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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. |
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4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/positions | |
6 | @node Positions, Markers, Frames, Top | |
7 | @chapter Positions | |
8 | @cindex position (in buffer) | |
9 | ||
29679a81 | 10 | A @dfn{position} is the index of a character in the text of a buffer. |
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11 | More precisely, a position identifies the place between two characters |
12 | (or before the first character, or after the last character), so we can | |
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13 | speak of the character before or after a given position. However, we |
14 | often speak of the character ``at'' a position, meaning the character | |
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15 | after that position. |
16 | ||
17 | Positions are usually represented as integers starting from 1, but can | |
29679a81 | 18 | also be represented as @dfn{markers}---special objects that relocate |
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19 | automatically when text is inserted or deleted so they stay with the |
20 | surrounding characters. @xref{Markers}. | |
21 | ||
22 | @menu | |
23 | * Point:: The special position where editing takes place. | |
24 | * Motion:: Changing point. | |
25 | * Excursions:: Temporary motion and buffer changes. | |
26 | * Narrowing:: Restricting editing to a portion of the buffer. | |
27 | @end menu | |
28 | ||
29 | @node Point | |
30 | @section Point | |
31 | @cindex point | |
32 | ||
33 | @dfn{Point} is a special buffer position used by many editing | |
34 | commands, including the self-inserting typed characters and text | |
35 | insertion functions. Other commands move point through the text | |
36 | to allow editing and insertion at different places. | |
37 | ||
38 | Like other positions, point designates a place between two characters | |
39 | (or before the first character, or after the last character), rather | |
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40 | than a particular character. Usually terminals display the cursor over |
41 | the character that immediately follows point; point is actually before | |
42 | the character on which the cursor sits. | |
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43 | |
44 | @cindex point with narrowing | |
45 | The value of point is a number between 1 and the buffer size plus 1. | |
46 | If narrowing is in effect (@pxref{Narrowing}), then point is constrained | |
47 | to fall within the accessible portion of the buffer (possibly at one end | |
48 | of it). | |
49 | ||
50 | Each buffer has its own value of point, which is independent of the | |
51 | value of point in other buffers. Each window also has a value of point, | |
52 | which is independent of the value of point in other windows on the same | |
53 | buffer. This is why point can have different values in various windows | |
54 | that display the same buffer. When a buffer appears in only one window, | |
55 | the buffer's point and the window's point normally have the same value, | |
56 | so the distinction is rarely important. @xref{Window Point}, for more | |
57 | details. | |
58 | ||
59 | @defun point | |
60 | @cindex current buffer position | |
29679a81 | 61 | This function returns the value of point in the current buffer, |
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62 | as an integer. |
63 | ||
64 | @need 700 | |
65 | @example | |
66 | @group | |
67 | (point) | |
68 | @result{} 175 | |
69 | @end group | |
70 | @end example | |
71 | @end defun | |
72 | ||
73 | @defun point-min | |
29679a81 RS |
74 | This function returns the minimum accessible value of point in the |
75 | current buffer. This is normally 1, but if narrowing is in effect, it | |
76 | is the position of the start of the region that you narrowed to. | |
77 | (@xref{Narrowing}.) | |
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78 | @end defun |
79 | ||
80 | @defun point-max | |
29679a81 | 81 | This function returns the maximum accessible value of point in the |
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82 | current buffer. This is @code{(1+ (buffer-size))}, unless narrowing is |
83 | in effect, in which case it is the position of the end of the region | |
84 | that you narrowed to. (@xref{Narrowing}). | |
85 | @end defun | |
86 | ||
87 | @defun buffer-end flag | |
29679a81 | 88 | This function returns @code{(point-min)} if @var{flag} is less than 1, |
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89 | @code{(point-max)} otherwise. The argument @var{flag} must be a number. |
90 | @end defun | |
91 | ||
92 | @defun buffer-size | |
29679a81 | 93 | This function returns the total number of characters in the current |
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94 | buffer. In the absence of any narrowing (@pxref{Narrowing}), |
95 | @code{point-max} returns a value one larger than this. | |
96 | ||
97 | @example | |
98 | @group | |
99 | (buffer-size) | |
100 | @result{} 35 | |
101 | @end group | |
102 | @group | |
103 | (point-max) | |
104 | @result{} 36 | |
105 | @end group | |
106 | @end example | |
107 | @end defun | |
108 | ||
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109 | @node Motion |
110 | @section Motion | |
111 | ||
112 | Motion functions change the value of point, either relative to the | |
113 | current value of point, relative to the beginning or end of the buffer, | |
114 | or relative to the edges of the selected window. @xref{Point}. | |
115 | ||
116 | @menu | |
117 | * Character Motion:: Moving in terms of characters. | |
118 | * Word Motion:: Moving in terms of words. | |
119 | * Buffer End Motion:: Moving to the beginning or end of the buffer. | |
