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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
ba318903 | 3 | @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software |
ab422c4d | 4 | @c Foundation, Inc. |
b8d4c8d0 | 5 | @c See the file elisp.texi for copying conditions. |
ecc6530d | 6 | @node Syntax Tables |
b8d4c8d0 GM |
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. | |
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26 | * Syntax Table Internals:: How syntax table information is stored. |
27 | * Categories:: Another way of classifying character syntax. | |
28 | @end menu | |
29 | ||
30 | @node Syntax Basics | |
31 | @section Syntax Table Concepts | |
32 | ||
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33 | A syntax table is a data structure which can be used to look up the |
34 | @dfn{syntax class} and other syntactic properties of each character. | |
35 | Syntax tables are used by Lisp programs for scanning and moving across | |
36 | text. | |
b8d4c8d0 | 37 | |
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38 | Internally, a syntax table is a char-table (@pxref{Char-Tables}). |
39 | The element at index @var{c} describes the character with code | |
40 | @var{c}; its value is a cons cell which specifies the syntax of the | |
41 | character in question. @xref{Syntax Table Internals}, for details. | |
42 | However, instead of using @code{aset} and @code{aref} to modify and | |
43 | inspect syntax table contents, you should usually use the higher-level | |
44 | functions @code{char-syntax} and @code{modify-syntax-entry}, which are | |
45 | described in @ref{Syntax Table Functions}. | |
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46 | |
47 | @defun syntax-table-p object | |
48 | This function returns @code{t} if @var{object} is a syntax table. | |
49 | @end defun | |
50 | ||
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51 | Each buffer has its own major mode, and each major mode has its own |
52 | idea of the syntax class of various characters. For example, in Lisp | |
53 | mode, the character @samp{;} begins a comment, but in C mode, it | |
54 | terminates a statement. To support these variations, the syntax table | |
55 | is local to each buffer. Typically, each major mode has its own | |
56 | syntax table, which it installs in all buffers that use that mode. | |
57 | For example, the variable @code{emacs-lisp-mode-syntax-table} holds | |
58 | the syntax table used by Emacs Lisp mode, and | |
59 | @code{c-mode-syntax-table} holds the syntax table used by C mode. | |
60 | Changing a major mode's syntax table alters the syntax in all of that | |
61 | mode's buffers, as well as in any buffers subsequently put in that | |
62 | mode. Occasionally, several similar modes share one syntax table. | |
63 | @xref{Example Major Modes}, for an example of how to set up a syntax | |
64 | table. | |
65 | ||
66 | @cindex standard syntax table | |
67 | @cindex inheritance, syntax table | |
68 | A syntax table can @dfn{inherit} from another syntax table, which is | |
69 | called its @dfn{parent syntax table}. A syntax table can leave the | |
70 | syntax class of some characters unspecified, by giving them the | |
71 | ``inherit'' syntax class; such a character then acquires the syntax | |
72 | class specified by the parent syntax table (@pxref{Syntax Class | |
73 | Table}). Emacs defines a @dfn{standard syntax table}, which is the | |
74 | default parent syntax table, and is also the syntax table used by | |
75 | Fundamental mode. | |
76 | ||
77 | @defun standard-syntax-table | |
78 | This function returns the standard syntax table, which is the syntax | |
79 | table used in Fundamental mode. | |
80 | @end defun | |
81 | ||
82 | Syntax tables are not used by the Emacs Lisp reader, which has its | |
83 | own built-in syntactic rules which cannot be changed. (Some Lisp | |
84 | systems provide ways to redefine the read syntax, but we decided to | |
85 | leave this feature out of Emacs Lisp for simplicity.) | |
86 | ||
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87 | @node Syntax Descriptors |
88 | @section Syntax Descriptors | |
89 | @cindex syntax class | |
90 | ||
02676e5d | 91 | The @dfn{syntax class} of a character describes its syntactic role. |
4230351b | 92 | Each syntax table specifies the syntax class of each character. There |
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93 | is no necessary relationship between the class of a character in one |
94 | syntax table and its class in any other table. | |
95 | ||
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96 | Each syntax class is designated by a mnemonic character, which |
97 | serves as the name of the class when you need to specify a class. | |
98 | Usually, this designator character is one that is often assigned that | |
99 | class; however, its meaning as a designator is unvarying and | |
100 | independent of what syntax that character currently has. Thus, | |
101 | @samp{\} as a designator character always means ``escape character'' | |
102 | syntax, regardless of whether the @samp{\} character actually has that | |
103 | syntax in the current syntax table. | |
104 | @ifnottex | |
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105 | @xref{Syntax Class Table}, for a list of syntax classes and their |
106 | designator characters. | |
4230351b | 107 | @end ifnottex |
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108 | |
109 | @cindex syntax descriptor | |
4230351b | 110 | A @dfn{syntax descriptor} is a Lisp string that describes the syntax |
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111 | class and other syntactic properties of a character. When you want to |
112 | modify the syntax of a character, that is done by calling the function | |
113 | @code{modify-syntax-entry} and passing a syntax descriptor as one of | |
114 | its arguments (@pxref{Syntax Table Functions}). | |
115 | ||
116 | The first character in a syntax descriptor must be a syntax class | |
117 | designator character. The second character, if present, specifies a | |
1df7defd | 118 | matching character (e.g., in Lisp, the matching character for |
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119 | @samp{(} is @samp{)}); a space specifies that there is no matching |
120 | character. Then come characters specifying additional syntax | |
121 | properties (@pxref{Syntax Flags}). | |
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122 | |
123 | If no matching character or flags are needed, only one character | |
124 | (specifying the syntax class) is sufficient. | |
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125 | |
126 | For example, the syntax descriptor for the character @samp{*} in C | |
ad21a12a | 127 | mode is @code{". 23"} (i.e., punctuation, matching character slot |
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128 | unused, second character of a comment-starter, first character of a |
129 | comment-ender), and the entry for @samp{/} is @samp{@w{. 14}} (i.e., | |
130 | punctuation, matching character slot unused, first character of a | |
131 | comment-starter, second character of a comment-ender). | |
132 | ||
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133 | Emacs also defines @dfn{raw syntax descriptors}, which are used to |
134 | describe syntax classes at a lower level. @xref{Syntax Table | |
135 | Internals}. | |
136 | ||
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137 | @menu |
138 | * Syntax Class Table:: Table of syntax classes. | |
139 | * Syntax Flags:: Additional flags each character can have. | |
140 | @end menu | |
141 | ||
142 | @node Syntax Class Table | |
143 | @subsection Table of Syntax Classes | |
