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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/syntax | |
6 | @node Syntax Tables, Abbrevs, Searching and Matching, Top | |
7 | @chapter Syntax Tables | |
8 | @cindex parsing | |
9 | @cindex syntax table | |
10 | @cindex text parsing | |
11 | ||
12 | A @dfn{syntax table} specifies the syntactic textual function of each | |
13 | character. This information is used by the parsing commands, the | |
14 | complex movement commands, and others to determine where words, symbols, | |
15 | and other syntactic constructs begin and end. The current syntax table | |
16 | controls the meaning of the word motion functions (@pxref{Word Motion}) | |
17 | and the list motion functions (@pxref{List Motion}) as well as the | |
18 | functions in this chapter. | |
19 | ||
20 | @menu | |
21 | * Basics: Syntax Basics. Basic concepts of syntax tables. | |
22 | * Desc: Syntax Descriptors. How characters are classified. | |
23 | * Syntax Table Functions:: How to create, examine and alter syntax tables. | |
24 | * Motion and Syntax:: Moving over characters with certain syntaxes. | |
25 | * Parsing Expressions:: Parsing balanced expressions | |
26 | using the syntax table. | |
27 | * Standard Syntax Tables:: Syntax tables used by various major modes. | |
28 | * Syntax Table Internals:: How syntax table information is stored. | |
29 | @end menu | |
30 | ||
31 | @node Syntax Basics | |
32 | @section Syntax Table Concepts | |
33 | ||
34 | @ifinfo | |
35 | A @dfn{syntax table} provides Emacs with the information that | |
36 | determines the syntactic use of each character in a buffer. This | |
37 | information is used by the parsing commands, the complex movement | |
38 | commands, and others to determine where words, symbols, and other | |
39 | syntactic constructs begin and end. The current syntax table controls | |
40 | the meaning of the word motion functions (@pxref{Word Motion}) and the | |
41 | list motion functions (@pxref{List Motion}) as well as the functions in | |
42 | this chapter. | |
43 | @end ifinfo | |
44 | ||
45 | A syntax table is a vector of 256 elements; it contains one entry for | |
bfe721d1 | 46 | each of the 256 possible characters in an 8-bit byte. Each element is |
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47 | an integer that encodes the syntax of the character in question. |
48 | ||
49 | Syntax tables are used only for moving across text, not for the Emacs | |
50 | Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp | |
51 | expressions, and these rules cannot be changed. | |
52 | ||
53 | Each buffer has its own major mode, and each major mode has its own | |
54 | idea of the syntactic class of various characters. For example, in Lisp | |
55 | mode, the character @samp{;} begins a comment, but in C mode, it | |
56 | terminates a statement. To support these variations, Emacs makes the | |
57 | choice of syntax table local to each buffer. Typically, each major | |
58 | mode has its own syntax table and installs that table in each buffer | |
7fd1911a | 59 | that uses that mode. Changing this table alters the syntax in all |
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60 | those buffers as well as in any buffers subsequently put in that mode. |
61 | Occasionally several similar modes share one syntax table. | |
62 | @xref{Example Major Modes}, for an example of how to set up a syntax | |
63 | table. | |
64 | ||
65 | A syntax table can inherit the data for some characters from the | |
66 | standard syntax table, while specifying other characters itself. The | |
67 | ``inherit'' syntax class means ``inherit this character's syntax from | |
68 | the standard syntax table.'' Most major modes' syntax tables inherit | |
69 | the syntax of character codes 0 through 31 and 128 through 255. This is | |
70 | useful with character sets such as ISO Latin-1 that have additional | |
71 | alphabetic characters in the range 128 to 255. Just changing the | |
72 | standard syntax for these characters affects all major modes. | |
73 | ||
74 | @defun syntax-table-p object | |
75 | This function returns @code{t} if @var{object} is a vector of length 256 | |
76 | elements. This means that the vector may be a syntax table. However, | |
77 | according to this test, any vector of length 256 is considered to be a | |
78 | syntax table, no matter what its contents. | |
