| 1 | @c -*-texinfo-*- |
| 2 | @c This is part of the GNU Emacs Lisp Reference Manual. |
| 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software |
| 4 | @c Foundation, Inc. |
| 5 | @c See the file elisp.texi for copying conditions. |
| 6 | @node Modes |
| 7 | @chapter Major and Minor Modes |
| 8 | @cindex mode |
| 9 | |
| 10 | A @dfn{mode} is a set of definitions that customize Emacs and can be |
| 11 | turned on and off while you edit. There are two varieties of modes: |
| 12 | @dfn{major modes}, which are mutually exclusive and used for editing |
| 13 | particular kinds of text, and @dfn{minor modes}, which provide features |
| 14 | that users can enable individually. |
| 15 | |
| 16 | This chapter describes how to write both major and minor modes, how to |
| 17 | indicate them in the mode line, and how they run hooks supplied by the |
| 18 | user. For related topics such as keymaps and syntax tables, see |
| 19 | @ref{Keymaps}, and @ref{Syntax Tables}. |
| 20 | |
| 21 | @menu |
| 22 | * 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. |
| 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 some 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 | |
| 50 | Every major mode command is supposed to run a normal hook called the |
| 51 | @dfn{mode hook} as one of the last steps of initialization. This makes |
| 52 | it easy for a user to customize the behavior of the mode, by overriding |
| 53 | the buffer-local variable assignments already made by the mode. Most |
| 54 | minor mode functions also run a mode hook at the end. But hooks are |
| 55 | used in other contexts too. For example, the hook @code{suspend-hook} |
| 56 | runs just before Emacs suspends itself (@pxref{Suspending Emacs}). |
| 57 | |
| 58 | The recommended way to add a hook function to a hook is by calling |
| 59 | @code{add-hook} (@pxref{Setting Hooks}). The hook functions may be any |
| 60 | of the valid kinds of functions that @code{funcall} accepts (@pxref{What |
| 61 | Is a Function}). Most normal hook variables are initially void; |
| 62 | @code{add-hook} knows how to deal with this. You can add hooks either |
| 63 | globally or buffer-locally with @code{add-hook}. |
| 64 | |
| 65 | @cindex abnormal hook |
| 66 | If the hook variable's name does not end with @samp{-hook}, that |
| 67 | indicates it is probably an @dfn{abnormal hook}. That means the hook |
| 68 | functions are called with arguments, or their return values are used |
| 69 | in some way. The hook's documentation says how the functions are |
| 70 | called. You can use @code{add-hook} to add a function to an abnormal |
| 71 | hook, but you must write the function to follow the hook's calling |
| 72 | convention. |
| 73 | |
| 74 | By convention, abnormal hook names end in @samp{-functions}. If the |
| 75 | variable's name ends in @samp{-function}, then its value is just a single |
| 76 | function, not a list of functions. |
| 77 | |
| 78 | @menu |
| 79 | * Running Hooks:: How to run a hook. |
| 80 | * Setting Hooks:: How to put functions on a hook, or remove them. |
| 81 | @end menu |
| 82 | |
| 83 | @node Running Hooks |
| 84 | @subsection Running Hooks |
| 85 | |
| 86 | In this section, we document the @code{run-hooks} function, which is |
| 87 | used to run a normal hook. We also document the functions for running |
| 88 | various kinds of abnormal hooks. |
| 89 | |
| 90 | @defun run-hooks &rest hookvars |
| 91 | This function takes one or more normal hook variable names as |
| 92 | arguments, and runs each hook in turn. Each argument should be a |
| 93 | symbol that is a normal hook variable. These arguments are processed |
| 94 | in the order specified. |
| 95 | |
| 96 | If a hook variable has a non-@code{nil} value, that value should be a |
| 97 | list of functions. @code{run-hooks} calls all the functions, one by |
| 98 | one, with no arguments. |
| 99 | |
| 100 | The hook variable's value can also be a single function---either a |
| 101 | lambda expression or a symbol with a function definition---which |
| 102 | @code{run-hooks} calls. But this usage is obsolete. |
| 103 | |
| 104 | If the hook variable is buffer-local, the buffer-local variable will |
| 105 | be used instead of the global variable. However, if the buffer-local |
| 106 | variable contains the element @code{t}, the global hook variable will |
| 107 | be run as well. |
| 108 | @end defun |
| 109 | |
| 110 | @defun run-hook-with-args hook &rest args |
| 111 | This function runs an abnormal hook by calling all the hook functions in |
| 112 | @var{hook}, passing each one the arguments @var{args}. |
| 113 | @end defun |
| 114 | |
| 115 | @defun run-hook-with-args-until-failure hook &rest args |
| 116 | This function runs an abnormal hook by calling each hook function in |
| 117 | turn, stopping if one of them ``fails'' by returning @code{nil}. Each |
| 118 | hook function is passed the arguments @var{args}. If this function |
| 119 | stops because one of the hook functions fails, it returns @code{nil}; |
| 120 | otherwise it returns a non-@code{nil} value. |
| 121 | @end defun |
| 122 | |
| 123 | @defun run-hook-with-args-until-success hook &rest args |
| 124 | This function runs an abnormal hook by calling each hook function, |
| 125 | stopping if one of them ``succeeds'' by returning a non-@code{nil} |
| 126 | value. Each hook function is passed the arguments @var{args}. If this |
| 127 | function stops because one of the hook functions returns a |
| 128 | non-@code{nil} value, it returns that value; otherwise it returns |
| 129 | @code{nil}. |
| 130 | @end defun |
| 131 | |
| 132 | @defmac with-wrapper-hook hook args &rest body |
| 133 | This macro runs the abnormal hook @code{hook} as a series of nested |
| 134 | ``wrapper functions'' around the @var{body} forms. The effect is |
| 135 | similar to nested @code{around} advices (@pxref{Around-Advice}). |
| 136 | |
| 137 | Each hook function should accept an argument list consisting of a function |
| 138 | @var{fun}, followed by the additional arguments listed in @var{args}. |
| 139 | The first hook function is passed a function @var{fun} that, if it is |
| 140 | called with arguments @var{args}, performs @var{body} (i.e., the default |
| 141 | operation). The @var{fun} passed to each successive hook function is |
| 142 | constructed from all the preceding hook functions (and @var{body}); if |
| 143 | this @var{fun} is called with arguments @var{args}, it does what the |
| 144 | @code{with-wrapper-hook} call would if the preceding hook functions were |
| 145 | the only ones in @var{hook}. |
| 146 | |
| 147 | Each hook function may call its @var{fun} argument as many times as it |
| 148 | wishes, including never. In that case, such a hook function acts to |
| 149 | replace the default definition altogether, and any preceding hook |
| 150 | functions. Of course, a subsequent hook function may do the same thing. |
| 151 | |
| 152 | Each hook function definition is used to construct the @var{fun} passed |
| 153 | to the next hook function in @var{hook}, if any. The last or |
| 154 | ``outermost'' @var{fun} is called once to produce the overall effect. |
| 155 | |
| 156 | When might you want to use a wrapper hook? The function |
| 157 | @code{filter-buffer-substring} illustrates a common case. There is a |
| 158 | basic functionality, performed by @var{body}---in this case, to extract |
| 159 | a buffer-substring. Then any number of hook functions can act in |
| 160 | sequence to modify that string, before returning the final result. |
| 161 | A wrapper-hook also allows for a hook function to completely replace the |
| 162 | default definition (by not calling @var{fun}). |
| 163 | @end defmac |
| 164 | |
| 165 | @defun run-hook-wrapped hook wrap-function &rest args |
| 166 | This function is similar to @code{run-hook-with-args-until-success}. |
| 167 | Like that function, it runs the functions on the abnormal hook |
| 168 | @code{hook}, stopping at the first one that returns non-@code{nil}. |
| 169 | Instead of calling the hook functions directly, though, it actually |
| 170 | calls @code{wrap-function} with arguments @code{fun} and @code{args}. |
| 171 | @end defun |
| 172 | |
| 173 | @node Setting Hooks |
| 174 | @subsection Setting Hooks |
| 175 | |
| 176 | Here's an example that uses a mode hook to turn on Auto Fill mode when |
| 177 | in Lisp Interaction mode: |
| 178 | |
| 179 | @example |
| 180 | (add-hook 'lisp-interaction-mode-hook 'auto-fill-mode) |
| 181 | @end example |
| 182 | |
| 183 | @defun add-hook hook function &optional append local |
| 184 | This function is the handy way to add function @var{function} to hook |
| 185 | variable @var{hook}. You can use it for abnormal hooks as well as for |
| 186 | normal hooks. @var{function} can be any Lisp function that can accept |
| 187 | the proper number of arguments for @var{hook}. For example, |
| 188 | |
| 189 | @example |
| 190 | (add-hook 'text-mode-hook 'my-text-hook-function) |
| 191 | @end example |
| 192 | |
| 193 | @noindent |
| 194 | adds @code{my-text-hook-function} to the hook called @code{text-mode-hook}. |
| 195 | |
| 196 | If @var{function} is already present in @var{hook} (comparing using |
| 197 | @code{equal}), then @code{add-hook} does not add it a second time. |
| 198 | |
| 199 | If @var{function} has a non-@code{nil} property |
| 200 | @code{permanent-local-hook}, then @code{kill-all-local-variables} (or |
| 201 | changing major modes) won't delete it from the hook variable's local |
| 202 | value. |
| 203 | |
| 204 | For a normal hook, hook functions should be designed so that the order |
| 205 | in which they are executed does not matter. Any dependence on the order |
| 206 | is asking for trouble. However, the order is predictable: normally, |
| 207 | @var{function} goes at the front of the hook list, so it is executed |
| 208 | first (barring another @code{add-hook} call). If the optional argument |
| 209 | @var{append} is non-@code{nil}, the new hook function goes at the end of |
| 210 | the hook list and is executed last. |
| 211 | |
| 212 | @code{add-hook} can handle the cases where @var{hook} is void or its |
| 213 | value is a single function; it sets or changes the value to a list of |
| 214 | functions. |
| 215 | |
| 216 | If @var{local} is non-@code{nil}, that says to add @var{function} to the |
| 217 | buffer-local hook list instead of to the global hook list. This makes |
| 218 | the hook buffer-local and adds @code{t} to the buffer-local value. The |
| 219 | latter acts as a flag to run the hook functions in the default value as |
| 220 | well as in the local value. |
| 221 | @end defun |
| 222 | |
| 223 | @defun remove-hook hook function &optional local |
| 224 | This function removes @var{function} from the hook variable |
| 225 | @var{hook}. It compares @var{function} with elements of @var{hook} |
| 226 | using @code{equal}, so it works for both symbols and lambda |
| 227 | expressions. |
| 228 | |
| 229 | If @var{local} is non-@code{nil}, that says to remove @var{function} |
| 230 | from the buffer-local hook list instead of from the global hook list. |
| 231 | @end defun |
| 232 | |
| 233 | @node Major Modes |
| 234 | @section Major Modes |
| 235 | @cindex major mode |
| 236 | |
| 237 | @cindex major mode command |
| 238 | Major modes specialize Emacs for editing particular kinds of text. |
| 239 | Each buffer has one major mode at a time. Every major mode is |
| 240 | associated with a @dfn{major mode command}, whose name should end in |
| 241 | @samp{-mode}. This command takes care of switching to that mode in the |
| 242 | current buffer, by setting various buffer-local variables such as a |
| 243 | local keymap. @xref{Major Mode Conventions}. |
| 244 | |
| 245 | The least specialized major mode is called @dfn{Fundamental mode}, |
| 246 | which has no mode-specific definitions or variable settings. |
| 247 | |
| 248 | @deffn Command fundamental-mode |
| 249 | This is the major mode command for Fundamental mode. Unlike other mode |
| 250 | commands, it does @emph{not} run any mode hooks (@pxref{Major Mode |
| 251 | Conventions}), since you are not supposed to customize this mode. |
| 252 | @end deffn |
| 253 | |
| 254 | The easiest way to write a major mode is to use the macro |
| 255 | @code{define-derived-mode}, which sets up the new mode as a variant of |
| 256 | an existing major mode. @xref{Derived Modes}. We recommend using |
| 257 | @code{define-derived-mode} even if the new mode is not an obvious |
| 258 | derivative of another mode, as it automatically enforces many coding |
| 259 | conventions for you. @xref{Basic Major Modes}, for common modes to |
| 260 | derive from. |
| 261 | |
| 262 | The standard GNU Emacs Lisp directory tree contains the code for |
| 263 | several major modes, in files such as @file{text-mode.el}, |
| 264 | @file{texinfo.el}, @file{lisp-mode.el}, and @file{rmail.el}. You can |
| 265 | study these libraries to see how modes are written. |
| 266 | |
| 267 | @defopt major-mode |
| 268 | The buffer-local value of this variable holds the symbol for the current |
| 269 | major mode. Its default value holds the default major mode for new |
| 270 | buffers. The standard default value is @code{fundamental-mode}. |
| 271 | |
| 272 | If the default value is @code{nil}, then whenever Emacs creates a new |
| 273 | buffer via a command such as @kbd{C-x b} (@code{switch-to-buffer}), the |
| 274 | new buffer is put in the major mode of the previously current buffer. |
| 275 | As an exception, if the major mode of the previous buffer has a |
| 276 | @code{mode-class} symbol property with value @code{special}, the new |
| 277 | buffer is put in Fundamental mode (@pxref{Major Mode Conventions}). |
| 278 | @end defopt |
| 279 | |
| 280 | @menu |
| 281 | * Major Mode Conventions:: Coding conventions for keymaps, etc. |
| 282 | * Auto Major Mode:: How Emacs chooses the major mode automatically. |
| 283 | * Mode Help:: Finding out how to use a mode. |
| 284 | * Derived Modes:: Defining a new major mode based on another major |
| 285 | mode. |
| 286 | * Basic Major Modes:: Modes that other modes are often derived from. |
| 287 | * Mode Hooks:: Hooks run at the end of major mode functions. |
| 288 | * Tabulated List Mode:: Parent mode for buffers containing tabulated data. |
| 289 | * Generic Modes:: Defining a simple major mode that supports |
| 290 | comment syntax and Font Lock mode. |
| 291 | * Example Major Modes:: Text mode and Lisp modes. |
| 292 | @end menu |
| 293 | |
| 294 | @node Major Mode Conventions |
| 295 | @subsection Major Mode Conventions |
| 296 | @cindex major mode conventions |
| 297 | @cindex conventions for writing major modes |
| 298 | |
| 299 | The code for every major mode should follow various coding |
| 300 | conventions, including conventions for local keymap and syntax table |
| 301 | initialization, function and variable names, and hooks. |
| 302 | |
| 303 | If you use the @code{define-derived-mode} macro, it will take care of |
| 304 | many of these conventions automatically. @xref{Derived Modes}. Note |
| 305 | also that Fundamental mode is an exception to many of these conventions, |
| 306 | because it represents the default state of Emacs. |
| 307 | |
| 308 | The following list of conventions is only partial. Each major mode |
| 309 | should aim for consistency in general with other Emacs major modes, as |
| 310 | this makes Emacs as a whole more coherent. It is impossible to list |
| 311 | here all the possible points where this issue might come up; if the |
| 312 | Emacs developers point out an area where your major mode deviates from |
| 313 | the usual conventions, please make it compatible. |
| 314 | |
| 315 | @itemize @bullet |
| 316 | @item |
| 317 | Define a major mode command whose name ends in @samp{-mode}. When |
| 318 | called with no arguments, this command should switch to the new mode in |
| 319 | the current buffer by setting up the keymap, syntax table, and |
| 320 | buffer-local variables in an existing buffer. It should not change the |
| 321 | buffer's contents. |
| 322 | |
| 323 | @item |
| 324 | Write a documentation string for this command that describes the special |
| 325 | commands available in this mode. @xref{Mode Help}. |
| 326 | |
| 327 | The documentation string may include the special documentation |
| 328 | substrings, @samp{\[@var{command}]}, @samp{\@{@var{keymap}@}}, and |
| 329 | @samp{\<@var{keymap}>}, which allow the help display to adapt |
| 330 | automatically to the user's own key bindings. @xref{Keys in |
| 331 | Documentation}. |
| 332 | |
| 333 | @item |
| 334 | The major mode command should start by calling |
| 335 | @code{kill-all-local-variables}. This runs the normal hook |
| 336 | @code{change-major-mode-hook}, then gets rid of the buffer-local |
| 337 | variables of the major mode previously in effect. @xref{Creating |
| 338 | Buffer-Local}. |
| 339 | |
| 340 | @item |
| 341 | The major mode command should set the variable @code{major-mode} to the |
| 342 | major mode command symbol. This is how @code{describe-mode} discovers |
| 343 | which documentation to print. |
| 344 | |
| 345 | @item |
| 346 | The major mode command should set the variable @code{mode-name} to the |
| 347 | ``pretty'' name of the mode, usually a string (but see @ref{Mode Line |
| 348 | Data}, for other possible forms). The name of the mode appears |
| 349 | in the mode line. |
| 350 | |
| 351 | @item |
| 352 | @cindex functions in modes |
| 353 | Since all global names are in the same name space, all the global |
| 354 | variables, constants, and functions that are part of the mode should |
| 355 | have names that start with the major mode name (or with an abbreviation |
| 356 | of it if the name is long). @xref{Coding Conventions}. |
| 357 | |
| 358 | @item |
| 359 | In a major mode for editing some kind of structured text, such as a |
| 360 | programming language, indentation of text according to structure is |
| 361 | probably useful. So the mode should set @code{indent-line-function} |
| 362 | to a suitable function, and probably customize other variables |
| 363 | for indentation. @xref{Auto-Indentation}. |
| 364 | |
| 365 | @item |
| 366 | @cindex keymaps in modes |
| 367 | The major mode should usually have its own keymap, which is used as the |
| 368 | local keymap in all buffers in that mode. The major mode command should |
| 369 | call @code{use-local-map} to install this local map. @xref{Active |
| 370 | Keymaps}, for more information. |
| 371 | |
| 372 | This keymap should be stored permanently in a global variable named |
| 373 | @code{@var{modename}-mode-map}. Normally the library that defines the |
| 374 | mode sets this variable. |
| 375 | |
| 376 | @xref{Tips for Defining}, for advice about how to write the code to set |
| 377 | up the mode's keymap variable. |
| 378 | |
| 379 | @item |
| 380 | The key sequences bound in a major mode keymap should usually start with |
| 381 | @kbd{C-c}, followed by a control character, a digit, or @kbd{@{}, |
| 382 | @kbd{@}}, @kbd{<}, @kbd{>}, @kbd{:} or @kbd{;}. The other punctuation |
| 383 | characters are reserved for minor modes, and ordinary letters are |
| 384 | reserved for users. |
| 385 | |
| 386 | A major mode can also rebind the keys @kbd{M-n}, @kbd{M-p} and |
| 387 | @kbd{M-s}. The bindings for @kbd{M-n} and @kbd{M-p} should normally |
| 388 | be some kind of ``moving forward and backward'', but this does not |
| 389 | necessarily mean cursor motion. |
| 390 | |
| 391 | It is legitimate for a major mode to rebind a standard key sequence if |
| 392 | it provides a command that does ``the same job'' in a way better |
| 393 | suited to the text this mode is used for. For example, a major mode |
| 394 | for editing a programming language might redefine @kbd{C-M-a} to |
| 395 | ``move to the beginning of a function'' in a way that works better for |
| 396 | that language. |
| 397 | |
| 398 | It is also legitimate for a major mode to rebind a standard key |
| 399 | sequence whose standard meaning is rarely useful in that mode. For |
| 400 | instance, minibuffer modes rebind @kbd{M-r}, whose standard meaning is |
| 401 | rarely of any use in the minibuffer. Major modes such as Dired or |
| 402 | Rmail that do not allow self-insertion of text can reasonably redefine |
| 403 | letters and other printing characters as special commands. |
| 404 | |
| 405 | @item |
| 406 | Major modes for editing text should not define @key{RET} to do |
| 407 | anything other than insert a newline. However, it is ok for |
| 408 | specialized modes for text that users don't directly edit, such as |
| 409 | Dired and Info modes, to redefine @key{RET} to do something entirely |
| 410 | different. |
| 411 | |
| 412 | @item |
| 413 | Major modes should not alter options that are primarily a matter of user |
| 414 | preference, such as whether Auto-Fill mode is enabled. Leave this to |
| 415 | each user to decide. However, a major mode should customize other |
| 416 | variables so that Auto-Fill mode will work usefully @emph{if} the user |
| 417 | decides to use it. |
| 418 | |
| 419 | @item |
| 420 | @cindex syntax tables in modes |
| 421 | The mode may have its own syntax table or may share one with other |
| 422 | related modes. If it has its own syntax table, it should store this in |
| 423 | a variable named @code{@var{modename}-mode-syntax-table}. @xref{Syntax |
| 424 | Tables}. |
| 425 | |
| 426 | @item |
| 427 | If the mode handles a language that has a syntax for comments, it should |
| 428 | set the variables that define the comment syntax. @xref{Options for |
| 429 | Comments,, Options Controlling Comments, emacs, The GNU Emacs Manual}. |
| 430 | |
| 431 | @item |
| 432 | @cindex abbrev tables in modes |
| 433 | The mode may have its own abbrev table or may share one with other |
| 434 | related modes. If it has its own abbrev table, it should store this |
| 435 | in a variable named @code{@var{modename}-mode-abbrev-table}. If the |
| 436 | major mode command defines any abbrevs itself, it should pass @code{t} |
| 437 | for the @var{system-flag} argument to @code{define-abbrev}. |
| 438 | @xref{Defining Abbrevs}. |
| 439 | |
| 440 | @item |
| 441 | The mode should specify how to do highlighting for Font Lock mode, by |
| 442 | setting up a buffer-local value for the variable |
| 443 | @code{font-lock-defaults} (@pxref{Font Lock Mode}). |
| 444 | |
| 445 | @item |
| 446 | Each face that the mode defines should, if possible, inherit from an |
| 447 | existing Emacs face. @xref{Basic Faces}, and @ref{Faces for Font Lock}. |
| 448 | |
| 449 | @item |
| 450 | The mode should specify how Imenu should find the definitions or |
| 451 | sections of a buffer, by setting up a buffer-local value for the |
| 452 | variable @code{imenu-generic-expression}, for the two variables |
| 453 | @code{imenu-prev-index-position-function} and |
| 454 | @code{imenu-extract-index-name-function}, or for the variable |
| 455 | @code{imenu-create-index-function} (@pxref{Imenu}). |
| 456 | |
| 457 | @item |
| 458 | The mode can specify a local value for |
| 459 | @code{eldoc-documentation-function} to tell ElDoc mode how to handle |
| 460 | this mode. |
| 461 | |
| 462 | @item |
| 463 | The mode can specify how to complete various keywords by adding one or |
| 464 | more buffer-local entries to the special hook |
| 465 | @code{completion-at-point-functions}. @xref{Completion in Buffers}. |
| 466 | |
| 467 | @item |
| 468 | @cindex buffer-local variables in modes |
| 469 | To make a buffer-local binding for an Emacs customization variable, use |
| 470 | @code{make-local-variable} in the major mode command, not |
| 471 | @code{make-variable-buffer-local}. The latter function would make the |
| 472 | variable local to every buffer in which it is subsequently set, which |
| 473 | would affect buffers that do not use this mode. It is undesirable for a |
| 474 | mode to have such global effects. @xref{Buffer-Local Variables}. |
| 475 | |
| 476 | With rare exceptions, the only reasonable way to use |
| 477 | @code{make-variable-buffer-local} in a Lisp package is for a variable |
| 478 | which is used only within that package. Using it on a variable used by |
| 479 | other packages would interfere with them. |
| 480 | |
| 481 | @item |
| 482 | @cindex mode hook |
| 483 | @cindex major mode hook |
| 484 | Each major mode should have a normal @dfn{mode hook} named |
| 485 | @code{@var{modename}-mode-hook}. The very last thing the major mode command |
| 486 | should do is to call @code{run-mode-hooks}. This runs the normal |
| 487 | hook @code{change-major-mode-after-body-hook}, the mode hook, |
| 488 | and then the normal hook @code{after-change-major-mode-hook}. |
| 489 | @xref{Mode Hooks}. |
| 490 | |
| 491 | @item |
| 492 | The major mode command may start by calling some other major mode |
| 493 | command (called the @dfn{parent mode}) and then alter some of its |
| 494 | settings. A mode that does this is called a @dfn{derived mode}. The |
| 495 | recommended way to define one is to use the @code{define-derived-mode} |
| 496 | macro, but this is not required. Such a mode should call the parent |
| 497 | mode command inside a @code{delay-mode-hooks} form. (Using |
| 498 | @code{define-derived-mode} does this automatically.) @xref{Derived |
| 499 | Modes}, and @ref{Mode Hooks}. |
| 500 | |
| 501 | @item |
| 502 | If something special should be done if the user switches a buffer from |
| 503 | this mode to any other major mode, this mode can set up a buffer-local |
| 504 | value for @code{change-major-mode-hook} (@pxref{Creating Buffer-Local}). |
| 505 | |
