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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
acaf905b | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2012 |
d24880de | 4 | @c Free Software Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 6 | @setfilename ../../info/syntax |
b8d4c8d0 GM |
7 | @node Syntax Tables, Abbrevs, Searching and Matching, Top |
8 | @chapter Syntax Tables | |
9 | @cindex parsing buffer text | |
10 | @cindex syntax table | |
11 | @cindex text parsing | |
12 | ||
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13 | A @dfn{syntax table} specifies the syntactic role of each character |
14 | in a buffer. It can be used to determine where words, symbols, and | |
15 | other syntactic constructs begin and end. This information is used by | |
16 | many Emacs facilities, including Font Lock mode (@pxref{Font Lock | |
17 | Mode}) and the various complex movement commands (@pxref{Motion}). | |
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18 | |
19 | @menu | |
20 | * Basics: Syntax Basics. Basic concepts of syntax tables. | |
4230351b | 21 | * Syntax Descriptors:: How characters are classified. |
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22 | * Syntax Table Functions:: How to create, examine and alter syntax tables. |
23 | * Syntax Properties:: Overriding syntax with text properties. | |
d24880de | 24 | * Motion and Syntax:: Moving over characters with certain syntaxes. |
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25 | * Parsing Expressions:: Parsing balanced expressions |
26 | using the syntax table. | |
27 | * Standard Syntax Tables:: Syntax tables used by various major modes. | |
28 | * Syntax Table Internals:: How syntax table information is stored. | |
29 | * Categories:: Another way of classifying character syntax. | |
30 | @end menu | |
31 | ||
32 | @node Syntax Basics | |
33 | @section Syntax Table Concepts | |
34 | ||
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35 | A syntax table is a char-table (@pxref{Char-Tables}). The element at |
36 | index @var{c} describes the character with code @var{c}. The element's | |
37 | value should be a list that encodes the syntax of the character in | |
38 | question. | |
39 | ||
40 | Syntax tables are used only for moving across text, not for the Emacs | |
41 | Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp | |
42 | expressions, and these rules cannot be changed. (Some Lisp systems | |
43 | provide ways to redefine the read syntax, but we decided to leave this | |
44 | feature out of Emacs Lisp for simplicity.) | |
45 | ||
46 | Each buffer has its own major mode, and each major mode has its own | |
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47 | idea of the syntactic class of various characters. For example, in |
48 | Lisp mode, the character @samp{;} begins a comment, but in C mode, it | |
b8d4c8d0 | 49 | terminates a statement. To support these variations, Emacs makes the |
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50 | syntax table local to each buffer. Typically, each major mode has its |
51 | own syntax table and installs that table in each buffer that uses that | |
52 | mode. Changing this table alters the syntax in all those buffers as | |
53 | well as in any buffers subsequently put in that mode. Occasionally | |
54 | several similar modes share one syntax table. @xref{Example Major | |
55 | Modes}, for an example of how to set up a syntax table. | |
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56 | |
57 | A syntax table can inherit the data for some characters from the | |
58 | standard syntax table, while specifying other characters itself. The | |
59 | ``inherit'' syntax class means ``inherit this character's syntax from | |
16152b76 | 60 | the standard syntax table''. Just changing the standard syntax for a |
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61 | character affects all syntax tables that inherit from it. |
62 | ||
63 | @defun syntax-table-p object | |
64 | This function returns @code{t} if @var{object} is a syntax table. | |
65 | @end defun | |
66 | ||
67 | @node Syntax Descriptors | |
68 | @section Syntax Descriptors | |
69 | @cindex syntax class | |
70 | ||
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71 | The syntactic role of a character is called its @dfn{syntax class}. |
72 | Each syntax table specifies the syntax class of each character. There | |
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73 | is no necessary relationship between the class of a character in one |
74 | syntax table and its class in any other table. | |
75 | ||
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76 | Each syntax class is designated by a mnemonic character, which |
77 | serves as the name of the class when you need to specify a class. | |
78 | Usually, this designator character is one that is often assigned that | |
79 | class; however, its meaning as a designator is unvarying and | |
80 | independent of what syntax that character currently has. Thus, | |
81 | @samp{\} as a designator character always means ``escape character'' | |
82 | syntax, regardless of whether the @samp{\} character actually has that | |
83 | syntax in the current syntax table. | |
84 | @ifnottex | |
85 | @xref{Syntax Class Table}, for a list of syntax classes. | |
86 | @end ifnottex | |
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87 | |
88 | @cindex syntax descriptor | |
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89 | A @dfn{syntax descriptor} is a Lisp string that describes the syntax |
90 | classes and other syntactic properties of a character. When you want | |
91 | to modify the syntax of a character, that is done by calling the | |
92 | function @code{modify-syntax-entry} and passing a syntax descriptor as | |
93 | one of its arguments (@pxref{Syntax Table Functions}). | |
94 | ||
95 | The first character in a syntax descriptor designates the syntax | |
96 | class. The second character specifies a matching character (e.g.@: in | |
97 | Lisp, the matching character for @samp{(} is @samp{)}); if there is no | |
98 | matching character, put a space there. Then come the characters for | |
99 | any desired flags. | |
100 | ||
101 | If no matching character or flags are needed, only one character | |
102 | (specifying the syntax class) is sufficient. | |
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103 | |
104 | For example, the syntax descriptor for the character @samp{*} in C | |
ad21a12a | 105 | mode is @code{". 23"} (i.e., punctuation, matching character slot |
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106 | unused, second character of a comment-starter, first character of a |
107 | comment-ender), and the entry for @samp{/} is @samp{@w{. 14}} (i.e., | |
108 | punctuation, matching character slot unused, first character of a | |
109 | comment-starter, second character of a comment-ender). | |
110 | ||
111 | @menu | |
112 | * Syntax Class Table:: Table of syntax classes. | |
113 | * Syntax Flags:: Additional flags each character can have. | |
114 | @end menu | |
115 | ||
116 | @node Syntax Class Table | |
117 | @subsection Table of Syntax Classes | |
118 | ||
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119 | Here is a table of syntax classes, the characters that designate |
120 | them, their meanings, and examples of their use. | |
b8d4c8d0 | 121 | |
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122 | @table @asis |
123 | @item Whitespace characters: @samp{@ } or @samp{-} | |
124 | Characters that separate symbols and words from each other. | |
125 | Typically, whitespace characters have no other syntactic significance, | |