79 | @end defun | |
80 | ||
81 | @node Syntax Descriptors | |
82 | @section Syntax Descriptors | |
83 | @cindex syntax classes | |
84 | ||
85 | This section describes the syntax classes and flags that denote the | |
86 | syntax of a character, and how they are represented as a @dfn{syntax | |
87 | descriptor}, which is a Lisp string that you pass to | |
88 | @code{modify-syntax-entry} to specify the desired syntax. | |
89 | ||
90 | Emacs defines a number of @dfn{syntax classes}. Each syntax table | |
91 | puts each character into one class. There is no necessary relationship | |
92 | between the class of a character in one syntax table and its class in | |
93 | any other table. | |
94 | ||
7fd1911a | 95 | Each class is designated by a mnemonic character, which serves as the |
7015aca4 | 96 | name of the class when you need to specify a class. Usually the |
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97 | designator character is one that is frequently in that class; however, |
98 | its meaning as a designator is unvarying and independent of what syntax | |
99 | that character currently has. | |
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100 | |
101 | @cindex syntax descriptor | |
7fd1911a | 102 | A syntax descriptor is a Lisp string that specifies a syntax class, a |
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103 | matching character (used only for the parenthesis classes) and flags. |
104 | The first character is the designator for a syntax class. The second | |
105 | character is the character to match; if it is unused, put a space there. | |
106 | Then come the characters for any desired flags. If no matching | |
107 | character or flags are needed, one character is sufficient. | |
108 | ||
109 | For example, the descriptor for the character @samp{*} in C mode is | |
110 | @samp{@w{. 23}} (i.e., punctuation, matching character slot unused, | |
111 | second character of a comment-starter, first character of an | |
112 | comment-ender), and the entry for @samp{/} is @samp{@w{. 14}} (i.e., | |
113 | punctuation, matching character slot unused, first character of a | |
114 | comment-starter, second character of a comment-ender). | |
115 | ||
116 | @menu | |
117 | * Syntax Class Table:: Table of syntax classes. | |
118 | * Syntax Flags:: Additional flags each character can have. | |
119 | @end menu | |
120 | ||
121 | @node Syntax Class Table | |
122 | @subsection Table of Syntax Classes | |
123 | ||
7fd1911a | 124 | Here is a table of syntax classes, the characters that stand for them, |
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125 | their meanings, and examples of their use. |
126 | ||
127 | @deffn {Syntax class} @w{whitespace character} | |
128 | @dfn{Whitespace characters} (designated with @w{@samp{@ }} or @samp{-}) | |
129 | separate symbols and words from each other. Typically, whitespace | |
130 | characters have no other syntactic significance, and multiple whitespace | |
131 | characters are syntactically equivalent to a single one. Space, tab, | |
132 | newline and formfeed are almost always classified as whitespace. | |
133 | @end deffn | |
134 | ||
135 | @deffn {Syntax class} @w{word constituent} | |
136 | @dfn{Word constituents} (designated with @samp{w}) are parts of normal | |
137 | English words and are typically used in variable and command names in | |
7fd1911a | 138 | programs. All upper- and lower-case letters, and the digits, are typically |
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139 | word constituents. |
140 | @end deffn | |
141 | ||
142 | @deffn {Syntax class} @w{symbol constituent} | |
143 | @dfn{Symbol constituents} (designated with @samp{_}) are the extra | |
144 | characters that are used in variable and command names along with word | |
145 | constituents. For example, the symbol constituents class is used in | |
146 | Lisp mode to indicate that certain characters may be part of symbol | |
147 | names even though they are not part of English words. These characters | |
148 | are @samp{$&*+-_<>}. In standard C, the only non-word-constituent | |
149 | character that is valid in symbols is underscore (@samp{_}). | |
150 | @end deffn | |
151 | ||
152 | @deffn {Syntax class} @w{punctuation character} | |
153 | @dfn{Punctuation characters} (@samp{.}) are those characters that are | |
154 | used as punctuation in English, or are used in some way in a programming | |
