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| author | Henry Thompson <ht@markup.co.uk> |
|---|---|
| date | Thu, 16 Dec 2021 18:48:58 +0000 |
| parents | 9fae6227ede5 |
| children |
| rev | line source |
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| 428 | 1 @c -*-texinfo-*- |
| 2 @c This is part of the XEmacs Lisp Reference Manual. | |
| 444 | 3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. |
| 428 | 4 @c See the file lispref.texi for copying conditions. |
| 5 @setfilename ../../info/positions.info | |
| 6 @node Positions, Markers, Consoles and Devices, Top | |
| 7 @chapter Positions | |
| 8 @cindex position (in buffer) | |
| 9 | |
| 10 A @dfn{position} is the index of a character in the text of a buffer. | |
| 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 | |
| 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 | |
| 15 after that position. | |
| 16 | |
| 17 Positions are usually represented as integers starting from 1, but can | |
| 18 also be represented as @dfn{markers}---special objects that relocate | |
| 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 | |
|
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29 @node Point, Motion, Positions, Positions |
| 428 | 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 | |
| 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. | |
| 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 &optional buffer | |
| 60 @cindex current buffer position | |
| 61 This function returns the value of point in @var{buffer}, as an integer. | |
| 62 @var{buffer} defaults to the current buffer if omitted. | |
| 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 &optional buffer | |
| 74 This function returns the minimum accessible value of point in | |
| 75 @var{buffer}. This is normally 1, but if narrowing is in effect, it is | |
| 76 the position of the start of the region that you narrowed to. | |
| 77 (@xref{Narrowing}.) @var{buffer} defaults to the current buffer if | |
| 78 omitted. | |
| 79 @end defun | |
| 80 | |
| 81 @defun point-max &optional buffer | |
| 82 This function returns the maximum accessible value of point in | |
| 83 @var{buffer}. This is @code{(1+ (buffer-size buffer))}, unless | |
| 84 narrowing is in effect, in which case it is the position of the end of | |
| 85 the region that you narrowed to. (@pxref{Narrowing}). @var{buffer} | |
| 86 defaults to the current buffer if omitted. | |
| 87 @end defun | |
| 88 | |
| 89 @defun buffer-end flag &optional buffer | |
| 90 This function returns @code{(point-min buffer)} if @var{flag} is less | |
| 91 than 1, @code{(point-max buffer)} otherwise. The argument @var{flag} | |
| 92 must be a number. @var{buffer} defaults to the current buffer if | |
| 93 omitted. | |
| 94 @end defun | |
| 95 | |
| 96 @defun buffer-size &optional buffer | |
| 97 This function returns the total number of characters in @var{buffer}. | |
| 98 In the absence of any narrowing (@pxref{Narrowing}), @code{point-max} | |
| 99 returns a value one larger than this. @var{buffer} defaults to the | |
| 100 current buffer if omitted. | |
| 101 | |
| 102 @example | |
| 103 @group | |
| 104 (buffer-size) | |
| 105 @result{} 35 | |
| 106 @end group | |
| 107 @group | |
| 108 (point-max) | |
| 109 @result{} 36 | |
| 110 @end group | |
| 111 @end example | |
| 112 @end defun | |
| 113 | |
| 114 @defvar buffer-saved-size | |
| 115 The value of this buffer-local variable is the former length of the | |
| 116 current buffer, as of the last time it was read in, saved or auto-saved. | |
| 117 @end defvar | |
| 118 | |
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119 @node Motion, Excursions, Point, Positions |
| 428 | 120 @section Motion |
| 121 | |
| 122 Motion functions change the value of point, either relative to the | |
| 123 current value of point, relative to the beginning or end of the buffer, | |
| 124 or relative to the edges of the selected window. @xref{Point}. | |
| 125 | |
| 126 @menu | |
| 127 * Character Motion:: Moving in terms of characters. | |
| 128 * Word Motion:: Moving in terms of words. | |
| 129 * Buffer End Motion:: Moving to the beginning or end of the buffer. | |
| 130 * Text Lines:: Moving in terms of lines of text. | |
| 131 * Screen Lines:: Moving in terms of lines as displayed. | |
| 132 * List Motion:: Moving by parsing lists and sexps. | |
| 133 * Skipping Characters:: Skipping characters belonging to a certain set. | |
| 134 @end menu | |
| 135 | |
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136 @node Character Motion, Word Motion, Motion, Motion |
| 428 | 137 @subsection Motion by Characters |
| 138 | |
| 139 These functions move point based on a count of characters. | |
| 140 @code{goto-char} is the fundamental primitive; the other functions use | |
| 141 that. | |
| 142 | |
| 143 @deffn Command goto-char position &optional buffer | |
| 144 This function sets point in @code{buffer} to the value @var{position}. | |
| 145 If @var{position} is less than 1, it moves point to the beginning of the | |
| 146 buffer. If @var{position} is greater than the length of the buffer, it | |
| 147 moves point to the end. @var{buffer} defaults to the current buffer if | |
| 148 omitted. | |
| 149 | |
| 150 If narrowing is in effect, @var{position} still counts from the | |
| 151 beginning of the buffer, but point cannot go outside the accessible | |
| 152 portion. If @var{position} is out of range, @code{goto-char} moves | |
| 153 point to the beginning or the end of the accessible portion. | |
| 154 | |
| 155 When this function is called interactively, @var{position} is the | |
| 156 numeric prefix argument, if provided; otherwise it is read from the | |
| 157 minibuffer. | |
| 158 | |
| 159 @code{goto-char} returns @var{position}. | |
| 160 @end deffn | |
| 161 | |
| 162 @deffn Command forward-char &optional count buffer | |
| 163 @c @kindex beginning-of-buffer | |
| 164 @c @kindex end-of-buffer | |
| 165 This function moves point @var{count} characters forward, towards the | |
| 166 end of the buffer (or backward, towards the beginning 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}. @var{buffer} | |
| 171 defaults to the current buffer if omitted. | |
| 172 | |
| 173 | |
| 174 In an interactive call, @var{count} is the numeric prefix argument. | |
