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1
2 @node Programs, Running, Text, Top
3 @chapter Editing Programs
4 @cindex Lisp
5 @cindex C
6
7 Emacs has many commands designed to understand the syntax of programming
8 languages such as Lisp and C. These commands can:
9
10 @itemize @bullet
11 @item
12 Move over or kill balanced expressions or @dfn{sexps} (@pxref{Lists}).
13 @item
14 Move over or mark top-level balanced expressions (@dfn{defuns}, in Lisp;
15 functions, in C).
16 @item
17 Show how parentheses balance (@pxref{Matching}).
18 @item
19 Insert, kill, or align comments (@pxref{Comments}).
20 @item
21 Follow the usual indentation conventions of the language
22 (@pxref{Grinding}).
23 @end itemize
24
25 The commands available for words, sentences, and paragraphs are useful in
26 editing code even though their canonical application is for editing human
27 language text. Most symbols contain words (@pxref{Words}); sentences can
28 be found in strings and comments (@pxref{Sentences}). Paragraphs per se
29 are not present in code, but the paragraph commands are useful anyway,
30 because Lisp mode and C mode define paragraphs to begin and end at blank
31 lines (@pxref{Paragraphs}). Judicious use of blank lines to make the
32 program clearer also provides interesting chunks of text for the
33 paragraph commands to work on.
34
35 The selective display feature is useful for looking at the overall
36 structure of a function (@pxref{Selective Display}). This feature causes
37 only the lines that are indented less than a specified amount to appear
38 on the screen.
39
40 @menu
41 * Program Modes:: Major modes for editing programs.
42 * Lists:: Expressions with balanced parentheses.
43 There are editing commands to operate on them.
44 * Defuns:: Each program is made up of separate functions.
45 There are editing commands to operate on them.
46 * Grinding:: Adjusting indentation to show the nesting.
47 * Matching:: Insertion of a close-delimiter flashes matching open.
48 * Comments:: Inserting, illing and aligning comments.
49 * Balanced Editing:: Inserting two matching parentheses at once, etc.
50 * Lisp Completion:: Completion on symbol names in Lisp code.
51 * Documentation:: Getting documentation of functions you plan to call.
52 * Change Log:: Maintaining a change history for your program.
53 * Tags:: Go direct to any function in your program in one
54 command. Tags remembers which file it is in.
55 * Fortran:: Fortran mode and its special features.
56 * Asm Mode:: Asm mode and its special features.
57 @end menu
58
59 @node Program Modes, Lists, Programs, Programs
60 @section Major Modes for Programming Languages
61
62 @cindex Lisp mode
63 @cindex C mode
64 @cindex Scheme mode
65 Emacs has several major modes for the programming languages Lisp, Scheme (a
66 variant of Lisp), C, Fortran, and Muddle. Ideally, a major mode should be
67 implemented for each programming language you might want to edit with
68 Emacs; but often the mode for one language can serve for other
69 syntactically similar languages. The language modes that exist are those
70 that someone decided to take the trouble to write.
71
72 There are several variants of Lisp mode, which differ in the way they
73 interface to Lisp execution. @xref{Lisp Modes}.
74
75 Each of the programming language modes defines the @key{TAB} key to run
76 an indentation function that knows the indentation conventions of that
77 language and updates the current line's indentation accordingly. For
78 example, in C mode @key{TAB} is bound to @code{c-indent-line}. @key{LFD}
79 is normally defined to do @key{RET} followed by @key{TAB}; thus it, too,
80 indents in a mode-specific fashion.
81
82 @kindex DEL
83 @findex backward-delete-char-untabify
84 In most programming languages, indentation is likely to vary from line to
85 line. So the major modes for those languages rebind @key{DEL} to treat a
86 tab as if it were the equivalent number of spaces (using the command
87 @code{backward-delete-char-untabify}). This makes it possible to rub out
88 indentation one column at a time without worrying whether it is made up of
89 spaces or tabs. In these modes, use @kbd{C-b C-d} to delete a tab
90 character before point.
91
92 Programming language modes define paragraphs to be separated only by
93 blank lines, so that the paragraph commands remain useful. Auto Fill mode,
94 if enabled in a programming language major mode, indents the new lines
95 which it creates.
96
97 @cindex mode hook
98 @vindex c-mode-hook
99 @vindex lisp-mode-hook
100 @vindex emacs-lisp-mode-hook
101 @vindex lisp-interaction-mode-hook
102 @vindex scheme-mode-hook
103 @vindex muddle-mode-hook
104 Turning on a major mode calls a user-supplied function called the
105 @dfn{mode hook}, which is the value of a Lisp variable. For example,
106 turning on C mode calls the value of the variable @code{c-mode-hook} if
107 that value exists and is non-@code{nil}. Mode hook variables for other
108 programming language modes include @code{lisp-mode-hook},
109 @code{emacs-lisp-mode-hook}, @code{lisp-interaction-mode-hook},
110 @code{scheme-mode-hook}, and @code{muddle-mode-hook}. The mode hook
111 function receives no arguments.@refill
112
113 @node Lists, Defuns, Program Modes, Programs
114 @section Lists and Sexps
115
116 @cindex Control-Meta
117 By convention, Emacs keys for dealing with balanced expressions are
118 usually @kbd{Control-Meta-} characters. They tend to be analogous in
119 function to their @kbd{Control-} and @kbd{Meta-} equivalents. These commands
120 are usually thought of as pertaining to expressions in programming
121 languages, but can be useful with any language in which some sort of
122 parentheses exist (including English).
123
124 @cindex list
125 @cindex sexp
126 @cindex expression
127 The commands fall into two classes. Some commands deal only with
128 @dfn{lists} (parenthetical groupings). They see nothing except
129 parentheses, brackets, braces (depending on what must balance in the
130 language you are working with), and escape characters that might be used
131 to quote those.