155 | language to separate symbols from one another. Most programming | |
156 | language modes, including Emacs Lisp mode, have no characters in this | |
157 | class since the few characters that are not symbol or word constituents | |
158 | all have other uses. | |
159 | @end deffn | |
160 | ||
161 | @deffn {Syntax class} @w{open parenthesis character} | |
162 | @deffnx {Syntax class} @w{close parenthesis character} | |
163 | @cindex parenthesis syntax | |
164 | Open and close @dfn{parenthesis characters} are characters used in | |
165 | dissimilar pairs to surround sentences or expressions. Such a grouping | |
166 | is begun with an open parenthesis character and terminated with a close. | |
167 | Each open parenthesis character matches a particular close parenthesis | |
168 | character, and vice versa. Normally, Emacs indicates momentarily the | |
169 | matching open parenthesis when you insert a close parenthesis. | |
170 | @xref{Blinking}. | |
171 | ||
172 | The class of open parentheses is designated with @samp{(}, and that of | |
173 | close parentheses with @samp{)}. | |
174 | ||
175 | In English text, and in C code, the parenthesis pairs are @samp{()}, | |
176 | @samp{[]}, and @samp{@{@}}. In Emacs Lisp, the delimiters for lists and | |
177 | vectors (@samp{()} and @samp{[]}) are classified as parenthesis | |
178 | characters. | |
179 | @end deffn | |
180 | ||
181 | @deffn {Syntax class} @w{string quote} | |
182 | @dfn{String quote characters} (designated with @samp{"}) are used in | |
183 | many languages, including Lisp and C, to delimit string constants. The | |
184 | same string quote character appears at the beginning and the end of a | |
185 | string. Such quoted strings do not nest. | |
186 | ||
187 | The parsing facilities of Emacs consider a string as a single token. | |
188 | The usual syntactic meanings of the characters in the string are | |
189 | suppressed. | |
190 | ||
191 | The Lisp modes have two string quote characters: double-quote (@samp{"}) | |
192 | and vertical bar (@samp{|}). @samp{|} is not used in Emacs Lisp, but it | |
193 | is used in Common Lisp. C also has two string quote characters: | |
194 | double-quote for strings, and single-quote (@samp{'}) for character | |
195 | constants. | |
196 | ||
197 | English text has no string quote characters because English is not a | |
198 | programming language. Although quotation marks are used in English, | |
199 | we do not want them to turn off the usual syntactic properties of | |
200 | other characters in the quotation. | |
201 | @end deffn | |
202 | ||
203 | @deffn {Syntax class} @w{escape} | |
204 | An @dfn{escape character} (designated with @samp{\}) starts an escape | |
205 | sequence such as is used in C string and character constants. The | |
206 | character @samp{\} belongs to this class in both C and Lisp. (In C, it | |
207 | is used thus only inside strings, but it turns out to cause no trouble | |
208 | to treat it this way throughout C code.) | |
209 | ||
210 | Characters in this class count as part of words if | |
211 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
212 | @end deffn | |
213 | ||
214 | @deffn {Syntax class} @w{character quote} | |
215 | A @dfn{character quote character} (designated with @samp{/}) quotes the | |
216 | following character so that it loses its normal syntactic meaning. This | |
217 | differs from an escape character in that only the character immediately | |
218 | following is ever affected. | |
219 | ||
220 | Characters in this class count as part of words if | |
221 | @code{words-include-escapes} is non-@code{nil}. @xref{Word Motion}. | |
222 | ||
e30ab160 | 223 | This class is used for backslash in @TeX{} mode. |
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224 | @end deffn |
225 | ||
226 | @deffn {Syntax class} @w{paired delimiter} | |
227 | @dfn{Paired delimiter characters} (designated with @samp{$}) are like | |
228 | string quote characters except that the syntactic properties of the | |
229 | characters between the delimiters are not suppressed. Only @TeX{} mode | |
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230 | uses a paired delimiter presently---the @samp{$} that both enters and |
231 | leaves math mode. | |
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232 | @end deffn |
233 | ||
234 | @deffn {Syntax class} @w{expression prefix} | |