126 | and multiple whitespace characters are syntactically equivalent to a | |
127 | single one. Space, tab, and formfeed are classified as whitespace in | |
128 | almost all major modes. | |
129 | ||
130 | This syntax class can be designated by either @w{@samp{@ }} or | |
131 | @samp{-}. Both designators are equivalent. | |
132 | ||
133 | @item Word constituents: @samp{w} | |
134 | Parts of words in human languages. These are typically used in | |
135 | variable and command names in programs. All upper- and lower-case | |
136 | letters, and the digits, are typically word constituents. | |
137 | ||
138 | @item Symbol constituents: @samp{_} | |
139 | Extra characters used in variable and command names along with word | |
140 | constituents. Examples include the characters @samp{$&*+-_<>} in Lisp | |
141 | mode, which may be part of a symbol name even though they are not part | |
142 | of English words. In standard C, the only non-word-constituent | |
b8d4c8d0 | 143 | character that is valid in symbols is underscore (@samp{_}). |
b8d4c8d0 | 144 | |
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145 | @item Punctuation characters: @samp{.} |
146 | Characters used as punctuation in a human language, or used in a | |
147 | programming language to separate symbols from one another. Some | |
148 | programming language modes, such as Emacs Lisp mode, have no | |
149 | characters in this class since the few characters that are not symbol | |
150 | or word constituents all have other uses. Other programming language | |
151 | modes, such as C mode, use punctuation syntax for operators. | |
152 | ||
153 | @item Open parenthesis characters: @samp{(} | |
154 | @itemx Close parenthesis characters: @samp{)} | |
155 | Characters used in dissimilar pairs to surround sentences or | |
156 | expressions. Such a grouping is begun with an open parenthesis | |
157 | character and terminated with a close. Each open parenthesis | |
158 | character matches a particular close parenthesis character, and vice | |
159 | versa. Normally, Emacs indicates momentarily the matching open | |
160 | parenthesis when you insert a close parenthesis. @xref{Blinking}. | |
161 | ||
162 | In human languages, and in C code, the parenthesis pairs are | |
163 | @samp{()}, @samp{[]}, and @samp{@{@}}. In Emacs Lisp, the delimiters | |
164 | for lists and vectors (@samp{()} and @samp{[]}) are classified as | |
165 | parenthesis characters. | |
166 | ||
167 | @item String quotes: @samp{"} | |
168 | Characters used to delimit string constants. The same string quote | |
169 | character appears at the beginning and the end of a string. Such | |
170 | quoted strings do not nest. | |
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171 | |
172 | The parsing facilities of Emacs consider a string as a single token. | |
173 | The usual syntactic meanings of the characters in the string are | |
174 | suppressed. | |
175 | ||
176 | The Lisp modes have two string quote characters: double-quote (@samp{"}) | |
177 | and vertical bar (@samp{|}). @samp{|} is not used in Emacs Lisp, but it | |
178 | is used in Common Lisp. C also has two string quote characters: | |
179 | double-quote for strings, and single-quote (@samp{'}) for character | |
180 | constants. | |
181 | ||
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182 | Human text has no string quote characters. We do not want quotation |
183 | marks to turn off the usual syntactic properties of other characters | |
184 | in the quotation. | |
b8d4c8d0 | 185 | |
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186 | @item Escape-syntax characters: @samp{\} |
187 | Characters that start an escape sequence, such as is used in string | |
188 | and character constants. The character @samp{\} belongs to this class | |
189 | in both C and Lisp. (In C, it is used thus only inside strings, but | |
190 | it turns out to cause no trouble to treat it this way throughout C | |
191 | code.) | |
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192 | |
193 | Characters in this class count as part of words if | |
194 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
b8d4c8d0 | 195 | |
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196 | @item Character quotes: @samp{/} |
197 | Characters used to quote the following character so that it loses its | |
198 | normal syntactic meaning. This differs from an escape character in | |
199 | that only the character immediately following is ever affected. | |
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200 | |
201 | Characters in this class count as part of words if | |
202 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
203 | ||
204 | This class is used for backslash in @TeX{} mode. | |
b8d4c8d0 | 205 | |
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206 | @item Paired delimiters: @samp{$} |
207 | Similar to string quote characters, except that the syntactic | |
208 | properties of the characters between the delimiters are not | |
209 | suppressed. Only @TeX{} mode uses a paired delimiter presently---the | |
210 | @samp{$} that both enters and leaves math mode. | |
211 | ||
212 | @item Expression prefixes: @samp{'} | |
213 | Characters used for syntactic operators that are considered as part of | |
214 | an expression if they appear next to one. In Lisp modes, these | |
215 | characters include the apostrophe, @samp{'} (used for quoting), the | |
216 | comma, @samp{,} (used in macros), and @samp{#} (used in the read | |
217 | syntax for certain data types). | |
218 | ||
219 | @item Comment starters: @samp{<} | |
220 | @itemx Comment enders: @samp{>} | |
b8d4c8d0 | 221 | @cindex comment syntax |
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222 | Characters used in various languages to delimit comments. Human text |
223 | has no comment characters. In Lisp, the semicolon (@samp{;}) starts a | |
224 | comment and a newline or formfeed ends one. | |
b8d4c8d0 | 225 | |
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226 | @item Inherit standard syntax: @samp{@@} |
227 | This syntax class does not specify a particular syntax. It says to | |
228 | look in the standard syntax table to find the syntax of this | |
229 | character. | |
b8d4c8d0 | 230 | |
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231 | @item Generic comment delimiters: @samp{!} |
232 | Characters that start or end a special kind of comment. @emph{Any} | |
233 | generic comment delimiter matches @emph{any} generic comment | |
234 | delimiter, but they cannot match a comment starter or comment ender; | |
235 | generic comment delimiters can only match each other. | |
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236 | |
237 | This syntax class is primarily meant for use with the | |
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238 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
239 | can mark any range of characters as forming a comment, by giving the | |
240 | first and last characters of the range @code{syntax-table} properties | |
b8d4c8d0 | 241 | identifying them as generic comment delimiters. |
b8d4c8d0 | 242 | |
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243 | @item Generic string delimiters: @samp{|} |
244 | Characters that start or end a string. This class differs from the | |
245 | string quote class in that @emph{any} generic string delimiter can | |
246 | match any other generic string delimiter; but they do not match | |
247 | ordinary string quote characters. | |
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248 | |
249 | This syntax class is primarily meant for use with the | |
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250 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