8c1f51ff | 144 | @cindex syntax class table |
b8d4c8d0 | 145 | |
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146 | Here is a table of syntax classes, the characters that designate |
147 | them, their meanings, and examples of their use. | |
b8d4c8d0 | 148 | |
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149 | @table @asis |
150 | @item Whitespace characters: @samp{@ } or @samp{-} | |
151 | Characters that separate symbols and words from each other. | |
152 | Typically, whitespace characters have no other syntactic significance, | |
153 | and multiple whitespace characters are syntactically equivalent to a | |
154 | single one. Space, tab, and formfeed are classified as whitespace in | |
155 | almost all major modes. | |
156 | ||
157 | This syntax class can be designated by either @w{@samp{@ }} or | |
158 | @samp{-}. Both designators are equivalent. | |
159 | ||
160 | @item Word constituents: @samp{w} | |
161 | Parts of words in human languages. These are typically used in | |
162 | variable and command names in programs. All upper- and lower-case | |
163 | letters, and the digits, are typically word constituents. | |
164 | ||
165 | @item Symbol constituents: @samp{_} | |
166 | Extra characters used in variable and command names along with word | |
167 | constituents. Examples include the characters @samp{$&*+-_<>} in Lisp | |
168 | mode, which may be part of a symbol name even though they are not part | |
169 | of English words. In standard C, the only non-word-constituent | |
b8d4c8d0 | 170 | character that is valid in symbols is underscore (@samp{_}). |
b8d4c8d0 | 171 | |
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172 | @item Punctuation characters: @samp{.} |
173 | Characters used as punctuation in a human language, or used in a | |
174 | programming language to separate symbols from one another. Some | |
175 | programming language modes, such as Emacs Lisp mode, have no | |
176 | characters in this class since the few characters that are not symbol | |
177 | or word constituents all have other uses. Other programming language | |
178 | modes, such as C mode, use punctuation syntax for operators. | |
179 | ||
180 | @item Open parenthesis characters: @samp{(} | |
181 | @itemx Close parenthesis characters: @samp{)} | |
182 | Characters used in dissimilar pairs to surround sentences or | |
183 | expressions. Such a grouping is begun with an open parenthesis | |
184 | character and terminated with a close. Each open parenthesis | |
185 | character matches a particular close parenthesis character, and vice | |
186 | versa. Normally, Emacs indicates momentarily the matching open | |
187 | parenthesis when you insert a close parenthesis. @xref{Blinking}. | |
188 | ||
189 | In human languages, and in C code, the parenthesis pairs are | |
190 | @samp{()}, @samp{[]}, and @samp{@{@}}. In Emacs Lisp, the delimiters | |
191 | for lists and vectors (@samp{()} and @samp{[]}) are classified as | |
192 | parenthesis characters. | |
193 | ||
194 | @item String quotes: @samp{"} | |
195 | Characters used to delimit string constants. The same string quote | |
196 | character appears at the beginning and the end of a string. Such | |
197 | quoted strings do not nest. | |
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198 | |
199 | The parsing facilities of Emacs consider a string as a single token. | |
200 | The usual syntactic meanings of the characters in the string are | |
201 | suppressed. | |
202 | ||
203 | The Lisp modes have two string quote characters: double-quote (@samp{"}) | |
204 | and vertical bar (@samp{|}). @samp{|} is not used in Emacs Lisp, but it | |
205 | is used in Common Lisp. C also has two string quote characters: | |
206 | double-quote for strings, and single-quote (@samp{'}) for character | |
207 | constants. | |
208 | ||
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209 | Human text has no string quote characters. We do not want quotation |
210 | marks to turn off the usual syntactic properties of other characters | |
211 | in the quotation. | |
b8d4c8d0 | 212 | |
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213 | @item Escape-syntax characters: @samp{\} |
214 | Characters that start an escape sequence, such as is used in string | |
215 | and character constants. The character @samp{\} belongs to this class | |
216 | in both C and Lisp. (In C, it is used thus only inside strings, but | |
217 | it turns out to cause no trouble to treat it this way throughout C | |
218 | code.) | |
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219 | |
220 | Characters in this class count as part of words if | |
221 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
b8d4c8d0 | 222 | |
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223 | @item Character quotes: @samp{/} |
224 | Characters used to quote the following character so that it loses its | |
225 | normal syntactic meaning. This differs from an escape character in | |
226 | that only the character immediately following is ever affected. | |
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227 | |
228 | Characters in this class count as part of words if | |
229 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
230 | ||
231 | This class is used for backslash in @TeX{} mode. | |
b8d4c8d0 | 232 | |
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233 | @item Paired delimiters: @samp{$} |
234 | Similar to string quote characters, except that the syntactic | |
235 | properties of the characters between the delimiters are not | |
236 | suppressed. Only @TeX{} mode uses a paired delimiter presently---the | |
237 | @samp{$} that both enters and leaves math mode. | |
238 | ||
239 | @item Expression prefixes: @samp{'} | |
240 | Characters used for syntactic operators that are considered as part of | |
241 | an expression if they appear next to one. In Lisp modes, these | |
242 | characters include the apostrophe, @samp{'} (used for quoting), the | |
243 | comma, @samp{,} (used in macros), and @samp{#} (used in the read | |
244 | syntax for certain data types). | |
245 | ||
246 | @item Comment starters: @samp{<} | |
247 | @itemx Comment enders: @samp{>} | |
b8d4c8d0 | 248 | @cindex comment syntax |
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249 | Characters used in various languages to delimit comments. Human text |
250 | has no comment characters. In Lisp, the semicolon (@samp{;}) starts a | |
251 | comment and a newline or formfeed ends one. | |
b8d4c8d0 | 252 | |
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253 | @item Inherit standard syntax: @samp{@@} |
254 | This syntax class does not specify a particular syntax. It says to | |
255 | look in the standard syntax table to find the syntax of this | |
256 | character. | |
b8d4c8d0 | 257 | |
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258 | @item Generic comment delimiters: @samp{!} |
259 | Characters that start or end a special kind of comment. @emph{Any} | |
260 | generic comment delimiter matches @emph{any} generic comment | |
261 | delimiter, but they cannot match a comment starter or comment ender; | |
262 | generic comment delimiters can only match each other. | |
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263 | |
264 | This syntax class is primarily meant for use with the | |
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265 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
266 | can mark any range of characters as forming a comment, by giving the | |
267 | first and last characters of the range @code{syntax-table} properties | |
b8d4c8d0 | 268 | identifying them as generic comment delimiters. |
b8d4c8d0 | 269 | |