120 | * Text Lines:: Moving in terms of lines of text. | |
121 | * Screen Lines:: Moving in terms of lines as displayed. | |
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122 | * List Motion:: Moving by parsing lists and sexps. |
123 | * Skipping Characters:: Skipping characters belonging to a certain set. | |
124 | @end menu | |
125 | ||
126 | @node Character Motion | |
127 | @subsection Motion by Characters | |
128 | ||
129 | These functions move point based on a count of characters. | |
29679a81 | 130 | @code{goto-char} is the fundamental primitive; the other functions use |
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131 | that. |
132 | ||
133 | @deffn Command goto-char position | |
134 | This function sets point in the current buffer to the value | |
135 | @var{position}. If @var{position} is less than 1, it moves point to the | |
136 | beginning of the buffer. If @var{position} is greater than the length | |
137 | of the buffer, it moves point to the end. | |
138 | ||
139 | If narrowing is in effect, @var{position} still counts from the | |
140 | beginning of the buffer, but point cannot go outside the accessible | |
141 | portion. If @var{position} is out of range, @code{goto-char} moves | |
142 | point to the beginning or the end of the accessible portion. | |
143 | ||
144 | When this function is called interactively, @var{position} is the | |
145 | numeric prefix argument, if provided; otherwise it is read from the | |
146 | minibuffer. | |
147 | ||
148 | @code{goto-char} returns @var{position}. | |
149 | @end deffn | |
150 | ||
151 | @deffn Command forward-char &optional count | |
152 | @c @kindex beginning-of-buffer | |
153 | @c @kindex end-of-buffer | |
154 | This function moves point @var{count} characters forward, towards the | |
155 | end of the buffer (or backward, towards the beginning of the buffer, if | |
156 | @var{count} is negative). If the function attempts to move point past | |
157 | the beginning or end of the buffer (or the limits of the accessible | |
158 | portion, when narrowing is in effect), an error is signaled with error | |
159 | code @code{beginning-of-buffer} or @code{end-of-buffer}. | |
160 | ||
161 | In an interactive call, @var{count} is the numeric prefix argument. | |
162 | @end deffn | |
163 | ||
164 | @deffn Command backward-char &optional count | |
165 | This function moves point @var{count} characters backward, towards the | |
166 | beginning of the buffer (or forward, towards the end of the buffer, if | |
167 | @var{count} is negative). If the function attempts to move point past | |
168 | the beginning or end of the buffer (or the limits of the accessible | |
169 | portion, when narrowing is in effect), an error is signaled with error | |
170 | code @code{beginning-of-buffer} or @code{end-of-buffer}. | |
171 | ||
172 | In an interactive call, @var{count} is the numeric prefix argument. | |
173 | @end deffn | |
174 | ||
175 | @node Word Motion | |
176 | @subsection Motion by Words | |
177 | ||
178 | These functions for parsing words use the syntax table to decide | |
179 | whether a given character is part of a word. @xref{Syntax Tables}. | |
180 | ||
181 | @deffn Command forward-word count | |
182 | This function moves point forward @var{count} words (or backward if | |
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183 | @var{count} is negative). More precisely, it keeps moving until it |
184 | moves across a word-constituent character and encounters a | |
185 | word-separator character, then returns @code{t}. | |
186 | ||
187 | If this motion encounters the beginning or end of the buffer, or the | |
188 | limits of the accessible portion when narrowing is in effect, point | |
189 | stops there and the value is @code{nil}. | |
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190 | |
191 | In an interactive call, @var{count} is set to the numeric prefix | |
192 | argument. | |
193 | @end deffn | |
194 | ||
195 | @deffn Command backward-word count | |
29679a81 | 196 | This function is just like @code{forward-word}, except that it moves |
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197 | backward until encountering the front of a word, rather than forward. |
198 | ||
199 | In an interactive call, @var{count} is set to the numeric prefix | |
200 | argument. | |
201 | ||
202 | This function is rarely used in programs, as it is more efficient to | |
29679a81 | 203 | call @code{forward-word} with a negative argument. |
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204 | @end deffn |
205 | ||
206 | @defvar words-include-escapes | |
207 | @c Emacs 19 feature | |
208 | This variable affects the behavior of @code{forward-word} and everything | |
209 | that uses it. If it is non-@code{nil}, then characters in the | |
210 | ``escape'' and ``character quote'' syntax classes count as part of | |
211 | words. Otherwise, they do not. | |
212 | @end defvar | |
213 | ||
214 | @node Buffer End Motion | |
215 | @subsection Motion to an End of the Buffer | |
216 | ||
217 | To move point to the beginning of the buffer, write: | |
218 | ||
219 | @example | |
220 | @group | |
221 | (goto-char (point-min)) | |
222 | @end group | |
223 | @end example | |
224 | ||
225 | @noindent | |
226 | Likewise, to move to the end of the buffer, use: | |
227 | ||
228 | @example | |
229 | @group | |
230 | (goto-char (point-max)) | |
231 | @end group | |
232 | @end example | |
233 | ||
29679a81 | 234 | Here are two commands that users use to do these things. They are |
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235 | documented here to warn you not to use them in Lisp programs, because |
236 | they set the mark and display messages in the echo area. | |
237 | ||
238 | @deffn Command beginning-of-buffer &optional n | |
239 | This function moves point to the beginning of the buffer (or the limits | |