235 | An @dfn{expression prefix operator} (designated with @samp{'}) is used | |
236 | for syntactic operators that are part of an expression if they appear | |
237 | next to one. These characters in Lisp include the apostrophe, @samp{'} | |
238 | (used for quoting), the comma, @samp{,} (used in macros), and @samp{#} | |
239 | (used in the read syntax for certain data types). | |
240 | @end deffn | |
241 | ||
242 | @deffn {Syntax class} @w{comment starter} | |
243 | @deffnx {Syntax class} @w{comment ender} | |
244 | @cindex comment syntax | |
245 | The @dfn{comment starter} and @dfn{comment ender} characters are used in | |
246 | various languages to delimit comments. These classes are designated | |
247 | with @samp{<} and @samp{>}, respectively. | |
248 | ||
249 | English text has no comment characters. In Lisp, the semicolon | |
250 | (@samp{;}) starts a comment and a newline or formfeed ends one. | |
251 | @end deffn | |
252 | ||
253 | @deffn {Syntax class} @w{inherit} | |
254 | This syntax class does not specify a syntax. It says to look in the | |
255 | standard syntax table to find the syntax of this character. The | |
256 | designator for this syntax code is @samp{@@}. | |
257 | @end deffn | |
258 | ||
259 | @node Syntax Flags | |
260 | @subsection Syntax Flags | |
261 | @cindex syntax flags | |
262 | ||
263 | In addition to the classes, entries for characters in a syntax table | |
264 | can include flags. There are six possible flags, represented by the | |
265 | characters @samp{1}, @samp{2}, @samp{3}, @samp{4}, @samp{b} and | |
266 | @samp{p}. | |
267 | ||
268 | All the flags except @samp{p} are used to describe multi-character | |
269 | comment delimiters. The digit flags indicate that a character can | |
270 | @emph{also} be part of a comment sequence, in addition to the syntactic | |
271 | properties associated with its character class. The flags are | |
272 | independent of the class and each other for the sake of characters such | |
273 | as @samp{*} in C mode, which is a punctuation character, @emph{and} the | |
274 | second character of a start-of-comment sequence (@samp{/*}), @emph{and} | |
275 | the first character of an end-of-comment sequence (@samp{*/}). | |
276 | ||
277 | The flags for a character @var{c} are: | |
278 | ||
279 | @itemize @bullet | |
280 | @item | |
7fd1911a | 281 | @samp{1} means @var{c} is the start of a two-character comment-start |
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282 | sequence. |
283 | ||
284 | @item | |
285 | @samp{2} means @var{c} is the second character of such a sequence. | |
286 | ||
287 | @item | |
7fd1911a | 288 | @samp{3} means @var{c} is the start of a two-character comment-end |
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289 | sequence. |
290 | ||
291 | @item | |
292 | @samp{4} means @var{c} is the second character of such a sequence. | |
293 | ||
294 | @item | |
295 | @c Emacs 19 feature | |
296 | @samp{b} means that @var{c} as a comment delimiter belongs to the | |
297 | alternative ``b'' comment style. | |
298 | ||
299 | Emacs supports two comment styles simultaneously in any one syntax | |
300 | table. This is for the sake of C++. Each style of comment syntax has | |
301 | its own comment-start sequence and its own comment-end sequence. Each | |
302 | comment must stick to one style or the other; thus, if it starts with | |
303 | the comment-start sequence of style ``b'', it must also end with the | |
304 | comment-end sequence of style ``b''. | |
305 | ||
306 | The two comment-start sequences must begin with the same character; only | |
307 | the second character may differ. Mark the second character of the | |
7fd1911a | 308 | ``b''-style comment-start sequence with the @samp{b} flag. |
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309 | |
310 | A comment-end sequence (one or two characters) applies to the ``b'' | |
311 | style if its first character has the @samp{b} flag set; otherwise, it | |
312 | applies to the ``a'' style. | |
313 | ||
314 | The appropriate comment syntax settings for C++ are as follows: | |
315 | ||
316 | @table @asis | |
317 | @item @samp{/} | |
318 | @samp{124b} | |
319 | @item @samp{*} | |
320 | @samp{23} | |
321 | @item newline | |
322 | @samp{>b} | |
323 | @end table | |
324 | ||
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325 | This defines four comment-delimiting sequences: |
326 | ||
