 | ||
326 | @item | |
327 | The major mode command should set the variable @code{mode-name} to the | |
9cf52b11 EZ |
328 | ``pretty'' name of the mode, usually a string (but see @ref{Mode Line |
329 | Data}, for other possible forms). The name of the mode appears | |
330 | in the mode line. | |
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331 | |
332 | @item | |
333 | @cindex functions in modes | |
334 | Since all global names are in the same name space, all the global | |
335 | variables, constants, and functions that are part of the mode should | |
336 | have names that start with the major mode name (or with an abbreviation | |
337 | of it if the name is long). @xref{Coding Conventions}. | |
338 | ||
339 | @item | |
340 | In a major mode for editing some kind of structured text, such as a | |
341 | programming language, indentation of text according to structure is | |
342 | probably useful. So the mode should set @code{indent-line-function} | |
343 | to a suitable function, and probably customize other variables | |
5dcb4c4e | 344 | for indentation. @xref{Auto-Indentation}. |
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345 | |
346 | @item | |
347 | @cindex keymaps in modes | |
348 | The major mode should usually have its own keymap, which is used as the | |
349 | local keymap in all buffers in that mode. The major mode command should | |
350 | call @code{use-local-map} to install this local map. @xref{Active | |
351 | Keymaps}, for more information. | |
352 | ||
353 | This keymap should be stored permanently in a global variable named | |
354 | @code{@var{modename}-mode-map}. Normally the library that defines the | |
355 | mode sets this variable. | |
356 | ||
357 | @xref{Tips for Defining}, for advice about how to write the code to set | |
358 | up the mode's keymap variable. | |
359 | ||
360 | @item | |
361 | The key sequences bound in a major mode keymap should usually start with | |
362 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, | |
363 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation | |
364 | characters are reserved for minor modes, and ordinary letters are | |
365 | reserved for users. | |
366 | ||
367 | A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and | |
368 | @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally | |
369 | be some kind of ``moving forward and backward,'' but this does not | |
370 | necessarily mean cursor motion. | |
371 | ||
372 | It is legitimate for a major mode to rebind a standard key sequence if | |
373 | it provides a command that does ``the same job'' in a way better | |
374 | suited to the text this mode is used for. For example, a major mode | |
375 | for editing a programming language might redefine @kbd{C-M-a} to | |
376 | ``move to the beginning of a function'' in a way that works better for | |
377 | that language. | |
378 | ||
379 | It is also legitimate for a major mode to rebind a standard key | |
380 | sequence whose standard meaning is rarely useful in that mode. For | |
381 | instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is | |
382 | rarely of any use in the minibuffer. Major modes such as Dired or | |
383 | Rmail that do not allow self-insertion of text can reasonably redefine | |
384 | letters and other printing characters as special commands. | |
385 | ||
386 | @item | |
867d4bb3 | 387 | Major modes for editing text should not define @key{RET} to do |
b8d4c8d0 GM |
388 | anything other than insert a newline. However, it is ok for |
389 | specialized modes for text that users don't directly edit, such as | |
390 | Dired and Info modes, to redefine @key{RET} to do something entirely | |
391 | different. | |
392 | ||
393 | @item | |
394 | Major modes should not alter options that are primarily a matter of user | |
395 | preference, such as whether Auto-Fill mode is enabled. Leave this to | |
396 | each user to decide. However, a major mode should customize other | |
397 | variables so that Auto-Fill mode will work usefully @emph{if} the user | |
398 | decides to use it. | |
399 | ||
400 | @item | |
401 | @cindex syntax tables in modes | |
402 | The mode may have its own syntax table or may share one with other | |
403 | related modes. If it has its own syntax table, it should store this in | |
404 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax | |
405 | Tables}. | |
406 | ||
407 | @item | |
408 | If the mode handles a language that has a syntax for comments, it should | |
409 | set the variables that define the comment syntax. @xref{Options for | |
410 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. | |
411 | ||
412 | @item | |
413 | @cindex abbrev tables in modes | |
414 | The mode may have its own abbrev table or may share one with other | |
415 | related modes. If it has its own abbrev table, it should store this | |
416 | in a variable named @code{@var{modename}-mode-abbrev-table}. If the | |
417 | major mode command defines any abbrevs itself, it should pass @code{t} | |
418 | for the @var{system-flag} argument to @code{define-abbrev}. | |
419 | @xref{Defining Abbrevs}. | |
420 | ||
421 | @item | |
422 | The mode should specify how to do highlighting for Font Lock mode, by | |
423 | setting up a buffer-local value for the variable | |
424 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). | |
425 | ||
e0dd6837 CY |
426 | @item |
427 | Each face that the mode defines should, if possible, inherit from an | |
35137ed3 | 428 | existing Emacs face. @xref{Basic Faces}, and @ref{Faces for Font Lock}. |
e0dd6837 | 429 | |
b8d4c8d0 GM |
430 | @item |
431 | The mode should specify how Imenu should find the definitions or | |
432 | sections of a buffer, by setting up a buffer-local value for the | |
433 | variable @code{imenu-generic-expression}, for the two variables | |
434 | @code{imenu-prev-index-position-function} and | |
435 | @code{imenu-extract-index-name-function}, or for the variable | |
436 | @code{imenu-create-index-function} (@pxref{Imenu}). | |
437 | ||
438 | @item | |
439 | The mode can specify a local value for | |
440 | @code{eldoc-documentation-function} to tell ElDoc mode how to handle | |
441 | this mode. | |
442 | ||
769741e3 SM |
443 | @item |
444 | The mode can specify how to complete various keywords by adding | |
445 | to the special hook @code{completion-at-point-functions}. | |
446 | ||
b8d4c8d0 GM |
447 | @item |
448 | Use @code{defvar} or @code{defcustom} to set mode-related variables, so | |
449 | that they are not reinitialized if they already have a value. (Such | |
450 | reinitialization could discard customizations made by the user.) | |
451 | ||
452 | @item | |
453 | @cindex buffer-local variables in modes | |
454 | To make a buffer-local binding for an Emacs customization variable, use | |
455 | @code{make-local-variable} in the major mode command, not | |
456 | @code{make-variable-buffer-local}. The latter function would make the | |
457 | variable local to every buffer in which it is subsequently set, which | |
458 | would affect buffers that do not use this mode. It is undesirable for a | |
459 | mode to have such global effects. @xref{Buffer-Local Variables}. | |
460 | ||
461 | With rare exceptions, the only reasonable way to use | |
462 | @code{make-variable-buffer-local} in a Lisp package is for a variable | |
463 | which is used only within that package. Using it on a variable used by | |
464 | other packages would interfere with them. | |
465 | ||
466 | @item | |
467 | @cindex mode hook | |
468 | @cindex major mode hook | |
469 | Each major mode should have a normal @dfn{mode hook} named | |
470 | @code{@var{modename}-mode-hook}. The very last thing the major mode command | |
471 | should do is to call @code{run-mode-hooks}. This runs the mode hook, | |
472 | and then runs the normal hook @code{after-change-major-mode-hook}. | |
473 | @xref{Mode Hooks}. | |
474 | ||
475 | @item | |
476 | The major mode command may start by calling some other major mode | |
477 | command (called the @dfn{parent mode}) and then alter some of its | |
478 | settings. A mode that does this is called a @dfn{derived mode}. The | |
41633740 CY |
479 | recommended way to define one is to use the @code{define-derived-mode} |
480 | macro, but this is not required. Such a mode should call the parent | |
481 | mode command inside a @code{delay-mode-hooks} form. (Using | |
b8d4c8d0 GM |
482 | @code{define-derived-mode} does this automatically.) @xref{Derived |
483 | Modes}, and @ref{Mode Hooks}. | |
484 | ||
485 | @item | |
486 | If something special should be done if the user switches a buffer from | |
487 | this mode to any other major mode, this mode can set up a buffer-local | |
488 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). | |
489 | ||
490 | @item | |
9adfcd0b EZ |
491 | If this mode is appropriate only for specially-prepared text produced by |
492 | the mode itself (rather than by the user typing at the keyboard or by an | |
493 | external file), then the major mode command symbol should have a | |
494 | property named @code{mode-class} with value @code{special}, put on as | |
495 | follows: | |
b8d4c8d0 GM |
496 | |
497 | @kindex mode-class @r{(property)} | |
9adfcd0b | 498 | @cindex @code{special} modes |
b8d4c8d0 GM |
499 | @example |
500 | (put 'funny-mode 'mode-class 'special) | |
501 | @end example | |
502 | ||
503 | @noindent | |
9adfcd0b EZ |
504 | This tells Emacs that new buffers created while the current buffer is in |
505 | Funny mode should not be put in Funny mode, even though the default | |
506 | value of @code{major-mode} is @code{nil}. By default, the value of | |
507 | @code{nil} for @code{major-mode} means to use the current buffer's major | |
508 | mode when creating new buffers (@pxref{Auto Major Mode}), but with such | |
509 | @code{special} modes, Fundamental mode is used instead. Modes such as | |
510 | Dired, Rmail, and Buffer List use this feature. | |
b8d4c8d0 | 511 | |
41633740 | 512 | The @code{define-derived-mode} macro automatically marks the derived |
3fd50d5c CY |
513 | mode as special if the parent mode is special. Special mode is a |
514 | convenient parent for such modes to inherit from; @xref{Basic Major | |
515 | Modes}. | |
41633740 | 516 | |
b8d4c8d0 GM |
517 | @item |
518 | If you want to make the new mode the default for files with certain | |
519 | recognizable names, add an element to @code{auto-mode-alist} to select | |
520 | the mode for those file names (@pxref{Auto Major Mode}). If you | |
521 | define the mode command to autoload, you should add this element in | |
522 | the same file that calls @code{autoload}. If you use an autoload | |
523 | cookie for the mode command, you can also use an autoload cookie for | |
524 | the form that adds the element (@pxref{autoload cookie}). If you do | |
525 | not autoload the mode command, it is sufficient to add the element in | |
526 | the file that contains the mode definition. | |
527 | ||
528 | @item | |
529 | In the comments that document the file, you should provide a sample | |
530 | @code{autoload} form and an example of how to add to | |
531 | @code{auto-mode-alist}, that users can include in their init files | |
532 | (@pxref{Init File}). | |
533 | ||
534 | @item | |
535 | @cindex mode loading | |
536 | The top-level forms in the file defining the mode should be written so | |
537 | that they may be evaluated more than once without adverse consequences. | |
538 | Even if you never load the file more than once, someone else will. | |
539 | @end itemize | |
540 | ||
541 | @node Auto Major Mode | |
542 | @subsection How Emacs Chooses a Major Mode | |
543 | @cindex major mode, automatic selection | |
544 | ||
545 | Based on information in the file name or in the file itself, Emacs | |
546 | automatically selects a major mode for the new buffer when a file is | |
547 | visited. It also processes local variables specified in the file text. | |
548 | ||
b8d4c8d0 GM |
549 | @deffn Command normal-mode &optional find-file |
550 | This function establishes the proper major mode and buffer-local variable | |
551 | bindings for the current buffer. First it calls @code{set-auto-mode} | |
552 | (see below), then it runs @code{hack-local-variables} to parse, and | |
553 | bind or evaluate as appropriate, the file's local variables | |
554 | (@pxref{File Local Variables}). | |
555 | ||
556 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, | |
557 | @code{normal-mode} assumes that the @code{find-file} function is calling | |
558 | it. In this case, it may process local variables in the @samp{-*-} | |
559 | line or at the end of the file. The variable | |
560 | @code{enable-local-variables} controls whether to do so. @xref{File | |
561 | Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, | |
562 | for the syntax of the local variables section of a file. | |
563 | ||
564 | If you run @code{normal-mode} interactively, the argument | |
565 | @var{find-file} is normally @code{nil}. In this case, | |
566 | @code{normal-mode} unconditionally processes any file local variables. | |
567 | ||
95459571 | 568 | The function calls @code{set-auto-mode} to choose a major mode. If this |
e145f188 GM |
569 | does not specify a mode, the buffer stays in the major mode determined |
570 | by the default value of @code{major-mode} (see below). | |
b8d4c8d0 GM |
571 | |
572 | @cindex file mode specification error | |
573 | @code{normal-mode} uses @code{condition-case} around the call to the | |
3fd50d5c CY |
574 | major mode command, so errors are caught and reported as a @samp{File |
575 | mode specification error}, followed by the original error message. | |
b8d4c8d0 GM |
576 | @end deffn |
577 | ||
578 | @defun set-auto-mode &optional keep-mode-if-same | |
579 | @cindex visited file mode | |
580 | This function selects the major mode that is appropriate for the | |
3fd50d5c CY |
581 | current buffer. It bases its decision (in order of precedence) on the |
582 | @w{@samp{-*-}} line, on any @samp{mode:} local variable near the end of | |
583 | a file, on the @w{@samp{#!}} line (using @code{interpreter-mode-alist}), | |
584 | on the text at the beginning of the buffer (using | |
585 | @code{magic-mode-alist}), and finally on the visited file name (using | |
586 | @code{auto-mode-alist}). @xref{Choosing Modes, , How Major Modes are | |
587 | Chosen, emacs, The GNU Emacs Manual}. If @code{enable-local-variables} | |
588 | is @code{nil}, @code{set-auto-mode} does not check the @w{@samp{-*-}} | |
589 | line, or near the end of the file, for any mode tag. | |
b8d4c8d0 | 590 | |
61086eb6 GM |
591 | @vindex inhibit-local-variables-regexps |
592 | There are some file types where it is not appropriate to scan the file | |
593 | contents for a mode specifier. For example, a tar archive may happen to | |
594 | contain, near the end of the file, a member file that has a local | |
595 | variables section specifying a mode for that particular file. This | |
596 | should not be applied to the containing tar file. Similarly, a tiff | |
597 | image file might just happen to contain a first line that seems to | |
598 | match the @w{@samp{-*-}} pattern. For these reasons, both these file | |
599 | extensions are members of the list @var{inhibit-local-variables-regexps}. | |
600 | Add patterns to this list to prevent Emacs searching them for local | |
601 | variables of any kind (not just mode specifiers). | |
602 | ||
b8d4c8d0 GM |
603 | If @var{keep-mode-if-same} is non-@code{nil}, this function does not |
604 | call the mode command if the buffer is already in the proper major | |
605 | mode. For instance, @code{set-visited-file-name} sets this to | |
606 | @code{t} to avoid killing buffer local variables that the user may | |
607 | have set. | |
608 | @end defun | |
609 | ||
b8d4c8d0 | 610 | @defun set-buffer-major-mode buffer |
4e3b4528 SM |
611 | This function sets the major mode of @var{buffer} to the default value of |
612 | @code{major-mode}; if that is @code{nil}, it uses the | |
b8d4c8d0 GM |
613 | current buffer's major mode (if that is suitable). As an exception, |
614 | if @var{buffer}'s name is @samp{*scratch*}, it sets the mode to | |
615 | @code{initial-major-mode}. | |
616 | ||
617 | The low-level primitives for creating buffers do not use this function, | |
618 | but medium-level commands such as @code{switch-to-buffer} and | |
619 | @code{find-file-noselect} use it whenever they create buffers. | |
620 | @end defun | |
621 | ||
622 | @defopt initial-major-mode | |
623 | @cindex @samp{*scratch*} | |
624 | The value of this variable determines the major mode of the initial | |
625 | @samp{*scratch*} buffer. The value should be a symbol that is a major | |
626 | mode command. The default value is @code{lisp-interaction-mode}. | |
627 | @end defopt | |
628 | ||
629 | @defvar interpreter-mode-alist | |
630 | This variable specifies major modes to use for scripts that specify a | |
631 | command interpreter in a @samp{#!} line. Its value is an alist with | |
632 | elements of the form @code{(@var{interpreter} . @var{mode})}; for | |
633 | example, @code{("perl" . perl-mode)} is one element present by | |
634 | default. The element says to use mode @var{mode} if the file | |
635 | specifies an interpreter which matches @var{interpreter}. | |
636 | @end defvar | |
637 | ||
638 | @defvar magic-mode-alist | |
639 | This variable's value is an alist with elements of the form | |
640 | @code{(@var{regexp} . @var{function})}, where @var{regexp} is a | |
641 | regular expression and @var{function} is a function or @code{nil}. | |
642 | After visiting a file, @code{set-auto-mode} calls @var{function} if | |
643 | the text at the beginning of the buffer matches @var{regexp} and | |
644 | @var{function} is non-@code{nil}; if @var{function} is @code{nil}, | |
645 | @code{auto-mode-alist} gets to decide the mode. | |
646 | @end defvar | |
647 | ||
648 | @defvar magic-fallback-mode-alist | |
649 | This works like @code{magic-mode-alist}, except that it is handled | |
650 | only if @code{auto-mode-alist} does not specify a mode for this file. | |
651 | @end defvar | |
652 | ||
653 | @defvar auto-mode-alist | |
654 | This variable contains an association list of file name patterns | |
655 | (regular expressions) and corresponding major mode commands. Usually, | |
656 | the file name patterns test for suffixes, such as @samp{.el} and | |
657 | @samp{.c}, but this need not be the case. An ordinary element of the | |
658 | alist looks like @code{(@var{regexp} . @var{mode-function})}. | |
659 | ||
660 | For example, | |
661 | ||
662 | @smallexample | |
663 | @group | |
664 | (("\\`/tmp/fol/" . text-mode) | |
665 | ("\\.texinfo\\'" . texinfo-mode) | |
666 | ("\\.texi\\'" . texinfo-mode) | |
667 | @end group | |
668 | @group | |
669 | ("\\.el\\'" . emacs-lisp-mode) | |
670 | ("\\.c\\'" . c-mode) | |
671 | ("\\.h\\'" . c-mode) | |
672 | @dots{}) | |
673 | @end group | |
674 | @end smallexample | |
675 | ||
676 | When you visit a file whose expanded file name (@pxref{File Name | |
677 | Expansion}), with version numbers and backup suffixes removed using | |
678 | @code{file-name-sans-versions} (@pxref{File Name Components}), matches | |
679 | a @var{regexp}, @code{set-auto-mode} calls the corresponding | |
680 | @var{mode-function}. This feature enables Emacs to select the proper | |
681 | major mode for most files. | |
682 | ||
683 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} | |
684 | @var{function} t)}, then after calling @var{function}, Emacs searches | |
685 | @code{auto-mode-alist} again for a match against the portion of the file | |
686 | name that did not match before. This feature is useful for | |
687 | uncompression packages: an entry of the form @code{("\\.gz\\'" | |
688 | @var{function} t)} can uncompress the file and then put the uncompressed | |
689 | file in the proper mode according to the name sans @samp{.gz}. | |
690 | ||
691 | Here is an example of how to prepend several pattern pairs to | |
692 | @code{auto-mode-alist}. (You might use this sort of expression in your | |
693 | init file.) | |
694 | ||
695 | @smallexample | |
696 | @group | |
697 | (setq auto-mode-alist | |
698 | (append | |
699 | ;; @r{File name (within directory) starts with a dot.} | |
700 | '(("/\\.[^/]*\\'" . fundamental-mode) | |
701 | ;; @r{File name has no dot.} | |
2674569b | 702 | ("/[^\\./]*\\'" . fundamental-mode) |
b8d4c8d0 GM |
703 | ;; @r{File name ends in @samp{.C}.} |
704 | ("\\.C\\'" . c++-mode)) | |
705 | auto-mode-alist)) | |
706 | @end group | |
707 | @end smallexample | |
708 | @end defvar | |
709 | ||
710 | @node Mode Help | |
711 | @subsection Getting Help about a Major Mode | |
712 | @cindex mode help | |
713 | @cindex help for major mode | |
714 | @cindex documentation for major mode | |
715 | ||
db7ab02f | 716 | The @code{describe-mode} function provides information about major |
3fd50d5c | 717 | modes. It is normally bound to @kbd{C-h m}. It uses the value of the |
35137ed3 CY |
718 | variable @code{major-mode} (@pxref{Major Modes}), which is why every |
719 | major mode command needs to set that variable. | |
b8d4c8d0 GM |
720 | |
721 | @deffn Command describe-mode | |
722 | This function displays the documentation of the current major mode. | |
723 | ||
724 | The @code{describe-mode} function calls the @code{documentation} | |
725 | function using the value of @code{major-mode} as an argument. Thus, it | |
3fd50d5c | 726 | displays the documentation string of the major mode command. |
b8d4c8d0 GM |
727 | (@xref{Accessing Documentation}.) |
728 | @end deffn | |
729 | ||
b8d4c8d0 GM |
730 | @node Derived Modes |
731 | @subsection Defining Derived Modes | |
732 | @cindex derived mode | |
733 | ||
3fd50d5c CY |
734 | The recommended way to define a new major mode is to derive it from an |
735 | existing one using @code{define-derived-mode}. If there is no closely | |
736 | related mode, you should inherit from either @code{text-mode}, | |
737 | @code{special-mode}, or @code{prog-mode}. @xref{Basic Major Modes}. If | |
738 | none of these are suitable, you can inherit from @code{fundamental-mode} | |
739 | (@pxref{Major Modes}). | |
b8d4c8d0 GM |
740 | |
741 | @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{} | |
c986813b | 742 | This macro defines @var{variant} as a major mode command, using |
b8d4c8d0 GM |
743 | @var{name} as the string form of the mode name. @var{variant} and |
744 | @var{parent} should be unquoted symbols. | |
745 | ||
746 | The new command @var{variant} is defined to call the function | |
747 | @var{parent}, then override certain aspects of that parent mode: | |
748 | ||
749 | @itemize @bullet | |
750 | @item | |
751 | The new mode has its own sparse keymap, named | |
752 | @code{@var{variant}-map}. @code{define-derived-mode} | |
753 | makes the parent mode's keymap the parent of the new map, unless | |
754 | @code{@var{variant}-map} is already set and already has a parent. | |
755 | ||
756 | @item | |
757 | The new mode has its own syntax table, kept in the variable | |
758 | @code{@var{variant}-syntax-table}, unless you override this using the | |
759 | @code{:syntax-table} keyword (see below). @code{define-derived-mode} | |