240 | of the accessible portion, when narrowing is in effect), setting the | |
241 | mark at the previous position. If @var{n} is non-@code{nil}, then it | |
242 | puts point @var{n} tenths of the way from the beginning of the buffer. | |
243 | ||
244 | In an interactive call, @var{n} is the numeric prefix argument, | |
245 | if provided; otherwise @var{n} defaults to @code{nil}. | |
246 | ||
969fe9b5 | 247 | @strong{Warning:} Don't use this function in Lisp programs! |
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248 | @end deffn |
249 | ||
250 | @deffn Command end-of-buffer &optional n | |
251 | This function moves point to the end of the buffer (or the limits of | |
252 | the accessible portion, when narrowing is in effect), setting the mark | |
253 | at the previous position. If @var{n} is non-@code{nil}, then it puts | |
29679a81 | 254 | point @var{n} tenths of the way from the end of the buffer. |
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255 | |
256 | In an interactive call, @var{n} is the numeric prefix argument, | |
257 | if provided; otherwise @var{n} defaults to @code{nil}. | |
258 | ||
969fe9b5 | 259 | @strong{Warning:} Don't use this function in Lisp programs! |
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260 | @end deffn |
261 | ||
262 | @node Text Lines | |
263 | @subsection Motion by Text Lines | |
264 | @cindex lines | |
265 | ||
266 | Text lines are portions of the buffer delimited by newline characters, | |
267 | which are regarded as part of the previous line. The first text line | |
268 | begins at the beginning of the buffer, and the last text line ends at | |
269 | the end of the buffer whether or not the last character is a newline. | |
270 | The division of the buffer into text lines is not affected by the width | |
271 | of the window, by line continuation in display, or by how tabs and | |
272 | control characters are displayed. | |
273 | ||
274 | @deffn Command goto-line line | |
275 | This function moves point to the front of the @var{line}th line, | |
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276 | counting from line 1 at beginning of the buffer. If @var{line} is less |
277 | than 1, it moves point to the beginning of the buffer. If @var{line} is | |
7015aca4 | 278 | greater than the number of lines in the buffer, it moves point to the |
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279 | end of the buffer---that is, the @emph{end of the last line} of the |
280 | buffer. This is the only case in which @code{goto-line} does not | |
281 | necessarily move to the beginning of a line. | |
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282 | |
283 | If narrowing is in effect, then @var{line} still counts from the | |
284 | beginning of the buffer, but point cannot go outside the accessible | |
285 | portion. So @code{goto-line} moves point to the beginning or end of the | |
286 | accessible portion, if the line number specifies an inaccessible | |
287 | position. | |
288 | ||
289 | The return value of @code{goto-line} is the difference between | |
290 | @var{line} and the line number of the line to which point actually was | |
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291 | able to move (in the full buffer, before taking account of narrowing). |
292 | Thus, the value is positive if the scan encounters the real end of the | |
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293 | buffer before finding the specified line. The value is zero if scan |
294 | encounters the end of the accessible portion but not the real end of the | |
295 | buffer. | |
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296 | |
297 | In an interactive call, @var{line} is the numeric prefix argument if | |
298 | one has been provided. Otherwise @var{line} is read in the minibuffer. | |
299 | @end deffn | |
300 | ||
301 | @deffn Command beginning-of-line &optional count | |
302 | This function moves point to the beginning of the current line. With an | |
303 | argument @var{count} not @code{nil} or 1, it moves forward | |
304 | @var{count}@minus{}1 lines and then to the beginning of the line. | |
305 | ||
306 | If this function reaches the end of the buffer (or of the accessible | |
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307 | portion, if narrowing is in effect), it positions point there. No error |
308 | is signaled. | |
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309 | @end deffn |
310 | ||
311 | @deffn Command end-of-line &optional count | |
312 | This function moves point to the end of the current line. With an | |
313 | argument @var{count} not @code{nil} or 1, it moves forward | |
314 | @var{count}@minus{}1 lines and then to the end of the line. | |
315 | ||
316 | If this function reaches the end of the buffer (or of the accessible | |
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317 | portion, if narrowing is in effect), it positions point there. No error |
318 | is signaled. | |
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319 | @end deffn |
320 | ||
321 | @deffn Command forward-line &optional count | |
322 | @cindex beginning of line | |
323 | This function moves point forward @var{count} lines, to the beginning of | |
324 | the line. If @var{count} is negative, it moves point | |
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325 | @minus{}@var{count} lines backward, to the beginning of a line. If |
326 | @var{count} is zero, it moves point to the beginning of the current | |
327 | line. | |
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328 | |
329 | If @code{forward-line} encounters the beginning or end of the buffer (or | |
330 | of the accessible portion) before finding that many lines, it sets point | |
331 | there. No error is signaled. | |
332 | ||
333 | @code{forward-line} returns the difference between @var{count} and the | |