251 | can mark any range of characters as forming a string constant, by | |
252 | giving the first and last characters of the range @code{syntax-table} | |
253 | properties identifying them as generic string delimiters. | |
254 | @end table | |
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255 | |
256 | @node Syntax Flags | |
257 | @subsection Syntax Flags | |
258 | @cindex syntax flags | |
259 | ||
260 | In addition to the classes, entries for characters in a syntax table | |
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261 | can specify flags. There are eight possible flags, represented by the |
262 | characters @samp{1}, @samp{2}, @samp{3}, @samp{4}, @samp{b}, @samp{c}, | |
263 | @samp{n}, and @samp{p}. | |
264 | ||
265 | All the flags except @samp{p} are used to describe comment | |
266 | delimiters. The digit flags are used for comment delimiters made up | |
267 | of 2 characters. They indicate that a character can @emph{also} be | |
268 | part of a comment sequence, in addition to the syntactic properties | |
269 | associated with its character class. The flags are independent of the | |
270 | class and each other for the sake of characters such as @samp{*} in | |
271 | C mode, which is a punctuation character, @emph{and} the second | |
272 | character of a start-of-comment sequence (@samp{/*}), @emph{and} the | |
273 | first character of an end-of-comment sequence (@samp{*/}). The flags | |
274 | @samp{b}, @samp{c}, and @samp{n} are used to qualify the corresponding | |
275 | comment delimiter. | |
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276 | |
277 | Here is a table of the possible flags for a character @var{c}, | |
278 | and what they mean: | |
279 | ||
280 | @itemize @bullet | |
281 | @item | |
282 | @samp{1} means @var{c} is the start of a two-character comment-start | |
283 | sequence. | |
284 | ||
285 | @item | |
286 | @samp{2} means @var{c} is the second character of such a sequence. | |
287 | ||
288 | @item | |
289 | @samp{3} means @var{c} is the start of a two-character comment-end | |
290 | sequence. | |
291 | ||
292 | @item | |
293 | @samp{4} means @var{c} is the second character of such a sequence. | |
294 | ||
295 | @item | |
b8d4c8d0 | 296 | @samp{b} means that @var{c} as a comment delimiter belongs to the |
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297 | alternative ``b'' comment style. For a two-character comment starter, |
298 | this flag is only significant on the second char, and for a 2-character | |
299 | comment ender it is only significant on the first char. | |
b8d4c8d0 | 300 | |
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301 | @item |
302 | @samp{c} means that @var{c} as a comment delimiter belongs to the | |
303 | alternative ``c'' comment style. For a two-character comment | |
304 | delimiter, @samp{c} on either character makes it of style ``c''. | |
b8d4c8d0 | 305 | |
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306 | @item |
307 | @samp{n} on a comment delimiter character specifies | |
308 | that this kind of comment can be nested. For a two-character | |
309 | comment delimiter, @samp{n} on either character makes it | |
310 | nestable. | |
b8d4c8d0 | 311 | |
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312 | Emacs supports several comment styles simultaneously in any one syntax |
313 | table. A comment style is a set of flags @samp{b}, @samp{c}, and | |
314 | @samp{n}, so there can be up to 8 different comment styles. | |
315 | Each comment delimiter has a style and only matches comment delimiters | |
316 | of the same style. Thus if a comment starts with the comment-start | |
317 | sequence of style ``bn'', it will extend until the next matching | |
318 | comment-end sequence of style ``bn''. | |
b8d4c8d0 | 319 | |
7cf78aac | 320 | The appropriate comment syntax settings for C++ can be as follows: |
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321 | |
322 | @table @asis | |
323 | @item @samp{/} | |
7cf78aac | 324 | @samp{124} |
b8d4c8d0 | 325 | @item @samp{*} |
7cf78aac | 326 | @samp{23b} |
b8d4c8d0 | 327 | @item newline |
7cf78aac | 328 | @samp{>} |
b8d4c8d0 GM |
329 | @end table |
330 | ||
331 | This defines four comment-delimiting sequences: | |
332 | ||
333 | @table @asis | |
334 | @item @samp{/*} | |
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335 | This is a comment-start sequence for ``b'' style because the |
336 | second character, @samp{*}, has the @samp{b} flag. | |
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337 | |
338 | @item @samp{//} | |
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339 | This is a comment-start sequence for ``a'' style because the second |
340 | character, @samp{/}, does not have the @samp{b} flag. | |
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341 | |
342 | @item @samp{*/} | |
7cf78aac | 343 | This is a comment-end sequence for ``b'' style because the first |
35a30759 | 344 | character, @samp{*}, has the @samp{b} flag. |
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345 | |
346 | @item newline | |
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347 | This is a comment-end sequence for ``a'' style, because the newline |
348 | character does not have the @samp{b} flag. | |
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349 | @end table |
350 | ||
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351 | @item |
352 | @c Emacs 19 feature | |
353 | @samp{p} identifies an additional ``prefix character'' for Lisp syntax. | |
354 | These characters are treated as whitespace when they appear between | |
355 | expressions. When they appear within an expression, they are handled | |
356 | according to their usual syntax classes. | |
357 | ||
358 | The function @code{backward-prefix-chars} moves back over these | |
359 | characters, as well as over characters whose primary syntax class is | |
360 | prefix (@samp{'}). @xref{Motion and Syntax}. | |
361 | @end itemize | |
362 | ||
363 | @node Syntax Table Functions | |
364 | @section Syntax Table Functions | |
365 | ||
366 | In this section we describe functions for creating, accessing and | |
367 | altering syntax tables. | |
368 | ||
369 | @defun make-syntax-table &optional table | |
370 | This function creates a new syntax table, with all values initialized | |
371 | to @code{nil}. If @var{table} is non-@code{nil}, it becomes the | |
372 | parent of the new syntax table, otherwise the standard syntax table is | |
373 | the parent. Like all char-tables, a syntax table inherits from its | |
374 | parent. Thus the original syntax of all characters in the returned | |
375 | syntax table is determined by the parent. @xref{Char-Tables}. | |
376 | ||
377 | Most major mode syntax tables are created in this way. | |
378 | @end defun | |
379 | ||
380 | @defun copy-syntax-table &optional table | |
381 | This function constructs a copy of @var{table} and returns it. If | |
382 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
383 | standard syntax table. Otherwise, an error is signaled if @var{table} is | |
384 | not a syntax table. | |
385 | @end defun | |
386 | ||
387 | @deffn Command modify-syntax-entry char syntax-descriptor &optional table | |
388 | This function sets the syntax entry for @var{char} according to | |
4230351b | 389 | @var{syntax-descriptor}. @var{char} must be a character, or a cons |
f147ff75 CY |
390 | cell of the form @code{(@var{min} . @var{max})}; in the latter case, |
391 | the function sets the syntax entries for all characters in the range | |
392 | between @var{min} and @var{max}, inclusive. | |
393 | ||
394 | The syntax is changed only for @var{table}, which defaults to the | |