760 | makes the parent mode's syntax-table the parent of | |
761 | @code{@var{variant}-syntax-table}, unless the latter is already set | |
762 | and already has a parent different from the standard syntax table. | |
763 | ||
764 | @item | |
765 | The new mode has its own abbrev table, kept in the variable | |
766 | @code{@var{variant}-abbrev-table}, unless you override this using the | |
767 | @code{:abbrev-table} keyword (see below). | |
768 | ||
769 | @item | |
770 | The new mode has its own mode hook, @code{@var{variant}-hook}. It | |
771 | runs this hook, after running the hooks of its ancestor modes, with | |
772 | @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}. | |
773 | @end itemize | |
774 | ||
775 | In addition, you can specify how to override other aspects of | |
776 | @var{parent} with @var{body}. The command @var{variant} | |
777 | evaluates the forms in @var{body} after setting up all its usual | |
778 | overrides, just before running the mode hooks. | |
779 | ||
c986813b CY |
780 | If @var{parent} has a non-@code{nil} @code{mode-class} symbol |
781 | property, then @code{define-derived-mode} sets the @code{mode-class} | |
782 | property of @var{variant} to the same value. This ensures, for | |
783 | example, that if @var{parent} is a special mode, then @var{variant} is | |
784 | also a special mode (@pxref{Major Mode Conventions}). | |
785 | ||
b8d4c8d0 GM |
786 | You can also specify @code{nil} for @var{parent}. This gives the new |
787 | mode no parent. Then @code{define-derived-mode} behaves as described | |
788 | above, but, of course, omits all actions connected with @var{parent}. | |
789 | ||
790 | The argument @var{docstring} specifies the documentation string for | |
791 | the new mode. @code{define-derived-mode} adds some general | |
792 | information about the mode's hook, followed by the mode's keymap, at | |
793 | the end of this docstring. If you omit @var{docstring}, | |
794 | @code{define-derived-mode} generates a documentation string. | |
795 | ||
796 | The @var{keyword-args} are pairs of keywords and values. The values | |
797 | are evaluated. The following keywords are currently supported: | |
798 | ||
799 | @table @code | |
800 | @item :syntax-table | |
801 | You can use this to explicitly specify a syntax table for the new | |
802 | mode. If you specify a @code{nil} value, the new mode uses the same | |
803 | syntax table as @var{parent}, or the standard syntax table if | |
804 | @var{parent} is @code{nil}. (Note that this does @emph{not} follow | |
805 | the convention used for non-keyword arguments that a @code{nil} value | |
806 | is equivalent with not specifying the argument.) | |
807 | ||
808 | @item :abbrev-table | |
809 | You can use this to explicitly specify an abbrev table for the new | |
810 | mode. If you specify a @code{nil} value, the new mode uses the same | |
811 | abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table} | |
812 | if @var{parent} is @code{nil}. (Again, a @code{nil} value is | |
813 | @emph{not} equivalent to not specifying this keyword.) | |
814 | ||
815 | @item :group | |
816 | If this is specified, the value should be the customization group for | |
817 | this mode. (Not all major modes have one.) Only the (still | |
818 | experimental and unadvertised) command @code{customize-mode} currently | |
819 | uses this. @code{define-derived-mode} does @emph{not} automatically | |
820 | define the specified customization group. | |
821 | @end table | |
822 | ||
823 | Here is a hypothetical example: | |
824 | ||
825 | @example | |
826 | (define-derived-mode hypertext-mode | |
827 | text-mode "Hypertext" | |
828 | "Major mode for hypertext. | |
829 | \\@{hypertext-mode-map@}" | |
830 | (setq case-fold-search nil)) | |
831 | ||
832 | (define-key hypertext-mode-map | |
833 | [down-mouse-3] 'do-hyper-link) | |
834 | @end example | |
835 | ||
836 | Do not write an @code{interactive} spec in the definition; | |
837 | @code{define-derived-mode} does that automatically. | |
838 | @end defmac | |
839 | ||
3fd50d5c CY |
840 | @defun derived-mode-p &rest modes |
841 | This function returns non-@code{nil} if the current major mode is | |
842 | derived from any of the major modes given by the symbols @var{modes}. | |
843 | @end defun | |
844 | ||
845 | @node Basic Major Modes | |
846 | @subsection Basic Major Modes | |
847 | ||
848 | Apart from Fundamental mode, there are three major modes that other | |
849 | major modes commonly derive from: Text mode, Prog mode, and Special | |
850 | mode. While Text mode is useful in its own right (e.g. for editing | |
851 | files ending in @file{.txt}), Prog mode and Special mode exist mainly to | |
852 | let other modes derive from them. | |
853 | ||
854 | @vindex prog-mode-hook | |
855 | As far as possible, new major modes should be derived, either directly | |
856 | or indirectly, from one of these three modes. One reason is that this | |
857 | allows users to customize a single mode hook | |
858 | (e.g. @code{prog-mode-hook}) for an entire family of relevant modes | |
859 | (e.g. all programming language modes). | |
860 | ||
861 | @deffn Command text-mode | |
862 | Text mode is a major mode for editing human languages. It defines the | |
863 | @samp{"} and @samp{\} characters as having punctuation syntax | |
864 | (@pxref{Syntax Class Table}), and binds @kbd{M-@key{TAB}} to | |
865 | @code{ispell-complete-word} (@pxref{Spelling,,, emacs, The GNU Emacs | |
866 | Manual}). | |
867 | ||
868 | An example of a major mode derived from Text mode is HTML mode. | |
869 | @xref{HTML Mode,,SGML and HTML Modes, emacs, The GNU Emacs Manual}. | |
870 | @end deffn | |
871 | ||
872 | @deffn Command prog-mode | |
873 | Prog mode is a basic major mode for buffers containing programming | |
874 | language source code. Most of the programming language major modes | |
875 | built into Emacs are derived from it. | |
876 | ||
877 | Prog mode binds @code{parse-sexp-ignore-comments} to @code{t} | |
878 | (@pxref{Motion via Parsing}) and @code{bidi-paragraph-direction} to | |
879 | @code{left-to-right} (@pxref{Bidirectional Display}). | |
880 | @end deffn | |
881 | ||
882 | @deffn Command special-mode | |
883 | Special mode is a basic major mode for buffers containing text that is | |
884 | produced specially by Emacs, rather than from a file. Major modes | |
885 | derived from Special mode are given a @code{mode-class} property of | |
886 | @code{special} (@pxref{Major Mode Conventions}). | |
887 | ||
888 | Special mode sets the buffer to read-only. Its keymap defines several | |
889 | common bindings, including @kbd{q} for @code{quit-window}, @kbd{z} for | |
890 | @code{kill-this-buffer}, and @kbd{g} for @code{revert-buffer} | |
891 | (@pxref{Reverting}). | |
892 | ||
893 | An example of a major mode derived from Special mode is Buffer Menu | |
894 | mode, which is used by the @samp{*Buffer List*} buffer. @xref{List | |
895 | Buffers,,Listing Existing Buffers, emacs, The GNU Emacs Manual}. | |
896 | @end deffn | |
897 | ||
b8d4c8d0 GM |
898 | @node Generic Modes |
899 | @subsection Generic Modes | |
900 | @cindex generic mode | |
901 | ||
902 | @dfn{Generic modes} are simple major modes with basic support for | |
903 | comment syntax and Font Lock mode. To define a generic mode, use the | |
904 | macro @code{define-generic-mode}. See the file @file{generic-x.el} | |
905 | for some examples of the use of @code{define-generic-mode}. | |
906 | ||
907 | @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring | |
908 | This macro defines a generic mode command named @var{mode} (a symbol, | |
909 | not quoted). The optional argument @var{docstring} is the | |
910 | documentation for the mode command. If you do not supply it, | |
911 | @code{define-generic-mode} generates one by default. | |
912 | ||
913 | The argument @var{comment-list} is a list in which each element is | |
914 | either a character, a string of one or two characters, or a cons cell. | |
915 | A character or a string is set up in the mode's syntax table as a | |
916 | ``comment starter.'' If the entry is a cons cell, the @sc{car} is set | |
917 | up as a ``comment starter'' and the @sc{cdr} as a ``comment ender.'' | |
918 | (Use @code{nil} for the latter if you want comments to end at the end | |
919 | of the line.) Note that the syntax table mechanism has limitations | |
920 | about what comment starters and enders are actually possible. | |
921 | @xref{Syntax Tables}. | |
922 | ||
923 | The argument @var{keyword-list} is a list of keywords to highlight | |
924 | with @code{font-lock-keyword-face}. Each keyword should be a string. | |
925 | Meanwhile, @var{font-lock-list} is a list of additional expressions to | |
926 | highlight. Each element of this list should have the same form as an | |
927 | element of @code{font-lock-keywords}. @xref{Search-based | |
928 | Fontification}. | |
929 | ||
930 | The argument @var{auto-mode-list} is a list of regular expressions to | |
931 | add to the variable @code{auto-mode-alist}. They are added by the execution | |
932 | of the @code{define-generic-mode} form, not by expanding the macro call. | |
933 | ||
934 | Finally, @var{function-list} is a list of functions for the mode | |
935 | command to call for additional setup. It calls these functions just | |
936 | before it runs the mode hook variable @code{@var{mode}-hook}. | |
937 | @end defmac | |
938 | ||
939 | @node Mode Hooks | |
940 | @subsection Mode Hooks | |
941 | ||
3fd50d5c | 942 | Every major mode command should finish by running its mode hook and |
b8d4c8d0 GM |
943 | the mode-independent normal hook @code{after-change-major-mode-hook}. |
944 | It does this by calling @code{run-mode-hooks}. If the major mode is a | |
945 | derived mode, that is if it calls another major mode (the parent mode) | |
946 | in its body, it should do this inside @code{delay-mode-hooks} so that | |
947 | the parent won't run these hooks itself. Instead, the derived mode's | |
948 | call to @code{run-mode-hooks} runs the parent's mode hook too. | |
949 | @xref{Major Mode Conventions}. | |
950 | ||
951 | Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}. | |
952 | When user-implemented major modes have not been updated to use it, | |
953 | they won't entirely follow these conventions: they may run the | |
954 | parent's mode hook too early, or fail to run | |
955 | @code{after-change-major-mode-hook}. If you encounter such a major | |
956 | mode, please correct it to follow these conventions. | |
957 | ||
958 | When you defined a major mode using @code{define-derived-mode}, it | |
959 | automatically makes sure these conventions are followed. If you | |
960 | define a major mode ``by hand,'' not using @code{define-derived-mode}, | |
961 | use the following functions to handle these conventions automatically. | |
962 | ||
963 | @defun run-mode-hooks &rest hookvars | |
964 | Major modes should run their mode hook using this function. It is | |
965 | similar to @code{run-hooks} (@pxref{Hooks}), but it also runs | |
966 | @code{after-change-major-mode-hook}. | |
967 | ||
968 | When this function is called during the execution of a | |
969 | @code{delay-mode-hooks} form, it does not run the hooks immediately. | |
970 | Instead, it arranges for the next call to @code{run-mode-hooks} to run | |
971 | them. | |
972 | @end defun | |
973 | ||
974 | @defmac delay-mode-hooks body@dots{} | |
975 | When one major mode command calls another, it should do so inside of | |
976 | @code{delay-mode-hooks}. | |
977 | ||
978 | This macro executes @var{body}, but tells all @code{run-mode-hooks} | |
979 | calls during the execution of @var{body} to delay running their hooks. | |
980 | The hooks will actually run during the next call to | |
981 | @code{run-mode-hooks} after the end of the @code{delay-mode-hooks} | |
982 | construct. | |
983 | @end defmac | |
984 | ||
985 | @defvar after-change-major-mode-hook | |
986 | This is a normal hook run by @code{run-mode-hooks}. It is run at the | |
3fd50d5c | 987 | very end of every properly-written major mode command. |
b8d4c8d0 GM |
988 | @end defvar |
989 | ||
990 | @node Example Major Modes | |
991 | @subsection Major Mode Examples | |
992 | ||
993 | Text mode is perhaps the simplest mode besides Fundamental mode. | |
994 | Here are excerpts from @file{text-mode.el} that illustrate many of | |
995 | the conventions listed above: | |
996 | ||
997 | @smallexample | |
998 | @group | |
999 | ;; @r{Create the syntax table for this mode.} | |
1000 | (defvar text-mode-syntax-table | |
1001 | (let ((st (make-syntax-table))) | |
1002 | (modify-syntax-entry ?\" ". " st) | |
1003 | (modify-syntax-entry ?\\ ". " st) | |
1004 | ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. | |
1005 | (modify-syntax-entry ?' "w p" st) | |
1006 | st) | |
1007 | "Syntax table used while in `text-mode'.") | |
1008 | @end group | |
1009 | ||
1010 | ;; @r{Create the keymap for this mode.} | |
1011 | @group | |
1012 | (defvar text-mode-map | |
1013 | (let ((map (make-sparse-keymap))) | |
1014 | (define-key map "\e\t" 'ispell-complete-word) | |
1015 | (define-key map "\es" 'center-line) | |
1016 | (define-key map "\eS" 'center-paragraph) | |
1017 | map) | |
1018 | "Keymap for `text-mode'. | |
1019 | Many other modes, such as Mail mode, Outline mode | |
1020 | and Indented Text mode, inherit all the commands | |
1021 | defined in this map.") | |
1022 | @end group | |
1023 | @end smallexample | |
1024 | ||
1025 | Here is how the actual mode command is defined now: | |
1026 | ||
1027 | @smallexample | |
1028 | @group | |
1029 | (define-derived-mode text-mode nil "Text" | |
1030 | "Major mode for editing text written for humans to read. | |
1031 | In this mode, paragraphs are delimited only by blank or white lines. | |
1032 | You can thus get the full benefit of adaptive filling | |
1033 | (see the variable `adaptive-fill-mode'). | |
1034 | \\@{text-mode-map@} | |
1035 | Turning on Text mode runs the normal hook `text-mode-hook'." | |
1036 | @end group | |
1037 | @group | |
769741e3 | 1038 | (set (make-local-variable 'text-mode-variant) t) |
b8d4c8d0 GM |
1039 | ;; @r{These two lines are a feature added recently.} |
1040 | (set (make-local-variable 'require-final-newline) | |
1041 | mode-require-final-newline) | |
1042 | (set (make-local-variable 'indent-line-function) 'indent-relative)) | |
1043 | @end group | |
1044 | @end smallexample | |
1045 | ||
1046 | @noindent | |
1047 | (The last line is redundant nowadays, since @code{indent-relative} is | |
1048 | the default value, and we'll delete it in a future version.) | |
1049 | ||
1050 | Here is how it was defined formerly, before | |
1051 | @code{define-derived-mode} existed: | |
1052 | ||
1053 | @smallexample | |
1054 | @group | |
1055 | ;; @r{This isn't needed nowadays, since @code{define-derived-mode} does it.} | |
769741e3 | 1056 | (define-abbrev-table 'text-mode-abbrev-table () |
b8d4c8d0 | 1057 | "Abbrev table used while in text mode.") |
b8d4c8d0 GM |
1058 | @end group |
1059 | ||
1060 | @group | |
1061 | (defun text-mode () | |
1062 | "Major mode for editing text intended for humans to read... | |
1063 | Special commands: \\@{text-mode-map@} | |
1064 | @end group | |
1065 | @group | |
1066 | Turning on text-mode runs the hook `text-mode-hook'." | |
1067 | (interactive) | |
1068 | (kill-all-local-variables) | |
1069 | (use-local-map text-mode-map) | |
1070 | @end group | |
1071 | @group | |
1072 | (setq local-abbrev-table text-mode-abbrev-table) | |
1073 | (set-syntax-table text-mode-syntax-table) | |
1074 | @end group | |
1075 | @group | |
1076 | ;; @r{These four lines are absent from the current version} | |
049bcbcb CY |
1077 | ;; @r{not because this is done some other way, but because} |
1078 | ;; @r{nowadays Text mode uses the normal definition of paragraphs.} | |
769741e3 SM |
1079 | (set (make-local-variable 'paragraph-start) |
1080 | (concat "[ \t]*$\\|" page-delimiter)) | |
1081 | (set (make-local-variable 'paragraph-separate) paragraph-start) | |
1082 | (set (make-local-variable 'indent-line-function) 'indent-relative-maybe) | |
b8d4c8d0 GM |
1083 | @end group |
1084 | @group | |
1085 | (setq mode-name "Text") | |
1086 | (setq major-mode 'text-mode) | |
1087 | (run-mode-hooks 'text-mode-hook)) ; @r{Finally, this permits the user to} | |
1088 | ; @r{customize the mode with a hook.} | |
1089 | @end group | |
1090 | @end smallexample | |
1091 | ||
1092 | @cindex @file{lisp-mode.el} | |
1093 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp | |
1094 | Interaction mode) have more features than Text mode and the code is | |
1095 | correspondingly more complicated. Here are excerpts from | |
1096 | @file{lisp-mode.el} that illustrate how these modes are written. | |
1097 | ||
1098 | @cindex syntax table example | |
1099 | @smallexample | |
1100 | @group | |
1101 | ;; @r{Create mode-specific table variables.} | |
1102 | (defvar lisp-mode-syntax-table nil "") | |
1103 | (defvar lisp-mode-abbrev-table nil "") | |
1104 | @end group | |
1105 | ||
1106 | @group | |
1107 | (defvar emacs-lisp-mode-syntax-table | |
1108 | (let ((table (make-syntax-table))) | |
1109 | (let ((i 0)) | |
1110 | @end group | |
1111 | ||
1112 | @group | |
1113 | ;; @r{Set syntax of chars up to @samp{0} to say they are} | |
1114 | ;; @r{part of symbol names but not words.} | |
1115 | ;; @r{(The digit @samp{0} is @code{48} in the @acronym{ASCII} character set.)} | |
1116 | (while (< i ?0) | |
2f3725cd EZ |
1117 | (modify-syntax-entry i "_ " table) |
1118 | (setq i (1+ i))) | |
b8d4c8d0 GM |
1119 | ;; @r{@dots{} similar code follows for other character ranges.} |
1120 | @end group | |
1121 | @group | |
1122 | ;; @r{Then set the syntax codes for characters that are special in Lisp.} | |
1123 | (modify-syntax-entry ? " " table) | |
1124 | (modify-syntax-entry ?\t " " table) | |
1125 | (modify-syntax-entry ?\f " " table) | |
1126 | (modify-syntax-entry ?\n "> " table) | |
1127 | @end group | |
1128 | @group | |
1129 | ;; @r{Give CR the same syntax as newline, for selective-display.} | |
1130 | (modify-syntax-entry ?\^m "> " table) | |
1131 | (modify-syntax-entry ?\; "< " table) | |
1132 | (modify-syntax-entry ?` "' " table) | |
1133 | (modify-syntax-entry ?' "' " table) | |
1134 | (modify-syntax-entry ?, "' " table) | |
1135 | @end group | |
1136 | @group | |
1137 | ;; @r{@dots{}likewise for many other characters@dots{}} | |
1138 | (modify-syntax-entry ?\( "() " table) | |
1139 | (modify-syntax-entry ?\) ")( " table) | |
1140 | (modify-syntax-entry ?\[ "(] " table) | |
1141 | (modify-syntax-entry ?\] ")[ " table)) | |
1142 | table)) | |
1143 | @end group | |
1144 | @group | |
1145 | ;; @r{Create an abbrev table for lisp-mode.} | |
1146 | (define-abbrev-table 'lisp-mode-abbrev-table ()) | |
1147 | @end group | |
1148 | @end smallexample | |
1149 | ||
1150 | The three modes for Lisp share much of their code. For instance, | |
1151 | each calls the following function to set various variables: | |
1152 | ||
1153 | @smallexample | |
1154 | @group | |
1155 | (defun lisp-mode-variables (lisp-syntax) | |
1156 | (when lisp-syntax | |
1157 | (set-syntax-table lisp-mode-syntax-table)) | |
1158 | (setq local-abbrev-table lisp-mode-abbrev-table) | |
1159 | @dots{} | |
1160 | @end group | |
1161 | @end smallexample | |
1162 | ||
1163 | In Lisp and most programming languages, we want the paragraph | |
1164 | commands to treat only blank lines as paragraph separators. And the | |
1165 | modes should understand the Lisp conventions for comments. The rest of | |
1166 | @code{lisp-mode-variables} sets this up: | |
1167 | ||
1168 | @smallexample | |
1169 | @group | |
049bcbcb CY |
1170 | (set (make-local-variable 'paragraph-start) |
1171 | (concat page-delimiter "\\|$" )) | |
1172 | (set (make-local-variable 'paragraph-separate) | |
1173 | paragraph-start) | |
b8d4c8d0 GM |
1174 | @dots{} |
1175 | @end group | |
1176 | @group | |
049bcbcb CY |
1177 | (set (make-local-variable 'comment-indent-function) |
1178 | 'lisp-comment-indent)) | |
b8d4c8d0 GM |
1179 | @dots{} |
1180 | @end group | |
1181 | @end smallexample | |
1182 | ||
1183 | Each of the different Lisp modes has a slightly different keymap. For | |
1184 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other | |
1185 | Lisp modes do not. However, all Lisp modes have some commands in | |
1186 | common. The following code sets up the common commands: | |
1187 | ||
1188 | @smallexample | |
1189 | @group | |
769741e3 SM |
1190 | (defvar shared-lisp-mode-map |
1191 | (let ((map (make-sparse-keymap))) | |
1192 | (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) | |
1193 | (define-key shared-lisp-mode-map "\177" | |
1194 | 'backward-delete-char-untabify) | |
1195 | map) | |
b8d4c8d0 | 1196 | "Keymap for commands shared by all sorts of Lisp modes.") |
b8d4c8d0 GM |
1197 | @end group |
1198 | @end smallexample | |
1199 | ||
1200 | @noindent | |
1201 | And here is the code to set up the keymap for Lisp mode: | |
1202 | ||
1203 | @smallexample | |
1204 | @group | |
769741e3 SM |
1205 | (defvar lisp-mode-map |
1206 | (let ((map (make-sparse-keymap))) | |
1207 | (set-keymap-parent map shared-lisp-mode-map) | |
1208 | (define-key map "\e\C-x" 'lisp-eval-defun) | |
1209 | (define-key map "\C-c\C-z" 'run-lisp) | |
1210 | map) | |
b8d4c8d0 | 1211 | "Keymap for ordinary Lisp mode...") |
b8d4c8d0 GM |
1212 | @end group |
1213 | @end smallexample | |
1214 | ||
3fd50d5c CY |
1215 | Finally, here is the complete major mode command definition for Lisp |
1216 | mode. | |
b8d4c8d0 GM |
1217 | |
1218 | @smallexample | |
1219 | @group | |
1220 | (defun lisp-mode () | |
1221 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. | |
1222 | Commands: | |
1223 | Delete converts tabs to spaces as it moves back. | |
1224 | Blank lines separate paragraphs. Semicolons start comments. | |
1225 | \\@{lisp-mode-map@} | |
1226 | Note that `run-lisp' may be used either to start an inferior Lisp job | |
1227 | or to switch back to an existing one. | |
1228 | @end group | |
1229 | ||
1230 | @group | |
1231 | Entry to this mode calls the value of `lisp-mode-hook' | |
1232 | if that value is non-nil." | |
1233 | (interactive) | |
1234 | (kill-all-local-variables) | |
1235 | @end group | |
1236 | @group | |
1237 | (use-local-map lisp-mode-map) ; @r{Select the mode's keymap.} | |
1238 | (setq major-mode 'lisp-mode) ; @r{This is how @code{describe-mode}} | |
1239 | ; @r{finds out what to describe.} | |
1240 | (setq mode-name "Lisp") ; @r{This goes into the mode line.} | |
1241 | (lisp-mode-variables t) ; @r{This defines various variables.} | |
769741e3 SM |
1242 | (set (make-local-variable 'comment-start-skip) |
1243 | "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") | |
1244 | (set (make-local-variable 'font-lock-keywords-case-fold-search) t) | |
b8d4c8d0 GM |
1245 | @end group |
1246 | @group | |
1247 | (setq imenu-case-fold-search t) | |
1248 | (set-syntax-table lisp-mode-syntax-table) | |
1249 | (run-mode-hooks 'lisp-mode-hook)) ; @r{This permits the user to use a} | |
1250 | ; @r{hook to customize the mode.} | |
1251 | @end group | |