334 | number of lines actually moved. If you attempt to move down five lines | |
335 | from the beginning of a buffer that has only three lines, point stops at | |
336 | the end of the last line, and the value will be 2. | |
337 | ||
338 | In an interactive call, @var{count} is the numeric prefix argument. | |
339 | @end deffn | |
340 | ||
341 | @defun count-lines start end | |
342 | @cindex lines in region | |
343 | This function returns the number of lines between the positions | |
344 | @var{start} and @var{end} in the current buffer. If @var{start} and | |
345 | @var{end} are equal, then it returns 0. Otherwise it returns at least | |
346 | 1, even if @var{start} and @var{end} are on the same line. This is | |
347 | because the text between them, considered in isolation, must contain at | |
348 | least one line unless it is empty. | |
349 | ||
350 | Here is an example of using @code{count-lines}: | |
351 | ||
352 | @example | |
353 | @group | |
354 | (defun current-line () | |
355 | "Return the vertical position of point@dots{}" | |
356 | (+ (count-lines (window-start) (point)) | |
357 | (if (= (current-column) 0) 1 0) | |
358 | -1)) | |
359 | @end group | |
360 | @end example | |
361 | @end defun | |
362 | ||
363 | @ignore | |
364 | @c ================ | |
365 | The @code{previous-line} and @code{next-line} commands are functions | |
366 | that should not be used in programs. They are for users and are | |
367 | mentioned here only for completeness. | |
368 | ||
369 | @deffn Command previous-line count | |
370 | @cindex goal column | |
371 | This function moves point up @var{count} lines (down if @var{count} | |
372 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
373 | (normally the same column that it was at the beginning of the move). | |
374 | ||
375 | If there is no character in the target line exactly under the current | |
376 | column, point is positioned after the character in that line which | |
377 | spans this column, or at the end of the line if it is not long enough. | |
378 | ||
379 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
380 | region), then point is positioned in the goal column in the top or | |
381 | bottom line. No error is signaled. | |
382 | ||
383 | In an interactive call, @var{count} will be the numeric | |
384 | prefix argument. | |
385 | ||
386 | The command @code{set-goal-column} can be used to create a semipermanent | |
387 | goal column to which this command always moves. Then it does not try to | |
388 | move vertically. | |
389 | ||
390 | If you are thinking of using this in a Lisp program, consider using | |
391 | @code{forward-line} with a negative argument instead. It is usually easier | |
392 | to use and more reliable (no dependence on goal column, etc.). | |
393 | @end deffn | |
394 | ||
395 | @deffn Command next-line count | |
396 | This function moves point down @var{count} lines (up if @var{count} | |
397 | is negative). In moving, it attempts to keep point in the ``goal column'' | |
398 | (normally the same column that it was at the beginning of the move). | |
399 | ||
400 | If there is no character in the target line exactly under the current | |
401 | column, point is positioned after the character in that line which | |
402 | spans this column, or at the end of the line if it is not long enough. | |
403 | ||
404 | If it attempts to move beyond the top or bottom of the buffer (or clipped | |
405 | region), then point is positioned in the goal column in the top or | |
406 | bottom line. No error is signaled. | |
407 | ||
408 | In the case where the @var{count} is 1, and point is on the last | |
409 | line of the buffer (or clipped region), a new empty line is inserted at the | |
410 | end of the buffer (or clipped region) and point moved there. | |
411 | ||
412 | In an interactive call, @var{count} will be the numeric | |
413 | prefix argument. | |
414 | ||
415 | The command @code{set-goal-column} can be used to create a semipermanent | |
416 | goal column to which this command always moves. Then it does not try to | |
417 | move vertically. | |
418 | ||
419 | If you are thinking of using this in a Lisp program, consider using | |
420 | @code{forward-line} instead. It is usually easier | |
421 | to use and more reliable (no dependence on goal column, etc.). | |
422 | @end deffn | |
423 | ||
424 | @c ================ | |
425 | @end ignore | |
426 | ||
427 | Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}. | |
428 | These functions do not move point, but test whether it is already at the | |
429 | beginning or end of a line. | |
430 | ||
431 | @node Screen Lines | |
432 | @subsection Motion by Screen Lines | |
433 | ||
434 | The line functions in the previous section count text lines, delimited | |
435 | only by newline characters. By contrast, these functions count screen | |
436 | lines, which are defined by the way the text appears on the screen. A | |
437 | text line is a single screen line if it is short enough to fit the width | |
438 | of the selected window, but otherwise it may occupy several screen | |
439 | lines. | |
440 | ||
441 | In some cases, text lines are truncated on the screen rather than | |
442 | continued onto additional screen lines. In these cases, | |
443 | @code{vertical-motion} moves point much like @code{forward-line}. | |
444 | @xref{Truncation}. | |
445 | ||
29679a81 | 446 | Because the width of a given string depends on the flags that control |
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447 | the appearance of certain characters, @code{vertical-motion} behaves |
448 | differently, for a given piece of text, depending on the buffer it is | |
449 | in, and even on the selected window (because the width, the truncation | |
450 | flag, and display table may vary between windows). @xref{Usual | |
451 | Display}. | |