| 506 | @item |
| 507 | If this mode is appropriate only for specially-prepared text produced by |
| 508 | the mode itself (rather than by the user typing at the keyboard or by an |
| 509 | external file), then the major mode command symbol should have a |
| 510 | property named @code{mode-class} with value @code{special}, put on as |
| 511 | follows: |
| 512 | |
| 513 | @kindex mode-class @r{(property)} |
| 514 | @cindex @code{special} modes |
| 515 | @example |
| 516 | (put 'funny-mode 'mode-class 'special) |
| 517 | @end example |
| 518 | |
| 519 | @noindent |
| 520 | This tells Emacs that new buffers created while the current buffer is in |
| 521 | Funny mode should not be put in Funny mode, even though the default |
| 522 | value of @code{major-mode} is @code{nil}. By default, the value of |
| 523 | @code{nil} for @code{major-mode} means to use the current buffer's major |
| 524 | mode when creating new buffers (@pxref{Auto Major Mode}), but with such |
| 525 | @code{special} modes, Fundamental mode is used instead. Modes such as |
| 526 | Dired, Rmail, and Buffer List use this feature. |
| 527 | |
| 528 | The function @code{view-buffer} does not enable View mode in buffers |
| 529 | whose mode-class is special, because such modes usually provide their |
| 530 | own View-like bindings. |
| 531 | |
| 532 | The @code{define-derived-mode} macro automatically marks the derived |
| 533 | mode as special if the parent mode is special. Special mode is a |
| 534 | convenient parent for such modes to inherit from; @xref{Basic Major |
| 535 | Modes}. |
| 536 | |
| 537 | @item |
| 538 | If you want to make the new mode the default for files with certain |
| 539 | recognizable names, add an element to @code{auto-mode-alist} to select |
| 540 | the mode for those file names (@pxref{Auto Major Mode}). If you |
| 541 | define the mode command to autoload, you should add this element in |
| 542 | the same file that calls @code{autoload}. If you use an autoload |
| 543 | cookie for the mode command, you can also use an autoload cookie for |
| 544 | the form that adds the element (@pxref{autoload cookie}). If you do |
| 545 | not autoload the mode command, it is sufficient to add the element in |
| 546 | the file that contains the mode definition. |
| 547 | |
| 548 | @item |
| 549 | @cindex mode loading |
| 550 | The top-level forms in the file defining the mode should be written so |
| 551 | that they may be evaluated more than once without adverse consequences. |
| 552 | For instance, use @code{defvar} or @code{defcustom} to set mode-related |
| 553 | variables, so that they are not reinitialized if they already have a |
| 554 | value (@pxref{Defining Variables}). |
| 555 | |
| 556 | @end itemize |
| 557 | |
| 558 | @node Auto Major Mode |
| 559 | @subsection How Emacs Chooses a Major Mode |
| 560 | @cindex major mode, automatic selection |
| 561 | |
| 562 | When Emacs visits a file, it automatically selects a major mode for |
| 563 | the buffer based on information in the file name or in the file itself. |
| 564 | It also processes local variables specified in the file text. |
| 565 | |
| 566 | @deffn Command normal-mode &optional find-file |
| 567 | This function establishes the proper major mode and buffer-local variable |
| 568 | bindings for the current buffer. First it calls @code{set-auto-mode} |
| 569 | (see below), then it runs @code{hack-local-variables} to parse, and |
| 570 | bind or evaluate as appropriate, the file's local variables |
| 571 | (@pxref{File Local Variables}). |
| 572 | |
| 573 | If the @var{find-file} argument to @code{normal-mode} is non-@code{nil}, |
| 574 | @code{normal-mode} assumes that the @code{find-file} function is calling |
| 575 | it. In this case, it may process local variables in the @samp{-*-} |
| 576 | line or at the end of the file. The variable |
| 577 | @code{enable-local-variables} controls whether to do so. @xref{File |
| 578 | Variables, , Local Variables in Files, emacs, The GNU Emacs Manual}, |
| 579 | for the syntax of the local variables section of a file. |
| 580 | |
| 581 | If you run @code{normal-mode} interactively, the argument |
| 582 | @var{find-file} is normally @code{nil}. In this case, |
| 583 | @code{normal-mode} unconditionally processes any file local variables. |
| 584 | |
| 585 | The function calls @code{set-auto-mode} to choose a major mode. If this |
| 586 | does not specify a mode, the buffer stays in the major mode determined |
| 587 | by the default value of @code{major-mode} (see below). |
| 588 | |
| 589 | @cindex file mode specification error |
| 590 | @code{normal-mode} uses @code{condition-case} around the call to the |
| 591 | major mode command, so errors are caught and reported as a @samp{File |
| 592 | mode specification error}, followed by the original error message. |
| 593 | @end deffn |
| 594 | |
| 595 | @defun set-auto-mode &optional keep-mode-if-same |
| 596 | @cindex visited file mode |
| 597 | This function selects the major mode that is appropriate for the |
| 598 | current buffer. It bases its decision (in order of precedence) on the |
| 599 | @w{@samp{-*-}} line, on any @samp{mode:} local variable near the end of |
| 600 | a file, on the @w{@samp{#!}} line (using @code{interpreter-mode-alist}), |
| 601 | on the text at the beginning of the buffer (using |
| 602 | @code{magic-mode-alist}), and finally on the visited file name (using |
| 603 | @code{auto-mode-alist}). @xref{Choosing Modes, , How Major Modes are |
| 604 | Chosen, emacs, The GNU Emacs Manual}. If @code{enable-local-variables} |
| 605 | is @code{nil}, @code{set-auto-mode} does not check the @w{@samp{-*-}} |
| 606 | line, or near the end of the file, for any mode tag. |
| 607 | |
| 608 | @vindex inhibit-local-variables-regexps |
| 609 | There are some file types where it is not appropriate to scan the file |
| 610 | contents for a mode specifier. For example, a tar archive may happen to |
| 611 | contain, near the end of the file, a member file that has a local |
| 612 | variables section specifying a mode for that particular file. This |
| 613 | should not be applied to the containing tar file. Similarly, a tiff |
| 614 | image file might just happen to contain a first line that seems to |
| 615 | match the @w{@samp{-*-}} pattern. For these reasons, both these file |
| 616 | extensions are members of the list @code{inhibit-local-variables-regexps}. |
| 617 | Add patterns to this list to prevent Emacs searching them for local |
| 618 | variables of any kind (not just mode specifiers). |
| 619 | |
| 620 | If @var{keep-mode-if-same} is non-@code{nil}, this function does not |
| 621 | call the mode command if the buffer is already in the proper major |
| 622 | mode. For instance, @code{set-visited-file-name} sets this to |
| 623 | @code{t} to avoid killing buffer local variables that the user may |
| 624 | have set. |
| 625 | @end defun |
| 626 | |
| 627 | @defun set-buffer-major-mode buffer |
| 628 | This function sets the major mode of @var{buffer} to the default value of |
| 629 | @code{major-mode}; if that is @code{nil}, it uses the |
| 630 | current buffer's major mode (if that is suitable). As an exception, |
| 631 | if @var{buffer}'s name is @file{*scratch*}, it sets the mode to |
| 632 | @code{initial-major-mode}. |
| 633 | |
| 634 | The low-level primitives for creating buffers do not use this function, |
| 635 | but medium-level commands such as @code{switch-to-buffer} and |
| 636 | @code{find-file-noselect} use it whenever they create buffers. |
| 637 | @end defun |
| 638 | |
| 639 | @defopt initial-major-mode |
| 640 | @cindex @file{*scratch*} |
| 641 | The value of this variable determines the major mode of the initial |
| 642 | @file{*scratch*} buffer. The value should be a symbol that is a major |
| 643 | mode command. The default value is @code{lisp-interaction-mode}. |
| 644 | @end defopt |
| 645 | |
| 646 | @defvar interpreter-mode-alist |
| 647 | This variable specifies major modes to use for scripts that specify a |
| 648 | command interpreter in a @samp{#!} line. Its value is an alist with |
| 649 | elements of the form @code{(@var{regexp} . @var{mode})}; this says to |
| 650 | use mode @var{mode} if the file specifies an interpreter which matches |
| 651 | @code{\\`@var{regexp}\\'}. For example, one of the default elements |
| 652 | is @code{("python[0-9.]*" . python-mode)}. |
| 653 | @end defvar |
| 654 | |
| 655 | @defvar magic-mode-alist |
| 656 | This variable's value is an alist with elements of the form |
| 657 | @code{(@var{regexp} . @var{function})}, where @var{regexp} is a |
| 658 | regular expression and @var{function} is a function or @code{nil}. |
| 659 | After visiting a file, @code{set-auto-mode} calls @var{function} if |
| 660 | the text at the beginning of the buffer matches @var{regexp} and |
| 661 | @var{function} is non-@code{nil}; if @var{function} is @code{nil}, |
| 662 | @code{auto-mode-alist} gets to decide the mode. |
| 663 | @end defvar |
| 664 | |
| 665 | @defvar magic-fallback-mode-alist |
| 666 | This works like @code{magic-mode-alist}, except that it is handled |
| 667 | only if @code{auto-mode-alist} does not specify a mode for this file. |
| 668 | @end defvar |
| 669 | |
| 670 | @defvar auto-mode-alist |
| 671 | This variable contains an association list of file name patterns |
| 672 | (regular expressions) and corresponding major mode commands. Usually, |
| 673 | the file name patterns test for suffixes, such as @samp{.el} and |
| 674 | @samp{.c}, but this need not be the case. An ordinary element of the |
| 675 | alist looks like @code{(@var{regexp} . @var{mode-function})}. |
| 676 | |
| 677 | For example, |
| 678 | |
| 679 | @smallexample |
| 680 | @group |
| 681 | (("\\`/tmp/fol/" . text-mode) |
| 682 | ("\\.texinfo\\'" . texinfo-mode) |
| 683 | ("\\.texi\\'" . texinfo-mode) |
| 684 | @end group |
| 685 | @group |
| 686 | ("\\.el\\'" . emacs-lisp-mode) |
| 687 | ("\\.c\\'" . c-mode) |
| 688 | ("\\.h\\'" . c-mode) |
| 689 | @dots{}) |
| 690 | @end group |
| 691 | @end smallexample |
| 692 | |
| 693 | When you visit a file whose expanded file name (@pxref{File Name |
| 694 | Expansion}), with version numbers and backup suffixes removed using |
| 695 | @code{file-name-sans-versions} (@pxref{File Name Components}), matches |
| 696 | a @var{regexp}, @code{set-auto-mode} calls the corresponding |
| 697 | @var{mode-function}. This feature enables Emacs to select the proper |
| 698 | major mode for most files. |
| 699 | |
| 700 | If an element of @code{auto-mode-alist} has the form @code{(@var{regexp} |
| 701 | @var{function} t)}, then after calling @var{function}, Emacs searches |
| 702 | @code{auto-mode-alist} again for a match against the portion of the file |
| 703 | name that did not match before. This feature is useful for |
| 704 | uncompression packages: an entry of the form @code{("\\.gz\\'" |
| 705 | @var{function} t)} can uncompress the file and then put the uncompressed |
| 706 | file in the proper mode according to the name sans @samp{.gz}. |
| 707 | |
| 708 | Here is an example of how to prepend several pattern pairs to |
| 709 | @code{auto-mode-alist}. (You might use this sort of expression in your |
| 710 | init file.) |
| 711 | |
| 712 | @smallexample |
| 713 | @group |
| 714 | (setq auto-mode-alist |
| 715 | (append |
| 716 | ;; @r{File name (within directory) starts with a dot.} |
| 717 | '(("/\\.[^/]*\\'" . fundamental-mode) |
| 718 | ;; @r{File name has no dot.} |
| 719 | ("/[^\\./]*\\'" . fundamental-mode) |
| 720 | ;; @r{File name ends in @samp{.C}.} |
| 721 | ("\\.C\\'" . c++-mode)) |
| 722 | auto-mode-alist)) |
| 723 | @end group |
| 724 | @end smallexample |
| 725 | @end defvar |
| 726 | |
| 727 | @node Mode Help |
| 728 | @subsection Getting Help about a Major Mode |
| 729 | @cindex mode help |
| 730 | @cindex help for major mode |
| 731 | @cindex documentation for major mode |
| 732 | |
| 733 | The @code{describe-mode} function provides information about major |
| 734 | modes. It is normally bound to @kbd{C-h m}. It uses the value of the |
| 735 | variable @code{major-mode} (@pxref{Major Modes}), which is why every |
| 736 | major mode command needs to set that variable. |
| 737 | |
| 738 | @deffn Command describe-mode &optional buffer |
| 739 | This command displays the documentation of the current buffer's major |
| 740 | mode and minor modes. It uses the @code{documentation} function to |
| 741 | retrieve the documentation strings of the major and minor mode |
| 742 | commands (@pxref{Accessing Documentation}). |
| 743 | |
| 744 | If called from Lisp with a non-nil @var{buffer} argument, this |
| 745 | function displays the documentation for that buffer's major and minor |
| 746 | modes, rather than those of the current buffer. |
| 747 | @end deffn |
| 748 | |
| 749 | @node Derived Modes |
| 750 | @subsection Defining Derived Modes |
| 751 | @cindex derived mode |
| 752 | |
| 753 | The recommended way to define a new major mode is to derive it from an |
| 754 | existing one using @code{define-derived-mode}. If there is no closely |
| 755 | related mode, you should inherit from either @code{text-mode}, |
| 756 | @code{special-mode}, or @code{prog-mode}. @xref{Basic Major Modes}. If |
| 757 | none of these are suitable, you can inherit from @code{fundamental-mode} |
| 758 | (@pxref{Major Modes}). |
| 759 | |
| 760 | @defmac define-derived-mode variant parent name docstring keyword-args@dots{} body@dots{} |
| 761 | This macro defines @var{variant} as a major mode command, using |
| 762 | @var{name} as the string form of the mode name. @var{variant} and |
| 763 | @var{parent} should be unquoted symbols. |
| 764 | |
| 765 | The new command @var{variant} is defined to call the function |
| 766 | @var{parent}, then override certain aspects of that parent mode: |
| 767 | |
| 768 | @itemize @bullet |
| 769 | @item |
| 770 | The new mode has its own sparse keymap, named |
| 771 | @code{@var{variant}-map}. @code{define-derived-mode} |
| 772 | makes the parent mode's keymap the parent of the new map, unless |
| 773 | @code{@var{variant}-map} is already set and already has a parent. |
| 774 | |
| 775 | @item |
| 776 | The new mode has its own syntax table, kept in the variable |
| 777 | @code{@var{variant}-syntax-table}, unless you override this using the |
| 778 | @code{:syntax-table} keyword (see below). @code{define-derived-mode} |
| 779 | makes the parent mode's syntax-table the parent of |
| 780 | @code{@var{variant}-syntax-table}, unless the latter is already set |
| 781 | and already has a parent different from the standard syntax table. |
| 782 | |
| 783 | @item |
| 784 | The new mode has its own abbrev table, kept in the variable |
| 785 | @code{@var{variant}-abbrev-table}, unless you override this using the |
| 786 | @code{:abbrev-table} keyword (see below). |
| 787 | |
| 788 | @item |
| 789 | The new mode has its own mode hook, @code{@var{variant}-hook}. It |
| 790 | runs this hook, after running the hooks of its ancestor modes, with |
| 791 | @code{run-mode-hooks}, as the last thing it does. @xref{Mode Hooks}. |
| 792 | @end itemize |
| 793 | |
| 794 | In addition, you can specify how to override other aspects of |
| 795 | @var{parent} with @var{body}. The command @var{variant} |
| 796 | evaluates the forms in @var{body} after setting up all its usual |
| 797 | overrides, just before running the mode hooks. |
| 798 | |
| 799 | If @var{parent} has a non-@code{nil} @code{mode-class} symbol |
| 800 | property, then @code{define-derived-mode} sets the @code{mode-class} |
| 801 | property of @var{variant} to the same value. This ensures, for |
| 802 | example, that if @var{parent} is a special mode, then @var{variant} is |
| 803 | also a special mode (@pxref{Major Mode Conventions}). |
| 804 | |
| 805 | You can also specify @code{nil} for @var{parent}. This gives the new |
| 806 | mode no parent. Then @code{define-derived-mode} behaves as described |
| 807 | above, but, of course, omits all actions connected with @var{parent}. |
| 808 | |
| 809 | The argument @var{docstring} specifies the documentation string for the |
| 810 | new mode. @code{define-derived-mode} adds some general information |
| 811 | about the mode's hook, followed by the mode's keymap, at the end of this |
| 812 | documentation string. If you omit @var{docstring}, |
| 813 | @code{define-derived-mode} generates a documentation string. |
| 814 | |
| 815 | The @var{keyword-args} are pairs of keywords and values. The values |
| 816 | are evaluated. The following keywords are currently supported: |
| 817 | |
| 818 | @table @code |
| 819 | @item :syntax-table |
| 820 | You can use this to explicitly specify a syntax table for the new |
| 821 | mode. If you specify a @code{nil} value, the new mode uses the same |
| 822 | syntax table as @var{parent}, or the standard syntax table if |
| 823 | @var{parent} is @code{nil}. (Note that this does @emph{not} follow |
| 824 | the convention used for non-keyword arguments that a @code{nil} value |
| 825 | is equivalent with not specifying the argument.) |
| 826 | |
| 827 | @item :abbrev-table |
| 828 | You can use this to explicitly specify an abbrev table for the new |
| 829 | mode. If you specify a @code{nil} value, the new mode uses the same |
| 830 | abbrev table as @var{parent}, or @code{fundamental-mode-abbrev-table} |
| 831 | if @var{parent} is @code{nil}. (Again, a @code{nil} value is |
| 832 | @emph{not} equivalent to not specifying this keyword.) |
| 833 | |
| 834 | @item :group |
| 835 | If this is specified, the value should be the customization group for |
| 836 | this mode. (Not all major modes have one.) Only the (still |
| 837 | experimental and unadvertised) command @code{customize-mode} currently |
| 838 | uses this. @code{define-derived-mode} does @emph{not} automatically |
| 839 | define the specified customization group. |
| 840 | @end table |
| 841 | |
| 842 | Here is a hypothetical example: |
| 843 | |
| 844 | @example |
| 845 | (define-derived-mode hypertext-mode |
| 846 | text-mode "Hypertext" |
| 847 | "Major mode for hypertext. |
| 848 | \\@{hypertext-mode-map@}" |
| 849 | (setq case-fold-search nil)) |
| 850 | |
| 851 | (define-key hypertext-mode-map |
| 852 | [down-mouse-3] 'do-hyper-link) |
| 853 | @end example |
| 854 | |
| 855 | Do not write an @code{interactive} spec in the definition; |
| 856 | @code{define-derived-mode} does that automatically. |
| 857 | @end defmac |
| 858 | |
| 859 | @defun derived-mode-p &rest modes |
| 860 | This function returns non-@code{nil} if the current major mode is |
| 861 | derived from any of the major modes given by the symbols @var{modes}. |
| 862 | @end defun |
| 863 | |
| 864 | @node Basic Major Modes |
| 865 | @subsection Basic Major Modes |
| 866 | |
| 867 | Apart from Fundamental mode, there are three major modes that other |
| 868 | major modes commonly derive from: Text mode, Prog mode, and Special |
| 869 | mode. While Text mode is useful in its own right (e.g., for editing |
| 870 | files ending in @file{.txt}), Prog mode and Special mode exist mainly to |
| 871 | let other modes derive from them. |
| 872 | |
| 873 | @vindex prog-mode-hook |
| 874 | As far as possible, new major modes should be derived, either directly |
| 875 | or indirectly, from one of these three modes. One reason is that this |
| 876 | allows users to customize a single mode hook |
| 877 | (e.g., @code{prog-mode-hook}) for an entire family of relevant modes |
| 878 | (e.g., all programming language modes). |
| 879 | |
| 880 | @deffn Command text-mode |
| 881 | Text mode is a major mode for editing human languages. It defines the |
| 882 | @samp{"} and @samp{\} characters as having punctuation syntax |
| 883 | (@pxref{Syntax Class Table}), and binds @kbd{M-@key{TAB}} to |
| 884 | @code{ispell-complete-word} (@pxref{Spelling,,, emacs, The GNU Emacs |
| 885 | Manual}). |
| 886 | |
| 887 | An example of a major mode derived from Text mode is HTML mode. |
| 888 | @xref{HTML Mode,,SGML and HTML Modes, emacs, The GNU Emacs Manual}. |
| 889 | @end deffn |
| 890 | |
| 891 | @deffn Command prog-mode |
| 892 | Prog mode is a basic major mode for buffers containing programming |
| 893 | language source code. Most of the programming language major modes |
| 894 | built into Emacs are derived from it. |
| 895 | |
| 896 | Prog mode binds @code{parse-sexp-ignore-comments} to @code{t} |
| 897 | (@pxref{Motion via Parsing}) and @code{bidi-paragraph-direction} to |
| 898 | @code{left-to-right} (@pxref{Bidirectional Display}). |
| 899 | @end deffn |
| 900 | |
| 901 | @deffn Command special-mode |
| 902 | Special mode is a basic major mode for buffers containing text that is |
| 903 | produced specially by Emacs, rather than directly from a file. Major |
| 904 | modes derived from Special mode are given a @code{mode-class} property |
| 905 | of @code{special} (@pxref{Major Mode Conventions}). |
| 906 | |
| 907 | Special mode sets the buffer to read-only. Its keymap defines several |
| 908 | common bindings, including @kbd{q} for @code{quit-window} and @kbd{g} |
| 909 | for @code{revert-buffer} (@pxref{Reverting}). |
| 910 | |
| 911 | An example of a major mode derived from Special mode is Buffer Menu |
| 912 | mode, which is used by the @file{*Buffer List*} buffer. @xref{List |
| 913 | Buffers,,Listing Existing Buffers, emacs, The GNU Emacs Manual}. |
| 914 | @end deffn |
| 915 | |
| 916 | In addition, modes for buffers of tabulated data can inherit from |
| 917 | Tabulated List mode, which is in turn derived from Special mode. |
| 918 | @xref{Tabulated List Mode}. |
| 919 | |
| 920 | @node Mode Hooks |
| 921 | @subsection Mode Hooks |
| 922 | |
| 923 | Every major mode command should finish by running the mode-independent |
| 924 | normal hook @code{change-major-mode-after-body-hook}, its mode hook, |
| 925 | and the normal hook @code{after-change-major-mode-hook}. |
| 926 | It does this by calling @code{run-mode-hooks}. If the major mode is a |
| 927 | derived mode, that is if it calls another major mode (the parent mode) |
| 928 | in its body, it should do this inside @code{delay-mode-hooks} so that |
| 929 | the parent won't run these hooks itself. Instead, the derived mode's |
| 930 | call to @code{run-mode-hooks} runs the parent's mode hook too. |
| 931 | @xref{Major Mode Conventions}. |
| 932 | |
| 933 | Emacs versions before Emacs 22 did not have @code{delay-mode-hooks}. |
| 934 | Versions before 24 did not have @code{change-major-mode-after-body-hook}. |
| 935 | When user-implemented major modes do not use @code{run-mode-hooks} and |
| 936 | have not been updated to use these newer features, they won't entirely |
| 937 | follow these conventions: they may run the parent's mode hook too early, |
| 938 | or fail to run @code{after-change-major-mode-hook}. If you encounter |
| 939 | such a major mode, please correct it to follow these conventions. |
| 940 | |
| 941 | When you defined a major mode using @code{define-derived-mode}, it |
| 942 | automatically makes sure these conventions are followed. If you |
| 943 | define a major mode ``by hand'', not using @code{define-derived-mode}, |
| 944 | use the following functions to handle these conventions automatically. |
| 945 | |
| 946 | @defun run-mode-hooks &rest hookvars |
| 947 | Major modes should run their mode hook using this function. It is |
| 948 | similar to @code{run-hooks} (@pxref{Hooks}), but it also runs |
| 949 | @code{change-major-mode-after-body-hook} and |
| 950 | @code{after-change-major-mode-hook}. |
| 951 | |
| 952 | When this function is called during the execution of a |
| 953 | @code{delay-mode-hooks} form, it does not run the hooks immediately. |
| 954 | Instead, it arranges for the next call to @code{run-mode-hooks} to run |
| 955 | them. |
| 956 | @end defun |
| 957 | |
| 958 | @defmac delay-mode-hooks body@dots{} |
| 959 | When one major mode command calls another, it should do so inside of |
| 960 | @code{delay-mode-hooks}. |
| 961 | |
| 962 | This macro executes @var{body}, but tells all @code{run-mode-hooks} |
| 963 | calls during the execution of @var{body} to delay running their hooks. |
| 964 | The hooks will actually run during the next call to |
| 965 | @code{run-mode-hooks} after the end of the @code{delay-mode-hooks} |
| 966 | construct. |
| 967 | @end defmac |
| 968 | |
| 969 | @defvar change-major-mode-after-body-hook |
| 970 | This is a normal hook run by @code{run-mode-hooks}. It is run before |
| 971 | the mode hooks. |
| 972 | @end defvar |
| 973 | |
| 974 | @defvar after-change-major-mode-hook |
| 975 | This is a normal hook run by @code{run-mode-hooks}. It is run at the |
| 976 | very end of every properly-written major mode command. |
| 977 | @end defvar |
| 978 | |
| 979 | @node Tabulated List Mode |
| 980 | @subsection Tabulated List mode |
| 981 | @cindex Tabulated List mode |
| 982 | |
| 983 | Tabulated List mode is a major mode for displaying tabulated data, |
| 984 | i.e., data consisting of @dfn{entries}, each entry occupying one row of |
| 985 | text with its contents divided into columns. Tabulated List mode |
| 986 | provides facilities for pretty-printing rows and columns, and sorting |
| 987 | the rows according to the values in each column. It is derived from |
| 988 | Special mode (@pxref{Basic Major Modes}). |
| 989 | |
| 990 | Tabulated List mode is intended to be used as a parent mode by a more |
| 991 | specialized major mode. Examples include Process Menu mode |
| 992 | (@pxref{Process Information}) and Package Menu mode (@pxref{Package |
| 993 | Menu,,, emacs, The GNU Emacs Manual}). |
| 994 | |
| 995 | @findex tabulated-list-mode |