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270 | @item Generic string delimiters: @samp{|} |
271 | Characters that start or end a string. This class differs from the | |
272 | string quote class in that @emph{any} generic string delimiter can | |
273 | match any other generic string delimiter; but they do not match | |
274 | ordinary string quote characters. | |
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275 | |
276 | This syntax class is primarily meant for use with the | |
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277 | @code{syntax-table} text property (@pxref{Syntax Properties}). You |
278 | can mark any range of characters as forming a string constant, by | |
279 | giving the first and last characters of the range @code{syntax-table} | |
280 | properties identifying them as generic string delimiters. | |
281 | @end table | |
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282 | |
283 | @node Syntax Flags | |
284 | @subsection Syntax Flags | |
285 | @cindex syntax flags | |
286 | ||
287 | In addition to the classes, entries for characters in a syntax table | |
7cf78aac SM |
288 | can specify flags. There are eight possible flags, represented by the |
289 | characters @samp{1}, @samp{2}, @samp{3}, @samp{4}, @samp{b}, @samp{c}, | |
290 | @samp{n}, and @samp{p}. | |
291 | ||
292 | All the flags except @samp{p} are used to describe comment | |
293 | delimiters. The digit flags are used for comment delimiters made up | |
294 | of 2 characters. They indicate that a character can @emph{also} be | |
295 | part of a comment sequence, in addition to the syntactic properties | |
296 | associated with its character class. The flags are independent of the | |
297 | class and each other for the sake of characters such as @samp{*} in | |
298 | C mode, which is a punctuation character, @emph{and} the second | |
299 | character of a start-of-comment sequence (@samp{/*}), @emph{and} the | |
300 | first character of an end-of-comment sequence (@samp{*/}). The flags | |
301 | @samp{b}, @samp{c}, and @samp{n} are used to qualify the corresponding | |
302 | comment delimiter. | |
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303 | |
304 | Here is a table of the possible flags for a character @var{c}, | |
305 | and what they mean: | |
306 | ||
307 | @itemize @bullet | |
308 | @item | |
309 | @samp{1} means @var{c} is the start of a two-character comment-start | |
310 | sequence. | |
311 | ||
312 | @item | |
313 | @samp{2} means @var{c} is the second character of such a sequence. | |
314 | ||
315 | @item | |
316 | @samp{3} means @var{c} is the start of a two-character comment-end | |
317 | sequence. | |
318 | ||
319 | @item | |
320 | @samp{4} means @var{c} is the second character of such a sequence. | |
321 | ||
322 | @item | |
b8d4c8d0 | 323 | @samp{b} means that @var{c} as a comment delimiter belongs to the |
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324 | alternative ``b'' comment style. For a two-character comment starter, |
325 | this flag is only significant on the second char, and for a 2-character | |
326 | comment ender it is only significant on the first char. | |
b8d4c8d0 | 327 | |
7cf78aac SM |
328 | @item |
329 | @samp{c} means that @var{c} as a comment delimiter belongs to the | |
330 | alternative ``c'' comment style. For a two-character comment | |
331 | delimiter, @samp{c} on either character makes it of style ``c''. | |
b8d4c8d0 | 332 | |
7cf78aac SM |
333 | @item |
334 | @samp{n} on a comment delimiter character specifies | |
335 | that this kind of comment can be nested. For a two-character | |
336 | comment delimiter, @samp{n} on either character makes it | |
337 | nestable. | |
b8d4c8d0 | 338 | |
79b3ad55 | 339 | @cindex comment style |
7cf78aac SM |
340 | Emacs supports several comment styles simultaneously in any one syntax |
341 | table. A comment style is a set of flags @samp{b}, @samp{c}, and | |
342 | @samp{n}, so there can be up to 8 different comment styles. | |
343 | Each comment delimiter has a style and only matches comment delimiters | |
344 | of the same style. Thus if a comment starts with the comment-start | |
345 | sequence of style ``bn'', it will extend until the next matching | |
346 | comment-end sequence of style ``bn''. | |
b8d4c8d0 | 347 | |
7cf78aac | 348 | The appropriate comment syntax settings for C++ can be as follows: |
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349 | |
350 | @table @asis | |
351 | @item @samp{/} | |
7cf78aac | 352 | @samp{124} |
b8d4c8d0 | 353 | @item @samp{*} |
7cf78aac | 354 | @samp{23b} |
b8d4c8d0 | 355 | @item newline |
7cf78aac | 356 | @samp{>} |
b8d4c8d0 GM |
357 | @end table |
358 | ||
359 | This defines four comment-delimiting sequences: | |
360 | ||
361 | @table @asis | |
362 | @item @samp{/*} | |
7cf78aac SM |
363 | This is a comment-start sequence for ``b'' style because the |
364 | second character, @samp{*}, has the @samp{b} flag. | |
b8d4c8d0 GM |
365 | |
366 | @item @samp{//} | |
7cf78aac SM |
367 | This is a comment-start sequence for ``a'' style because the second |
368 | character, @samp{/}, does not have the @samp{b} flag. | |
b8d4c8d0 GM |
369 | |
370 | @item @samp{*/} | |
7cf78aac | 371 | This is a comment-end sequence for ``b'' style because the first |
35a30759 | 372 | character, @samp{*}, has the @samp{b} flag. |
b8d4c8d0 GM |
373 | |
374 | @item newline | |
7cf78aac SM |
375 | This is a comment-end sequence for ``a'' style, because the newline |
376 | character does not have the @samp{b} flag. | |
b8d4c8d0 GM |
377 | @end table |
378 | ||
b8d4c8d0 | 379 | @item |
b8d4c8d0 GM |
380 | @samp{p} identifies an additional ``prefix character'' for Lisp syntax. |
381 | These characters are treated as whitespace when they appear between | |
382 | expressions. When they appear within an expression, they are handled | |
383 | according to their usual syntax classes. | |
384 | ||
385 | The function @code{backward-prefix-chars} moves back over these | |
386 | characters, as well as over characters whose primary syntax class is | |
387 | prefix (@samp{'}). @xref{Motion and Syntax}. | |
388 | @end itemize | |
389 | ||
390 | @node Syntax Table Functions | |
391 | @section Syntax Table Functions | |
392 | ||
393 | In this section we describe functions for creating, accessing and | |
394 | altering syntax tables. | |
395 | ||
396 | @defun make-syntax-table &optional table | |
02676e5d CY |
397 | This function creates a new syntax table. If @var{table} is |
398 | non-@code{nil}, the parent of the new syntax table is @var{table}; | |
399 | otherwise, the parent is the standard syntax table. | |
400 | ||
401 | In the new syntax table, all characters are initially given the | |
1df7defd | 402 | ``inherit'' (@samp{@@}) syntax class, i.e., their syntax is inherited |
02676e5d | 403 | from the parent table (@pxref{Syntax Class Table}). |
b8d4c8d0 GM |
404 | @end defun |
405 | ||
406 | @defun copy-syntax-table &optional table | |
407 | This function constructs a copy of @var{table} and returns it. If | |
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408 | @var{table} is omitted or @code{nil}, it returns a copy of the |
409 | standard syntax table. Otherwise, an error is signaled if @var{table} | |
410 | is not a syntax table. | |
b8d4c8d0 GM |
411 | @end defun |
412 | ||
413 | @deffn Command modify-syntax-entry char syntax-descriptor &optional table | |
c9358b45 | 414 | @cindex syntax entry, setting |
b8d4c8d0 | 415 | This function sets the syntax entry for @var{char} according to |
4230351b | 416 | @var{syntax-descriptor}. @var{char} must be a character, or a cons |
f147ff75 CY |
417 | cell of the form @code{(@var{min} . @var{max})}; in the latter case, |