327 | @table @asis | |
328 | @item @samp{/*} | |
329 | This is a comment-start sequence for ``a'' style because the | |
330 | second character, @samp{*}, does not have the @samp{b} flag. | |
331 | ||
332 | @item @samp{//} | |
333 | This is a comment-start sequence for ``b'' style because the second | |
334 | character, @samp{/}, does have the @samp{b} flag. | |
335 | ||
336 | @item @samp{*/} | |
337 | This is a comment-end sequence for ``a'' style because the first | |
338 | character, @samp{*}, does not have the @samp{b} flag | |
339 | ||
340 | @item newline | |
341 | This is a comment-end sequence for ``b'' style, because the newline | |
342 | character has the @samp{b} flag. | |
343 | @end table | |
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344 | |
345 | @item | |
346 | @c Emacs 19 feature | |
347 | @samp{p} identifies an additional ``prefix character'' for Lisp syntax. | |
348 | These characters are treated as whitespace when they appear between | |
349 | expressions. When they appear within an expression, they are handled | |
350 | according to their usual syntax codes. | |
351 | ||
352 | The function @code{backward-prefix-chars} moves back over these | |
353 | characters, as well as over characters whose primary syntax class is | |
354 | prefix (@samp{'}). @xref{Motion and Syntax}. | |
355 | @end itemize | |
356 | ||
357 | @node Syntax Table Functions | |
358 | @section Syntax Table Functions | |
359 | ||
360 | In this section we describe functions for creating, accessing and | |
361 | altering syntax tables. | |
362 | ||
363 | @defun make-syntax-table | |
364 | This function creates a new syntax table. Character codes 0 through | |
7fd1911a | 365 | 31 and 128 through 255 are set up to inherit from the standard syntax |
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366 | table. The other character codes are set up by copying what the |
367 | standard syntax table says about them. | |
368 | ||
369 | Most major mode syntax tables are created in this way. | |
370 | @end defun | |
371 | ||
372 | @defun copy-syntax-table &optional table | |
373 | This function constructs a copy of @var{table} and returns it. If | |
374 | @var{table} is not supplied (or is @code{nil}), it returns a copy of the | |
375 | current syntax table. Otherwise, an error is signaled if @var{table} is | |
376 | not a syntax table. | |
377 | @end defun | |
378 | ||
379 | @deffn Command modify-syntax-entry char syntax-descriptor &optional table | |
380 | This function sets the syntax entry for @var{char} according to | |
381 | @var{syntax-descriptor}. The syntax is changed only for @var{table}, | |
382 | which defaults to the current buffer's syntax table, and not in any | |
383 | other syntax table. The argument @var{syntax-descriptor} specifies the | |
384 | desired syntax; this is a string beginning with a class designator | |
385 | character, and optionally containing a matching character and flags as | |
386 | well. @xref{Syntax Descriptors}. | |
387 | ||
388 | This function always returns @code{nil}. The old syntax information in | |
389 | the table for this character is discarded. | |
390 | ||
391 | An error is signaled if the first character of the syntax descriptor is not | |
392 | one of the twelve syntax class designator characters. An error is also | |
393 | signaled if @var{char} is not a character. | |
394 | ||
395 | @example | |
396 | @group | |
397 | @exdent @r{Examples:} | |
398 | ||
399 | ;; @r{Put the space character in class whitespace.} | |
400 | (modify-syntax-entry ?\ " ") | |
401 | @result{} nil | |
402 | @end group | |
403 | ||
404 | @group | |
405 | ;; @r{Make @samp{$} an open parenthesis character,} | |
406 | ;; @r{with @samp{^} as its matching close.} | |
407 | (modify-syntax-entry ?$ "(^") | |
408 | @result{} nil | |
409 | @end group | |
410 | ||
411 | @group | |
412 | ;; @r{Make @samp{^} a close parenthesis character,} | |
413 | ;; @r{with @samp{$} as its matching open.} | |
414 | (modify-syntax-entry ?^ ")$") | |
415 | @result{} nil | |
416 | @end group | |
417 | ||
418 | @group | |
419 | ;; @r{Make @samp{/} a punctuation character,} | |
420 | ;; @r{the first character of a start-comment sequence,} | |
421 | ;; @r{and the second character of an end-comment sequence.} | |
422 | ;; @r{This is used in C mode.} | |
7fd1911a | 423 | (modify-syntax-entry ?/ ". 14") |
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424 | @result{} nil |