| 996 | Such a derived mode should use @code{define-derived-mode} in the usual |
| 997 | way, specifying @code{tabulated-list-mode} as the second argument |
| 998 | (@pxref{Derived Modes}). The body of the @code{define-derived-mode} |
| 999 | form should specify the format of the tabulated data, by assigning |
| 1000 | values to the variables documented below; then, it should call the |
| 1001 | function @code{tabulated-list-init-header} to initialize the header |
| 1002 | line. |
| 1003 | |
| 1004 | The derived mode should also define a @dfn{listing command}. This, |
| 1005 | not the mode command, is what the user calls (e.g., @kbd{M-x |
| 1006 | list-processes}). The listing command should create or switch to a |
| 1007 | buffer, turn on the derived mode, specify the tabulated data, and |
| 1008 | finally call @code{tabulated-list-print} to populate the buffer. |
| 1009 | |
| 1010 | @defvar tabulated-list-format |
| 1011 | This buffer-local variable specifies the format of the Tabulated List |
| 1012 | data. Its value should be a vector. Each element of the vector |
| 1013 | represents a data column, and should be a list @code{(@var{name} |
| 1014 | @var{width} @var{sort})}, where |
| 1015 | |
| 1016 | @itemize |
| 1017 | @item |
| 1018 | @var{name} is the column's name (a string). |
| 1019 | |
| 1020 | @item |
| 1021 | @var{width} is the width to reserve for the column (an integer). This |
| 1022 | is meaningless for the last column, which runs to the end of each line. |
| 1023 | |
| 1024 | @item |
| 1025 | @var{sort} specifies how to sort entries by the column. If @code{nil}, |
| 1026 | the column cannot be used for sorting. If @code{t}, the column is |
| 1027 | sorted by comparing string values. Otherwise, this should be a |
| 1028 | predicate function for @code{sort} (@pxref{Rearrangement}), which |
| 1029 | accepts two arguments with the same form as the elements of |
| 1030 | @code{tabulated-list-entries} (see below). |
| 1031 | @end itemize |
| 1032 | @end defvar |
| 1033 | |
| 1034 | @defvar tabulated-list-entries |
| 1035 | This buffer-local variable specifies the entries displayed in the |
| 1036 | Tabulated List buffer. Its value should be either a list, or a |
| 1037 | function. |
| 1038 | |
| 1039 | If the value is a list, each list element corresponds to one entry, and |
| 1040 | should have the form @w{@code{(@var{id} @var{contents})}}, where |
| 1041 | |
| 1042 | @itemize |
| 1043 | @item |
| 1044 | @var{id} is either @code{nil}, or a Lisp object that identifies the |
| 1045 | entry. If the latter, the cursor stays on the ``same'' entry when |
| 1046 | re-sorting entries. Comparison is done with @code{equal}. |
| 1047 | |
| 1048 | @item |
| 1049 | @var{contents} is a vector with the same number of elements as |
| 1050 | @code{tabulated-list-format}. Each vector element is either a string, |
| 1051 | which is inserted into the buffer as-is, or a list @code{(@var{label} |
| 1052 | . @var{properties})}, which means to insert a text button by calling |
| 1053 | @code{insert-text-button} with @var{label} and @var{properties} as |
| 1054 | arguments (@pxref{Making Buttons}). |
| 1055 | |
| 1056 | There should be no newlines in any of these strings. |
| 1057 | @end itemize |
| 1058 | |
| 1059 | Otherwise, the value should be a function which returns a list of the |
| 1060 | above form when called with no arguments. |
| 1061 | @end defvar |
| 1062 | |
| 1063 | @defvar tabulated-list-revert-hook |
| 1064 | This normal hook is run prior to reverting a Tabulated List buffer. A |
| 1065 | derived mode can add a function to this hook to recompute |
| 1066 | @code{tabulated-list-entries}. |
| 1067 | @end defvar |
| 1068 | |
| 1069 | @defvar tabulated-list-printer |
| 1070 | The value of this variable is the function called to insert an entry at |
| 1071 | point, including its terminating newline. The function should accept |
| 1072 | two arguments, @var{id} and @var{contents}, having the same meanings as |
| 1073 | in @code{tabulated-list-entries}. The default value is a function which |
| 1074 | inserts an entry in a straightforward way; a mode which uses Tabulated |
| 1075 | List mode in a more complex way can specify another function. |
| 1076 | @end defvar |
| 1077 | |
| 1078 | @defvar tabulated-list-sort-key |
| 1079 | The value of this variable specifies the current sort key for the |
| 1080 | Tabulated List buffer. If it is @code{nil}, no sorting is done. |
| 1081 | Otherwise, it should have the form @code{(@var{name} . @var{flip})}, |
| 1082 | where @var{name} is a string matching one of the column names in |
| 1083 | @code{tabulated-list-format}, and @var{flip}, if non-@code{nil}, means |
| 1084 | to invert the sort order. |
| 1085 | @end defvar |
| 1086 | |
| 1087 | @defun tabulated-list-init-header |
| 1088 | This function computes and sets @code{header-line-format} for the |
| 1089 | Tabulated List buffer (@pxref{Header Lines}), and assigns a keymap to |
| 1090 | the header line to allow sort entries by clicking on column headers. |
| 1091 | |
| 1092 | Modes derived from Tabulated List mode should call this after setting |
| 1093 | the above variables (in particular, only after setting |
| 1094 | @code{tabulated-list-format}). |
| 1095 | @end defun |
| 1096 | |
| 1097 | @defun tabulated-list-print &optional remember-pos |
| 1098 | This function populates the current buffer with entries. It should be |
| 1099 | called by the listing command. It erases the buffer, sorts the entries |
| 1100 | specified by @code{tabulated-list-entries} according to |
| 1101 | @code{tabulated-list-sort-key}, then calls the function specified by |
| 1102 | @code{tabulated-list-printer} to insert each entry. |
| 1103 | |
| 1104 | If the optional argument @var{remember-pos} is non-@code{nil}, this |
| 1105 | function looks for the @var{id} element on the current line, if any, and |
| 1106 | tries to move to that entry after all the entries are (re)inserted. |
| 1107 | @end defun |
| 1108 | |
| 1109 | @node Generic Modes |
| 1110 | @subsection Generic Modes |
| 1111 | @cindex generic mode |
| 1112 | |
| 1113 | @dfn{Generic modes} are simple major modes with basic support for |
| 1114 | comment syntax and Font Lock mode. To define a generic mode, use the |
| 1115 | macro @code{define-generic-mode}. See the file @file{generic-x.el} |
| 1116 | for some examples of the use of @code{define-generic-mode}. |
| 1117 | |
| 1118 | @defmac define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring |
| 1119 | This macro defines a generic mode command named @var{mode} (a symbol, |
| 1120 | not quoted). The optional argument @var{docstring} is the |
| 1121 | documentation for the mode command. If you do not supply it, |
| 1122 | @code{define-generic-mode} generates one by default. |
| 1123 | |
| 1124 | The argument @var{comment-list} is a list in which each element is |
| 1125 | either a character, a string of one or two characters, or a cons cell. |
| 1126 | A character or a string is set up in the mode's syntax table as a |
| 1127 | ``comment starter''. If the entry is a cons cell, the @sc{car} is set |
| 1128 | up as a ``comment starter'' and the @sc{cdr} as a ``comment ender''. |
| 1129 | (Use @code{nil} for the latter if you want comments to end at the end |
| 1130 | of the line.) Note that the syntax table mechanism has limitations |
| 1131 | about what comment starters and enders are actually possible. |
| 1132 | @xref{Syntax Tables}. |
| 1133 | |
| 1134 | The argument @var{keyword-list} is a list of keywords to highlight |
| 1135 | with @code{font-lock-keyword-face}. Each keyword should be a string. |
| 1136 | Meanwhile, @var{font-lock-list} is a list of additional expressions to |
| 1137 | highlight. Each element of this list should have the same form as an |
| 1138 | element of @code{font-lock-keywords}. @xref{Search-based |
| 1139 | Fontification}. |
| 1140 | |
| 1141 | The argument @var{auto-mode-list} is a list of regular expressions to |
| 1142 | add to the variable @code{auto-mode-alist}. They are added by the execution |
| 1143 | of the @code{define-generic-mode} form, not by expanding the macro call. |
| 1144 | |
| 1145 | Finally, @var{function-list} is a list of functions for the mode |
| 1146 | command to call for additional setup. It calls these functions just |
| 1147 | before it runs the mode hook variable @code{@var{mode}-hook}. |
| 1148 | @end defmac |
| 1149 | |
| 1150 | @node Example Major Modes |
| 1151 | @subsection Major Mode Examples |
| 1152 | |
| 1153 | Text mode is perhaps the simplest mode besides Fundamental mode. |
| 1154 | Here are excerpts from @file{text-mode.el} that illustrate many of |
| 1155 | the conventions listed above: |
| 1156 | |
| 1157 | @smallexample |
| 1158 | @group |
| 1159 | ;; @r{Create the syntax table for this mode.} |
| 1160 | (defvar text-mode-syntax-table |
| 1161 | (let ((st (make-syntax-table))) |
| 1162 | (modify-syntax-entry ?\" ". " st) |
| 1163 | (modify-syntax-entry ?\\ ". " st) |
| 1164 | ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. |
| 1165 | (modify-syntax-entry ?' "w p" st) |
| 1166 | st) |
| 1167 | "Syntax table used while in `text-mode'.") |
| 1168 | @end group |
| 1169 | |
| 1170 | ;; @r{Create the keymap for this mode.} |
| 1171 | @group |
| 1172 | (defvar text-mode-map |
| 1173 | (let ((map (make-sparse-keymap))) |
| 1174 | (define-key map "\e\t" 'ispell-complete-word) |
| 1175 | map) |
| 1176 | "Keymap for `text-mode'. |
| 1177 | Many other modes, such as `mail-mode', `outline-mode' and |
| 1178 | `indented-text-mode', inherit all the commands defined in this map.") |
| 1179 | @end group |
| 1180 | @end smallexample |
| 1181 | |
| 1182 | Here is how the actual mode command is defined now: |
| 1183 | |
| 1184 | @smallexample |
| 1185 | @group |
| 1186 | (define-derived-mode text-mode nil "Text" |
| 1187 | "Major mode for editing text written for humans to read. |
| 1188 | In this mode, paragraphs are delimited only by blank or white lines. |
| 1189 | You can thus get the full benefit of adaptive filling |
| 1190 | (see the variable `adaptive-fill-mode'). |
| 1191 | \\@{text-mode-map@} |
| 1192 | Turning on Text mode runs the normal hook `text-mode-hook'." |
| 1193 | @end group |
| 1194 | @group |
| 1195 | (set (make-local-variable 'text-mode-variant) t) |
| 1196 | (set (make-local-variable 'require-final-newline) |
| 1197 | mode-require-final-newline) |
| 1198 | (set (make-local-variable 'indent-line-function) 'indent-relative)) |
| 1199 | @end group |
| 1200 | @end smallexample |
| 1201 | |
| 1202 | @noindent |
| 1203 | (The last line is redundant nowadays, since @code{indent-relative} is |
| 1204 | the default value, and we'll delete it in a future version.) |
| 1205 | |
| 1206 | @cindex @file{lisp-mode.el} |
| 1207 | The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction |
| 1208 | mode) have more features than Text mode and the code is correspondingly |
| 1209 | more complicated. Here are excerpts from @file{lisp-mode.el} that |
| 1210 | illustrate how these modes are written. |
| 1211 | |
| 1212 | Here is how the Lisp mode syntax and abbrev tables are defined: |
| 1213 | |
| 1214 | @cindex syntax table example |
| 1215 | @smallexample |
| 1216 | @group |
| 1217 | ;; @r{Create mode-specific table variables.} |
| 1218 | (defvar lisp-mode-abbrev-table nil) |
| 1219 | (define-abbrev-table 'lisp-mode-abbrev-table ()) |
| 1220 | |
| 1221 | (defvar lisp-mode-syntax-table |
| 1222 | (let ((table (copy-syntax-table emacs-lisp-mode-syntax-table))) |
| 1223 | (modify-syntax-entry ?\[ "_ " table) |
| 1224 | (modify-syntax-entry ?\] "_ " table) |
| 1225 | (modify-syntax-entry ?# "' 14" table) |
| 1226 | (modify-syntax-entry ?| "\" 23bn" table) |
| 1227 | table) |
| 1228 | "Syntax table used in `lisp-mode'.") |
| 1229 | @end group |
| 1230 | @end smallexample |
| 1231 | |
| 1232 | The three modes for Lisp share much of their code. For instance, |
| 1233 | each calls the following function to set various variables: |
| 1234 | |
| 1235 | @smallexample |
| 1236 | @group |
| 1237 | (defun lisp-mode-variables (&optional syntax keywords-case-insensitive) |
| 1238 | (when syntax |
| 1239 | (set-syntax-table lisp-mode-syntax-table)) |
| 1240 | (setq local-abbrev-table lisp-mode-abbrev-table) |
| 1241 | @dots{} |
| 1242 | @end group |
| 1243 | @end smallexample |
| 1244 | |
| 1245 | @noindent |
| 1246 | Amongst other things, this function sets up the @code{comment-start} |
| 1247 | variable to handle Lisp comments: |
| 1248 | |
| 1249 | @smallexample |
| 1250 | @group |
| 1251 | (make-local-variable 'comment-start) |
| 1252 | (setq comment-start ";") |
| 1253 | @dots{} |
| 1254 | @end group |
| 1255 | @end smallexample |
| 1256 | |
| 1257 | Each of the different Lisp modes has a slightly different keymap. For |
| 1258 | example, Lisp mode binds @kbd{C-c C-z} to @code{run-lisp}, but the other |
| 1259 | Lisp modes do not. However, all Lisp modes have some commands in |
| 1260 | common. The following code sets up the common commands: |
| 1261 | |
| 1262 | @smallexample |
| 1263 | @group |
| 1264 | (defvar lisp-mode-shared-map |
| 1265 | (let ((map (make-sparse-keymap))) |
| 1266 | (define-key map "\e\C-q" 'indent-sexp) |
| 1267 | (define-key map "\177" 'backward-delete-char-untabify) |
| 1268 | map) |
| 1269 | "Keymap for commands shared by all sorts of Lisp modes.") |
| 1270 | @end group |
| 1271 | @end smallexample |
| 1272 | |
| 1273 | @noindent |
| 1274 | And here is the code to set up the keymap for Lisp mode: |
| 1275 | |
| 1276 | @smallexample |
| 1277 | @group |
| 1278 | (defvar lisp-mode-map |
| 1279 | (let ((map (make-sparse-keymap)) |
| 1280 | (menu-map (make-sparse-keymap "Lisp"))) |
| 1281 | (set-keymap-parent map lisp-mode-shared-map) |
| 1282 | (define-key map "\e\C-x" 'lisp-eval-defun) |
| 1283 | (define-key map "\C-c\C-z" 'run-lisp) |
| 1284 | @dots{} |
| 1285 | map) |
| 1286 | "Keymap for ordinary Lisp mode. |
| 1287 | All commands in `lisp-mode-shared-map' are inherited by this map.") |
| 1288 | @end group |
| 1289 | @end smallexample |
| 1290 | |
| 1291 | @noindent |
| 1292 | Finally, here is the major mode command for Lisp mode: |
| 1293 | |
| 1294 | @smallexample |
| 1295 | @group |
| 1296 | (define-derived-mode lisp-mode prog-mode "Lisp" |
| 1297 | "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. |
| 1298 | Commands: |
| 1299 | Delete converts tabs to spaces as it moves back. |
| 1300 | Blank lines separate paragraphs. Semicolons start comments. |
| 1301 | |
| 1302 | \\@{lisp-mode-map@} |
| 1303 | Note that `run-lisp' may be used either to start an inferior Lisp job |
| 1304 | or to switch back to an existing one. |
| 1305 | @end group |
| 1306 | |
| 1307 | @group |
| 1308 | Entry to this mode calls the value of `lisp-mode-hook' |
| 1309 | if that value is non-nil." |
| 1310 | (lisp-mode-variables nil t) |
| 1311 | (set (make-local-variable 'find-tag-default-function) |
| 1312 | 'lisp-find-tag-default) |
| 1313 | (set (make-local-variable 'comment-start-skip) |
| 1314 | "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") |
| 1315 | (setq imenu-case-fold-search t)) |
| 1316 | @end group |
| 1317 | @end smallexample |
| 1318 | |
| 1319 | @node Minor Modes |
| 1320 | @section Minor Modes |
| 1321 | @cindex minor mode |
| 1322 | |
| 1323 | A @dfn{minor mode} provides optional features that users may enable or |
| 1324 | disable independently of the choice of major mode. Minor modes can be |
| 1325 | enabled individually or in combination. |
| 1326 | |
| 1327 | Most minor modes implement features that are independent of the major |
| 1328 | mode, and can thus be used with most major modes. For example, Auto |
| 1329 | Fill mode works with any major mode that permits text insertion. A few |
| 1330 | minor modes, however, are specific to a particular major mode. For |
| 1331 | example, Diff Auto Refine mode is a minor mode that is intended to be |
| 1332 | used only with Diff mode. |
| 1333 | |
| 1334 | Ideally, a minor mode should have its desired effect regardless of the |
| 1335 | other minor modes in effect. It should be possible to activate and |
| 1336 | deactivate minor modes in any order. |
| 1337 | |
| 1338 | @defvar minor-mode-list |
| 1339 | The value of this variable is a list of all minor mode commands. |
| 1340 | @end defvar |
| 1341 | |
| 1342 | @menu |
| 1343 | * Minor Mode Conventions:: Tips for writing a minor mode. |
| 1344 | * Keymaps and Minor Modes:: How a minor mode can have its own keymap. |
| 1345 | * Defining Minor Modes:: A convenient facility for defining minor modes. |
| 1346 | @end menu |
| 1347 | |
| 1348 | @node Minor Mode Conventions |
| 1349 | @subsection Conventions for Writing Minor Modes |
| 1350 | @cindex minor mode conventions |
| 1351 | @cindex conventions for writing minor modes |
| 1352 | |
| 1353 | There are conventions for writing minor modes just as there are for |
| 1354 | major modes. These conventions are described below. The easiest way to |
| 1355 | follow them is to use the macro @code{define-minor-mode}. |
| 1356 | @xref{Defining Minor Modes}. |
| 1357 | |
| 1358 | @itemize @bullet |
| 1359 | @item |
| 1360 | @cindex mode variable |
| 1361 | Define a variable whose name ends in @samp{-mode}. We call this the |
| 1362 | @dfn{mode variable}. The minor mode command should set this variable. |
| 1363 | The value will be @code{nil} if the mode is disabled, and non-@code{nil} |
| 1364 | if the mode is enabled. The variable should be buffer-local if the |
| 1365 | minor mode is buffer-local. |
| 1366 | |
| 1367 | This variable is used in conjunction with the @code{minor-mode-alist} to |
| 1368 | display the minor mode name in the mode line. It also determines |
| 1369 | whether the minor mode keymap is active, via @code{minor-mode-map-alist} |
| 1370 | (@pxref{Controlling Active Maps}). Individual commands or hooks can |
| 1371 | also check its value. |
| 1372 | |
| 1373 | @item |
| 1374 | Define a command, called the @dfn{mode command}, whose name is the same |
| 1375 | as the mode variable. Its job is to set the value of the mode variable, |
| 1376 | plus anything else that needs to be done to actually enable or disable |
| 1377 | the mode's features. |
| 1378 | |
| 1379 | The mode command should accept one optional argument. If called |
| 1380 | interactively with no prefix argument, it should toggle the mode |
| 1381 | (i.e., enable if it is disabled, and disable if it is enabled). If |
| 1382 | called interactively with a prefix argument, it should enable the mode |
| 1383 | if the argument is positive and disable it otherwise. |
| 1384 | |
| 1385 | If the mode command is called from Lisp (i.e., non-interactively), it |
| 1386 | should enable the mode if the argument is omitted or @code{nil}; it |
| 1387 | should toggle the mode if the argument is the symbol @code{toggle}; |
| 1388 | otherwise it should treat the argument in the same way as for an |
| 1389 | interactive call with a numeric prefix argument, as described above. |
| 1390 | |
| 1391 | The following example shows how to implement this behavior (it is |
| 1392 | similar to the code generated by the @code{define-minor-mode} macro): |
| 1393 | |
| 1394 | @example |
| 1395 | (interactive (list (or current-prefix-arg 'toggle))) |
| 1396 | (let ((enable (if (eq arg 'toggle) |
| 1397 | (not foo-mode) ; @r{this mode's mode variable} |
| 1398 | (> (prefix-numeric-value arg) 0)))) |
| 1399 | (if enable |
| 1400 | @var{do-enable} |
| 1401 | @var{do-disable})) |
| 1402 | @end example |
| 1403 | |
| 1404 | The reason for this somewhat complex behavior is that it lets users |
| 1405 | easily toggle the minor mode interactively, and also lets the minor mode |
| 1406 | be easily enabled in a mode hook, like this: |
| 1407 | |
| 1408 | @example |
| 1409 | (add-hook 'text-mode-hook 'foo-mode) |
| 1410 | @end example |
| 1411 | |
| 1412 | @noindent |
| 1413 | This behaves correctly whether or not @code{foo-mode} was already |
| 1414 | enabled, since the @code{foo-mode} mode command unconditionally enables |
| 1415 | the minor mode when it is called from Lisp with no argument. Disabling |
| 1416 | a minor mode in a mode hook is a little uglier: |
| 1417 | |
| 1418 | @example |
| 1419 | (add-hook 'text-mode-hook (lambda () (foo-mode -1))) |
| 1420 | @end example |
| 1421 | |
| 1422 | @noindent |
| 1423 | However, this is not very commonly done. |
| 1424 | |
| 1425 | @item |
| 1426 | Add an element to @code{minor-mode-alist} for each minor mode |
| 1427 | (@pxref{Definition of minor-mode-alist}), if you want to indicate the |
| 1428 | minor mode in the mode line. This element should be a list of the |
| 1429 | following form: |
| 1430 | |
| 1431 | @smallexample |
| 1432 | (@var{mode-variable} @var{string}) |
| 1433 | @end smallexample |
| 1434 | |
| 1435 | Here @var{mode-variable} is the variable that controls enabling of the |
| 1436 | minor mode, and @var{string} is a short string, starting with a space, |
| 1437 | to represent the mode in the mode line. These strings must be short so |
| 1438 | that there is room for several of them at once. |
| 1439 | |
| 1440 | When you add an element to @code{minor-mode-alist}, use @code{assq} to |
| 1441 | check for an existing element, to avoid duplication. For example: |
| 1442 | |
| 1443 | @smallexample |
| 1444 | @group |
| 1445 | (unless (assq 'leif-mode minor-mode-alist) |
| 1446 | (push '(leif-mode " Leif") minor-mode-alist)) |
| 1447 | @end group |
| 1448 | @end smallexample |
| 1449 | |
| 1450 | @noindent |
| 1451 | or like this, using @code{add-to-list} (@pxref{List Variables}): |
| 1452 | |
| 1453 | @smallexample |
| 1454 | @group |
| 1455 | (add-to-list 'minor-mode-alist '(leif-mode " Leif")) |
| 1456 | @end group |
| 1457 | @end smallexample |
| 1458 | @end itemize |
| 1459 | |
| 1460 | In addition, several major mode conventions apply to minor modes as |
| 1461 | well: those regarding the names of global symbols, the use of a hook at |
| 1462 | the end of the initialization function, and the use of keymaps and other |
| 1463 | tables. |
| 1464 | |
| 1465 | The minor mode should, if possible, support enabling and disabling via |
| 1466 | Custom (@pxref{Customization}). To do this, the mode variable should be |
| 1467 | defined with @code{defcustom}, usually with @code{:type 'boolean}. If |
| 1468 | just setting the variable is not sufficient to enable the mode, you |
| 1469 | should also specify a @code{:set} method which enables the mode by |
| 1470 | invoking the mode command. Note in the variable's documentation string |
| 1471 | that setting the variable other than via Custom may not take effect. |
| 1472 | Also, mark the definition with an autoload cookie (@pxref{autoload |
| 1473 | cookie}), and specify a @code{:require} so that customizing the variable |
| 1474 | will load the library that defines the mode. For example: |
| 1475 | |
| 1476 | @smallexample |
| 1477 | @group |
| 1478 | ;;;###autoload |
| 1479 | (defcustom msb-mode nil |
| 1480 | "Toggle msb-mode. |
| 1481 | Setting this variable directly does not take effect; |
| 1482 | use either \\[customize] or the function `msb-mode'." |
| 1483 | :set 'custom-set-minor-mode |
| 1484 | :initialize 'custom-initialize-default |
| 1485 | :version "20.4" |
| 1486 | :type 'boolean |
| 1487 | :group 'msb |
| 1488 | :require 'msb) |
| 1489 | @end group |
| 1490 | @end smallexample |
| 1491 | |
| 1492 | @node Keymaps and Minor Modes |
| 1493 | @subsection Keymaps and Minor Modes |
| 1494 | |
| 1495 | Each minor mode can have its own keymap, which is active when the mode |
| 1496 | is enabled. To set up a keymap for a minor mode, add an element to the |
| 1497 | alist @code{minor-mode-map-alist}. @xref{Definition of minor-mode-map-alist}. |
| 1498 | |
| 1499 | @cindex @code{self-insert-command}, minor modes |
| 1500 | One use of minor mode keymaps is to modify the behavior of certain |
| 1501 | self-inserting characters so that they do something else as well as |
| 1502 | self-insert. (Another way to customize @code{self-insert-command} is |
| 1503 | through @code{post-self-insert-hook}. Apart from this, the facilities |
| 1504 | for customizing @code{self-insert-command} are limited to special cases, |
| 1505 | designed for abbrevs and Auto Fill mode. Do not try substituting your |
| 1506 | own definition of @code{self-insert-command} for the standard one. The |
| 1507 | editor command loop handles this function specially.) |
| 1508 | |
| 1509 | Minor modes may bind commands to key sequences consisting of @kbd{C-c} |
| 1510 | followed by a punctuation character. However, sequences consisting of |
| 1511 | @kbd{C-c} followed by one of @kbd{@{@}<>:;}, or a control character or |
| 1512 | digit, are reserved for major modes. Also, @kbd{C-c @var{letter}} is |
| 1513 | reserved for users. @xref{Key Binding Conventions}. |
| 1514 | |
| 1515 | @node Defining Minor Modes |
| 1516 | @subsection Defining Minor Modes |
| 1517 | |
| 1518 | The macro @code{define-minor-mode} offers a convenient way of |
| 1519 | implementing a mode in one self-contained definition. |
| 1520 | |
| 1521 | @defmac define-minor-mode mode doc [init-value [lighter [keymap]]] keyword-args@dots{} body@dots{} |
| 1522 | This macro defines a new minor mode whose name is @var{mode} (a |
| 1523 | symbol). It defines a command named @var{mode} to toggle the minor |
| 1524 | mode, with @var{doc} as its documentation string. |
| 1525 | |
| 1526 | The toggle command takes one optional (prefix) argument. |
| 1527 | If called interactively with no argument it toggles the mode on or off. |
| 1528 | A positive prefix argument enables the mode, any other prefix argument |