418 | the function sets the syntax entries for all characters in the range | |
419 | between @var{min} and @var{max}, inclusive. | |
420 | ||
421 | The syntax is changed only for @var{table}, which defaults to the | |
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422 | current buffer's syntax table, and not in any other syntax table. |
423 | ||
1df7defd | 424 | The argument @var{syntax-descriptor} is a syntax descriptor, i.e., a |
02676e5d CY |
425 | string whose first character is a syntax class designator and whose |
426 | second and subsequent characters optionally specify a matching | |
427 | character and syntax flags. @xref{Syntax Descriptors}. An error is | |
428 | signaled if @var{syntax-descriptor} is not a valid syntax descriptor. | |
b8d4c8d0 GM |
429 | |
430 | This function always returns @code{nil}. The old syntax information in | |
431 | the table for this character is discarded. | |
432 | ||
b8d4c8d0 GM |
433 | @example |
434 | @group | |
435 | @exdent @r{Examples:} | |
436 | ||
437 | ;; @r{Put the space character in class whitespace.} | |
438 | (modify-syntax-entry ?\s " ") | |
439 | @result{} nil | |
440 | @end group | |
441 | ||
442 | @group | |
443 | ;; @r{Make @samp{$} an open parenthesis character,} | |
444 | ;; @r{with @samp{^} as its matching close.} | |
445 | (modify-syntax-entry ?$ "(^") | |
446 | @result{} nil | |
447 | @end group | |
448 | ||
449 | @group | |
450 | ;; @r{Make @samp{^} a close parenthesis character,} | |
451 | ;; @r{with @samp{$} as its matching open.} | |
452 | (modify-syntax-entry ?^ ")$") | |
453 | @result{} nil | |
454 | @end group | |
455 | ||
456 | @group | |
457 | ;; @r{Make @samp{/} a punctuation character,} | |
458 | ;; @r{the first character of a start-comment sequence,} | |
459 | ;; @r{and the second character of an end-comment sequence.} | |
460 | ;; @r{This is used in C mode.} | |
461 | (modify-syntax-entry ?/ ". 14") | |
462 | @result{} nil | |
463 | @end group | |
464 | @end example | |
465 | @end deffn | |
466 | ||
467 | @defun char-syntax character | |
468 | This function returns the syntax class of @var{character}, represented | |
02676e5d CY |
469 | by its designator character (@pxref{Syntax Class Table}). This |
470 | returns @emph{only} the class, not its matching character or syntax | |
471 | flags. | |
b8d4c8d0 | 472 | |
02676e5d CY |
473 | The following examples apply to C mode. (We use @code{string} to make |
474 | it easier to see the character returned by @code{char-syntax}.) | |
b8d4c8d0 GM |
475 | |
476 | @example | |
477 | @group | |
02676e5d | 478 | ;; Space characters have whitespace syntax class. |
b8d4c8d0 GM |
479 | (string (char-syntax ?\s)) |
480 | @result{} " " | |
481 | @end group | |
482 | ||
483 | @group | |
75e78d1e GM |
484 | ;; Forward slash characters have punctuation syntax. |
485 | ;; Note that this @code{char-syntax} call does not reveal | |
486 | ;; that it is also part of comment-start and -end sequences. | |
b8d4c8d0 GM |
487 | (string (char-syntax ?/)) |
488 | @result{} "." | |
489 | @end group | |
490 | ||
491 | @group | |
75e78d1e GM |
492 | ;; Open parenthesis characters have open parenthesis syntax. |
493 | ;; Note that this @code{char-syntax} call does not reveal that | |
494 | ;; it has a matching character, @samp{)}. | |
b8d4c8d0 GM |
495 | (string (char-syntax ?\()) |
496 | @result{} "(" | |
497 | @end group | |
498 | @end example | |
499 | ||
b8d4c8d0 GM |
500 | @end defun |
501 | ||
502 | @defun set-syntax-table table | |
503 | This function makes @var{table} the syntax table for the current buffer. | |
504 | It returns @var{table}. | |
505 | @end defun | |
506 | ||
507 | @defun syntax-table | |
508 | This function returns the current syntax table, which is the table for | |
509 | the current buffer. | |
510 | @end defun | |
511 | ||
253e30aa GM |
512 | @deffn Command describe-syntax &optional buffer |
513 | This command displays the contents of the syntax table of | |
514 | @var{buffer} (by default, the current buffer) in a help buffer. | |
515 | @end deffn | |
516 | ||
151d9088 | 517 | @defmac with-syntax-table table body@dots{} |
b8d4c8d0 GM |
518 | This macro executes @var{body} using @var{table} as the current syntax |
519 | table. It returns the value of the last form in @var{body}, after | |
520 | restoring the old current syntax table. | |
521 | ||
522 | Since each buffer has its own current syntax table, we should make that | |
523 | more precise: @code{with-syntax-table} temporarily alters the current | |
524 | syntax table of whichever buffer is current at the time the macro | |
525 | execution starts. Other buffers are not affected. | |
526 | @end defmac | |
527 | ||
528 | @node Syntax Properties | |
529 | @section Syntax Properties | |
530 | @kindex syntax-table @r{(text property)} | |
531 | ||
532 | When the syntax table is not flexible enough to specify the syntax of | |
4230351b CY |
533 | a language, you can override the syntax table for specific character |
534 | occurrences in the buffer, by applying a @code{syntax-table} text | |
535 | property. @xref{Text Properties}, for how to apply text properties. | |
b8d4c8d0 | 536 | |
4230351b | 537 | The valid values of @code{syntax-table} text property are: |
b8d4c8d0 GM |
538 | |
539 | @table @asis | |
540 | @item @var{syntax-table} | |
541 | If the property value is a syntax table, that table is used instead of | |
4230351b CY |
542 | the current buffer's syntax table to determine the syntax for the |
543 | underlying text character. | |
b8d4c8d0 GM |
544 | |
545 | @item @code{(@var{syntax-code} . @var{matching-char})} | |
6dcef6ec CY |
546 | A cons cell of this format is a raw syntax descriptor (@pxref{Syntax |
547 | Table Internals}), which directly specifies a syntax class for the | |
548 | underlying text character. | |
b8d4c8d0 GM |
549 | |
550 | @item @code{nil} | |
551 | If the property is @code{nil}, the character's syntax is determined from | |
552 | the current syntax table in the usual way. | |
553 | @end table | |
554 | ||
555 | @defvar parse-sexp-lookup-properties | |
4230351b CY |
556 | If this is non-@code{nil}, the syntax scanning functions, like |
557 | @code{forward-sexp}, pay attention to syntax text properties. | |
558 | Otherwise they use only the current syntax table. | |
559 | @end defvar | |
560 | ||
561 | @defvar syntax-propertize-function | |
562 | This variable, if non-@code{nil}, should store a function for applying | |
563 | @code{syntax-table} properties to a specified stretch of text. It is | |
564 | intended to be used by major modes to install a function which applies | |
565 | @code{syntax-table} properties in some mode-appropriate way. | |
566 | ||
567 | The function is called by @code{syntax-ppss} (@pxref{Position Parse}), | |
568 | and by Font Lock mode during syntactic fontification (@pxref{Syntactic | |
569 | Font Lock}). It is called with two arguments, @var{start} and | |
570 | @var{end}, which are the starting and ending positions of the text on | |
571 | which it should act. It is allowed to call @code{syntax-ppss} on any | |
572 | position before @var{end}. However, it should not call | |
573 | @code{syntax-ppss-flush-cache}; so, it is not allowed to call | |
574 | @code{syntax-ppss} on some position and later modify the buffer at an | |
575 | earlier position. | |
576 | @end defvar | |
577 | ||
578 | @defvar syntax-propertize-extend-region-functions | |
579 | This abnormal hook is run by the syntax parsing code prior to calling | |
580 | @code{syntax-propertize-function}. Its role is to help locate safe | |
581 | starting and ending buffer positions for passing to | |
582 | @code{syntax-propertize-function}. For example, a major mode can add | |
