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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. |
ecc6530d | 6 | @node Syntax Tables |
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7 | @chapter Syntax Tables |
8 | @cindex parsing buffer text | |
9 | @cindex syntax table | |
10 | @cindex text parsing | |
11 | ||
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12 | A @dfn{syntax table} specifies the syntactic role of each character |
13 | in a buffer. It can be used to determine where words, symbols, and | |
14 | other syntactic constructs begin and end. This information is used by | |
15 | many Emacs facilities, including Font Lock mode (@pxref{Font Lock | |
16 | Mode}) and the various complex movement commands (@pxref{Motion}). | |
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17 | |
18 | @menu | |
19 | * Basics: Syntax Basics. Basic concepts of syntax tables. | |
4230351b | 20 | * Syntax Descriptors:: How characters are classified. |
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21 | * Syntax Table Functions:: How to create, examine and alter syntax tables. |
22 | * Syntax Properties:: Overriding syntax with text properties. | |
d24880de | 23 | * Motion and Syntax:: Moving over characters with certain syntaxes. |
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24 | * Parsing Expressions:: Parsing balanced expressions |
25 | using the syntax table. | |
26 | * Standard Syntax Tables:: Syntax tables used by various major modes. | |
27 | * Syntax Table Internals:: How syntax table information is stored. | |
28 | * Categories:: Another way of classifying character syntax. | |
29 | @end menu | |
30 | ||
31 | @node Syntax Basics | |
32 | @section Syntax Table Concepts | |
33 | ||
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34 | A syntax table is a char-table (@pxref{Char-Tables}). The element at |
35 | index @var{c} describes the character with code @var{c}. The element's | |
36 | value should be a list that encodes the syntax of the character in | |
37 | question. | |
38 | ||
39 | Syntax tables are used only for moving across text, not for the Emacs | |
40 | Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp | |
41 | expressions, and these rules cannot be changed. (Some Lisp systems | |
42 | provide ways to redefine the read syntax, but we decided to leave this | |
43 | feature out of Emacs Lisp for simplicity.) | |
44 | ||
45 | Each buffer has its own major mode, and each major mode has its own | |
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46 | idea of the syntactic class of various characters. For example, in |
47 | Lisp mode, the character @samp{;} begins a comment, but in C mode, it | |
b8d4c8d0 | 48 | terminates a statement. To support these variations, Emacs makes the |
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49 | syntax table local to each buffer. Typically, each major mode has its |
50 | own syntax table and installs that table in each buffer that uses that | |
51 | mode. Changing this table alters the syntax in all those buffers as | |
52 | well as in any buffers subsequently put in that mode. Occasionally | |
53 | several similar modes share one syntax table. @xref{Example Major | |
54 | Modes}, for an example of how to set up a syntax table. | |
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55 | |
56 | A syntax table can inherit the data for some characters from the | |
57 | standard syntax table, while specifying other characters itself. The | |
58 | ``inherit'' syntax class means ``inherit this character's syntax from | |
16152b76 | 59 | the standard syntax table''. Just changing the standard syntax for a |
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60 | character affects all syntax tables that inherit from it. |
61 | ||
62 | @defun syntax-table-p object | |
63 | This function returns @code{t} if @var{object} is a syntax table. | |
64 | @end defun | |
65 | ||
66 | @node Syntax Descriptors | |
67 | @section Syntax Descriptors | |
68 | @cindex syntax class | |
69 | ||
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70 | The syntactic role of a character is called its @dfn{syntax class}. |
71 | Each syntax table specifies the syntax class of each character. There | |
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72 | is no necessary relationship between the class of a character in one |
73 | syntax table and its class in any other table. | |
74 | ||
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75 | Each syntax class is designated by a mnemonic character, which |
76 | serves as the name of the class when you need to specify a class. | |
77 | Usually, this designator character is one that is often assigned that | |
78 | class; however, its meaning as a designator is unvarying and | |
79 | independent of what syntax that character currently has. Thus, | |
80 | @samp{\} as a designator character always means ``escape character'' | |
81 | syntax, regardless of whether the @samp{\} character actually has that | |
82 | syntax in the current syntax table. | |
83 | @ifnottex | |
84 | @xref{Syntax Class Table}, for a list of syntax classes. | |
85 | @end ifnottex | |
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86 | |
87 | @cindex syntax descriptor | |
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88 | A @dfn{syntax descriptor} is a Lisp string that describes the syntax |
89 | classes and other syntactic properties of a character. When you want | |
90 | to modify the syntax of a character, that is done by calling the | |
91 | function @code{modify-syntax-entry} and passing a syntax descriptor as | |
92 | one of its arguments (@pxref{Syntax Table Functions}). | |
93 | ||
94 | The first character in a syntax descriptor designates the syntax | |
95 | class. The second character specifies a matching character (e.g.@: in | |
96 | Lisp, the matching character for @samp{(} is @samp{)}); if there is no | |
97 | matching character, put a space there. Then come the characters for | |
98 | any desired flags. | |
99 | ||
100 | If no matching character or flags are needed, only one character | |
101 | (specifying the syntax class) is sufficient. | |
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102 | |
103 | For example, the syntax descriptor for the character @samp{*} in C | |
ad21a12a | 104 | mode is @code{". 23"} (i.e., punctuation, matching character slot |
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105 | unused, second character of a comment-starter, first character of a |
106 | comment-ender), and the entry for @samp{/} is @samp{@w{. 14}} (i.e., | |
107 | punctuation, matching character slot unused, first character of a | |
108 | comment-starter, second character of a comment-ender). | |
109 | ||
110 | @menu | |
111 | * Syntax Class Table:: Table of syntax classes. | |
112 | * Syntax Flags:: Additional flags each character can have. | |
113 | @end menu | |
114 | ||
115 | @node Syntax Class Table | |
116 | @subsection Table of Syntax Classes | |
117 | ||
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118 | Here is a table of syntax classes, the characters that designate |
119 | them, their meanings, and examples of their use. | |
b8d4c8d0 | 120 | |
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121 | @table @asis |
122 | @item Whitespace characters: @samp{@ } or @samp{-} | |
123 | Characters that separate symbols and words from each other. | |
124 | Typically, whitespace characters have no other syntactic significance, | |
125 | and multiple whitespace characters are syntactically equivalent to a | |
126 | single one. Space, tab, and formfeed are classified as whitespace in | |