132
133 The other commands deal with expressions or @dfn{sexps}. The word `sexp'
134 is derived from @dfn{s-expression}, the term for a symbolic expression in
135 Lisp. In Emacs, the notion of `sexp' is not limited to Lisp. It
136 refers to an expression in the language your program is written in.
137 Each programming language has its own major mode, which customizes the
138 syntax tables so that expressions in that language count as sexps.
139
140 Sexps typically include symbols, numbers, and string constants, as well
141 as anything contained in parentheses, brackets, or braces.
142
143 In languages that use prefix and infix operators, such as C, it is not
144 possible for all expressions to be sexps. For example, C mode does not
145 recognize @samp{foo + bar} as an sexp, even though it @i{is} a C expression;
146 it recognizes @samp{foo} as one sexp and @samp{bar} as another, with the
147 @samp{+} as punctuation between them. This is a fundamental ambiguity:
148 both @samp{foo + bar} and @samp{foo} are legitimate choices for the sexp to
149 move over if point is at the @samp{f}. Note that @samp{(foo + bar)} is a
150 sexp in C mode.
151
152 Some languages have obscure forms of syntax for expressions that nobody
153 has bothered to make Emacs understand properly.
154
155 @c doublewidecommands
156 @table @kbd
157 @item C-M-f
158 Move forward over an sexp (@code{forward-sexp}).
159 @item C-M-b
160 Move backward over an sexp (@code{backward-sexp}).
161 @item C-M-k
162 Kill sexp forward (@code{kill-sexp}).
163 @item C-M-u
164 Move up and backward in list structure (@code{backward-up-list}).
165 @item C-M-d
166 Move down and forward in list structure (@code{down-list}).
167 @item C-M-n
168 Move forward over a list (@code{forward-list}).
169 @item C-M-p
170 Move backward over a list (@code{backward-list}).
171 @item C-M-t
172 Transpose expressions (@code{transpose-sexps}).
173 @item C-M-@@
174 Put mark after following expression (@code{mark-sexp}).
175 @end table
176
177 @kindex C-M-f
178 @kindex C-M-b
179 @findex forward-sexp
180 @findex backward-sexp
181 To move forward over an sexp, use @kbd{C-M-f} (@code{forward-sexp}). If
182 the first significant character after point is an opening delimiter
183 (@samp{(} in Lisp; @samp{(}, @samp{[}, or @samp{@{} in C), @kbd{C-M-f}
184 moves past the matching closing delimiter. If the character begins a
185 symbol, string, or number, @kbd{C-M-f} moves over that. If the character
186 after point is a closing delimiter, @kbd{C-M-f} just moves past it. (This
187 last is not really moving across an sexp; it is an exception which is
188 included in the definition of @kbd{C-M-f} because it is as useful a
189 behavior as anyone can think of for that situation.)@refill
190
191 The command @kbd{C-M-b} (@code{backward-sexp}) moves backward over a
192 sexp. The detailed rules are like those above for @kbd{C-M-f}, but with
193 directions reversed. If there are any prefix characters (single quote,
194 back quote, and comma, in Lisp) preceding the sexp, @kbd{C-M-b} moves back
195 over them as well.
196
197 @kbd{C-M-f} or @kbd{C-M-b} with an argument repeats that operation the
198 specified number of times; with a negative argument, it moves in the
199 opposite direction.
200
201 In languages such as C where the comment-terminator can be recognized,
202 the sexp commands move across comments as if they were whitespace. In
203 Lisp and other languages where comments run until the end of a line, it
204 is very difficult to ignore comments when parsing backwards; therefore,
205 in such languages the sexp commands treat the text of comments as if it
206 were code.
207
208 @kindex C-M-k
209 @findex kill-sexp
210 Killing an sexp at a time can be done with @kbd{C-M-k} (@code{kill-sexp}).
211 @kbd{C-M-k} kills the characters that @kbd{C-M-f} would move over.
212
213 @kindex C-M-n
214 @kindex C-M-p
215 @findex forward-list
216 @findex backward-list
217 The @dfn{list commands}, @kbd{C-M-n} (@code{forward-list}) and
218 @kbd{C-M-p} (@code{backward-list}), move over lists like the sexp
219 commands but skip over any number of other kinds of sexps (symbols,
220 strings, etc). In some situations, these commands are useful because
221 they usually ignore comments, since the comments usually do not contain
222 any lists.@refill
223
224 @kindex C-M-u
225 @kindex C-M-d
226 @findex backward-up-list
227 @findex down-list
228 @kbd{C-M-n} and @kbd{C-M-p} stay at the same level in parentheses, when
229 that is possible. To move @i{up} one (or @var{n}) levels, use @kbd{C-M-u}
230 (@code{backward-up-list}).
231 @kbd{C-M-u} moves backward up past one unmatched opening delimiter. A
232 positive argument serves as a repeat count; a negative argument reverses
233 direction of motion and also requests repetition, so it moves forward and
234 up one or more levels.@refill
235
236 To move @i{down} in list structure, use @kbd{C-M-d}
237 (@code{down-list}). In Lisp mode, where @samp{(} is the only opening
238 delimiter, this is nearly the same as searching for a @samp{(}. An
239 argument specifies the number of levels of parentheses to go down.
240
241 @cindex transposition
242 @kindex C-M-t
243 @findex transpose-sexps
244 @kbd{C-M-t} (@code{transpose-sexps}) drags the previous sexp across
245 the next one. An argument serves as a repeat count, and a negative
246 argument drags backwards (thus canceling out the effect of @kbd{C-M-t} with
247 a positive argument). An argument of zero, rather than doing nothing,
248 transposes the sexps ending after point and the mark.