583 | a function to this hook to identify multi-line syntactic constructs, | |
584 | and ensure that the boundaries do not fall in the middle of one. | |
585 | ||
586 | Each function in this hook should accept two arguments, @var{start} | |
587 | and @var{end}. It should return either a cons cell of two adjusted | |
588 | buffer positions, @code{(@var{new-start} . @var{new-end})}, or | |
589 | @code{nil} if no adjustment is necessary. The hook functions are run | |
590 | in turn, repeatedly, until they all return @code{nil}. | |
b8d4c8d0 GM |
591 | @end defvar |
592 | ||
593 | @node Motion and Syntax | |
594 | @section Motion and Syntax | |
595 | ||
596 | This section describes functions for moving across characters that | |
597 | have certain syntax classes. | |
598 | ||
599 | @defun skip-syntax-forward syntaxes &optional limit | |
600 | This function moves point forward across characters having syntax | |
601 | classes mentioned in @var{syntaxes} (a string of syntax class | |
602 | characters). It stops when it encounters the end of the buffer, or | |
603 | position @var{limit} (if specified), or a character it is not supposed | |
604 | to skip. | |
605 | ||
606 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
607 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
608 | ||
609 | The return value is the distance traveled, which is a nonnegative | |
610 | integer. | |
611 | @end defun | |
612 | ||
613 | @defun skip-syntax-backward syntaxes &optional limit | |
614 | This function moves point backward across characters whose syntax | |
615 | classes are mentioned in @var{syntaxes}. It stops when it encounters | |
616 | the beginning of the buffer, or position @var{limit} (if specified), or | |
617 | a character it is not supposed to skip. | |
618 | ||
619 | If @var{syntaxes} starts with @samp{^}, then the function skips | |
620 | characters whose syntax is @emph{not} in @var{syntaxes}. | |
621 | ||
622 | The return value indicates the distance traveled. It is an integer that | |
623 | is zero or less. | |
624 | @end defun | |
625 | ||
626 | @defun backward-prefix-chars | |
627 | This function moves point backward over any number of characters with | |
628 | expression prefix syntax. This includes both characters in the | |
629 | expression prefix syntax class, and characters with the @samp{p} flag. | |
630 | @end defun | |
631 | ||
632 | @node Parsing Expressions | |
633 | @section Parsing Expressions | |
634 | ||
635 | This section describes functions for parsing and scanning balanced | |
a037c171 CY |
636 | expressions. We will refer to such expressions as @dfn{sexps}, |
637 | following the terminology of Lisp, even though these functions can act | |
638 | on languages other than Lisp. Basically, a sexp is either a balanced | |
1df7defd | 639 | parenthetical grouping, a string, or a ``symbol'' (i.e., a sequence |
a037c171 | 640 | of characters whose syntax is either word constituent or symbol |
4230351b CY |
641 | constituent). However, characters in the expression prefix syntax |
642 | class (@pxref{Syntax Class Table}) are treated as part of the sexp if | |
643 | they appear next to it. | |
b8d4c8d0 GM |
644 | |
645 | The syntax table controls the interpretation of characters, so these | |
646 | functions can be used for Lisp expressions when in Lisp mode and for C | |
647 | expressions when in C mode. @xref{List Motion}, for convenient | |
648 | higher-level functions for moving over balanced expressions. | |
649 | ||
650 | A character's syntax controls how it changes the state of the | |
651 | parser, rather than describing the state itself. For example, a | |
652 | string delimiter character toggles the parser state between | |
16152b76 | 653 | ``in-string'' and ``in-code'', but the syntax of characters does not |
b8d4c8d0 GM |
654 | directly say whether they are inside a string. For example (note that |
655 | 15 is the syntax code for generic string delimiters), | |
656 | ||
657 | @example | |
658 | (put-text-property 1 9 'syntax-table '(15 . nil)) | |
659 | @end example | |
660 | ||
661 | @noindent | |
662 | does not tell Emacs that the first eight chars of the current buffer | |
663 | are a string, but rather that they are all string delimiters. As a | |
664 | result, Emacs treats them as four consecutive empty string constants. | |
665 | ||
666 | @menu | |
667 | * Motion via Parsing:: Motion functions that work by parsing. | |
668 | * Position Parse:: Determining the syntactic state of a position. | |
669 | * Parser State:: How Emacs represents a syntactic state. | |
670 | * Low-Level Parsing:: Parsing across a specified region. | |
671 | * Control Parsing:: Parameters that affect parsing. | |
672 | @end menu | |
673 | ||
674 | @node Motion via Parsing | |
675 | @subsection Motion Commands Based on Parsing | |
676 | ||
677 | This section describes simple point-motion functions that operate | |
678 | based on parsing expressions. | |
679 | ||
680 | @defun scan-lists from count depth | |
7b926f3f CY |
681 | This function scans forward @var{count} balanced parenthetical |
682 | groupings from position @var{from}. It returns the position where the | |
683 | scan stops. If @var{count} is negative, the scan moves backwards. | |
684 | ||
685 | If @var{depth} is nonzero, treat the starting position as being | |
686 | @var{depth} parentheses deep. The scanner moves forward or backward | |
687 | through the buffer until the depth changes to zero @var{count} times. | |
688 | Hence, a positive value for @var{depth} has the effect of moving out | |
689 | @var{depth} levels of parenthesis from the starting position, while a | |
690 | negative @var{depth} has the effect of moving deeper by @var{-depth} | |
691 | levels of parenthesis. | |
b8d4c8d0 GM |
692 | |
693 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
694 | non-@code{nil}. | |
695 | ||
7b926f3f CY |
696 | If the scan reaches the beginning or end of the accessible part of the |
697 | buffer before it has scanned over @var{count} parenthetical groupings, | |
698 | the return value is @code{nil} if the depth at that point is zero; if | |
699 | the depth is non-zero, a @code{scan-error} error is signaled. | |
b8d4c8d0 GM |
700 | @end defun |
701 | ||
702 | @defun scan-sexps from count | |
703 | This function scans forward @var{count} sexps from position @var{from}. | |
704 | It returns the position where the scan stops. If @var{count} is | |
705 | negative, the scan moves backwards. | |
706 | ||
707 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
708 | non-@code{nil}. | |
709 | ||
710 | If the scan reaches the beginning or end of (the accessible part of) the | |
711 | buffer while in the middle of a parenthetical grouping, an error is | |
712 | signaled. If it reaches the beginning or end between groupings but | |
713 | before count is used up, @code{nil} is returned. | |
714 | @end defun | |
715 | ||
716 | @defun forward-comment count | |
717 | This function moves point forward across @var{count} complete comments | |
718 | (that is, including the starting delimiter and the terminating | |
719 | delimiter if any), plus any whitespace encountered on the way. It | |
720 | moves backward if @var{count} is negative. If it encounters anything | |
721 | other than a comment or whitespace, it stops, leaving point at the | |
722 | place where it stopped. This includes (for instance) finding the end | |
723 | of a comment when moving forward and expecting the beginning of one. | |
724 | The function also stops immediately after moving over the specified | |
725 | number of complete comments. If @var{count} comments are found as | |
726 | expected, with nothing except whitespace between them, it returns | |