425 | @end group | |
426 | @end example | |
427 | @end deffn | |
428 | ||
429 | @defun char-syntax character | |
430 | This function returns the syntax class of @var{character}, represented | |
431 | by its mnemonic designator character. This @emph{only} returns the | |
432 | class, not any matching parenthesis or flags. | |
433 | ||
434 | An error is signaled if @var{char} is not a character. | |
435 | ||
436 | The following examples apply to C mode. The first example shows that | |
437 | the syntax class of space is whitespace (represented by a space). The | |
438 | second example shows that the syntax of @samp{/} is punctuation. This | |
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439 | does not show the fact that it is also part of comment-start and -end |
440 | sequences. The third example shows that open parenthesis is in the class | |
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441 | of open parentheses. This does not show the fact that it has a matching |
442 | character, @samp{)}. | |
443 | ||
444 | @example | |
445 | @group | |
446 | (char-to-string (char-syntax ?\ )) | |
447 | @result{} " " | |
448 | @end group | |
449 | ||
450 | @group | |
451 | (char-to-string (char-syntax ?/)) | |
452 | @result{} "." | |
453 | @end group | |
454 | ||
455 | @group | |
456 | (char-to-string (char-syntax ?\()) | |
457 | @result{} "(" | |
458 | @end group | |
459 | @end example | |
460 | @end defun | |
461 | ||
462 | @defun set-syntax-table table | |
463 | This function makes @var{table} the syntax table for the current buffer. | |
464 | It returns @var{table}. | |
465 | @end defun | |
466 | ||
467 | @defun syntax-table | |
468 | This function returns the current syntax table, which is the table for | |
469 | the current buffer. | |
470 | @end defun | |
471 | ||
472 | @node Motion and Syntax | |
473 | @section Motion and Syntax | |
474 | ||
475 | This section describes functions for moving across characters in | |
476 | certain syntax classes. None of these functions exists in Emacs | |
477 | version 18 or earlier. | |
478 | ||
479 | @defun skip-syntax-forward syntaxes &optional limit | |
480 | This function moves point forward across characters having syntax classes | |
481 | mentioned in @var{syntaxes}. It stops when it encounters the end of | |
7fd1911a | 482 | the buffer, or position @var{limit} (if specified), or a character it is |
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483 | not supposed to skip. |
484 | @ignore @c may want to change this. | |
485 | The return value is the distance traveled, which is a nonnegative | |
486 | integer. | |
487 | @end ignore | |
488 | @end defun | |
489 | ||
490 | @defun skip-syntax-backward syntaxes &optional limit | |
491 | This function moves point backward across characters whose syntax | |
492 | classes are mentioned in @var{syntaxes}. It stops when it encounters | |
7fd1911a | 493 | the beginning of the buffer, or position @var{limit} (if specified), or a |
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494 | character it is not supposed to skip. |
495 | @ignore @c may want to change this. | |
496 | The return value indicates the distance traveled. It is an integer that | |
497 | is zero or less. | |
498 | @end ignore | |
499 | @end defun | |
500 | ||
501 | @defun backward-prefix-chars | |
502 | This function moves point backward over any number of characters with | |
503 | expression prefix syntax. This includes both characters in the | |
504 | expression prefix syntax class, and characters with the @samp{p} flag. | |
505 | @end defun | |
506 | ||
507 | @node Parsing Expressions | |
508 | @section Parsing Balanced Expressions | |
509 | ||
510 | Here are several functions for parsing and scanning balanced | |
511 | expressions, also known as @dfn{sexps}, in which parentheses match in | |
512 | pairs. The syntax table controls the interpretation of characters, so | |
513 | these functions can be used for Lisp expressions when in Lisp mode and | |
514 | for C expressions when in C mode. @xref{List Motion}, for convenient | |
515 | higher-level functions for moving over balanced expressions. | |
516 | ||
517 | @defun parse-partial-sexp start limit &optional target-depth stop-before state stop-comment | |
518 | This function parses a sexp in the current buffer starting at | |