127 | almost all major modes. | |
128 | ||
129 | This syntax class can be designated by either @w{@samp{@ }} or | |
130 | @samp{-}. Both designators are equivalent. | |
131 | ||
132 | @item Word constituents: @samp{w} | |
133 | Parts of words in human languages. These are typically used in | |
134 | variable and command names in programs. All upper- and lower-case | |
135 | letters, and the digits, are typically word constituents. | |
136 | ||
137 | @item Symbol constituents: @samp{_} | |
138 | Extra characters used in variable and command names along with word | |
139 | constituents. Examples include the characters @samp{$&*+-_<>} in Lisp | |
140 | mode, which may be part of a symbol name even though they are not part | |
141 | of English words. In standard C, the only non-word-constituent | |
b8d4c8d0 | 142 | character that is valid in symbols is underscore (@samp{_}). |
b8d4c8d0 | 143 | |
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144 | @item Punctuation characters: @samp{.} |
145 | Characters used as punctuation in a human language, or used in a | |
146 | programming language to separate symbols from one another. Some | |
147 | programming language modes, such as Emacs Lisp mode, have no | |
148 | characters in this class since the few characters that are not symbol | |
149 | or word constituents all have other uses. Other programming language | |
150 | modes, such as C mode, use punctuation syntax for operators. | |
151 | ||
152 | @item Open parenthesis characters: @samp{(} | |
153 | @itemx Close parenthesis characters: @samp{)} | |
154 | Characters used in dissimilar pairs to surround sentences or | |
155 | expressions. Such a grouping is begun with an open parenthesis | |
156 | character and terminated with a close. Each open parenthesis | |
157 | character matches a particular close parenthesis character, and vice | |
158 | versa. Normally, Emacs indicates momentarily the matching open | |
159 | parenthesis when you insert a close parenthesis. @xref{Blinking}. | |
160 | ||
161 | In human languages, and in C code, the parenthesis pairs are | |
162 | @samp{()}, @samp{[]}, and @samp{@{@}}. In Emacs Lisp, the delimiters | |
163 | for lists and vectors (@samp{()} and @samp{[]}) are classified as | |
164 | parenthesis characters. | |
165 | ||
166 | @item String quotes: @samp{"} | |
167 | Characters used to delimit string constants. The same string quote | |
168 | character appears at the beginning and the end of a string. Such | |
169 | quoted strings do not nest. | |
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170 | |
171 | The parsing facilities of Emacs consider a string as a single token. | |
172 | The usual syntactic meanings of the characters in the string are | |
173 | suppressed. | |
174 | ||
175 | The Lisp modes have two string quote characters: double-quote (@samp{"}) | |
176 | and vertical bar (@samp{|}). @samp{|} is not used in Emacs Lisp, but it | |
177 | is used in Common Lisp. C also has two string quote characters: | |
178 | double-quote for strings, and single-quote (@samp{'}) for character | |
179 | constants. | |
180 | ||
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181 | Human text has no string quote characters. We do not want quotation |
182 | marks to turn off the usual syntactic properties of other characters | |
183 | in the quotation. | |
b8d4c8d0 | 184 | |
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185 | @item Escape-syntax characters: @samp{\} |
186 | Characters that start an escape sequence, such as is used in string | |
187 | and character constants. The character @samp{\} belongs to this class | |
188 | in both C and Lisp. (In C, it is used thus only inside strings, but | |
189 | it turns out to cause no trouble to treat it this way throughout C | |
190 | code.) | |
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191 | |
192 | Characters in this class count as part of words if | |
193 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
b8d4c8d0 | 194 | |
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195 | @item Character quotes: @samp{/} |
196 | Characters used to quote the following character so that it loses its | |
197 | normal syntactic meaning. This differs from an escape character in | |
198 | that only the character immediately following is ever affected. | |
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199 | |
200 | Characters in this class count as part of words if | |
201 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
202 | ||
203 | This class is used for backslash in @TeX{} mode. | |
b8d4c8d0 | 204 | |
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205 | @item Paired delimiters: @samp{$} |
206 | Similar to string quote characters, except that the syntactic | |
207 | properties of the characters between the delimiters are not | |
208 | suppressed. Only @TeX{} mode uses a paired delimiter presently---the | |
209 | @samp{$} that both enters and leaves math mode. | |
210 | ||
211 | @item Expression prefixes: @samp{'} | |
212 | Characters used for syntactic operators that are considered as part of | |
213 | an expression if they appear next to one. In Lisp modes, these | |
214 | characters include the apostrophe, @samp{'} (used for quoting), the | |
215 | comma, @samp{,} (used in macros), and @samp{#} (used in the read | |
216 | syntax for certain data types). | |
217 | ||
218 | @item Comment starters: @samp{<} | |
219 | @itemx Comment enders: @samp{>} | |
b8d4c8d0 | 220 | @cindex comment syntax |
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221 | Characters used in various languages to delimit comments. Human text |
222 | has no comment characters. In Lisp, the semicolon (@samp{;}) starts a | |
223 | comment and a newline or formfeed ends one. | |
b8d4c8d0 | 224 | |
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225 | @item Inherit standard syntax: @samp{@@} |
226 | This syntax class does not specify a particular syntax. It says to | |
227 | look in the standard syntax table to find the syntax of this | |
228 | character. | |
b8d4c8d0 | 229 | |
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230 | @item Generic comment delimiters: @samp{!} |
231 | Characters that start or end a special kind of comment. @emph{Any} | |
232 | generic comment delimiter matches @emph{any} generic comment | |
233 | delimiter, but they cannot match a comment starter or comment ender; | |
234 | generic comment delimiters can only match each other. | |
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235 | |
236 | This syntax class is primarily meant for use with the | |
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237 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
238 | can mark any range of characters as forming a comment, by giving the | |
239 | first and last characters of the range @code{syntax-table} properties | |
b8d4c8d0 | 240 | identifying them as generic comment delimiters. |
b8d4c8d0 | 241 | |
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242 | @item Generic string delimiters: @samp{|} |
243 | Characters that start or end a string. This class differs from the | |
244 | string quote class in that @emph{any} generic string delimiter can | |
245 | match any other generic string delimiter; but they do not match | |
246 | ordinary string quote characters. | |
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247 | |
248 | This syntax class is primarily meant for use with the | |
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249 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
250 | can mark any range of characters as forming a string constant, by | |
251 | giving the first and last characters of the range @code{syntax-table} | |