249
250 @kindex C-M-@@
251 @findex mark-sexp
252 To make the region be the next sexp in the buffer, use @kbd{C-M-@@}
253 (@code{mark-sexp}) which sets the mark at the same place that
254 @kbd{C-M-f} would move to. @kbd{C-M-@@} takes arguments like
255 @kbd{C-M-f}. In particular, a negative argument is useful for putting
256 the mark at the beginning of the previous sexp.
257
258 The list and sexp commands' understanding of syntax is completely
259 controlled by the syntax table. Any character can, for example, be
260 declared to be an opening delimiter and act like an open parenthesis.
261 @xref{Syntax}.
262
263 @node Defuns, Grinding, Lists, Programs
264 @section Defuns
265 @cindex defuns
266
267 In Emacs, a parenthetical grouping at the top level in the buffer is
268 called a @dfn{defun}. The name derives from the fact that most
269 top-level lists in Lisp are instances of the special form
270 @code{defun}, but Emacs calls any top-level parenthetical
271 grouping counts a defun regardless of its contents or
272 the programming language. For example, in C, the body of a
273 function definition is a defun.
274
275 @c doublewidecommands
276 @table @kbd
277 @item C-M-a
278 Move to beginning of current or preceding defun
279 (@code{beginning-of-defun}).
280 @item C-M-e
281 Move to end of current or following defun (@code{end-of-defun}).
282 @item C-M-h
283 Put region around whole current or following defun (@code{mark-defun}).
284 @end table
285
286 @kindex C-M-a
287 @kindex C-M-e
288 @kindex C-M-h
289 @findex beginning-of-defun
290 @findex end-of-defun
291 @findex mark-defun
292 The commands to move to the beginning and end of the current defun are
293 @kbd{C-M-a} (@code{beginning-of-defun}) and @kbd{C-M-e} (@code{end-of-defun}).
294
295 To operate on the current defun, use @kbd{C-M-h} (@code{mark-defun})
296 which puts point at the beginning and the mark at the end of the current
297 or next defun. This is the easiest way to prepare for moving the defun
298 to a different place. In C mode, @kbd{C-M-h} runs the function
299 @code{mark-c-function}, which is almost the same as @code{mark-defun},
300 but which backs up over the argument declarations, function name, and
301 returned data type so that the entire C function is inside the region.
302
303 @findex compile-defun
304 To compile and evaluate the current defun, use @kbd{M-x compile-defun}.
305 This function prints the results in the minibuffer. If you include an
306 argument, it inserts the value in the current buffer after the defun.
307
308 Emacs assumes that any open-parenthesis found in the leftmost column is
309 the start of a defun. Therefore, @i{never put an open-parenthesis at the
310 left margin in a Lisp file unless it is the start of a top level list.
311 Never put an open-brace or other opening delimiter at the beginning of a
312 line of C code unless it starts the body of a function.} The most likely
313 problem case is when you want an opening delimiter at the start of a line
314 inside a string. To avoid trouble, put an escape character (@samp{\} in C
315 and Emacs Lisp, @samp{/} in some other Lisp dialects) before the opening
316 delimiter. It will not affect the contents of the string.
317
318 The original Emacs found defuns by moving upward a
319 level of parentheses until there were no more levels to go up. This
320 required scanning back to the beginning of the buffer for every
321 function. To speed this up, Emacs was changed to assume
322 that any @samp{(} (or other character assigned the syntactic class of
323 opening-delimiter) at the left margin is the start of a defun. This
324 heuristic is nearly always right; however, it mandates the convention
325 described above.
326
327 @node Grinding, Matching, Defuns, Programs
328 @section Indentation for Programs
329 @cindex indentation
330 @cindex grinding
331
332 The best way to keep a program properly indented (``ground'') is to
333 use Emacs to re-indent it as you change the program. Emacs has commands
334 to indent properly either a single line, a specified number of lines, or
335 all of the lines inside a single parenthetical grouping.
336
337 @menu
338 * Basic Indent::
339 * Multi-line Indent:: Commands to reindent many lines at once.
340 * Lisp Indent:: Specifying how each Lisp function should be indented.
341 * C Indent:: Choosing an indentation style for C code.
342 @end menu
343
344 @node Basic Indent, Multi-line Indent, Grinding, Grinding
345 @subsection Basic Program Indentation Commands
346
347 @c WideCommands
348 @table @kbd
349 @item @key{TAB}
350 Adjust indentation of current line.
351 @item @key{LFD}
352 Equivalent to @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
353 @end table
354
355 @kindex TAB
356 @findex c-indent-line
357 @findex lisp-indent-line
358 The basic indentation command is @key{TAB}, which gives the current
359 line the correct indentation as determined from the previous lines. The
360 function that @key{TAB} runs depends on the major mode; it is
361 @code{lisp-indent-line} in Lisp mode, @code{c-indent-line} in C mode,
362 etc. These functions understand different syntaxes for different
363 languages, but they all do about the same thing. @key{TAB} in any
364 programming language major mode inserts or deletes whitespace at the
365 beginning of the current line, independent of where point is in the
366 line. If point is inside the whitespace at the beginning of the line,
367 @key{TAB} leaves it at the end of that whitespace; otherwise, @key{TAB}
368 leaves point fixed with respect to the characters around it.
369
370 Use @kbd{C-q @key{TAB}} to insert a tab at point.
371
372 @kindex LFD
373 @findex newline-and-indent
374 When entering a large amount of new code, use @key{LFD}
375 (@code{newline-and-indent}), which is equivalent to a @key{RET} followed
376 by a @key{TAB}. @key{LFD} creates a blank line, then gives it the
377 appropriate indentation.
378
379 @key{TAB} indents the second and following lines of the body of a
380 parenthetical grouping each under the preceding one; therefore, if you
381 alter one line's indentation to be nonstandard, the lines below tend
382 to follow it. This is the right behavior in cases where the standard
383 result of @key{TAB} does not look good.