| 1529 | disables it. From Lisp, an argument of @code{toggle} toggles the mode, |
| 1530 | whereas an omitted or @code{nil} argument enables the mode. |
| 1531 | This makes it easy to enable the minor mode in a major mode hook, for example. |
| 1532 | If @var{doc} is nil, the macro supplies a default documentation string |
| 1533 | explaining the above. |
| 1534 | |
| 1535 | By default, it also defines a variable named @var{mode}, which is set to |
| 1536 | @code{t} or @code{nil} by enabling or disabling the mode. The variable |
| 1537 | is initialized to @var{init-value}. Except in unusual circumstances |
| 1538 | (see below), this value must be @code{nil}. |
| 1539 | |
| 1540 | The string @var{lighter} says what to display in the mode line |
| 1541 | when the mode is enabled; if it is @code{nil}, the mode is not displayed |
| 1542 | in the mode line. |
| 1543 | |
| 1544 | The optional argument @var{keymap} specifies the keymap for the minor |
| 1545 | mode. If non-@code{nil}, it should be a variable name (whose value is |
| 1546 | a keymap), a keymap, or an alist of the form |
| 1547 | |
| 1548 | @example |
| 1549 | (@var{key-sequence} . @var{definition}) |
| 1550 | @end example |
| 1551 | |
| 1552 | @noindent |
| 1553 | where each @var{key-sequence} and @var{definition} are arguments |
| 1554 | suitable for passing to @code{define-key} (@pxref{Changing Key |
| 1555 | Bindings}). If @var{keymap} is a keymap or an alist, this also |
| 1556 | defines the variable @code{@var{mode}-map}. |
| 1557 | |
| 1558 | The above three arguments @var{init-value}, @var{lighter}, and |
| 1559 | @var{keymap} can be (partially) omitted when @var{keyword-args} are |
| 1560 | used. The @var{keyword-args} consist of keywords followed by |
| 1561 | corresponding values. A few keywords have special meanings: |
| 1562 | |
| 1563 | @table @code |
| 1564 | @item :group @var{group} |
| 1565 | Custom group name to use in all generated @code{defcustom} forms. |
| 1566 | Defaults to @var{mode} without the possible trailing @samp{-mode}. |
| 1567 | @strong{Warning:} don't use this default group name unless you have |
| 1568 | written a @code{defgroup} to define that group properly. @xref{Group |
| 1569 | Definitions}. |
| 1570 | |
| 1571 | @item :global @var{global} |
| 1572 | If non-@code{nil}, this specifies that the minor mode should be global |
| 1573 | rather than buffer-local. It defaults to @code{nil}. |
| 1574 | |
| 1575 | One of the effects of making a minor mode global is that the |
| 1576 | @var{mode} variable becomes a customization variable. Toggling it |
| 1577 | through the Customize interface turns the mode on and off, and its |
| 1578 | value can be saved for future Emacs sessions (@pxref{Saving |
| 1579 | Customizations,,, emacs, The GNU Emacs Manual}. For the saved |
| 1580 | variable to work, you should ensure that the @code{define-minor-mode} |
| 1581 | form is evaluated each time Emacs starts; for packages that are not |
| 1582 | part of Emacs, the easiest way to do this is to specify a |
| 1583 | @code{:require} keyword. |
| 1584 | |
| 1585 | @item :init-value @var{init-value} |
| 1586 | This is equivalent to specifying @var{init-value} positionally. |
| 1587 | |
| 1588 | @item :lighter @var{lighter} |
| 1589 | This is equivalent to specifying @var{lighter} positionally. |
| 1590 | |
| 1591 | @item :keymap @var{keymap} |
| 1592 | This is equivalent to specifying @var{keymap} positionally. |
| 1593 | |
| 1594 | @item :variable @var{place} |
| 1595 | This replaces the default variable @var{mode}, used to store the state |
| 1596 | of the mode. If you specify this, the @var{mode} variable is not |
| 1597 | defined, and any @var{init-value} argument is unused. @var{place} |
| 1598 | can be a different named variable (which you must define yourself), or |
| 1599 | anything that can be used with the @code{setf} function |
| 1600 | (@pxref{Generalized Variables}). |
| 1601 | @var{place} can also be a cons @code{(@var{get} . @var{set})}, |
| 1602 | where @var{get} is an expression that returns the current state, |
| 1603 | and @var{set} is a function of one argument (a state) that sets it. |
| 1604 | |
| 1605 | @item :after-hook @var{after-hook} |
| 1606 | This defines a single Lisp form which is evaluated after the mode hooks |
| 1607 | have run. It should not be quoted. |
| 1608 | @end table |
| 1609 | |
| 1610 | Any other keyword arguments are passed directly to the |
| 1611 | @code{defcustom} generated for the variable @var{mode}. |
| 1612 | |
| 1613 | The command named @var{mode} first performs the standard actions such as |
| 1614 | setting the variable named @var{mode} and then executes the @var{body} |
| 1615 | forms, if any. It then runs the mode hook variable |
| 1616 | @code{@var{mode}-hook} and finishes by evaluating any form in |
| 1617 | @code{:after-hook}. |
| 1618 | @end defmac |
| 1619 | |
| 1620 | The initial value must be @code{nil} except in cases where (1) the |
| 1621 | mode is preloaded in Emacs, or (2) it is painless for loading to |
| 1622 | enable the mode even though the user did not request it. For |
| 1623 | instance, if the mode has no effect unless something else is enabled, |
| 1624 | and will always be loaded by that time, enabling it by default is |
| 1625 | harmless. But these are unusual circumstances. Normally, the |
| 1626 | initial value must be @code{nil}. |
| 1627 | |
| 1628 | @findex easy-mmode-define-minor-mode |
| 1629 | The name @code{easy-mmode-define-minor-mode} is an alias |
| 1630 | for this macro. |
| 1631 | |
| 1632 | Here is an example of using @code{define-minor-mode}: |
| 1633 | |
| 1634 | @smallexample |
| 1635 | (define-minor-mode hungry-mode |
| 1636 | "Toggle Hungry mode. |
| 1637 | Interactively with no argument, this command toggles the mode. |
| 1638 | A positive prefix argument enables the mode, any other prefix |
| 1639 | argument disables it. From Lisp, argument omitted or nil enables |
| 1640 | the mode, `toggle' toggles the state. |
| 1641 | |
| 1642 | When Hungry mode is enabled, the control delete key |
| 1643 | gobbles all preceding whitespace except the last. |
| 1644 | See the command \\[hungry-electric-delete]." |
| 1645 | ;; The initial value. |
| 1646 | nil |
| 1647 | ;; The indicator for the mode line. |
| 1648 | " Hungry" |
| 1649 | ;; The minor mode bindings. |
| 1650 | '(([C-backspace] . hungry-electric-delete)) |
| 1651 | :group 'hunger) |
| 1652 | @end smallexample |
| 1653 | |
| 1654 | @noindent |
| 1655 | This defines a minor mode named ``Hungry mode'', a command named |
| 1656 | @code{hungry-mode} to toggle it, a variable named @code{hungry-mode} |
| 1657 | which indicates whether the mode is enabled, and a variable named |
| 1658 | @code{hungry-mode-map} which holds the keymap that is active when the |
| 1659 | mode is enabled. It initializes the keymap with a key binding for |
| 1660 | @kbd{C-@key{DEL}}. It puts the variable @code{hungry-mode} into |
| 1661 | custom group @code{hunger}. There are no @var{body} forms---many |
| 1662 | minor modes don't need any. |
| 1663 | |
| 1664 | Here's an equivalent way to write it: |
| 1665 | |
| 1666 | @smallexample |
| 1667 | (define-minor-mode hungry-mode |
| 1668 | "Toggle Hungry mode. |
| 1669 | ...rest of documentation as before..." |
| 1670 | ;; The initial value. |
| 1671 | :init-value nil |
| 1672 | ;; The indicator for the mode line. |
| 1673 | :lighter " Hungry" |
| 1674 | ;; The minor mode bindings. |
| 1675 | :keymap |
| 1676 | '(([C-backspace] . hungry-electric-delete) |
| 1677 | ([C-M-backspace] |
| 1678 | . (lambda () |
| 1679 | (interactive) |
| 1680 | (hungry-electric-delete t)))) |
| 1681 | :group 'hunger) |
| 1682 | @end smallexample |
| 1683 | |
| 1684 | @defmac define-globalized-minor-mode global-mode mode turn-on keyword-args@dots{} |
| 1685 | This defines a global toggle named @var{global-mode} whose meaning is |
| 1686 | to enable or disable the buffer-local minor mode @var{mode} in all |
| 1687 | buffers. To turn on the minor mode in a buffer, it uses the function |
| 1688 | @var{turn-on}; to turn off the minor mode, it calls @var{mode} with |
| 1689 | @minus{}1 as argument. |
| 1690 | |
| 1691 | Globally enabling the mode also affects buffers subsequently created |
| 1692 | by visiting files, and buffers that use a major mode other than |
| 1693 | Fundamental mode; but it does not detect the creation of a new buffer |
| 1694 | in Fundamental mode. |
| 1695 | |
| 1696 | This defines the customization option @var{global-mode} (@pxref{Customization}), |
| 1697 | which can be toggled in the Customize interface to turn the minor mode on |
| 1698 | and off. As with @code{define-minor-mode}, you should ensure that the |
| 1699 | @code{define-globalized-minor-mode} form is evaluated each time Emacs |
| 1700 | starts, for example by providing a @code{:require} keyword. |
| 1701 | |
| 1702 | Use @code{:group @var{group}} in @var{keyword-args} to specify the |
| 1703 | custom group for the mode variable of the global minor mode. |
| 1704 | |
| 1705 | Generally speaking, when you define a globalized minor mode, you should |
| 1706 | also define a non-globalized version, so that people can use (or |
| 1707 | disable) it in individual buffers. This also allows them to disable a |
| 1708 | globally enabled minor mode in a specific major mode, by using that |
| 1709 | mode's hook. |
| 1710 | @end defmac |
| 1711 | |
| 1712 | |
| 1713 | @node Mode Line Format |
| 1714 | @section Mode Line Format |
| 1715 | @cindex mode line |
| 1716 | |
| 1717 | Each Emacs window (aside from minibuffer windows) typically has a mode |
| 1718 | line at the bottom, which displays status information about the buffer |
| 1719 | displayed in the window. The mode line contains information about the |
| 1720 | buffer, such as its name, associated file, depth of recursive editing, |
| 1721 | and major and minor modes. A window can also have a @dfn{header |
| 1722 | line}, which is much like the mode line but appears at the top of the |
| 1723 | window. |
| 1724 | |
| 1725 | This section describes how to control the contents of the mode line |
| 1726 | and header line. We include it in this chapter because much of the |
| 1727 | information displayed in the mode line relates to the enabled major and |
| 1728 | minor modes. |
| 1729 | |
| 1730 | @menu |
| 1731 | * Base: Mode Line Basics. Basic ideas of mode line control. |
| 1732 | * Data: Mode Line Data. The data structure that controls the mode line. |
| 1733 | * Top: Mode Line Top. The top level variable, mode-line-format. |
| 1734 | * Mode Line Variables:: Variables used in that data structure. |
| 1735 | * %-Constructs:: Putting information into a mode line. |
| 1736 | * Properties in Mode:: Using text properties in the mode line. |
| 1737 | * Header Lines:: Like a mode line, but at the top. |
| 1738 | * Emulating Mode Line:: Formatting text as the mode line would. |
| 1739 | @end menu |
| 1740 | |
| 1741 | @node Mode Line Basics |
| 1742 | @subsection Mode Line Basics |
| 1743 | |
| 1744 | The contents of each mode line are specified by the buffer-local |
| 1745 | variable @code{mode-line-format} (@pxref{Mode Line Top}). This variable |
| 1746 | holds a @dfn{mode line construct}: a template that controls what is |
| 1747 | displayed on the buffer's mode line. The value of |
| 1748 | @code{header-line-format} specifies the buffer's header line in the same |
| 1749 | way. All windows for the same buffer use the same |
| 1750 | @code{mode-line-format} and @code{header-line-format}. |
| 1751 | |
| 1752 | For efficiency, Emacs does not continuously recompute each window's |
| 1753 | mode line and header line. It does so when circumstances appear to call |
| 1754 | for it---for instance, if you change the window configuration, switch |
| 1755 | buffers, narrow or widen the buffer, scroll, or modify the buffer. If |
| 1756 | you alter any of the variables referenced by @code{mode-line-format} or |
| 1757 | @code{header-line-format} (@pxref{Mode Line Variables}), or any other |
| 1758 | data structures that affect how text is displayed (@pxref{Display}), you |
| 1759 | should use the function @code{force-mode-line-update} to update the |
| 1760 | display. |
| 1761 | |
| 1762 | @defun force-mode-line-update &optional all |
| 1763 | This function forces Emacs to update the current buffer's mode line and |
| 1764 | header line, based on the latest values of all relevant variables, |
| 1765 | during its next redisplay cycle. If the optional argument @var{all} is |
| 1766 | non-@code{nil}, it forces an update for all mode lines and header lines. |
| 1767 | |
| 1768 | This function also forces an update of the menu bar and frame title. |
| 1769 | @end defun |
| 1770 | |
| 1771 | The selected window's mode line is usually displayed in a different |
| 1772 | color using the face @code{mode-line}. Other windows' mode lines appear |
| 1773 | in the face @code{mode-line-inactive} instead. @xref{Faces}. |
| 1774 | |
| 1775 | @node Mode Line Data |
| 1776 | @subsection The Data Structure of the Mode Line |
| 1777 | @cindex mode line construct |
| 1778 | |
| 1779 | The mode line contents are controlled by a data structure called a |
| 1780 | @dfn{mode line construct}, made up of lists, strings, symbols, and |
| 1781 | numbers kept in buffer-local variables. Each data type has a specific |
| 1782 | meaning for the mode line appearance, as described below. The same data |
| 1783 | structure is used for constructing frame titles (@pxref{Frame Titles}) |
| 1784 | and header lines (@pxref{Header Lines}). |
| 1785 | |
| 1786 | A mode line construct may be as simple as a fixed string of text, |
| 1787 | but it usually specifies how to combine fixed strings with variables' |
| 1788 | values to construct the text. Many of these variables are themselves |
| 1789 | defined to have mode line constructs as their values. |
| 1790 | |
| 1791 | Here are the meanings of various data types as mode line constructs: |
| 1792 | |
| 1793 | @table @code |
| 1794 | @cindex percent symbol in mode line |
| 1795 | @item @var{string} |
| 1796 | A string as a mode line construct appears verbatim except for |
| 1797 | @dfn{@code{%}-constructs} in it. These stand for substitution of |
| 1798 | other data; see @ref{%-Constructs}. |
| 1799 | |
| 1800 | If parts of the string have @code{face} properties, they control |
| 1801 | display of the text just as they would text in the buffer. Any |
| 1802 | characters which have no @code{face} properties are displayed, by |
| 1803 | default, in the face @code{mode-line} or @code{mode-line-inactive} |
| 1804 | (@pxref{Standard Faces,,, emacs, The GNU Emacs Manual}). The |
| 1805 | @code{help-echo} and @code{keymap} properties in @var{string} have |
| 1806 | special meanings. @xref{Properties in Mode}. |
| 1807 | |
| 1808 | @item @var{symbol} |
| 1809 | A symbol as a mode line construct stands for its value. The value of |
| 1810 | @var{symbol} is used as a mode line construct, in place of @var{symbol}. |
| 1811 | However, the symbols @code{t} and @code{nil} are ignored, as is any |
| 1812 | symbol whose value is void. |
| 1813 | |
| 1814 | There is one exception: if the value of @var{symbol} is a string, it is |
| 1815 | displayed verbatim: the @code{%}-constructs are not recognized. |
| 1816 | |
| 1817 | Unless @var{symbol} is marked as ``risky'' (i.e., it has a |
| 1818 | non-@code{nil} @code{risky-local-variable} property), all text |
| 1819 | properties specified in @var{symbol}'s value are ignored. This includes |
| 1820 | the text properties of strings in @var{symbol}'s value, as well as all |
| 1821 | @code{:eval} and @code{:propertize} forms in it. (The reason for this |
| 1822 | is security: non-risky variables could be set automatically from file |
| 1823 | variables without prompting the user.) |
| 1824 | |
| 1825 | @item (@var{string} @var{rest}@dots{}) |
| 1826 | @itemx (@var{list} @var{rest}@dots{}) |
| 1827 | A list whose first element is a string or list means to process all the |
| 1828 | elements recursively and concatenate the results. This is the most |
| 1829 | common form of mode line construct. |
| 1830 | |
| 1831 | @item (:eval @var{form}) |
| 1832 | A list whose first element is the symbol @code{:eval} says to evaluate |
| 1833 | @var{form}, and use the result as a string to display. Make sure this |
| 1834 | evaluation cannot load any files, as doing so could cause infinite |
| 1835 | recursion. |
| 1836 | |
| 1837 | @item (:propertize @var{elt} @var{props}@dots{}) |
| 1838 | A list whose first element is the symbol @code{:propertize} says to |
| 1839 | process the mode line construct @var{elt} recursively, then add the text |
| 1840 | properties specified by @var{props} to the result. The argument |
| 1841 | @var{props} should consist of zero or more pairs @var{text-property} |
| 1842 | @var{value}. |
| 1843 | |
| 1844 | @item (@var{symbol} @var{then} @var{else}) |
| 1845 | A list whose first element is a symbol that is not a keyword specifies |
| 1846 | a conditional. Its meaning depends on the value of @var{symbol}. If |
| 1847 | @var{symbol} has a non-@code{nil} value, the second element, |
| 1848 | @var{then}, is processed recursively as a mode line construct. |
| 1849 | Otherwise, the third element, @var{else}, is processed recursively. |
| 1850 | You may omit @var{else}; then the mode line construct displays nothing |
| 1851 | if the value of @var{symbol} is @code{nil} or void. |
| 1852 | |
| 1853 | @item (@var{width} @var{rest}@dots{}) |
| 1854 | A list whose first element is an integer specifies truncation or |
| 1855 | padding of the results of @var{rest}. The remaining elements |
| 1856 | @var{rest} are processed recursively as mode line constructs and |
| 1857 | concatenated together. When @var{width} is positive, the result is |
| 1858 | space filled on the right if its width is less than @var{width}. When |
| 1859 | @var{width} is negative, the result is truncated on the right to |
| 1860 | @minus{}@var{width} columns if its width exceeds @minus{}@var{width}. |
| 1861 | |
| 1862 | For example, the usual way to show what percentage of a buffer is above |
| 1863 | the top of the window is to use a list like this: @code{(-3 "%p")}. |
| 1864 | @end table |
| 1865 | |
| 1866 | @node Mode Line Top |
| 1867 | @subsection The Top Level of Mode Line Control |
| 1868 | |
| 1869 | The variable in overall control of the mode line is |
| 1870 | @code{mode-line-format}. |
| 1871 | |
| 1872 | @defopt mode-line-format |
| 1873 | The value of this variable is a mode line construct that controls the |
| 1874 | contents of the mode-line. It is always buffer-local in all buffers. |
| 1875 | |
| 1876 | If you set this variable to @code{nil} in a buffer, that buffer does not |
| 1877 | have a mode line. (A window that is just one line tall also does not |
| 1878 | display a mode line.) |
| 1879 | @end defopt |
| 1880 | |
| 1881 | The default value of @code{mode-line-format} is designed to use the |
| 1882 | values of other variables such as @code{mode-line-position} and |
| 1883 | @code{mode-line-modes} (which in turn incorporates the values of the |
| 1884 | variables @code{mode-name} and @code{minor-mode-alist}). Very few |
| 1885 | modes need to alter @code{mode-line-format} itself. For most |
| 1886 | purposes, it is sufficient to alter some of the variables that |
| 1887 | @code{mode-line-format} either directly or indirectly refers to. |
| 1888 | |
| 1889 | If you do alter @code{mode-line-format} itself, the new value should |
| 1890 | use the same variables that appear in the default value (@pxref{Mode |
| 1891 | Line Variables}), rather than duplicating their contents or displaying |
| 1892 | the information in another fashion. This way, customizations made by |
| 1893 | the user or by Lisp programs (such as @code{display-time} and major |
| 1894 | modes) via changes to those variables remain effective. |
| 1895 | |
| 1896 | Here is a hypothetical example of a @code{mode-line-format} that might |
| 1897 | be useful for Shell mode (in reality, Shell mode does not set |
| 1898 | @code{mode-line-format}): |
| 1899 | |
| 1900 | @example |
| 1901 | @group |
| 1902 | (setq mode-line-format |
| 1903 | (list "-" |
| 1904 | 'mode-line-mule-info |
| 1905 | 'mode-line-modified |
| 1906 | 'mode-line-frame-identification |
| 1907 | "%b--" |
| 1908 | @end group |
| 1909 | @group |
| 1910 | ;; @r{Note that this is evaluated while making the list.} |
| 1911 | ;; @r{It makes a mode line construct which is just a string.} |
| 1912 | (getenv "HOST") |
| 1913 | @end group |
| 1914 | ":" |
| 1915 | 'default-directory |
| 1916 | " " |
| 1917 | 'global-mode-string |
| 1918 | " %[(" |
| 1919 | '(:eval (mode-line-mode-name)) |
| 1920 | 'mode-line-process |
| 1921 | 'minor-mode-alist |
| 1922 | "%n" |
| 1923 | ")%]--" |
| 1924 | @group |
| 1925 | '(which-func-mode ("" which-func-format "--")) |
| 1926 | '(line-number-mode "L%l--") |
| 1927 | '(column-number-mode "C%c--") |
| 1928 | '(-3 "%p"))) |
| 1929 | @end group |
| 1930 | @end example |
| 1931 | |
| 1932 | @noindent |
| 1933 | (The variables @code{line-number-mode}, @code{column-number-mode} |
| 1934 | and @code{which-func-mode} enable particular minor modes; as usual, |
| 1935 | these variable names are also the minor mode command names.) |
| 1936 | |
| 1937 | @node Mode Line Variables |
| 1938 | @subsection Variables Used in the Mode Line |
| 1939 | |
| 1940 | This section describes variables incorporated by the standard value of |
| 1941 | @code{mode-line-format} into the text of the mode line. There is |
| 1942 | nothing inherently special about these variables; any other variables |
| 1943 | could have the same effects on the mode line if the value of |
| 1944 | @code{mode-line-format} is changed to use them. However, various parts |
| 1945 | of Emacs set these variables on the understanding that they will control |
| 1946 | parts of the mode line; therefore, practically speaking, it is essential |
| 1947 | for the mode line to use them. |
| 1948 | |
| 1949 | @defvar mode-line-mule-info |
| 1950 | This variable holds the value of the mode line construct that displays |
| 1951 | information about the language environment, buffer coding system, and |
| 1952 | current input method. @xref{Non-ASCII Characters}. |
| 1953 | @end defvar |
| 1954 | |
| 1955 | @defvar mode-line-modified |
| 1956 | This variable holds the value of the mode line construct that displays |
| 1957 | whether the current buffer is modified. Its default value displays |
| 1958 | @samp{**} if the buffer is modified, @samp{--} if the buffer is not |
| 1959 | modified, @samp{%%} if the buffer is read only, and @samp{%*} if the |
| 1960 | buffer is read only and modified. |
| 1961 | |
| 1962 | Changing this variable does not force an update of the mode line. |
| 1963 | @end defvar |
| 1964 | |
| 1965 | @defvar mode-line-frame-identification |
| 1966 | This variable identifies the current frame. Its default value |
| 1967 | displays @code{" "} if you are using a window system which can show |
| 1968 | multiple frames, or @code{"-%F "} on an ordinary terminal which shows |
| 1969 | only one frame at a time. |
| 1970 | @end defvar |
| 1971 | |
| 1972 | @defvar mode-line-buffer-identification |
| 1973 | This variable identifies the buffer being displayed in the window. |
| 1974 | Its default value displays the buffer name, padded with spaces to at |
| 1975 | least 12 columns. |
| 1976 | @end defvar |
| 1977 | |
| 1978 | @defopt mode-line-position |
| 1979 | This variable indicates the position in the buffer. Its default value |
| 1980 | displays the buffer percentage and, optionally, the buffer size, the |
| 1981 | line number and the column number. |
| 1982 | @end defopt |
| 1983 | |
| 1984 | @defvar vc-mode |
| 1985 | The variable @code{vc-mode}, buffer-local in each buffer, records |
| 1986 | whether the buffer's visited file is maintained with version control, |
| 1987 | and, if so, which kind. Its value is a string that appears in the mode |
| 1988 | line, or @code{nil} for no version control. |
| 1989 | @end defvar |
| 1990 | |
| 1991 | @defopt mode-line-modes |
| 1992 | This variable displays the buffer's major and minor modes. Its |
| 1993 | default value also displays the recursive editing level, information |
| 1994 | on the process status, and whether narrowing is in effect. |
| 1995 | @end defopt |
| 1996 | |
| 1997 | @defvar mode-line-remote |
| 1998 | This variable is used to show whether @code{default-directory} for the |
| 1999 | current buffer is remote. |
| 2000 | @end defvar |
| 2001 | |
| 2002 | @defvar mode-line-client |
| 2003 | This variable is used to identify @code{emacsclient} frames. |
| 2004 | @end defvar |
| 2005 | |
| 2006 | The following three variables are used in @code{mode-line-modes}: |
| 2007 | |
| 2008 | @defvar mode-name |
| 2009 | This buffer-local variable holds the ``pretty'' name of the current |
| 2010 | buffer's major mode. Each major mode should set this variable so that |
| 2011 | the mode name will appear in the mode line. The value does not have |
| 2012 | to be a string, but can use any of the data types valid in a mode-line |
| 2013 | construct (@pxref{Mode Line Data}). To compute the string that will |
| 2014 | identify the mode name in the mode line, use @code{format-mode-line} |
| 2015 | (@pxref{Emulating Mode Line}). |
| 2016 | @end defvar |
| 2017 | |
| 2018 | @defvar mode-line-process |
| 2019 | This buffer-local variable contains the mode line information on process |
| 2020 | status in modes used for communicating with subprocesses. It is |