| 175 @end deffn | |
| 176 | |
| 177 @deffn Command backward-char &optional count buffer | |
| 178 This function moves point @var{count} characters backward, towards the | |
| 179 beginning of the buffer (or forward, towards the end of the buffer, if | |
| 180 @var{count} is negative). If the function attempts to move point past | |
| 181 the beginning or end of the buffer (or the limits of the accessible | |
| 182 portion, when narrowing is in effect), an error is signaled with error | |
| 183 code @code{beginning-of-buffer} or @code{end-of-buffer}. @var{buffer} | |
| 184 defaults to the current buffer if omitted. | |
| 185 | |
| 186 | |
| 187 In an interactive call, @var{count} is the numeric prefix argument. | |
| 188 @end deffn | |
| 189 | |
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190 @node Word Motion, Buffer End Motion, Character Motion, Motion |
| 428 | 191 @subsection Motion by Words |
| 192 | |
| 193 These functions for parsing words use the syntax table to decide | |
| 194 whether a given character is part of a word. @xref{Syntax Tables}. | |
| 195 | |
| 446 | 196 @deffn Command forward-word &optional count buffer |
| 428 | 197 This function moves point forward @var{count} words (or backward if |
| 198 @var{count} is negative). Normally it returns @code{t}. If this motion | |
| 199 encounters the beginning or end of the buffer, or the limits of the | |
| 200 accessible portion when narrowing is in effect, point stops there and | |
| 446 | 201 the value is @code{nil}. |
| 202 | |
| 203 @var{count} defaults to @code{1} and @var{buffer} defaults to the | |
| 204 current buffer. | |
| 428 | 205 |
| 206 In an interactive call, @var{count} is set to the numeric prefix | |
| 207 argument. | |
| 208 @end deffn | |
| 209 | |
| 446 | 210 @deffn Command backward-word &optional count buffer |
| 428 | 211 This function is just like @code{forward-word}, except that it moves |
| 212 backward until encountering the front of a word, rather than forward. | |
| 213 @var{buffer} defaults to the current buffer if omitted. | |
| 214 | |
| 215 In an interactive call, @var{count} is set to the numeric prefix | |
| 216 argument. | |
| 217 @end deffn | |
| 218 | |
| 219 @defvar words-include-escapes | |
| 220 @c Emacs 19 feature | |
| 221 This variable affects the behavior of @code{forward-word} and everything | |
| 222 that uses it. If it is non-@code{nil}, then characters in the | |
| 223 ``escape'' and ``character quote'' syntax classes count as part of | |
| 224 words. Otherwise, they do not. | |
| 225 @end defvar | |
| 226 | |
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227 @node Buffer End Motion, Text Lines, Word Motion, Motion |
| 428 | 228 @subsection Motion to an End of the Buffer |
| 229 | |
| 230 To move point to the beginning of the buffer, write: | |
| 231 | |
| 232 @example | |
| 233 @group | |
| 234 (goto-char (point-min)) | |
| 235 @end group | |
| 236 @end example | |
| 237 | |
| 238 @noindent | |
| 239 Likewise, to move to the end of the buffer, use: | |
| 240 | |
| 241 @example | |
| 242 @group | |
| 243 (goto-char (point-max)) | |
| 244 @end group | |
| 245 @end example | |
| 246 | |
| 247 Here are two commands that users use to do these things. They are | |
| 248 documented here to warn you not to use them in Lisp programs, because | |
| 249 they set the mark and display messages in the echo area. | |
| 250 | |
| 444 | 251 @deffn Command beginning-of-buffer &optional count |
| 428 | 252 This function moves point to the beginning of the buffer (or the limits |
| 253 of the accessible portion, when narrowing is in effect), setting the | |
| 444 | 254 mark at the previous position. If @var{count} is non-@code{nil}, then it |
| 255 puts point @var{count} tenths of the way from the beginning of the buffer. | |
| 428 | 256 |
| 444 | 257 In an interactive call, @var{count} is the numeric prefix argument, |
| 258 if provided; otherwise @var{count} defaults to @code{nil}. | |
| 428 | 259 |
| 260 Don't use this function in Lisp programs! | |
| 261 @end deffn | |
| 262 | |
| 444 | 263 @deffn Command end-of-buffer &optional count |
| 428 | 264 This function moves point to the end of the buffer (or the limits of |
| 265 the accessible portion, when narrowing is in effect), setting the mark | |
| 444 | 266 at the previous position. If @var{count} is non-@code{nil}, then it puts |
| 267 point @var{count} tenths of the way from the end of the buffer. | |
| 428 | 268 |
| 444 | 269 In an interactive call, @var{count} is the numeric prefix argument, |
| 270 if provided; otherwise @var{count} defaults to @code{nil}. | |
| 428 | 271 |
| 272 Don't use this function in Lisp programs! | |
| 273 @end deffn | |
| 274 | |
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275 @node Text Lines, Screen Lines, Buffer End Motion, Motion |
| 428 | 276 @subsection Motion by Text Lines |
| 277 @cindex lines | |
| 278 | |
| 279 Text lines are portions of the buffer delimited by newline characters, | |
| 280 which are regarded as part of the previous line. The first text line | |
| 281 begins at the beginning of the buffer, and the last text line ends at | |
| 282 the end of the buffer whether or not the last character is a newline. | |
| 283 The division of the buffer into text lines is not affected by the width | |
| 284 of the window, by line continuation in display, or by how tabs and | |
| 285 control characters are displayed. | |
| 286 | |
| 287 @deffn Command goto-line line | |
| 288 This function moves point to the front of the @var{line}th line, | |
| 289 counting from line 1 at beginning of the buffer. If @var{line} is less | |
| 290 than 1, it moves point to the beginning of the buffer. If @var{line} is | |
| 291 greater than the number of lines in the buffer, it moves point to the | |
| 292 end of the buffer---that is, the @emph{end of the last line} of the | |
| 293 buffer. This is the only case in which @code{goto-line} does not | |
| 294 necessarily move to the beginning of a line. | |
| 295 | |
| 296 If narrowing is in effect, then @var{line} still counts from the | |
| 297 beginning of the buffer, but point cannot go outside the accessible | |
| 298 portion. So @code{goto-line} moves point to the beginning or end of the | |
| 299 accessible portion, if the line number specifies an inaccessible | |