1252 | @end smallexample | |
1253 | ||
1254 | @node Minor Modes | |
1255 | @section Minor Modes | |
1256 | @cindex minor mode | |
1257 | ||
1258 | A @dfn{minor mode} provides features that users may enable or disable | |
1259 | independently of the choice of major mode. Minor modes can be enabled | |
1260 | individually or in combination. Minor modes would be better named | |
1261 | ``generally available, optional feature modes,'' except that such a name | |
1262 | would be unwieldy. | |
1263 | ||
1264 | A minor mode is not usually meant as a variation of a single major mode. | |
1265 | Usually they are general and can apply to many major modes. For | |
1266 | example, Auto Fill mode works with any major mode that permits text | |
1267 | insertion. To be general, a minor mode must be effectively independent | |
1268 | of the things major modes do. | |
1269 | ||
1270 | A minor mode is often much more difficult to implement than a major | |
1271 | mode. One reason is that you should be able to activate and deactivate | |
1272 | minor modes in any order. A minor mode should be able to have its | |
1273 | desired effect regardless of the major mode and regardless of the other | |
1274 | minor modes in effect. | |
1275 | ||
1276 | Often the biggest problem in implementing a minor mode is finding a | |
1277 | way to insert the necessary hook into the rest of Emacs. Minor mode | |
1278 | keymaps make this easier than it used to be. | |
1279 | ||
1280 | @defvar minor-mode-list | |
1281 | The value of this variable is a list of all minor mode commands. | |
1282 | @end defvar | |
1283 | ||
1284 | @menu | |
1285 | * Minor Mode Conventions:: Tips for writing a minor mode. | |
1286 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. | |
1287 | * Defining Minor Modes:: A convenient facility for defining minor modes. | |
1288 | @end menu | |
1289 | ||
1290 | @node Minor Mode Conventions | |
1291 | @subsection Conventions for Writing Minor Modes | |
1292 | @cindex minor mode conventions | |
1293 | @cindex conventions for writing minor modes | |
1294 | ||
1295 | There are conventions for writing minor modes just as there are for | |
1296 | major modes. Several of the major mode conventions apply to minor | |
1297 | modes as well: those regarding the name of the mode initialization | |
1298 | function, the names of global symbols, the use of a hook at the end of | |
1299 | the initialization function, and the use of keymaps and other tables. | |
1300 | ||
1301 | In addition, there are several conventions that are specific to | |
1302 | minor modes. (The easiest way to follow all the conventions is to use | |
1303 | the macro @code{define-minor-mode}; @ref{Defining Minor Modes}.) | |
1304 | ||
1305 | @itemize @bullet | |
1306 | @item | |
1307 | @cindex mode variable | |
1308 | Make a variable whose name ends in @samp{-mode} to control the minor | |
1309 | mode. We call this the @dfn{mode variable}. The minor mode command | |
1310 | should set this variable (@code{nil} to disable; anything else to | |
1311 | enable). | |
1312 | ||
1313 | If possible, implement the mode so that setting the variable | |
1314 | automatically enables or disables the mode. Then the minor mode command | |
1315 | does not need to do anything except set the variable. | |
1316 | ||
1317 | This variable is used in conjunction with the @code{minor-mode-alist} to | |
1318 | display the minor mode name in the mode line. It can also enable | |
1319 | or disable a minor mode keymap. Individual commands or hooks can also | |
1320 | check the variable's value. | |
1321 | ||
1322 | If you want the minor mode to be enabled separately in each buffer, | |
1323 | make the variable buffer-local. | |
1324 | ||
1325 | @item | |
1326 | Define a command whose name is the same as the mode variable. | |
1327 | Its job is to enable and disable the mode by setting the variable. | |
1328 | ||
1329 | The command should accept one optional argument. If the argument is | |
1330 | @code{nil}, it should toggle the mode (turn it on if it is off, and | |
1331 | off if it is on). It should turn the mode on if the argument is a | |
1332 | positive integer, the symbol @code{t}, or a list whose @sc{car} is one | |
1333 | of those. It should turn the mode off if the argument is a negative | |
1334 | integer or zero, the symbol @code{-}, or a list whose @sc{car} is a | |
1335 | negative integer or zero. The meaning of other arguments is not | |
1336 | specified. | |
1337 | ||
1338 | Here is an example taken from the definition of @code{transient-mark-mode}. | |
1339 | It shows the use of @code{transient-mark-mode} as a variable that enables or | |
1340 | disables the mode's behavior, and also shows the proper way to toggle, | |
1341 | enable or disable the minor mode based on the raw prefix argument value. | |
1342 | ||
1343 | @smallexample | |
1344 | @group | |
1345 | (setq transient-mark-mode | |
1346 | (if (null arg) (not transient-mark-mode) | |
1347 | (> (prefix-numeric-value arg) 0))) | |
1348 | @end group | |
1349 | @end smallexample | |
1350 | ||
1351 | @item | |
1352 | Add an element to @code{minor-mode-alist} for each minor mode | |
1353 | (@pxref{Definition of minor-mode-alist}), if you want to indicate the | |
1354 | minor mode in the mode line. This element should be a list of the | |
1355 | following form: | |
1356 | ||
1357 | @smallexample | |
1358 | (@var{mode-variable} @var{string}) | |
1359 | @end smallexample | |
1360 | ||
1361 | Here @var{mode-variable} is the variable that controls enabling of the | |
1362 | minor mode, and @var{string} is a short string, starting with a space, | |
1363 | to represent the mode in the mode line. These strings must be short so | |
1364 | that there is room for several of them at once. | |
1365 | ||
1366 | When you add an element to @code{minor-mode-alist}, use @code{assq} to | |
1367 | check for an existing element, to avoid duplication. For example: | |
1368 | ||
1369 | @smallexample | |
1370 | @group | |
1371 | (unless (assq 'leif-mode minor-mode-alist) | |
1372 | (setq minor-mode-alist | |
1373 | (cons '(leif-mode " Leif") minor-mode-alist))) | |
1374 | @end group | |
1375 | @end smallexample | |
1376 | ||
1377 | @noindent | |
1378 | or like this, using @code{add-to-list} (@pxref{List Variables}): | |
1379 | ||
1380 | @smallexample | |
1381 | @group | |
1382 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) | |
1383 | @end group | |
1384 | @end smallexample | |
1385 | @end itemize | |
1386 | ||
1387 | Global minor modes distributed with Emacs should if possible support | |
1388 | enabling and disabling via Custom (@pxref{Customization}). To do this, | |
1389 | the first step is to define the mode variable with @code{defcustom}, and | |
0fc76035 | 1390 | specify @code{:type 'boolean}. |
b8d4c8d0 GM |
1391 | |
1392 | If just setting the variable is not sufficient to enable the mode, you | |
1393 | should also specify a @code{:set} method which enables the mode by | |
1394 | invoking the mode command. Note in the variable's documentation string that | |
1395 | setting the variable other than via Custom may not take effect. | |
1396 | ||
1397 | Also mark the definition with an autoload cookie (@pxref{autoload cookie}), | |
1398 | and specify a @code{:require} so that customizing the variable will load | |
1399 | the library that defines the mode. This will copy suitable definitions | |
1400 | into @file{loaddefs.el} so that users can use @code{customize-option} to | |
1401 | enable the mode. For example: | |
1402 | ||
1403 | @smallexample | |
1404 | @group | |
1405 | ||
1406 | ;;;###autoload | |
1407 | (defcustom msb-mode nil | |
1408 | "Toggle msb-mode. | |
1409 | Setting this variable directly does not take effect; | |
1410 | use either \\[customize] or the function `msb-mode'." | |
1411 | :set 'custom-set-minor-mode | |
1412 | :initialize 'custom-initialize-default | |
1413 | :version "20.4" | |
1414 | :type 'boolean | |
1415 | :group 'msb | |
1416 | :require 'msb) | |
1417 | @end group | |
1418 | @end smallexample | |
1419 | ||
1420 | @node Keymaps and Minor Modes | |
1421 | @subsection Keymaps and Minor Modes | |
1422 | ||
1423 | Each minor mode can have its own keymap, which is active when the mode | |
1424 | is enabled. To set up a keymap for a minor mode, add an element to the | |
1425 | alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}. | |
1426 | ||
1427 | @cindex @code{self-insert-command}, minor modes | |
1428 | One use of minor mode keymaps is to modify the behavior of certain | |
1429 | self-inserting characters so that they do something else as well as | |
1430 | self-insert. In general, this is the only way to do that, since the | |
1431 | facilities for customizing @code{self-insert-command} are limited to | |
1432 | special cases (designed for abbrevs and Auto Fill mode). (Do not try | |
1433 | substituting your own definition of @code{self-insert-command} for the | |
1434 | standard one. The editor command loop handles this function specially.) | |
1435 | ||
1436 | The key sequences bound in a minor mode should consist of @kbd{C-c} | |
1437 | followed by one of @kbd{.,/?`'"[]\|~!#$%^&*()-_+=}. (The other | |
1438 | punctuation characters are reserved for major modes.) | |
1439 | ||
1440 | @node Defining Minor Modes | |
1441 | @subsection Defining Minor Modes | |
1442 | ||
1443 | The macro @code{define-minor-mode} offers a convenient way of | |
1444 | implementing a mode in one self-contained definition. | |
1445 | ||
1446 | @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{} | |
1447 | This macro defines a new minor mode whose name is @var{mode} (a | |
1448 | symbol). It defines a command named @var{mode} to toggle the minor | |
1449 | mode, with @var{doc} as its documentation string. It also defines a | |
1450 | variable named @var{mode}, which is set to @code{t} or @code{nil} by | |
1451 | enabling or disabling the mode. The variable is initialized to | |
1452 | @var{init-value}. Except in unusual circumstances (see below), this | |
1453 | value must be @code{nil}. | |
1454 | ||
1455 | The string @var{lighter} says what to display in the mode line | |
1456 | when the mode is enabled; if it is @code{nil}, the mode is not displayed | |
1457 | in the mode line. | |
1458 | ||
bc7d7ea6 CY |
1459 | The optional argument @var{keymap} specifies the keymap for the minor |
1460 | mode. If non-@code{nil}, it should be a variable name (whose value is | |
1461 | a keymap), a keymap, or an alist of the form | |
b8d4c8d0 GM |
1462 | |
1463 | @example | |
1464 | (@var{key-sequence} . @var{definition}) | |
1465 | @end example | |
1466 | ||
bc7d7ea6 CY |
1467 | @noindent |
1468 | where each @var{key-sequence} and @var{definition} are arguments | |
1469 | suitable for passing to @code{define-key} (@pxref{Changing Key | |
1470 | Bindings}). If @var{keymap} is a keymap or an alist, this also | |
1471 | defines the variable @code{@var{mode}-map}. | |
1472 | ||
b8d4c8d0 GM |
1473 | The above three arguments @var{init-value}, @var{lighter}, and |
1474 | @var{keymap} can be (partially) omitted when @var{keyword-args} are | |
1475 | used. The @var{keyword-args} consist of keywords followed by | |
1476 | corresponding values. A few keywords have special meanings: | |
1477 | ||
1478 | @table @code | |
1479 | @item :group @var{group} | |
1480 | Custom group name to use in all generated @code{defcustom} forms. | |
1481 | Defaults to @var{mode} without the possible trailing @samp{-mode}. | |
1482 | @strong{Warning:} don't use this default group name unless you have | |
1483 | written a @code{defgroup} to define that group properly. @xref{Group | |
1484 | Definitions}. | |
1485 | ||
1486 | @item :global @var{global} | |
1487 | If non-@code{nil}, this specifies that the minor mode should be global | |
1488 | rather than buffer-local. It defaults to @code{nil}. | |
1489 | ||
1490 | One of the effects of making a minor mode global is that the | |
1491 | @var{mode} variable becomes a customization variable. Toggling it | |
1492 | through the Custom interface turns the mode on and off, and its value | |
1493 | can be saved for future Emacs sessions (@pxref{Saving | |
1494 | Customizations,,, emacs, The GNU Emacs Manual}. For the saved | |
1495 | variable to work, you should ensure that the @code{define-minor-mode} | |
1496 | form is evaluated each time Emacs starts; for packages that are not | |
1497 | part of Emacs, the easiest way to do this is to specify a | |
1498 | @code{:require} keyword. | |
1499 | ||
1500 | @item :init-value @var{init-value} | |
1501 | This is equivalent to specifying @var{init-value} positionally. | |
1502 | ||
1503 | @item :lighter @var{lighter} | |
1504 | This is equivalent to specifying @var{lighter} positionally. | |
1505 | ||
1506 | @item :keymap @var{keymap} | |
1507 | This is equivalent to specifying @var{keymap} positionally. | |
1508 | @end table | |
1509 | ||
1510 | Any other keyword arguments are passed directly to the | |
1511 | @code{defcustom} generated for the variable @var{mode}. | |
1512 | ||
1513 | The command named @var{mode} first performs the standard actions such | |
1514 | as setting the variable named @var{mode} and then executes the | |
1515 | @var{body} forms, if any. It finishes by running the mode hook | |
1516 | variable @code{@var{mode}-hook}. | |
1517 | @end defmac | |
1518 | ||
1519 | The initial value must be @code{nil} except in cases where (1) the | |
1520 | mode is preloaded in Emacs, or (2) it is painless for loading to | |
1521 | enable the mode even though the user did not request it. For | |
1522 | instance, if the mode has no effect unless something else is enabled, | |
1523 | and will always be loaded by that time, enabling it by default is | |
1524 | harmless. But these are unusual circumstances. Normally, the | |
1525 | initial value must be @code{nil}. | |
1526 | ||
1527 | @findex easy-mmode-define-minor-mode | |
1528 | The name @code{easy-mmode-define-minor-mode} is an alias | |
1529 | for this macro. | |
1530 | ||
1531 | Here is an example of using @code{define-minor-mode}: | |
1532 | ||
1533 | @smallexample | |
1534 | (define-minor-mode hungry-mode | |
1535 | "Toggle Hungry mode. | |
1536 | With no argument, this command toggles the mode. | |
1537 | Non-null prefix argument turns on the mode. | |
1538 | Null prefix argument turns off the mode. | |
1539 | ||
1540 | When Hungry mode is enabled, the control delete key | |
1541 | gobbles all preceding whitespace except the last. | |
1542 | See the command \\[hungry-electric-delete]." | |
1543 | ;; The initial value. | |
1544 | nil | |
1545 | ;; The indicator for the mode line. | |
1546 | " Hungry" | |
1547 | ;; The minor mode bindings. | |
e8bf5266 | 1548 | '(([C-backspace] . hungry-electric-delete)) |
b8d4c8d0 GM |
1549 | :group 'hunger) |
1550 | @end smallexample | |
1551 | ||
1552 | @noindent | |
1553 | This defines a minor mode named ``Hungry mode,'' a command named | |
1554 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} | |
1555 | which indicates whether the mode is enabled, and a variable named | |
1556 | @code{hungry-mode-map} which holds the keymap that is active when the | |
1557 | mode is enabled. It initializes the keymap with a key binding for | |
1558 | @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into | |
1559 | custom group @code{hunger}. There are no @var{body} forms---many | |
1560 | minor modes don't need any. | |
1561 | ||
1562 | Here's an equivalent way to write it: | |
1563 | ||
1564 | @smallexample | |
1565 | (define-minor-mode hungry-mode | |
1566 | "Toggle Hungry mode. | |
1567 | With no argument, this command toggles the mode. | |
1568 | Non-null prefix argument turns on the mode. | |
1569 | Null prefix argument turns off the mode. | |
1570 | ||
1571 | When Hungry mode is enabled, the control delete key | |
1572 | gobbles all preceding whitespace except the last. | |
1573 | See the command \\[hungry-electric-delete]." | |
1574 | ;; The initial value. | |
1575 | :init-value nil | |
1576 | ;; The indicator for the mode line. | |
1577 | :lighter " Hungry" | |
1578 | ;; The minor mode bindings. | |
1579 | :keymap | |
e8bf5266 JB |
1580 | '(([C-backspace] . hungry-electric-delete) |
1581 | ([C-M-backspace] | |
b8d4c8d0 GM |
1582 | . (lambda () |
1583 | (interactive) | |
1584 | (hungry-electric-delete t)))) | |
1585 | :group 'hunger) | |
1586 | @end smallexample | |
1587 | ||
1588 | @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{} | |
1589 | This defines a global toggle named @var{global-mode} whose meaning is | |
1590 | to enable or disable the buffer-local minor mode @var{mode} in all | |
1591 | buffers. To turn on the minor mode in a buffer, it uses the function | |
1592 | @var{turn-on}; to turn off the minor mode, it calls @code{mode} with | |
1593 | @minus{}1 as argument. | |
1594 | ||
1595 | Globally enabling the mode also affects buffers subsequently created | |
1596 | by visiting files, and buffers that use a major mode other than | |
1597 | Fundamental mode; but it does not detect the creation of a new buffer | |
1598 | in Fundamental mode. | |
1599 | ||
1600 | This defines the customization option @var{global-mode} (@pxref{Customization}), | |
1601 | which can be toggled in the Custom interface to turn the minor mode on | |
1602 | and off. As with @code{define-minor-mode}, you should ensure that the | |
1603 | @code{define-globalized-minor-mode} form is evaluated each time Emacs | |
1604 | starts, for example by providing a @code{:require} keyword. | |
1605 | ||
1606 | Use @code{:group @var{group}} in @var{keyword-args} to specify the | |
1607 | custom group for the mode variable of the global minor mode. | |
1608 | @end defmac | |
1609 | ||
1610 | @node Mode Line Format | |
1611 | @section Mode-Line Format | |
1612 | @cindex mode line | |
1613 | ||
1614 | Each Emacs window (aside from minibuffer windows) typically has a mode | |
1615 | line at the bottom, which displays status information about the buffer | |
1616 | displayed in the window. The mode line contains information about the | |
1617 | buffer, such as its name, associated file, depth of recursive editing, | |
1618 | and major and minor modes. A window can also have a @dfn{header | |
1619 | line}, which is much like the mode line but appears at the top of the | |
1620 | window. | |
1621 | ||
1622 | This section describes how to control the contents of the mode line | |
1623 | and header line. We include it in this chapter because much of the | |
1624 | information displayed in the mode line relates to the enabled major and | |
1625 | minor modes. | |
1626 | ||
1627 | @menu | |
769741e3 SM |
1628 | * Base: Mode Line Basics. Basic ideas of mode line control. |
1629 | * Data: Mode Line Data. The data structure that controls the mode line. | |
1630 | * Top: Mode Line Top. The top level variable, mode-line-format. | |
1631 | * Mode Line Variables:: Variables used in that data structure. | |
1632 | * %-Constructs:: Putting information into a mode line. | |
1633 | * Properties in Mode:: Using text properties in the mode line. | |
1634 | * Header Lines:: Like a mode line, but at the top. | |
1635 | * Emulating Mode Line:: Formatting text as the mode line would. | |
b8d4c8d0 GM |
1636 | @end menu |
1637 | ||
1638 | @node Mode Line Basics | |
1639 | @subsection Mode Line Basics | |
1640 | ||
1641 | @code{mode-line-format} is a buffer-local variable that holds a | |
1642 | @dfn{mode line construct}, a kind of template, which controls what is | |
1643 | displayed on the mode line of the current buffer. The value of | |
1644 | @code{header-line-format} specifies the buffer's header line in the | |
1645 | same way. All windows for the same buffer use the same | |
1646 | @code{mode-line-format} and @code{header-line-format}. | |
1647 | ||
1648 | For efficiency, Emacs does not continuously recompute the mode | |
1649 | line and header line of a window. It does so when circumstances | |
1650 | appear to call for it---for instance, if you change the window | |
1651 | configuration, switch buffers, narrow or widen the buffer, scroll, or | |
1652 | change the buffer's modification status. If you modify any of the | |
1653 | variables referenced by @code{mode-line-format} (@pxref{Mode Line | |
1654 | Variables}), or any other variables and data structures that affect | |
1655 | how text is displayed (@pxref{Display}), you may want to force an | |
1656 | update of the mode line so as to display the new information or | |
1657 | display it in the new way. | |
1658 | ||
1659 | @defun force-mode-line-update &optional all | |
1660 | Force redisplay of the current buffer's mode line and header line. | |
1661 | The next redisplay will update the mode line and header line based on | |
1662 | the latest values of all relevant variables. With optional | |
1663 | non-@code{nil} @var{all}, force redisplay of all mode lines and header | |
1664 | lines. | |
1665 | ||
1666 | This function also forces recomputation of the menu bar menus | |
1667 | and the frame title. | |
1668 | @end defun | |
1669 | ||
1670 | The selected window's mode line is usually displayed in a different | |
1671 | color using the face @code{mode-line}. Other windows' mode lines | |
1672 | appear in the face @code{mode-line-inactive} instead. @xref{Faces}. | |
1673 | ||
1674 | @node Mode Line Data | |
1675 | @subsection The Data Structure of the Mode Line | |
1676 | @cindex mode-line construct | |
1677 | ||
1678 | The mode-line contents are controlled by a data structure called a | |
1679 | @dfn{mode-line construct}, made up of lists, strings, symbols, and | |
1680 | numbers kept in buffer-local variables. Each data type has a specific | |
1681 | meaning for the mode-line appearance, as described below. The same | |
1682 | data structure is used for constructing frame titles (@pxref{Frame | |
1683 | Titles}) and header lines (@pxref{Header Lines}). | |
1684 | ||
1685 | A mode-line construct may be as simple as a fixed string of text, | |
1686 | but it usually specifies how to combine fixed strings with variables' | |
1687 | values to construct the text. Many of these variables are themselves | |
1688 | defined to have mode-line constructs as their values. | |
1689 | ||
1690 | Here are the meanings of various data types as mode-line constructs: | |
1691 | ||
1692 | @table @code | |
1693 | @cindex percent symbol in mode line | |
1694 | @item @var{string} | |
1695 | A string as a mode-line construct appears verbatim except for | |
1696 | @dfn{@code{%}-constructs} in it. These stand for substitution of | |
1697 | other data; see @ref{%-Constructs}. | |
1698 | ||
1699 | If parts of the string have @code{face} properties, they control | |
1700 | display of the text just as they would text in the buffer. Any | |
1701 | characters which have no @code{face} properties are displayed, by | |
1702 | default, in the face @code{mode-line} or @code{mode-line-inactive} | |
1703 | (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The | |
1704 | @code{help-echo} and @code{local-map} properties in @var{string} have | |
1705 | special meanings. @xref{Properties in Mode}. | |
1706 | ||
1707 | @item @var{symbol} | |