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395 | current buffer's syntax table, and not in any other syntax table. |
396 | ||
397 | The argument @var{syntax-descriptor} is a syntax descriptor for the | |
398 | desired syntax (i.e.@: a string beginning with a class designator | |
399 | character, and optionally containing a matching character and syntax | |
400 | flags). An error is signaled if the first character is not one of the | |
401 | seventeen syntax class designators. @xref{Syntax Descriptors}. | |
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402 | |
403 | This function always returns @code{nil}. The old syntax information in | |
404 | the table for this character is discarded. | |
405 | ||
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406 | @example |
407 | @group | |
408 | @exdent @r{Examples:} | |
409 | ||
410 | ;; @r{Put the space character in class whitespace.} | |
411 | (modify-syntax-entry ?\s " ") | |
412 | @result{} nil | |
413 | @end group | |
414 | ||
415 | @group | |
416 | ;; @r{Make @samp{$} an open parenthesis character,} | |
417 | ;; @r{with @samp{^} as its matching close.} | |
418 | (modify-syntax-entry ?$ "(^") | |
419 | @result{} nil | |
420 | @end group | |
421 | ||
422 | @group | |
423 | ;; @r{Make @samp{^} a close parenthesis character,} | |
424 | ;; @r{with @samp{$} as its matching open.} | |
425 | (modify-syntax-entry ?^ ")$") | |
426 | @result{} nil | |
427 | @end group | |
428 | ||
429 | @group | |
430 | ;; @r{Make @samp{/} a punctuation character,} | |
431 | ;; @r{the first character of a start-comment sequence,} | |
432 | ;; @r{and the second character of an end-comment sequence.} | |
433 | ;; @r{This is used in C mode.} | |
434 | (modify-syntax-entry ?/ ". 14") | |
435 | @result{} nil | |
436 | @end group | |
437 | @end example | |
438 | @end deffn | |
439 | ||
440 | @defun char-syntax character | |
441 | This function returns the syntax class of @var{character}, represented | |
442 | by its mnemonic designator character. This returns @emph{only} the | |
443 | class, not any matching parenthesis or flags. | |
444 | ||
445 | An error is signaled if @var{char} is not a character. | |
446 | ||
447 | The following examples apply to C mode. The first example shows that | |
448 | the syntax class of space is whitespace (represented by a space). The | |
449 | second example shows that the syntax of @samp{/} is punctuation. This | |
450 | does not show the fact that it is also part of comment-start and -end | |
451 | sequences. The third example shows that open parenthesis is in the class | |
452 | of open parentheses. This does not show the fact that it has a matching | |
453 | character, @samp{)}. | |
454 | ||
455 | @example | |
456 | @group | |
457 | (string (char-syntax ?\s)) | |
458 | @result{} " " | |
459 | @end group | |
460 | ||
461 | @group | |
462 | (string (char-syntax ?/)) | |
463 | @result{} "." | |
464 | @end group | |
465 | ||
466 | @group | |
467 | (string (char-syntax ?\()) | |
468 | @result{} "(" | |
469 | @end group | |
470 | @end example | |
471 | ||
472 | We use @code{string} to make it easier to see the character returned by | |
473 | @code{char-syntax}. | |
474 | @end defun | |
475 | ||
476 | @defun set-syntax-table table | |
477 | This function makes @var{table} the syntax table for the current buffer. | |
478 | It returns @var{table}. | |
479 | @end defun | |
480 | ||
481 | @defun syntax-table | |
482 | This function returns the current syntax table, which is the table for | |
483 | the current buffer. | |
484 | @end defun | |
485 | ||
486 | @defmac with-syntax-table @var{table} @var{body}@dots{} | |
487 | This macro executes @var{body} using @var{table} as the current syntax | |
488 | table. It returns the value of the last form in @var{body}, after | |
489 | restoring the old current syntax table. | |
490 | ||
491 | Since each buffer has its own current syntax table, we should make that | |
492 | more precise: @code{with-syntax-table} temporarily alters the current | |
493 | syntax table of whichever buffer is current at the time the macro | |
494 | execution starts. Other buffers are not affected. | |
495 | @end defmac | |
496 | ||
497 | @node Syntax Properties | |
498 | @section Syntax Properties | |
499 | @kindex syntax-table @r{(text property)} | |
500 | ||
501 | When the syntax table is not flexible enough to specify the syntax of | |
4230351b CY |
502 | a language, you can override the syntax table for specific character |
503 | occurrences in the buffer, by applying a @code{syntax-table} text | |
504 | property. @xref{Text Properties}, for how to apply text properties. | |
b8d4c8d0 | 505 | |
4230351b | 506 | The valid values of @code{syntax-table} text property are: |
b8d4c8d0 GM |
507 | |
508 | @table @asis | |
509 | @item @var{syntax-table} | |
510 | If the property value is a syntax table, that table is used instead of | |
4230351b CY |
511 | the current buffer's syntax table to determine the syntax for the |
512 | underlying text character. | |
b8d4c8d0 GM |
513 | |
514 | @item @code{(@var{syntax-code} . @var{matching-char})} | |
4230351b CY |
515 | A cons cell of this format specifies the syntax for the underlying |
516 | text character. (@pxref{Syntax Table Internals}) | |
b8d4c8d0 GM |
517 | |
518 | @item @code{nil} | |
519 | If the property is @code{nil}, the character's syntax is determined from | |
520 | the current syntax table in the usual way. | |
521 | @end table | |
522 | ||
523 | @defvar parse-sexp-lookup-properties | |
4230351b CY |
524 | If this is non-@code{nil}, the syntax scanning functions, like |
525 | @code{forward-sexp}, pay attention to syntax text properties. | |
526 | Otherwise they use only the current syntax table. | |
527 | @end defvar | |
528 | ||
529 | @defvar syntax-propertize-function | |
530 | This variable, if non-@code{nil}, should store a function for applying | |
531 | @code{syntax-table} properties to a specified stretch of text. It is | |
532 | intended to be used by major modes to install a function which applies | |
533 | @code{syntax-table} properties in some mode-appropriate way. | |
534 | ||
535 | The function is called by @code{syntax-ppss} (@pxref{Position Parse}), | |
536 | and by Font Lock mode during syntactic fontification (@pxref{Syntactic | |
537 | Font Lock}). It is called with two arguments, @var{start} and | |
538 | @var{end}, which are the starting and ending positions of the text on | |
539 | which it should act. It is allowed to call @code{syntax-ppss} on any | |
540 | position before @var{end}. However, it should not call | |
541 | @code{syntax-ppss-flush-cache}; so, it is not allowed to call | |
542 | @code{syntax-ppss} on some position and later modify the buffer at an | |
543 | earlier position. | |
544 | @end defvar | |
545 | ||
546 | @defvar syntax-propertize-extend-region-functions | |
547 | This abnormal hook is run by the syntax parsing code prior to calling | |
548 | @code{syntax-propertize-function}. Its role is to help locate safe | |
549 | starting and ending buffer positions for passing to | |
550 | @code{syntax-propertize-function}. For example, a major mode can add | |
551 | a function to this hook to identify multi-line syntactic constructs, | |
552 | and ensure that the boundaries do not fall in the middle of one. | |
553 | ||
554 | Each function in this hook should accept two arguments, @var{start} | |
555 | and @var{end}. It should return either a cons cell of two adjusted | |
556 | buffer positions, @code{(@var{new-start} . @var{new-end})}, or | |
557 | @code{nil} if no adjustment is necessary. The hook functions are run | |
558 | in turn, repeatedly, until they all return @code{nil}. | |