| 300 position. | |
| 301 | |
| 302 The return value of @code{goto-line} is the difference between | |
| 303 @var{line} and the line number of the line to which point actually was | |
| 304 able to move (in the full buffer, before taking account of narrowing). | |
| 305 Thus, the value is positive if the scan encounters the real end of the | |
| 306 buffer. The value is zero if scan encounters the end of the accessible | |
| 307 portion but not the real end of the buffer. | |
| 308 | |
| 309 In an interactive call, @var{line} is the numeric prefix argument if | |
| 310 one has been provided. Otherwise @var{line} is read in the minibuffer. | |
| 311 @end deffn | |
| 312 | |
| 313 @deffn Command beginning-of-line &optional count buffer | |
| 314 This function moves point to the beginning of the current line. With an | |
| 315 argument @var{count} not @code{nil} or 1, it moves forward | |
| 316 @var{count}@minus{}1 lines and then to the beginning of the line. | |
| 317 @var{buffer} defaults to the current buffer if omitted. | |
| 318 | |
| 319 If this function reaches the end of the buffer (or of the accessible | |
| 320 portion, if narrowing is in effect), it positions point there. No error | |
| 321 is signaled. | |
| 322 @end deffn | |
| 323 | |
| 324 @deffn Command end-of-line &optional count buffer | |
| 325 This function moves point to the end of the current line. With an | |
| 326 argument @var{count} not @code{nil} or 1, it moves forward | |
| 327 @var{count}@minus{}1 lines and then to the end of the line. | |
| 328 @var{buffer} defaults to the current buffer if omitted. | |
| 329 | |
| 330 If this function reaches the end of the buffer (or of the accessible | |
| 331 portion, if narrowing is in effect), it positions point there. No error | |
| 332 is signaled. | |
| 333 @end deffn | |
| 334 | |
| 335 @deffn Command forward-line &optional count buffer | |
| 336 @cindex beginning of line | |
| 337 This function moves point forward @var{count} lines, to the beginning of | |
| 338 the line. If @var{count} is negative, it moves point | |
| 339 @minus{}@var{count} lines backward, to the beginning of a line. If | |
| 340 @var{count} is zero, it moves point to the beginning of the current | |
| 341 line. @var{buffer} defaults to the current buffer if omitted. | |
| 342 | |
| 343 If @code{forward-line} encounters the beginning or end of the buffer (or | |
| 344 of the accessible portion) before finding that many lines, it sets point | |
| 345 there. No error is signaled. | |
| 346 | |
| 347 @code{forward-line} returns the difference between @var{count} and the | |
| 348 number of lines actually moved. If you attempt to move down five lines | |
| 349 from the beginning of a buffer that has only three lines, point stops at | |
| 350 the end of the last line, and the value will be 2. | |
| 351 | |
| 352 In an interactive call, @var{count} is the numeric prefix argument. | |
| 353 @end deffn | |
| 354 | |
| 444 | 355 @defun count-lines start end &optional ignore-invisible-lines-flag |
| 428 | 356 @cindex lines in region |
| 357 This function returns the number of lines between the positions | |
| 358 @var{start} and @var{end} in the current buffer. If @var{start} and | |
| 359 @var{end} are equal, then it returns 0. Otherwise it returns at least | |
| 360 1, even if @var{start} and @var{end} are on the same line. This is | |
| 361 because the text between them, considered in isolation, must contain at | |
| 362 least one line unless it is empty. | |
| 363 | |
| 444 | 364 With optional @var{ignore-invisible-lines-flag} non-@code{nil}, lines |
| 365 collapsed with selective-display are excluded from the line count. | |
| 366 | |
| 2214 | 367 @strong{N.B.} The expression to return the current line number is not |
| 444 | 368 obvious: |
| 369 | |
| 370 @example | |
| 371 (1+ (count-lines 1 (point-at-bol))) | |
| 372 @end example | |
| 373 | |
| 428 | 374 Here is an example of using @code{count-lines}: |
| 375 | |
| 376 @example | |
| 377 @group | |
| 378 (defun current-line () | |
| 379 "Return the vertical position of point@dots{}" | |
| 380 (+ (count-lines (window-start) (point)) | |
| 381 (if (= (current-column) 0) 1 0) | |
| 382 -1)) | |
| 383 @end group | |
| 384 @end example | |
| 385 @end defun | |
| 386 | |
| 387 @ignore | |
| 388 @c ================ | |
| 389 The @code{previous-line} and @code{next-line} commands are functions | |
| 390 that should not be used in programs. They are for users and are | |
| 391 mentioned here only for completeness. | |
| 392 | |
| 393 @deffn Command previous-line count | |
| 394 @cindex goal column | |
| 395 This function moves point up @var{count} lines (down if @var{count} | |
| 396 is negative). In moving, it attempts to keep point in the ``goal column'' | |
| 397 (normally the same column that it was at the beginning of the move). | |
| 398 | |
| 399 If there is no character in the target line exactly under the current | |
| 400 column, point is positioned after the character in that line which | |
| 401 spans this column, or at the end of the line if it is not long enough. | |
| 402 | |
| 403 If it attempts to move beyond the top or bottom of the buffer (or clipped | |
| 404 region), then point is positioned in the goal column in the top or | |
| 405 bottom line. No error is signaled. | |
| 406 | |
| 407 In an interactive call, @var{count} will be the numeric | |
| 408 prefix argument. | |
| 409 | |
| 410 The command @code{set-goal-column} can be used to create a semipermanent | |
| 411 goal column to which this command always moves. Then it does not try to | |
| 412 move vertically. | |
| 413 | |
| 414 If you are thinking of using this in a Lisp program, consider using | |
| 415 @code{forward-line} with a negative argument instead. It is usually easier | |
| 416 to use and more reliable (no dependence on goal column, etc.). | |
| 417 @end deffn | |
| 418 | |
| 419 @deffn Command next-line count | |
| 420 This function moves point down @var{count} lines (up if @var{count} | |
| 421 is negative). In moving, it attempts to keep point in the ``goal column'' | |
| 422 (normally the same column that it was at the beginning of the move). | |
| 423 | |
| 424 If there is no character in the target line exactly under the current | |
| 425 column, point is positioned after the character in that line which | |