252 | properties identifying them as generic string delimiters. | |
253 | @end table | |
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254 | |
255 | @node Syntax Flags | |
256 | @subsection Syntax Flags | |
257 | @cindex syntax flags | |
258 | ||
259 | In addition to the classes, entries for characters in a syntax table | |
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260 | can specify flags. There are eight possible flags, represented by the |
261 | characters @samp{1}, @samp{2}, @samp{3}, @samp{4}, @samp{b}, @samp{c}, | |
262 | @samp{n}, and @samp{p}. | |
263 | ||
264 | All the flags except @samp{p} are used to describe comment | |
265 | delimiters. The digit flags are used for comment delimiters made up | |
266 | of 2 characters. They indicate that a character can @emph{also} be | |
267 | part of a comment sequence, in addition to the syntactic properties | |
268 | associated with its character class. The flags are independent of the | |
269 | class and each other for the sake of characters such as @samp{*} in | |
270 | C mode, which is a punctuation character, @emph{and} the second | |
271 | character of a start-of-comment sequence (@samp{/*}), @emph{and} the | |
272 | first character of an end-of-comment sequence (@samp{*/}). The flags | |
273 | @samp{b}, @samp{c}, and @samp{n} are used to qualify the corresponding | |
274 | comment delimiter. | |
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275 | |
276 | Here is a table of the possible flags for a character @var{c}, | |
277 | and what they mean: | |
278 | ||
279 | @itemize @bullet | |
280 | @item | |
281 | @samp{1} means @var{c} is the start of a two-character comment-start | |
282 | sequence. | |
283 | ||
284 | @item | |
285 | @samp{2} means @var{c} is the second character of such a sequence. | |
286 | ||
287 | @item | |
288 | @samp{3} means @var{c} is the start of a two-character comment-end | |
289 | sequence. | |
290 | ||
291 | @item | |
292 | @samp{4} means @var{c} is the second character of such a sequence. | |
293 | ||
294 | @item | |
b8d4c8d0 | 295 | @samp{b} means that @var{c} as a comment delimiter belongs to the |
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296 | alternative ``b'' comment style. For a two-character comment starter, |
297 | this flag is only significant on the second char, and for a 2-character | |
298 | comment ender it is only significant on the first char. | |
b8d4c8d0 | 299 | |
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300 | @item |
301 | @samp{c} means that @var{c} as a comment delimiter belongs to the | |
302 | alternative ``c'' comment style. For a two-character comment | |
303 | delimiter, @samp{c} on either character makes it of style ``c''. | |
b8d4c8d0 | 304 | |
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305 | @item |
306 | @samp{n} on a comment delimiter character specifies | |
307 | that this kind of comment can be nested. For a two-character | |
308 | comment delimiter, @samp{n} on either character makes it | |
309 | nestable. | |
b8d4c8d0 | 310 | |
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311 | Emacs supports several comment styles simultaneously in any one syntax |
312 | table. A comment style is a set of flags @samp{b}, @samp{c}, and | |
313 | @samp{n}, so there can be up to 8 different comment styles. | |
314 | Each comment delimiter has a style and only matches comment delimiters | |
315 | of the same style. Thus if a comment starts with the comment-start | |
316 | sequence of style ``bn'', it will extend until the next matching | |
317 | comment-end sequence of style ``bn''. | |
b8d4c8d0 | 318 | |
7cf78aac | 319 | The appropriate comment syntax settings for C++ can be as follows: |
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320 | |
321 | @table @asis | |
322 | @item @samp{/} | |
7cf78aac | 323 | @samp{124} |
b8d4c8d0 | 324 | @item @samp{*} |
7cf78aac | 325 | @samp{23b} |
b8d4c8d0 | 326 | @item newline |
7cf78aac | 327 | @samp{>} |
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328 | @end table |
329 | ||
330 | This defines four comment-delimiting sequences: | |
331 | ||
332 | @table @asis | |
333 | @item @samp{/*} | |
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334 | This is a comment-start sequence for ``b'' style because the |
335 | second character, @samp{*}, has the @samp{b} flag. | |
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336 | |
337 | @item @samp{//} | |
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338 | This is a comment-start sequence for ``a'' style because the second |
339 | character, @samp{/}, does not have the @samp{b} flag. | |
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340 | |
341 | @item @samp{*/} | |
7cf78aac | 342 | This is a comment-end sequence for ``b'' style because the first |
35a30759 | 343 | character, @samp{*}, has the @samp{b} flag. |
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344 | |
345 | @item newline | |
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346 | This is a comment-end sequence for ``a'' style, because the newline |
347 | character does not have the @samp{b} flag. | |
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348 | @end table |
349 | ||
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350 | @item |
351 | @c Emacs 19 feature | |
352 | @samp{p} identifies an additional ``prefix character'' for Lisp syntax. | |
353 | These characters are treated as whitespace when they appear between | |
354 | expressions. When they appear within an expression, they are handled | |
355 | according to their usual syntax classes. | |
356 | ||
357 | The function @code{backward-prefix-chars} moves back over these | |
358 | characters, as well as over characters whose primary syntax class is | |
359 | prefix (@samp{'}). @xref{Motion and Syntax}. | |
360 | @end itemize | |
361 | ||
362 | @node Syntax Table Functions | |
363 | @section Syntax Table Functions | |
364 | ||
365 | In this section we describe functions for creating, accessing and | |
366 | altering syntax tables. | |
367 | ||
368 | @defun make-syntax-table &optional table | |
369 | This function creates a new syntax table, with all values initialized | |
370 | to @code{nil}. If @var{table} is non-@code{nil}, it becomes the | |
371 | parent of the new syntax table, otherwise the standard syntax table is | |
372 | the parent. Like all char-tables, a syntax table inherits from its | |
373 | parent. Thus the original syntax of all characters in the returned | |
374 | syntax table is determined by the parent. @xref{Char-Tables}. | |
375 | ||
376 | Most major mode syntax tables are created in this way. | |
377 | @end defun | |
378 | ||
379 | @defun copy-syntax-table &optional table | |
380 | This function constructs a copy of @var{table} and returns it. If | |
381 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
382 | standard syntax table. Otherwise, an error is signaled if @var{table} is | |
383 | not a syntax table. | |
384 | @end defun | |
385 | ||
386 | @deffn Command modify-syntax-entry char syntax-descriptor &optional table | |
387 | This function sets the syntax entry for @var{char} according to | |
4230351b | 388 | @var{syntax-descriptor}. @var{char} must be a character, or a cons |
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389 | cell of the form @code{(@var{min} . @var{max})}; in the latter case, |
390 | the function sets the syntax entries for all characters in the range | |
391 | between @var{min} and @var{max}, inclusive. | |
392 | ||
393 | The syntax is changed only for @var{table}, which defaults to the | |