b8d4c8d0 GM |
559 | @end defvar |
560 | ||
561 | @node Motion and Syntax | |
562 | @section Motion and Syntax | |
563 | ||
564 | This section describes functions for moving across characters that | |
565 | have certain syntax classes. | |
566 | ||
567 | @defun skip-syntax-forward syntaxes &optional limit | |
568 | This function moves point forward across characters having syntax | |
569 | classes mentioned in @var{syntaxes} (a string of syntax class | |
570 | characters). It stops when it encounters the end of the buffer, or | |
571 | position @var{limit} (if specified), or a character it is not supposed | |
572 | to skip. | |
573 | ||
574 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
575 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
576 | ||
577 | The return value is the distance traveled, which is a nonnegative | |
578 | integer. | |
579 | @end defun | |
580 | ||
581 | @defun skip-syntax-backward syntaxes &optional limit | |
582 | This function moves point backward across characters whose syntax | |
583 | classes are mentioned in @var{syntaxes}. It stops when it encounters | |
584 | the beginning of the buffer, or position @var{limit} (if specified), or | |
585 | a character it is not supposed to skip. | |
586 | ||
587 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
588 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
589 | ||
590 | The return value indicates the distance traveled. It is an integer that | |
591 | is zero or less. | |
592 | @end defun | |
593 | ||
594 | @defun backward-prefix-chars | |
595 | This function moves point backward over any number of characters with | |
596 | expression prefix syntax. This includes both characters in the | |
597 | expression prefix syntax class, and characters with the @samp{p} flag. | |
598 | @end defun | |
599 | ||
600 | @node Parsing Expressions | |
601 | @section Parsing Expressions | |
602 | ||
603 | This section describes functions for parsing and scanning balanced | |
a037c171 CY |
604 | expressions. We will refer to such expressions as @dfn{sexps}, |
605 | following the terminology of Lisp, even though these functions can act | |
606 | on languages other than Lisp. Basically, a sexp is either a balanced | |
607 | parenthetical grouping, a string, or a ``symbol'' (i.e.@: a sequence | |
608 | of characters whose syntax is either word constituent or symbol | |
4230351b CY |
609 | constituent). However, characters in the expression prefix syntax |
610 | class (@pxref{Syntax Class Table}) are treated as part of the sexp if | |
611 | they appear next to it. | |
b8d4c8d0 GM |
612 | |
613 | The syntax table controls the interpretation of characters, so these | |
614 | functions can be used for Lisp expressions when in Lisp mode and for C | |
615 | expressions when in C mode. @xref{List Motion}, for convenient | |
616 | higher-level functions for moving over balanced expressions. | |
617 | ||
618 | A character's syntax controls how it changes the state of the | |
619 | parser, rather than describing the state itself. For example, a | |
620 | string delimiter character toggles the parser state between | |
16152b76 | 621 | ``in-string'' and ``in-code'', but the syntax of characters does not |
b8d4c8d0 GM |
622 | directly say whether they are inside a string. For example (note that |
623 | 15 is the syntax code for generic string delimiters), | |
624 | ||
625 | @example | |
626 | (put-text-property 1 9 'syntax-table '(15 . nil)) | |
627 | @end example | |
628 | ||
629 | @noindent | |
630 | does not tell Emacs that the first eight chars of the current buffer | |
631 | are a string, but rather that they are all string delimiters. As a | |
632 | result, Emacs treats them as four consecutive empty string constants. | |
633 | ||
634 | @menu | |
635 | * Motion via Parsing:: Motion functions that work by parsing. | |
636 | * Position Parse:: Determining the syntactic state of a position. | |
637 | * Parser State:: How Emacs represents a syntactic state. | |
638 | * Low-Level Parsing:: Parsing across a specified region. | |
639 | * Control Parsing:: Parameters that affect parsing. | |
640 | @end menu | |
641 | ||
642 | @node Motion via Parsing | |
643 | @subsection Motion Commands Based on Parsing | |
644 | ||
645 | This section describes simple point-motion functions that operate | |
646 | based on parsing expressions. | |
647 | ||
648 | @defun scan-lists from count depth | |
7b926f3f CY |
649 | This function scans forward @var{count} balanced parenthetical |
650 | groupings from position @var{from}. It returns the position where the | |
651 | scan stops. If @var{count} is negative, the scan moves backwards. | |
652 | ||
653 | If @var{depth} is nonzero, treat the starting position as being | |
654 | @var{depth} parentheses deep. The scanner moves forward or backward | |
655 | through the buffer until the depth changes to zero @var{count} times. | |
656 | Hence, a positive value for @var{depth} has the effect of moving out | |
657 | @var{depth} levels of parenthesis from the starting position, while a | |
658 | negative @var{depth} has the effect of moving deeper by @var{-depth} | |
659 | levels of parenthesis. | |
b8d4c8d0 GM |
660 | |
661 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
662 | non-@code{nil}. | |
663 | ||
7b926f3f CY |
664 | If the scan reaches the beginning or end of the accessible part of the |
665 | buffer before it has scanned over @var{count} parenthetical groupings, | |
666 | the return value is @code{nil} if the depth at that point is zero; if | |
667 | the depth is non-zero, a @code{scan-error} error is signaled. | |
b8d4c8d0 GM |
668 | @end defun |
669 | ||
670 | @defun scan-sexps from count | |
671 | This function scans forward @var{count} sexps from position @var{from}. | |
672 | It returns the position where the scan stops. If @var{count} is | |
673 | negative, the scan moves backwards. | |
674 | ||
675 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
676 | non-@code{nil}. | |
677 | ||
678 | If the scan reaches the beginning or end of (the accessible part of) the | |
679 | buffer while in the middle of a parenthetical grouping, an error is | |
680 | signaled. If it reaches the beginning or end between groupings but | |
681 | before count is used up, @code{nil} is returned. | |
682 | @end defun | |
683 | ||
684 | @defun forward-comment count | |
685 | This function moves point forward across @var{count} complete comments | |
686 | (that is, including the starting delimiter and the terminating | |
687 | delimiter if any), plus any whitespace encountered on the way. It | |
688 | moves backward if @var{count} is negative. If it encounters anything | |
689 | other than a comment or whitespace, it stops, leaving point at the | |
690 | place where it stopped. This includes (for instance) finding the end | |
691 | of a comment when moving forward and expecting the beginning of one. | |
692 | The function also stops immediately after moving over the specified | |
693 | number of complete comments. If @var{count} comments are found as | |
694 | expected, with nothing except whitespace between them, it returns | |
695 | @code{t}; otherwise it returns @code{nil}. | |
696 | ||
697 | This function cannot tell whether the ``comments'' it traverses are | |
698 | embedded within a string. If they look like comments, it treats them | |
699 | as comments. | |
b8d4c8d0 GM |
700 | |
701 | To move forward over all comments and whitespace following point, use | |
4230351b CY |
702 | @code{(forward-comment (buffer-size))}. @code{(buffer-size)} is a |
703 | good argument to use, because the number of comments in the buffer | |
704 | cannot exceed that many. | |