1708 | A symbol as a mode-line construct stands for its value. The value of | |
1709 | @var{symbol} is used as a mode-line construct, in place of @var{symbol}. | |
1710 | However, the symbols @code{t} and @code{nil} are ignored, as is any | |
1711 | symbol whose value is void. | |
1712 | ||
1713 | There is one exception: if the value of @var{symbol} is a string, it is | |
1714 | displayed verbatim: the @code{%}-constructs are not recognized. | |
1715 | ||
1716 | Unless @var{symbol} is marked as ``risky'' (i.e., it has a | |
1717 | non-@code{nil} @code{risky-local-variable} property), all text | |
1718 | properties specified in @var{symbol}'s value are ignored. This | |
1719 | includes the text properties of strings in @var{symbol}'s value, as | |
1720 | well as all @code{:eval} and @code{:propertize} forms in it. (The | |
1721 | reason for this is security: non-risky variables could be set | |
1722 | automatically from file variables without prompting the user.) | |
1723 | ||
1724 | @item (@var{string} @var{rest}@dots{}) | |
1725 | @itemx (@var{list} @var{rest}@dots{}) | |
1726 | A list whose first element is a string or list means to process all the | |
1727 | elements recursively and concatenate the results. This is the most | |
1728 | common form of mode-line construct. | |
1729 | ||
1730 | @item (:eval @var{form}) | |
1731 | A list whose first element is the symbol @code{:eval} says to evaluate | |
1732 | @var{form}, and use the result as a string to display. Make sure this | |
1733 | evaluation cannot load any files, as doing so could cause infinite | |
1734 | recursion. | |
1735 | ||
1736 | @item (:propertize @var{elt} @var{props}@dots{}) | |
1737 | A list whose first element is the symbol @code{:propertize} says to | |
1738 | process the mode-line construct @var{elt} recursively, then add the text | |
1739 | properties specified by @var{props} to the result. The argument | |
1740 | @var{props} should consist of zero or more pairs @var{text-property} | |
1741 | @var{value}. (This feature is new as of Emacs 22.1.) | |
1742 | ||
1743 | @item (@var{symbol} @var{then} @var{else}) | |
1744 | A list whose first element is a symbol that is not a keyword specifies | |
1745 | a conditional. Its meaning depends on the value of @var{symbol}. If | |
1746 | @var{symbol} has a non-@code{nil} value, the second element, | |
1747 | @var{then}, is processed recursively as a mode-line element. | |
1748 | Otherwise, the third element, @var{else}, is processed recursively. | |
1749 | You may omit @var{else}; then the mode-line element displays nothing | |
1750 | if the value of @var{symbol} is @code{nil} or void. | |
1751 | ||
1752 | @item (@var{width} @var{rest}@dots{}) | |
1753 | A list whose first element is an integer specifies truncation or | |
1754 | padding of the results of @var{rest}. The remaining elements | |
1755 | @var{rest} are processed recursively as mode-line constructs and | |
1756 | concatenated together. When @var{width} is positive, the result is | |
1757 | space filled on the right if its width is less than @var{width}. When | |
1758 | @var{width} is negative, the result is truncated on the right to | |
1759 | @minus{}@var{width} columns if its width exceeds @minus{}@var{width}. | |
1760 | ||
1761 | For example, the usual way to show what percentage of a buffer is above | |
1762 | the top of the window is to use a list like this: @code{(-3 "%p")}. | |
1763 | @end table | |
1764 | ||
1765 | @node Mode Line Top | |
1766 | @subsection The Top Level of Mode Line Control | |
1767 | ||
1768 | The variable in overall control of the mode line is | |
1769 | @code{mode-line-format}. | |
1770 | ||
01f17ae2 | 1771 | @defopt mode-line-format |
b8d4c8d0 GM |
1772 | The value of this variable is a mode-line construct that controls the |
1773 | contents of the mode-line. It is always buffer-local in all buffers. | |
1774 | ||
1775 | If you set this variable to @code{nil} in a buffer, that buffer does | |
1776 | not have a mode line. (A window that is just one line tall never | |
1777 | displays a mode line.) | |
01f17ae2 | 1778 | @end defopt |
b8d4c8d0 GM |
1779 | |
1780 | The default value of @code{mode-line-format} is designed to use the | |
1781 | values of other variables such as @code{mode-line-position} and | |
1782 | @code{mode-line-modes} (which in turn incorporates the values of the | |
1783 | variables @code{mode-name} and @code{minor-mode-alist}). Very few | |
1784 | modes need to alter @code{mode-line-format} itself. For most | |
1785 | purposes, it is sufficient to alter some of the variables that | |
1786 | @code{mode-line-format} either directly or indirectly refers to. | |
1787 | ||
1788 | If you do alter @code{mode-line-format} itself, the new value should | |
1789 | use the same variables that appear in the default value (@pxref{Mode | |
1790 | Line Variables}), rather than duplicating their contents or displaying | |
1791 | the information in another fashion. This way, customizations made by | |
1792 | the user or by Lisp programs (such as @code{display-time} and major | |
1793 | modes) via changes to those variables remain effective. | |
1794 | ||
1795 | Here is an example of a @code{mode-line-format} that might be | |
1796 | useful for @code{shell-mode}, since it contains the host name and default | |
1797 | directory. | |
1798 | ||
1799 | @example | |
1800 | @group | |
1801 | (setq mode-line-format | |
1802 | (list "-" | |
1803 | 'mode-line-mule-info | |
1804 | 'mode-line-modified | |
1805 | 'mode-line-frame-identification | |
1806 | "%b--" | |
1807 | @end group | |
1808 | @group | |
1809 | ;; @r{Note that this is evaluated while making the list.} | |
1810 | ;; @r{It makes a mode-line construct which is just a string.} | |
1811 | (getenv "HOST") | |
1812 | @end group | |
1813 | ":" | |
1814 | 'default-directory | |
1815 | " " | |
1816 | 'global-mode-string | |
1817 | " %[(" | |
1818 | '(:eval (mode-line-mode-name)) | |
1819 | 'mode-line-process | |
1820 | 'minor-mode-alist | |
1821 | "%n" | |
1822 | ")%]--" | |
1823 | @group | |
1824 | '(which-func-mode ("" which-func-format "--")) | |
1825 | '(line-number-mode "L%l--") | |
1826 | '(column-number-mode "C%c--") | |
1827 | '(-3 "%p") | |
1828 | "-%-")) | |
1829 | @end group | |
1830 | @end example | |
1831 | ||
1832 | @noindent | |
1833 | (The variables @code{line-number-mode}, @code{column-number-mode} | |
1834 | and @code{which-func-mode} enable particular minor modes; as usual, | |
1835 | these variable names are also the minor mode command names.) | |
1836 | ||
1837 | @node Mode Line Variables | |
1838 | @subsection Variables Used in the Mode Line | |
1839 | ||
1840 | This section describes variables incorporated by the standard value | |
1841 | of @code{mode-line-format} into the text of the mode line. There is | |
1842 | nothing inherently special about these variables; any other variables | |
1843 | could have the same effects on the mode line if | |
1844 | @code{mode-line-format}'s value were changed to use them. However, | |
1845 | various parts of Emacs set these variables on the understanding that | |
1846 | they will control parts of the mode line; therefore, practically | |
1847 | speaking, it is essential for the mode line to use them. | |
1848 | ||
1849 | @defvar mode-line-mule-info | |
1850 | This variable holds the value of the mode-line construct that displays | |
1851 | information about the language environment, buffer coding system, and | |
1852 | current input method. @xref{Non-ASCII Characters}. | |
1853 | @end defvar | |
1854 | ||
1855 | @defvar mode-line-modified | |
1856 | This variable holds the value of the mode-line construct that displays | |
2079438a CY |
1857 | whether the current buffer is modified. Its default value displays |
1858 | @samp{**} if the buffer is modified, @samp{--} if the buffer is not | |
1859 | modified, @samp{%%} if the buffer is read only, and @samp{%*} if the | |
1860 | buffer is read only and modified. | |
b8d4c8d0 GM |
1861 | |
1862 | Changing this variable does not force an update of the mode line. | |
1863 | @end defvar | |
1864 | ||
1865 | @defvar mode-line-frame-identification | |
2079438a CY |
1866 | This variable identifies the current frame. Its default value |
1867 | displays @code{" "} if you are using a window system which can show | |
1868 | multiple frames, or @code{"-%F "} on an ordinary terminal which shows | |
1869 | only one frame at a time. | |
b8d4c8d0 GM |
1870 | @end defvar |
1871 | ||
1872 | @defvar mode-line-buffer-identification | |
2079438a CY |
1873 | This variable identifies the buffer being displayed in the window. |
1874 | Its default value displays the buffer name, padded with spaces to at | |
1875 | least 12 columns. | |
b8d4c8d0 GM |
1876 | @end defvar |
1877 | ||
01f17ae2 | 1878 | @defopt mode-line-position |
2079438a CY |
1879 | This variable indicates the position in the buffer. Its default value |
1880 | displays the buffer percentage and, optionally, the buffer size, the | |
1881 | line number and the column number. | |
01f17ae2 | 1882 | @end defopt |
b8d4c8d0 GM |
1883 | |
1884 | @defvar vc-mode | |
1885 | The variable @code{vc-mode}, buffer-local in each buffer, records | |
1886 | whether the buffer's visited file is maintained with version control, | |
1887 | and, if so, which kind. Its value is a string that appears in the mode | |
1888 | line, or @code{nil} for no version control. | |
1889 | @end defvar | |
1890 | ||
01f17ae2 | 1891 | @defopt mode-line-modes |
2079438a CY |
1892 | This variable displays the buffer's major and minor modes. Its |
1893 | default value also displays the recursive editing level, information | |
1894 | on the process status, and whether narrowing is in effect. | |
18d59e29 LMI |
1895 | @end defopt |
1896 | ||
1897 | @defopt mode-line-remote | |
1898 | This variable is used to show whether @code{default-directory} for the | |
1899 | current buffer is remote. | |
1900 | @end defopt | |
1901 | ||
1902 | @defopt mode-line-client | |
1903 | This variable is used to identify @code{emacsclient} frames. | |
01f17ae2 | 1904 | @end defopt |
b8d4c8d0 GM |
1905 | |
1906 | The following three variables are used in @code{mode-line-modes}: | |
1907 | ||
1908 | @defvar mode-name | |
1909 | This buffer-local variable holds the ``pretty'' name of the current | |
9cf52b11 EZ |
1910 | buffer's major mode. Each major mode should set this variable so that |
1911 | the mode name will appear in the mode line. The value does not have | |
1912 | to be a string, but can use any of the data types valid in a mode-line | |
1913 | construct (@pxref{Mode Line Data}). To compute the string that will | |
1914 | identify the mode name in the mode line, use @code{format-mode-line} | |
1915 | (@pxref{Emulating Mode Line}). | |
b8d4c8d0 GM |
1916 | @end defvar |
1917 | ||
1918 | @defvar mode-line-process | |
1919 | This buffer-local variable contains the mode-line information on process | |
1920 | status in modes used for communicating with subprocesses. It is | |
1921 | displayed immediately following the major mode name, with no intervening | |
1922 | space. For example, its value in the @samp{*shell*} buffer is | |
1923 | @code{(":%s")}, which allows the shell to display its status along | |
1924 | with the major mode as: @samp{(Shell:run)}. Normally this variable | |
1925 | is @code{nil}. | |
1926 | @end defvar | |
1927 | ||
1928 | @defvar minor-mode-alist | |
1929 | @anchor{Definition of minor-mode-alist} | |
1930 | This variable holds an association list whose elements specify how the | |
1931 | mode line should indicate that a minor mode is active. Each element of | |
1932 | the @code{minor-mode-alist} should be a two-element list: | |
1933 | ||
1934 | @example | |
1935 | (@var{minor-mode-variable} @var{mode-line-string}) | |
1936 | @end example | |
1937 | ||
1938 | More generally, @var{mode-line-string} can be any mode-line spec. It | |
1939 | appears in the mode line when the value of @var{minor-mode-variable} | |
1940 | is non-@code{nil}, and not otherwise. These strings should begin with | |
1941 | spaces so that they don't run together. Conventionally, the | |
1942 | @var{minor-mode-variable} for a specific mode is set to a | |
1943 | non-@code{nil} value when that minor mode is activated. | |
1944 | ||
1945 | @code{minor-mode-alist} itself is not buffer-local. Each variable | |
1946 | mentioned in the alist should be buffer-local if its minor mode can be | |
1947 | enabled separately in each buffer. | |
1948 | @end defvar | |
1949 | ||
1950 | @defvar global-mode-string | |
1951 | This variable holds a mode-line spec that, by default, appears in the | |
1952 | mode line just after the @code{which-func-mode} minor mode if set, | |
1953 | else after @code{mode-line-modes}. The command @code{display-time} | |
1954 | sets @code{global-mode-string} to refer to the variable | |
1955 | @code{display-time-string}, which holds a string containing the time | |
1956 | and load information. | |
1957 | ||
1958 | The @samp{%M} construct substitutes the value of | |
1959 | @code{global-mode-string}, but that is obsolete, since the variable is | |
1960 | included in the mode line from @code{mode-line-format}. | |
1961 | @end defvar | |
1962 | ||
b8d4c8d0 | 1963 | Here is a simplified version of the default value of |
4e3b4528 | 1964 | @code{mode-line-format}. The real default value also |
b8d4c8d0 GM |
1965 | specifies addition of text properties. |
1966 | ||
1967 | @example | |
1968 | @group | |
1969 | ("-" | |
1970 | mode-line-mule-info | |
1971 | mode-line-modified | |
1972 | mode-line-frame-identification | |
1973 | mode-line-buffer-identification | |
1974 | @end group | |
1975 | " " | |
1976 | mode-line-position | |
1977 | (vc-mode vc-mode) | |
1978 | " " | |
1979 | @group | |
1980 | mode-line-modes | |
1981 | (which-func-mode ("" which-func-format "--")) | |
1982 | (global-mode-string ("--" global-mode-string)) | |
1983 | "-%-") | |
1984 | @end group | |
1985 | @end example | |
b8d4c8d0 GM |
1986 | |
1987 | @node %-Constructs | |
1988 | @subsection @code{%}-Constructs in the Mode Line | |
1989 | ||
1990 | Strings used as mode-line constructs can use certain | |
1991 | @code{%}-constructs to substitute various kinds of data. Here is a | |
1992 | list of the defined @code{%}-constructs, and what they mean. In any | |
1993 | construct except @samp{%%}, you can add a decimal integer after the | |
1994 | @samp{%} to specify a minimum field width. If the width is less, the | |
1995 | field is padded with spaces to the right. | |
1996 | ||
1997 | @table @code | |
1998 | @item %b | |
1999 | The current buffer name, obtained with the @code{buffer-name} function. | |
2000 | @xref{Buffer Names}. | |
2001 | ||
2002 | @item %c | |
2003 | The current column number of point. | |
2004 | ||
2005 | @item %e | |
2006 | When Emacs is nearly out of memory for Lisp objects, a brief message | |
2007 | saying so. Otherwise, this is empty. | |
2008 | ||
2009 | @item %f | |
2010 | The visited file name, obtained with the @code{buffer-file-name} | |
2011 | function. @xref{Buffer File Name}. | |
2012 | ||
2013 | @item %F | |
2014 | The title (only on a window system) or the name of the selected frame. | |
2015 | @xref{Basic Parameters}. | |
2016 | ||
2017 | @item %i | |
2018 | The size of the accessible part of the current buffer; basically | |
2019 | @code{(- (point-max) (point-min))}. | |
2020 | ||
2021 | @item %I | |
2022 | Like @samp{%i}, but the size is printed in a more readable way by using | |
2023 | @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to | |
2024 | abbreviate. | |
2025 | ||
2026 | @item %l | |
2027 | The current line number of point, counting within the accessible portion | |
2028 | of the buffer. | |
2029 | ||
2030 | @item %n | |
2031 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see | |
2032 | @code{narrow-to-region} in @ref{Narrowing}). | |
2033 | ||
2034 | @item %p | |
2035 | The percentage of the buffer text above the @strong{top} of window, or | |
2036 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default | |
2037 | mode-line specification truncates this to three characters. | |
2038 | ||
2039 | @item %P | |
2040 | The percentage of the buffer text that is above the @strong{bottom} of | |
2041 | the window (which includes the text visible in the window, as well as | |
2042 | the text above the top), plus @samp{Top} if the top of the buffer is | |
2043 | visible on screen; or @samp{Bottom} or @samp{All}. | |
2044 | ||
2045 | @item %s | |
2046 | The status of the subprocess belonging to the current buffer, obtained with | |
2047 | @code{process-status}. @xref{Process Information}. | |
2048 | ||
2049 | @item %t | |
2050 | Whether the visited file is a text file or a binary file. This is a | |
2051 | meaningful distinction only on certain operating systems (@pxref{MS-DOS | |
2052 | File Types}). | |
2053 | ||
2054 | @item %z | |
2055 | The mnemonics of keyboard, terminal, and buffer coding systems. | |
2056 | ||
2057 | @item %Z | |
2058 | Like @samp{%z}, but including the end-of-line format. | |
2059 | ||
2060 | @item %* | |
2061 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2062 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2063 | @samp{-} otherwise. @xref{Buffer Modification}. | |
2064 | ||
2065 | @item %+ | |
2066 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* | |
2067 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* | |
2068 | @samp{-} otherwise. This differs from @samp{%*} only for a modified | |
2069 | read-only buffer. @xref{Buffer Modification}. | |
2070 | ||
2071 | @item %& | |
2072 | @samp{*} if the buffer is modified, and @samp{-} otherwise. | |
2073 | ||
2074 | @item %[ | |
2075 | An indication of the depth of recursive editing levels (not counting | |
2076 | minibuffer levels): one @samp{[} for each editing level. | |
2077 | @xref{Recursive Editing}. | |
2078 | ||
2079 | @item %] | |
2080 | One @samp{]} for each recursive editing level (not counting minibuffer | |
2081 | levels). | |
2082 | ||
2083 | @item %- | |
2084 | Dashes sufficient to fill the remainder of the mode line. | |
2085 | ||
2086 | @item %% | |
2087 | The character @samp{%}---this is how to include a literal @samp{%} in a | |
2088 | string in which @code{%}-constructs are allowed. | |
2089 | @end table | |
2090 | ||
2091 | The following two @code{%}-constructs are still supported, but they are | |
2092 | obsolete, since you can get the same results with the variables | |
2093 | @code{mode-name} and @code{global-mode-string}. | |
2094 | ||
2095 | @table @code | |
2096 | @item %m | |
2097 | The value of @code{mode-name}. | |
2098 | ||
2099 | @item %M | |
2100 | The value of @code{global-mode-string}. | |
2101 | @end table | |
2102 | ||
2103 | @node Properties in Mode | |
2104 | @subsection Properties in the Mode Line | |
2105 | @cindex text properties in the mode line | |
2106 | ||
2107 | Certain text properties are meaningful in the | |
2108 | mode line. The @code{face} property affects the appearance of text; the | |
2109 | @code{help-echo} property associates help strings with the text, and | |
2110 | @code{local-map} can make the text mouse-sensitive. | |
2111 | ||
2112 | There are four ways to specify text properties for text in the mode | |
2113 | line: | |
2114 | ||
2115 | @enumerate | |
2116 | @item | |
2117 | Put a string with a text property directly into the mode-line data | |
2118 | structure. | |
2119 | ||
2120 | @item | |
2121 | Put a text property on a mode-line %-construct such as @samp{%12b}; then | |
2122 | the expansion of the %-construct will have that same text property. | |
2123 | ||
2124 | @item | |
2125 | Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to | |
2126 | give @var{elt} a text property specified by @var{props}. | |
2127 | ||
2128 | @item | |
2129 | Use a list containing @code{:eval @var{form}} in the mode-line data | |
2130 | structure, and make @var{form} evaluate to a string that has a text | |
2131 | property. | |
2132 | @end enumerate | |
2133 | ||
2134 | You can use the @code{local-map} property to specify a keymap. This | |
2135 | keymap only takes real effect for mouse clicks; binding character keys | |
2136 | and function keys to it has no effect, since it is impossible to move | |
2137 | point into the mode line. | |
2138 | ||
2139 | When the mode line refers to a variable which does not have a | |
2140 | non-@code{nil} @code{risky-local-variable} property, any text | |
2141 | properties given or specified within that variable's values are | |
2142 | ignored. This is because such properties could otherwise specify | |
2143 | functions to be called, and those functions could come from file | |
2144 | local variables. | |
2145 | ||
2146 | @node Header Lines | |
2147 | @subsection Window Header Lines | |
2148 | @cindex header line (of a window) | |
2149 | @cindex window header line | |
2150 | ||
2151 | A window can have a @dfn{header line} at the | |
2152 | top, just as it can have a mode line at the bottom. The header line | |
2153 | feature works just like the mode-line feature, except that it's | |
2154 | controlled by different variables. | |
2155 | ||
2156 | @defvar header-line-format | |
2157 | This variable, local in every buffer, specifies how to display the | |
2158 | header line, for windows displaying the buffer. The format of the value | |
2159 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). | |
b8d4c8d0 GM |
2160 | It is normally @code{nil}, so that ordinary buffers have no header line. |
2161 | @end defvar | |
2162 | ||
2163 | A window that is just one line tall never displays a header line. A | |
2164 | window that is two lines tall cannot display both a mode line and a | |
2165 | header line at once; if it has a mode line, then it does not display a | |
2166 | header line. | |
2167 | ||
2168 | @node Emulating Mode Line | |
2169 | @subsection Emulating Mode-Line Formatting | |
2170 | ||
2171 | You can use the function @code{format-mode-line} to compute | |
2172 | the text that would appear in a mode line or header line | |
2173 | based on a certain mode-line specification. | |
2174 | ||
2175 | @defun format-mode-line format &optional face window buffer | |
287e63bb EZ |
2176 | This function formats a line of text according to @var{format} as if it |
2177 | were generating the mode line for @var{window}, but it also returns the | |
2178 | text as a string. The argument @var{window} defaults to the selected | |
2179 | window. If @var{buffer} is non-@code{nil}, all the information used is | |
2180 | taken from @var{buffer}; by default, it comes from @var{window}'s | |
2181 | buffer. | |
b8d4c8d0 GM |
2182 | |
2183 | The value string normally has text properties that correspond to the | |
2e4ab211 EZ |
2184 | faces, keymaps, etc., that the mode line would have. Any character for |
2185 | which no @code{face} property is specified by @var{format} gets a | |
2186 | default value determined by @var{face}. If @var{face} is @code{t}, that | |
2187 | stands for either @code{mode-line} if @var{window} is selected, | |
b8d4c8d0 | 2188 | otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or |
2e4ab211 EZ |