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394 | current buffer's syntax table, and not in any other syntax table. |
395 | ||
396 | The argument @var{syntax-descriptor} is a syntax descriptor for the | |
397 | desired syntax (i.e.@: a string beginning with a class designator | |
398 | character, and optionally containing a matching character and syntax | |
399 | flags). An error is signaled if the first character is not one of the | |
400 | seventeen syntax class designators. @xref{Syntax Descriptors}. | |
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401 | |
402 | This function always returns @code{nil}. The old syntax information in | |
403 | the table for this character is discarded. | |
404 | ||
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405 | @example |
406 | @group | |
407 | @exdent @r{Examples:} | |
408 | ||
409 | ;; @r{Put the space character in class whitespace.} | |
410 | (modify-syntax-entry ?\s " ") | |
411 | @result{} nil | |
412 | @end group | |
413 | ||
414 | @group | |
415 | ;; @r{Make @samp{$} an open parenthesis character,} | |
416 | ;; @r{with @samp{^} as its matching close.} | |
417 | (modify-syntax-entry ?$ "(^") | |
418 | @result{} nil | |
419 | @end group | |
420 | ||
421 | @group | |
422 | ;; @r{Make @samp{^} a close parenthesis character,} | |
423 | ;; @r{with @samp{$} as its matching open.} | |
424 | (modify-syntax-entry ?^ ")$") | |
425 | @result{} nil | |
426 | @end group | |
427 | ||
428 | @group | |
429 | ;; @r{Make @samp{/} a punctuation character,} | |
430 | ;; @r{the first character of a start-comment sequence,} | |
431 | ;; @r{and the second character of an end-comment sequence.} | |
432 | ;; @r{This is used in C mode.} | |
433 | (modify-syntax-entry ?/ ". 14") | |
434 | @result{} nil | |
435 | @end group | |
436 | @end example | |
437 | @end deffn | |
438 | ||
439 | @defun char-syntax character | |
440 | This function returns the syntax class of @var{character}, represented | |
441 | by its mnemonic designator character. This returns @emph{only} the | |
442 | class, not any matching parenthesis or flags. | |
443 | ||
444 | An error is signaled if @var{char} is not a character. | |
445 | ||
446 | The following examples apply to C mode. The first example shows that | |
447 | the syntax class of space is whitespace (represented by a space). The | |
448 | second example shows that the syntax of @samp{/} is punctuation. This | |
449 | does not show the fact that it is also part of comment-start and -end | |
450 | sequences. The third example shows that open parenthesis is in the class | |
451 | of open parentheses. This does not show the fact that it has a matching | |
452 | character, @samp{)}. | |
453 | ||
454 | @example | |
455 | @group | |
456 | (string (char-syntax ?\s)) | |
457 | @result{} " " | |
458 | @end group | |
459 | ||
460 | @group | |
461 | (string (char-syntax ?/)) | |
462 | @result{} "." | |
463 | @end group | |
464 | ||
465 | @group | |
466 | (string (char-syntax ?\()) | |
467 | @result{} "(" | |
468 | @end group | |
469 | @end example | |
470 | ||
471 | We use @code{string} to make it easier to see the character returned by | |
472 | @code{char-syntax}. | |
473 | @end defun | |
474 | ||
475 | @defun set-syntax-table table | |
476 | This function makes @var{table} the syntax table for the current buffer. | |
477 | It returns @var{table}. | |
478 | @end defun | |
479 | ||
480 | @defun syntax-table | |
481 | This function returns the current syntax table, which is the table for | |
482 | the current buffer. | |
483 | @end defun | |
484 | ||
485 | @defmac with-syntax-table @var{table} @var{body}@dots{} | |
486 | This macro executes @var{body} using @var{table} as the current syntax | |
487 | table. It returns the value of the last form in @var{body}, after | |
488 | restoring the old current syntax table. | |
489 | ||
490 | Since each buffer has its own current syntax table, we should make that | |
491 | more precise: @code{with-syntax-table} temporarily alters the current | |
492 | syntax table of whichever buffer is current at the time the macro | |
493 | execution starts. Other buffers are not affected. | |
494 | @end defmac | |
495 | ||
496 | @node Syntax Properties | |
497 | @section Syntax Properties | |
498 | @kindex syntax-table @r{(text property)} | |
499 | ||
500 | When the syntax table is not flexible enough to specify the syntax of | |
4230351b CY |
501 | a language, you can override the syntax table for specific character |
502 | occurrences in the buffer, by applying a @code{syntax-table} text | |
503 | property. @xref{Text Properties}, for how to apply text properties. | |
b8d4c8d0 | 504 | |
4230351b | 505 | The valid values of @code{syntax-table} text property are: |
b8d4c8d0 GM |
506 | |
507 | @table @asis | |
508 | @item @var{syntax-table} | |
509 | If the property value is a syntax table, that table is used instead of | |
4230351b CY |
510 | the current buffer's syntax table to determine the syntax for the |
511 | underlying text character. | |
b8d4c8d0 GM |
512 | |
513 | @item @code{(@var{syntax-code} . @var{matching-char})} | |
4230351b CY |
514 | A cons cell of this format specifies the syntax for the underlying |
515 | text character. (@pxref{Syntax Table Internals}) | |
b8d4c8d0 GM |
516 | |
517 | @item @code{nil} | |
518 | If the property is @code{nil}, the character's syntax is determined from | |
519 | the current syntax table in the usual way. | |
520 | @end table | |
521 | ||
522 | @defvar parse-sexp-lookup-properties | |
4230351b CY |
523 | If this is non-@code{nil}, the syntax scanning functions, like |
524 | @code{forward-sexp}, pay attention to syntax text properties. | |
525 | Otherwise they use only the current syntax table. | |
526 | @end defvar | |
527 | ||
528 | @defvar syntax-propertize-function | |
529 | This variable, if non-@code{nil}, should store a function for applying | |
530 | @code{syntax-table} properties to a specified stretch of text. It is | |
531 | intended to be used by major modes to install a function which applies | |
532 | @code{syntax-table} properties in some mode-appropriate way. | |
533 | ||
534 | The function is called by @code{syntax-ppss} (@pxref{Position Parse}), | |
535 | and by Font Lock mode during syntactic fontification (@pxref{Syntactic | |
536 | Font Lock}). It is called with two arguments, @var{start} and | |
537 | @var{end}, which are the starting and ending positions of the text on | |
538 | which it should act. It is allowed to call @code{syntax-ppss} on any | |
539 | position before @var{end}. However, it should not call | |
540 | @code{syntax-ppss-flush-cache}; so, it is not allowed to call | |
541 | @code{syntax-ppss} on some position and later modify the buffer at an | |
542 | earlier position. | |
543 | @end defvar | |
544 | ||
545 | @defvar syntax-propertize-extend-region-functions | |
546 | This abnormal hook is run by the syntax parsing code prior to calling | |
547 | @code{syntax-propertize-function}. Its role is to help locate safe | |
548 | starting and ending buffer positions for passing to | |
549 | @code{syntax-propertize-function}. For example, a major mode can add | |
550 | a function to this hook to identify multi-line syntactic constructs, | |
551 | and ensure that the boundaries do not fall in the middle of one. | |
552 | ||
553 | Each function in this hook should accept two arguments, @var{start} | |
554 | and @var{end}. It should return either a cons cell of two adjusted | |
555 | buffer positions, @code{(@var{new-start} . @var{new-end})}, or | |
556 | @code{nil} if no adjustment is necessary. The hook functions are run | |
557 | in turn, repeatedly, until they all return @code{nil}. | |
b8d4c8d0 GM |