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519 | @var{start}, not scanning past @var{limit}. It stops at position |
520 | @var{limit} or when certain criteria described below are met, and sets | |
521 | point to the location where parsing stops. It returns a value | |
522 | describing the status of the parse at the point where it stops. | |
7015aca4 RS |
523 | |
524 | If @var{state} is @code{nil}, @var{start} is assumed to be at the top | |
525 | level of parenthesis structure, such as the beginning of a function | |
526 | definition. Alternatively, you might wish to resume parsing in the | |
527 | middle of the structure. To do this, you must provide a @var{state} | |
528 | argument that describes the initial status of parsing. | |
529 | ||
530 | @cindex parenthesis depth | |
531 | If the third argument @var{target-depth} is non-@code{nil}, parsing | |
532 | stops if the depth in parentheses becomes equal to @var{target-depth}. | |
533 | The depth starts at 0, or at whatever is given in @var{state}. | |
534 | ||
535 | If the fourth argument @var{stop-before} is non-@code{nil}, parsing | |
536 | stops when it comes to any character that starts a sexp. If | |
537 | @var{stop-comment} is non-@code{nil}, parsing stops when it comes to the | |
538 | start of a comment. | |
539 | ||
540 | @cindex parse state | |
541 | The fifth argument @var{state} is an eight-element list of the same | |
542 | form as the value of this function, described below. The return value | |
543 | of one call may be used to initialize the state of the parse on another | |
544 | call to @code{parse-partial-sexp}. | |
545 | ||
546 | The result is a list of eight elements describing the final state of | |
547 | the parse: | |
548 | ||
549 | @enumerate 0 | |
550 | @item | |
551 | The depth in parentheses, counting from 0. | |
552 | ||
553 | @item | |
554 | @cindex innermost containing parentheses | |
7fd1911a RS |
555 | The character position of the start of the innermost parenthetical |
556 | grouping containing the stopping point; @code{nil} if none. | |
7015aca4 RS |
557 | |
558 | @item | |
559 | @cindex previous complete subexpression | |
560 | The character position of the start of the last complete subexpression | |
561 | terminated; @code{nil} if none. | |
562 | ||
563 | @item | |
564 | @cindex inside string | |
565 | Non-@code{nil} if inside a string. More precisely, this is the | |
566 | character that will terminate the string. | |
567 | ||
568 | @item | |
569 | @cindex inside comment | |
7fd1911a | 570 | @code{t} if inside a comment (of either style). |
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571 | |
572 | @item | |
573 | @cindex quote character | |
574 | @code{t} if point is just after a quote character. | |
575 | ||
576 | @item | |
577 | The minimum parenthesis depth encountered during this scan. | |
578 | ||
579 | @item | |
580 | @code{t} if inside a comment of style ``b''. | |
581 | @end enumerate | |
582 | ||
583 | Elements 0, 3, 4, 5 and 7 are significant in the argument @var{state}. | |
584 | ||
585 | @cindex indenting with parentheses | |
586 | This function is most often used to compute indentation for languages | |
587 | that have nested parentheses. | |
588 | @end defun | |
589 | ||
590 | @defun scan-lists from count depth | |
591 | This function scans forward @var{count} balanced parenthetical groupings | |
592 | from character number @var{from}. It returns the character position | |
593 | where the scan stops. | |
594 | ||
595 | If @var{depth} is nonzero, parenthesis depth counting begins from that | |
596 | value. The only candidates for stopping are places where the depth in | |
597 | parentheses becomes zero; @code{scan-lists} counts @var{count} such | |
598 | places and then stops. Thus, a positive value for @var{depth} means go | |
7fd1911a | 599 | out @var{depth} levels of parenthesis. |
7015aca4 RS |
600 | |
601 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
602 | non-@code{nil}. | |
603 | ||
7fd1911a RS |
604 | If the scan reaches the beginning or end of the buffer (or its |
605 | accessible portion), and the depth is not zero, an error is signaled. | |
606 | If the depth is zero but the count is not used up, @code{nil} is | |
607 | returned. | |
7015aca4 RS |
608 | @end defun |
609 | ||
610 | @defun scan-sexps from count | |
611 | This function scans forward @var{count} sexps from character position | |