2189 | omitted, that stands for the default face. If @var{face} is an integer, |
2190 | the value returned by this function will have no text properties. | |
b8d4c8d0 | 2191 | |
287e63bb | 2192 | You can also specify other valid faces as the value of @var{face}. |
2e4ab211 EZ |
2193 | If specified, that face provides the @code{face} property for characters |
2194 | whose face is not specified by @var{format}. | |
287e63bb EZ |
2195 | |
2196 | Note that using @code{mode-line}, @code{mode-line-inactive}, or | |
2197 | @code{header-line} as @var{face} will actually redisplay the mode line | |
2198 | or the header line, respectively, using the current definitions of the | |
2199 | corresponding face, in addition to returning the formatted string. | |
2200 | (Other faces do not cause redisplay.) | |
b8d4c8d0 GM |
2201 | |
2202 | For example, @code{(format-mode-line header-line-format)} returns the | |
2203 | text that would appear in the selected window's header line (@code{""} | |
2204 | if it has no header line). @code{(format-mode-line header-line-format | |
2205 | 'header-line)} returns the same text, with each character | |
287e63bb EZ |
2206 | carrying the face that it will have in the header line itself, and also |
2207 | redraws the header line. | |
b8d4c8d0 GM |
2208 | @end defun |
2209 | ||
2210 | @node Imenu | |
2211 | @section Imenu | |
2212 | ||
2213 | @cindex Imenu | |
2214 | @dfn{Imenu} is a feature that lets users select a definition or | |
2215 | section in the buffer, from a menu which lists all of them, to go | |
2216 | directly to that location in the buffer. Imenu works by constructing | |
2217 | a buffer index which lists the names and buffer positions of the | |
2218 | definitions, or other named portions of the buffer; then the user can | |
2219 | choose one of them and move point to it. Major modes can add a menu | |
2220 | bar item to use Imenu using @code{imenu-add-to-menubar}. | |
2221 | ||
2222 | @defun imenu-add-to-menubar name | |
2223 | This function defines a local menu bar item named @var{name} | |
2224 | to run Imenu. | |
2225 | @end defun | |
2226 | ||
2227 | The user-level commands for using Imenu are described in the Emacs | |
2228 | Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section | |
2229 | explains how to customize Imenu's method of finding definitions or | |
2230 | buffer portions for a particular major mode. | |
2231 | ||
2232 | The usual and simplest way is to set the variable | |
2233 | @code{imenu-generic-expression}: | |
2234 | ||
2235 | @defvar imenu-generic-expression | |
2236 | This variable, if non-@code{nil}, is a list that specifies regular | |
2237 | expressions for finding definitions for Imenu. Simple elements of | |
2238 | @code{imenu-generic-expression} look like this: | |
2239 | ||
2240 | @example | |
2241 | (@var{menu-title} @var{regexp} @var{index}) | |
2242 | @end example | |
2243 | ||
2244 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches | |
2245 | for this element should go in a submenu of the buffer index; | |
2246 | @var{menu-title} itself specifies the name for the submenu. If | |
2247 | @var{menu-title} is @code{nil}, the matches for this element go directly | |
2248 | in the top level of the buffer index. | |
2249 | ||
2250 | The second item in the list, @var{regexp}, is a regular expression | |
2251 | (@pxref{Regular Expressions}); anything in the buffer that it matches | |
2252 | is considered a definition, something to mention in the buffer index. | |
2253 | The third item, @var{index}, is a non-negative integer that indicates | |
2254 | which subexpression in @var{regexp} matches the definition's name. | |
2255 | ||
2256 | An element can also look like this: | |
2257 | ||
2258 | @example | |
2259 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) | |
2260 | @end example | |
2261 | ||
2262 | Each match for this element creates an index item, and when the index | |
2263 | item is selected by the user, it calls @var{function} with arguments | |
2264 | consisting of the item name, the buffer position, and @var{arguments}. | |
2265 | ||
2266 | For Emacs Lisp mode, @code{imenu-generic-expression} could look like | |
2267 | this: | |
2268 | ||
2269 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] | |
2270 | @example | |
2271 | @group | |
2272 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ | |
2273 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2274 | @end group | |
2275 | @group | |
2276 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ | |
2277 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) | |
2278 | @end group | |
2279 | @group | |
2280 | ("*Types*" | |
2281 | "^\\s-*\ | |
2282 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ | |
2283 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) | |
2284 | @end group | |
2285 | @end example | |
2286 | ||
2287 | Setting this variable makes it buffer-local in the current buffer. | |
2288 | @end defvar | |
2289 | ||
2290 | @defvar imenu-case-fold-search | |
2291 | This variable controls whether matching against the regular | |
2292 | expressions in the value of @code{imenu-generic-expression} is | |
2293 | case-sensitive: @code{t}, the default, means matching should ignore | |
2294 | case. | |
2295 | ||
2296 | Setting this variable makes it buffer-local in the current buffer. | |
2297 | @end defvar | |
2298 | ||
2299 | @defvar imenu-syntax-alist | |
2300 | This variable is an alist of syntax table modifiers to use while | |
2301 | processing @code{imenu-generic-expression}, to override the syntax table | |
2302 | of the current buffer. Each element should have this form: | |
2303 | ||
2304 | @example | |
2305 | (@var{characters} . @var{syntax-description}) | |
2306 | @end example | |
2307 | ||
2308 | The @sc{car}, @var{characters}, can be either a character or a string. | |
2309 | The element says to give that character or characters the syntax | |
2310 | specified by @var{syntax-description}, which is passed to | |
2311 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). | |
2312 | ||
2313 | This feature is typically used to give word syntax to characters which | |
2314 | normally have symbol syntax, and thus to simplify | |
2315 | @code{imenu-generic-expression} and speed up matching. | |
2316 | For example, Fortran mode uses it this way: | |
2317 | ||
2318 | @example | |
2319 | (setq imenu-syntax-alist '(("_$" . "w"))) | |
2320 | @end example | |
2321 | ||
2322 | The @code{imenu-generic-expression} regular expressions can then use | |
2323 | @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this | |
2324 | technique may be inconvenient when the mode needs to limit the initial | |
2325 | character of a name to a smaller set of characters than are allowed in | |
2326 | the rest of a name. | |
2327 | ||
2328 | Setting this variable makes it buffer-local in the current buffer. | |
2329 | @end defvar | |
2330 | ||
2331 | Another way to customize Imenu for a major mode is to set the | |
2332 | variables @code{imenu-prev-index-position-function} and | |
2333 | @code{imenu-extract-index-name-function}: | |
2334 | ||
2335 | @defvar imenu-prev-index-position-function | |
2336 | If this variable is non-@code{nil}, its value should be a function that | |
2337 | finds the next ``definition'' to put in the buffer index, scanning | |
2338 | backward in the buffer from point. It should return @code{nil} if it | |
2339 | doesn't find another ``definition'' before point. Otherwise it should | |
2340 | leave point at the place it finds a ``definition'' and return any | |
2341 | non-@code{nil} value. | |
2342 | ||
2343 | Setting this variable makes it buffer-local in the current buffer. | |
2344 | @end defvar | |
2345 | ||
2346 | @defvar imenu-extract-index-name-function | |
2347 | If this variable is non-@code{nil}, its value should be a function to | |
2348 | return the name for a definition, assuming point is in that definition | |
2349 | as the @code{imenu-prev-index-position-function} function would leave | |
2350 | it. | |
2351 | ||
2352 | Setting this variable makes it buffer-local in the current buffer. | |
2353 | @end defvar | |
2354 | ||
2355 | The last way to customize Imenu for a major mode is to set the | |
2356 | variable @code{imenu-create-index-function}: | |
2357 | ||
2358 | @defvar imenu-create-index-function | |
2359 | This variable specifies the function to use for creating a buffer | |
2360 | index. The function should take no arguments, and return an index | |
2361 | alist for the current buffer. It is called within | |
2362 | @code{save-excursion}, so where it leaves point makes no difference. | |
2363 | ||
2364 | The index alist can have three types of elements. Simple elements | |
2365 | look like this: | |
2366 | ||
2367 | @example | |
2368 | (@var{index-name} . @var{index-position}) | |
2369 | @end example | |
2370 | ||
2371 | Selecting a simple element has the effect of moving to position | |
2372 | @var{index-position} in the buffer. Special elements look like this: | |
2373 | ||
2374 | @example | |
2375 | (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{}) | |
2376 | @end example | |
2377 | ||
2378 | Selecting a special element performs: | |
2379 | ||
2380 | @example | |
2381 | (funcall @var{function} | |
2382 | @var{index-name} @var{index-position} @var{arguments}@dots{}) | |
2383 | @end example | |
2384 | ||
2385 | A nested sub-alist element looks like this: | |
2386 | ||
2387 | @example | |
2388 | (@var{menu-title} @var{sub-alist}) | |
2389 | @end example | |
2390 | ||
2391 | It creates the submenu @var{menu-title} specified by @var{sub-alist}. | |
2392 | ||
2393 | The default value of @code{imenu-create-index-function} is | |
2394 | @code{imenu-default-create-index-function}. This function calls the | |
2395 | value of @code{imenu-prev-index-position-function} and the value of | |
2396 | @code{imenu-extract-index-name-function} to produce the index alist. | |
2397 | However, if either of these two variables is @code{nil}, the default | |
2398 | function uses @code{imenu-generic-expression} instead. | |
2399 | ||
2400 | Setting this variable makes it buffer-local in the current buffer. | |
2401 | @end defvar | |
2402 | ||
2403 | @node Font Lock Mode | |
2404 | @section Font Lock Mode | |
2405 | @cindex Font Lock mode | |
2406 | ||
2407 | @dfn{Font Lock mode} is a feature that automatically attaches | |
2408 | @code{face} properties to certain parts of the buffer based on their | |
2409 | syntactic role. How it parses the buffer depends on the major mode; | |
2410 | most major modes define syntactic criteria for which faces to use in | |
2411 | which contexts. This section explains how to customize Font Lock for a | |
2412 | particular major mode. | |
2413 | ||
2414 | Font Lock mode finds text to highlight in two ways: through | |
2415 | syntactic parsing based on the syntax table, and through searching | |
2416 | (usually for regular expressions). Syntactic fontification happens | |
2417 | first; it finds comments and string constants and highlights them. | |
2418 | Search-based fontification happens second. | |
2419 | ||
2420 | @menu | |
2421 | * Font Lock Basics:: Overview of customizing Font Lock. | |
2422 | * Search-based Fontification:: Fontification based on regexps. | |
2423 | * Customizing Keywords:: Customizing search-based fontification. | |
2424 | * Other Font Lock Variables:: Additional customization facilities. | |
2425 | * Levels of Font Lock:: Each mode can define alternative levels | |
2426 | so that the user can select more or less. | |
769741e3 | 2427 | * Precalculated Fontification:: How Lisp programs that produce the buffer |
b8d4c8d0 GM |
2428 | contents can also specify how to fontify it. |
2429 | * Faces for Font Lock:: Special faces specifically for Font Lock. | |
2430 | * Syntactic Font Lock:: Fontification based on syntax tables. | |
2431 | * Setting Syntax Properties:: Defining character syntax based on context | |
2432 | using the Font Lock mechanism. | |
2433 | * Multiline Font Lock:: How to coerce Font Lock into properly | |
2434 | highlighting multiline constructs. | |
2435 | @end menu | |
2436 | ||
2437 | @node Font Lock Basics | |
2438 | @subsection Font Lock Basics | |
2439 | ||
2440 | There are several variables that control how Font Lock mode highlights | |
2441 | text. But major modes should not set any of these variables directly. | |
2442 | Instead, they should set @code{font-lock-defaults} as a buffer-local | |
2443 | variable. The value assigned to this variable is used, if and when Font | |
2444 | Lock mode is enabled, to set all the other variables. | |
2445 | ||
2446 | @defvar font-lock-defaults | |
2447 | This variable is set by major modes, as a buffer-local variable, to | |
2448 | specify how to fontify text in that mode. It automatically becomes | |
2449 | buffer-local when you set it. If its value is @code{nil}, Font-Lock | |
2450 | mode does no highlighting, and you can use the @samp{Faces} menu | |
2451 | (under @samp{Edit} and then @samp{Text Properties} in the menu bar) to | |
2452 | assign faces explicitly to text in the buffer. | |
2453 | ||
2454 | If non-@code{nil}, the value should look like this: | |
2455 | ||
2456 | @example | |
2457 | (@var{keywords} [@var{keywords-only} [@var{case-fold} | |
2458 | [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]]) | |
2459 | @end example | |
2460 | ||
2461 | The first element, @var{keywords}, indirectly specifies the value of | |
2462 | @code{font-lock-keywords} which directs search-based fontification. | |
2463 | It can be a symbol, a variable or a function whose value is the list | |
2464 | to use for @code{font-lock-keywords}. It can also be a list of | |
2465 | several such symbols, one for each possible level of fontification. | |
caef3ed2 GM |
2466 | The first symbol specifies the @samp{mode default} level of |
2467 | fontification, the next symbol level 1 fontification, the next level 2, | |
2468 | and so on. The @samp{mode default} level is normally the same as level | |
2469 | 1. It is used when @code{font-lock-maximum-decoration} has a @code{nil} | |
2470 | value. @xref{Levels of Font Lock}. | |
b8d4c8d0 GM |
2471 | |
2472 | The second element, @var{keywords-only}, specifies the value of the | |
2473 | variable @code{font-lock-keywords-only}. If this is omitted or | |
2474 | @code{nil}, syntactic fontification (of strings and comments) is also | |
2475 | performed. If this is non-@code{nil}, such fontification is not | |
2476 | performed. @xref{Syntactic Font Lock}. | |
2477 | ||
2478 | The third element, @var{case-fold}, specifies the value of | |
2479 | @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, | |
2480 | Font Lock mode ignores case when searching as directed by | |
2481 | @code{font-lock-keywords}. | |
2482 | ||
2483 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it | |
2484 | should be a list of cons cells of the form @code{(@var{char-or-string} | |
2485 | . @var{string})}. These are used to set up a syntax table for | |
2486 | syntactic fontification (@pxref{Syntax Table Functions}). The | |
2487 | resulting syntax table is stored in @code{font-lock-syntax-table}. | |
2488 | ||
2489 | The fifth element, @var{syntax-begin}, specifies the value of | |
2490 | @code{font-lock-beginning-of-syntax-function}. We recommend setting | |
2491 | this variable to @code{nil} and using @code{syntax-begin-function} | |
2492 | instead. | |
2493 | ||
2494 | All the remaining elements (if any) are collectively called | |
2495 | @var{other-vars}. Each of these elements should have the form | |
2496 | @code{(@var{variable} . @var{value})}---which means, make | |
2497 | @var{variable} buffer-local and then set it to @var{value}. You can | |
2498 | use these @var{other-vars} to set other variables that affect | |
2499 | fontification, aside from those you can control with the first five | |
2500 | elements. @xref{Other Font Lock Variables}. | |
2501 | @end defvar | |
2502 | ||
2503 | If your mode fontifies text explicitly by adding | |
2504 | @code{font-lock-face} properties, it can specify @code{(nil t)} for | |
2505 | @code{font-lock-defaults} to turn off all automatic fontification. | |
2506 | However, this is not required; it is possible to fontify some things | |
2507 | using @code{font-lock-face} properties and set up automatic | |
2508 | fontification for other parts of the text. | |
2509 | ||
2510 | @node Search-based Fontification | |
2511 | @subsection Search-based Fontification | |
2512 | ||
2513 | The most important variable for customizing Font Lock mode is | |
2514 | @code{font-lock-keywords}. It specifies the search criteria for | |
2515 | search-based fontification. You should specify the value of this | |
2516 | variable with @var{keywords} in @code{font-lock-defaults}. | |
2517 | ||
2518 | @defvar font-lock-keywords | |
2519 | This variable's value is a list of the keywords to highlight. Be | |
2520 | careful when composing regular expressions for this list; a poorly | |
2521 | written pattern can dramatically slow things down! | |
2522 | @end defvar | |
2523 | ||
2524 | Each element of @code{font-lock-keywords} specifies how to find | |
2525 | certain cases of text, and how to highlight those cases. Font Lock mode | |
2526 | processes the elements of @code{font-lock-keywords} one by one, and for | |
2527 | each element, it finds and handles all matches. Ordinarily, once | |
2528 | part of the text has been fontified already, this cannot be overridden | |
2529 | by a subsequent match in the same text; but you can specify different | |
2530 | behavior using the @var{override} element of a @var{subexp-highlighter}. | |
2531 | ||
2532 | Each element of @code{font-lock-keywords} should have one of these | |
2533 | forms: | |
2534 | ||
2535 | @table @code | |
2536 | @item @var{regexp} | |
2537 | Highlight all matches for @var{regexp} using | |
2538 | @code{font-lock-keyword-face}. For example, | |
2539 | ||
2540 | @example | |
2541 | ;; @r{Highlight occurrences of the word @samp{foo}} | |
2542 | ;; @r{using @code{font-lock-keyword-face}.} | |
2543 | "\\<foo\\>" | |
2544 | @end example | |
2545 | ||
2546 | The function @code{regexp-opt} (@pxref{Regexp Functions}) is useful | |
2547 | for calculating optimal regular expressions to match a number of | |
2548 | different keywords. | |
2549 | ||
2550 | @item @var{function} | |
2551 | Find text by calling @var{function}, and highlight the matches | |
2552 | it finds using @code{font-lock-keyword-face}. | |
2553 | ||
2554 | When @var{function} is called, it receives one argument, the limit of | |
2555 | the search; it should begin searching at point, and not search beyond the | |
2556 | limit. It should return non-@code{nil} if it succeeds, and set the | |
2557 | match data to describe the match that was found. Returning @code{nil} | |
2558 | indicates failure of the search. | |
2559 | ||
2560 | Fontification will call @var{function} repeatedly with the same limit, | |
2561 | and with point where the previous invocation left it, until | |
2562 | @var{function} fails. On failure, @var{function} need not reset point | |
2563 | in any particular way. | |
2564 | ||
2565 | @item (@var{matcher} . @var{subexp}) | |
2566 | In this kind of element, @var{matcher} is either a regular | |
2567 | expression or a function, as described above. The @sc{cdr}, | |
2568 | @var{subexp}, specifies which subexpression of @var{matcher} should be | |
2569 | highlighted (instead of the entire text that @var{matcher} matched). | |
2570 | ||
2571 | @example | |
2572 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} | |
2573 | ;; @r{using @code{font-lock-keyword-face}.} | |
2574 | ("fu\\(bar\\)" . 1) | |
2575 | @end example | |
2576 | ||
2577 | If you use @code{regexp-opt} to produce the regular expression | |
2578 | @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp | |
2579 | Functions}) to calculate the value for @var{subexp}. | |
2580 | ||
2581 | @item (@var{matcher} . @var{facespec}) | |
2582 | In this kind of element, @var{facespec} is an expression whose value | |
2583 | specifies the face to use for highlighting. In the simplest case, | |
2584 | @var{facespec} is a Lisp variable (a symbol) whose value is a face | |
2585 | name. | |
2586 | ||
2587 | @example | |
2588 | ;; @r{Highlight occurrences of @samp{fubar},} | |
2589 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2590 | ("fubar" . fubar-face) | |
2591 | @end example | |
2592 | ||
2593 | However, @var{facespec} can also evaluate to a list of this form: | |
2594 | ||
2595 | @example | |
2596 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) | |
2597 | @end example | |
2598 | ||
2599 | @noindent | |
2600 | to specify the face @var{face} and various additional text properties | |
2601 | to put on the text that matches. If you do this, be sure to add the | |
2602 | other text property names that you set in this way to the value of | |
2603 | @code{font-lock-extra-managed-props} so that the properties will also | |
2604 | be cleared out when they are no longer appropriate. Alternatively, | |
2605 | you can set the variable @code{font-lock-unfontify-region-function} to | |
2606 | a function that clears these properties. @xref{Other Font Lock | |
2607 | Variables}. | |
2608 | ||
2609 | @item (@var{matcher} . @var{subexp-highlighter}) | |
2610 | In this kind of element, @var{subexp-highlighter} is a list | |
2611 | which specifies how to highlight matches found by @var{matcher}. | |
2612 | It has the form: | |
2613 | ||
2614 | @example | |
e6c815ae | 2615 | (@var{subexp} @var{facespec} [@var{override} [@var{laxmatch}]]) |
b8d4c8d0 GM |
2616 | @end example |
2617 | ||
2618 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression | |
2619 | of the match to fontify (0 means the entire matching text). The second | |
2620 | subelement, @var{facespec}, is an expression whose value specifies the | |
2621 | face, as described above. | |
2622 | ||
2623 | The last two values in @var{subexp-highlighter}, @var{override} and | |
2624 | @var{laxmatch}, are optional flags. If @var{override} is @code{t}, | |
2625 | this element can override existing fontification made by previous | |
2626 | elements of @code{font-lock-keywords}. If it is @code{keep}, then | |
2627 | each character is fontified if it has not been fontified already by | |
2628 | some other element. If it is @code{prepend}, the face specified by | |
2629 | @var{facespec} is added to the beginning of the @code{font-lock-face} | |
2630 | property. If it is @code{append}, the face is added to the end of the | |
2631 | @code{font-lock-face} property. | |
2632 | ||
2633 | If @var{laxmatch} is non-@code{nil}, it means there should be no error | |
2634 | if there is no subexpression numbered @var{subexp} in @var{matcher}. | |
2635 | Obviously, fontification of the subexpression numbered @var{subexp} will | |
2636 | not occur. However, fontification of other subexpressions (and other | |
2637 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the | |
2638 | specified subexpression is missing, then an error is signaled which | |
2639 | terminates search-based fontification. | |
2640 | ||