558 | @end defvar |
559 | ||
560 | @node Motion and Syntax | |
561 | @section Motion and Syntax | |
562 | ||
563 | This section describes functions for moving across characters that | |
564 | have certain syntax classes. | |
565 | ||
566 | @defun skip-syntax-forward syntaxes &optional limit | |
567 | This function moves point forward across characters having syntax | |
568 | classes mentioned in @var{syntaxes} (a string of syntax class | |
569 | characters). It stops when it encounters the end of the buffer, or | |
570 | position @var{limit} (if specified), or a character it is not supposed | |
571 | to skip. | |
572 | ||
573 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
574 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
575 | ||
576 | The return value is the distance traveled, which is a nonnegative | |
577 | integer. | |
578 | @end defun | |
579 | ||
580 | @defun skip-syntax-backward syntaxes &optional limit | |
581 | This function moves point backward across characters whose syntax | |
582 | classes are mentioned in @var{syntaxes}. It stops when it encounters | |
583 | the beginning of the buffer, or position @var{limit} (if specified), or | |
584 | a character it is not supposed to skip. | |
585 | ||
586 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
587 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
588 | ||
589 | The return value indicates the distance traveled. It is an integer that | |
590 | is zero or less. | |
591 | @end defun | |
592 | ||
593 | @defun backward-prefix-chars | |
594 | This function moves point backward over any number of characters with | |
595 | expression prefix syntax. This includes both characters in the | |
596 | expression prefix syntax class, and characters with the @samp{p} flag. | |
597 | @end defun | |
598 | ||
599 | @node Parsing Expressions | |
600 | @section Parsing Expressions | |
601 | ||
602 | This section describes functions for parsing and scanning balanced | |
a037c171 CY |
603 | expressions. We will refer to such expressions as @dfn{sexps}, |
604 | following the terminology of Lisp, even though these functions can act | |
605 | on languages other than Lisp. Basically, a sexp is either a balanced | |
606 | parenthetical grouping, a string, or a ``symbol'' (i.e.@: a sequence | |
607 | of characters whose syntax is either word constituent or symbol | |
4230351b CY |
608 | constituent). However, characters in the expression prefix syntax |
609 | class (@pxref{Syntax Class Table}) are treated as part of the sexp if | |
610 | they appear next to it. | |
b8d4c8d0 GM |
611 | |
612 | The syntax table controls the interpretation of characters, so these | |
613 | functions can be used for Lisp expressions when in Lisp mode and for C | |
614 | expressions when in C mode. @xref{List Motion}, for convenient | |
615 | higher-level functions for moving over balanced expressions. | |
616 | ||
617 | A character's syntax controls how it changes the state of the | |
618 | parser, rather than describing the state itself. For example, a | |
619 | string delimiter character toggles the parser state between | |
16152b76 | 620 | ``in-string'' and ``in-code'', but the syntax of characters does not |
b8d4c8d0 GM |
621 | directly say whether they are inside a string. For example (note that |
622 | 15 is the syntax code for generic string delimiters), | |
623 | ||
624 | @example | |
625 | (put-text-property 1 9 'syntax-table '(15 . nil)) | |
626 | @end example | |
627 | ||
628 | @noindent | |
629 | does not tell Emacs that the first eight chars of the current buffer | |
630 | are a string, but rather that they are all string delimiters. As a | |
631 | result, Emacs treats them as four consecutive empty string constants. | |
632 | ||
633 | @menu | |
634 | * Motion via Parsing:: Motion functions that work by parsing. | |
635 | * Position Parse:: Determining the syntactic state of a position. | |
636 | * Parser State:: How Emacs represents a syntactic state. | |
637 | * Low-Level Parsing:: Parsing across a specified region. | |
638 | * Control Parsing:: Parameters that affect parsing. | |
639 | @end menu | |
640 | ||
641 | @node Motion via Parsing | |
642 | @subsection Motion Commands Based on Parsing | |
643 | ||
644 | This section describes simple point-motion functions that operate | |
645 | based on parsing expressions. | |
646 | ||
647 | @defun scan-lists from count depth | |
7b926f3f CY |
648 | This function scans forward @var{count} balanced parenthetical |
649 | groupings from position @var{from}. It returns the position where the | |
650 | scan stops. If @var{count} is negative, the scan moves backwards. | |
651 | ||
652 | If @var{depth} is nonzero, treat the starting position as being | |
653 | @var{depth} parentheses deep. The scanner moves forward or backward | |
654 | through the buffer until the depth changes to zero @var{count} times. | |
655 | Hence, a positive value for @var{depth} has the effect of moving out | |
656 | @var{depth} levels of parenthesis from the starting position, while a | |
657 | negative @var{depth} has the effect of moving deeper by @var{-depth} | |
658 | levels of parenthesis. | |
b8d4c8d0 GM |
659 | |
660 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
661 | non-@code{nil}. | |
662 | ||
7b926f3f CY |
663 | If the scan reaches the beginning or end of the accessible part of the |
664 | buffer before it has scanned over @var{count} parenthetical groupings, | |
665 | the return value is @code{nil} if the depth at that point is zero; if | |
666 | the depth is non-zero, a @code{scan-error} error is signaled. | |
b8d4c8d0 GM |
667 | @end defun |
668 | ||
669 | @defun scan-sexps from count | |
670 | This function scans forward @var{count} sexps from position @var{from}. | |
671 | It returns the position where the scan stops. If @var{count} is | |
672 | negative, the scan moves backwards. | |
673 | ||
674 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
675 | non-@code{nil}. | |
676 | ||
677 | If the scan reaches the beginning or end of (the accessible part of) the | |
678 | buffer while in the middle of a parenthetical grouping, an error is | |
679 | signaled. If it reaches the beginning or end between groupings but | |
680 | before count is used up, @code{nil} is returned. | |
681 | @end defun | |
682 | ||
683 | @defun forward-comment count | |
684 | This function moves point forward across @var{count} complete comments | |
685 | (that is, including the starting delimiter and the terminating | |
686 | delimiter if any), plus any whitespace encountered on the way. It | |
687 | moves backward if @var{count} is negative. If it encounters anything | |
688 | other than a comment or whitespace, it stops, leaving point at the | |
689 | place where it stopped. This includes (for instance) finding the end | |
690 | of a comment when moving forward and expecting the beginning of one. | |
691 | The function also stops immediately after moving over the specified | |
692 | number of complete comments. If @var{count} comments are found as | |
693 | expected, with nothing except whitespace between them, it returns | |
694 | @code{t}; otherwise it returns @code{nil}. | |
695 | ||
696 | This function cannot tell whether the ``comments'' it traverses are | |
697 | embedded within a string. If they look like comments, it treats them | |
698 | as comments. | |
b8d4c8d0 GM |
699 | |
700 | To move forward over all comments and whitespace following point, use | |
4230351b CY |
701 | @code{(forward-comment (buffer-size))}. @code{(buffer-size)} is a |
702 | good argument to use, because the number of comments in the buffer | |
703 | cannot exceed that many. | |
704 | @end defun | |