| 2021 | displayed immediately following the major mode name, with no intervening |
| 2022 | space. For example, its value in the @file{*shell*} buffer is |
| 2023 | @code{(":%s")}, which allows the shell to display its status along |
| 2024 | with the major mode as: @samp{(Shell:run)}. Normally this variable |
| 2025 | is @code{nil}. |
| 2026 | @end defvar |
| 2027 | |
| 2028 | @defvar minor-mode-alist |
| 2029 | @anchor{Definition of minor-mode-alist} |
| 2030 | This variable holds an association list whose elements specify how the |
| 2031 | mode line should indicate that a minor mode is active. Each element of |
| 2032 | the @code{minor-mode-alist} should be a two-element list: |
| 2033 | |
| 2034 | @example |
| 2035 | (@var{minor-mode-variable} @var{mode-line-string}) |
| 2036 | @end example |
| 2037 | |
| 2038 | More generally, @var{mode-line-string} can be any mode line construct. |
| 2039 | It appears in the mode line when the value of @var{minor-mode-variable} |
| 2040 | is non-@code{nil}, and not otherwise. These strings should begin with |
| 2041 | spaces so that they don't run together. Conventionally, the |
| 2042 | @var{minor-mode-variable} for a specific mode is set to a non-@code{nil} |
| 2043 | value when that minor mode is activated. |
| 2044 | |
| 2045 | @code{minor-mode-alist} itself is not buffer-local. Each variable |
| 2046 | mentioned in the alist should be buffer-local if its minor mode can be |
| 2047 | enabled separately in each buffer. |
| 2048 | @end defvar |
| 2049 | |
| 2050 | @defvar global-mode-string |
| 2051 | This variable holds a mode line construct that, by default, appears in |
| 2052 | the mode line just after the @code{which-func-mode} minor mode if set, |
| 2053 | else after @code{mode-line-modes}. The command @code{display-time} sets |
| 2054 | @code{global-mode-string} to refer to the variable |
| 2055 | @code{display-time-string}, which holds a string containing the time and |
| 2056 | load information. |
| 2057 | |
| 2058 | The @samp{%M} construct substitutes the value of |
| 2059 | @code{global-mode-string}, but that is obsolete, since the variable is |
| 2060 | included in the mode line from @code{mode-line-format}. |
| 2061 | @end defvar |
| 2062 | |
| 2063 | Here is a simplified version of the default value of |
| 2064 | @code{mode-line-format}. The real default value also |
| 2065 | specifies addition of text properties. |
| 2066 | |
| 2067 | @example |
| 2068 | @group |
| 2069 | ("-" |
| 2070 | mode-line-mule-info |
| 2071 | mode-line-modified |
| 2072 | mode-line-frame-identification |
| 2073 | mode-line-buffer-identification |
| 2074 | @end group |
| 2075 | " " |
| 2076 | mode-line-position |
| 2077 | (vc-mode vc-mode) |
| 2078 | " " |
| 2079 | @group |
| 2080 | mode-line-modes |
| 2081 | (which-func-mode ("" which-func-format "--")) |
| 2082 | (global-mode-string ("--" global-mode-string)) |
| 2083 | "-%-") |
| 2084 | @end group |
| 2085 | @end example |
| 2086 | |
| 2087 | @node %-Constructs |
| 2088 | @subsection @code{%}-Constructs in the Mode Line |
| 2089 | |
| 2090 | Strings used as mode line constructs can use certain |
| 2091 | @code{%}-constructs to substitute various kinds of data. The |
| 2092 | following is a list of the defined @code{%}-constructs, and what they |
| 2093 | mean. |
| 2094 | |
| 2095 | In any construct except @samp{%%}, you can add a decimal integer |
| 2096 | after the @samp{%} to specify a minimum field width. If the width is |
| 2097 | less, the field is padded to that width. Purely numeric constructs |
| 2098 | (@samp{c}, @samp{i}, @samp{I}, and @samp{l}) are padded by inserting |
| 2099 | spaces to the left, and others are padded by inserting spaces to the |
| 2100 | right. |
| 2101 | |
| 2102 | @table @code |
| 2103 | @item %b |
| 2104 | The current buffer name, obtained with the @code{buffer-name} function. |
| 2105 | @xref{Buffer Names}. |
| 2106 | |
| 2107 | @item %c |
| 2108 | The current column number of point. |
| 2109 | |
| 2110 | @item %e |
| 2111 | When Emacs is nearly out of memory for Lisp objects, a brief message |
| 2112 | saying so. Otherwise, this is empty. |
| 2113 | |
| 2114 | @item %f |
| 2115 | The visited file name, obtained with the @code{buffer-file-name} |
| 2116 | function. @xref{Buffer File Name}. |
| 2117 | |
| 2118 | @item %F |
| 2119 | The title (only on a window system) or the name of the selected frame. |
| 2120 | @xref{Basic Parameters}. |
| 2121 | |
| 2122 | @item %i |
| 2123 | The size of the accessible part of the current buffer; basically |
| 2124 | @code{(- (point-max) (point-min))}. |
| 2125 | |
| 2126 | @item %I |
| 2127 | Like @samp{%i}, but the size is printed in a more readable way by using |
| 2128 | @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., to |
| 2129 | abbreviate. |
| 2130 | |
| 2131 | @item %l |
| 2132 | The current line number of point, counting within the accessible portion |
| 2133 | of the buffer. |
| 2134 | |
| 2135 | @item %n |
| 2136 | @samp{Narrow} when narrowing is in effect; nothing otherwise (see |
| 2137 | @code{narrow-to-region} in @ref{Narrowing}). |
| 2138 | |
| 2139 | @item %p |
| 2140 | The percentage of the buffer text above the @strong{top} of window, or |
| 2141 | @samp{Top}, @samp{Bottom} or @samp{All}. Note that the default mode |
| 2142 | line construct truncates this to three characters. |
| 2143 | |
| 2144 | @item %P |
| 2145 | The percentage of the buffer text that is above the @strong{bottom} of |
| 2146 | the window (which includes the text visible in the window, as well as |
| 2147 | the text above the top), plus @samp{Top} if the top of the buffer is |
| 2148 | visible on screen; or @samp{Bottom} or @samp{All}. |
| 2149 | |
| 2150 | @item %s |
| 2151 | The status of the subprocess belonging to the current buffer, obtained with |
| 2152 | @code{process-status}. @xref{Process Information}. |
| 2153 | |
| 2154 | @item %z |
| 2155 | The mnemonics of keyboard, terminal, and buffer coding systems. |
| 2156 | |
| 2157 | @item %Z |
| 2158 | Like @samp{%z}, but including the end-of-line format. |
| 2159 | |
| 2160 | @item %* |
| 2161 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* |
| 2162 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* |
| 2163 | @samp{-} otherwise. @xref{Buffer Modification}. |
| 2164 | |
| 2165 | @item %+ |
| 2166 | @samp{*} if the buffer is modified (see @code{buffer-modified-p}); @* |
| 2167 | @samp{%} if the buffer is read only (see @code{buffer-read-only}); @* |
| 2168 | @samp{-} otherwise. This differs from @samp{%*} only for a modified |
| 2169 | read-only buffer. @xref{Buffer Modification}. |
| 2170 | |
| 2171 | @item %& |
| 2172 | @samp{*} if the buffer is modified, and @samp{-} otherwise. |
| 2173 | |
| 2174 | @item %[ |
| 2175 | An indication of the depth of recursive editing levels (not counting |
| 2176 | minibuffer levels): one @samp{[} for each editing level. |
| 2177 | @xref{Recursive Editing}. |
| 2178 | |
| 2179 | @item %] |
| 2180 | One @samp{]} for each recursive editing level (not counting minibuffer |
| 2181 | levels). |
| 2182 | |
| 2183 | @item %- |
| 2184 | Dashes sufficient to fill the remainder of the mode line. |
| 2185 | |
| 2186 | @item %% |
| 2187 | The character @samp{%}---this is how to include a literal @samp{%} in a |
| 2188 | string in which @code{%}-constructs are allowed. |
| 2189 | @end table |
| 2190 | |
| 2191 | The following two @code{%}-constructs are still supported, but they are |
| 2192 | obsolete, since you can get the same results with the variables |
| 2193 | @code{mode-name} and @code{global-mode-string}. |
| 2194 | |
| 2195 | @table @code |
| 2196 | @item %m |
| 2197 | The value of @code{mode-name}. |
| 2198 | |
| 2199 | @item %M |
| 2200 | The value of @code{global-mode-string}. |
| 2201 | @end table |
| 2202 | |
| 2203 | @node Properties in Mode |
| 2204 | @subsection Properties in the Mode Line |
| 2205 | @cindex text properties in the mode line |
| 2206 | |
| 2207 | Certain text properties are meaningful in the |
| 2208 | mode line. The @code{face} property affects the appearance of text; the |
| 2209 | @code{help-echo} property associates help strings with the text, and |
| 2210 | @code{keymap} can make the text mouse-sensitive. |
| 2211 | |
| 2212 | There are four ways to specify text properties for text in the mode |
| 2213 | line: |
| 2214 | |
| 2215 | @enumerate |
| 2216 | @item |
| 2217 | Put a string with a text property directly into the mode line data |
| 2218 | structure. |
| 2219 | |
| 2220 | @item |
| 2221 | Put a text property on a mode line %-construct such as @samp{%12b}; then |
| 2222 | the expansion of the %-construct will have that same text property. |
| 2223 | |
| 2224 | @item |
| 2225 | Use a @code{(:propertize @var{elt} @var{props}@dots{})} construct to |
| 2226 | give @var{elt} a text property specified by @var{props}. |
| 2227 | |
| 2228 | @item |
| 2229 | Use a list containing @code{:eval @var{form}} in the mode line data |
| 2230 | structure, and make @var{form} evaluate to a string that has a text |
| 2231 | property. |
| 2232 | @end enumerate |
| 2233 | |
| 2234 | You can use the @code{keymap} property to specify a keymap. This |
| 2235 | keymap only takes real effect for mouse clicks; binding character keys |
| 2236 | and function keys to it has no effect, since it is impossible to move |
| 2237 | point into the mode line. |
| 2238 | |
| 2239 | When the mode line refers to a variable which does not have a |
| 2240 | non-@code{nil} @code{risky-local-variable} property, any text |
| 2241 | properties given or specified within that variable's values are |
| 2242 | ignored. This is because such properties could otherwise specify |
| 2243 | functions to be called, and those functions could come from file |
| 2244 | local variables. |
| 2245 | |
| 2246 | @node Header Lines |
| 2247 | @subsection Window Header Lines |
| 2248 | @cindex header line (of a window) |
| 2249 | @cindex window header line |
| 2250 | |
| 2251 | A window can have a @dfn{header line} at the top, just as it can have |
| 2252 | a mode line at the bottom. The header line feature works just like the |
| 2253 | mode line feature, except that it's controlled by |
| 2254 | @code{header-line-format}: |
| 2255 | |
| 2256 | @defvar header-line-format |
| 2257 | This variable, local in every buffer, specifies how to display the |
| 2258 | header line, for windows displaying the buffer. The format of the value |
| 2259 | is the same as for @code{mode-line-format} (@pxref{Mode Line Data}). |
| 2260 | It is normally @code{nil}, so that ordinary buffers have no header line. |
| 2261 | @end defvar |
| 2262 | |
| 2263 | A window that is just one line tall never displays a header line. A |
| 2264 | window that is two lines tall cannot display both a mode line and a |
| 2265 | header line at once; if it has a mode line, then it does not display a |
| 2266 | header line. |
| 2267 | |
| 2268 | @node Emulating Mode Line |
| 2269 | @subsection Emulating Mode Line Formatting |
| 2270 | |
| 2271 | You can use the function @code{format-mode-line} to compute the text |
| 2272 | that would appear in a mode line or header line based on a certain |
| 2273 | mode line construct. |
| 2274 | |
| 2275 | @defun format-mode-line format &optional face window buffer |
| 2276 | This function formats a line of text according to @var{format} as if it |
| 2277 | were generating the mode line for @var{window}, but it also returns the |
| 2278 | text as a string. The argument @var{window} defaults to the selected |
| 2279 | window. If @var{buffer} is non-@code{nil}, all the information used is |
| 2280 | taken from @var{buffer}; by default, it comes from @var{window}'s |
| 2281 | buffer. |
| 2282 | |
| 2283 | The value string normally has text properties that correspond to the |
| 2284 | faces, keymaps, etc., that the mode line would have. Any character for |
| 2285 | which no @code{face} property is specified by @var{format} gets a |
| 2286 | default value determined by @var{face}. If @var{face} is @code{t}, that |
| 2287 | stands for either @code{mode-line} if @var{window} is selected, |
| 2288 | otherwise @code{mode-line-inactive}. If @var{face} is @code{nil} or |
| 2289 | omitted, that stands for the default face. If @var{face} is an integer, |
| 2290 | the value returned by this function will have no text properties. |
| 2291 | |
| 2292 | You can also specify other valid faces as the value of @var{face}. |
| 2293 | If specified, that face provides the @code{face} property for characters |
| 2294 | whose face is not specified by @var{format}. |
| 2295 | |
| 2296 | Note that using @code{mode-line}, @code{mode-line-inactive}, or |
| 2297 | @code{header-line} as @var{face} will actually redisplay the mode line |
| 2298 | or the header line, respectively, using the current definitions of the |
| 2299 | corresponding face, in addition to returning the formatted string. |
| 2300 | (Other faces do not cause redisplay.) |
| 2301 | |
| 2302 | For example, @code{(format-mode-line header-line-format)} returns the |
| 2303 | text that would appear in the selected window's header line (@code{""} |
| 2304 | if it has no header line). @code{(format-mode-line header-line-format |
| 2305 | 'header-line)} returns the same text, with each character |
| 2306 | carrying the face that it will have in the header line itself, and also |
| 2307 | redraws the header line. |
| 2308 | @end defun |
| 2309 | |
| 2310 | @node Imenu |
| 2311 | @section Imenu |
| 2312 | |
| 2313 | @cindex Imenu |
| 2314 | @dfn{Imenu} is a feature that lets users select a definition or |
| 2315 | section in the buffer, from a menu which lists all of them, to go |
| 2316 | directly to that location in the buffer. Imenu works by constructing |
| 2317 | a buffer index which lists the names and buffer positions of the |
| 2318 | definitions, or other named portions of the buffer; then the user can |
| 2319 | choose one of them and move point to it. Major modes can add a menu |
| 2320 | bar item to use Imenu using @code{imenu-add-to-menubar}. |
| 2321 | |
| 2322 | @deffn Command imenu-add-to-menubar name |
| 2323 | This function defines a local menu bar item named @var{name} |
| 2324 | to run Imenu. |
| 2325 | @end deffn |
| 2326 | |
| 2327 | The user-level commands for using Imenu are described in the Emacs |
| 2328 | Manual (@pxref{Imenu,, Imenu, emacs, the Emacs Manual}). This section |
| 2329 | explains how to customize Imenu's method of finding definitions or |
| 2330 | buffer portions for a particular major mode. |
| 2331 | |
| 2332 | The usual and simplest way is to set the variable |
| 2333 | @code{imenu-generic-expression}: |
| 2334 | |
| 2335 | @defvar imenu-generic-expression |
| 2336 | This variable, if non-@code{nil}, is a list that specifies regular |
| 2337 | expressions for finding definitions for Imenu. Simple elements of |
| 2338 | @code{imenu-generic-expression} look like this: |
| 2339 | |
| 2340 | @example |
| 2341 | (@var{menu-title} @var{regexp} @var{index}) |
| 2342 | @end example |
| 2343 | |
| 2344 | Here, if @var{menu-title} is non-@code{nil}, it says that the matches |
| 2345 | for this element should go in a submenu of the buffer index; |
| 2346 | @var{menu-title} itself specifies the name for the submenu. If |
| 2347 | @var{menu-title} is @code{nil}, the matches for this element go directly |
| 2348 | in the top level of the buffer index. |
| 2349 | |
| 2350 | The second item in the list, @var{regexp}, is a regular expression |
| 2351 | (@pxref{Regular Expressions}); anything in the buffer that it matches |
| 2352 | is considered a definition, something to mention in the buffer index. |
| 2353 | The third item, @var{index}, is a non-negative integer that indicates |
| 2354 | which subexpression in @var{regexp} matches the definition's name. |
| 2355 | |
| 2356 | An element can also look like this: |
| 2357 | |
| 2358 | @example |
| 2359 | (@var{menu-title} @var{regexp} @var{index} @var{function} @var{arguments}@dots{}) |
| 2360 | @end example |
| 2361 | |
| 2362 | Each match for this element creates an index item, and when the index |
| 2363 | item is selected by the user, it calls @var{function} with arguments |
| 2364 | consisting of the item name, the buffer position, and @var{arguments}. |
| 2365 | |
| 2366 | For Emacs Lisp mode, @code{imenu-generic-expression} could look like |
| 2367 | this: |
| 2368 | |
| 2369 | @c should probably use imenu-syntax-alist and \\sw rather than [-A-Za-z0-9+] |
| 2370 | @example |
| 2371 | @group |
| 2372 | ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ |
| 2373 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) |
| 2374 | @end group |
| 2375 | @group |
| 2376 | ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ |
| 2377 | \\s-+\\([-A-Za-z0-9+]+\\)" 2) |
| 2378 | @end group |
| 2379 | @group |
| 2380 | ("*Types*" |
| 2381 | "^\\s-*\ |
| 2382 | (def\\(type\\|struct\\|class\\|ine-condition\\)\ |
| 2383 | \\s-+\\([-A-Za-z0-9+]+\\)" 2)) |
| 2384 | @end group |
| 2385 | @end example |
| 2386 | |
| 2387 | Setting this variable makes it buffer-local in the current buffer. |
| 2388 | @end defvar |
| 2389 | |
| 2390 | @defvar imenu-case-fold-search |
| 2391 | This variable controls whether matching against the regular |
| 2392 | expressions in the value of @code{imenu-generic-expression} is |
| 2393 | case-sensitive: @code{t}, the default, means matching should ignore |
| 2394 | case. |
| 2395 | |
| 2396 | Setting this variable makes it buffer-local in the current buffer. |
| 2397 | @end defvar |
| 2398 | |
| 2399 | @defvar imenu-syntax-alist |
| 2400 | This variable is an alist of syntax table modifiers to use while |
| 2401 | processing @code{imenu-generic-expression}, to override the syntax table |
| 2402 | of the current buffer. Each element should have this form: |
| 2403 | |
| 2404 | @example |
| 2405 | (@var{characters} . @var{syntax-description}) |
| 2406 | @end example |
| 2407 | |
| 2408 | The @sc{car}, @var{characters}, can be either a character or a string. |
| 2409 | The element says to give that character or characters the syntax |
| 2410 | specified by @var{syntax-description}, which is passed to |
| 2411 | @code{modify-syntax-entry} (@pxref{Syntax Table Functions}). |
| 2412 | |
| 2413 | This feature is typically used to give word syntax to characters which |
| 2414 | normally have symbol syntax, and thus to simplify |
| 2415 | @code{imenu-generic-expression} and speed up matching. |
| 2416 | For example, Fortran mode uses it this way: |
| 2417 | |
| 2418 | @example |
| 2419 | (setq imenu-syntax-alist '(("_$" . "w"))) |
| 2420 | @end example |
| 2421 | |
| 2422 | The @code{imenu-generic-expression} regular expressions can then use |
| 2423 | @samp{\\sw+} instead of @samp{\\(\\sw\\|\\s_\\)+}. Note that this |
| 2424 | technique may be inconvenient when the mode needs to limit the initial |
| 2425 | character of a name to a smaller set of characters than are allowed in |
| 2426 | the rest of a name. |
| 2427 | |
| 2428 | Setting this variable makes it buffer-local in the current buffer. |
| 2429 | @end defvar |
| 2430 | |
| 2431 | Another way to customize Imenu for a major mode is to set the |
| 2432 | variables @code{imenu-prev-index-position-function} and |
| 2433 | @code{imenu-extract-index-name-function}: |
| 2434 | |
| 2435 | @defvar imenu-prev-index-position-function |
| 2436 | If this variable is non-@code{nil}, its value should be a function that |
| 2437 | finds the next ``definition'' to put in the buffer index, scanning |
| 2438 | backward in the buffer from point. It should return @code{nil} if it |
| 2439 | doesn't find another ``definition'' before point. Otherwise it should |
| 2440 | leave point at the place it finds a ``definition'' and return any |
| 2441 | non-@code{nil} value. |
| 2442 | |
| 2443 | Setting this variable makes it buffer-local in the current buffer. |
| 2444 | @end defvar |
| 2445 | |
| 2446 | @defvar imenu-extract-index-name-function |
| 2447 | If this variable is non-@code{nil}, its value should be a function to |
| 2448 | return the name for a definition, assuming point is in that definition |
| 2449 | as the @code{imenu-prev-index-position-function} function would leave |
| 2450 | it. |
| 2451 | |
| 2452 | Setting this variable makes it buffer-local in the current buffer. |
| 2453 | @end defvar |
| 2454 | |
| 2455 | The last way to customize Imenu for a major mode is to set the |
| 2456 | variable @code{imenu-create-index-function}: |
| 2457 | |
| 2458 | @defvar imenu-create-index-function |
| 2459 | This variable specifies the function to use for creating a buffer |
| 2460 | index. The function should take no arguments, and return an index |
| 2461 | alist for the current buffer. It is called within |
| 2462 | @code{save-excursion}, so where it leaves point makes no difference. |
| 2463 | |
| 2464 | The index alist can have three types of elements. Simple elements |
| 2465 | look like this: |
| 2466 | |
| 2467 | @example |
| 2468 | (@var{index-name} . @var{index-position}) |
| 2469 | @end example |
| 2470 | |
| 2471 | Selecting a simple element has the effect of moving to position |
| 2472 | @var{index-position} in the buffer. Special elements look like this: |
| 2473 | |
| 2474 | @example |
| 2475 | (@var{index-name} @var{index-position} @var{function} @var{arguments}@dots{}) |
| 2476 | @end example |
| 2477 | |
| 2478 | Selecting a special element performs: |
| 2479 | |
| 2480 | @example |
| 2481 | (funcall @var{function} |
| 2482 | @var{index-name} @var{index-position} @var{arguments}@dots{}) |
| 2483 | @end example |
| 2484 | |
| 2485 | A nested sub-alist element looks like this: |
| 2486 | |
| 2487 | @example |
| 2488 | (@var{menu-title} . @var{sub-alist}) |
| 2489 | @end example |
| 2490 | |
| 2491 | It creates the submenu @var{menu-title} specified by @var{sub-alist}. |
| 2492 | |
| 2493 | The default value of @code{imenu-create-index-function} is |
| 2494 | @code{imenu-default-create-index-function}. This function calls the |
| 2495 | value of @code{imenu-prev-index-position-function} and the value of |
| 2496 | @code{imenu-extract-index-name-function} to produce the index alist. |
| 2497 | However, if either of these two variables is @code{nil}, the default |
| 2498 | function uses @code{imenu-generic-expression} instead. |
| 2499 | |
| 2500 | Setting this variable makes it buffer-local in the current buffer. |
| 2501 | @end defvar |
| 2502 | |
| 2503 | @node Font Lock Mode |
| 2504 | @section Font Lock Mode |
| 2505 | @cindex Font Lock mode |
| 2506 | |
| 2507 | @dfn{Font Lock mode} is a buffer-local minor mode that automatically |
| 2508 | attaches @code{face} properties to certain parts of the buffer based on |
| 2509 | their syntactic role. How it parses the buffer depends on the major |
| 2510 | mode; most major modes define syntactic criteria for which faces to use |
| 2511 | in which contexts. This section explains how to customize Font Lock for |
| 2512 | a particular major mode. |
| 2513 | |
| 2514 | Font Lock mode finds text to highlight in two ways: through |
| 2515 | syntactic parsing based on the syntax table, and through searching |
| 2516 | (usually for regular expressions). Syntactic fontification happens |
| 2517 | first; it finds comments and string constants and highlights them. |
| 2518 | Search-based fontification happens second. |
| 2519 | |
| 2520 | @menu |
| 2521 | * Font Lock Basics:: Overview of customizing Font Lock. |
| 2522 | * Search-based Fontification:: Fontification based on regexps. |
| 2523 | * Customizing Keywords:: Customizing search-based fontification. |
| 2524 | * Other Font Lock Variables:: Additional customization facilities. |
| 2525 | * Levels of Font Lock:: Each mode can define alternative levels |
| 2526 | so that the user can select more or less. |
| 2527 | * Precalculated Fontification:: How Lisp programs that produce the buffer |
| 2528 | contents can also specify how to fontify it. |
| 2529 | * Faces for Font Lock:: Special faces specifically for Font Lock. |
| 2530 | * Syntactic Font Lock:: Fontification based on syntax tables. |
| 2531 | * Multiline Font Lock:: How to coerce Font Lock into properly |
| 2532 | highlighting multiline constructs. |
| 2533 | @end menu |
| 2534 | |
| 2535 | @node Font Lock Basics |
| 2536 | @subsection Font Lock Basics |
| 2537 | |
| 2538 | There are several variables that control how Font Lock mode highlights |
| 2539 | text. But major modes should not set any of these variables directly. |
| 2540 | Instead, they should set @code{font-lock-defaults} as a buffer-local |
| 2541 | variable. The value assigned to this variable is used, if and when Font |
| 2542 | Lock mode is enabled, to set all the other variables. |
| 2543 | |
| 2544 | @defvar font-lock-defaults |
| 2545 | This variable is set by major modes to specify how to fontify text in |
| 2546 | that mode. It automatically becomes buffer-local when set. If its |
| 2547 | value is @code{nil}, Font Lock mode does no highlighting, and you can |
| 2548 | use the @samp{Faces} menu (under @samp{Edit} and then @samp{Text |
| 2549 | Properties} in the menu bar) to assign faces explicitly to text in the |
| 2550 | buffer. |
| 2551 | |
| 2552 | If non-@code{nil}, the value should look like this: |
| 2553 | |
| 2554 | @example |
| 2555 | (@var{keywords} [@var{keywords-only} [@var{case-fold} |
| 2556 | [@var{syntax-alist} [@var{syntax-begin} @var{other-vars}@dots{}]]]]) |
| 2557 | @end example |
| 2558 | |
| 2559 | The first element, @var{keywords}, indirectly specifies the value of |
| 2560 | @code{font-lock-keywords} which directs search-based fontification. |
| 2561 | It can be a symbol, a variable or a function whose value is the list |