384
385 Remember that Emacs assumes that an open-parenthesis, open-brace, or
386 other opening delimiter at the left margin (including the indentation
387 routines) is the start of a function. You should therefore never have
388 an opening delimiter in column zero that is not the beginning of a
389 function, not even inside a string. This restriction is vital for
390 making the indentation commands fast. @xref{Defuns}, for more
391 information on this behavior.
392
393 @node Multi-line Indent, Lisp Indent, Basic Indent, Grinding
394 @subsection Indenting Several Lines
395
396 Several commands are available to re-indent several lines of code
397 which have been altered or moved to a different level in a list
398 structure.
399
400
401 @table @kbd
402 @item C-M-q
403 Re-indent all the lines within one list (@code{indent-sexp}).
404 @item C-u @key{TAB}
405 Shift an entire list rigidly sideways so that its first line
406 is properly indented.
407 @item C-M-\
408 Re-indent all lines in the region (@code{indent-region}).
409 @end table
410
411 @kindex C-M-q
412 @findex indent-sexp
413 @findex indent-c-exp
414 To re-indent the contents of a single list, position point before the
415 beginning of it and type @kbd{C-M-q}. This key is bound to
416 @code{indent-sexp} in Lisp mode, @code{indent-c-exp} in C mode, and
417 bound to other suitable functions in other modes. The indentation of
418 the line the sexp starts on is not changed; therefore, only the relative
419 indentation within the list, and not its position, is changed. To
420 correct the position as well, type a @key{TAB} before @kbd{C-M-q}.
421
422 @kindex C-u TAB
423 If the relative indentation within a list is correct but the
424 indentation of its beginning is not, go to the line on which the list
425 begins and type @kbd{C-u @key{TAB}}. When you give @key{TAB} a numeric
426 argument, it moves all the lines in the group, starting on the current
427 line, sideways the same amount that the current line moves. The command
428 does not move lines that start inside strings, or C
429 preprocessor lines when in C mode.
430
431 @kindex C-M-\
432 @findex indent-region
433 Another way to specify a range to be re-indented is with point and
434 mark. The command @kbd{C-M-\} (@code{indent-region}) applies @key{TAB}
435 to every line whose first character is between point and mark.
436
437 @node Lisp Indent, C Indent, Multi-line Indent, Grinding
438 @subsection Customizing Lisp Indentation
439 @cindex customization
440
441 The indentation pattern for a Lisp expression can depend on the function
442 called by the expression. For each Lisp function, you can choose among
443 several predefined patterns of indentation, or define an arbitrary one with
444 a Lisp program.
445
446 The standard pattern of indentation is as follows: the second line of the
447 expression is indented under the first argument, if that is on the same
448 line as the beginning of the expression; otherwise, the second line is
449 indented underneath the function name. Each following line is indented
450 under the previous line whose nesting depth is the same.
451
452 @vindex lisp-indent-offset
453 If the variable @code{lisp-indent-offset} is non-@code{nil}, it overrides
454 the usual indentation pattern for the second line of an expression, so that
455 such lines are always indented @code{lisp-indent-offset} more columns than
456 the containing list.
457
458 @vindex lisp-body-indention
459 Certain functions override the standard pattern. Functions
460 whose names start with @code{def} always indent the second line by
461 @code{lisp-body-indention} extra columns beyond the open-parenthesis
462 starting the expression.
463
464 Individual functions can override the standard pattern in various
465 ways, according to the @code{lisp-indent-function} property of the
466 function name. (Note: @code{lisp-indent-function} was formerly called
467 @code{lisp-indent-hook}). There are four possibilities for this
468 property:
469
470 @table @asis
471 @item @code{nil}
472 This is the same as no property; the standard indentation pattern is used.
473 @item @code{defun}
474 The pattern used for function names that start with @code{def} is used for
475 this function also.
476 @item a number, @var{number}
477 The first @var{number} arguments of the function are
478 @dfn{distinguished} arguments; the rest are considered the @dfn{body}
479 of the expression. A line in the expression is indented according to
480 whether the first argument on it is distinguished or not. If the
481 argument is part of the body, the line is indented @code{lisp-body-indent}
482 more columns than the open-parenthesis starting the containing
483 expression. If the argument is distinguished and is either the first
484 or second argument, it is indented @i{twice} that many extra columns.
485 If the argument is distinguished and not the first or second argument,
486 the standard pattern is followed for that line.
487 @item a symbol, @var{symbol}
488 @var{symbol} should be a function name; that function is called to
489 calculate the indentation of a line within this expression. The
490 function receives two arguments:
491 @table @asis
492 @item @var{state}
493 The value returned by @code{parse-partial-sexp} (a Lisp primitive for
494 indentation and nesting computation) when it parses up to the
495 beginning of this line.
496 @item @var{pos}
497 The position at which the line being indented begins.
498 @end table
499 @noindent
500 It should return either a number, which is the number of columns of
501 indentation for that line, or a list whose first element is such a
502 number. The difference between returning a number and returning a list
503 is that a number says that all following lines at the same nesting level
504 should be indented just like this one; a list says that following lines
505 might call for different indentations. This makes a difference when the
506 indentation is computed by @kbd{C-M-q}; if the value is a number,
507 @kbd{C-M-q} need not recalculate indentation for the following lines
508 until the end of the list.
509 @end table
510
511 @node C Indent,, Lisp Indent, Grinding
512 @subsection Customizing C Indentation
513
514 Two variables control which commands perform C indentation and when.
515
516 @vindex c-auto-newline
517 If @code{c-auto-newline} is non-@code{nil}, newlines are inserted both
518 before and after braces that you insert and after colons and semicolons.