727 | @code{t}; otherwise it returns @code{nil}. | |
728 | ||
729 | This function cannot tell whether the ``comments'' it traverses are | |
730 | embedded within a string. If they look like comments, it treats them | |
731 | as comments. | |
b8d4c8d0 GM |
732 | |
733 | To move forward over all comments and whitespace following point, use | |
4230351b CY |
734 | @code{(forward-comment (buffer-size))}. @code{(buffer-size)} is a |
735 | good argument to use, because the number of comments in the buffer | |
736 | cannot exceed that many. | |
737 | @end defun | |
b8d4c8d0 GM |
738 | |
739 | @node Position Parse | |
740 | @subsection Finding the Parse State for a Position | |
741 | ||
742 | For syntactic analysis, such as in indentation, often the useful | |
743 | thing is to compute the syntactic state corresponding to a given buffer | |
744 | position. This function does that conveniently. | |
745 | ||
746 | @defun syntax-ppss &optional pos | |
4230351b CY |
747 | This function returns the parser state that the parser would reach at |
748 | position @var{pos} starting from the beginning of the buffer. | |
749 | @iftex | |
750 | See the next section for | |
751 | @end iftex | |
752 | @ifnottex | |
753 | @xref{Parser State}, | |
754 | @end ifnottex | |
755 | for a description of the parser state. | |
756 | ||
757 | The return value is the same as if you call the low-level parsing | |
758 | function @code{parse-partial-sexp} to parse from the beginning of the | |
759 | buffer to @var{pos} (@pxref{Low-Level Parsing}). However, | |
760 | @code{syntax-ppss} uses a cache to speed up the computation. Due to | |
761 | this optimization, the second value (previous complete subexpression) | |
762 | and sixth value (minimum parenthesis depth) in the returned parser | |
763 | state are not meaningful. | |
764 | ||
765 | This function has a side effect: it adds a buffer-local entry to | |
766 | @code{before-change-functions} (@pxref{Change Hooks}) for | |
767 | @code{syntax-ppss-flush-cache} (see below). This entry keeps the | |
768 | cache consistent as the buffer is modified. However, the cache might | |
769 | not be updated if @code{syntax-ppss} is called while | |
b8d4c8d0 | 770 | @code{before-change-functions} is temporarily let-bound, or if the |
4230351b CY |
771 | buffer is modified without running the hook, such as when using |
772 | @code{inhibit-modification-hooks}. In those cases, it is necessary to | |
773 | call @code{syntax-ppss-flush-cache} explicitly. | |
774 | @end defun | |
b8d4c8d0 | 775 | |
106e6894 CY |
776 | @defun syntax-ppss-flush-cache beg &rest ignored-args |
777 | This function flushes the cache used by @code{syntax-ppss}, starting | |
778 | at position @var{beg}. The remaining arguments, @var{ignored-args}, | |
779 | are ignored; this function accepts them so that it can be directly | |
780 | used on hooks such as @code{before-change-functions} (@pxref{Change | |
781 | Hooks}). | |
b8d4c8d0 GM |
782 | @end defun |
783 | ||
784 | Major modes can make @code{syntax-ppss} run faster by specifying | |
785 | where it needs to start parsing. | |
786 | ||
787 | @defvar syntax-begin-function | |
788 | If this is non-@code{nil}, it should be a function that moves to an | |
789 | earlier buffer position where the parser state is equivalent to | |
790 | @code{nil}---in other words, a position outside of any comment, | |
791 | string, or parenthesis. @code{syntax-ppss} uses it to further | |
792 | optimize its computations, when the cache gives no help. | |
793 | @end defvar | |
794 | ||
795 | @node Parser State | |
796 | @subsection Parser State | |
797 | @cindex parser state | |
798 | ||
4230351b CY |
799 | A @dfn{parser state} is a list of ten elements describing the state |
800 | of the syntactic parser, after it parses the text between a specified | |
801 | starting point and a specified end point in the buffer. Parsing | |
802 | functions such as @code{syntax-ppss} | |
803 | @ifnottex | |
804 | (@pxref{Position Parse}) | |
805 | @end ifnottex | |
806 | return a parser state as the value. Some parsing functions accept a | |
807 | parser state as an argument, for resuming parsing. | |
808 | ||
809 | Here are the meanings of the elements of the parser state: | |
b8d4c8d0 GM |
810 | |
811 | @enumerate 0 | |
812 | @item | |
813 | The depth in parentheses, counting from 0. @strong{Warning:} this can | |
814 | be negative if there are more close parens than open parens between | |
4230351b | 815 | the parser's starting point and end point. |
b8d4c8d0 GM |
816 | |
817 | @item | |
818 | @cindex innermost containing parentheses | |
819 | The character position of the start of the innermost parenthetical | |
820 | grouping containing the stopping point; @code{nil} if none. | |
821 | ||
822 | @item | |
823 | @cindex previous complete subexpression | |
824 | The character position of the start of the last complete subexpression | |
825 | terminated; @code{nil} if none. | |
826 | ||
827 | @item | |
828 | @cindex inside string | |
829 | Non-@code{nil} if inside a string. More precisely, this is the | |
830 | character that will terminate the string, or @code{t} if a generic | |
831 | string delimiter character should terminate it. | |
832 | ||
833 | @item | |
834 | @cindex inside comment | |
4230351b CY |
835 | @code{t} if inside a non-nestable comment (of any comment style; |
836 | @pxref{Syntax Flags}); or the comment nesting level if inside a | |
837 | comment that can be nested. | |
b8d4c8d0 GM |
838 | |
839 | @item | |
840 | @cindex quote character | |
4230351b | 841 | @code{t} if the end point is just after a quote character. |
b8d4c8d0 GM |
842 | |
843 | @item | |
844 | The minimum parenthesis depth encountered during this scan. | |
845 | ||
846 | @item | |
4230351b CY |
847 | What kind of comment is active: @code{nil} if not in a comment or in a |
848 | comment of style @samp{a}; 1 for a comment of style @samp{b}; 2 for a | |
849 | comment of style @samp{c}; and @code{syntax-table} for a comment that | |
850 | should be ended by a generic comment delimiter character. | |
b8d4c8d0 GM |
851 | |
852 | @item | |
853 | The string or comment start position. While inside a comment, this is | |
854 | the position where the comment began; while inside a string, this is the | |
855 | position where the string began. When outside of strings and comments, | |
856 | this element is @code{nil}. | |
857 | ||
858 | @item | |
859 | Internal data for continuing the parsing. The meaning of this | |
860 | data is subject to change; it is used if you pass this list | |
861 | as the @var{state} argument to another call. | |
862 | @end enumerate | |
863 | ||
864 | Elements 1, 2, and 6 are ignored in a state which you pass as an | |
865 | argument to continue parsing, and elements 8 and 9 are used only in | |
4230351b CY |
866 | trivial cases. Those elements are mainly used internally by the |
867 | parser code. | |
b8d4c8d0 GM |
868 | |
869 | One additional piece of useful information is available from a | |
870 | parser state using this function: | |
871 | ||
872 | @defun syntax-ppss-toplevel-pos state | |
873 | This function extracts, from parser state @var{state}, the last | |
874 | position scanned in the parse which was at top level in grammatical | |
875 | structure. ``At top level'' means outside of any parentheses, | |
876 | comments, or strings. | |
877 | ||
878 | The value is @code{nil} if @var{state} represents a parse which has | |
879 | arrived at a top level position. | |
880 | @end defun | |
881 | ||
b8d4c8d0 GM |
882 | @node Low-Level Parsing |
883 | @subsection Low-Level Parsing | |
884 | ||
885 | The most basic way to use the expression parser is to tell it | |