| 426 spans this column, or at the end of the line if it is not long enough. | |
| 427 | |
| 428 If it attempts to move beyond the top or bottom of the buffer (or clipped | |
| 429 region), then point is positioned in the goal column in the top or | |
| 430 bottom line. No error is signaled. | |
| 431 | |
| 432 In the case where the @var{count} is 1, and point is on the last | |
| 433 line of the buffer (or clipped region), a new empty line is inserted at the | |
| 434 end of the buffer (or clipped region) and point moved there. | |
| 435 | |
| 436 In an interactive call, @var{count} will be the numeric | |
| 437 prefix argument. | |
| 438 | |
| 439 The command @code{set-goal-column} can be used to create a semipermanent | |
| 440 goal column to which this command always moves. Then it does not try to | |
| 441 move vertically. | |
| 442 | |
| 443 If you are thinking of using this in a Lisp program, consider using | |
| 444 @code{forward-line} instead. It is usually easier | |
| 445 to use and more reliable (no dependence on goal column, etc.). | |
| 446 @end deffn | |
| 447 | |
| 448 @c ================ | |
| 449 @end ignore | |
| 450 | |
| 451 Also see the functions @code{bolp} and @code{eolp} in @ref{Near Point}. | |
| 452 These functions do not move point, but test whether it is already at the | |
| 453 beginning or end of a line. | |
| 454 | |
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455 @node Screen Lines, List Motion, Text Lines, Motion |
| 428 | 456 @subsection Motion by Screen Lines |
| 457 | |
| 458 The line functions in the previous section count text lines, delimited | |
| 459 only by newline characters. By contrast, these functions count screen | |
| 460 lines, which are defined by the way the text appears on the screen. A | |
| 461 text line is a single screen line if it is short enough to fit the width | |
| 462 of the selected window, but otherwise it may occupy several screen | |
| 463 lines. | |
| 464 | |
| 465 In some cases, text lines are truncated on the screen rather than | |
| 466 continued onto additional screen lines. In these cases, | |
| 467 @code{vertical-motion} moves point much like @code{forward-line}. | |
| 468 @xref{Truncation}. | |
| 469 | |
| 470 Because the width of a given string depends on the flags that control | |
| 471 the appearance of certain characters, @code{vertical-motion} behaves | |
| 472 differently, for a given piece of text, depending on the buffer it is | |
| 473 in, and even on the selected window (because the width, the truncation | |
| 474 flag, and display table may vary between windows). @xref{Usual | |
| 475 Display}. | |
| 476 | |
| 477 These functions scan text to determine where screen lines break, and | |
| 478 thus take time proportional to the distance scanned. If you intend to | |
| 479 use them heavily, Emacs provides caches which may improve the | |
| 480 performance of your code. @xref{Text Lines, cache-long-line-scans}. | |
| 481 | |
| 482 | |
| 483 @defun vertical-motion count &optional window pixels | |
| 484 This function moves point to the start of the frame line @var{count} | |
| 485 frame lines down from the frame line containing point. If @var{count} | |
| 486 is negative, it moves up instead. The optional second argument | |
| 444 | 487 @var{window} may be used to specify a window other than the |
| 428 | 488 selected window in which to perform the motion. |
| 489 | |
| 490 Normally, @code{vertical-motion} returns the number of lines moved. The | |
| 491 value may be less in absolute value than @var{count} if the beginning or | |
| 492 end of the buffer was reached. If the optional third argument, | |
| 493 @var{pixels} is non-@code{nil}, the vertical pixel height of the motion | |
| 494 which took place is returned instead of the actual number of lines | |
| 495 moved. A motion of zero lines returns the height of the current line. | |
| 496 | |
| 497 Note that @code{vertical-motion} sets @var{window}'s buffer's point, not | |
| 498 @var{window}'s point. (This differs from FSF Emacs, which buggily always | |
| 499 sets current buffer's point, regardless of @var{window}.) | |
| 500 @end defun | |
| 501 | |
| 502 @defun vertical-motion-pixels count &optional window how | |
| 503 This function moves point to the start of the frame line @var{pixels} | |
| 504 vertical pixels down from the frame line containing point, or up if | |
| 505 @var{pixels} is negative. The optional second argument @var{window} is | |
| 506 the window to move in, and defaults to the selected window. The | |
| 507 optional third argument @var{how} specifies the stopping condition. A | |
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508 negative fixnum indicates that the motion should be no more |
| 428 | 509 than @var{pixels}. A positive value indicates that the |
| 510 motion should be at least @var{pixels}. Any other value indicates | |
| 511 that the motion should be as close as possible to @var{pixels}. | |
| 512 @end defun | |
| 513 | |
| 514 @deffn Command move-to-window-line count &optional window | |
| 515 This function moves point with respect to the text currently displayed | |
| 516 in @var{window}, which defaults to the selected window. It moves point | |
| 517 to the beginning of the screen line @var{count} screen lines from the | |
| 518 top of the window. If @var{count} is negative, that specifies a | |
| 519 position @w{@minus{}@var{count}} lines from the bottom (or the last line | |
| 520 of the buffer, if the buffer ends above the specified screen position). | |
| 521 | |
| 522 If @var{count} is @code{nil}, then point moves to the beginning of the | |
| 523 line in the middle of the window. If the absolute value of @var{count} | |
| 524 is greater than the size of the window, then point moves to the place | |
| 525 that would appear on that screen line if the window were tall enough. | |
| 526 This will probably cause the next redisplay to scroll to bring that | |
| 527 location onto the screen. | |
| 528 | |
| 529 In an interactive call, @var{count} is the numeric prefix argument. | |
| 530 | |
| 531 The value returned is the window line number point has moved to, with | |
| 532 the top line in the window numbered 0. | |
| 533 @end deffn | |
| 534 | |
| 535 @ignore Not in XEmacs | |