2641 | Here are some examples of elements of this kind, and what they do: | |
2642 | ||
2643 | @smallexample | |
2644 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using} | |
2645 | ;; @r{@code{foo-bar-face}, even if they have already been highlighted.} | |
2646 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} | |
2647 | ("foo\\|bar" 0 foo-bar-face t) | |
2648 | ||
2649 | ;; @r{Highlight the first subexpression within each occurrence} | |
2650 | ;; @r{that the function @code{fubar-match} finds,} | |
2651 | ;; @r{using the face which is the value of @code{fubar-face}.} | |
2652 | (fubar-match 1 fubar-face) | |
2653 | @end smallexample | |
2654 | ||
2655 | @item (@var{matcher} . @var{anchored-highlighter}) | |
2656 | In this kind of element, @var{anchored-highlighter} specifies how to | |
2657 | highlight text that follows a match found by @var{matcher}. So a | |
2658 | match found by @var{matcher} acts as the anchor for further searches | |
2659 | specified by @var{anchored-highlighter}. @var{anchored-highlighter} | |
2660 | is a list of the following form: | |
2661 | ||
2662 | @example | |
2663 | (@var{anchored-matcher} @var{pre-form} @var{post-form} | |
2664 | @var{subexp-highlighters}@dots{}) | |
2665 | @end example | |
2666 | ||
2667 | Here, @var{anchored-matcher}, like @var{matcher}, is either a regular | |
2668 | expression or a function. After a match of @var{matcher} is found, | |
2669 | point is at the end of the match. Now, Font Lock evaluates the form | |
2670 | @var{pre-form}. Then it searches for matches of | |
2671 | @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight | |
2672 | these. A @var{subexp-highlighter} is as described above. Finally, | |
2673 | Font Lock evaluates @var{post-form}. | |
2674 | ||
2675 | The forms @var{pre-form} and @var{post-form} can be used to initialize | |
2676 | before, and cleanup after, @var{anchored-matcher} is used. Typically, | |
2677 | @var{pre-form} is used to move point to some position relative to the | |
2678 | match of @var{matcher}, before starting with @var{anchored-matcher}. | |
2679 | @var{post-form} might be used to move back, before resuming with | |
2680 | @var{matcher}. | |
2681 | ||
2682 | After Font Lock evaluates @var{pre-form}, it does not search for | |
2683 | @var{anchored-matcher} beyond the end of the line. However, if | |
2684 | @var{pre-form} returns a buffer position that is greater than the | |
2685 | position of point after @var{pre-form} is evaluated, then the position | |
2686 | returned by @var{pre-form} is used as the limit of the search instead. | |
2687 | It is generally a bad idea to return a position greater than the end | |
2688 | of the line; in other words, the @var{anchored-matcher} search should | |
2689 | not span lines. | |
2690 | ||
2691 | For example, | |
2692 | ||
2693 | @smallexample | |
2694 | ;; @r{Highlight occurrences of the word @samp{item} following} | |
2695 | ;; @r{an occurrence of the word @samp{anchor} (on the same line)} | |
2696 | ;; @r{in the value of @code{item-face}.} | |
2697 | ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) | |
2698 | @end smallexample | |
2699 | ||
2700 | Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore | |
2701 | searching for @samp{item} starts at the end of the match of | |
2702 | @samp{anchor}, and searching for subsequent instances of @samp{anchor} | |
2703 | resumes from where searching for @samp{item} concluded. | |
2704 | ||
2705 | @item (@var{matcher} @var{highlighters}@dots{}) | |
2706 | This sort of element specifies several @var{highlighter} lists for a | |
2707 | single @var{matcher}. A @var{highlighter} list can be of the type | |
2708 | @var{subexp-highlighter} or @var{anchored-highlighter} as described | |
2709 | above. | |
2710 | ||
2711 | For example, | |
2712 | ||
2713 | @smallexample | |
2714 | ;; @r{Highlight occurrences of the word @samp{anchor} in the value} | |
2715 | ;; @r{of @code{anchor-face}, and subsequent occurrences of the word} | |
2716 | ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.} | |
2717 | ("\\<anchor\\>" (0 anchor-face) | |
2718 | ("\\<item\\>" nil nil (0 item-face))) | |
2719 | @end smallexample | |
2720 | ||
2721 | @item (eval . @var{form}) | |
2722 | Here @var{form} is an expression to be evaluated the first time | |
2723 | this value of @code{font-lock-keywords} is used in a buffer. | |
2724 | Its value should have one of the forms described in this table. | |
2725 | @end table | |
2726 | ||
2727 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} | |
2728 | to match text which spans lines; this does not work reliably. | |
2729 | For details, see @xref{Multiline Font Lock}. | |
2730 | ||
2731 | You can use @var{case-fold} in @code{font-lock-defaults} to specify | |
2732 | the value of @code{font-lock-keywords-case-fold-search} which says | |
2733 | whether search-based fontification should be case-insensitive. | |
2734 | ||
2735 | @defvar font-lock-keywords-case-fold-search | |
2736 | Non-@code{nil} means that regular expression matching for the sake of | |
2737 | @code{font-lock-keywords} should be case-insensitive. | |
2738 | @end defvar | |
2739 | ||
2740 | @node Customizing Keywords | |
2741 | @subsection Customizing Search-Based Fontification | |
2742 | ||
2743 | You can use @code{font-lock-add-keywords} to add additional | |
2744 | search-based fontification rules to a major mode, and | |
867d4bb3 | 2745 | @code{font-lock-remove-keywords} to remove rules. |
b8d4c8d0 GM |
2746 | |
2747 | @defun font-lock-add-keywords mode keywords &optional how | |
2748 | This function adds highlighting @var{keywords}, for the current buffer | |
2749 | or for major mode @var{mode}. The argument @var{keywords} should be a | |
2750 | list with the same format as the variable @code{font-lock-keywords}. | |
2751 | ||
2752 | If @var{mode} is a symbol which is a major mode command name, such as | |
2753 | @code{c-mode}, the effect is that enabling Font Lock mode in | |
2754 | @var{mode} will add @var{keywords} to @code{font-lock-keywords}. | |
2755 | Calling with a non-@code{nil} value of @var{mode} is correct only in | |
2756 | your @file{~/.emacs} file. | |
2757 | ||
2758 | If @var{mode} is @code{nil}, this function adds @var{keywords} to | |
2759 | @code{font-lock-keywords} in the current buffer. This way of calling | |
2760 | @code{font-lock-add-keywords} is usually used in mode hook functions. | |
2761 | ||
2762 | By default, @var{keywords} are added at the beginning of | |
2763 | @code{font-lock-keywords}. If the optional argument @var{how} is | |
2764 | @code{set}, they are used to replace the value of | |
2765 | @code{font-lock-keywords}. If @var{how} is any other non-@code{nil} | |
2766 | value, they are added at the end of @code{font-lock-keywords}. | |
2767 | ||
2768 | Some modes provide specialized support you can use in additional | |
2769 | highlighting patterns. See the variables | |
2770 | @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types}, | |
2771 | and @code{java-font-lock-extra-types}, for example. | |
2772 | ||
3fd50d5c | 2773 | @strong{Warning:} major mode commands must not call |
b8d4c8d0 | 2774 | @code{font-lock-add-keywords} under any circumstances, either directly |
3fd50d5c CY |
2775 | or indirectly, except through their mode hooks. (Doing so would lead to |
2776 | incorrect behavior for some minor modes.) They should set up their | |
b8d4c8d0 GM |
2777 | rules for search-based fontification by setting |
2778 | @code{font-lock-keywords}. | |
2779 | @end defun | |
2780 | ||
2781 | @defun font-lock-remove-keywords mode keywords | |
2782 | This function removes @var{keywords} from @code{font-lock-keywords} | |
2783 | for the current buffer or for major mode @var{mode}. As in | |
2784 | @code{font-lock-add-keywords}, @var{mode} should be a major mode | |
2785 | command name or @code{nil}. All the caveats and requirements for | |
2786 | @code{font-lock-add-keywords} apply here too. | |
2787 | @end defun | |
2788 | ||
2789 | For example, this code | |
2790 | ||
2791 | @smallexample | |
2792 | (font-lock-add-keywords 'c-mode | |
2793 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2794 | ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) | |
2795 | @end smallexample | |
2796 | ||
2797 | @noindent | |
2798 | adds two fontification patterns for C mode: one to fontify the word | |
2799 | @samp{FIXME}, even in comments, and another to fontify the words | |
2800 | @samp{and}, @samp{or} and @samp{not} as keywords. | |
2801 | ||
2802 | @noindent | |
2803 | That example affects only C mode proper. To add the same patterns to | |
2804 | C mode @emph{and} all modes derived from it, do this instead: | |
2805 | ||
2806 | @smallexample | |
2807 | (add-hook 'c-mode-hook | |
2808 | (lambda () | |
2809 | (font-lock-add-keywords nil | |
2810 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) | |
2811 | ("\\<\\(and\\|or\\|not\\)\\>" . | |
2812 | font-lock-keyword-face))))) | |
2813 | @end smallexample | |
2814 | ||
2815 | @node Other Font Lock Variables | |
2816 | @subsection Other Font Lock Variables | |
2817 | ||
2818 | This section describes additional variables that a major mode can | |
2819 | set by means of @var{other-vars} in @code{font-lock-defaults} | |
2820 | (@pxref{Font Lock Basics}). | |
2821 | ||
2822 | @defvar font-lock-mark-block-function | |
2823 | If this variable is non-@code{nil}, it should be a function that is | |
2824 | called with no arguments, to choose an enclosing range of text for | |
2825 | refontification for the command @kbd{M-o M-o} | |
2826 | (@code{font-lock-fontify-block}). | |
2827 | ||
2828 | The function should report its choice by placing the region around it. | |
2829 | A good choice is a range of text large enough to give proper results, | |
2830 | but not too large so that refontification becomes slow. Typical values | |
2831 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for | |
2832 | textual modes. | |
2833 | @end defvar | |
2834 | ||
2835 | @defvar font-lock-extra-managed-props | |
2836 | This variable specifies additional properties (other than | |
2837 | @code{font-lock-face}) that are being managed by Font Lock mode. It | |
2838 | is used by @code{font-lock-default-unfontify-region}, which normally | |
2839 | only manages the @code{font-lock-face} property. If you want Font | |
2840 | Lock to manage other properties as well, you must specify them in a | |
2841 | @var{facespec} in @code{font-lock-keywords} as well as add them to | |
2842 | this list. @xref{Search-based Fontification}. | |
2843 | @end defvar | |
2844 | ||
2845 | @defvar font-lock-fontify-buffer-function | |
2846 | Function to use for fontifying the buffer. The default value is | |
2847 | @code{font-lock-default-fontify-buffer}. | |
2848 | @end defvar | |
2849 | ||
2850 | @defvar font-lock-unfontify-buffer-function | |
2851 | Function to use for unfontifying the buffer. This is used when | |
2852 | turning off Font Lock mode. The default value is | |
2853 | @code{font-lock-default-unfontify-buffer}. | |
2854 | @end defvar | |
2855 | ||
2856 | @defvar font-lock-fontify-region-function | |
2857 | Function to use for fontifying a region. It should take two | |
2858 | arguments, the beginning and end of the region, and an optional third | |
2859 | argument @var{verbose}. If @var{verbose} is non-@code{nil}, the | |
2860 | function should print status messages. The default value is | |
2861 | @code{font-lock-default-fontify-region}. | |
2862 | @end defvar | |
2863 | ||
2864 | @defvar font-lock-unfontify-region-function | |
2865 | Function to use for unfontifying a region. It should take two | |
2866 | arguments, the beginning and end of the region. The default value is | |
2867 | @code{font-lock-default-unfontify-region}. | |
2868 | @end defvar | |
2869 | ||
e070558d CY |
2870 | @defun jit-lock-register function &optional contextual |
2871 | This function tells Font Lock mode to run the Lisp function | |
2872 | @var{function} any time it has to fontify or refontify part of the | |
2873 | current buffer. It calls @var{function} before calling the default | |
2874 | fontification functions, and gives it two arguments, @var{start} and | |
2875 | @var{end}, which specify the region to be fontified or refontified. | |
2876 | ||
2877 | The optional argument @var{contextual}, if non-@code{nil}, forces Font | |
2878 | Lock mode to always refontify a syntactically relevant part of the | |
2879 | buffer, and not just the modified lines. This argument can usually be | |
2880 | omitted. | |
2881 | @end defun | |
2882 | ||
2883 | @defun jit-lock-unregister function | |
2884 | If @var{function} was previously registered as a fontification | |
2885 | function using @code{jit-lock-register}, this function unregisters it. | |
2886 | @end defun | |
b8d4c8d0 GM |
2887 | |
2888 | @node Levels of Font Lock | |
2889 | @subsection Levels of Font Lock | |
2890 | ||
2891 | Many major modes offer three different levels of fontification. You | |
2892 | can define multiple levels by using a list of symbols for @var{keywords} | |
2893 | in @code{font-lock-defaults}. Each symbol specifies one level of | |
caef3ed2 GM |
2894 | fontification; it is up to the user to choose one of these levels, |
2895 | normally by setting @code{font-lock-maximum-decoration} (@pxref{Font | |
2896 | Lock,,, emacs, the GNU Emacs Manual}). The chosen level's symbol | |
2897 | value is used to initialize @code{font-lock-keywords}. | |
b8d4c8d0 GM |
2898 | |
2899 | Here are the conventions for how to define the levels of | |
2900 | fontification: | |
2901 | ||
2902 | @itemize @bullet | |
2903 | @item | |
2904 | Level 1: highlight function declarations, file directives (such as include or | |
2905 | import directives), strings and comments. The idea is speed, so only | |
2906 | the most important and top-level components are fontified. | |
2907 | ||
2908 | @item | |
2909 | Level 2: in addition to level 1, highlight all language keywords, | |
2910 | including type names that act like keywords, as well as named constant | |
2911 | values. The idea is that all keywords (either syntactic or semantic) | |
2912 | should be fontified appropriately. | |
2913 | ||
2914 | @item | |
2915 | Level 3: in addition to level 2, highlight the symbols being defined in | |
2916 | function and variable declarations, and all builtin function names, | |
2917 | wherever they appear. | |
2918 | @end itemize | |
2919 | ||
2920 | @node Precalculated Fontification | |
2921 | @subsection Precalculated Fontification | |
2922 | ||
eae7d8f8 RS |
2923 | Some major modes such as @code{list-buffers} and @code{occur} |
2924 | construct the buffer text programmatically. The easiest way for them | |
2925 | to support Font Lock mode is to specify the faces of text when they | |
2926 | insert the text in the buffer. | |
2927 | ||
2928 | The way to do this is to specify the faces in the text with the | |
2929 | special text property @code{font-lock-face} (@pxref{Special | |
2930 | Properties}). When Font Lock mode is enabled, this property controls | |
2931 | the display, just like the @code{face} property. When Font Lock mode | |
2932 | is disabled, @code{font-lock-face} has no effect on the display. | |
2933 | ||
2934 | It is ok for a mode to use @code{font-lock-face} for some text and | |
2935 | also use the normal Font Lock machinery. But if the mode does not use | |
2936 | the normal Font Lock machinery, it should not set the variable | |
2937 | @code{font-lock-defaults}. | |
b8d4c8d0 GM |
2938 | |
2939 | @node Faces for Font Lock | |
2940 | @subsection Faces for Font Lock | |
2941 | @cindex faces for font lock | |
2942 | @cindex font lock faces | |
2943 | ||
e0dd6837 CY |
2944 | Font Lock mode can highlight using any face, but Emacs defines several |
2945 | faces specifically for syntactic highlighting. These @dfn{Font Lock | |
2946 | faces} are listed below. They can also be used by major modes for | |
2947 | syntactic highlighting outside of Font Lock mode (@pxref{Major Mode | |
2948 | Conventions}). | |
b8d4c8d0 | 2949 | |
e0dd6837 CY |
2950 | Each of these symbols is both a face name, and a variable whose |
2951 | default value is the symbol itself. Thus, the default value of | |
2952 | @code{font-lock-comment-face} is @code{font-lock-comment-face}. | |
b8d4c8d0 | 2953 | |
e0dd6837 CY |
2954 | The faces are listed with descriptions of their typical usage, and in |
2955 | order of greater to lesser ``prominence''. If a mode's syntactic | |
2956 | categories do not fit well with the usage descriptions, the faces can be | |
2957 | assigned using the ordering as a guide. | |
b8d4c8d0 | 2958 | |
e0dd6837 CY |
2959 | @table @code |
2960 | @item font-lock-warning-face | |
2961 | @vindex font-lock-warning-face | |
2962 | for a construct that is peculiar, or that greatly changes the meaning of | |
2963 | other text, like @samp{;;;###autoload} in Emacs Lisp and @samp{#error} | |
2964 | in C. | |
b8d4c8d0 GM |
2965 | |
2966 | @item font-lock-function-name-face | |
2967 | @vindex font-lock-function-name-face | |
e0dd6837 | 2968 | for the name of a function being defined or declared. |
b8d4c8d0 GM |
2969 | |
2970 | @item font-lock-variable-name-face | |
2971 | @vindex font-lock-variable-name-face | |
e0dd6837 CY |
2972 | for the name of a variable being defined or declared. |
2973 | ||
2974 | @item font-lock-keyword-face | |
2975 | @vindex font-lock-keyword-face | |
2976 | for a keyword with special syntactic significance, like @samp{for} and | |
2977 | @samp{if} in C. | |
2978 | ||
2979 | @item font-lock-comment-face | |
2980 | @vindex font-lock-comment-face | |
2981 | for comments. | |
2982 | ||
2983 | @item font-lock-comment-delimiter-face | |
2984 | @vindex font-lock-comment-delimiter-face | |
2985 | for comments delimiters, like @samp{/*} and @samp{*/} in C. On most | |
2986 | terminals, this inherits from @code{font-lock-comment-face}. | |
b8d4c8d0 GM |
2987 | |
2988 | @item font-lock-type-face | |
2989 | @vindex font-lock-type-face | |
e0dd6837 | 2990 | for the names of user-defined data types. |
b8d4c8d0 GM |
2991 | |
2992 | @item font-lock-constant-face | |
2993 | @vindex font-lock-constant-face | |
e0dd6837 CY |
2994 | for the names of constants, like @samp{NULL} in C. |
2995 | ||
2996 | @item font-lock-builtin-face | |
2997 | @vindex font-lock-builtin-face | |
2998 | for the names of built-in functions. | |
b8d4c8d0 GM |
2999 | |
3000 | @item font-lock-preprocessor-face | |
3001 | @vindex font-lock-preprocessor-face | |
e0dd6837 CY |
3002 | for preprocessor commands. This inherits, by default, from |
3003 | @code{font-lock-builtin-face}. | |
3004 | ||
3005 | @item font-lock-string-face | |
3006 | @vindex font-lock-string-face | |
3007 | for string constants. | |
3008 | ||
3009 | @item font-lock-doc-face | |
3010 | @vindex font-lock-doc-face | |
3011 | for documentation strings in the code. This inherits, by default, from | |
3012 | @code{font-lock-string-face}. | |
b8d4c8d0 GM |
3013 | |
3014 | @item font-lock-negation-char-face | |
3015 | @vindex font-lock-negation-char-face | |
e0dd6837 | 3016 | for easily-overlooked negation characters. |
b8d4c8d0 GM |
3017 | @end table |
3018 | ||
3019 | @node Syntactic Font Lock | |
3020 | @subsection Syntactic Font Lock | |
3021 | @cindex syntactic font lock | |
3022 | ||
3023 | Syntactic fontification uses the syntax table to find comments and | |
3024 | string constants (@pxref{Syntax Tables}). It highlights them using | |
3025 | @code{font-lock-comment-face} and @code{font-lock-string-face} | |
3026 | (@pxref{Faces for Font Lock}), or whatever | |
3027 | @code{font-lock-syntactic-face-function} chooses. There are several | |
3028 | variables that affect syntactic fontification; you should set them by | |
3029 | means of @code{font-lock-defaults} (@pxref{Font Lock Basics}). | |
3030 | ||
3031 | @defvar font-lock-keywords-only | |
3032 | Non-@code{nil} means Font Lock should not do syntactic fontification; | |
3033 | it should only fontify based on @code{font-lock-keywords}. The normal | |
3034 | way for a mode to set this variable to @code{t} is with | |
3035 | @var{keywords-only} in @code{font-lock-defaults}. | |
3036 | @end defvar | |
3037 | ||
3038 | @defvar font-lock-syntax-table | |
3039 | This variable holds the syntax table to use for fontification of | |
3040 | comments and strings. Specify it using @var{syntax-alist} in | |
3041 | @code{font-lock-defaults}. If this is @code{nil}, fontification uses | |
3042 | the buffer's syntax table. | |
3043 | @end defvar | |
3044 | ||
3045 | @defvar font-lock-beginning-of-syntax-function | |
3046 | If this variable is non-@code{nil}, it should be a function to move | |
3047 | point back to a position that is syntactically at ``top level'' and | |
3048 | outside of strings or comments. Font Lock uses this when necessary | |
3049 | to get the right results for syntactic fontification. | |
3050 | ||
3051 | This function is called with no arguments. It should leave point at | |
3052 | the beginning of any enclosing syntactic block. Typical values are | |
3053 | @code{beginning-of-line} (used when the start of the line is known to | |
3054 | be outside a syntactic block), or @code{beginning-of-defun} for | |
3055 | programming modes, or @code{backward-paragraph} for textual modes. | |
3056 | ||
3057 | If the value is @code{nil}, Font Lock uses | |
3058 | @code{syntax-begin-function} to move back outside of any comment, | |
3059 | string, or sexp. This variable is semi-obsolete; we recommend setting | |
3060 | @code{syntax-begin-function} instead. | |
3061 | ||
3062 | Specify this variable using @var{syntax-begin} in | |
3063 | @code{font-lock-defaults}. | |
3064 | @end defvar | |
3065 | ||
3066 | @defvar font-lock-syntactic-face-function | |
3067 | A function to determine which face to use for a given syntactic | |
3068 | element (a string or a comment). The function is called with one | |
3069 | argument, the parse state at point returned by | |
3070 | @code{parse-partial-sexp}, and should return a face. The default | |
3071 | value returns @code{font-lock-comment-face} for comments and | |
3072 | @code{font-lock-string-face} for strings. | |
3073 | ||
3074 | This can be used to highlighting different kinds of strings or | |
3075 | comments differently. It is also sometimes abused together with | |
3076 | @code{font-lock-syntactic-keywords} to highlight constructs that span | |
3077 | multiple lines, but this is too esoteric to document here. | |
3078 | ||
3079 | Specify this variable using @var{other-vars} in | |
3080 | @code{font-lock-defaults}. | |
3081 | @end defvar | |
3082 | ||
3083 | @node Setting Syntax Properties | |
3084 | @subsection Setting Syntax Properties | |
3085 | ||
3086 | Font Lock mode can be used to update @code{syntax-table} properties | |
3087 | automatically (@pxref{Syntax Properties}). This is useful in | |
3088 | languages for which a single syntax table by itself is not sufficient. | |
3089 | ||
3090 | @defvar font-lock-syntactic-keywords | |
3091 | This variable enables and controls updating @code{syntax-table} | |
3092 | properties by Font Lock. Its value should be a list of elements of | |