886 | to start at a given position with a certain state, and parse up to | |
887 | a specified end position. | |
888 | ||
889 | @defun parse-partial-sexp start limit &optional target-depth stop-before state stop-comment | |
890 | This function parses a sexp in the current buffer starting at | |
891 | @var{start}, not scanning past @var{limit}. It stops at position | |
892 | @var{limit} or when certain criteria described below are met, and sets | |
893 | point to the location where parsing stops. It returns a parser state | |
52404181 CY |
894 | @ifinfo |
895 | (@pxref{Parser State}) | |
896 | @end ifinfo | |
b8d4c8d0 GM |
897 | describing the status of the parse at the point where it stops. |
898 | ||
899 | @cindex parenthesis depth | |
900 | If the third argument @var{target-depth} is non-@code{nil}, parsing | |
901 | stops if the depth in parentheses becomes equal to @var{target-depth}. | |
902 | The depth starts at 0, or at whatever is given in @var{state}. | |
903 | ||
904 | If the fourth argument @var{stop-before} is non-@code{nil}, parsing | |
905 | stops when it comes to any character that starts a sexp. If | |
906 | @var{stop-comment} is non-@code{nil}, parsing stops when it comes to the | |
907 | start of a comment. If @var{stop-comment} is the symbol | |
908 | @code{syntax-table}, parsing stops after the start of a comment or a | |
909 | string, or the end of a comment or a string, whichever comes first. | |
910 | ||
911 | If @var{state} is @code{nil}, @var{start} is assumed to be at the top | |
912 | level of parenthesis structure, such as the beginning of a function | |
913 | definition. Alternatively, you might wish to resume parsing in the | |
914 | middle of the structure. To do this, you must provide a @var{state} | |
915 | argument that describes the initial status of parsing. The value | |
916 | returned by a previous call to @code{parse-partial-sexp} will do | |
917 | nicely. | |
918 | @end defun | |
919 | ||
920 | @node Control Parsing | |
921 | @subsection Parameters to Control Parsing | |
922 | ||
923 | @defvar multibyte-syntax-as-symbol | |
924 | If this variable is non-@code{nil}, @code{scan-sexps} treats all | |
925 | non-@acronym{ASCII} characters as symbol constituents regardless | |
926 | of what the syntax table says about them. (However, text properties | |
927 | can still override the syntax.) | |
928 | @end defvar | |
929 | ||
930 | @defopt parse-sexp-ignore-comments | |
931 | @cindex skipping comments | |
932 | If the value is non-@code{nil}, then comments are treated as | |
933 | whitespace by the functions in this section and by @code{forward-sexp}, | |
934 | @code{scan-lists} and @code{scan-sexps}. | |
935 | @end defopt | |
936 | ||
937 | @vindex parse-sexp-lookup-properties | |
938 | The behavior of @code{parse-partial-sexp} is also affected by | |
939 | @code{parse-sexp-lookup-properties} (@pxref{Syntax Properties}). | |
940 | ||
941 | You can use @code{forward-comment} to move forward or backward over | |
942 | one comment or several comments. | |
943 | ||
b8d4c8d0 GM |
944 | @node Syntax Table Internals |
945 | @section Syntax Table Internals | |
946 | @cindex syntax table internals | |
947 | ||
02676e5d CY |
948 | Syntax tables are implemented as char-tables (@pxref{Char-Tables}), |
949 | but most Lisp programs don't work directly with their elements. | |
950 | Syntax tables do not store syntax data as syntax descriptors | |
951 | (@pxref{Syntax Descriptors}); they use an internal format, which is | |
952 | documented in this section. This internal format can also be assigned | |
953 | as syntax properties (@pxref{Syntax Properties}). | |
954 | ||
955 | @cindex syntax code | |
6dcef6ec CY |
956 | @cindex raw syntax descriptor |
957 | Each entry in a syntax table is a @dfn{raw syntax descriptor}: a | |
958 | cons cell of the form @code{(@var{syntax-code} | |
959 | . @var{matching-char})}. @var{syntax-code} is an integer which | |
960 | encodes the syntax class and syntax flags, according to the table | |
961 | below. @var{matching-char}, if non-@code{nil}, specifies a matching | |
962 | character (similar to the second character in a syntax descriptor). | |
963 | ||
964 | Here are the syntax codes corresponding to the various syntax | |
965 | classes: | |
02676e5d CY |
966 | |
967 | @multitable @columnfractions .2 .3 .2 .3 | |
b8d4c8d0 | 968 | @item |
6dcef6ec | 969 | @i{Code} @tab @i{Class} @tab @i{Code} @tab @i{Class} |
b8d4c8d0 | 970 | @item |
02676e5d | 971 | 0 @tab whitespace @tab 8 @tab paired delimiter |
b8d4c8d0 | 972 | @item |
02676e5d | 973 | 1 @tab punctuation @tab 9 @tab escape |
b8d4c8d0 | 974 | @item |
02676e5d | 975 | 2 @tab word @tab 10 @tab character quote |
b8d4c8d0 | 976 | @item |
02676e5d | 977 | 3 @tab symbol @tab 11 @tab comment-start |
b8d4c8d0 | 978 | @item |
02676e5d | 979 | 4 @tab open parenthesis @tab 12 @tab comment-end |
b8d4c8d0 | 980 | @item |
02676e5d CY |
981 | 5 @tab close parenthesis @tab 13 @tab inherit |
982 | @item | |
983 | 6 @tab expression prefix @tab 14 @tab generic comment | |
984 | @item | |
985 | 7 @tab string quote @tab 15 @tab generic string | |
b8d4c8d0 GM |
986 | @end multitable |
987 | ||
02676e5d CY |
988 | @noindent |
989 | For example, in the standard syntax table, the entry for @samp{(} is | |
6dcef6ec | 990 | @code{(4 . 41)}. 41 is the character code for @samp{)}. |
b8d4c8d0 | 991 | |
02676e5d CY |
992 | Syntax flags are encoded in higher order bits, starting 16 bits from |
993 | the least significant bit. This table gives the power of two which | |
b8d4c8d0 GM |
994 | corresponds to each syntax flag. |
995 | ||
02676e5d CY |
996 | @multitable @columnfractions .15 .3 .15 .3 |
997 | @item | |
998 | @i{Prefix} @tab @i{Flag} @tab @i{Prefix} @tab @i{Flag} | |
b8d4c8d0 | 999 | @item |
02676e5d | 1000 | @samp{1} @tab @code{(lsh 1 16)} @tab @samp{p} @tab @code{(lsh 1 20)} |
b8d4c8d0 | 1001 | @item |
02676e5d | 1002 | @samp{2} @tab @code{(lsh 1 17)} @tab @samp{b} @tab @code{(lsh 1 21)} |
b8d4c8d0 | 1003 | @item |
02676e5d | 1004 | @samp{3} @tab @code{(lsh 1 18)} @tab @samp{n} @tab @code{(lsh 1 22)} |
b8d4c8d0 | 1005 | @item |
02676e5d | 1006 | @samp{4} @tab @code{(lsh 1 19)} |
b8d4c8d0 GM |
1007 | @end multitable |
1008 | ||
151d9088 | 1009 | @defun string-to-syntax desc |
6dcef6ec CY |
1010 | Given a syntax descriptor @var{desc} (a string), this function returns |
1011 | the corresponding raw syntax descriptor. | |
b8d4c8d0 GM |
1012 | @end defun |
1013 | ||
1014 | @defun syntax-after pos | |
6dcef6ec CY |
1015 | This function returns the raw syntax descriptor for the character in |
1016 | the buffer after position @var{pos}, taking account of syntax | |
1017 | properties as well as the syntax table. If @var{pos} is outside the | |
1018 | buffer's accessible portion (@pxref{Narrowing, accessible portion}), | |
1019 | the return value is @code{nil}. | |
b8d4c8d0 GM |
1020 | @end defun |
1021 | ||
1022 | @defun syntax-class syntax | |
6dcef6ec CY |
1023 | This function returns the syntax code for the raw syntax descriptor |
1024 | @var{syntax}. More precisely, it takes the raw syntax descriptor's | |
1025 | @var{syntax-code} component, masks off the high 16 bits which record | |
1026 | the syntax flags, and returns the resulting integer. | |
1027 | ||
1028 | If @var{syntax} is @code{nil}, the return value is returns @code{nil}. | |
1029 | This is so that the expression | |
b8d4c8d0 GM |
1030 | |
1031 | @example | |
1032 | (syntax-class (syntax-after pos)) | |
1033 | @end example | |
1034 | ||
1035 | @noindent | |
6dcef6ec CY |
1036 | evaluates to @code{nil} if @code{pos} is outside the buffer's |
1037 | accessible portion, without throwing errors or returning an incorrect | |
1038 | code. | |
b8d4c8d0 GM |