519 Correct C indentation is done on all the lines that are made this way.
520
521 @vindex c-tab-always-indent
522 If @code{c-tab-always-indent} is non-@code{nil}, the @key{TAB} command
523 in C mode does indentation only if point is at the left margin or within
524 the line's indentation. If there is non-whitespace to the left of point,
525 @key{TAB} just inserts a tab character in the buffer. Normally,
526 this variable is @code{nil}, and @key{TAB} always reindents the current line.
527
528 C does not have anything analogous to particular function names for which
529 special forms of indentation are desirable. However, it has a different
530 need for customization facilities: many different styles of C indentation
531 are in common use.
532
533 There are six variables you can set to control the style that Emacs C
534 mode will use.
535
536 @table @code
537 @item c-indent-level
538 Indentation of C statements within surrounding block. The surrounding
539 block's indentation is the indentation of the line on which the
540 open-brace appears.
541 @item c-continued-statement-offset
542 Extra indentation given to a substatement, such as the then-clause of
543 an @code{if} or body of a @code{while}.
544 @item c-brace-offset
545 Extra indentation for lines that start with an open brace.
546 @item c-brace-imaginary-offset
547 An open brace following other text is treated as if it were this far
548 to the right of the start of its line.
549 @item c-argdecl-indent
550 Indentation level of declarations of C function arguments.
551 @item c-label-offset
552 Extra indentation for a line that is a label, case, or default.
553 @end table
554
555 @vindex c-indent-level
556 The variable @code{c-indent-level} controls the indentation for C
557 statements with respect to the surrounding block. In the example:
558
559 @example
560 @{
561 foo ();
562 @end example
563
564 @noindent
565 the difference in indentation between the lines is @code{c-indent-level}.
566 Its standard value is 2.
567
568 If the open-brace beginning the compound statement is not at the beginning
569 of its line, the @code{c-indent-level} is added to the indentation of the
570 line, not the column of the open-brace. For example,
571
572 @example
573 if (losing) @{
574 do_this ();
575 @end example
576
577 @noindent
578 One popular indentation style is that which results from setting
579 @code{c-indent-level} to 8 and putting open-braces at the end of a line
580 in this way. Another popular style prefers to put the open-brace on a
581 separate line.
582
583 @vindex c-brace-imaginary-offset
584 In fact, the value of the variable @code{c-brace-imaginary-offset} is
585 also added to the indentation of such a statement. Normally this variable
586 is zero. Think of this variable as the imaginary position of the open
587 brace, relative to the first non-blank character on the line. By setting
588 the variable to 4 and @code{c-indent-level} to 0, you can get this style:
589
590 @example
591 if (x == y) @{
592 do_it ();
593 @}
594 @end example
595
596 When @code{c-indent-level} is zero, the statements inside most braces
597 line up exactly under the open brace. An exception are braces in column
598 zero, like those surrounding a function's body. The statements inside
599 those braces are not placed at column zero. Instead,
600 @code{c-brace-offset} and @code{c-continued-statement-offset} (see
601 below) are added to produce a typical offset between brace levels, and
602 the statements are indented that far.
603
604 @vindex c-continued-statement-offset
605 @code{c-continued-statement-offset} controls the extra indentation for
606 a line that starts within a statement (but not within parentheses or
607 brackets). These lines are usually statements inside other statements,
608 like the then-clauses of @code{if} statements and the bodies of
609 @code{while} statements. The @code{c-continued-statement-offset}
610 parameter determines the difference in indentation between the two lines in:
611
612 @example
613 if (x == y)
614 do_it ();
615 @end example
616
617 @noindent
618 The default value for @code{c-continued-statement-offset} is 2. Some
619 popular indentation styles correspond to a value of zero for
620 @code{c-continued-statement-offset}.
621
622 @vindex c-brace-offset
623 @code{c-brace-offset} is the extra indentation given to a line that
624 starts with an open-brace. Its standard value is zero;
625 compare:
626
627 @example
628 if (x == y)
629 @{
630 @end example
631
632 @noindent
633 with:
634
635 @example
636 if (x == y)
637 do_it ();
638 @end example
639
640 @noindent
641 If you set @code{c-brace-offset} to 4, the first example becomes:
642
643 @example
644 if (x == y)
645 @{
646 @end example
647
648 @vindex c-argdecl-indent
649 @code{c-argdecl-indent} controls the indentation of declarations of the
650 arguments of a C function. It is absolute: argument declarations receive
651 exactly @code{c-argdecl-indent} spaces. The standard value is 5 and
652 results in code like this:
653
654 @example
655 char *
656 index (string, char)
657 char *string;
658 int char;
659 @end example
660
661 @vindex c-label-offset
662 @code{c-label-offset} is the extra indentation given to a line that
663 contains a label, a case statement, or a @code{default:} statement. Its
664 standard value is @minus{}2 and results in code like this:
665
666 @example
667 switch (c)
668 @{
669 case 'x':
670 @end example
671
672 @noindent
673 If @code{c-label-offset} were zero, the same code would be indented as:
674
675 @example
676 switch (c)
677 @{
678 case 'x':
679 @end example
680
681 @noindent
682 This example assumes that the other variables above also have their
683 default values.
684
685 Using the indentation style produced by the default settings of the
686 variables just discussed and putting open braces on separate lines
687 produces clear and readable files. For an example, look at any of the C
688 source files of XEmacs.
689
690 @node Matching, Comments, Grinding, Programs
691 @section Automatic Display of Matching Parentheses
692 @cindex matching parentheses
693 @cindex parentheses
694
695 The Emacs parenthesis-matching feature shows you automatically how
696 parentheses match in the text. Whenever a self-inserting character that
697 is a closing delimiter is typed, the cursor moves momentarily to the
698 location of the matching opening delimiter, provided that is visible on
699 the screen. If it is not on the screen, some text starting with that
700 opening delimiter is displayed in the echo area. Either way, you see
701 the grouping you are closing off.