b8d4c8d0 GM |
705 | |
706 | @node Position Parse | |
707 | @subsection Finding the Parse State for a Position | |
708 | ||
709 | For syntactic analysis, such as in indentation, often the useful | |
710 | thing is to compute the syntactic state corresponding to a given buffer | |
711 | position. This function does that conveniently. | |
712 | ||
713 | @defun syntax-ppss &optional pos | |
4230351b CY |
714 | This function returns the parser state that the parser would reach at |
715 | position @var{pos} starting from the beginning of the buffer. | |
716 | @iftex | |
717 | See the next section for | |
718 | @end iftex | |
719 | @ifnottex | |
720 | @xref{Parser State}, | |
721 | @end ifnottex | |
722 | for a description of the parser state. | |
723 | ||
724 | The return value is the same as if you call the low-level parsing | |
725 | function @code{parse-partial-sexp} to parse from the beginning of the | |
726 | buffer to @var{pos} (@pxref{Low-Level Parsing}). However, | |
727 | @code{syntax-ppss} uses a cache to speed up the computation. Due to | |
728 | this optimization, the second value (previous complete subexpression) | |
729 | and sixth value (minimum parenthesis depth) in the returned parser | |
730 | state are not meaningful. | |
731 | ||
732 | This function has a side effect: it adds a buffer-local entry to | |
733 | @code{before-change-functions} (@pxref{Change Hooks}) for | |
734 | @code{syntax-ppss-flush-cache} (see below). This entry keeps the | |
735 | cache consistent as the buffer is modified. However, the cache might | |
736 | not be updated if @code{syntax-ppss} is called while | |
b8d4c8d0 | 737 | @code{before-change-functions} is temporarily let-bound, or if the |
4230351b CY |
738 | buffer is modified without running the hook, such as when using |
739 | @code{inhibit-modification-hooks}. In those cases, it is necessary to | |
740 | call @code{syntax-ppss-flush-cache} explicitly. | |
741 | @end defun | |
b8d4c8d0 | 742 | |
106e6894 CY |
743 | @defun syntax-ppss-flush-cache beg &rest ignored-args |
744 | This function flushes the cache used by @code{syntax-ppss}, starting | |
745 | at position @var{beg}. The remaining arguments, @var{ignored-args}, | |
746 | are ignored; this function accepts them so that it can be directly | |
747 | used on hooks such as @code{before-change-functions} (@pxref{Change | |
748 | Hooks}). | |
b8d4c8d0 GM |
749 | @end defun |
750 | ||
751 | Major modes can make @code{syntax-ppss} run faster by specifying | |
752 | where it needs to start parsing. | |
753 | ||
754 | @defvar syntax-begin-function | |
755 | If this is non-@code{nil}, it should be a function that moves to an | |
756 | earlier buffer position where the parser state is equivalent to | |
757 | @code{nil}---in other words, a position outside of any comment, | |
758 | string, or parenthesis. @code{syntax-ppss} uses it to further | |
759 | optimize its computations, when the cache gives no help. | |
760 | @end defvar | |
761 | ||
762 | @node Parser State | |
763 | @subsection Parser State | |
764 | @cindex parser state | |
765 | ||
4230351b CY |
766 | A @dfn{parser state} is a list of ten elements describing the state |
767 | of the syntactic parser, after it parses the text between a specified | |
768 | starting point and a specified end point in the buffer. Parsing | |
769 | functions such as @code{syntax-ppss} | |
770 | @ifnottex | |
771 | (@pxref{Position Parse}) | |
772 | @end ifnottex | |
773 | return a parser state as the value. Some parsing functions accept a | |
774 | parser state as an argument, for resuming parsing. | |
775 | ||
776 | Here are the meanings of the elements of the parser state: | |
b8d4c8d0 GM |
777 | |
778 | @enumerate 0 | |
779 | @item | |
780 | The depth in parentheses, counting from 0. @strong{Warning:} this can | |
781 | be negative if there are more close parens than open parens between | |
4230351b | 782 | the parser's starting point and end point. |
b8d4c8d0 GM |
783 | |
784 | @item | |
785 | @cindex innermost containing parentheses | |
786 | The character position of the start of the innermost parenthetical | |
787 | grouping containing the stopping point; @code{nil} if none. | |
788 | ||
789 | @item | |
790 | @cindex previous complete subexpression | |
791 | The character position of the start of the last complete subexpression | |
792 | terminated; @code{nil} if none. | |
793 | ||
794 | @item | |
795 | @cindex inside string | |
796 | Non-@code{nil} if inside a string. More precisely, this is the | |
797 | character that will terminate the string, or @code{t} if a generic | |
798 | string delimiter character should terminate it. | |
799 | ||
800 | @item | |
801 | @cindex inside comment | |
4230351b CY |
802 | @code{t} if inside a non-nestable comment (of any comment style; |
803 | @pxref{Syntax Flags}); or the comment nesting level if inside a | |
804 | comment that can be nested. | |
b8d4c8d0 GM |
805 | |
806 | @item | |
807 | @cindex quote character | |
4230351b | 808 | @code{t} if the end point is just after a quote character. |
b8d4c8d0 GM |
809 | |
810 | @item | |
811 | The minimum parenthesis depth encountered during this scan. | |
812 | ||
813 | @item | |
4230351b CY |
814 | What kind of comment is active: @code{nil} if not in a comment or in a |
815 | comment of style @samp{a}; 1 for a comment of style @samp{b}; 2 for a | |
816 | comment of style @samp{c}; and @code{syntax-table} for a comment that | |
817 | should be ended by a generic comment delimiter character. | |
b8d4c8d0 GM |
818 | |
819 | @item | |
820 | The string or comment start position. While inside a comment, this is | |
821 | the position where the comment began; while inside a string, this is the | |
822 | position where the string began. When outside of strings and comments, | |
823 | this element is @code{nil}. | |
824 | ||
825 | @item | |
826 | Internal data for continuing the parsing. The meaning of this | |
827 | data is subject to change; it is used if you pass this list | |
828 | as the @var{state} argument to another call. | |
829 | @end enumerate | |
830 | ||
831 | Elements 1, 2, and 6 are ignored in a state which you pass as an | |
832 | argument to continue parsing, and elements 8 and 9 are used only in | |
4230351b CY |
833 | trivial cases. Those elements are mainly used internally by the |
834 | parser code. | |
b8d4c8d0 GM |
835 | |
836 | One additional piece of useful information is available from a | |
837 | parser state using this function: | |
838 | ||
839 | @defun syntax-ppss-toplevel-pos state | |
840 | This function extracts, from parser state @var{state}, the last | |
841 | position scanned in the parse which was at top level in grammatical | |
842 | structure. ``At top level'' means outside of any parentheses, | |
843 | comments, or strings. | |
844 | ||
845 | The value is @code{nil} if @var{state} represents a parse which has | |
846 | arrived at a top level position. | |
847 | @end defun | |
848 | ||
b8d4c8d0 GM |
849 | @node Low-Level Parsing |
850 | @subsection Low-Level Parsing | |
851 | ||
852 | The most basic way to use the expression parser is to tell it | |
853 | to start at a given position with a certain state, and parse up to | |
854 | a specified end position. | |
855 | ||
856 | @defun parse-partial-sexp start limit &optional target-depth stop-before state stop-comment | |
857 | This function parses a sexp in the current buffer starting at | |
858 | @var{start}, not scanning past @var{limit}. It stops at position | |
859 | @var{limit} or when certain criteria described below are met, and sets | |
860 | point to the location where parsing stops. It returns a parser state | |