| 2562 | to use for @code{font-lock-keywords}. It can also be a list of |
| 2563 | several such symbols, one for each possible level of fontification. |
| 2564 | The first symbol specifies the @samp{mode default} level of |
| 2565 | fontification, the next symbol level 1 fontification, the next level 2, |
| 2566 | and so on. The @samp{mode default} level is normally the same as level |
| 2567 | 1. It is used when @code{font-lock-maximum-decoration} has a @code{nil} |
| 2568 | value. @xref{Levels of Font Lock}. |
| 2569 | |
| 2570 | The second element, @var{keywords-only}, specifies the value of the |
| 2571 | variable @code{font-lock-keywords-only}. If this is omitted or |
| 2572 | @code{nil}, syntactic fontification (of strings and comments) is also |
| 2573 | performed. If this is non-@code{nil}, syntactic fontification is not |
| 2574 | performed. @xref{Syntactic Font Lock}. |
| 2575 | |
| 2576 | The third element, @var{case-fold}, specifies the value of |
| 2577 | @code{font-lock-keywords-case-fold-search}. If it is non-@code{nil}, |
| 2578 | Font Lock mode ignores case during search-based fontification. |
| 2579 | |
| 2580 | If the fourth element, @var{syntax-alist}, is non-@code{nil}, it should |
| 2581 | be a list of cons cells of the form @code{(@var{char-or-string} |
| 2582 | . @var{string})}. These are used to set up a syntax table for syntactic |
| 2583 | fontification; the resulting syntax table is stored in |
| 2584 | @code{font-lock-syntax-table}. If @var{syntax-alist} is omitted or |
| 2585 | @code{nil}, syntactic fontification uses the syntax table returned by |
| 2586 | the @code{syntax-table} function. @xref{Syntax Table Functions}. |
| 2587 | |
| 2588 | The fifth element, @var{syntax-begin}, specifies the value of |
| 2589 | @code{font-lock-beginning-of-syntax-function}. We recommend setting |
| 2590 | this variable to @code{nil} and using @code{syntax-begin-function} |
| 2591 | instead. |
| 2592 | |
| 2593 | All the remaining elements (if any) are collectively called |
| 2594 | @var{other-vars}. Each of these elements should have the form |
| 2595 | @code{(@var{variable} . @var{value})}---which means, make |
| 2596 | @var{variable} buffer-local and then set it to @var{value}. You can |
| 2597 | use these @var{other-vars} to set other variables that affect |
| 2598 | fontification, aside from those you can control with the first five |
| 2599 | elements. @xref{Other Font Lock Variables}. |
| 2600 | @end defvar |
| 2601 | |
| 2602 | If your mode fontifies text explicitly by adding |
| 2603 | @code{font-lock-face} properties, it can specify @code{(nil t)} for |
| 2604 | @code{font-lock-defaults} to turn off all automatic fontification. |
| 2605 | However, this is not required; it is possible to fontify some things |
| 2606 | using @code{font-lock-face} properties and set up automatic |
| 2607 | fontification for other parts of the text. |
| 2608 | |
| 2609 | @node Search-based Fontification |
| 2610 | @subsection Search-based Fontification |
| 2611 | |
| 2612 | The variable which directly controls search-based fontification is |
| 2613 | @code{font-lock-keywords}, which is typically specified via the |
| 2614 | @var{keywords} element in @code{font-lock-defaults}. |
| 2615 | |
| 2616 | @defvar font-lock-keywords |
| 2617 | The value of this variable is a list of the keywords to highlight. Lisp |
| 2618 | programs should not set this variable directly. Normally, the value is |
| 2619 | automatically set by Font Lock mode, using the @var{keywords} element in |
| 2620 | @code{font-lock-defaults}. The value can also be altered using the |
| 2621 | functions @code{font-lock-add-keywords} and |
| 2622 | @code{font-lock-remove-keywords} (@pxref{Customizing Keywords}). |
| 2623 | @end defvar |
| 2624 | |
| 2625 | Each element of @code{font-lock-keywords} specifies how to find |
| 2626 | certain cases of text, and how to highlight those cases. Font Lock mode |
| 2627 | processes the elements of @code{font-lock-keywords} one by one, and for |
| 2628 | each element, it finds and handles all matches. Ordinarily, once |
| 2629 | part of the text has been fontified already, this cannot be overridden |
| 2630 | by a subsequent match in the same text; but you can specify different |
| 2631 | behavior using the @var{override} element of a @var{subexp-highlighter}. |
| 2632 | |
| 2633 | Each element of @code{font-lock-keywords} should have one of these |
| 2634 | forms: |
| 2635 | |
| 2636 | @table @code |
| 2637 | @item @var{regexp} |
| 2638 | Highlight all matches for @var{regexp} using |
| 2639 | @code{font-lock-keyword-face}. For example, |
| 2640 | |
| 2641 | @example |
| 2642 | ;; @r{Highlight occurrences of the word @samp{foo}} |
| 2643 | ;; @r{using @code{font-lock-keyword-face}.} |
| 2644 | "\\<foo\\>" |
| 2645 | @end example |
| 2646 | |
| 2647 | Be careful when composing these regular expressions; a poorly written |
| 2648 | pattern can dramatically slow things down! The function |
| 2649 | @code{regexp-opt} (@pxref{Regexp Functions}) is useful for calculating |
| 2650 | optimal regular expressions to match several keywords. |
| 2651 | |
| 2652 | @item @var{function} |
| 2653 | Find text by calling @var{function}, and highlight the matches |
| 2654 | it finds using @code{font-lock-keyword-face}. |
| 2655 | |
| 2656 | When @var{function} is called, it receives one argument, the limit of |
| 2657 | the search; it should begin searching at point, and not search beyond the |
| 2658 | limit. It should return non-@code{nil} if it succeeds, and set the |
| 2659 | match data to describe the match that was found. Returning @code{nil} |
| 2660 | indicates failure of the search. |
| 2661 | |
| 2662 | Fontification will call @var{function} repeatedly with the same limit, |
| 2663 | and with point where the previous invocation left it, until |
| 2664 | @var{function} fails. On failure, @var{function} need not reset point |
| 2665 | in any particular way. |
| 2666 | |
| 2667 | @item (@var{matcher} . @var{subexp}) |
| 2668 | In this kind of element, @var{matcher} is either a regular |
| 2669 | expression or a function, as described above. The @sc{cdr}, |
| 2670 | @var{subexp}, specifies which subexpression of @var{matcher} should be |
| 2671 | highlighted (instead of the entire text that @var{matcher} matched). |
| 2672 | |
| 2673 | @example |
| 2674 | ;; @r{Highlight the @samp{bar} in each occurrence of @samp{fubar},} |
| 2675 | ;; @r{using @code{font-lock-keyword-face}.} |
| 2676 | ("fu\\(bar\\)" . 1) |
| 2677 | @end example |
| 2678 | |
| 2679 | If you use @code{regexp-opt} to produce the regular expression |
| 2680 | @var{matcher}, you can use @code{regexp-opt-depth} (@pxref{Regexp |
| 2681 | Functions}) to calculate the value for @var{subexp}. |
| 2682 | |
| 2683 | @item (@var{matcher} . @var{facespec}) |
| 2684 | In this kind of element, @var{facespec} is an expression whose value |
| 2685 | specifies the face to use for highlighting. In the simplest case, |
| 2686 | @var{facespec} is a Lisp variable (a symbol) whose value is a face |
| 2687 | name. |
| 2688 | |
| 2689 | @example |
| 2690 | ;; @r{Highlight occurrences of @samp{fubar},} |
| 2691 | ;; @r{using the face which is the value of @code{fubar-face}.} |
| 2692 | ("fubar" . fubar-face) |
| 2693 | @end example |
| 2694 | |
| 2695 | However, @var{facespec} can also evaluate to a list of this form: |
| 2696 | |
| 2697 | @example |
| 2698 | (face @var{face} @var{prop1} @var{val1} @var{prop2} @var{val2}@dots{}) |
| 2699 | @end example |
| 2700 | |
| 2701 | @noindent |
| 2702 | to specify the face @var{face} and various additional text properties |
| 2703 | to put on the text that matches. If you do this, be sure to add the |
| 2704 | other text property names that you set in this way to the value of |
| 2705 | @code{font-lock-extra-managed-props} so that the properties will also |
| 2706 | be cleared out when they are no longer appropriate. Alternatively, |
| 2707 | you can set the variable @code{font-lock-unfontify-region-function} to |
| 2708 | a function that clears these properties. @xref{Other Font Lock |
| 2709 | Variables}. |
| 2710 | |
| 2711 | @item (@var{matcher} . @var{subexp-highlighter}) |
| 2712 | In this kind of element, @var{subexp-highlighter} is a list |
| 2713 | which specifies how to highlight matches found by @var{matcher}. |
| 2714 | It has the form: |
| 2715 | |
| 2716 | @example |
| 2717 | (@var{subexp} @var{facespec} [@var{override} [@var{laxmatch}]]) |
| 2718 | @end example |
| 2719 | |
| 2720 | The @sc{car}, @var{subexp}, is an integer specifying which subexpression |
| 2721 | of the match to fontify (0 means the entire matching text). The second |
| 2722 | subelement, @var{facespec}, is an expression whose value specifies the |
| 2723 | face, as described above. |
| 2724 | |
| 2725 | The last two values in @var{subexp-highlighter}, @var{override} and |
| 2726 | @var{laxmatch}, are optional flags. If @var{override} is @code{t}, |
| 2727 | this element can override existing fontification made by previous |
| 2728 | elements of @code{font-lock-keywords}. If it is @code{keep}, then |
| 2729 | each character is fontified if it has not been fontified already by |
| 2730 | some other element. If it is @code{prepend}, the face specified by |
| 2731 | @var{facespec} is added to the beginning of the @code{font-lock-face} |
| 2732 | property. If it is @code{append}, the face is added to the end of the |
| 2733 | @code{font-lock-face} property. |
| 2734 | |
| 2735 | If @var{laxmatch} is non-@code{nil}, it means there should be no error |
| 2736 | if there is no subexpression numbered @var{subexp} in @var{matcher}. |
| 2737 | Obviously, fontification of the subexpression numbered @var{subexp} will |
| 2738 | not occur. However, fontification of other subexpressions (and other |
| 2739 | regexps) will continue. If @var{laxmatch} is @code{nil}, and the |
| 2740 | specified subexpression is missing, then an error is signaled which |
| 2741 | terminates search-based fontification. |
| 2742 | |
| 2743 | Here are some examples of elements of this kind, and what they do: |
| 2744 | |
| 2745 | @smallexample |
| 2746 | ;; @r{Highlight occurrences of either @samp{foo} or @samp{bar}, using} |
| 2747 | ;; @r{@code{foo-bar-face}, even if they have already been highlighted.} |
| 2748 | ;; @r{@code{foo-bar-face} should be a variable whose value is a face.} |
| 2749 | ("foo\\|bar" 0 foo-bar-face t) |
| 2750 | |
| 2751 | ;; @r{Highlight the first subexpression within each occurrence} |
| 2752 | ;; @r{that the function @code{fubar-match} finds,} |
| 2753 | ;; @r{using the face which is the value of @code{fubar-face}.} |
| 2754 | (fubar-match 1 fubar-face) |
| 2755 | @end smallexample |
| 2756 | |
| 2757 | @item (@var{matcher} . @var{anchored-highlighter}) |
| 2758 | In this kind of element, @var{anchored-highlighter} specifies how to |
| 2759 | highlight text that follows a match found by @var{matcher}. So a |
| 2760 | match found by @var{matcher} acts as the anchor for further searches |
| 2761 | specified by @var{anchored-highlighter}. @var{anchored-highlighter} |
| 2762 | is a list of the following form: |
| 2763 | |
| 2764 | @example |
| 2765 | (@var{anchored-matcher} @var{pre-form} @var{post-form} |
| 2766 | @var{subexp-highlighters}@dots{}) |
| 2767 | @end example |
| 2768 | |
| 2769 | Here, @var{anchored-matcher}, like @var{matcher}, is either a regular |
| 2770 | expression or a function. After a match of @var{matcher} is found, |
| 2771 | point is at the end of the match. Now, Font Lock evaluates the form |
| 2772 | @var{pre-form}. Then it searches for matches of |
| 2773 | @var{anchored-matcher} and uses @var{subexp-highlighters} to highlight |
| 2774 | these. A @var{subexp-highlighter} is as described above. Finally, |
| 2775 | Font Lock evaluates @var{post-form}. |
| 2776 | |
| 2777 | The forms @var{pre-form} and @var{post-form} can be used to initialize |
| 2778 | before, and cleanup after, @var{anchored-matcher} is used. Typically, |
| 2779 | @var{pre-form} is used to move point to some position relative to the |
| 2780 | match of @var{matcher}, before starting with @var{anchored-matcher}. |
| 2781 | @var{post-form} might be used to move back, before resuming with |
| 2782 | @var{matcher}. |
| 2783 | |
| 2784 | After Font Lock evaluates @var{pre-form}, it does not search for |
| 2785 | @var{anchored-matcher} beyond the end of the line. However, if |
| 2786 | @var{pre-form} returns a buffer position that is greater than the |
| 2787 | position of point after @var{pre-form} is evaluated, then the position |
| 2788 | returned by @var{pre-form} is used as the limit of the search instead. |
| 2789 | It is generally a bad idea to return a position greater than the end |
| 2790 | of the line; in other words, the @var{anchored-matcher} search should |
| 2791 | not span lines. |
| 2792 | |
| 2793 | For example, |
| 2794 | |
| 2795 | @smallexample |
| 2796 | ;; @r{Highlight occurrences of the word @samp{item} following} |
| 2797 | ;; @r{an occurrence of the word @samp{anchor} (on the same line)} |
| 2798 | ;; @r{in the value of @code{item-face}.} |
| 2799 | ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) |
| 2800 | @end smallexample |
| 2801 | |
| 2802 | Here, @var{pre-form} and @var{post-form} are @code{nil}. Therefore |
| 2803 | searching for @samp{item} starts at the end of the match of |
| 2804 | @samp{anchor}, and searching for subsequent instances of @samp{anchor} |
| 2805 | resumes from where searching for @samp{item} concluded. |
| 2806 | |
| 2807 | @item (@var{matcher} @var{highlighters}@dots{}) |
| 2808 | This sort of element specifies several @var{highlighter} lists for a |
| 2809 | single @var{matcher}. A @var{highlighter} list can be of the type |
| 2810 | @var{subexp-highlighter} or @var{anchored-highlighter} as described |
| 2811 | above. |
| 2812 | |
| 2813 | For example, |
| 2814 | |
| 2815 | @smallexample |
| 2816 | ;; @r{Highlight occurrences of the word @samp{anchor} in the value} |
| 2817 | ;; @r{of @code{anchor-face}, and subsequent occurrences of the word} |
| 2818 | ;; @r{@samp{item} (on the same line) in the value of @code{item-face}.} |
| 2819 | ("\\<anchor\\>" (0 anchor-face) |
| 2820 | ("\\<item\\>" nil nil (0 item-face))) |
| 2821 | @end smallexample |
| 2822 | |
| 2823 | @item (eval . @var{form}) |
| 2824 | Here @var{form} is an expression to be evaluated the first time |
| 2825 | this value of @code{font-lock-keywords} is used in a buffer. |
| 2826 | Its value should have one of the forms described in this table. |
| 2827 | @end table |
| 2828 | |
| 2829 | @strong{Warning:} Do not design an element of @code{font-lock-keywords} |
| 2830 | to match text which spans lines; this does not work reliably. |
| 2831 | For details, see @xref{Multiline Font Lock}. |
| 2832 | |
| 2833 | You can use @var{case-fold} in @code{font-lock-defaults} to specify |
| 2834 | the value of @code{font-lock-keywords-case-fold-search} which says |
| 2835 | whether search-based fontification should be case-insensitive. |
| 2836 | |
| 2837 | @defvar font-lock-keywords-case-fold-search |
| 2838 | Non-@code{nil} means that regular expression matching for the sake of |
| 2839 | @code{font-lock-keywords} should be case-insensitive. |
| 2840 | @end defvar |
| 2841 | |
| 2842 | @node Customizing Keywords |
| 2843 | @subsection Customizing Search-Based Fontification |
| 2844 | |
| 2845 | You can use @code{font-lock-add-keywords} to add additional |
| 2846 | search-based fontification rules to a major mode, and |
| 2847 | @code{font-lock-remove-keywords} to remove rules. |
| 2848 | |
| 2849 | @defun font-lock-add-keywords mode keywords &optional how |
| 2850 | This function adds highlighting @var{keywords}, for the current buffer |
| 2851 | or for major mode @var{mode}. The argument @var{keywords} should be a |
| 2852 | list with the same format as the variable @code{font-lock-keywords}. |
| 2853 | |
| 2854 | If @var{mode} is a symbol which is a major mode command name, such as |
| 2855 | @code{c-mode}, the effect is that enabling Font Lock mode in |
| 2856 | @var{mode} will add @var{keywords} to @code{font-lock-keywords}. |
| 2857 | Calling with a non-@code{nil} value of @var{mode} is correct only in |
| 2858 | your @file{~/.emacs} file. |
| 2859 | |
| 2860 | If @var{mode} is @code{nil}, this function adds @var{keywords} to |
| 2861 | @code{font-lock-keywords} in the current buffer. This way of calling |
| 2862 | @code{font-lock-add-keywords} is usually used in mode hook functions. |
| 2863 | |
| 2864 | By default, @var{keywords} are added at the beginning of |
| 2865 | @code{font-lock-keywords}. If the optional argument @var{how} is |
| 2866 | @code{set}, they are used to replace the value of |
| 2867 | @code{font-lock-keywords}. If @var{how} is any other non-@code{nil} |
| 2868 | value, they are added at the end of @code{font-lock-keywords}. |
| 2869 | |
| 2870 | Some modes provide specialized support you can use in additional |
| 2871 | highlighting patterns. See the variables |
| 2872 | @code{c-font-lock-extra-types}, @code{c++-font-lock-extra-types}, |
| 2873 | and @code{java-font-lock-extra-types}, for example. |
| 2874 | |
| 2875 | @strong{Warning:} Major mode commands must not call |
| 2876 | @code{font-lock-add-keywords} under any circumstances, either directly |
| 2877 | or indirectly, except through their mode hooks. (Doing so would lead to |
| 2878 | incorrect behavior for some minor modes.) They should set up their |
| 2879 | rules for search-based fontification by setting |
| 2880 | @code{font-lock-keywords}. |
| 2881 | @end defun |
| 2882 | |
| 2883 | @defun font-lock-remove-keywords mode keywords |
| 2884 | This function removes @var{keywords} from @code{font-lock-keywords} |
| 2885 | for the current buffer or for major mode @var{mode}. As in |
| 2886 | @code{font-lock-add-keywords}, @var{mode} should be a major mode |
| 2887 | command name or @code{nil}. All the caveats and requirements for |
| 2888 | @code{font-lock-add-keywords} apply here too. |
| 2889 | @end defun |
| 2890 | |
| 2891 | For example, the following code adds two fontification patterns for C |
| 2892 | mode: one to fontify the word @samp{FIXME}, even in comments, and |
| 2893 | another to fontify the words @samp{and}, @samp{or} and @samp{not} as |
| 2894 | keywords. |
| 2895 | |
| 2896 | @smallexample |
| 2897 | (font-lock-add-keywords 'c-mode |
| 2898 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) |
| 2899 | ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) |
| 2900 | @end smallexample |
| 2901 | |
| 2902 | @noindent |
| 2903 | This example affects only C mode proper. To add the same patterns to C |
| 2904 | mode @emph{and} all modes derived from it, do this instead: |
| 2905 | |
| 2906 | @smallexample |
| 2907 | (add-hook 'c-mode-hook |
| 2908 | (lambda () |
| 2909 | (font-lock-add-keywords nil |
| 2910 | '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) |
| 2911 | ("\\<\\(and\\|or\\|not\\)\\>" . |
| 2912 | font-lock-keyword-face))))) |
| 2913 | @end smallexample |
| 2914 | |
| 2915 | @node Other Font Lock Variables |
| 2916 | @subsection Other Font Lock Variables |
| 2917 | |
| 2918 | This section describes additional variables that a major mode can |
| 2919 | set by means of @var{other-vars} in @code{font-lock-defaults} |
| 2920 | (@pxref{Font Lock Basics}). |
| 2921 | |
| 2922 | @defvar font-lock-mark-block-function |
| 2923 | If this variable is non-@code{nil}, it should be a function that is |
| 2924 | called with no arguments, to choose an enclosing range of text for |
| 2925 | refontification for the command @kbd{M-o M-o} |
| 2926 | (@code{font-lock-fontify-block}). |
| 2927 | |
| 2928 | The function should report its choice by placing the region around it. |
| 2929 | A good choice is a range of text large enough to give proper results, |
| 2930 | but not too large so that refontification becomes slow. Typical values |
| 2931 | are @code{mark-defun} for programming modes or @code{mark-paragraph} for |
| 2932 | textual modes. |
| 2933 | @end defvar |
| 2934 | |
| 2935 | @defvar font-lock-extra-managed-props |
| 2936 | This variable specifies additional properties (other than |
| 2937 | @code{font-lock-face}) that are being managed by Font Lock mode. It |
| 2938 | is used by @code{font-lock-default-unfontify-region}, which normally |
| 2939 | only manages the @code{font-lock-face} property. If you want Font |
| 2940 | Lock to manage other properties as well, you must specify them in a |
| 2941 | @var{facespec} in @code{font-lock-keywords} as well as add them to |
| 2942 | this list. @xref{Search-based Fontification}. |
| 2943 | @end defvar |
| 2944 | |
| 2945 | @defvar font-lock-fontify-buffer-function |
| 2946 | Function to use for fontifying the buffer. The default value is |
| 2947 | @code{font-lock-default-fontify-buffer}. |
| 2948 | @end defvar |
| 2949 | |
| 2950 | @defvar font-lock-unfontify-buffer-function |
| 2951 | Function to use for unfontifying the buffer. This is used when |
| 2952 | turning off Font Lock mode. The default value is |
| 2953 | @code{font-lock-default-unfontify-buffer}. |
| 2954 | @end defvar |
| 2955 | |
| 2956 | @defvar font-lock-fontify-region-function |
| 2957 | Function to use for fontifying a region. It should take two |
| 2958 | arguments, the beginning and end of the region, and an optional third |
| 2959 | argument @var{verbose}. If @var{verbose} is non-@code{nil}, the |
| 2960 | function should print status messages. The default value is |
| 2961 | @code{font-lock-default-fontify-region}. |
| 2962 | @end defvar |
| 2963 | |
| 2964 | @defvar font-lock-unfontify-region-function |
| 2965 | Function to use for unfontifying a region. It should take two |
| 2966 | arguments, the beginning and end of the region. The default value is |
| 2967 | @code{font-lock-default-unfontify-region}. |
| 2968 | @end defvar |
| 2969 | |
| 2970 | @defun jit-lock-register function &optional contextual |
| 2971 | This function tells Font Lock mode to run the Lisp function |
| 2972 | @var{function} any time it has to fontify or refontify part of the |
| 2973 | current buffer. It calls @var{function} before calling the default |
| 2974 | fontification functions, and gives it two arguments, @var{start} and |
| 2975 | @var{end}, which specify the region to be fontified or refontified. |
| 2976 | |
| 2977 | The optional argument @var{contextual}, if non-@code{nil}, forces Font |
| 2978 | Lock mode to always refontify a syntactically relevant part of the |
| 2979 | buffer, and not just the modified lines. This argument can usually be |
| 2980 | omitted. |
| 2981 | @end defun |
| 2982 | |
| 2983 | @defun jit-lock-unregister function |
| 2984 | If @var{function} was previously registered as a fontification |
| 2985 | function using @code{jit-lock-register}, this function unregisters it. |
| 2986 | @end defun |
| 2987 | |
| 2988 | @node Levels of Font Lock |
| 2989 | @subsection Levels of Font Lock |
| 2990 | |
| 2991 | Some major modes offer three different levels of fontification. You |
| 2992 | can define multiple levels by using a list of symbols for @var{keywords} |
| 2993 | in @code{font-lock-defaults}. Each symbol specifies one level of |
| 2994 | fontification; it is up to the user to choose one of these levels, |
| 2995 | normally by setting @code{font-lock-maximum-decoration} (@pxref{Font |
| 2996 | Lock,,, emacs, the GNU Emacs Manual}). The chosen level's symbol value |
| 2997 | is used to initialize @code{font-lock-keywords}. |
| 2998 | |
| 2999 | Here are the conventions for how to define the levels of |
| 3000 | fontification: |
| 3001 | |
| 3002 | @itemize @bullet |
| 3003 | @item |
| 3004 | Level 1: highlight function declarations, file directives (such as include or |
| 3005 | import directives), strings and comments. The idea is speed, so only |
| 3006 | the most important and top-level components are fontified. |
| 3007 | |
| 3008 | @item |
| 3009 | Level 2: in addition to level 1, highlight all language keywords, |
| 3010 | including type names that act like keywords, as well as named constant |
| 3011 | values. The idea is that all keywords (either syntactic or semantic) |
| 3012 | should be fontified appropriately. |
| 3013 | |
| 3014 | @item |
| 3015 | Level 3: in addition to level 2, highlight the symbols being defined in |
| 3016 | function and variable declarations, and all builtin function names, |
| 3017 | wherever they appear. |
| 3018 | @end itemize |
| 3019 | |
| 3020 | @node Precalculated Fontification |
| 3021 | @subsection Precalculated Fontification |
| 3022 | |
| 3023 | Some major modes such as @code{list-buffers} and @code{occur} |
| 3024 | construct the buffer text programmatically. The easiest way for them |
| 3025 | to support Font Lock mode is to specify the faces of text when they |
| 3026 | insert the text in the buffer. |
| 3027 | |
| 3028 | The way to do this is to specify the faces in the text with the |
| 3029 | special text property @code{font-lock-face} (@pxref{Special |
| 3030 | Properties}). When Font Lock mode is enabled, this property controls |
| 3031 | the display, just like the @code{face} property. When Font Lock mode |
| 3032 | is disabled, @code{font-lock-face} has no effect on the display. |
| 3033 | |
| 3034 | It is ok for a mode to use @code{font-lock-face} for some text and |
| 3035 | also use the normal Font Lock machinery. But if the mode does not use |
| 3036 | the normal Font Lock machinery, it should not set the variable |
| 3037 | @code{font-lock-defaults}. |
| 3038 | |
| 3039 | @node Faces for Font Lock |