702
703 In Lisp, automatic matching applies only to parentheses. In C, it
704 also applies to braces and brackets. Emacs knows which characters to regard
705 as matching delimiters based on the syntax table set by the major
706 mode. @xref{Syntax}.
707
708 If the opening delimiter and closing delimiter are mismatched---as
709 in @samp{[x)}---the echo area displays a warning message. The
710 correct matches are specified in the syntax table.
711
712 @vindex blink-matching-paren
713 @vindex blink-matching-paren-distance
714 Two variables control parenthesis matching displays.
715 @code{blink-matching-paren} turns the feature on or off. The default is
716 @code{t} (match display is on); @code{nil} turns it off.
717 @code{blink-matching-paren-distance} specifies how many characters back
718 Emacs searches to find a matching opening delimiter. If the match is
719 not found in the specified region, scanning stops, and nothing is
720 displayed. This prevents wasting lots of time scanning when there is no
721 match. The default is 4000.
722
723 @node Comments, Balanced Editing, Matching, Programs
724 @section Manipulating Comments
725 @cindex comments
726 @kindex M-;
727 @cindex indentation
728 @findex indent-for-comment
729
730 The comment commands insert, kill and align comments.
731
732 @c WideCommands
733 @table @kbd
734 @item M-;
735 Insert or align comment (@code{indent-for-comment}).
736 @item C-x ;
737 Set comment column (@code{set-comment-column}).
738 @item C-u - C-x ;
739 Kill comment on current line (@code{kill-comment}).
740 @item M-@key{LFD}
741 Like @key{RET} followed by inserting and aligning a comment
742 (@code{indent-new-comment-line}).
743 @end table
744
745 The command that creates a comment is @kbd{Meta-;}
746 (@code{indent-for-comment}). If there is no comment already on the
747 line, a new comment is created and aligned at a specific column called
748 the @dfn{comment column}. Emacs creates the comment by inserting the
749 string at the value of @code{comment-start}; see below. Point is left
750 after that string. If the text of the line extends past the comment
751 column, indentation is done to a suitable boundary (usually, at least
752 one space is inserted). If the major mode has specified a string to
753 terminate comments, that string is inserted after point, to keep the
754 syntax valid.
755
756 You can also use @kbd{Meta-;} to align an existing comment. If a line
757 already contains the string that starts comments, @kbd{M-;} just moves
758 point after it and re-indents it to the conventional place. Exception:
759 comments starting in column 0 are not moved.
760
761 Some major modes have special rules for indenting certain kinds of
762 comments in certain contexts. For example, in Lisp code, comments which
763 start with two semicolons are indented as if they were lines of code,
764 instead of at the comment column. Comments which start with three
765 semicolons are supposed to start at the left margin. Emacs understands
766 these conventions by indenting a double-semicolon comment using @key{TAB}
767 and by not changing the indentation of a triple-semicolon comment at all.
768
769 @example
770 ;; This function is just an example.
771 ;;; Here either two or three semicolons are appropriate.
772 (defun foo (x)
773 ;;; And now, the first part of the function:
774 ;; The following line adds one.
775 (1+ x)) ; This line adds one.
776 @end example
777
778 In C code, a comment preceded on its line by nothing but whitespace
779 is indented like a line of code.
780
781 Even when an existing comment is properly aligned, @kbd{M-;} is still
782 useful for moving directly to the start of the comment.
783
784 @kindex C-u - C-x ;
785 @findex kill-comment
786 @kbd{C-u - C-x ;} (@code{kill-comment}) kills the comment on the
787 current line, if there is one. The indentation before the start of the
788 comment is killed as well. If there does not appear to be a comment in
789 the line, nothing happens. To reinsert the comment on another line,
790 move to the end of that line, type first @kbd{C-y}, and then @kbd{M-;}
791 to realign the comment. Note that @kbd{C-u - C-x ;} is not a distinct
792 key; it is @kbd{C-x ;} (@code{set-comment-column}) with a negative
793 argument. That command is programmed to call @code{kill-comment} when
794 called with a negative argument. However, @code{kill-comment} is a
795 valid command which you could bind directly to a key if you wanted to.
796
797 @subsection Multiple Lines of Comments
798
799 @kindex M-LFD
800 @cindex blank lines
801 @cindex Auto Fill mode
802 @findex indent-new-comment-line
803 If you are typing a comment and want to continue it on another line,
804 use the command @kbd{Meta-@key{LFD}} (@code{indent-new-comment-line}),
805 which terminates the comment you are typing, creates a new blank line
806 afterward, and begins a new comment indented under the old one. If
807 Auto Fill mode is on and you go past the fill column while typing, the
808 comment is continued in just this fashion. If point is
809 not at the end of the line when you type @kbd{M-@key{LFD}}, the text on
810 the rest of the line becomes part of the new comment line.
811
812 @subsection Options Controlling Comments
813
814 @vindex comment-column
815 @kindex C-x ;
816 @findex set-comment-column
817 The comment column is stored in the variable @code{comment-column}. You
818 can explicitly set it to a number. Alternatively, the command @kbd{C-x ;}
819 (@code{set-comment-column}) sets the comment column to the column point is
820 at. @kbd{C-u C-x ;} sets the comment column to match the last comment
821 before point in the buffer, and then calls @kbd{Meta-;} to align the
822 current line's comment under the previous one. Note that @kbd{C-u - C-x ;}
823 runs the function @code{kill-comment} as described above.
824
825 @code{comment-column} is a per-buffer variable; altering the variable
826 affects only the current buffer. You can also change the default value.
827 @xref{Locals}. Many major modes initialize this variable
828 for the current buffer.