452 | ||
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453 | These functions scan text to determine where screen lines break, and |
454 | thus take time proportional to the distance scanned. If you intend to | |
455 | use them heavily, Emacs provides caches which may improve the | |
a9f0a989 | 456 | performance of your code. @xref{Truncation, cache-long-line-scans}. |
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457 | |
458 | ||
a890e1b0 | 459 | @defun vertical-motion count &optional window |
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460 | This function moves point to the start of the screen line @var{count} |
461 | screen lines down from the screen line containing point. If @var{count} | |
462 | is negative, it moves up instead. | |
463 | ||
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464 | @code{vertical-motion} returns the number of screen lines over which it |
465 | moved point. The value may be less in absolute value than @var{count} | |
466 | if the beginning or end of the buffer was reached. | |
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467 | |
468 | The window @var{window} is used for obtaining parameters such as the | |
469 | width, the horizontal scrolling, and the display table. But | |
470 | @code{vertical-motion} always operates on the current buffer, even if | |
471 | @var{window} currently displays some other buffer. | |
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472 | @end defun |
473 | ||
474 | @deffn Command move-to-window-line count | |
475 | This function moves point with respect to the text currently displayed | |
476 | in the selected window. It moves point to the beginning of the screen | |
477 | line @var{count} screen lines from the top of the window. If | |
478 | @var{count} is negative, that specifies a position | |
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479 | @w{@minus{}@var{count}} lines from the bottom (or the last line of the |
480 | buffer, if the buffer ends above the specified screen position). | |
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481 | |
482 | If @var{count} is @code{nil}, then point moves to the beginning of the | |
483 | line in the middle of the window. If the absolute value of @var{count} | |
484 | is greater than the size of the window, then point moves to the place | |
29679a81 | 485 | that would appear on that screen line if the window were tall enough. |
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486 | This will probably cause the next redisplay to scroll to bring that |
487 | location onto the screen. | |
488 | ||
489 | In an interactive call, @var{count} is the numeric prefix argument. | |
490 | ||
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491 | The value returned is the window line number point has moved to, with |
492 | the top line in the window numbered 0. | |
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493 | @end deffn |
494 | ||
a890e1b0 | 495 | @defun compute-motion from frompos to topos width offsets window |
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496 | This function scans the current buffer, calculating screen positions. |
497 | It scans the buffer forward from position @var{from}, assuming that is | |
498 | at screen coordinates @var{frompos}, to position @var{to} or coordinates | |
499 | @var{topos}, whichever comes first. It returns the ending buffer | |
500 | position and screen coordinates. | |
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501 | |
502 | The coordinate arguments @var{frompos} and @var{topos} are cons cells of | |
503 | the form @code{(@var{hpos} . @var{vpos})}. | |
504 | ||
505 | The argument @var{width} is the number of columns available to display | |
506 | text; this affects handling of continuation lines. Use the value | |
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507 | returned by @code{window-width} for the window of your choice; |
508 | normally, use @code{(window-width @var{window})}. | |
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509 | |
510 | The argument @var{offsets} is either @code{nil} or a cons cell of the | |
511 | form @code{(@var{hscroll} . @var{tab-offset})}. Here @var{hscroll} is | |
a890e1b0 | 512 | the number of columns not being displayed at the left margin; most |
a9f0a989 | 513 | callers get this by calling @code{window-hscroll}. Meanwhile, |
a890e1b0 RS |
514 | @var{tab-offset} is the offset between column numbers on the screen and |
515 | column numbers in the buffer. This can be nonzero in a continuation | |
516 | line, when the previous screen lines' widths do not add up to a multiple | |
517 | of @code{tab-width}. It is always zero in a non-continuation line. | |
518 | ||
29679a81 RS |
519 | The window @var{window} serves only to specify which display table to |
520 | use. @code{compute-motion} always operates on the current buffer, | |
521 | regardless of what buffer is displayed in @var{window}. | |
7015aca4 RS |
522 | |
523 | The return value is a list of five elements: | |
524 | ||
525 | @example | |
526 | (@var{pos} @var{vpos} @var{hpos} @var{prevhpos} @var{contin}) | |
527 | @end example | |
528 | ||
529 | @noindent | |
530 | Here @var{pos} is the buffer position where the scan stopped, @var{vpos} | |
29679a81 RS |
531 | is the vertical screen position, and @var{hpos} is the horizontal screen |
532 | position. | |
7015aca4 RS |
533 | |
534 | The result @var{prevhpos} is the horizontal position one character back | |
29679a81 RS |
535 | from @var{pos}. The result @var{contin} is @code{t} if the last line |
536 | was continued after (or within) the previous character. | |
7015aca4 | 537 | |
f9f59935 | 538 | For example, to find the buffer position of column @var{col} of screen line |
7015aca4 RS |
539 | @var{line} of a certain window, pass the window's display start location |