| 3040 | @subsection Faces for Font Lock |
| 3041 | @cindex faces for font lock |
| 3042 | @cindex font lock faces |
| 3043 | |
| 3044 | Font Lock mode can highlight using any face, but Emacs defines several |
| 3045 | faces specifically for Font Lock to use to highlight text. These |
| 3046 | @dfn{Font Lock faces} are listed below. They can also be used by major |
| 3047 | modes for syntactic highlighting outside of Font Lock mode (@pxref{Major |
| 3048 | Mode Conventions}). |
| 3049 | |
| 3050 | Each of these symbols is both a face name, and a variable whose |
| 3051 | default value is the symbol itself. Thus, the default value of |
| 3052 | @code{font-lock-comment-face} is @code{font-lock-comment-face}. |
| 3053 | |
| 3054 | The faces are listed with descriptions of their typical usage, and in |
| 3055 | order of greater to lesser ``prominence''. If a mode's syntactic |
| 3056 | categories do not fit well with the usage descriptions, the faces can be |
| 3057 | assigned using the ordering as a guide. |
| 3058 | |
| 3059 | @table @code |
| 3060 | @item font-lock-warning-face |
| 3061 | @vindex font-lock-warning-face |
| 3062 | for a construct that is peculiar, or that greatly changes the meaning of |
| 3063 | other text, like @samp{;;;###autoload} in Emacs Lisp and @samp{#error} |
| 3064 | in C. |
| 3065 | |
| 3066 | @item font-lock-function-name-face |
| 3067 | @vindex font-lock-function-name-face |
| 3068 | for the name of a function being defined or declared. |
| 3069 | |
| 3070 | @item font-lock-variable-name-face |
| 3071 | @vindex font-lock-variable-name-face |
| 3072 | for the name of a variable being defined or declared. |
| 3073 | |
| 3074 | @item font-lock-keyword-face |
| 3075 | @vindex font-lock-keyword-face |
| 3076 | for a keyword with special syntactic significance, like @samp{for} and |
| 3077 | @samp{if} in C. |
| 3078 | |
| 3079 | @item font-lock-comment-face |
| 3080 | @vindex font-lock-comment-face |
| 3081 | for comments. |
| 3082 | |
| 3083 | @item font-lock-comment-delimiter-face |
| 3084 | @vindex font-lock-comment-delimiter-face |
| 3085 | for comments delimiters, like @samp{/*} and @samp{*/} in C@. On most |
| 3086 | terminals, this inherits from @code{font-lock-comment-face}. |
| 3087 | |
| 3088 | @item font-lock-type-face |
| 3089 | @vindex font-lock-type-face |
| 3090 | for the names of user-defined data types. |
| 3091 | |
| 3092 | @item font-lock-constant-face |
| 3093 | @vindex font-lock-constant-face |
| 3094 | for the names of constants, like @samp{NULL} in C. |
| 3095 | |
| 3096 | @item font-lock-builtin-face |
| 3097 | @vindex font-lock-builtin-face |
| 3098 | for the names of built-in functions. |
| 3099 | |
| 3100 | @item font-lock-preprocessor-face |
| 3101 | @vindex font-lock-preprocessor-face |
| 3102 | for preprocessor commands. This inherits, by default, from |
| 3103 | @code{font-lock-builtin-face}. |
| 3104 | |
| 3105 | @item font-lock-string-face |
| 3106 | @vindex font-lock-string-face |
| 3107 | for string constants. |
| 3108 | |
| 3109 | @item font-lock-doc-face |
| 3110 | @vindex font-lock-doc-face |
| 3111 | for documentation strings in the code. This inherits, by default, from |
| 3112 | @code{font-lock-string-face}. |
| 3113 | |
| 3114 | @item font-lock-negation-char-face |
| 3115 | @vindex font-lock-negation-char-face |
| 3116 | for easily-overlooked negation characters. |
| 3117 | @end table |
| 3118 | |
| 3119 | @node Syntactic Font Lock |
| 3120 | @subsection Syntactic Font Lock |
| 3121 | @cindex syntactic font lock |
| 3122 | |
| 3123 | Syntactic fontification uses a syntax table (@pxref{Syntax Tables}) to |
| 3124 | find and highlight syntactically relevant text. If enabled, it runs |
| 3125 | prior to search-based fontification. The variable |
| 3126 | @code{font-lock-syntactic-face-function}, documented below, determines |
| 3127 | which syntactic constructs to highlight. There are several variables |
| 3128 | that affect syntactic fontification; you should set them by means of |
| 3129 | @code{font-lock-defaults} (@pxref{Font Lock Basics}). |
| 3130 | |
| 3131 | Whenever Font Lock mode performs syntactic fontification on a stretch |
| 3132 | of text, it first calls the function specified by |
| 3133 | @code{syntax-propertize-function}. Major modes can use this to apply |
| 3134 | @code{syntax-table} text properties to override the buffer's syntax |
| 3135 | table in special cases. @xref{Syntax Properties}. |
| 3136 | |
| 3137 | @defvar font-lock-keywords-only |
| 3138 | If the value of this variable is non-@code{nil}, Font Lock does not do |
| 3139 | syntactic fontification, only search-based fontification based on |
| 3140 | @code{font-lock-keywords}. It is normally set by Font Lock mode based |
| 3141 | on the @var{keywords-only} element in @code{font-lock-defaults}. |
| 3142 | @end defvar |
| 3143 | |
| 3144 | @defvar font-lock-syntax-table |
| 3145 | This variable holds the syntax table to use for fontification of |
| 3146 | comments and strings. It is normally set by Font Lock mode based on the |
| 3147 | @var{syntax-alist} element in @code{font-lock-defaults}. If this value |
| 3148 | is @code{nil}, syntactic fontification uses the buffer's syntax table |
| 3149 | (the value returned by the function @code{syntax-table}; @pxref{Syntax |
| 3150 | Table Functions}). |
| 3151 | @end defvar |
| 3152 | |
| 3153 | @defvar font-lock-beginning-of-syntax-function |
| 3154 | If this variable is non-@code{nil}, it should be a function to move |
| 3155 | point back to a position that is syntactically at ``top level'' and |
| 3156 | outside of strings or comments. The value is normally set through an |
| 3157 | @var{other-vars} element in @code{font-lock-defaults}. If it is |
| 3158 | @code{nil}, Font Lock uses @code{syntax-begin-function} to move back |
| 3159 | outside of any comment, string, or sexp (@pxref{Position Parse}). |
| 3160 | |
| 3161 | This variable is semi-obsolete; we usually recommend setting |
| 3162 | @code{syntax-begin-function} instead. One of its uses is to tune the |
| 3163 | behavior of syntactic fontification, e.g., to ensure that different |
| 3164 | kinds of strings or comments are highlighted differently. |
| 3165 | |
| 3166 | The specified function is called with no arguments. It should leave |
| 3167 | point at the beginning of any enclosing syntactic block. Typical values |
| 3168 | are @code{beginning-of-line} (used when the start of the line is known |
| 3169 | to be outside a syntactic block), or @code{beginning-of-defun} for |
| 3170 | programming modes, or @code{backward-paragraph} for textual modes. |
| 3171 | @end defvar |
| 3172 | |
| 3173 | @defvar font-lock-syntactic-face-function |
| 3174 | If this variable is non-@code{nil}, it should be a function to determine |
| 3175 | which face to use for a given syntactic element (a string or a comment). |
| 3176 | The value is normally set through an @var{other-vars} element in |
| 3177 | @code{font-lock-defaults}. |
| 3178 | |
| 3179 | The function is called with one argument, the parse state at point |
| 3180 | returned by @code{parse-partial-sexp}, and should return a face. The |
| 3181 | default value returns @code{font-lock-comment-face} for comments and |
| 3182 | @code{font-lock-string-face} for strings (@pxref{Faces for Font Lock}). |
| 3183 | @end defvar |
| 3184 | |
| 3185 | @node Multiline Font Lock |
| 3186 | @subsection Multiline Font Lock Constructs |
| 3187 | @cindex multiline font lock |
| 3188 | |
| 3189 | Normally, elements of @code{font-lock-keywords} should not match |
| 3190 | across multiple lines; that doesn't work reliably, because Font Lock |
| 3191 | usually scans just part of the buffer, and it can miss a multi-line |
| 3192 | construct that crosses the line boundary where the scan starts. (The |
| 3193 | scan normally starts at the beginning of a line.) |
| 3194 | |
| 3195 | Making elements that match multiline constructs work properly has |
| 3196 | two aspects: correct @emph{identification} and correct |
| 3197 | @emph{rehighlighting}. The first means that Font Lock finds all |
| 3198 | multiline constructs. The second means that Font Lock will correctly |
| 3199 | rehighlight all the relevant text when a multiline construct is |
| 3200 | changed---for example, if some of the text that was previously part of |
| 3201 | a multiline construct ceases to be part of it. The two aspects are |
| 3202 | closely related, and often getting one of them to work will appear to |
| 3203 | make the other also work. However, for reliable results you must |
| 3204 | attend explicitly to both aspects. |
| 3205 | |
| 3206 | There are three ways to ensure correct identification of multiline |
| 3207 | constructs: |
| 3208 | |
| 3209 | @itemize |
| 3210 | @item |
| 3211 | Add a function to @code{font-lock-extend-region-functions} that does |
| 3212 | the @emph{identification} and extends the scan so that the scanned |
| 3213 | text never starts or ends in the middle of a multiline construct. |
| 3214 | @item |
| 3215 | Use the @code{font-lock-fontify-region-function} hook similarly to |
| 3216 | extend the scan so that the scanned text never starts or ends in the |
| 3217 | middle of a multiline construct. |
| 3218 | @item |
| 3219 | Somehow identify the multiline construct right when it gets inserted |
| 3220 | into the buffer (or at any point after that but before font-lock |
| 3221 | tries to highlight it), and mark it with a @code{font-lock-multiline} |
| 3222 | which will instruct font-lock not to start or end the scan in the |
| 3223 | middle of the construct. |
| 3224 | @end itemize |
| 3225 | |
| 3226 | There are three ways to do rehighlighting of multiline constructs: |
| 3227 | |
| 3228 | @itemize |
| 3229 | @item |
| 3230 | Place a @code{font-lock-multiline} property on the construct. This |
| 3231 | will rehighlight the whole construct if any part of it is changed. In |
| 3232 | some cases you can do this automatically by setting the |
| 3233 | @code{font-lock-multiline} variable, which see. |
| 3234 | @item |
| 3235 | Make sure @code{jit-lock-contextually} is set and rely on it doing its |
| 3236 | job. This will only rehighlight the part of the construct that |
| 3237 | follows the actual change, and will do it after a short delay. |
| 3238 | This only works if the highlighting of the various parts of your |
| 3239 | multiline construct never depends on text in subsequent lines. |
| 3240 | Since @code{jit-lock-contextually} is activated by default, this can |
| 3241 | be an attractive solution. |
| 3242 | @item |
| 3243 | Place a @code{jit-lock-defer-multiline} property on the construct. |
| 3244 | This works only if @code{jit-lock-contextually} is used, and with the |
| 3245 | same delay before rehighlighting, but like @code{font-lock-multiline}, |
| 3246 | it also handles the case where highlighting depends on |
| 3247 | subsequent lines. |
| 3248 | @end itemize |
| 3249 | |
| 3250 | @menu |
| 3251 | * Font Lock Multiline:: Marking multiline chunks with a text property. |
| 3252 | * Region to Refontify:: Controlling which region gets refontified |
| 3253 | after a buffer change. |
| 3254 | @end menu |
| 3255 | |
| 3256 | @node Font Lock Multiline |
| 3257 | @subsubsection Font Lock Multiline |
| 3258 | |
| 3259 | One way to ensure reliable rehighlighting of multiline Font Lock |
| 3260 | constructs is to put on them the text property @code{font-lock-multiline}. |
| 3261 | It should be present and non-@code{nil} for text that is part of a |
| 3262 | multiline construct. |
| 3263 | |
| 3264 | When Font Lock is about to highlight a range of text, it first |
| 3265 | extends the boundaries of the range as necessary so that they do not |
| 3266 | fall within text marked with the @code{font-lock-multiline} property. |
| 3267 | Then it removes any @code{font-lock-multiline} properties from the |
| 3268 | range, and highlights it. The highlighting specification (mostly |
| 3269 | @code{font-lock-keywords}) must reinstall this property each time, |
| 3270 | whenever it is appropriate. |
| 3271 | |
| 3272 | @strong{Warning:} don't use the @code{font-lock-multiline} property |
| 3273 | on large ranges of text, because that will make rehighlighting slow. |
| 3274 | |
| 3275 | @defvar font-lock-multiline |
| 3276 | If the @code{font-lock-multiline} variable is set to @code{t}, Font |
| 3277 | Lock will try to add the @code{font-lock-multiline} property |
| 3278 | automatically on multiline constructs. This is not a universal |
| 3279 | solution, however, since it slows down Font Lock somewhat. It can |
| 3280 | miss some multiline constructs, or make the property larger or smaller |
| 3281 | than necessary. |
| 3282 | |
| 3283 | For elements whose @var{matcher} is a function, the function should |
| 3284 | ensure that submatch 0 covers the whole relevant multiline construct, |
| 3285 | even if only a small subpart will be highlighted. It is often just as |
| 3286 | easy to add the @code{font-lock-multiline} property by hand. |
| 3287 | @end defvar |
| 3288 | |
| 3289 | The @code{font-lock-multiline} property is meant to ensure proper |
| 3290 | refontification; it does not automatically identify new multiline |
| 3291 | constructs. Identifying the requires that Font Lock mode operate on |
| 3292 | large enough chunks at a time. This will happen by accident on many |
| 3293 | cases, which may give the impression that multiline constructs magically |
| 3294 | work. If you set the @code{font-lock-multiline} variable |
| 3295 | non-@code{nil}, this impression will be even stronger, since the |
| 3296 | highlighting of those constructs which are found will be properly |
| 3297 | updated from then on. But that does not work reliably. |
| 3298 | |
| 3299 | To find multiline constructs reliably, you must either manually place |
| 3300 | the @code{font-lock-multiline} property on the text before Font Lock |
| 3301 | mode looks at it, or use @code{font-lock-fontify-region-function}. |
| 3302 | |
| 3303 | @node Region to Refontify |
| 3304 | @subsubsection Region to Fontify after a Buffer Change |
| 3305 | |
| 3306 | When a buffer is changed, the region that Font Lock refontifies is |
| 3307 | by default the smallest sequence of whole lines that spans the change. |
| 3308 | While this works well most of the time, sometimes it doesn't---for |
| 3309 | example, when a change alters the syntactic meaning of text on an |
| 3310 | earlier line. |
| 3311 | |
| 3312 | You can enlarge (or even reduce) the region to refontify by setting |
| 3313 | the following variable: |
| 3314 | |
| 3315 | @defvar font-lock-extend-after-change-region-function |
| 3316 | This buffer-local variable is either @code{nil} or a function for Font |
| 3317 | Lock mode to call to determine the region to scan and fontify. |
| 3318 | |
| 3319 | The function is given three parameters, the standard @var{beg}, |
| 3320 | @var{end}, and @var{old-len} from @code{after-change-functions} |
| 3321 | (@pxref{Change Hooks}). It should return either a cons of the |
| 3322 | beginning and end buffer positions (in that order) of the region to |
| 3323 | fontify, or @code{nil} (which means choose the region in the standard |
| 3324 | way). This function needs to preserve point, the match-data, and the |
| 3325 | current restriction. The region it returns may start or end in the |
| 3326 | middle of a line. |
| 3327 | |
| 3328 | Since this function is called after every buffer change, it should be |
| 3329 | reasonably fast. |
| 3330 | @end defvar |
| 3331 | |
| 3332 | @node Auto-Indentation |
| 3333 | @section Automatic Indentation of code |
| 3334 | |
| 3335 | For programming languages, an important feature of a major mode is to |
| 3336 | provide automatic indentation. This is controlled in Emacs by |
| 3337 | @code{indent-line-function} (@pxref{Mode-Specific Indent}). |
| 3338 | Writing a good indentation function can be difficult and to a large |
| 3339 | extent it is still a black art. |
| 3340 | |
| 3341 | Many major mode authors will start by writing a simple indentation |
| 3342 | function that works for simple cases, for example by comparing with the |
| 3343 | indentation of the previous text line. For most programming languages |
| 3344 | that are not really line-based, this tends to scale very poorly: |
| 3345 | improving such a function to let it handle more diverse situations tends |
| 3346 | to become more and more difficult, resulting in the end with a large, |
| 3347 | complex, unmaintainable indentation function which nobody dares to touch. |
| 3348 | |
| 3349 | A good indentation function will usually need to actually parse the |
| 3350 | text, according to the syntax of the language. Luckily, it is not |
| 3351 | necessary to parse the text in as much detail as would be needed |
| 3352 | for a compiler, but on the other hand, the parser embedded in the |
| 3353 | indentation code will want to be somewhat friendly to syntactically |
| 3354 | incorrect code. |
| 3355 | |
| 3356 | Good maintainable indentation functions usually fall into two categories: |
| 3357 | either parsing forward from some ``safe'' starting point until the |
| 3358 | position of interest, or parsing backward from the position of interest. |
| 3359 | Neither of the two is a clearly better choice than the other: parsing |
| 3360 | backward is often more difficult than parsing forward because |
| 3361 | programming languages are designed to be parsed forward, but for the |
| 3362 | purpose of indentation it has the advantage of not needing to |
| 3363 | guess a ``safe'' starting point, and it generally enjoys the property |
| 3364 | that only a minimum of text will be analyzed to decide the indentation |
| 3365 | of a line, so indentation will tend to be unaffected by syntax errors in |
| 3366 | some earlier unrelated piece of code. Parsing forward on the other hand |
| 3367 | is usually easier and has the advantage of making it possible to |
| 3368 | reindent efficiently a whole region at a time, with a single parse. |
| 3369 | |
| 3370 | Rather than write your own indentation function from scratch, it is |
| 3371 | often preferable to try and reuse some existing ones or to rely |
| 3372 | on a generic indentation engine. There are sadly few such |
| 3373 | engines. The CC-mode indentation code (used with C, C++, Java, Awk |
| 3374 | and a few other such modes) has been made more generic over the years, |
| 3375 | so if your language seems somewhat similar to one of those languages, |
| 3376 | you might try to use that engine. @c FIXME: documentation? |
| 3377 | Another one is SMIE which takes an approach in the spirit |
| 3378 | of Lisp sexps and adapts it to non-Lisp languages. |
| 3379 | |
| 3380 | @menu |
| 3381 | * SMIE:: A simple minded indentation engine. |
| 3382 | @end menu |
| 3383 | |
| 3384 | @node SMIE |
| 3385 | @subsection Simple Minded Indentation Engine |
| 3386 | @cindex SMIE |
| 3387 | |
| 3388 | SMIE is a package that provides a generic navigation and indentation |
| 3389 | engine. Based on a very simple parser using an ``operator precedence |
| 3390 | grammar'', it lets major modes extend the sexp-based navigation of Lisp |
| 3391 | to non-Lisp languages as well as provide a simple to use but reliable |
| 3392 | auto-indentation. |
| 3393 | |
| 3394 | Operator precedence grammar is a very primitive technology for parsing |
| 3395 | compared to some of the more common techniques used in compilers. |
| 3396 | It has the following characteristics: its parsing power is very limited, |
| 3397 | and it is largely unable to detect syntax errors, but it has the |
| 3398 | advantage of being algorithmically efficient and able to parse forward |
| 3399 | just as well as backward. In practice that means that SMIE can use it |
| 3400 | for indentation based on backward parsing, that it can provide both |
| 3401 | @code{forward-sexp} and @code{backward-sexp} functionality, and that it |
| 3402 | will naturally work on syntactically incorrect code without any extra |
| 3403 | effort. The downside is that it also means that most programming |
| 3404 | languages cannot be parsed correctly using SMIE, at least not without |
| 3405 | resorting to some special tricks (@pxref{SMIE Tricks}). |
| 3406 | |
| 3407 | @menu |
| 3408 | * SMIE setup:: SMIE setup and features. |
| 3409 | * Operator Precedence Grammars:: A very simple parsing technique. |
| 3410 | * SMIE Grammar:: Defining the grammar of a language. |
| 3411 | * SMIE Lexer:: Defining tokens. |
| 3412 | * SMIE Tricks:: Working around the parser's limitations. |
| 3413 | * SMIE Indentation:: Specifying indentation rules. |
| 3414 | * SMIE Indentation Helpers:: Helper functions for indentation rules. |
| 3415 | * SMIE Indentation Example:: Sample indentation rules. |
| 3416 | @end menu |
| 3417 | |
| 3418 | @node SMIE setup |
| 3419 | @subsubsection SMIE Setup and Features |
| 3420 | |
| 3421 | SMIE is meant to be a one-stop shop for structural navigation and |
| 3422 | various other features which rely on the syntactic structure of code, in |
| 3423 | particular automatic indentation. The main entry point is |
| 3424 | @code{smie-setup} which is a function typically called while setting |
| 3425 | up a major mode. |
| 3426 | |
| 3427 | @defun smie-setup grammar rules-function &rest keywords |
| 3428 | Setup SMIE navigation and indentation. |
| 3429 | @var{grammar} is a grammar table generated by @code{smie-prec2->grammar}. |
| 3430 | @var{rules-function} is a set of indentation rules for use on |
| 3431 | @code{smie-rules-function}. |
| 3432 | @var{keywords} are additional arguments, which can include the following |
| 3433 | keywords: |
| 3434 | @itemize |
| 3435 | @item |
| 3436 | @code{:forward-token} @var{fun}: Specify the forward lexer to use. |
| 3437 | @item |
| 3438 | @code{:backward-token} @var{fun}: Specify the backward lexer to use. |
| 3439 | @end itemize |
| 3440 | @end defun |
| 3441 | |
| 3442 | Calling this function is sufficient to make commands such as |
| 3443 | @code{forward-sexp}, @code{backward-sexp}, and @code{transpose-sexps} be |
| 3444 | able to properly handle structural elements other than just the paired |
| 3445 | parentheses already handled by syntax tables. For example, if the |
| 3446 | provided grammar is precise enough, @code{transpose-sexps} can correctly |
| 3447 | transpose the two arguments of a @code{+} operator, taking into account |
| 3448 | the precedence rules of the language. |
| 3449 | |
| 3450 | Calling `smie-setup' is also sufficient to make TAB indentation work in |
| 3451 | the expected way, extends @code{blink-matching-paren} to apply to |
| 3452 | elements like @code{begin...end}, and provides some commands that you |
| 3453 | can bind in the major mode keymap. |
| 3454 | |
| 3455 | @deffn Command smie-close-block |
| 3456 | This command closes the most recently opened (and not yet closed) block. |
| 3457 | @end deffn |
| 3458 | |
| 3459 | @deffn Command smie-down-list &optional arg |
| 3460 | This command is like @code{down-list} but it also pays attention to |
| 3461 | nesting of tokens other than parentheses, such as @code{begin...end}. |
| 3462 | @end deffn |
| 3463 | |
| 3464 | @node Operator Precedence Grammars |
| 3465 | @subsubsection Operator Precedence Grammars |
| 3466 | |
| 3467 | SMIE's precedence grammars simply give to each token a pair of |
| 3468 | precedences: the left-precedence and the right-precedence. We say |
| 3469 | @code{T1 < T2} if the right-precedence of token @code{T1} is less than |
| 3470 | the left-precedence of token @code{T2}. A good way to read this |
| 3471 | @code{<} is as a kind of parenthesis: if we find @code{... T1 something |
| 3472 | T2 ...} then that should be parsed as @code{... T1 (something T2 ...} |
| 3473 | rather than as @code{... T1 something) T2 ...}. The latter |
| 3474 | interpretation would be the case if we had @code{T1 > T2}. If we have |
| 3475 | @code{T1 = T2}, it means that token T2 follows token T1 in the same |
| 3476 | syntactic construction, so typically we have @code{"begin" = "end"}. |
| 3477 | Such pairs of precedences are sufficient to express left-associativity |
| 3478 | or right-associativity of infix operators, nesting of tokens like |
| 3479 | parentheses and many other cases. |
| 3480 | |
| 3481 | @c Let's leave this undocumented to leave it more open for change! |
| 3482 | @c @defvar smie-grammar |
| 3483 | @c The value of this variable is an alist specifying the left and right |
| 3484 | @c precedence of each token. It is meant to be initialized by using one of |
| 3485 | @c the functions below. |
| 3486 | @c @end defvar |
| 3487 | |
| 3488 | @defun smie-prec2->grammar table |
| 3489 | This function takes a @emph{prec2} grammar @var{table} and returns an |
| 3490 | alist suitable for use in @code{smie-setup}. The @emph{prec2} |
| 3491 | @var{table} is itself meant to be built by one of the functions below. |
| 3492 | @end defun |
| 3493 | |
| 3494 | @defun smie-merge-prec2s &rest tables |
| 3495 | This function takes several @emph{prec2} @var{tables} and merges them |
| 3496 | into a new @emph{prec2} table. |
| 3497 | @end defun |
| 3498 | |
| 3499 | @defun smie-precs->prec2 precs |
| 3500 | This function builds a @emph{prec2} table from a table of precedences |
| 3501 | @var{precs}. @var{precs} should be a list, sorted by precedence (for |
| 3502 | example @code{"+"} will come before @code{"*"}), of elements of the form |
| 3503 | @code{(@var{assoc} @var{op} ...)}, where each @var{op} is a token that |
| 3504 | acts as an operator; @var{assoc} is their associativity, which can be |
| 3505 | either @code{left}, @code{right}, @code{assoc}, or @code{nonassoc}. |