861 | describing the status of the parse at the point where it stops. | |
862 | ||
863 | @cindex parenthesis depth | |
864 | If the third argument @var{target-depth} is non-@code{nil}, parsing | |
865 | stops if the depth in parentheses becomes equal to @var{target-depth}. | |
866 | The depth starts at 0, or at whatever is given in @var{state}. | |
867 | ||
868 | If the fourth argument @var{stop-before} is non-@code{nil}, parsing | |
869 | stops when it comes to any character that starts a sexp. If | |
870 | @var{stop-comment} is non-@code{nil}, parsing stops when it comes to the | |
871 | start of a comment. If @var{stop-comment} is the symbol | |
872 | @code{syntax-table}, parsing stops after the start of a comment or a | |
873 | string, or the end of a comment or a string, whichever comes first. | |
874 | ||
875 | If @var{state} is @code{nil}, @var{start} is assumed to be at the top | |
876 | level of parenthesis structure, such as the beginning of a function | |
877 | definition. Alternatively, you might wish to resume parsing in the | |
878 | middle of the structure. To do this, you must provide a @var{state} | |
879 | argument that describes the initial status of parsing. The value | |
880 | returned by a previous call to @code{parse-partial-sexp} will do | |
881 | nicely. | |
882 | @end defun | |
883 | ||
884 | @node Control Parsing | |
885 | @subsection Parameters to Control Parsing | |
886 | ||
887 | @defvar multibyte-syntax-as-symbol | |
888 | If this variable is non-@code{nil}, @code{scan-sexps} treats all | |
889 | non-@acronym{ASCII} characters as symbol constituents regardless | |
890 | of what the syntax table says about them. (However, text properties | |
891 | can still override the syntax.) | |
892 | @end defvar | |
893 | ||
894 | @defopt parse-sexp-ignore-comments | |
895 | @cindex skipping comments | |
896 | If the value is non-@code{nil}, then comments are treated as | |
897 | whitespace by the functions in this section and by @code{forward-sexp}, | |
898 | @code{scan-lists} and @code{scan-sexps}. | |
899 | @end defopt | |
900 | ||
901 | @vindex parse-sexp-lookup-properties | |
902 | The behavior of @code{parse-partial-sexp} is also affected by | |
903 | @code{parse-sexp-lookup-properties} (@pxref{Syntax Properties}). | |
904 | ||
905 | You can use @code{forward-comment} to move forward or backward over | |
906 | one comment or several comments. | |
907 | ||
908 | @node Standard Syntax Tables | |
909 | @section Some Standard Syntax Tables | |
910 | ||
911 | Most of the major modes in Emacs have their own syntax tables. Here | |
912 | are several of them: | |
913 | ||
914 | @defun standard-syntax-table | |
915 | This function returns the standard syntax table, which is the syntax | |
916 | table used in Fundamental mode. | |
917 | @end defun | |
918 | ||
919 | @defvar text-mode-syntax-table | |
920 | The value of this variable is the syntax table used in Text mode. | |
921 | @end defvar | |
922 | ||
923 | @defvar c-mode-syntax-table | |
924 | The value of this variable is the syntax table for C-mode buffers. | |
925 | @end defvar | |
926 | ||
927 | @defvar emacs-lisp-mode-syntax-table | |
928 | The value of this variable is the syntax table used in Emacs Lisp mode | |
929 | by editing commands. (It has no effect on the Lisp @code{read} | |
930 | function.) | |
931 | @end defvar | |
932 | ||
933 | @node Syntax Table Internals | |
934 | @section Syntax Table Internals | |
935 | @cindex syntax table internals | |
936 | ||
937 | Lisp programs don't usually work with the elements directly; the | |
938 | Lisp-level syntax table functions usually work with syntax descriptors | |
939 | (@pxref{Syntax Descriptors}). Nonetheless, here we document the | |
940 | internal format. This format is used mostly when manipulating | |
941 | syntax properties. | |
942 | ||
943 | Each element of a syntax table is a cons cell of the form | |
944 | @code{(@var{syntax-code} . @var{matching-char})}. The @sc{car}, | |
945 | @var{syntax-code}, is an integer that encodes the syntax class, and any | |
946 | flags. The @sc{cdr}, @var{matching-char}, is non-@code{nil} if | |
947 | a character to match was specified. | |
948 | ||
949 | This table gives the value of @var{syntax-code} which corresponds | |
950 | to each syntactic type. | |
951 | ||
952 | @multitable @columnfractions .05 .3 .3 .31 | |
953 | @item | |
954 | @tab | |
955 | @i{Integer} @i{Class} | |
956 | @tab | |
957 | @i{Integer} @i{Class} | |
958 | @tab | |
959 | @i{Integer} @i{Class} | |
960 | @item | |
961 | @tab | |
962 | 0 @ @ whitespace | |
963 | @tab | |
964 | 5 @ @ close parenthesis | |
965 | @tab | |
966 | 10 @ @ character quote | |
967 | @item | |
968 | @tab | |
969 | 1 @ @ punctuation | |
970 | @tab | |
971 | 6 @ @ expression prefix | |
972 | @tab | |
973 | 11 @ @ comment-start | |
974 | @item | |
975 | @tab | |
976 | 2 @ @ word | |
977 | @tab | |
978 | 7 @ @ string quote | |
979 | @tab | |
980 | 12 @ @ comment-end | |
981 | @item | |
982 | @tab | |
983 | 3 @ @ symbol | |
984 | @tab | |
985 | 8 @ @ paired delimiter | |
986 | @tab | |
987 | 13 @ @ inherit | |
988 | @item | |
989 | @tab | |
990 | 4 @ @ open parenthesis | |
991 | @tab | |
992 | 9 @ @ escape | |
993 | @tab | |
994 | 14 @ @ generic comment | |
995 | @item | |
996 | @tab | |
997 | 15 @ generic string | |
998 | @end multitable | |
999 | ||
1000 | For example, the usual syntax value for @samp{(} is @code{(4 . 41)}. | |
1001 | (41 is the character code for @samp{)}.) | |
1002 | ||
1003 | The flags are encoded in higher order bits, starting 16 bits from the | |
1004 | least significant bit. This table gives the power of two which | |
1005 | corresponds to each syntax flag. | |
1006 | ||
1007 | @multitable @columnfractions .05 .3 .3 .3 | |
1008 | @item | |
1009 | @tab | |
1010 | @i{Prefix} @i{Flag} | |
1011 | @tab | |
1012 | @i{Prefix} @i{Flag} | |
1013 | @tab | |
1014 | @i{Prefix} @i{Flag} | |
1015 | @item | |
1016 | @tab | |
1017 | @samp{1} @ @ @code{(lsh 1 16)} | |
1018 | @tab | |
1019 | @samp{4} @ @ @code{(lsh 1 19)} | |
1020 | @tab | |
1021 | @samp{b} @ @ @code{(lsh 1 21)} | |
1022 | @item | |
1023 | @tab | |
1024 | @samp{2} @ @ @code{(lsh 1 17)} | |
1025 | @tab | |
1026 | @samp{p} @ @ @code{(lsh 1 20)} | |
1027 | @tab | |
1028 | @samp{n} @ @ @code{(lsh 1 22)} | |
1029 | @item | |
1030 | @tab | |
1031 | @samp{3} @ @ @code{(lsh 1 18)} | |
1032 | @end multitable | |
1033 | ||
1034 | @defun string-to-syntax @var{desc} | |
1035 | This function returns the internal form corresponding to the syntax | |
1036 | descriptor @var{desc}, a cons cell @code{(@var{syntax-code} | |
1037 | . @var{matching-char})}. | |
1038 | @end defun | |
1039 | ||
1040 | @defun syntax-after pos | |
1041 | This function returns the syntax code of the character in the buffer | |
1042 | after position @var{pos}, taking account of syntax properties as well | |
1043 | as the syntax table. If @var{pos} is outside the buffer's accessible | |
1044 | portion (@pxref{Narrowing, accessible portion}), this function returns | |
1045 | @code{nil}. | |
1046 | @end defun | |
1047 | ||
1048 | @defun syntax-class syntax | |
1049 | This function returns the syntax class of the syntax code | |
1050 | @var{syntax}. (It masks off the high 16 bits that hold the flags | |
1051 | encoded in the syntax descriptor.) If @var{syntax} is @code{nil}, it | |
1052 | returns @code{nil}; this is so evaluating the expression | |
1053 | ||
1054 | @example | |
1055 | (syntax-class (syntax-after pos)) | |
1056 | @end example | |
1057 | ||
1058 | @noindent | |
1059 | where @code{pos} is outside the buffer's accessible portion, will | |
1060 | yield @code{nil} without throwing errors or producing wrong syntax | |