540 | as @var{from} and the window's upper-left coordinates as @var{frompos}. | |
541 | Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to | |
29679a81 | 542 | the end of the accessible portion of the buffer, and pass @var{line} and |
7015aca4 RS |
543 | @var{col} as @var{topos}. Here's a function that does this: |
544 | ||
545 | @example | |
546 | (defun coordinates-of-position (col line) | |
547 | (car (compute-motion (window-start) | |
548 | '(0 . 0) | |
29679a81 | 549 | (point-max) |
7015aca4 RS |
550 | (cons col line) |
551 | (window-width) | |
29679a81 RS |
552 | (cons (window-hscroll) 0) |
553 | (selected-window)))) | |
7015aca4 | 554 | @end example |
a890e1b0 RS |
555 | |
556 | When you use @code{compute-motion} for the minibuffer, you need to use | |
557 | @code{minibuffer-prompt-width} to get the horizontal position of the | |
558 | beginning of the first screen line. @xref{Minibuffer Misc}. | |
7015aca4 RS |
559 | @end defun |
560 | ||
7015aca4 RS |
561 | @node List Motion |
562 | @comment node-name, next, previous, up | |
563 | @subsection Moving over Balanced Expressions | |
564 | @cindex sexp motion | |
565 | @cindex Lisp expression motion | |
566 | @cindex list motion | |
567 | ||
568 | Here are several functions concerned with balanced-parenthesis | |
569 | expressions (also called @dfn{sexps} in connection with moving across | |
570 | them in Emacs). The syntax table controls how these functions interpret | |
571 | various characters; see @ref{Syntax Tables}. @xref{Parsing | |
572 | Expressions}, for lower-level primitives for scanning sexps or parts of | |
79d828e7 | 573 | sexps. For user-level commands, see @ref{Lists Commands,,, emacs, GNU |
7015aca4 RS |
574 | Emacs Manual}. |
575 | ||
576 | @deffn Command forward-list arg | |
a890e1b0 RS |
577 | This function moves forward across @var{arg} balanced groups of |
578 | parentheses. (Other syntactic entities such as words or paired string | |
579 | quotes are ignored.) | |
7015aca4 RS |
580 | @end deffn |
581 | ||
582 | @deffn Command backward-list arg | |
a890e1b0 RS |
583 | This function moves backward across @var{arg} balanced groups of |
584 | parentheses. (Other syntactic entities such as words or paired string | |
585 | quotes are ignored.) | |
7015aca4 RS |
586 | @end deffn |
587 | ||
588 | @deffn Command up-list arg | |
a890e1b0 | 589 | This function moves forward out of @var{arg} levels of parentheses. |
7015aca4 RS |
590 | A negative argument means move backward but still to a less deep spot. |
591 | @end deffn | |
592 | ||
593 | @deffn Command down-list arg | |
29679a81 | 594 | This function moves forward into @var{arg} levels of parentheses. A |
ec221d13 RS |
595 | negative argument means move backward but still go |
596 | deeper in parentheses (@minus{}@var{arg} levels). | |
7015aca4 RS |
597 | @end deffn |
598 | ||
599 | @deffn Command forward-sexp arg | |
a890e1b0 RS |
600 | This function moves forward across @var{arg} balanced expressions. |
601 | Balanced expressions include both those delimited by parentheses and | |
602 | other kinds, such as words and string constants. For example, | |
7015aca4 RS |
603 | |
604 | @example | |
605 | @group | |
606 | ---------- Buffer: foo ---------- | |
607 | (concat@point{} "foo " (car x) y z) | |
608 | ---------- Buffer: foo ---------- | |
609 | @end group | |
610 | ||
611 | @group | |
612 | (forward-sexp 3) | |
613 | @result{} nil | |
614 | ||
615 | ---------- Buffer: foo ---------- | |
616 | (concat "foo " (car x) y@point{} z) | |
617 | ---------- Buffer: foo ---------- | |
618 | @end group | |
619 | @end example | |
620 | @end deffn | |
621 | ||
622 | @deffn Command backward-sexp arg | |
a890e1b0 | 623 | This function moves backward across @var{arg} balanced expressions. |
7015aca4 RS |
624 | @end deffn |
625 | ||
a890e1b0 RS |
626 | @deffn Command beginning-of-defun arg |
627 | This function moves back to the @var{arg}th beginning of a defun. If | |
628 | @var{arg} is negative, this actually moves forward, but it still moves | |
629 | to the beginning of a defun, not to the end of one. | |
630 | @end deffn | |
631 | ||
632 | @deffn Command end-of-defun arg | |
29679a81 RS |
633 | This function moves forward to the @var{arg}th end of a defun. If |
634 | @var{arg} is negative, this actually moves backward, but it still moves | |
635 | to the end of a defun, not to the beginning of one. | |
a890e1b0 RS |
636 | @end deffn |
637 | ||
638 | @defopt defun-prompt-regexp | |
639 | If non-@code{nil}, this variable holds a regular expression that | |
640 | specifies what text can appear before the open-parenthesis that starts a | |
29679a81 RS |
641 | defun. That is to say, a defun begins on a line that starts with a |
642 | match for this regular expression, followed by a character with | |
643 | open-parenthesis syntax. | |
a890e1b0 RS |
644 | @end defopt |
645 | ||
7015aca4 RS |
646 | @node Skipping Characters |
647 | @comment node-name, next, previous, up | |
648 | @subsection Skipping Characters | |
649 | @cindex skipping characters | |
650 | ||
651 | The following two functions move point over a specified set of | |
652 | characters. For example, they are often used to skip whitespace. For | |
653 | related functions, see @ref{Motion and Syntax}. | |
654 | ||
655 | @defun skip-chars-forward character-set &optional limit | |
656 | This function moves point in the current buffer forward, skipping over a | |
657 | given set of characters. It examines the character following point, | |
658 | then advances point if the character matches @var{character-set}. This | |
659 | continues until it reaches a character that does not match. The | |
660 | function returns @code{nil}. | |
661 | ||
662 | The argument @var{character-set} is like the inside of a | |
663 | @samp{[@dots{}]} in a regular expression except that @samp{]} is never | |