829
830 @vindex comment-start-skip
831 The comment commands recognize comments based on the regular expression
832 that is the value of the variable @code{comment-start-skip}. This regexp
833 should not match the null string. It may match more than the comment
834 starting delimiter in the strictest sense of the word; for example, in C
835 mode the value of the variable is @code{@t{"/\\*+ *"}}, which matches extra
836 stars and spaces after the @samp{/*} itself. (Note that @samp{\\} is
837 needed in Lisp syntax to include a @samp{\} in the string, which is needed
838 to deny the first star its special meaning in regexp syntax. @xref{Regexps}.)
839
840 @vindex comment-start
841 @vindex comment-end
842 When a comment command makes a new comment, it inserts the value of
843 @code{comment-start} to begin it. The value of @code{comment-end} is
844 inserted after point and will follow the text you will insert
845 into the comment. In C mode, @code{comment-start} has the value
846 @w{@code{"/* "}} and @code{comment-end} has the value @w{@code{" */"}}.
847
848 @vindex comment-multi-line
849 @code{comment-multi-line} controls how @kbd{M-@key{LFD}}
850 (@code{indent-new-comment-line}) behaves when used inside a comment. If
851 @code{comment-multi-line} is @code{nil}, as it normally is, then
852 @kbd{M-@key{LFD}} terminates the comment on the starting line and starts
853 a new comment on the new following line. If @code{comment-multi-line}
854 is not @code{nil}, then @kbd{M-@key{LFD}} sets up the new following line
855 as part of the same comment that was found on the starting line. This
856 is done by not inserting a terminator on the old line and not inserting
857 a starter on the new line. In languages where multi-line comments are legal,
858 the value you choose for this variable is a matter of taste.
859
860 @vindex comment-indent-hook
861 The variable @code{comment-indent-hook} should contain a function that
862 is called to compute the indentation for a newly inserted comment or for
863 aligning an existing comment. Major modes set this variable differently.
864 The function is called with no arguments, but with point at the
865 beginning of the comment, or at the end of a line if a new comment is to
866 be inserted. The function should return the column in which the comment
867 ought to start. For example, in Lisp mode, the indent hook function
868 bases its decision on the number of semicolons that begin an existing
869 comment and on the code in the preceding lines.
870
871 @node Balanced Editing, Lisp Completion, Comments, Programs
872 @section Editing Without Unbalanced Parentheses
873
874 @table @kbd
875 @item M-(
876 Put parentheses around next sexp(s) (@code{insert-parentheses}).
877 @item M-)
878 Move past next close parenthesis and re-indent
879 (@code{move-over-close-and-reindent}).
880 @end table
881
882 @kindex M-(
883 @kindex M-)
884 @findex insert-parentheses
885 @findex move-over-close-and-reindent
886 The commands @kbd{M-(} (@code{insert-parentheses}) and @kbd{M-)}
887 (@code{move-over-close-@*and-reindent}) are designed to facilitate a style of
888 editing which keeps parentheses balanced at all times. @kbd{M-(} inserts a
889 pair of parentheses, either together as in @samp{()}, or, if given an
890 argument, around the next several sexps, and leaves point after the open
891 parenthesis. Instead of typing @kbd{( F O O )}, you can type @kbd{M-( F O
892 O}, which has the same effect except for leaving the cursor before the
893 close parenthesis. You can then type @kbd{M-)}, which moves past the
894 close parenthesis, deletes any indentation preceding it (in this example
895 there is none), and indents with @key{LFD} after it.
896
897 @node Lisp Completion, Documentation, Balanced Editing, Programs
898 @section Completion for Lisp Symbols
899 @cindex completion (symbol names)
900
901 Completion usually happens in the minibuffer. An exception is
902 completion for Lisp symbol names, which is available in all buffers.
903
904 @kindex M-TAB
905 @findex lisp-complete-symbol
906 The command @kbd{M-@key{TAB}} (@code{lisp-complete-symbol}) takes the
907 partial Lisp symbol before point to be an abbreviation, and compares it
908 against all non-trivial Lisp symbols currently known to Emacs. Any
909 additional characters that they all have in common are inserted at point.
910 Non-trivial symbols are those that have function definitions, values, or
911 properties.
912
913 If there is an open-parenthesis immediately before the beginning of
914 the partial symbol, only symbols with function definitions are considered
915 as completions.
916
917 If the partial name in the buffer has more than one possible completion
918 and they have no additional characters in common, a list of all possible
919 completions is displayed in another window.
920
921 @node Documentation, Change Log, Lisp Completion, Programs
922 @section Documentation Commands
923
924 @kindex C-h f
925 @findex describe-function
926 @kindex C-h v
927 @findex describe-variable
928 As you edit Lisp code to be run in Emacs, you can use the commands
929 @kbd{C-h f} (@code{describe-function}) and @kbd{C-h v}
930 (@code{describe-variable}) to print documentation of functions and
931 variables you want to call. These commands use the minibuffer to
932 read the name of a function or variable to document, and display the
933 documentation in a window.
934
935 For extra convenience, these commands provide default arguments based on
936 the code in the neighborhood of point. @kbd{C-h f} sets the default to the
937 function called in the innermost list containing point. @kbd{C-h v} uses
938 the symbol name around or adjacent to point as its default.
939
940 @findex manual-entry
941 The @kbd{M-x manual-entry} command gives you access to documentation
942 on Unix commands, system calls, and libraries. The command reads a
943 topic as an argument, and displays the Unix manual page for that topic.
944 @code{manual-entry} always searches all 8 sections of the
945 manual and concatenates all the entries it finds. For example,
946 the topic @samp{termcap} finds the description of the termcap library
947 from section 3, followed by the description of the termcap data base
948 from section 5.
949
950 @node Change Log, Tags, Documentation, Programs
951 @section Change Logs
952
953 @cindex change log
954 @findex add-change-log-entry
955 The Emacs command @kbd{M-x add-change-log-entry} helps you keep a record
956 of when and why you have changed a program. It assumes that you have a
957 file in which you write a chronological sequence of entries describing
958 individual changes. The default is to store the change entries in a file
959 called @file{ChangeLog} in the same directory as the file you are editing.