705 | @end defun | |
b8d4c8d0 GM |
706 | |
707 | @node Position Parse | |
708 | @subsection Finding the Parse State for a Position | |
709 | ||
710 | For syntactic analysis, such as in indentation, often the useful | |
711 | thing is to compute the syntactic state corresponding to a given buffer | |
712 | position. This function does that conveniently. | |
713 | ||
714 | @defun syntax-ppss &optional pos | |
4230351b CY |
715 | This function returns the parser state that the parser would reach at |
716 | position @var{pos} starting from the beginning of the buffer. | |
717 | @iftex | |
718 | See the next section for | |
719 | @end iftex | |
720 | @ifnottex | |
721 | @xref{Parser State}, | |
722 | @end ifnottex | |
723 | for a description of the parser state. | |
724 | ||
725 | The return value is the same as if you call the low-level parsing | |
726 | function @code{parse-partial-sexp} to parse from the beginning of the | |
727 | buffer to @var{pos} (@pxref{Low-Level Parsing}). However, | |
728 | @code{syntax-ppss} uses a cache to speed up the computation. Due to | |
729 | this optimization, the second value (previous complete subexpression) | |
730 | and sixth value (minimum parenthesis depth) in the returned parser | |
731 | state are not meaningful. | |
732 | ||
733 | This function has a side effect: it adds a buffer-local entry to | |
734 | @code{before-change-functions} (@pxref{Change Hooks}) for | |
735 | @code{syntax-ppss-flush-cache} (see below). This entry keeps the | |
736 | cache consistent as the buffer is modified. However, the cache might | |
737 | not be updated if @code{syntax-ppss} is called while | |
b8d4c8d0 | 738 | @code{before-change-functions} is temporarily let-bound, or if the |
4230351b CY |
739 | buffer is modified without running the hook, such as when using |
740 | @code{inhibit-modification-hooks}. In those cases, it is necessary to | |
741 | call @code{syntax-ppss-flush-cache} explicitly. | |
742 | @end defun | |
b8d4c8d0 | 743 | |
106e6894 CY |
744 | @defun syntax-ppss-flush-cache beg &rest ignored-args |
745 | This function flushes the cache used by @code{syntax-ppss}, starting | |
746 | at position @var{beg}. The remaining arguments, @var{ignored-args}, | |
747 | are ignored; this function accepts them so that it can be directly | |
748 | used on hooks such as @code{before-change-functions} (@pxref{Change | |
749 | Hooks}). | |
b8d4c8d0 GM |
750 | @end defun |
751 | ||
752 | Major modes can make @code{syntax-ppss} run faster by specifying | |
753 | where it needs to start parsing. | |
754 | ||
755 | @defvar syntax-begin-function | |
756 | If this is non-@code{nil}, it should be a function that moves to an | |
757 | earlier buffer position where the parser state is equivalent to | |
758 | @code{nil}---in other words, a position outside of any comment, | |
759 | string, or parenthesis. @code{syntax-ppss} uses it to further | |
760 | optimize its computations, when the cache gives no help. | |
761 | @end defvar | |
762 | ||
763 | @node Parser State | |
764 | @subsection Parser State | |
765 | @cindex parser state | |
766 | ||
4230351b CY |
767 | A @dfn{parser state} is a list of ten elements describing the state |
768 | of the syntactic parser, after it parses the text between a specified | |
769 | starting point and a specified end point in the buffer. Parsing | |
770 | functions such as @code{syntax-ppss} | |
771 | @ifnottex | |
772 | (@pxref{Position Parse}) | |
773 | @end ifnottex | |
774 | return a parser state as the value. Some parsing functions accept a | |
775 | parser state as an argument, for resuming parsing. | |
776 | ||
777 | Here are the meanings of the elements of the parser state: | |
b8d4c8d0 GM |
778 | |
779 | @enumerate 0 | |
780 | @item | |
781 | The depth in parentheses, counting from 0. @strong{Warning:} this can | |
782 | be negative if there are more close parens than open parens between | |
4230351b | 783 | the parser's starting point and end point. |
b8d4c8d0 GM |
784 | |
785 | @item | |
786 | @cindex innermost containing parentheses | |
787 | The character position of the start of the innermost parenthetical | |
788 | grouping containing the stopping point; @code{nil} if none. | |
789 | ||
790 | @item | |
791 | @cindex previous complete subexpression | |
792 | The character position of the start of the last complete subexpression | |
793 | terminated; @code{nil} if none. | |
794 | ||
795 | @item | |
796 | @cindex inside string | |
797 | Non-@code{nil} if inside a string. More precisely, this is the | |
798 | character that will terminate the string, or @code{t} if a generic | |
799 | string delimiter character should terminate it. | |
800 | ||
801 | @item | |
802 | @cindex inside comment | |
4230351b CY |
803 | @code{t} if inside a non-nestable comment (of any comment style; |
804 | @pxref{Syntax Flags}); or the comment nesting level if inside a | |
805 | comment that can be nested. | |
b8d4c8d0 GM |
806 | |
807 | @item | |
808 | @cindex quote character | |
4230351b | 809 | @code{t} if the end point is just after a quote character. |
b8d4c8d0 GM |
810 | |
811 | @item | |
812 | The minimum parenthesis depth encountered during this scan. | |
813 | ||
814 | @item | |
4230351b CY |
815 | What kind of comment is active: @code{nil} if not in a comment or in a |
816 | comment of style @samp{a}; 1 for a comment of style @samp{b}; 2 for a | |
817 | comment of style @samp{c}; and @code{syntax-table} for a comment that | |
818 | should be ended by a generic comment delimiter character. | |
b8d4c8d0 GM |
819 | |
820 | @item | |
821 | The string or comment start position. While inside a comment, this is | |
822 | the position where the comment began; while inside a string, this is the | |
823 | position where the string began. When outside of strings and comments, | |
824 | this element is @code{nil}. | |
825 | ||
826 | @item | |
827 | Internal data for continuing the parsing. The meaning of this | |
828 | data is subject to change; it is used if you pass this list | |
829 | as the @var{state} argument to another call. | |
830 | @end enumerate | |
831 | ||
832 | Elements 1, 2, and 6 are ignored in a state which you pass as an | |
833 | argument to continue parsing, and elements 8 and 9 are used only in | |
4230351b CY |
834 | trivial cases. Those elements are mainly used internally by the |
835 | parser code. | |
b8d4c8d0 GM |
836 | |
837 | One additional piece of useful information is available from a | |
838 | parser state using this function: | |
839 | ||
840 | @defun syntax-ppss-toplevel-pos state | |
841 | This function extracts, from parser state @var{state}, the last | |
842 | position scanned in the parse which was at top level in grammatical | |
843 | structure. ``At top level'' means outside of any parentheses, | |
844 | comments, or strings. | |
845 | ||
846 | The value is @code{nil} if @var{state} represents a parse which has | |
847 | arrived at a top level position. | |
848 | @end defun | |
849 | ||
b8d4c8d0 GM |
850 | @node Low-Level Parsing |
851 | @subsection Low-Level Parsing | |
852 | ||
853 | The most basic way to use the expression parser is to tell it | |
854 | to start at a given position with a certain state, and parse up to | |
855 | a specified end position. | |
856 | ||
857 | @defun parse-partial-sexp start limit &optional target-depth stop-before state stop-comment | |
858 | This function parses a sexp in the current buffer starting at | |
859 | @var{start}, not scanning past @var{limit}. It stops at position | |
860 | @var{limit} or when certain criteria described below are met, and sets | |
861 | point to the location where parsing stops. It returns a parser state | |