| 536 @defun compute-motion from frompos to topos width offsets window | |
| 537 This function scans the current buffer, calculating screen positions. | |
| 538 It scans the buffer forward from position @var{from}, assuming that is | |
| 539 at screen coordinates @var{frompos}, to position @var{to} or coordinates | |
| 540 @var{topos}, whichever comes first. It returns the ending buffer | |
| 541 position and screen coordinates. | |
| 542 | |
| 543 The coordinate arguments @var{frompos} and @var{topos} are cons cells of | |
| 544 the form @code{(@var{hpos} . @var{vpos})}. | |
| 545 | |
| 546 The argument @var{width} is the number of columns available to display | |
| 547 text; this affects handling of continuation lines. Use the value | |
| 548 returned by @code{window-width} for the window of your choice; | |
| 549 normally, use @code{(window-width @var{window})}. | |
| 550 | |
| 551 The argument @var{offsets} is either @code{nil} or a cons cell of the | |
| 552 form @code{(@var{hscroll} . @var{tab-offset})}. Here @var{hscroll} is | |
| 553 the number of columns not being displayed at the left margin; most | |
| 554 callers get this from @code{window-hscroll}. Meanwhile, | |
| 555 @var{tab-offset} is the offset between column numbers on the screen and | |
| 556 column numbers in the buffer. This can be nonzero in a continuation | |
| 557 line, when the previous screen lines' widths do not add up to a multiple | |
| 558 of @code{tab-width}. It is always zero in a non-continuation line. | |
| 559 | |
| 560 The window @var{window} serves only to specify which display table to | |
| 561 use. @code{compute-motion} always operates on the current buffer, | |
| 562 regardless of what buffer is displayed in @var{window}. | |
| 563 | |
| 564 The return value is a list of five elements: | |
| 565 | |
| 566 @example | |
| 567 (@var{pos} @var{vpos} @var{hpos} @var{prevhpos} @var{contin}) | |
| 568 @end example | |
| 569 | |
| 570 @noindent | |
| 571 Here @var{pos} is the buffer position where the scan stopped, @var{vpos} | |
| 572 is the vertical screen position, and @var{hpos} is the horizontal screen | |
| 573 position. | |
| 574 | |
| 575 The result @var{prevhpos} is the horizontal position one character back | |
| 576 from @var{pos}. The result @var{contin} is @code{t} if the last line | |
| 577 was continued after (or within) the previous character. | |
| 578 | |
| 579 For example, to find the buffer position of column @var{col} of line | |
| 580 @var{line} of a certain window, pass the window's display start location | |
| 581 as @var{from} and the window's upper-left coordinates as @var{frompos}. | |
| 582 Pass the buffer's @code{(point-max)} as @var{to}, to limit the scan to | |
| 583 the end of the accessible portion of the buffer, and pass @var{line} and | |
| 584 @var{col} as @var{topos}. Here's a function that does this: | |
| 585 | |
| 586 @example | |
| 587 (defun coordinates-of-position (col line) | |
| 588 (car (compute-motion (window-start) | |
| 589 '(0 . 0) | |
| 590 (point-max) | |
| 591 (cons col line) | |
| 592 (window-width) | |
| 593 (cons (window-hscroll) 0) | |
| 594 (selected-window)))) | |
| 595 @end example | |
| 596 | |
| 597 When you use @code{compute-motion} for the minibuffer, you need to use | |
| 598 @code{minibuffer-prompt-width} to get the horizontal position of the | |
| 599 beginning of the first screen line. @xref{Minibuffer Misc}. | |
| 600 @end defun | |
| 601 @end ignore | |
| 602 | |
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603 @node List Motion, Skipping Characters, Screen Lines, Motion |
| 444 | 604 @subsection Moving over Balanced Expressions |
| 428 | 605 @cindex sexp motion |
| 606 @cindex Lisp expression motion | |
| 607 @cindex list motion | |
| 608 | |
| 609 Here are several functions concerned with balanced-parenthesis | |
| 610 expressions (also called @dfn{sexps} in connection with moving across | |
| 611 them in XEmacs). The syntax table controls how these functions interpret | |
| 612 various characters; see @ref{Syntax Tables}. @xref{Parsing | |
| 613 Expressions}, for lower-level primitives for scanning sexps or parts of | |
| 446 | 614 sexps. For user-level commands, see @ref{Lists and Sexps,,, xemacs, XEmacs |
| 428 | 615 Reference Manual}. |
| 616 | |
| 617 @deffn Command forward-list &optional arg | |
| 618 This function moves forward across @var{arg} balanced groups of | |
| 619 parentheses. (Other syntactic entities such as words or paired string | |
| 620 quotes are ignored.) @var{arg} defaults to 1 if omitted. If @var{arg} | |
| 621 is negative, move backward across that many groups of parentheses. | |
| 622 @end deffn | |
| 623 | |
| 444 | 624 @deffn Command backward-list &optional count |
| 625 This function moves backward across @var{count} balanced groups of | |
| 428 | 626 parentheses. (Other syntactic entities such as words or paired string |
| 444 | 627 quotes are ignored.) @var{count} defaults to 1 if omitted. If |
| 628 @var{count} is negative, move forward across that many groups of | |
| 629 parentheses. | |
| 428 | 630 @end deffn |
| 631 | |
| 444 | 632 @deffn Command up-list &optional count |
| 633 This function moves forward out of @var{count} levels of parentheses. | |
| 428 | 634 A negative argument means move backward but still to a less deep spot. |
| 635 @end deffn | |
| 636 | |
| 444 | 637 @deffn Command down-list &optional count |
| 638 This function moves forward into @var{count} levels of parentheses. | |
| 639 A negative argument means move backward but still go deeper in | |
| 640 parentheses (@minus{}@var{count} levels). | |
| 428 | 641 @end deffn |
| 642 | |
| 444 | 643 @deffn Command forward-sexp &optional count |
| 644 This function moves forward across @var{count} balanced expressions. | |
| 428 | 645 Balanced expressions include both those delimited by parentheses and |
| 444 | 646 other kinds, such as words and string constants. @var{count} defaults to |
| 647 1 if omitted. If @var{count} is negative, move backward across that many | |
| 428 | 648 balanced expressions. For example, |
| 649 | |
| 650 @example | |
| 651 @group | |
| 652 ---------- Buffer: foo ---------- | |
| 653 (concat@point{} "foo " (car x) y z) | |
| 654 ---------- Buffer: foo ---------- | |
| 655 @end group | |
| 656 | |
| 657 @group | |
| 658 (forward-sexp 3) | |