| 3506 | All operators in a given element share the same precedence level |
| 3507 | and associativity. |
| 3508 | @end defun |
| 3509 | |
| 3510 | @defun smie-bnf->prec2 bnf &rest resolvers |
| 3511 | This function lets you specify the grammar using a BNF notation. |
| 3512 | It accepts a @var{bnf} description of the grammar along with a set of |
| 3513 | conflict resolution rules @var{resolvers}, and |
| 3514 | returns a @emph{prec2} table. |
| 3515 | |
| 3516 | @var{bnf} is a list of nonterminal definitions of the form |
| 3517 | @code{(@var{nonterm} @var{rhs1} @var{rhs2} ...)} where each @var{rhs} |
| 3518 | is a (non-empty) list of terminals (aka tokens) or non-terminals. |
| 3519 | |
| 3520 | Not all grammars are accepted: |
| 3521 | @itemize |
| 3522 | @item |
| 3523 | An @var{rhs} cannot be an empty list (an empty list is never needed, |
| 3524 | since SMIE allows all non-terminals to match the empty string anyway). |
| 3525 | @item |
| 3526 | An @var{rhs} cannot have 2 consecutive non-terminals: each pair of |
| 3527 | non-terminals needs to be separated by a terminal (aka token). |
| 3528 | This is a fundamental limitation of operator precedence grammars. |
| 3529 | @end itemize |
| 3530 | |
| 3531 | Additionally, conflicts can occur: |
| 3532 | @itemize |
| 3533 | @item |
| 3534 | The returned @emph{prec2} table holds constraints between pairs of tokens, and |
| 3535 | for any given pair only one constraint can be present: T1 < T2, |
| 3536 | T1 = T2, or T1 > T2. |
| 3537 | @item |
| 3538 | A token can be an @code{opener} (something similar to an open-paren), |
| 3539 | a @code{closer} (like a close-paren), or @code{neither} of the two |
| 3540 | (e.g., an infix operator, or an inner token like @code{"else"}). |
| 3541 | @end itemize |
| 3542 | |
| 3543 | Precedence conflicts can be resolved via @var{resolvers}, which |
| 3544 | is a list of @emph{precs} tables (see @code{smie-precs->prec2}): for |
| 3545 | each precedence conflict, if those @code{precs} tables |
| 3546 | specify a particular constraint, then the conflict is resolved by using |
| 3547 | this constraint instead, else a conflict is reported and one of the |
| 3548 | conflicting constraints is picked arbitrarily and the others are |
| 3549 | simply ignored. |
| 3550 | @end defun |
| 3551 | |
| 3552 | @node SMIE Grammar |
| 3553 | @subsubsection Defining the Grammar of a Language |
| 3554 | @cindex SMIE grammar |
| 3555 | @cindex grammar, SMIE |
| 3556 | |
| 3557 | The usual way to define the SMIE grammar of a language is by |
| 3558 | defining a new global variable that holds the precedence table by |
| 3559 | giving a set of BNF rules. |
| 3560 | For example, the grammar definition for a small Pascal-like language |
| 3561 | could look like: |
| 3562 | @example |
| 3563 | @group |
| 3564 | (require 'smie) |
| 3565 | (defvar sample-smie-grammar |
| 3566 | (smie-prec2->grammar |
| 3567 | (smie-bnf->prec2 |
| 3568 | @end group |
| 3569 | @group |
| 3570 | '((id) |
| 3571 | (inst ("begin" insts "end") |
| 3572 | ("if" exp "then" inst "else" inst) |
| 3573 | (id ":=" exp) |
| 3574 | (exp)) |
| 3575 | (insts (insts ";" insts) (inst)) |
| 3576 | (exp (exp "+" exp) |
| 3577 | (exp "*" exp) |
| 3578 | ("(" exps ")")) |
| 3579 | (exps (exps "," exps) (exp))) |
| 3580 | @end group |
| 3581 | @group |
| 3582 | '((assoc ";")) |
| 3583 | '((assoc ",")) |
| 3584 | '((assoc "+") (assoc "*"))))) |
| 3585 | @end group |
| 3586 | @end example |
| 3587 | |
| 3588 | @noindent |
| 3589 | A few things to note: |
| 3590 | |
| 3591 | @itemize |
| 3592 | @item |
| 3593 | The above grammar does not explicitly mention the syntax of function |
| 3594 | calls: SMIE will automatically allow any sequence of sexps, such as |
| 3595 | identifiers, balanced parentheses, or @code{begin ... end} blocks |
| 3596 | to appear anywhere anyway. |
| 3597 | @item |
| 3598 | The grammar category @code{id} has no right hand side: this does not |
| 3599 | mean that it can match only the empty string, since as mentioned any |
| 3600 | sequence of sexps can appear anywhere anyway. |
| 3601 | @item |
| 3602 | Because non terminals cannot appear consecutively in the BNF grammar, it |
| 3603 | is difficult to correctly handle tokens that act as terminators, so the |
| 3604 | above grammar treats @code{";"} as a statement @emph{separator} instead, |
| 3605 | which SMIE can handle very well. |
| 3606 | @item |
| 3607 | Separators used in sequences (such as @code{","} and @code{";"} above) |
| 3608 | are best defined with BNF rules such as @code{(foo (foo "separator" foo) ...)} |
| 3609 | which generate precedence conflicts which are then resolved by giving |
| 3610 | them an explicit @code{(assoc "separator")}. |
| 3611 | @item |
| 3612 | The @code{("(" exps ")")} rule was not needed to pair up parens, since |
| 3613 | SMIE will pair up any characters that are marked as having paren syntax |
| 3614 | in the syntax table. What this rule does instead (together with the |
| 3615 | definition of @code{exps}) is to make it clear that @code{","} should |
| 3616 | not appear outside of parentheses. |
| 3617 | @item |
| 3618 | Rather than have a single @emph{precs} table to resolve conflicts, it is |
| 3619 | preferable to have several tables, so as to let the BNF part of the |
| 3620 | grammar specify relative precedences where possible. |
| 3621 | @item |
| 3622 | Unless there is a very good reason to prefer @code{left} or |
| 3623 | @code{right}, it is usually preferable to mark operators as associative, |
| 3624 | using @code{assoc}. For that reason @code{"+"} and @code{"*"} are |
| 3625 | defined above as @code{assoc}, although the language defines them |
| 3626 | formally as left associative. |
| 3627 | @end itemize |
| 3628 | |
| 3629 | @node SMIE Lexer |
| 3630 | @subsubsection Defining Tokens |
| 3631 | @cindex SMIE lexer |
| 3632 | @cindex defining tokens, SMIE |
| 3633 | |
| 3634 | SMIE comes with a predefined lexical analyzer which uses syntax tables |
| 3635 | in the following way: any sequence of characters that have word or |
| 3636 | symbol syntax is considered a token, and so is any sequence of |
| 3637 | characters that have punctuation syntax. This default lexer is |
| 3638 | often a good starting point but is rarely actually correct for any given |
| 3639 | language. For example, it will consider @code{"2,+3"} to be composed |
| 3640 | of 3 tokens: @code{"2"}, @code{",+"}, and @code{"3"}. |
| 3641 | |
| 3642 | To describe the lexing rules of your language to SMIE, you need |
| 3643 | 2 functions, one to fetch the next token, and another to fetch the |
| 3644 | previous token. Those functions will usually first skip whitespace and |
| 3645 | comments and then look at the next chunk of text to see if it |
| 3646 | is a special token. If so it should skip the token and |
| 3647 | return a description of this token. Usually this is simply the string |
| 3648 | extracted from the buffer, but it can be anything you want. |
| 3649 | For example: |
| 3650 | @example |
| 3651 | @group |
| 3652 | (defvar sample-keywords-regexp |
| 3653 | (regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "="))) |
| 3654 | @end group |
| 3655 | @group |
| 3656 | (defun sample-smie-forward-token () |
| 3657 | (forward-comment (point-max)) |
| 3658 | (cond |
| 3659 | ((looking-at sample-keywords-regexp) |
| 3660 | (goto-char (match-end 0)) |
| 3661 | (match-string-no-properties 0)) |
| 3662 | (t (buffer-substring-no-properties |
| 3663 | (point) |
| 3664 | (progn (skip-syntax-forward "w_") |
| 3665 | (point)))))) |
| 3666 | @end group |
| 3667 | @group |
| 3668 | (defun sample-smie-backward-token () |
| 3669 | (forward-comment (- (point))) |
| 3670 | (cond |
| 3671 | ((looking-back sample-keywords-regexp (- (point) 2) t) |
| 3672 | (goto-char (match-beginning 0)) |
| 3673 | (match-string-no-properties 0)) |
| 3674 | (t (buffer-substring-no-properties |
| 3675 | (point) |
| 3676 | (progn (skip-syntax-backward "w_") |
| 3677 | (point)))))) |
| 3678 | @end group |
| 3679 | @end example |
| 3680 | |
| 3681 | Notice how those lexers return the empty string when in front of |
| 3682 | parentheses. This is because SMIE automatically takes care of the |
| 3683 | parentheses defined in the syntax table. More specifically if the lexer |
| 3684 | returns nil or an empty string, SMIE tries to handle the corresponding |
| 3685 | text as a sexp according to syntax tables. |
| 3686 | |
| 3687 | @node SMIE Tricks |
| 3688 | @subsubsection Living With a Weak Parser |
| 3689 | |
| 3690 | The parsing technique used by SMIE does not allow tokens to behave |
| 3691 | differently in different contexts. For most programming languages, this |
| 3692 | manifests itself by precedence conflicts when converting the |
| 3693 | BNF grammar. |
| 3694 | |
| 3695 | Sometimes, those conflicts can be worked around by expressing the |
| 3696 | grammar slightly differently. For example, for Modula-2 it might seem |
| 3697 | natural to have a BNF grammar that looks like this: |
| 3698 | |
| 3699 | @example |
| 3700 | ... |
| 3701 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") |
| 3702 | ("CASE" exp "OF" cases "END") |
| 3703 | ...) |
| 3704 | (cases (cases "|" cases) |
| 3705 | (caselabel ":" insts) |
| 3706 | ("ELSE" insts)) |
| 3707 | ... |
| 3708 | @end example |
| 3709 | |
| 3710 | But this will create conflicts for @code{"ELSE"}: on the one hand, the |
| 3711 | IF rule implies (among many other things) that @code{"ELSE" = "END"}; |
| 3712 | but on the other hand, since @code{"ELSE"} appears within @code{cases}, |
| 3713 | which appears left of @code{"END"}, we also have @code{"ELSE" > "END"}. |
| 3714 | We can solve the conflict either by using: |
| 3715 | @example |
| 3716 | ... |
| 3717 | (inst ("IF" exp "THEN" insts "ELSE" insts "END") |
| 3718 | ("CASE" exp "OF" cases "END") |
| 3719 | ("CASE" exp "OF" cases "ELSE" insts "END") |
| 3720 | ...) |
| 3721 | (cases (cases "|" cases) (caselabel ":" insts)) |
| 3722 | ... |
| 3723 | @end example |
| 3724 | or |
| 3725 | @example |
| 3726 | ... |
| 3727 | (inst ("IF" exp "THEN" else "END") |
| 3728 | ("CASE" exp "OF" cases "END") |
| 3729 | ...) |
| 3730 | (else (insts "ELSE" insts)) |
| 3731 | (cases (cases "|" cases) (caselabel ":" insts) (else)) |
| 3732 | ... |
| 3733 | @end example |
| 3734 | |
| 3735 | Reworking the grammar to try and solve conflicts has its downsides, tho, |
| 3736 | because SMIE assumes that the grammar reflects the logical structure of |
| 3737 | the code, so it is preferable to keep the BNF closer to the intended |
| 3738 | abstract syntax tree. |
| 3739 | |
| 3740 | Other times, after careful consideration you may conclude that those |
| 3741 | conflicts are not serious and simply resolve them via the |
| 3742 | @var{resolvers} argument of @code{smie-bnf->prec2}. Usually this is |
| 3743 | because the grammar is simply ambiguous: the conflict does not affect |
| 3744 | the set of programs described by the grammar, but only the way those |
| 3745 | programs are parsed. This is typically the case for separators and |
| 3746 | associative infix operators, where you want to add a resolver like |
| 3747 | @code{'((assoc "|"))}. Another case where this can happen is for the |
| 3748 | classic @emph{dangling else} problem, where you will use @code{'((assoc |
| 3749 | "else" "then"))}. It can also happen for cases where the conflict is |
| 3750 | real and cannot really be resolved, but it is unlikely to pose a problem |
| 3751 | in practice. |
| 3752 | |
| 3753 | Finally, in many cases some conflicts will remain despite all efforts to |
| 3754 | restructure the grammar. Do not despair: while the parser cannot be |
| 3755 | made more clever, you can make the lexer as smart as you want. So, the |
| 3756 | solution is then to look at the tokens involved in the conflict and to |
| 3757 | split one of those tokens into 2 (or more) different tokens. E.g., if |
| 3758 | the grammar needs to distinguish between two incompatible uses of the |
| 3759 | token @code{"begin"}, make the lexer return different tokens (say |
| 3760 | @code{"begin-fun"} and @code{"begin-plain"}) depending on which kind of |
| 3761 | @code{"begin"} it finds. This pushes the work of distinguishing the |
| 3762 | different cases to the lexer, which will thus have to look at the |
| 3763 | surrounding text to find ad-hoc clues. |
| 3764 | |
| 3765 | @node SMIE Indentation |
| 3766 | @subsubsection Specifying Indentation Rules |
| 3767 | @cindex indentation rules, SMIE |
| 3768 | |
| 3769 | Based on the provided grammar, SMIE will be able to provide automatic |
| 3770 | indentation without any extra effort. But in practice, this default |
| 3771 | indentation style will probably not be good enough. You will want to |
| 3772 | tweak it in many different cases. |
| 3773 | |
| 3774 | SMIE indentation is based on the idea that indentation rules should be |
| 3775 | as local as possible. To this end, it relies on the idea of |
| 3776 | @emph{virtual} indentation, which is the indentation that a particular |
| 3777 | program point would have if it were at the beginning of a line. |
| 3778 | Of course, if that program point is indeed at the beginning of a line, |
| 3779 | its virtual indentation is its current indentation. But if not, then |
| 3780 | SMIE uses the indentation algorithm to compute the virtual indentation |
| 3781 | of that point. Now in practice, the virtual indentation of a program |
| 3782 | point does not have to be identical to the indentation it would have if |
| 3783 | we inserted a newline before it. To see how this works, the SMIE rule |
| 3784 | for indentation after a @code{@{} in C does not care whether the |
| 3785 | @code{@{} is standing on a line of its own or is at the end of the |
| 3786 | preceding line. Instead, these different cases are handled in the |
| 3787 | indentation rule that decides how to indent before a @code{@{}. |
| 3788 | |
| 3789 | Another important concept is the notion of @emph{parent}: The |
| 3790 | @emph{parent} of a token, is the head token of the nearest enclosing |
| 3791 | syntactic construct. For example, the parent of an @code{else} is the |
| 3792 | @code{if} to which it belongs, and the parent of an @code{if}, in turn, |
| 3793 | is the lead token of the surrounding construct. The command |
| 3794 | @code{backward-sexp} jumps from a token to its parent, but there are |
| 3795 | some caveats: for @emph{openers} (tokens which start a construct, like |
| 3796 | @code{if}), you need to start with point before the token, while for |
| 3797 | others you need to start with point after the token. |
| 3798 | @code{backward-sexp} stops with point before the parent token if that is |
| 3799 | the @emph{opener} of the token of interest, and otherwise it stops with |
| 3800 | point after the parent token. |
| 3801 | |
| 3802 | SMIE indentation rules are specified using a function that takes two |
| 3803 | arguments @var{method} and @var{arg} where the meaning of @var{arg} and the |
| 3804 | expected return value depend on @var{method}. |
| 3805 | |
| 3806 | @var{method} can be: |
| 3807 | @itemize |
| 3808 | @item |
| 3809 | @code{:after}, in which case @var{arg} is a token and the function |
| 3810 | should return the @var{offset} to use for indentation after @var{arg}. |
| 3811 | @item |
| 3812 | @code{:before}, in which case @var{arg} is a token and the function |
| 3813 | should return the @var{offset} to use to indent @var{arg} itself. |
| 3814 | @item |
| 3815 | @code{:elem}, in which case the function should return either the offset |
| 3816 | to use to indent function arguments (if @var{arg} is the symbol |
| 3817 | @code{arg}) or the basic indentation step (if @var{arg} is the symbol |
| 3818 | @code{basic}). |
| 3819 | @item |
| 3820 | @code{:list-intro}, in which case @var{arg} is a token and the function |
| 3821 | should return non-@code{nil} if the token is followed by a list of |
| 3822 | expressions (not separated by any token) rather than an expression. |
| 3823 | @end itemize |
| 3824 | |
| 3825 | When @var{arg} is a token, the function is called with point just before |
| 3826 | that token. A return value of nil always means to fallback on the |
| 3827 | default behavior, so the function should return nil for arguments it |
| 3828 | does not expect. |
| 3829 | |
| 3830 | @var{offset} can be: |
| 3831 | @itemize |
| 3832 | @item |
| 3833 | @code{nil}: use the default indentation rule. |
| 3834 | @item |
| 3835 | @code{(column . @var{column})}: indent to column @var{column}. |
| 3836 | @item |
| 3837 | @var{number}: offset by @var{number}, relative to a base token which is |
| 3838 | the current token for @code{:after} and its parent for @code{:before}. |
| 3839 | @end itemize |
| 3840 | |
| 3841 | @node SMIE Indentation Helpers |
| 3842 | @subsubsection Helper Functions for Indentation Rules |
| 3843 | |
| 3844 | SMIE provides various functions designed specifically for use in the |
| 3845 | indentation rules function (several of those functions break if used in |
| 3846 | another context). These functions all start with the prefix |
| 3847 | @code{smie-rule-}. |
| 3848 | |
| 3849 | @defun smie-rule-bolp |
| 3850 | Return non-@code{nil} if the current token is the first on the line. |
| 3851 | @end defun |
| 3852 | |
| 3853 | @defun smie-rule-hanging-p |
| 3854 | Return non-@code{nil} if the current token is @emph{hanging}. |
| 3855 | A token is @emph{hanging} if it is the last token on the line |
| 3856 | and if it is preceded by other tokens: a lone token on a line is not |
| 3857 | hanging. |
| 3858 | @end defun |
| 3859 | |
| 3860 | @defun smie-rule-next-p &rest tokens |
| 3861 | Return non-@code{nil} if the next token is among @var{tokens}. |
| 3862 | @end defun |
| 3863 | |
| 3864 | @defun smie-rule-prev-p &rest tokens |
| 3865 | Return non-@code{nil} if the previous token is among @var{tokens}. |
| 3866 | @end defun |
| 3867 | |
| 3868 | @defun smie-rule-parent-p &rest parents |
| 3869 | Return non-@code{nil} if the current token's parent is among @var{parents}. |
| 3870 | @end defun |
| 3871 | |
| 3872 | @defun smie-rule-sibling-p |
| 3873 | Return non-@code{nil} if the current token's parent is actually a |
| 3874 | sibling. This is the case for example when the parent of a @code{","} |
| 3875 | is just the previous @code{","}. |
| 3876 | @end defun |
| 3877 | |
| 3878 | @defun smie-rule-parent &optional offset |
| 3879 | Return the proper offset to align the current token with the parent. |
| 3880 | If non-@code{nil}, @var{offset} should be an integer giving an |
| 3881 | additional offset to apply. |
| 3882 | @end defun |
| 3883 | |
| 3884 | @defun smie-rule-separator method |
| 3885 | Indent current token as a @emph{separator}. |
| 3886 | |
| 3887 | By @emph{separator}, we mean here a token whose sole purpose is to |
| 3888 | separate various elements within some enclosing syntactic construct, and |
| 3889 | which does not have any semantic significance in itself (i.e., it would |
| 3890 | typically not exist as a node in an abstract syntax tree). |
| 3891 | |
| 3892 | Such a token is expected to have an associative syntax and be closely |
| 3893 | tied to its syntactic parent. Typical examples are @code{","} in lists |
| 3894 | of arguments (enclosed inside parentheses), or @code{";"} in sequences |
| 3895 | of instructions (enclosed in a @code{@{...@}} or @code{begin...end} |
| 3896 | block). |
| 3897 | |
| 3898 | @var{method} should be the method name that was passed to |
| 3899 | `smie-rules-function'. |
| 3900 | @end defun |
| 3901 | |
| 3902 | @node SMIE Indentation Example |
| 3903 | @subsubsection Sample Indentation Rules |
| 3904 | |
| 3905 | Here is an example of an indentation function: |
| 3906 | |
| 3907 | @example |
| 3908 | (defun sample-smie-rules (kind token) |
| 3909 | (pcase (cons kind token) |
| 3910 | (`(:elem . basic) sample-indent-basic) |
| 3911 | (`(,_ . ",") (smie-rule-separator kind)) |
| 3912 | (`(:after . ":=") sample-indent-basic) |
| 3913 | (`(:before . ,(or `"begin" `"(" `"@{"))) |
| 3914 | (if (smie-rule-hanging-p) (smie-rule-parent))) |
| 3915 | (`(:before . "if") |
| 3916 | (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") |
| 3917 | (smie-rule-parent))))) |
| 3918 | @end example |
| 3919 | |
| 3920 | @noindent |
| 3921 | A few things to note: |
| 3922 | |
| 3923 | @itemize |
| 3924 | @item |
| 3925 | The first case indicates the basic indentation increment to use. |
| 3926 | If @code{sample-indent-basic} is nil, then SMIE uses the global |
| 3927 | setting @code{smie-indent-basic}. The major mode could have set |
| 3928 | @code{smie-indent-basic} buffer-locally instead, but that |
| 3929 | is discouraged. |
| 3930 | |
| 3931 | @item |
| 3932 | The rule for the token @code{","} make SMIE try to be more clever when |
| 3933 | the comma separator is placed at the beginning of lines. It tries to |
| 3934 | outdent the separator so as to align the code after the comma; for |
| 3935 | example: |
| 3936 | |
| 3937 | @example |
| 3938 | x = longfunctionname ( |
| 3939 | arg1 |
| 3940 | , arg2 |
| 3941 | ); |
| 3942 | @end example |
| 3943 | |
| 3944 | @item |
| 3945 | The rule for indentation after @code{":="} exists because otherwise |
| 3946 | SMIE would treat @code{":="} as an infix operator and would align the |
| 3947 | right argument with the left one. |
| 3948 | |
| 3949 | @item |
| 3950 | The rule for indentation before @code{"begin"} is an example of the use |
| 3951 | of virtual indentation: This rule is used only when @code{"begin"} is |
| 3952 | hanging, which can happen only when @code{"begin"} is not at the |
| 3953 | beginning of a line. So this is not used when indenting |
| 3954 | @code{"begin"} itself but only when indenting something relative to this |
| 3955 | @code{"begin"}. Concretely, this rule changes the indentation from: |
| 3956 | |
| 3957 | @example |
| 3958 | if x > 0 then begin |
| 3959 | dosomething(x); |
| 3960 | end |
| 3961 | @end example |
| 3962 | to |
| 3963 | @example |
| 3964 | if x > 0 then begin |
| 3965 | dosomething(x); |
| 3966 | end |
| 3967 | @end example |
| 3968 | |
| 3969 | @item |
| 3970 | The rule for indentation before @code{"if"} is similar to the one for |
| 3971 | @code{"begin"}, but where the purpose is to treat @code{"else if"} |
| 3972 | as a single unit, so as to align a sequence of tests rather than indent |
| 3973 | each test further to the right. This function does this only in the |
| 3974 | case where the @code{"if"} is not placed on a separate line, hence the |
| 3975 | @code{smie-rule-bolp} test. |
| 3976 | |
| 3977 | If we know that the @code{"else"} is always aligned with its @code{"if"} |
| 3978 | and is always at the beginning of a line, we can use a more efficient |
| 3979 | rule: |
| 3980 | @example |
| 3981 | ((equal token "if") |
| 3982 | (and (not (smie-rule-bolp)) |
| 3983 | (smie-rule-prev-p "else") |
| 3984 | (save-excursion |
| 3985 | (sample-smie-backward-token) |
| 3986 | (cons 'column (current-column))))) |
| 3987 | @end example |
| 3988 | |
| 3989 | The advantage of this formulation is that it reuses the indentation of |
| 3990 | the previous @code{"else"}, rather than going all the way back to the |
| 3991 | first @code{"if"} of the sequence. |
| 3992 | @end itemize |
| 3993 | |
| 3994 | @node Desktop Save Mode |
| 3995 | @section Desktop Save Mode |
| 3996 | @cindex desktop save mode |
| 3997 | |
| 3998 | @dfn{Desktop Save Mode} is a feature to save the state of Emacs from |
| 3999 | one session to another. The user-level commands for using Desktop |
| 4000 | Save Mode are described in the GNU Emacs Manual (@pxref{Saving Emacs |
| 4001 | Sessions,,, emacs, the GNU Emacs Manual}). Modes whose buffers visit |
| 4002 | a file, don't have to do anything to use this feature. |
| 4003 | |
| 4004 | For buffers not visiting a file to have their state saved, the major |
| 4005 | mode must bind the buffer local variable @code{desktop-save-buffer} to |
| 4006 | a non-@code{nil} value. |
| 4007 | |
| 4008 | @defvar desktop-save-buffer |
| 4009 | If this buffer-local variable is non-@code{nil}, the buffer will have |
| 4010 | its state saved in the desktop file at desktop save. If the value is |
| 4011 | a function, it is called at desktop save with argument |
| 4012 | @var{desktop-dirname}, and its value is saved in the desktop file along |
| 4013 | with the state of the buffer for which it was called. When file names |
| 4014 | are returned as part of the auxiliary information, they should be |
| 4015 | formatted using the call |
| 4016 | |
| 4017 | @example |
| 4018 | (desktop-file-name @var{file-name} @var{desktop-dirname}) |
| 4019 | @end example |
| 4020 | |
| 4021 | @end defvar |
| 4022 | |
| 4023 | For buffers not visiting a file to be restored, the major mode must |
| 4024 | define a function to do the job, and that function must be listed in |
| 4025 | the alist @code{desktop-buffer-mode-handlers}. |
| 4026 | |
| 4027 | @defvar desktop-buffer-mode-handlers |
| 4028 | Alist with elements |
| 4029 | |
| 4030 | @example |
| 4031 | (@var{major-mode} . @var{restore-buffer-function}) |
| 4032 | @end example |
| 4033 | |
| 4034 | The function @var{restore-buffer-function} will be called with |
| 4035 | argument list |
| 4036 | |
| 4037 | @example |
| 4038 | (@var{buffer-file-name} @var{buffer-name} @var{desktop-buffer-misc}) |
| 4039 | @end example |
| 4040 | |
| 4041 | and it should return the restored buffer. |
| 4042 | Here @var{desktop-buffer-misc} is the value returned by the function |
| 4043 | optionally bound to @code{desktop-save-buffer}. |
| 4044 | @end defvar |