862 | describing the status of the parse at the point where it stops. | |
863 | ||
864 | @cindex parenthesis depth | |
865 | If the third argument @var{target-depth} is non-@code{nil}, parsing | |
866 | stops if the depth in parentheses becomes equal to @var{target-depth}. | |
867 | The depth starts at 0, or at whatever is given in @var{state}. | |
868 | ||
869 | If the fourth argument @var{stop-before} is non-@code{nil}, parsing | |
870 | stops when it comes to any character that starts a sexp. If | |
871 | @var{stop-comment} is non-@code{nil}, parsing stops when it comes to the | |
872 | start of a comment. If @var{stop-comment} is the symbol | |
873 | @code{syntax-table}, parsing stops after the start of a comment or a | |
874 | string, or the end of a comment or a string, whichever comes first. | |
875 | ||
876 | If @var{state} is @code{nil}, @var{start} is assumed to be at the top | |
877 | level of parenthesis structure, such as the beginning of a function | |
878 | definition. Alternatively, you might wish to resume parsing in the | |
879 | middle of the structure. To do this, you must provide a @var{state} | |
880 | argument that describes the initial status of parsing. The value | |
881 | returned by a previous call to @code{parse-partial-sexp} will do | |
882 | nicely. | |
883 | @end defun | |
884 | ||
885 | @node Control Parsing | |
886 | @subsection Parameters to Control Parsing | |
887 | ||
888 | @defvar multibyte-syntax-as-symbol | |
889 | If this variable is non-@code{nil}, @code{scan-sexps} treats all | |
890 | non-@acronym{ASCII} characters as symbol constituents regardless | |
891 | of what the syntax table says about them. (However, text properties | |
892 | can still override the syntax.) | |
893 | @end defvar | |
894 | ||
895 | @defopt parse-sexp-ignore-comments | |
896 | @cindex skipping comments | |
897 | If the value is non-@code{nil}, then comments are treated as | |
898 | whitespace by the functions in this section and by @code{forward-sexp}, | |
899 | @code{scan-lists} and @code{scan-sexps}. | |
900 | @end defopt | |
901 | ||
902 | @vindex parse-sexp-lookup-properties | |
903 | The behavior of @code{parse-partial-sexp} is also affected by | |
904 | @code{parse-sexp-lookup-properties} (@pxref{Syntax Properties}). | |
905 | ||
906 | You can use @code{forward-comment} to move forward or backward over | |
907 | one comment or several comments. | |
908 | ||
909 | @node Standard Syntax Tables | |
910 | @section Some Standard Syntax Tables | |
911 | ||
912 | Most of the major modes in Emacs have their own syntax tables. Here | |
913 | are several of them: | |
914 | ||
915 | @defun standard-syntax-table | |
916 | This function returns the standard syntax table, which is the syntax | |
917 | table used in Fundamental mode. | |
918 | @end defun | |
919 | ||
920 | @defvar text-mode-syntax-table | |
921 | The value of this variable is the syntax table used in Text mode. | |
922 | @end defvar | |
923 | ||
924 | @defvar c-mode-syntax-table | |
925 | The value of this variable is the syntax table for C-mode buffers. | |
926 | @end defvar | |
927 | ||
928 | @defvar emacs-lisp-mode-syntax-table | |
929 | The value of this variable is the syntax table used in Emacs Lisp mode | |
930 | by editing commands. (It has no effect on the Lisp @code{read} | |
931 | function.) | |
932 | @end defvar | |
933 | ||
934 | @node Syntax Table Internals | |
935 | @section Syntax Table Internals | |
936 | @cindex syntax table internals | |
937 | ||
938 | Lisp programs don't usually work with the elements directly; the | |
939 | Lisp-level syntax table functions usually work with syntax descriptors | |
940 | (@pxref{Syntax Descriptors}). Nonetheless, here we document the | |
941 | internal format. This format is used mostly when manipulating | |
942 | syntax properties. | |
943 | ||
944 | Each element of a syntax table is a cons cell of the form | |
945 | @code{(@var{syntax-code} . @var{matching-char})}. The @sc{car}, | |
946 | @var{syntax-code}, is an integer that encodes the syntax class, and any | |
947 | flags. The @sc{cdr}, @var{matching-char}, is non-@code{nil} if | |
948 | a character to match was specified. | |
949 | ||
950 | This table gives the value of @var{syntax-code} which corresponds | |
951 | to each syntactic type. | |
952 | ||
953 | @multitable @columnfractions .05 .3 .3 .31 | |
954 | @item | |
955 | @tab | |
956 | @i{Integer} @i{Class} | |
957 | @tab | |
958 | @i{Integer} @i{Class} | |
959 | @tab | |
960 | @i{Integer} @i{Class} | |
961 | @item | |
962 | @tab | |
963 | 0 @ @ whitespace | |
964 | @tab | |
965 | 5 @ @ close parenthesis | |
966 | @tab | |
967 | 10 @ @ character quote | |
968 | @item | |
969 | @tab | |
970 | 1 @ @ punctuation | |
971 | @tab | |
972 | 6 @ @ expression prefix | |
973 | @tab | |
974 | 11 @ @ comment-start | |
975 | @item | |
976 | @tab | |
977 | 2 @ @ word | |
978 | @tab | |
979 | 7 @ @ string quote | |
980 | @tab | |
981 | 12 @ @ comment-end | |
982 | @item | |
983 | @tab | |
984 | 3 @ @ symbol | |
985 | @tab | |
986 | 8 @ @ paired delimiter | |
987 | @tab | |
988 | 13 @ @ inherit | |
989 | @item | |
990 | @tab | |
991 | 4 @ @ open parenthesis | |
992 | @tab | |
993 | 9 @ @ escape | |
994 | @tab | |
995 | 14 @ @ generic comment | |
996 | @item | |
997 | @tab | |
998 | 15 @ generic string | |
999 | @end multitable | |
1000 | ||
1001 | For example, the usual syntax value for @samp{(} is @code{(4 . 41)}. | |
1002 | (41 is the character code for @samp{)}.) | |
1003 | ||
1004 | The flags are encoded in higher order bits, starting 16 bits from the | |
1005 | least significant bit. This table gives the power of two which | |
1006 | corresponds to each syntax flag. | |
1007 | ||
1008 | @multitable @columnfractions .05 .3 .3 .3 | |
1009 | @item | |
1010 | @tab | |
1011 | @i{Prefix} @i{Flag} | |
1012 | @tab | |
1013 | @i{Prefix} @i{Flag} | |
1014 | @tab | |
1015 | @i{Prefix} @i{Flag} | |
1016 | @item | |
1017 | @tab | |
1018 | @samp{1} @ @ @code{(lsh 1 16)} | |
1019 | @tab | |
1020 | @samp{4} @ @ @code{(lsh 1 19)} | |
1021 | @tab | |
1022 | @samp{b} @ @ @code{(lsh 1 21)} | |
1023 | @item | |
1024 | @tab | |
1025 | @samp{2} @ @ @code{(lsh 1 17)} | |
1026 | @tab | |
1027 | @samp{p} @ @ @code{(lsh 1 20)} | |
1028 | @tab | |
1029 | @samp{n} @ @ @code{(lsh 1 22)} | |
1030 | @item | |
1031 | @tab | |
1032 | @samp{3} @ @ @code{(lsh 1 18)} | |
1033 | @end multitable | |
1034 | ||
1035 | @defun string-to-syntax @var{desc} | |
1036 | This function returns the internal form corresponding to the syntax | |
1037 | descriptor @var{desc}, a cons cell @code{(@var{syntax-code} | |
1038 | . @var{matching-char})}. | |
1039 | @end defun | |
1040 | ||
1041 | @defun syntax-after pos | |
1042 | This function returns the syntax code of the character in the buffer | |
1043 | after position @var{pos}, taking account of syntax properties as well | |
1044 | as the syntax table. If @var{pos} is outside the buffer's accessible | |
1045 | portion (@pxref{Narrowing, accessible portion}), this function returns | |
1046 | @code{nil}. | |
1047 | @end defun | |
1048 | ||
1049 | @defun syntax-class syntax | |
1050 | This function returns the syntax class of the syntax code | |
1051 | @var{syntax}. (It masks off the high 16 bits that hold the flags | |
1052 | encoded in the syntax descriptor.) If @var{syntax} is @code{nil}, it | |
1053 | returns @code{nil}; this is so evaluating the expression | |
1054 | ||
1055 | @example | |
1056 | (syntax-class (syntax-after pos)) | |
1057 | @end example | |
1058 | ||
1059 | @noindent | |
1060 | where @code{pos} is outside the buffer's accessible portion, will | |
1061 | yield @code{nil} without throwing errors or producing wrong syntax | |