| 659 @result{} nil | |
| 660 | |
| 661 ---------- Buffer: foo ---------- | |
| 662 (concat "foo " (car x) y@point{} z) | |
| 663 ---------- Buffer: foo ---------- | |
| 664 @end group | |
| 665 @end example | |
| 666 @end deffn | |
| 667 | |
| 444 | 668 @deffn Command backward-sexp &optional count |
| 669 This function moves backward across @var{count} balanced expressions. | |
| 670 @var{count} defaults to 1 if omitted. If @var{count} is negative, move | |
| 428 | 671 forward across that many balanced expressions. |
| 672 @end deffn | |
| 673 | |
| 444 | 674 @deffn Command beginning-of-defun &optional count |
| 675 This function moves back to the @var{count}th beginning of a defun. | |
| 676 If @var{count} is negative, this actually moves forward, but it still | |
| 677 moves to the beginning of a defun, not to the end of one. @var{count} | |
| 678 defaults to 1 if omitted. | |
| 428 | 679 @end deffn |
| 680 | |
| 444 | 681 @deffn Command end-of-defun &optional count |
| 682 This function moves forward to the @var{count}th end of a defun. | |
| 683 If @var{count} is negative, this actually moves backward, but it still | |
| 684 moves to the end of a defun, not to the beginning of one. @var{count} | |
| 685 defaults to 1 if omitted. | |
| 428 | 686 @end deffn |
| 687 | |
| 688 @defopt defun-prompt-regexp | |
| 689 If non-@code{nil}, this variable holds a regular expression that | |
| 690 specifies what text can appear before the open-parenthesis that starts a | |
| 691 defun. That is to say, a defun begins on a line that starts with a | |
| 692 match for this regular expression, followed by a character with | |
| 693 open-parenthesis syntax. | |
| 694 @end defopt | |
| 695 | |
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696 @node Skipping Characters, , List Motion, Motion |
| 428 | 697 @subsection Skipping Characters |
| 698 @cindex skipping characters | |
| 699 | |
| 700 The following two functions move point over a specified set of | |
| 701 characters. For example, they are often used to skip whitespace. For | |
| 702 related functions, see @ref{Motion and Syntax}. | |
| 703 | |
| 704 @defun skip-chars-forward character-set &optional limit buffer | |
| 705 This function moves point in @var{buffer} forward, skipping over a | |
| 706 given set of characters. It examines the character following point, | |
| 707 then advances point if the character matches @var{character-set}. This | |
| 708 continues until it reaches a character that does not match. The | |
| 709 function returns @code{nil}. @var{buffer} defaults to the current | |
| 710 buffer if omitted. | |
| 711 | |
| 712 The argument @var{character-set} is like the inside of a | |
| 713 @samp{[@dots{}]} in a regular expression except that @samp{]} is never | |
| 714 special and @samp{\} quotes @samp{^}, @samp{-} or @samp{\}. Thus, | |
| 715 @code{"a-zA-Z"} skips over all letters, stopping before the first | |
| 716 non-letter, and @code{"^a-zA-Z}" skips non-letters stopping before the | |
| 717 first letter. @xref{Regular Expressions}. | |
| 718 | |
| 719 If @var{limit} is supplied (it must be a number or a marker), it | |
| 720 specifies the maximum position in the buffer that point can be skipped | |
| 721 to. Point will stop at or before @var{limit}. | |
| 722 | |
| 723 In the following example, point is initially located directly before the | |
| 724 @samp{T}. After the form is evaluated, point is located at the end of | |
| 725 that line (between the @samp{t} of @samp{hat} and the newline). The | |
| 726 function skips all letters and spaces, but not newlines. | |
| 727 | |
| 728 @example | |
| 729 @group | |
| 730 ---------- Buffer: foo ---------- | |
| 731 I read "@point{}The cat in the hat | |
| 732 comes back" twice. | |
| 733 ---------- Buffer: foo ---------- | |
| 734 @end group | |
| 735 | |
| 736 @group | |
| 737 (skip-chars-forward "a-zA-Z ") | |
| 738 @result{} nil | |
| 739 | |
| 740 ---------- Buffer: foo ---------- | |
| 741 I read "The cat in the hat@point{} | |
| 742 comes back" twice. | |
| 743 ---------- Buffer: foo ---------- | |
| 744 @end group | |
| 745 @end example | |
| 746 @end defun | |
| 747 | |
| 748 @defun skip-chars-backward character-set &optional limit buffer | |
| 749 This function moves point backward, skipping characters that match | |
| 750 @var{character-set}, until @var{limit}. It just like | |
| 751 @code{skip-chars-forward} except for the direction of motion. | |
| 752 @end defun | |
| 753 | |
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754 @node Excursions, Narrowing, Motion, Positions |
| 428 | 755 @section Excursions |
| 756 @cindex excursion | |
| 757 | |
| 758 It is often useful to move point ``temporarily'' within a localized | |
| 759 portion of the program, or to switch buffers temporarily. This is | |
| 760 called an @dfn{excursion}, and it is done with the @code{save-excursion} | |
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761 special operator. This construct saves the current buffer and its values of |
| 428 | 762 point and the mark so they can be restored after the completion of the |
| 763 excursion. | |
| 764 | |
| 765 The forms for saving and restoring the configuration of windows are | |
| 766 described elsewhere (see @ref{Window Configurations} and @pxref{Frame | |
| 767 Configurations}). | |
| 768 | |
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769 @deffn {Special Operator} save-excursion forms@dots{} |
| 428 | 770 @cindex mark excursion |
| 771 @cindex point excursion | |
| 772 @cindex current buffer excursion | |
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773 The @code{save-excursion} special operator saves the identity of the current |
| 428 | 774 buffer and the values of point and the mark in it, evaluates |
| 775 @var{forms}, and finally restores the buffer and its saved values of | |
| 776 point and the mark. All three saved values are restored even in case of | |
| 777 an abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
| 778 | |
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779 The @code{save-excursion} special operator is the standard way to switch |
| 428 | 780 buffers or move point within one part of a program and avoid affecting |
| 781 the rest of the program. It is used more than 500 times in the Lisp | |