1061 | class codes. | |
1062 | @end defun | |
1063 | ||
1064 | @node Categories | |
1065 | @section Categories | |
1066 | @cindex categories of characters | |
1067 | @cindex character categories | |
1068 | ||
1069 | @dfn{Categories} provide an alternate way of classifying characters | |
1070 | syntactically. You can define several categories as needed, then | |
1071 | independently assign each character to one or more categories. Unlike | |
1072 | syntax classes, categories are not mutually exclusive; it is normal for | |
1073 | one character to belong to several categories. | |
1074 | ||
1075 | @cindex category table | |
1076 | Each buffer has a @dfn{category table} which records which categories | |
1077 | are defined and also which characters belong to each category. Each | |
1078 | category table defines its own categories, but normally these are | |
1079 | initialized by copying from the standard categories table, so that the | |
1080 | standard categories are available in all modes. | |
1081 | ||
1082 | Each category has a name, which is an @acronym{ASCII} printing character in | |
1083 | the range @w{@samp{ }} to @samp{~}. You specify the name of a category | |
1084 | when you define it with @code{define-category}. | |
1085 | ||
1086 | The category table is actually a char-table (@pxref{Char-Tables}). | |
1087 | The element of the category table at index @var{c} is a @dfn{category | |
1088 | set}---a bool-vector---that indicates which categories character @var{c} | |
1089 | belongs to. In this category set, if the element at index @var{cat} is | |
1090 | @code{t}, that means category @var{cat} is a member of the set, and that | |
1091 | character @var{c} belongs to category @var{cat}. | |
1092 | ||
1093 | For the next three functions, the optional argument @var{table} | |
1094 | defaults to the current buffer's category table. | |
1095 | ||
1096 | @defun define-category char docstring &optional table | |
1097 | This function defines a new category, with name @var{char} and | |
1098 | documentation @var{docstring}, for the category table @var{table}. | |
1ea897d5 EZ |
1099 | |
1100 | Here's an example of defining a new category for characters that have | |
1101 | strong right-to-left directionality (@pxref{Bidirectional Display}) | |
1102 | and using it in a special category table: | |
1103 | ||
1104 | @example | |
1105 | (defvar special-category-table-for-bidi | |
1106 | (let ((category-table (make-category-table)) | |
1107 | (uniprop-table (unicode-property-table-internal 'bidi-class))) | |
1108 | (define-category ?R "Characters of bidi-class R, AL, or RLO" | |
1109 | category-table) | |
1110 | (map-char-table | |
1111 | #'(lambda (key val) | |
1112 | (if (memq val '(R AL RLO)) | |
1113 | (modify-category-entry key ?R category-table))) | |
1114 | uniprop-table) | |
1115 | category-table)) | |
1116 | @end example | |
b8d4c8d0 GM |
1117 | @end defun |
1118 | ||
1119 | @defun category-docstring category &optional table | |
1120 | This function returns the documentation string of category @var{category} | |
1121 | in category table @var{table}. | |
1122 | ||
1123 | @example | |
1124 | (category-docstring ?a) | |
1125 | @result{} "ASCII" | |
1126 | (category-docstring ?l) | |
1127 | @result{} "Latin" | |
1128 | @end example | |
1129 | @end defun | |
1130 | ||
1131 | @defun get-unused-category &optional table | |
1132 | This function returns a category name (a character) which is not | |
1133 | currently defined in @var{table}. If all possible categories are in use | |
1134 | in @var{table}, it returns @code{nil}. | |
1135 | @end defun | |
1136 | ||
1137 | @defun category-table | |
1138 | This function returns the current buffer's category table. | |
1139 | @end defun | |
1140 | ||
1141 | @defun category-table-p object | |
1142 | This function returns @code{t} if @var{object} is a category table, | |
1143 | otherwise @code{nil}. | |
1144 | @end defun | |
1145 | ||
1146 | @defun standard-category-table | |
1147 | This function returns the standard category table. | |
1148 | @end defun | |
1149 | ||
1150 | @defun copy-category-table &optional table | |
1151 | This function constructs a copy of @var{table} and returns it. If | |
1152 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
1153 | standard category table. Otherwise, an error is signaled if @var{table} | |
1154 | is not a category table. | |
1155 | @end defun | |
1156 | ||
1157 | @defun set-category-table table | |
1158 | This function makes @var{table} the category table for the current | |
1159 | buffer. It returns @var{table}. | |
1160 | @end defun | |
1161 | ||
1162 | @defun make-category-table | |
1163 | This creates and returns an empty category table. In an empty category | |
1164 | table, no categories have been allocated, and no characters belong to | |
1165 | any categories. | |
1166 | @end defun | |
1167 | ||
1168 | @defun make-category-set categories | |
1169 | This function returns a new category set---a bool-vector---whose initial | |
1170 | contents are the categories listed in the string @var{categories}. The | |
1171 | elements of @var{categories} should be category names; the new category | |
1172 | set has @code{t} for each of those categories, and @code{nil} for all | |
1173 | other categories. | |
1174 | ||
1175 | @example | |
1176 | (make-category-set "al") | |
1177 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1178 | @end example | |
1179 | @end defun | |
1180 | ||
1181 | @defun char-category-set char | |
1182 | This function returns the category set for character @var{char} in the | |
1183 | current buffer's category table. This is the bool-vector which | |
1184 | records which categories the character @var{char} belongs to. The | |
1185 | function @code{char-category-set} does not allocate storage, because | |
1186 | it returns the same bool-vector that exists in the category table. | |
1187 | ||
1188 | @example | |
1189 | (char-category-set ?a) | |
1190 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1191 | @end example | |
1192 | @end defun | |
1193 | ||
1194 | @defun category-set-mnemonics category-set | |
1195 | This function converts the category set @var{category-set} into a string | |
1196 | containing the characters that designate the categories that are members | |
1197 | of the set. | |
1198 | ||
1199 | @example | |
1200 | (category-set-mnemonics (char-category-set ?a)) | |
1201 | @result{} "al" | |
1202 | @end example | |
1203 | @end defun | |
1204 | ||
f147ff75 CY |
1205 | @defun modify-category-entry char category &optional table reset |
1206 | This function modifies the category set of @var{char} in category | |
b8d4c8d0 | 1207 | table @var{table} (which defaults to the current buffer's category |
f147ff75 CY |
1208 | table). @var{char} can be a character, or a cons cell of the form |
1209 | @code{(@var{min} . @var{max})}; in the latter case, the function | |
1210 | modifies the category sets of all characters in the range between | |
1211 | @var{min} and @var{max}, inclusive. | |
b8d4c8d0 | 1212 | |
f147ff75 | 1213 | Normally, it modifies a category set by adding @var{category} to it. |
b8d4c8d0 GM |
1214 | But if @var{reset} is non-@code{nil}, then it deletes @var{category} |
1215 | instead. | |
1216 | @end defun | |
1217 | ||
1218 | @deffn Command describe-categories &optional buffer-or-name | |
1219 | This function describes the category specifications in the current | |
1220 | category table. It inserts the descriptions in a buffer, and then | |
1221 | displays that buffer. If @var{buffer-or-name} is non-@code{nil}, it | |
1222 | describes the category table of that buffer instead. | |
1223 | @end deffn |