3093 | this form: | |
3094 | ||
3095 | @example | |
3096 | (@var{matcher} @var{subexp} @var{syntax} @var{override} @var{laxmatch}) | |
3097 | @end example | |
3098 | ||
3099 | The parts of this element have the same meanings as in the corresponding | |
3100 | sort of element of @code{font-lock-keywords}, | |
3101 | ||
3102 | @example | |
3103 | (@var{matcher} @var{subexp} @var{facespec} @var{override} @var{laxmatch}) | |
3104 | @end example | |
3105 | ||
3106 | However, instead of specifying the value @var{facespec} to use for the | |
3107 | @code{face} property, it specifies the value @var{syntax} to use for | |
3108 | the @code{syntax-table} property. Here, @var{syntax} can be a string | |
3109 | (as taken by @code{modify-syntax-entry}), a syntax table, a cons cell | |
3110 | (as returned by @code{string-to-syntax}), or an expression whose value | |
3111 | is one of those two types. @var{override} cannot be @code{prepend} or | |
3112 | @code{append}. | |
3113 | ||
3114 | For example, an element of the form: | |
3115 | ||
3116 | @example | |
3117 | ("\\$\\(#\\)" 1 ".") | |
3118 | @end example | |
3119 | ||
3120 | highlights syntactically a hash character when following a dollar | |
3121 | character, with a SYNTAX of @code{"."} (meaning punctuation syntax). | |
3122 | Assuming that the buffer syntax table specifies hash characters to | |
3123 | have comment start syntax, the element will only highlight hash | |
3124 | characters that do not follow dollar characters as comments | |
3125 | syntactically. | |
3126 | ||
3127 | An element of the form: | |
3128 | ||
3129 | @example | |
3130 | ("\\('\\).\\('\\)" | |
3131 | (1 "\"") | |
3132 | (2 "\"")) | |
3133 | @end example | |
3134 | ||
3135 | highlights syntactically both single quotes which surround a single | |
3136 | character, with a SYNTAX of @code{"\""} (meaning string quote syntax). | |
3137 | Assuming that the buffer syntax table does not specify single quotes | |
3138 | to have quote syntax, the element will only highlight single quotes of | |
3139 | the form @samp{'@var{c}'} as strings syntactically. Other forms, such | |
3140 | as @samp{foo'bar} or @samp{'fubar'}, will not be highlighted as | |
3141 | strings. | |
3142 | ||
3143 | Major modes normally set this variable with @var{other-vars} in | |
3144 | @code{font-lock-defaults}. | |
3145 | @end defvar | |
3146 | ||
3147 | @node Multiline Font Lock | |
3148 | @subsection Multiline Font Lock Constructs | |
3149 | @cindex multiline font lock | |
3150 | ||
3151 | Normally, elements of @code{font-lock-keywords} should not match | |
3152 | across multiple lines; that doesn't work reliably, because Font Lock | |
3153 | usually scans just part of the buffer, and it can miss a multi-line | |
3154 | construct that crosses the line boundary where the scan starts. (The | |
3155 | scan normally starts at the beginning of a line.) | |
3156 | ||
3157 | Making elements that match multiline constructs work properly has | |
3158 | two aspects: correct @emph{identification} and correct | |
3159 | @emph{rehighlighting}. The first means that Font Lock finds all | |
3160 | multiline constructs. The second means that Font Lock will correctly | |
3161 | rehighlight all the relevant text when a multiline construct is | |
3162 | changed---for example, if some of the text that was previously part of | |
3163 | a multiline construct ceases to be part of it. The two aspects are | |
3164 | closely related, and often getting one of them to work will appear to | |
3165 | make the other also work. However, for reliable results you must | |
3166 | attend explicitly to both aspects. | |
3167 | ||
3168 | There are three ways to ensure correct identification of multiline | |
3169 | constructs: | |
3170 | ||
3171 | @itemize | |
3172 | @item | |
3173 | Add a function to @code{font-lock-extend-region-functions} that does | |
3174 | the @emph{identification} and extends the scan so that the scanned | |
3175 | text never starts or ends in the middle of a multiline construct. | |
3176 | @item | |
3177 | Use the @code{font-lock-fontify-region-function} hook similarly to | |
3178 | extend the scan so that the scanned text never starts or ends in the | |
3179 | middle of a multiline construct. | |
3180 | @item | |
3181 | Somehow identify the multiline construct right when it gets inserted | |
3182 | into the buffer (or at any point after that but before font-lock | |
3183 | tries to highlight it), and mark it with a @code{font-lock-multiline} | |
3184 | which will instruct font-lock not to start or end the scan in the | |
3185 | middle of the construct. | |
3186 | @end itemize | |
3187 | ||
3188 | There are three ways to do rehighlighting of multiline constructs: | |
3189 | ||
3190 | @itemize | |
3191 | @item | |
3192 | Place a @code{font-lock-multiline} property on the construct. This | |
3193 | will rehighlight the whole construct if any part of it is changed. In | |
3194 | some cases you can do this automatically by setting the | |
3195 | @code{font-lock-multiline} variable, which see. | |
3196 | @item | |
3197 | Make sure @code{jit-lock-contextually} is set and rely on it doing its | |
3198 | job. This will only rehighlight the part of the construct that | |
3199 | follows the actual change, and will do it after a short delay. | |
3200 | This only works if the highlighting of the various parts of your | |
3201 | multiline construct never depends on text in subsequent lines. | |
3202 | Since @code{jit-lock-contextually} is activated by default, this can | |
3203 | be an attractive solution. | |
3204 | @item | |
3205 | Place a @code{jit-lock-defer-multiline} property on the construct. | |
3206 | This works only if @code{jit-lock-contextually} is used, and with the | |
3207 | same delay before rehighlighting, but like @code{font-lock-multiline}, | |
3208 | it also handles the case where highlighting depends on | |
3209 | subsequent lines. | |
3210 | @end itemize | |
3211 | ||
3212 | @menu | |
fe42c16a | 3213 | * Font Lock Multiline:: Marking multiline chunks with a text property. |
bc3bea9c | 3214 | * Region to Refontify:: Controlling which region gets refontified |
b8d4c8d0 GM |
3215 | after a buffer change. |
3216 | @end menu | |
3217 | ||
3218 | @node Font Lock Multiline | |
3219 | @subsubsection Font Lock Multiline | |
3220 | ||
3221 | One way to ensure reliable rehighlighting of multiline Font Lock | |
3222 | constructs is to put on them the text property @code{font-lock-multiline}. | |
3223 | It should be present and non-@code{nil} for text that is part of a | |
3224 | multiline construct. | |
3225 | ||
3226 | When Font Lock is about to highlight a range of text, it first | |
3227 | extends the boundaries of the range as necessary so that they do not | |
3228 | fall within text marked with the @code{font-lock-multiline} property. | |
3229 | Then it removes any @code{font-lock-multiline} properties from the | |
3230 | range, and highlights it. The highlighting specification (mostly | |
3231 | @code{font-lock-keywords}) must reinstall this property each time, | |
3232 | whenever it is appropriate. | |
3233 | ||
3234 | @strong{Warning:} don't use the @code{font-lock-multiline} property | |
3235 | on large ranges of text, because that will make rehighlighting slow. | |
3236 | ||
3237 | @defvar font-lock-multiline | |
3238 | If the @code{font-lock-multiline} variable is set to @code{t}, Font | |
3239 | Lock will try to add the @code{font-lock-multiline} property | |
3240 | automatically on multiline constructs. This is not a universal | |
3241 | solution, however, since it slows down Font Lock somewhat. It can | |
3242 | miss some multiline constructs, or make the property larger or smaller | |
3243 | than necessary. | |
3244 | ||
3245 | For elements whose @var{matcher} is a function, the function should | |
3246 | ensure that submatch 0 covers the whole relevant multiline construct, | |
3247 | even if only a small subpart will be highlighted. It is often just as | |
3248 | easy to add the @code{font-lock-multiline} property by hand. | |
3249 | @end defvar | |
3250 | ||
3251 | The @code{font-lock-multiline} property is meant to ensure proper | |
3252 | refontification; it does not automatically identify new multiline | |
3253 | constructs. Identifying the requires that Font-Lock operate on large | |
3254 | enough chunks at a time. This will happen by accident on many cases, | |
3255 | which may give the impression that multiline constructs magically work. | |
3256 | If you set the @code{font-lock-multiline} variable non-@code{nil}, | |
3257 | this impression will be even stronger, since the highlighting of those | |
3258 | constructs which are found will be properly updated from then on. | |
3259 | But that does not work reliably. | |
3260 | ||
3261 | To find multiline constructs reliably, you must either manually | |
3262 | place the @code{font-lock-multiline} property on the text before | |
3263 | Font-Lock looks at it, or use | |
3264 | @code{font-lock-fontify-region-function}. | |
3265 | ||
bc3bea9c | 3266 | @node Region to Refontify |
b8d4c8d0 GM |
3267 | @subsubsection Region to Fontify after a Buffer Change |
3268 | ||
3269 | When a buffer is changed, the region that Font Lock refontifies is | |
3270 | by default the smallest sequence of whole lines that spans the change. | |
3271 | While this works well most of the time, sometimes it doesn't---for | |
3272 | example, when a change alters the syntactic meaning of text on an | |
3273 | earlier line. | |
3274 | ||
bc3bea9c | 3275 | You can enlarge (or even reduce) the region to refontify by setting |
e6dc6206 | 3276 | the following variable: |
b8d4c8d0 GM |
3277 | |
3278 | @defvar font-lock-extend-after-change-region-function | |
3279 | This buffer-local variable is either @code{nil} or a function for | |
3280 | Font-Lock to call to determine the region to scan and fontify. | |
3281 | ||
3282 | The function is given three parameters, the standard @var{beg}, | |
bc3bea9c | 3283 | @var{end}, and @var{old-len} from @code{after-change-functions} |
b8d4c8d0 GM |
3284 | (@pxref{Change Hooks}). It should return either a cons of the |
3285 | beginning and end buffer positions (in that order) of the region to | |
3286 | fontify, or @code{nil} (which means choose the region in the standard | |
3287 | way). This function needs to preserve point, the match-data, and the | |
3288 | current restriction. The region it returns may start or end in the | |
3289 | middle of a line. | |
3290 | ||
3291 | Since this function is called after every buffer change, it should be | |
3292 | reasonably fast. | |
3293 | @end defvar | |
3294 | ||
5dcb4c4e | 3295 | @node Auto-Indentation |
35a30759 | 3296 | @section Auto-indentation of code |
5dcb4c4e SM |
3297 | |
3298 | For programming languages, an important feature of a major mode is to | |
3299 | provide automatic indentation. This is controlled in Emacs by | |
3300 | @code{indent-line-function} (@pxref{Mode-Specific Indent}). | |
3301 | Writing a good indentation function can be difficult and to a large | |
3302 | extent it is still a black art. | |
3303 | ||
3304 | Many major mode authors will start by writing a simple indentation | |
3305 | function that works for simple cases, for example by comparing with the | |
3306 | indentation of the previous text line. For most programming languages | |
3307 | that are not really line-based, this tends to scale very poorly: | |
3308 | improving such a function to let it handle more diverse situations tends | |
3309 | to become more and more difficult, resulting in the end with a large, | |
3310 | complex, unmaintainable indentation function which nobody dares to touch. | |
3311 | ||
3312 | A good indentation function will usually need to actually parse the | |
3313 | text, according to the syntax of the language. Luckily, it is not | |
3314 | necessary to parse the text in as much detail as would be needed | |
3315 | for a compiler, but on the other hand, the parser embedded in the | |
3316 | indentation code will want to be somewhat friendly to syntactically | |
3317 | incorrect code. | |
3318 | ||
3319 | Good maintainable indentation functions usually fall into 2 categories: | |
3320 | either parsing forward from some ``safe'' starting point until the | |
3321 | position of interest, or parsing backward from the position of interest. | |
3322 | Neither of the two is a clearly better choice than the other: parsing | |
3323 | backward is often more difficult than parsing forward because | |
3324 | programming languages are designed to be parsed forward, but for the | |
3325 | purpose of indentation it has the advantage of not needing to | |
3326 | guess a ``safe'' starting point, and it generally enjoys the property | |
3327 | that only a minimum of text will be analyzed to decide the indentation | |
3328 | of a line, so indentation will tend to be unaffected by syntax errors in | |
3329 | some earlier unrelated piece of code. Parsing forward on the other hand | |
3330 | is usually easier and has the advantage of making it possible to | |
3331 | reindent efficiently a whole region at a time, with a single parse. | |
3332 | ||
3333 | Rather than write your own indentation function from scratch, it is | |
3334 | often preferable to try and reuse some existing ones or to rely | |
3335 | on a generic indentation engine. There are sadly few such | |
3336 | engines. The CC-mode indentation code (used with C, C++, Java, Awk | |
3337 | and a few other such modes) has been made more generic over the years, | |
3338 | so if your language seems somewhat similar to one of those languages, | |
3339 | you might try to use that engine. @c FIXME: documentation? | |
3340 | Another one is SMIE which takes an approach in the spirit | |
3341 | of Lisp sexps and adapts it to non-Lisp languages. | |
3342 | ||
3343 | @menu | |
3344 | * SMIE:: A simple minded indentation engine | |
3345 | @end menu | |
3346 | ||
3347 | @node SMIE | |
3348 | @subsection Simple Minded Indentation Engine | |
3349 | ||
3350 | SMIE is a package that provides a generic navigation and indentation | |
3351 | engine. Based on a very simple parser using an ``operator precedence | |
3352 | grammar'', it lets major modes extend the sexp-based navigation of Lisp | |
3353 | to non-Lisp languages as well as provide a simple to use but reliable | |
3354 | auto-indentation. | |
3355 | ||
3356 | Operator precedence grammar is a very primitive technology for parsing | |
3357 | compared to some of the more common techniques used in compilers. | |
3358 | It has the following characteristics: its parsing power is very limited, | |
3359 | and it is largely unable to detect syntax errors, but it has the | |
3360 | advantage of being algorithmically efficient and able to parse forward | |
3361 | just as well as backward. In practice that means that SMIE can use it | |
3362 | for indentation based on backward parsing, that it can provide both | |
3363 | @code{forward-sexp} and @code{backward-sexp} functionality, and that it | |
3364 | will naturally work on syntactically incorrect code without any extra | |
3365 | effort. The downside is that it also means that most programming | |
3366 | languages cannot be parsed correctly using SMIE, at least not without | |
3367 | resorting to some special tricks (@pxref{SMIE Tricks}). | |
3368 | ||
3369 | @menu | |
3370 | * SMIE setup:: SMIE setup and features | |
3371 | * Operator Precedence Grammars:: A very simple parsing technique | |
3372 | * SMIE Grammar:: Defining the grammar of a language | |
3373 | * SMIE Lexer:: Defining tokens | |
3374 | * SMIE Tricks:: Working around the parser's limitations | |
3375 | * SMIE Indentation:: Specifying indentation rules | |
3376 | * SMIE Indentation Helpers:: Helper functions for indentation rules | |
3377 | * SMIE Indentation Example:: Sample indentation rules | |
3378 | @end menu | |
3379 | ||
3380 | @node SMIE setup | |
3381 | @subsubsection SMIE Setup and Features | |
3382 | ||
3383 | SMIE is meant to be a one-stop shop for structural navigation and | |
3384 | various other features which rely on the syntactic structure of code, in | |
3385 | particular automatic indentation. The main entry point is | |
3386 | @code{smie-setup} which is a function typically called while setting | |
3387 | up a major mode. | |
3388 | ||
3389 | @defun smie-setup grammar rules-function &rest keywords | |
3390 | Setup SMIE navigation and indentation. | |
3391 | @var{grammar} is a grammar table generated by @code{smie-prec2->grammar}. | |
3392 | @var{rules-function} is a set of indentation rules for use on | |
3393 | @code{smie-rules-function}. | |
3394 | @var{keywords} are additional arguments, which can include the following | |
3395 | keywords: | |
3396 | @itemize | |
3397 | @item | |
3398 | @code{:forward-token} @var{fun}: Specify the forward lexer to use. | |
3399 | @item | |
3400 | @code{:backward-token} @var{fun}: Specify the backward lexer to use. | |
3401 | @end itemize | |
3402 | @end defun | |
3403 | ||
3404 | Calling this function is sufficient to make commands such as | |
3405 | @code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be | |
3406 | able to properly handle structural elements other than just the paired | |
3407 | parentheses already handled by syntax tables. For example, if the | |
3408 | provided grammar is precise enough, @code{transpose-sexps} can correctly | |
3409 | transpose the two arguments of a @code{+} operator, taking into account | |
3410 | the precedence rules of the language. | |
3411 | ||
3412 | Calling `smie-setup' is also sufficient to make TAB indentation work in | |
f49d1f52 SM |
3413 | the expected way, extends @code{blink-matching-paren} to apply to |
3414 | elements like @code{begin...end}, and provides some commands that you | |
3415 | can bind in the major mode keymap. | |
5dcb4c4e SM |
3416 | |
3417 | @deffn Command smie-close-block | |
3418 | This command closes the most recently opened (and not yet closed) block. | |
3419 | @end deffn | |
3420 | ||
3421 | @deffn Command smie-down-list &optional arg | |
3422 | This command is like @code{down-list} but it also pays attention to | |
3423 | nesting of tokens other than parentheses, such as @code{begin...end}. | |
3424 | @end deffn | |
3425 | ||
3426 | @node Operator Precedence Grammars | |
3427 | @subsubsection Operator Precedence Grammars | |
3428 | ||
3429 | SMIE's precedence grammars simply give to each token a pair of | |
3430 | precedences: the left-precedence and the right-precedence. We say | |
3431 | @code{T1 < T2} if the right-precedence of token @code{T1} is less than | |
3432 | the left-precedence of token @code{T2}. A good way to read this | |
3433 | @code{<} is as a kind of parenthesis: if we find @code{... T1 something | |
3434 | T2 ...} then that should be parsed as @code{... T1 (something T2 ...} | |
3435 | rather than as @code{... T1 something) T2 ...}. The latter | |
3436 | interpretation would be the case if we had @code{T1 > T2}. If we have | |
3437 | @code{T1 = T2}, it means that token T2 follows token T1 in the same | |
3438 | syntactic construction, so typically we have @code{"begin" = "end"}. | |
3439 | Such pairs of precedences are sufficient to express left-associativity | |
3440 | or right-associativity of infix operators, nesting of tokens like | |
3441 | parentheses and many other cases. | |
3442 | ||
62d94509 | 3443 | @c Let's leave this undocumented to leave it more open for change! |
5dcb4c4e SM |
3444 | @c @defvar smie-grammar |
3445 | @c The value of this variable is an alist specifying the left and right | |
3446 | @c precedence of each token. It is meant to be initialized by using one of | |
3447 | @c the functions below. | |
3448 | @c @end defvar | |
3449 | ||
3450 | @defun smie-prec2->grammar table | |
3451 | This function takes a @emph{prec2} grammar @var{table} and returns an | |
3452 | alist suitable for use in @code{smie-setup}. The @emph{prec2} | |
3453 | @var{table} is itself meant to be built by one of the functions below. | |
3454 | @end defun | |
3455 | ||
3456 | @defun smie-merge-prec2s &rest tables | |
3457 | This function takes several @emph{prec2} @var{tables} and merges them | |
3458 | into a new @emph{prec2} table. | |
3459 | @end defun | |
3460 | ||
3461 | @defun smie-precs->prec2 precs | |
3462 | This function builds a @emph{prec2} table from a table of precedences | |
3463 | @var{precs}. @var{precs} should be a list, sorted by precedence (for | |
3464 | example @code{"+"} will come before @code{"*"}), of elements of the form | |
3465 | @code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that | |
3466 | acts as an operator; @var{assoc} is their associativity, which can be | |
3467 | either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}. | |
3468 | All operators in a given element share the same precedence level | |
3469 | and associativity. | |
3470 | @end defun | |
3471 | ||
3472 | @defun smie-bnf->prec2 bnf &rest resolvers | |
3473 | This function lets you specify the grammar using a BNF notation. | |
3474 | It accepts a @var{bnf} description of the grammar along with a set of | |
3475 | conflict resolution rules @var{resolvers}, and | |
3476 | returns a @emph{prec2} table. | |
3477 | ||
3478 | @var{bnf} is a list of nonterminal definitions of the form | |
3479 | @code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs} | |
3480 | is a (non-empty) list of terminals (aka tokens) or non-terminals. | |
3481 | ||
3482 | Not all grammars are accepted: | |
3483 | @itemize | |
3484 | @item | |
3485 | An @var{rhs} cannot be an empty list (an empty list is never needed, | |
3486 | since SMIE allows all non-terminals to match the empty string anyway). | |
3487 | @item | |
3488 | An @var{rhs} cannot have 2 consecutive non-terminals: each pair of | |
3489 | non-terminals needs to be separated by a terminal (aka token). | |
3490 | This is a fundamental limitation of operator precedence grammars. | |
3491 | @end itemize | |
3492 | ||
3493 | Additionally, conflicts can occur: | |
3494 | @itemize | |
3495 | @item | |
3496 | The returned @emph{prec2} table holds constraints between pairs of tokens, and | |
3497 | for any given pair only one constraint can be present: T1 < T2, | |
3498 | T1 = T2, or T1 > T2. | |
3499 | @item | |
3500 | A token can be an @code{opener} (something similar to an open-paren), | |
3501 | a @code{closer} (like a close-paren), or @code{neither} of the two | |
3502 | (e.g. an infix operator, or an inner token like @code{"else"}). | |
3503 | @end itemize | |
3504 | ||
3505 | Precedence conflicts can be resolved via @var{resolvers}, which | |
3506 | is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for | |
3507 | each precedence conflict, if those @code{precs} tables | |
3508 | specify a particular constraint, then the conflict is resolved by using | |
3509 | this constraint instead, else a conflict is reported and one of the | |
3510 | conflicting constraints is picked arbitrarily and the others are | |
3511 | simply ignored. | |
3512 | @end defun | |
3513 | ||
3514 | @node SMIE Grammar | |
3515 | @subsubsection Defining the Grammar of a Language | |
3516 | ||