| 782 sources of XEmacs. | |
| 783 | |
| 784 @code{save-excursion} does not save the values of point and the mark for | |
| 785 other buffers, so changes in other buffers remain in effect after | |
| 786 @code{save-excursion} exits. | |
| 787 | |
| 788 @cindex window excursions | |
| 789 Likewise, @code{save-excursion} does not restore window-buffer | |
| 790 correspondences altered by functions such as @code{switch-to-buffer}. | |
| 791 One way to restore these correspondences, and the selected window, is to | |
| 792 use @code{save-window-excursion} inside @code{save-excursion} | |
| 793 (@pxref{Window Configurations}). | |
| 794 | |
| 795 The value returned by @code{save-excursion} is the result of the last of | |
| 796 @var{forms}, or @code{nil} if no @var{forms} are given. | |
| 797 | |
| 798 @example | |
| 799 @group | |
| 800 (save-excursion | |
| 801 @var{forms}) | |
| 802 @equiv{} | |
| 803 (let ((old-buf (current-buffer)) | |
| 804 (old-pnt (point-marker)) | |
| 805 (old-mark (copy-marker (mark-marker)))) | |
| 806 (unwind-protect | |
| 807 (progn @var{forms}) | |
| 808 (set-buffer old-buf) | |
| 809 (goto-char old-pnt) | |
| 810 (set-marker (mark-marker) old-mark))) | |
| 811 @end group | |
| 812 @end example | |
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813 @end deffn |
| 428 | 814 |
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815 @deffn {Special Operator} save-current-buffer forms@dots{} |
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816 This special operator is similar to @code{save-excursion} but it only |
| 428 | 817 saves and restores the current buffer. Beginning with XEmacs 20.3, |
| 818 @code{save-current-buffer} is a primitive. | |
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819 @end deffn |
| 428 | 820 |
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821 @defmac with-current-buffer buffer forms@dots{} |
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822 This macro evaluates @var{forms} with @var{buffer} as the current |
| 428 | 823 buffer. It returns the value of the last form. |
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824 @end defmac |
| 428 | 825 |
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826 @defmac with-temp-file filename forms@dots{} |
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827 This macro creates a new buffer, evaluates @var{forms} there, and |
| 444 | 828 writes the buffer to @var{filename}. It returns the value of the last form |
| 428 | 829 evaluated. |
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830 @end defmac |
| 428 | 831 |
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832 @defmac save-selected-window forms@dots{} |
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833 This macro is similar to @code{save-excursion} but it saves and |
| 428 | 834 restores the selected window and nothing else. |
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835 @end defmac |
| 428 | 836 |
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837 @node Narrowing, , Excursions, Positions |
| 428 | 838 @section Narrowing |
| 839 @cindex narrowing | |
| 840 @cindex restriction (in a buffer) | |
| 841 @cindex accessible portion (of a buffer) | |
| 842 | |
| 843 @dfn{Narrowing} means limiting the text addressable by XEmacs editing | |
| 844 commands to a limited range of characters in a buffer. The text that | |
| 845 remains addressable is called the @dfn{accessible portion} of the | |
| 846 buffer. | |
| 847 | |
| 848 Narrowing is specified with two buffer positions which become the | |
| 849 beginning and end of the accessible portion. For most editing commands | |
| 850 and most Emacs primitives, these positions replace the values of the | |
| 851 beginning and end of the buffer. While narrowing is in effect, no text | |
| 852 outside the accessible portion is displayed, and point cannot move | |
| 853 outside the accessible portion. | |
| 854 | |
| 855 Values such as positions or line numbers, which usually count from the | |
| 856 beginning of the buffer, do so despite narrowing, but the functions | |
| 857 which use them refuse to operate on text that is inaccessible. | |
| 858 | |
| 859 The commands for saving buffers are unaffected by narrowing; they save | |
| 860 the entire buffer regardless of any narrowing. | |
| 861 | |
| 862 @deffn Command narrow-to-region start end &optional buffer | |
| 863 This function sets the accessible portion of @var{buffer} to start at | |
| 864 @var{start} and end at @var{end}. Both arguments should be character | |
| 865 positions. @var{buffer} defaults to the current buffer if omitted. | |
| 866 | |
| 867 In an interactive call, @var{start} and @var{end} are set to the bounds | |
| 868 of the current region (point and the mark, with the smallest first). | |
| 869 @end deffn | |
| 870 | |
| 871 @deffn Command narrow-to-page &optional move-count | |
| 872 This function sets the accessible portion of the current buffer to | |
| 873 include just the current page. An optional first argument | |
| 874 @var{move-count} non-@code{nil} means to move forward or backward by | |
| 875 @var{move-count} pages and then narrow. The variable | |
| 876 @code{page-delimiter} specifies where pages start and end | |
| 877 (@pxref{Standard Regexps}). | |
| 878 | |
| 879 In an interactive call, @var{move-count} is set to the numeric prefix | |
| 880 argument. | |
| 881 @end deffn | |
| 882 | |
| 883 @deffn Command widen &optional buffer | |
| 884 @cindex widening | |
| 885 This function cancels any narrowing in @var{buffer}, so that the | |
| 886 entire contents are accessible. This is called @dfn{widening}. | |
| 887 It is equivalent to the following expression: | |
| 888 | |
| 889 @example | |
| 890 (narrow-to-region 1 (1+ (buffer-size))) | |
| 891 @end example | |
| 892 | |
| 893 @var{buffer} defaults to the current buffer if omitted. | |
| 894 @end deffn | |
| 895 | |
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Change "special form" to "special operator" in the manuals, too
Aidan Kehoe <kehoea@parhasard.net>
parents:
4905
diff
changeset
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896 @deffn {Special Operator} save-restriction body@dots{} |
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Change "special form" to "special operator" in our sources.