664 | special and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}. Thus, | |
665 | @code{"a-zA-Z"} skips over all letters, stopping before the first | |
67f09a62 | 666 | nonletter, and @code{"^a-zA-Z"} skips nonletters stopping before the |
7015aca4 RS |
667 | first letter. @xref{Regular Expressions}. |
668 | ||
669 | If @var{limit} is supplied (it must be a number or a marker), it | |
670 | specifies the maximum position in the buffer that point can be skipped | |
671 | to. Point will stop at or before @var{limit}. | |
672 | ||
673 | In the following example, point is initially located directly before the | |
674 | @samp{T}. After the form is evaluated, point is located at the end of | |
675 | that line (between the @samp{t} of @samp{hat} and the newline). The | |
676 | function skips all letters and spaces, but not newlines. | |
677 | ||
678 | @example | |
679 | @group | |
680 | ---------- Buffer: foo ---------- | |
681 | I read "@point{}The cat in the hat | |
682 | comes back" twice. | |
683 | ---------- Buffer: foo ---------- | |
684 | @end group | |
685 | ||
686 | @group | |
687 | (skip-chars-forward "a-zA-Z ") | |
688 | @result{} nil | |
689 | ||
690 | ---------- Buffer: foo ---------- | |
691 | I read "The cat in the hat@point{} | |
692 | comes back" twice. | |
693 | ---------- Buffer: foo ---------- | |
694 | @end group | |
695 | @end example | |
696 | @end defun | |
697 | ||
698 | @defun skip-chars-backward character-set &optional limit | |
699 | This function moves point backward, skipping characters that match | |
f9f59935 | 700 | @var{character-set}, until @var{limit}. It is just like |
7015aca4 RS |
701 | @code{skip-chars-forward} except for the direction of motion. |
702 | @end defun | |
703 | ||
704 | @node Excursions | |
705 | @section Excursions | |
706 | @cindex excursion | |
707 | ||
708 | It is often useful to move point ``temporarily'' within a localized | |
709 | portion of the program, or to switch buffers temporarily. This is | |
710 | called an @dfn{excursion}, and it is done with the @code{save-excursion} | |
711 | special form. This construct saves the current buffer and its values of | |
712 | point and the mark so they can be restored after the completion of the | |
713 | excursion. | |
714 | ||
715 | The forms for saving and restoring the configuration of windows are | |
716 | described elsewhere (see @ref{Window Configurations}, and @pxref{Frame | |
717 | Configurations}). | |
718 | ||
719 | @defspec save-excursion forms@dots{} | |
720 | @cindex mark excursion | |
721 | @cindex point excursion | |
722 | @cindex current buffer excursion | |
723 | The @code{save-excursion} special form saves the identity of the current | |
29679a81 RS |
724 | buffer and the values of point and the mark in it, evaluates |
725 | @var{forms}, and finally restores the buffer and its saved values of | |
726 | point and the mark. All three saved values are restored even in case of | |
727 | an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
7015aca4 RS |
728 | |
729 | The @code{save-excursion} special form is the standard way to switch | |
730 | buffers or move point within one part of a program and avoid affecting | |
a9f0a989 | 731 | the rest of the program. It is used more than 4000 times in the Lisp |
7015aca4 RS |
732 | sources of Emacs. |
733 | ||
734 | @code{save-excursion} does not save the values of point and the mark for | |
735 | other buffers, so changes in other buffers remain in effect after | |
736 | @code{save-excursion} exits. | |
737 | ||
738 | @cindex window excursions | |
739 | Likewise, @code{save-excursion} does not restore window-buffer | |
740 | correspondences altered by functions such as @code{switch-to-buffer}. | |
741 | One way to restore these correspondences, and the selected window, is to | |
742 | use @code{save-window-excursion} inside @code{save-excursion} | |
743 | (@pxref{Window Configurations}). | |
744 | ||
745 | The value returned by @code{save-excursion} is the result of the last of | |
746 | @var{forms}, or @code{nil} if no @var{forms} are given. | |
747 | ||
748 | @example | |
749 | @group | |
750 | (save-excursion | |
751 | @var{forms}) | |
752 | @equiv{} | |
753 | (let ((old-buf (current-buffer)) | |
754 | (old-pnt (point-marker)) | |
755 | (old-mark (copy-marker (mark-marker)))) | |
756 | (unwind-protect | |
757 | (progn @var{forms}) | |
758 | (set-buffer old-buf) | |
759 | (goto-char old-pnt) | |
760 | (set-marker (mark-marker) old-mark))) | |
761 | @end group | |
762 | @end example | |
763 | @end defspec | |
764 | ||
a9f0a989 RS |
765 | @strong{Warning:} Ordinary insertion of text adjacent to the saved |
766 | point value relocates the saved value, just as it relocates all markers. | |
767 | Therefore, when the saved point value is restored, it normally comes | |
768 | after the inserted text. | |
769 | ||
969fe9b5 RS |
770 | Although @code{save-excursion} saves the location of the mark, it does |
771 | not prevent functions which modify the buffer from setting | |
772 | @code{deactivate-mark}, and thus causing the deactivation of the mark | |
773 | after the command finishes. @xref{The Mark}. | |
774 | ||
7015aca4 RS |
775 | @node Narrowing |
776 | @section Narrowing | |
777 | @cindex narrowing | |
778 | @cindex restriction (in a buffer) | |
779 | @cindex accessible portion (of a buffer) | |
780 | ||
781 | @dfn{Narrowing} means limiting the text addressable by Emacs editing | |
782 | commands to a limited range of characters in a buffer. The text that | |
783 | remains addressable is called the @dfn{accessible portion} of the | |
784 | buffer. | |
785 | ||
786 | Narrowing is specified with two buffer positions which become the | |
787 | beginning and end of the accessible portion. For most editing commands | |
788 | and most Emacs primitives, these positions replace the values of the | |