1039 | @end defun |
1040 | ||
1041 | @node Categories | |
1042 | @section Categories | |
1043 | @cindex categories of characters | |
1044 | @cindex character categories | |
1045 | ||
1046 | @dfn{Categories} provide an alternate way of classifying characters | |
1047 | syntactically. You can define several categories as needed, then | |
1048 | independently assign each character to one or more categories. Unlike | |
1049 | syntax classes, categories are not mutually exclusive; it is normal for | |
1050 | one character to belong to several categories. | |
1051 | ||
1052 | @cindex category table | |
1053 | Each buffer has a @dfn{category table} which records which categories | |
1054 | are defined and also which characters belong to each category. Each | |
1055 | category table defines its own categories, but normally these are | |
1056 | initialized by copying from the standard categories table, so that the | |
1057 | standard categories are available in all modes. | |
1058 | ||
1059 | Each category has a name, which is an @acronym{ASCII} printing character in | |
1060 | the range @w{@samp{ }} to @samp{~}. You specify the name of a category | |
1061 | when you define it with @code{define-category}. | |
1062 | ||
9e73b242 | 1063 | @cindex category set |
b8d4c8d0 GM |
1064 | The category table is actually a char-table (@pxref{Char-Tables}). |
1065 | The element of the category table at index @var{c} is a @dfn{category | |
1066 | set}---a bool-vector---that indicates which categories character @var{c} | |
1067 | belongs to. In this category set, if the element at index @var{cat} is | |
1068 | @code{t}, that means category @var{cat} is a member of the set, and that | |
1069 | character @var{c} belongs to category @var{cat}. | |
1070 | ||
1071 | For the next three functions, the optional argument @var{table} | |
1072 | defaults to the current buffer's category table. | |
1073 | ||
1074 | @defun define-category char docstring &optional table | |
1075 | This function defines a new category, with name @var{char} and | |
1076 | documentation @var{docstring}, for the category table @var{table}. | |
1ea897d5 EZ |
1077 | |
1078 | Here's an example of defining a new category for characters that have | |
1079 | strong right-to-left directionality (@pxref{Bidirectional Display}) | |
1080 | and using it in a special category table: | |
1081 | ||
1082 | @example | |
1083 | (defvar special-category-table-for-bidi | |
1084 | (let ((category-table (make-category-table)) | |
1085 | (uniprop-table (unicode-property-table-internal 'bidi-class))) | |
1086 | (define-category ?R "Characters of bidi-class R, AL, or RLO" | |
1087 | category-table) | |
1088 | (map-char-table | |
1089 | #'(lambda (key val) | |
1090 | (if (memq val '(R AL RLO)) | |
1091 | (modify-category-entry key ?R category-table))) | |
1092 | uniprop-table) | |
1093 | category-table)) | |
1094 | @end example | |
b8d4c8d0 GM |
1095 | @end defun |
1096 | ||
1097 | @defun category-docstring category &optional table | |
1098 | This function returns the documentation string of category @var{category} | |
1099 | in category table @var{table}. | |
1100 | ||
1101 | @example | |
1102 | (category-docstring ?a) | |
1103 | @result{} "ASCII" | |
1104 | (category-docstring ?l) | |
1105 | @result{} "Latin" | |
1106 | @end example | |
1107 | @end defun | |
1108 | ||
1109 | @defun get-unused-category &optional table | |
1110 | This function returns a category name (a character) which is not | |
1111 | currently defined in @var{table}. If all possible categories are in use | |
1112 | in @var{table}, it returns @code{nil}. | |
1113 | @end defun | |
1114 | ||
1115 | @defun category-table | |
1116 | This function returns the current buffer's category table. | |
1117 | @end defun | |
1118 | ||
1119 | @defun category-table-p object | |
1120 | This function returns @code{t} if @var{object} is a category table, | |
1121 | otherwise @code{nil}. | |
1122 | @end defun | |
1123 | ||
1124 | @defun standard-category-table | |
1125 | This function returns the standard category table. | |
1126 | @end defun | |
1127 | ||
1128 | @defun copy-category-table &optional table | |
1129 | This function constructs a copy of @var{table} and returns it. If | |
1130 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
1131 | standard category table. Otherwise, an error is signaled if @var{table} | |
1132 | is not a category table. | |
1133 | @end defun | |
1134 | ||
1135 | @defun set-category-table table | |
1136 | This function makes @var{table} the category table for the current | |
1137 | buffer. It returns @var{table}. | |
1138 | @end defun | |
1139 | ||
1140 | @defun make-category-table | |
1141 | This creates and returns an empty category table. In an empty category | |
1142 | table, no categories have been allocated, and no characters belong to | |
1143 | any categories. | |
1144 | @end defun | |
1145 | ||
1146 | @defun make-category-set categories | |
1147 | This function returns a new category set---a bool-vector---whose initial | |
1148 | contents are the categories listed in the string @var{categories}. The | |
1149 | elements of @var{categories} should be category names; the new category | |
1150 | set has @code{t} for each of those categories, and @code{nil} for all | |
1151 | other categories. | |
1152 | ||
1153 | @example | |
1154 | (make-category-set "al") | |
1155 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1156 | @end example | |
1157 | @end defun | |
1158 | ||
1159 | @defun char-category-set char | |
1160 | This function returns the category set for character @var{char} in the | |
1161 | current buffer's category table. This is the bool-vector which | |
1162 | records which categories the character @var{char} belongs to. The | |
1163 | function @code{char-category-set} does not allocate storage, because | |
1164 | it returns the same bool-vector that exists in the category table. | |
1165 | ||
1166 | @example | |
1167 | (char-category-set ?a) | |
1168 | @result{} #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" | |
1169 | @end example | |
1170 | @end defun | |
1171 | ||
1172 | @defun category-set-mnemonics category-set | |
1173 | This function converts the category set @var{category-set} into a string | |
1174 | containing the characters that designate the categories that are members | |
1175 | of the set. | |
1176 | ||
1177 | @example | |
1178 | (category-set-mnemonics (char-category-set ?a)) | |
1179 | @result{} "al" | |
1180 | @end example | |
1181 | @end defun | |
1182 | ||
f147ff75 CY |
1183 | @defun modify-category-entry char category &optional table reset |
1184 | This function modifies the category set of @var{char} in category | |
b8d4c8d0 | 1185 | table @var{table} (which defaults to the current buffer's category |
f147ff75 CY |
1186 | table). @var{char} can be a character, or a cons cell of the form |
1187 | @code{(@var{min} . @var{max})}; in the latter case, the function | |
1188 | modifies the category sets of all characters in the range between | |
1189 | @var{min} and @var{max}, inclusive. | |
b8d4c8d0 | 1190 | |
f147ff75 | 1191 | Normally, it modifies a category set by adding @var{category} to it. |
b8d4c8d0 GM |
1192 | But if @var{reset} is non-@code{nil}, then it deletes @var{category} |
1193 | instead. | |
1194 | @end defun | |
1195 | ||
1196 | @deffn Command describe-categories &optional buffer-or-name | |
1197 | This function describes the category specifications in the current | |
1198 | category table. It inserts the descriptions in a buffer, and then | |
1199 | displays that buffer. If @var{buffer-or-name} is non-@code{nil}, it | |
1200 | describes the category table of that buffer instead. | |
1201 | @end deffn |