Aidan Kehoe <kehoea@parhasard.net>
parents:
4885
diff
changeset
|
897 This special operator saves the current bounds of the accessible portion, |
| 428 | 898 evaluates the @var{body} forms, and finally restores the saved bounds, |
| 899 thus restoring the same state of narrowing (or absence thereof) formerly | |
| 900 in effect. The state of narrowing is restored even in the event of an | |
| 901 abnormal exit via @code{throw} or error (@pxref{Nonlocal Exits}). | |
| 902 Therefore, this construct is a clean way to narrow a buffer temporarily. | |
| 903 | |
| 904 The value returned by @code{save-restriction} is that returned by the | |
| 905 last form in @var{body}, or @code{nil} if no body forms were given. | |
| 906 | |
| 907 @c Wordy to avoid overfull hbox. --rjc 16mar92 | |
| 908 @strong{Caution:} it is easy to make a mistake when using the | |
| 909 @code{save-restriction} construct. Read the entire description here | |
| 910 before you try it. | |
| 911 | |
| 912 If @var{body} changes the current buffer, @code{save-restriction} still | |
| 913 restores the restrictions on the original buffer (the buffer whose | |
| 914 restrictions it saved from), but it does not restore the identity of the | |
| 915 current buffer. | |
| 916 | |
| 917 @code{save-restriction} does @emph{not} restore point and the mark; use | |
| 918 @code{save-excursion} for that. If you use both @code{save-restriction} | |
| 919 and @code{save-excursion} together, @code{save-excursion} should come | |
| 920 first (on the outside). Otherwise, the old point value would be | |
| 921 restored with temporary narrowing still in effect. If the old point | |
| 922 value were outside the limits of the temporary narrowing, this would | |
| 923 fail to restore it accurately. | |
| 924 | |
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4905
755ae5b97edb
Change "special form" to "special operator" in our sources.
Aidan Kehoe <kehoea@parhasard.net>
parents:
4885
diff
changeset
|
925 The @code{save-restriction} special operator records the values of the |
| 428 | 926 beginning and end of the accessible portion as distances from the |
| 927 beginning and end of the buffer. In other words, it records the amount | |
| 928 of inaccessible text before and after the accessible portion. | |
| 929 | |
| 930 This method yields correct results if @var{body} does further narrowing. | |
| 931 However, @code{save-restriction} can become confused if the body widens | |
| 932 and then make changes outside the range of the saved narrowing. When | |
| 933 this is what you want to do, @code{save-restriction} is not the right | |
| 934 tool for the job. Here is what you must use instead: | |
| 935 | |
| 936 @example | |
| 937 @group | |
| 444 | 938 (let ((start (point-min-marker)) |
| 428 | 939 (end (point-max-marker))) |
| 940 (unwind-protect | |
| 941 (progn @var{body}) | |
| 942 (save-excursion | |
| 444 | 943 (set-buffer (marker-buffer start)) |
| 944 (narrow-to-region start end)))) | |
| 428 | 945 @end group |
| 946 @end example | |
| 947 | |
| 948 Here is a simple example of correct use of @code{save-restriction}: | |
| 949 | |
| 950 @example | |
| 951 @group | |
| 952 ---------- Buffer: foo ---------- | |
| 953 This is the contents of foo | |
| 954 This is the contents of foo | |
| 955 This is the contents of foo@point{} | |
| 956 ---------- Buffer: foo ---------- | |
| 957 @end group | |
| 958 | |
| 959 @group | |
| 960 (save-excursion | |
| 961 (save-restriction | |
| 962 (goto-char 1) | |
| 963 (forward-line 2) | |
| 964 (narrow-to-region 1 (point)) | |
| 965 (goto-char (point-min)) | |
| 966 (replace-string "foo" "bar"))) | |
| 967 | |
| 968 ---------- Buffer: foo ---------- | |
| 969 This is the contents of bar | |
| 970 This is the contents of bar | |
| 971 This is the contents of foo@point{} | |
| 972 ---------- Buffer: foo ---------- | |
| 973 @end group | |
| 974 @end example | |
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5361
62b9ef1ed4ac
Change "special form" to "special operator" in the manuals, too
Aidan Kehoe <kehoea@parhasard.net>
parents:
4905
diff
changeset
|
975 @end deffn |