1062 | class codes. | |
1063 | @end defun | |
1064 | ||
1065 | @node Categories | |
1066 | @section Categories | |
1067 | @cindex categories of characters | |
1068 | @cindex character categories | |
1069 | ||
1070 | @dfn{Categories} provide an alternate way of classifying characters | |
1071 | syntactically. You can define several categories as needed, then | |
1072 | independently assign each character to one or more categories. Unlike | |
1073 | syntax classes, categories are not mutually exclusive; it is normal for | |
1074 | one character to belong to several categories. | |
1075 | ||
1076 | @cindex category table | |
1077 | Each buffer has a @dfn{category table} which records which categories | |
1078 | are defined and also which characters belong to each category. Each | |
1079 | category table defines its own categories, but normally these are | |
1080 | initialized by copying from the standard categories table, so that the | |
1081 | standard categories are available in all modes. | |
1082 | ||
1083 | Each category has a name, which is an @acronym{ASCII} printing character in | |
1084 | the range @w{@samp{ }} to @samp{~}. You specify the name of a category | |
1085 | when you define it with @code{define-category}. | |
1086 | ||
1087 | The category table is actually a char-table (@pxref{Char-Tables}). | |
1088 | The element of the category table at index @var{c} is a @dfn{category | |
1089 | set}---a bool-vector---that indicates which categories character @var{c} | |
1090 | belongs to. In this category set, if the element at index @var{cat} is | |
1091 | @code{t}, that means category @var{cat} is a member of the set, and that | |
1092 | character @var{c} belongs to category @var{cat}. | |
1093 | ||
1094 | For the next three functions, the optional argument @var{table} | |
1095 | defaults to the current buffer's category table. | |
1096 | ||
1097 | @defun define-category char docstring &optional table | |
1098 | This function defines a new category, with name @var{char} and | |
1099 | documentation @var{docstring}, for the category table @var{table}. | |
1ea897d5 EZ |
1100 | |
1101 | Here's an example of defining a new category for characters that have | |
1102 | strong right-to-left directionality (@pxref{Bidirectional Display}) | |
1103 | and using it in a special category table: | |
1104 | ||
1105 | @example | |
1106 | (defvar special-category-table-for-bidi | |
1107 | (let ((category-table (make-category-table)) | |
1108 | (uniprop-table (unicode-property-table-internal 'bidi-class))) | |
1109 | (define-category ?R "Characters of bidi-class R, AL, or RLO" | |
1110 | category-table) | |
1111 | (map-char-table | |
1112 | #'(lambda (key val) | |
1113 | (if (memq val '(R AL RLO)) | |
1114 | (modify-category-entry key ?R category-table))) | |
1115 | uniprop-table) | |
1116 | category-table)) | |
1117 | @end example | |
b8d4c8d0 GM |
1118 | @end defun |
1119 | ||
1120 | @defun category-docstring category &optional table | |
1121 | This function returns the documentation string of category @var{category} | |
1122 | in category table @var{table}. | |
1123 | ||
1124 | @example | |
1125 | (category-docstring ?a) | |
1126 | @result{} "ASCII" | |
1127 | (category-docstring ?l) | |
1128 | @result{} "Latin" | |
1129 | @end example | |
1130 | @end defun | |
1131 | ||
1132 | @defun get-unused-category &optional table | |
1133 | This function returns a category name (a character) which is not | |
1134 | currently defined in @var{table}. If all possible categories are in use | |
1135 | in @var{table}, it returns @code{nil}. | |
1136 | @end defun | |
1137 | ||
1138 | @defun category-table | |
1139 | This function returns the current buffer's category table. | |
1140 | @end defun | |
1141 | ||
1142 | @defun category-table-p object | |
1143 | This function returns @code{t} if @var{object} is a category table, | |
1144 | otherwise @code{nil}. | |
1145 | @end defun | |
1146 | ||
1147 | @defun standard-category-table | |
1148 | This function returns the standard category table. | |
1149 | @end defun | |
1150 | ||
1151 | @defun copy-category-table &optional table | |
1152 | This function constructs a copy of @var{table} and returns it. If | |
1153 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
1154 | standard category table. Otherwise, an error is signaled if @var{table} | |
1155 | is not a category table. | |
1156 | @end defun | |
1157 | ||
1158 | @defun set-category-table table | |
1159 | This function makes @var{table} the category table for the current | |
1160 | buffer. It returns @var{table}. | |
1161 | @end defun | |
1162 | ||
1163 | @defun make-category-table | |
1164 | This creates and returns an empty category table. In an empty category | |
1165 | table, no categories have been allocated, and no characters belong to | |
1166 | any categories. | |
1167 | @end defun | |
1168 | ||
1169 | @defun make-category-set categories | |
1170 | This function returns a new category set---a bool-vector---whose initial | |
1171 | contents are the categories listed in the string @var{categories}. The | |
1172 | elements of @var{categories} should be category names; the new category | |
1173 | set has @code{t} for each of those categories, and @code{nil} for all | |
1174 | other categories. | |
1175 | ||
1176 | @example | |
1177 | (make-category-set "al") | |
1178 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1179 | @end example | |
1180 | @end defun | |
1181 | ||
1182 | @defun char-category-set char | |
1183 | This function returns the category set for character @var{char} in the | |
1184 | current buffer's category table. This is the bool-vector which | |
1185 | records which categories the character @var{char} belongs to. The | |
1186 | function @code{char-category-set} does not allocate storage, because | |
1187 | it returns the same bool-vector that exists in the category table. | |
1188 | ||
1189 | @example | |
1190 | (char-category-set ?a) | |
1191 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1192 | @end example | |
1193 | @end defun | |
1194 | ||
1195 | @defun category-set-mnemonics category-set | |
1196 | This function converts the category set @var{category-set} into a string | |
1197 | containing the characters that designate the categories that are members | |
1198 | of the set. | |
1199 | ||
1200 | @example | |
1201 | (category-set-mnemonics (char-category-set ?a)) | |
1202 | @result{} "al" | |
1203 | @end example | |
1204 | @end defun | |
1205 | ||
f147ff75 CY |
1206 | @defun modify-category-entry char category &optional table reset |
1207 | This function modifies the category set of @var{char} in category | |
b8d4c8d0 | 1208 | table @var{table} (which defaults to the current buffer's category |
f147ff75 CY |
1209 | table). @var{char} can be a character, or a cons cell of the form |
1210 | @code{(@var{min} . @var{max})}; in the latter case, the function | |
1211 | modifies the category sets of all characters in the range between | |
1212 | @var{min} and @var{max}, inclusive. | |
b8d4c8d0 | 1213 | |
f147ff75 | 1214 | Normally, it modifies a category set by adding @var{category} to it. |
b8d4c8d0 GM |
1215 | But if @var{reset} is non-@code{nil}, then it deletes @var{category} |
1216 | instead. | |
1217 | @end defun | |
1218 | ||
1219 | @deffn Command describe-categories &optional buffer-or-name | |
1220 | This function describes the category specifications in the current | |
1221 | category table. It inserts the descriptions in a buffer, and then | |
1222 | displays that buffer. If @var{buffer-or-name} is non-@code{nil}, it | |
1223 | describes the category table of that buffer instead. | |
1224 | @end deffn |