612 | @var{from}. It returns the character position where the scan stops. | |
613 | ||
614 | Scanning ignores comments if @code{parse-sexp-ignore-comments} is | |
615 | non-@code{nil}. | |
616 | ||
7fd1911a | 617 | If the scan reaches the beginning or end of (the accessible part of) the |
7015aca4 RS |
618 | buffer in the middle of a parenthetical grouping, an error is signaled. |
619 | If it reaches the beginning or end between groupings but before count is | |
620 | used up, @code{nil} is returned. | |
621 | @end defun | |
622 | ||
623 | @defvar parse-sexp-ignore-comments | |
624 | @cindex skipping comments | |
625 | If the value is non-@code{nil}, then comments are treated as | |
626 | whitespace by the functions in this section and by @code{forward-sexp}. | |
627 | ||
628 | In older Emacs versions, this feature worked only when the comment | |
629 | terminator is something like @samp{*/}, and appears only to end a | |
630 | comment. In languages where newlines terminate comments, it was | |
631 | necessary make this variable @code{nil}, since not every newline is the | |
632 | end of a comment. This limitation no longer exists. | |
633 | @end defvar | |
634 | ||
635 | You can use @code{forward-comment} to move forward or backward over | |
636 | one comment or several comments. | |
637 | ||
638 | @defun forward-comment count | |
639 | This function moves point forward across @var{count} comments (backward, | |
640 | if @var{count} is negative). If it finds anything other than a comment | |
641 | or whitespace, it stops, leaving point at the place where it stopped. | |
642 | It also stops after satisfying @var{count}. | |
643 | @end defun | |
644 | ||
645 | To move forward over all comments and whitespace following point, use | |
646 | @code{(forward-comment (buffer-size))}. @code{(buffer-size)} is a good | |
7fd1911a | 647 | argument to use, because the number of comments in the buffer cannot |
7015aca4 RS |
648 | exceed that many. |
649 | ||
650 | @node Standard Syntax Tables | |
651 | @section Some Standard Syntax Tables | |
652 | ||
bfe721d1 KH |
653 | Most of the major modes in Emacs have their own syntax tables. Here |
654 | are several of them: | |
7015aca4 RS |
655 | |
656 | @defun standard-syntax-table | |
657 | This function returns the standard syntax table, which is the syntax | |
658 | table used in Fundamental mode. | |
659 | @end defun | |
660 | ||
661 | @defvar text-mode-syntax-table | |
662 | The value of this variable is the syntax table used in Text mode. | |
663 | @end defvar | |
664 | ||
665 | @defvar c-mode-syntax-table | |
666 | The value of this variable is the syntax table for C-mode buffers. | |
667 | @end defvar | |
668 | ||
669 | @defvar emacs-lisp-mode-syntax-table | |
670 | The value of this variable is the syntax table used in Emacs Lisp mode | |
671 | by editing commands. (It has no effect on the Lisp @code{read} | |
672 | function.) | |
673 | @end defvar | |
674 | ||
675 | @node Syntax Table Internals | |
676 | @section Syntax Table Internals | |
677 | @cindex syntax table internals | |
678 | ||
679 | Each element of a syntax table is an integer that encodes the syntax | |
680 | of one character: the syntax class, possible matching character, and | |
681 | flags. Lisp programs don't usually work with the elements directly; the | |
682 | Lisp-level syntax table functions usually work with syntax descriptors | |
683 | (@pxref{Syntax Descriptors}). | |
684 | ||
685 | The low 8 bits of each element of a syntax table indicate the | |
686 | syntax class. | |
687 | ||
688 | @table @asis | |
689 | @item @i{Integer} | |
690 | @i{Class} | |
691 | @item 0 | |
692 | whitespace | |
693 | @item 1 | |
694 | punctuation | |
695 | @item 2 | |
696 | word | |
697 | @item 3 | |
698 | symbol | |
699 | @item 4 | |
700 | open parenthesis | |
701 | @item 5 | |
702 | close parenthesis | |
703 | @item 6 | |
704 | expression prefix | |
705 | @item 7 | |
706 | string quote | |
707 | @item 8 | |
708 | paired delimiter | |
709 | @item 9 | |
710 | escape | |
711 | @item 10 | |
712 | character quote | |
713 | @item 11 | |
714 | comment-start | |
715 | @item 12 | |
716 | comment-end | |
717 | @item 13 | |
718 | inherit | |
719 | @end table | |
720 | ||
721 | The next 8 bits are the matching opposite parenthesis (if the | |
722 | character has parenthesis syntax); otherwise, they are not meaningful. | |
723 | The next 6 bits are the flags. |