3517 | The usual way to define the SMIE grammar of a language is by | |
3518 | defining a new global variable that holds the precedence table by | |
3519 | giving a set of BNF rules. | |
3520 | For example, the grammar definition for a small Pascal-like language | |
3521 | could look like: | |
3522 | @example | |
3523 | @group | |
3524 | (require 'smie) | |
3525 | (defvar sample-smie-grammar | |
3526 | (smie-prec2->grammar | |
3527 | (smie-bnf->prec2 | |
3528 | @end group | |
3529 | @group | |
3530 | '((id) | |
3531 | (inst ("begin" insts "end") | |
3532 | ("if" exp "then" inst "else" inst) | |
3533 | (id ":=" exp) | |
3534 | (exp)) | |
3535 | (insts (insts ";" insts) (inst)) | |
3536 | (exp (exp "+" exp) | |
3537 | (exp "*" exp) | |
3538 | ("(" exps ")")) | |
3539 | (exps (exps "," exps) (exp))) | |
3540 | @end group | |
3541 | @group | |
3542 | '((assoc ";")) | |
3543 | '((assoc ",")) | |
3544 | '((assoc "+") (assoc "*"))))) | |
3545 | @end group | |
3546 | @end example | |
3547 | ||
3548 | @noindent | |
3549 | A few things to note: | |
3550 | ||
3551 | @itemize | |
3552 | @item | |
3553 | The above grammar does not explicitly mention the syntax of function | |
3554 | calls: SMIE will automatically allow any sequence of sexps, such as | |
3555 | identifiers, balanced parentheses, or @code{begin ... end} blocks | |
3556 | to appear anywhere anyway. | |
3557 | @item | |
3558 | The grammar category @code{id} has no right hand side: this does not | |
3559 | mean that it can match only the empty string, since as mentioned any | |
3560 | sequence of sexps can appear anywhere anyway. | |
3561 | @item | |
3562 | Because non terminals cannot appear consecutively in the BNF grammar, it | |
3563 | is difficult to correctly handle tokens that act as terminators, so the | |
3564 | above grammar treats @code{";"} as a statement @emph{separator} instead, | |
3565 | which SMIE can handle very well. | |
3566 | @item | |
3567 | Separators used in sequences (such as @code{","} and @code{";"} above) | |
3568 | are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)} | |
3569 | which generate precedence conflicts which are then resolved by giving | |
3570 | them an explicit @code{(assoc "separator")}. | |
3571 | @item | |
3572 | The @code{("(" exps ")")} rule was not needed to pair up parens, since | |
3573 | SMIE will pair up any characters that are marked as having paren syntax | |
3574 | in the syntax table. What this rule does instead (together with the | |
3575 | definition of @code{exps}) is to make it clear that @code{","} should | |
3576 | not appear outside of parentheses. | |
3577 | @item | |
3578 | Rather than have a single @emph{precs} table to resolve conflicts, it is | |
3579 | preferable to have several tables, so as to let the BNF part of the | |
3580 | grammar specify relative precedences where possible. | |
3581 | @item | |
3582 | Unless there is a very good reason to prefer @code{left} or | |
3583 | @code{right}, it is usually preferable to mark operators as associative, | |
3584 | using @code{assoc}. For that reason @code{"+"} and @code{"*"} are | |
3585 | defined above as @code{assoc}, although the language defines them | |
3586 | formally as left associative. | |
3587 | @end itemize | |
3588 | ||
3589 | @node SMIE Lexer | |
3590 | @subsubsection Defining Tokens | |
3591 | ||
3592 | SMIE comes with a predefined lexical analyzer which uses syntax tables | |
3593 | in the following way: any sequence of characters that have word or | |
3594 | symbol syntax is considered a token, and so is any sequence of | |
3595 | characters that have punctuation syntax. This default lexer is | |
3596 | often a good starting point but is rarely actually correct for any given | |
3597 | language. For example, it will consider @code{"2,+3"} to be composed | |
3598 | of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}. | |
3599 | ||
3600 | To describe the lexing rules of your language to SMIE, you need | |
3601 | 2 functions, one to fetch the next token, and another to fetch the | |
3602 | previous token. Those functions will usually first skip whitespace and | |
3603 | comments and then look at the next chunk of text to see if it | |
3604 | is a special token. If so it should skip the token and | |
3605 | return a description of this token. Usually this is simply the string | |
3606 | extracted from the buffer, but it can be anything you want. | |
3607 | For example: | |
3608 | @example | |
3609 | @group | |
3610 | (defvar sample-keywords-regexp | |
3611 | (regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "="))) | |
3612 | @end group | |
3613 | @group | |
3614 | (defun sample-smie-forward-token () | |
3615 | (forward-comment (point-max)) | |
3616 | (cond | |
3617 | ((looking-at sample-keywords-regexp) | |
3618 | (goto-char (match-end 0)) | |
3619 | (match-string-no-properties 0)) | |
3620 | (t (buffer-substring-no-properties | |
3621 | (point) | |
3622 | (progn (skip-syntax-forward "w_") | |
3623 | (point)))))) | |
3624 | @end group | |
3625 | @group | |
3626 | (defun sample-smie-backward-token () | |
3627 | (forward-comment (- (point))) | |
3628 | (cond | |
3629 | ((looking-back sample-keywords-regexp (- (point) 2) t) | |
3630 | (goto-char (match-beginning 0)) | |
3631 | (match-string-no-properties 0)) | |
3632 | (t (buffer-substring-no-properties | |
3633 | (point) | |
3634 | (progn (skip-syntax-backward "w_") | |
3635 | (point)))))) | |
3636 | @end group | |
3637 | @end example | |
3638 | ||
3639 | Notice how those lexers return the empty string when in front of | |
3640 | parentheses. This is because SMIE automatically takes care of the | |
3641 | parentheses defined in the syntax table. More specifically if the lexer | |
3642 | returns nil or an empty string, SMIE tries to handle the corresponding | |
3643 | text as a sexp according to syntax tables. | |
3644 | ||
3645 | @node SMIE Tricks | |
3646 | @subsubsection Living With a Weak Parser | |
3647 | ||
3648 | The parsing technique used by SMIE does not allow tokens to behave | |
3649 | differently in different contexts. For most programming languages, this | |
3650 | manifests itself by precedence conflicts when converting the | |
3651 | BNF grammar. | |
3652 | ||
3653 | Sometimes, those conflicts can be worked around by expressing the | |
3654 | grammar slightly differently. For example, for Modula-2 it might seem | |
3655 | natural to have a BNF grammar that looks like this: | |
3656 | ||
3657 | @example | |
3658 | ... | |
3659 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3660 | ("CASE" exp "OF" cases "END") | |
3661 | ...) | |
049bcbcb CY |
3662 | (cases (cases "|" cases) |
3663 | (caselabel ":" insts) | |
3664 | ("ELSE" insts)) | |
5dcb4c4e SM |
3665 | ... |
3666 | @end example | |
3667 | ||
3668 | But this will create conflicts for @code{"ELSE"}: on the one hand, the | |
3669 | IF rule implies (among many other things) that @code{"ELSE" = "END"}; | |
3670 | but on the other hand, since @code{"ELSE"} appears within @code{cases}, | |
3671 | which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}. | |
3672 | We can solve the conflict either by using: | |
3673 | @example | |
3674 | ... | |
3675 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") | |
3676 | ("CASE" exp "OF" cases "END") | |
3677 | ("CASE" exp "OF" cases "ELSE" insts "END") | |
3678 | ...) | |
3679 | (cases (cases "|" cases) (caselabel ":" insts)) | |
3680 | ... | |
3681 | @end example | |
3682 | or | |
3683 | @example | |
3684 | ... | |
3685 | (inst ("IF" exp "THEN" else "END") | |
3686 | ("CASE" exp "OF" cases "END") | |
3687 | ...) | |
3688 | (else (insts "ELSE" insts)) | |
3689 | (cases (cases "|" cases) (caselabel ":" insts) (else)) | |
3690 | ... | |
3691 | @end example | |
3692 | ||
3693 | Reworking the grammar to try and solve conflicts has its downsides, tho, | |
3694 | because SMIE assumes that the grammar reflects the logical structure of | |
3695 | the code, so it is preferable to keep the BNF closer to the intended | |
3696 | abstract syntax tree. | |
3697 | ||
3698 | Other times, after careful consideration you may conclude that those | |
3699 | conflicts are not serious and simply resolve them via the | |
3700 | @var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is | |
3701 | because the grammar is simply ambiguous: the conflict does not affect | |
3702 | the set of programs described by the grammar, but only the way those | |
3703 | programs are parsed. This is typically the case for separators and | |
3704 | associative infix operators, where you want to add a resolver like | |
3705 | @code{'((assoc "|"))}. Another case where this can happen is for the | |
3706 | classic @emph{dangling else} problem, where you will use @code{'((assoc | |
3707 | "else" "then"))}. It can also happen for cases where the conflict is | |
3708 | real and cannot really be resolved, but it is unlikely to pose a problem | |
3709 | in practice. | |
3710 | ||
3711 | Finally, in many cases some conflicts will remain despite all efforts to | |
3712 | restructure the grammar. Do not despair: while the parser cannot be | |
3713 | made more clever, you can make the lexer as smart as you want. So, the | |
3714 | solution is then to look at the tokens involved in the conflict and to | |
3715 | split one of those tokens into 2 (or more) different tokens. E.g. if | |
3716 | the grammar needs to distinguish between two incompatible uses of the | |
3717 | token @code{"begin"}, make the lexer return different tokens (say | |
3718 | @code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of | |
3719 | @code{"begin"} it finds. This pushes the work of distinguishing the | |
3720 | different cases to the lexer, which will thus have to look at the | |
3721 | surrounding text to find ad-hoc clues. | |
3722 | ||
3723 | @node SMIE Indentation | |
3724 | @subsubsection Specifying Indentation Rules | |
3725 | ||
3726 | Based on the provided grammar, SMIE will be able to provide automatic | |
3727 | indentation without any extra effort. But in practice, this default | |
3728 | indentation style will probably not be good enough. You will want to | |
3729 | tweak it in many different cases. | |
3730 | ||
3731 | SMIE indentation is based on the idea that indentation rules should be | |
3732 | as local as possible. To this end, it relies on the idea of | |
3733 | @emph{virtual} indentation, which is the indentation that a particular | |
3734 | program point would have if it were at the beginning of a line. | |
3735 | Of course, if that program point is indeed at the beginning of a line, | |
3736 | its virtual indentation is its current indentation. But if not, then | |
3737 | SMIE uses the indentation algorithm to compute the virtual indentation | |
3738 | of that point. Now in practice, the virtual indentation of a program | |
3739 | point does not have to be identical to the indentation it would have if | |
3740 | we inserted a newline before it. To see how this works, the SMIE rule | |
3741 | for indentation after a @code{@{} in C does not care whether the | |
3742 | @code{@{} is standing on a line of its own or is at the end of the | |
3743 | preceding line. Instead, these different cases are handled in the | |
3744 | indentation rule that decides how to indent before a @code{@{}. | |
3745 | ||
3746 | Another important concept is the notion of @emph{parent}: The | |
3747 | @emph{parent} of a token, is the head token of the nearest enclosing | |
3748 | syntactic construct. For example, the parent of an @code{else} is the | |
3749 | @code{if} to which it belongs, and the parent of an @code{if}, in turn, | |
3750 | is the lead token of the surrounding construct. The command | |
3751 | @code{backward-sexp} jumps from a token to its parent, but there are | |
3752 | some caveats: for @emph{openers} (tokens which start a construct, like | |
3753 | @code{if}), you need to start with point before the token, while for | |
3754 | others you need to start with point after the token. | |
3755 | @code{backward-sexp} stops with point before the parent token if that is | |
3756 | the @emph{opener} of the token of interest, and otherwise it stops with | |
3757 | point after the parent token. | |
3758 | ||
3759 | SMIE indentation rules are specified using a function that takes two | |
3760 | arguments @var{method} and @var{arg} where the meaning of @var{arg} and the | |
3761 | expected return value depend on @var{method}. | |
3762 | ||
3763 | @var{method} can be: | |
3764 | @itemize | |
3765 | @item | |
3766 | @code{:after}, in which case @var{arg} is a token and the function | |
3767 | should return the @var{offset} to use for indentation after @var{arg}. | |
3768 | @item | |
3769 | @code{:before}, in which case @var{arg} is a token and the function | |
3770 | should return the @var{offset} to use to indent @var{arg} itself. | |
3771 | @item | |
3772 | @code{:elem}, in which case the function should return either the offset | |
3773 | to use to indent function arguments (if @var{arg} is the symbol | |
3774 | @code{arg}) or the basic indentation step (if @var{arg} is the symbol | |
3775 | @code{basic}). | |
3776 | @item | |
3777 | @code{:list-intro}, in which case @var{arg} is a token and the function | |
3778 | should return non-@code{nil} if the token is followed by a list of | |
3779 | expressions (not separated by any token) rather than an expression. | |
3780 | @end itemize | |
3781 | ||
3782 | When @var{arg} is a token, the function is called with point just before | |
3783 | that token. A return value of nil always means to fallback on the | |
3784 | default behavior, so the function should return nil for arguments it | |
3785 | does not expect. | |
3786 | ||
3787 | @var{offset} can be: | |
3788 | @itemize | |
3789 | @item | |
3790 | @code{nil}: use the default indentation rule. | |
3791 | @item | |
3792 | @code{(column . @var{column})}: indent to column @var{column}. | |
3793 | @item | |
3794 | @var{number}: offset by @var{number}, relative to a base token which is | |
3795 | the current token for @code{:after} and its parent for @code{:before}. | |
3796 | @end itemize | |
3797 | ||
3798 | @node SMIE Indentation Helpers | |
3799 | @subsubsection Helper Functions for Indentation Rules | |
3800 | ||
3801 | SMIE provides various functions designed specifically for use in the | |
3802 | indentation rules function (several of those functions break if used in | |
3803 | another context). These functions all start with the prefix | |
3804 | @code{smie-rule-}. | |
3805 | ||
3806 | @defun smie-rule-bolp | |
3807 | Return non-@code{nil} if the current token is the first on the line. | |
3808 | @end defun | |
3809 | ||
3810 | @defun smie-rule-hanging-p | |
3811 | Return non-@code{nil} if the current token is @emph{hanging}. | |
3812 | A token is @emph{hanging} if it is the last token on the line | |
3813 | and if it is preceded by other tokens: a lone token on a line is not | |
3814 | hanging. | |
3815 | @end defun | |
3816 | ||
3817 | @defun smie-rule-next-p &rest tokens | |
3818 | Return non-@code{nil} if the next token is among @var{tokens}. | |
3819 | @end defun | |
3820 | ||
3821 | @defun smie-rule-prev-p &rest tokens | |
3822 | Return non-@code{nil} if the previous token is among @var{tokens}. | |
3823 | @end defun | |
3824 | ||
3825 | @defun smie-rule-parent-p &rest parents | |
3826 | Return non-@code{nil} if the current token's parent is among @var{parents}. | |
3827 | @end defun | |
3828 | ||
3829 | @defun smie-rule-sibling-p | |
3830 | Return non-nil if the current token's parent is actually a sibling. | |
3831 | This is the case for example when the parent of a @code{","} is just the | |
3832 | previous @code{","}. | |
3833 | @end defun | |
3834 | ||
3835 | @defun smie-rule-parent &optional offset | |
3836 | Return the proper offset to align the current token with the parent. | |
3837 | If non-@code{nil}, @var{offset} should be an integer giving an | |
3838 | additional offset to apply. | |
3839 | @end defun | |
3840 | ||
3841 | @defun smie-rule-separator method | |
3842 | Indent current token as a @emph{separator}. | |
3843 | ||
3844 | By @emph{separator}, we mean here a token whose sole purpose is to | |
3845 | separate various elements within some enclosing syntactic construct, and | |
3846 | which does not have any semantic significance in itself (i.e. it would | |
3847 | typically not exist as a node in an abstract syntax tree). | |
3848 | ||
3849 | Such a token is expected to have an associative syntax and be closely | |
3850 | tied to its syntactic parent. Typical examples are @code{","} in lists | |
3851 | of arguments (enclosed inside parentheses), or @code{";"} in sequences | |
3852 | of instructions (enclosed in a @code{@{...@}} or @code{begin...end} | |
3853 | block). | |
3854 | ||
3855 | @var{method} should be the method name that was passed to | |
3856 | `smie-rules-function'. | |
3857 | @end defun | |
3858 | ||
3859 | @node SMIE Indentation Example | |
3860 | @subsubsection Sample Indentation Rules | |
3861 | ||
3862 | Here is an example of an indentation function: | |
3863 | ||
3864 | @example | |
5dcb4c4e | 3865 | (defun sample-smie-rules (kind token) |
f49d1f52 SM |
3866 | (pcase (cons kind token) |
3867 | (`(:elem . basic) sample-indent-basic) | |
3868 | (`(,_ . ",") (smie-rule-separator kind)) | |
3869 | (`(:after . ":=") sample-indent-basic) | |
3870 | (`(:before . ,(or `"begin" `"(" `"@{"))) | |
3871 | (if (smie-rule-hanging-p) (smie-rule-parent))) | |
3872 | (`(:before . "if") | |
3873 | (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") | |
3874 | (smie-rule-parent))))) | |
5dcb4c4e SM |
3875 | @end example |
3876 | ||
3877 | @noindent | |
3878 | A few things to note: | |
3879 | ||
3880 | @itemize | |
3881 | @item | |
3882 | The first case indicates the basic indentation increment to use. | |
3883 | If @code{sample-indent-basic} is nil, then SMIE uses the global | |
3884 | setting @code{smie-indent-basic}. The major mode could have set | |
3885 | @code{smie-indent-basic} buffer-locally instead, but that | |
3886 | is discouraged. | |
3887 | ||
3888 | @item | |
f49d1f52 SM |
3889 | The rule for the token @code{","} make SMIE try to be more clever when |
3890 | the comma separator is placed at the beginning of lines. It tries to | |
3891 | outdent the separator so as to align the code after the comma; for | |
3892 | example: | |
5dcb4c4e SM |
3893 | |
3894 | @example | |
3895 | x = longfunctionname ( | |
3896 | arg1 | |
3897 | , arg2 | |
3898 | ); | |
3899 | @end example | |
3900 | ||
3901 | @item | |
3902 | The rule for indentation after @code{":="} exists because otherwise | |
3903 | SMIE would treat @code{":="} as an infix operator and would align the | |
3904 | right argument with the left one. | |
3905 | ||
3906 | @item | |
3907 | The rule for indentation before @code{"begin"} is an example of the use | |
3908 | of virtual indentation: This rule is used only when @code{"begin"} is | |
3909 | hanging, which can happen only when @code{"begin"} is not at the | |
3910 | beginning of a line. So this is not used when indenting | |
3911 | @code{"begin"} itself but only when indenting something relative to this | |
3912 | @code{"begin"}. Concretely, this rule changes the indentation from: | |
3913 | ||
3914 | @example | |
3915 | if x > 0 then begin | |
3916 | dosomething(x); | |
3917 | end | |
3918 | @end example | |
3919 | to | |
3920 | @example | |
3921 | if x > 0 then begin | |
3922 | dosomething(x); | |
3923 | end | |
3924 | @end example | |
3925 | ||
3926 | @item | |
3927 | The rule for indentation before @code{"if"} is similar to the one for | |
3928 | @code{"begin"}, but where the purpose is to treat @code{"else if"} | |
3929 | as a single unit, so as to align a sequence of tests rather than indent | |
3930 | each test further to the right. This function does this only in the | |
3931 | case where the @code{"if"} is not placed on a separate line, hence the | |
3932 | @code{smie-rule-bolp} test. | |
3933 | ||
3934 | If we know that the @code{"else"} is always aligned with its @code{"if"} | |
3935 | and is always at the beginning of a line, we can use a more efficient | |
3936 | rule: | |
3937 | @example | |
3938 | ((equal token "if") | |
049bcbcb CY |
3939 | (and (not (smie-rule-bolp)) |
3940 | (smie-rule-prev-p "else") | |
5dcb4c4e | 3941 | (save-excursion |
049bcbcb | 3942 | (sample-smie-backward-token) |
5dcb4c4e SM |
3943 | (cons 'column (current-column))))) |
3944 | @end example | |
3945 | ||
3946 | The advantage of this formulation is that it reuses the indentation of | |
3947 | the previous @code{"else"}, rather than going all the way back to the | |
3948 | first @code{"if"} of the sequence. | |
3949 | @end itemize | |
3950 | ||
b8d4c8d0 GM |
3951 | @node Desktop Save Mode |
3952 | @section Desktop Save Mode | |
3953 | @cindex desktop save mode | |
3954 | ||
3955 | @dfn{Desktop Save Mode} is a feature to save the state of Emacs from | |
3956 | one session to another. The user-level commands for using Desktop | |
3957 | Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs | |
3958 | Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit | |
3959 | a file, don't have to do anything to use this feature. | |
3960 | ||
3961 | For buffers not visiting a file to have their state saved, the major | |
3962 | mode must bind the buffer local variable @code{desktop-save-buffer} to | |
3963 | a non-@code{nil} value. | |
3964 | ||
3965 | @defvar desktop-save-buffer | |
3966 | If this buffer-local variable is non-@code{nil}, the buffer will have | |
3967 | its state saved in the desktop file at desktop save. If the value is | |
3968 | a function, it is called at desktop save with argument | |
3969 | @var{desktop-dirname}, and its value is saved in the desktop file along | |
3970 | with the state of the buffer for which it was called. When file names | |
3971 | are returned as part of the auxiliary information, they should be | |
3972 | formatted using the call | |
3973 | ||
3974 | @example | |
3975 | (desktop-file-name @var{file-name} @var{desktop-dirname}) | |
3976 | @end example | |
3977 | ||
3978 | @end defvar | |
3979 | ||
3980 | For buffers not visiting a file to be restored, the major mode must | |
3981 | define a function to do the job, and that function must be listed in | |
3982 | the alist @code{desktop-buffer-mode-handlers}. | |
3983 | ||
3984 | @defvar desktop-buffer-mode-handlers | |
3985 | Alist with elements | |
3986 | ||
3987 | @example | |
3988 | (@var{major-mode} . @var{restore-buffer-function}) | |
3989 | @end example | |
3990 | ||
3991 | The function @var{restore-buffer-function} will be called with | |
3992 | argument list | |
3993 | ||
3994 | @example | |
3995 | (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc}) | |
3996 | @end example | |
3997 | ||
3998 | and it should return the restored buffer. | |
3999 | Here @var{desktop-buffer-misc} is the value returned by the function | |
4000 | optionally bound to @code{desktop-save-buffer}. | |
4001 | @end defvar | |
4002 | ||
4003 | @ignore | |
769741e3 SM |
4004 | Local Variables: |
4005 | fill-column: 72 | |
4006 | End: | |
b8d4c8d0 | 4007 | @end ignore |