789 | beginning and end of the buffer. While narrowing is in effect, no text | |
790 | outside the accessible portion is displayed, and point cannot move | |
791 | outside the accessible portion. | |
792 | ||
29679a81 | 793 | Values such as positions or line numbers, which usually count from the |
7015aca4 RS |
794 | beginning of the buffer, do so despite narrowing, but the functions |
795 | which use them refuse to operate on text that is inaccessible. | |
796 | ||
797 | The commands for saving buffers are unaffected by narrowing; they save | |
29679a81 | 798 | the entire buffer regardless of any narrowing. |
7015aca4 RS |
799 | |
800 | @deffn Command narrow-to-region start end | |
801 | This function sets the accessible portion of the current buffer to start | |
802 | at @var{start} and end at @var{end}. Both arguments should be character | |
803 | positions. | |
804 | ||
805 | In an interactive call, @var{start} and @var{end} are set to the bounds | |
806 | of the current region (point and the mark, with the smallest first). | |
807 | @end deffn | |
808 | ||
809 | @deffn Command narrow-to-page move-count | |
810 | This function sets the accessible portion of the current buffer to | |
811 | include just the current page. An optional first argument | |
812 | @var{move-count} non-@code{nil} means to move forward or backward by | |
f9f59935 | 813 | @var{move-count} pages and then narrow to one page. The variable |
7015aca4 RS |
814 | @code{page-delimiter} specifies where pages start and end |
815 | (@pxref{Standard Regexps}). | |
816 | ||
817 | In an interactive call, @var{move-count} is set to the numeric prefix | |
818 | argument. | |
819 | @end deffn | |
820 | ||
821 | @deffn Command widen | |
822 | @cindex widening | |
823 | This function cancels any narrowing in the current buffer, so that the | |
824 | entire contents are accessible. This is called @dfn{widening}. | |
825 | It is equivalent to the following expression: | |
826 | ||
827 | @example | |
828 | (narrow-to-region 1 (1+ (buffer-size))) | |
829 | @end example | |
830 | @end deffn | |
831 | ||
832 | @defspec save-restriction body@dots{} | |
833 | This special form saves the current bounds of the accessible portion, | |
834 | evaluates the @var{body} forms, and finally restores the saved bounds, | |
835 | thus restoring the same state of narrowing (or absence thereof) formerly | |
836 | in effect. The state of narrowing is restored even in the event of an | |
29679a81 RS |
837 | abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). |
838 | Therefore, this construct is a clean way to narrow a buffer temporarily. | |
7015aca4 RS |
839 | |
840 | The value returned by @code{save-restriction} is that returned by the | |
841 | last form in @var{body}, or @code{nil} if no body forms were given. | |
842 | ||
843 | @c Wordy to avoid overfull hbox. --rjc 16mar92 | |
844 | @strong{Caution:} it is easy to make a mistake when using the | |
845 | @code{save-restriction} construct. Read the entire description here | |
846 | before you try it. | |
847 | ||
848 | If @var{body} changes the current buffer, @code{save-restriction} still | |
849 | restores the restrictions on the original buffer (the buffer whose | |
f9f59935 | 850 | restrictions it saved from), but it does not restore the identity of the |
7015aca4 RS |
851 | current buffer. |
852 | ||
853 | @code{save-restriction} does @emph{not} restore point and the mark; use | |
854 | @code{save-excursion} for that. If you use both @code{save-restriction} | |
855 | and @code{save-excursion} together, @code{save-excursion} should come | |
856 | first (on the outside). Otherwise, the old point value would be | |
857 | restored with temporary narrowing still in effect. If the old point | |
858 | value were outside the limits of the temporary narrowing, this would | |
859 | fail to restore it accurately. | |
860 | ||
861 | The @code{save-restriction} special form records the values of the | |
862 | beginning and end of the accessible portion as distances from the | |
863 | beginning and end of the buffer. In other words, it records the amount | |
864 | of inaccessible text before and after the accessible portion. | |
865 | ||
866 | This method yields correct results if @var{body} does further narrowing. | |
867 | However, @code{save-restriction} can become confused if the body widens | |
a9f0a989 | 868 | and then makes changes outside the range of the saved narrowing. When |
7015aca4 RS |
869 | this is what you want to do, @code{save-restriction} is not the right |
870 | tool for the job. Here is what you must use instead: | |
871 | ||
872 | @example | |
873 | @group | |
874 | (let ((beg (point-min-marker)) | |
875 | (end (point-max-marker))) | |
876 | (unwind-protect | |
877 | (progn @var{body}) | |
878 | (save-excursion | |
879 | (set-buffer (marker-buffer beg)) | |
880 | (narrow-to-region beg end)))) | |
881 | @end group | |
882 | @end example | |
883 | ||
884 | Here is a simple example of correct use of @code{save-restriction}: | |
885 | ||
886 | @example | |
887 | @group | |
888 | ---------- Buffer: foo ---------- | |
889 | This is the contents of foo | |
890 | This is the contents of foo | |
891 | This is the contents of foo@point{} | |
892 | ---------- Buffer: foo ---------- | |
893 | @end group | |
894 | ||
895 | @group | |
896 | (save-excursion | |
897 | (save-restriction | |
898 | (goto-char 1) | |
899 | (forward-line 2) | |
900 | (narrow-to-region 1 (point)) | |
901 | (goto-char (point-min)) | |
902 | (replace-string "foo" "bar"))) | |
903 | ||
904 | ---------- Buffer: foo ---------- | |
905 | This is the contents of bar | |
906 | This is the contents of bar | |
907 | This is the contents of foo@point{} | |
908 | ---------- Buffer: foo ---------- | |
909 | @end group | |
910 | @end example | |
911 | @end defspec |