960 The same @file{ChangeLog} file therefore records changes for all the files
961 in a directory.
962
963 A change log entry starts with a header line that contains your name
964 and the current date. Except for these header lines, every line in the
965 change log starts with a tab. One entry can describe several changes;
966 each change starts with a line starting with a tab and a star. @kbd{M-x
967 add-change-log-entry} visits the change log file and creates a new entry
968 unless the most recent entry is for today's date and your name. In
969 either case, it adds a new line to start the description of another
970 change just after the header line of the entry. When @kbd{M-x
971 add-change-log-entry} is finished, all is prepared for you to edit in
972 the description of what you changed and how. You must then save the
973 change log file yourself.
974
975 The change log file is always visited in Indented Text mode, which means
976 that @key{LFD} and auto-filling indent each new line like the previous
977 line. This is convenient for entering the contents of an entry, which must
978 be indented. @xref{Text Mode}.
979
980 Here is an example of the formatting conventions used in the change log
981 for Emacs:
982
983 @smallexample
984 Wed Jun 26 19:29:32 1985 Richard M. Stallman (rms at mit-prep)
985
986 * xdisp.c (try_window_id):
987 If C-k is done at end of next-to-last line,
988 this fn updates window_end_vpos and cannot leave
989 window_end_pos nonnegative (it is zero, in fact).
990 If display is preempted before lines are output,
991 this is inconsistent. Fix by setting
992 blank_end_of_window to nonzero.
993
994 Tue Jun 25 05:25:33 1985 Richard M. Stallman (rms at mit-prep)
995
996 * cmds.c (Fnewline):
997 Call the auto fill hook if appropriate.
998
999 * xdisp.c (try_window_id):
1000 If point is found by compute_motion after xp, record that
1001 permanently. If display_text_line sets point position wrong
1002 (case where line is killed, point is at eob and that line is
1003 not displayed), set it again in final compute_motion.
1004 @end smallexample
1005
1006 @node Tags, Fortran, Change Log, Programs
1007 @section Tag Tables
1008 @cindex tag table
1009
1010 A @dfn{tag table} is a description of how a multi-file program is
1011 broken up into files. It lists the names of the component files and the
1012 names and positions of the functions in each file. Grouping the related
1013 files makes it possible to search or replace through all the files with
1014 one command. Recording the function names and positions makes it
1015 possible to use the @kbd{Meta-.} command, which finds the definition of a
1016 function without asking for information on the file it is in.
1017
1018 Tag tables are stored in files called @dfn{tag table files}. The
1019 conventional name for a tag table file is @file{TAGS}.
1020
1021 Each entry in the tag table records the name of one tag, the name of the
1022 file that the tag is defined in (implicitly), and the position in that file
1023 of the tag's definition.
1024
1025 The programming language of a file determines what names are recorded
1026 in the tag table depends on. Normally, Emacs includes all functions and
1027 subroutines, and may also include global variables, data types, and
1028 anything else convenient. Each recorded name is called a @dfn{tag}.
1029
1030 @menu
1031 * Tag Syntax::
1032 * Create Tag Table::
1033 * Select Tag Table::
1034 * Find Tag::
1035 * Tags Search::
1036 * Tags Stepping::
1037 * List Tags::
1038 @end menu
1039
1040 @node Tag Syntax, Create Tag Table, Tags, Tags
1041 @subsection Source File Tag Syntax
1042
1043 In Lisp code, any function defined with @code{defun}, any variable
1044 defined with @code{defvar} or @code{defconst}, and the first argument of
1045 any expression that starts with @samp{(def} in column zero, is a tag.
1046
1047 In C code, any C function is a tag, and so is any typedef if @code{-t} is
1048 specified when the tag table is constructed.
1049
1050 In Fortran code, functions and subroutines are tags.
1051
1052 In La@TeX{} text, the argument of any of the commands @code{\chapter},
1053 @code{\section}, @code{\subsection}, @code{\subsubsection}, @code{\eqno},
1054 @code{\label}, @code{\ref}, @code{\cite}, @code{\bibitem}, and
1055 @*@code{\typeout} is a tag.@refill
1056
1057 @node Create Tag Table, Select Tag Table, Tag Syntax, Tags
1058 @subsection Creating Tag Tables
1059 @cindex etags program
1060
1061 The @code{etags} program is used to create a tag table file. It knows
1062 the syntax of C, Fortran, La@TeX{}, Scheme, and Emacs Lisp/Common Lisp. To
1063 use @code{etags}, use it as a shell command:
1064
1065 @example
1066 etags @var{inputfiles}@dots{}
1067 @end example
1068 @noindent
1069
1070 The program reads the specified files and writes a tag table
1071 named @file{TAGS} in the current working directory. @code{etags}
1072 recognizes the language used in an input file based on the name and
1073 contents of the file; there are no switches for specifying the language.
1074 The @code{-t} switch tells @code{etags} to record typedefs in C code as
1075 tags.
1076
1077 If the tag table data become outdated due to changes in the files
1078 described in the table, you can update the tag table by running the
1079 program from the shell again. It is not necessary to do this often.
1080
1081 If the tag table fails to record a tag, or records it for the wrong file,
1082 Emacs cannot find its definition. However, if the position
1083 recorded in the tag table becomes a little bit wrong (due to some editing
1084 in the file that the tag definition is in), the only consequence is to slow
1085 down finding the tag slightly. Even if the stored position is very wrong,
1086 Emacs will still find the tag, but it must search the entire file for it.
1087
1088 You should update a tag table when you define new tags you want
1089 to have listed, when you move tag definitions from one file to another,
1090 or when changes become substantial. You don't have to update
1091 the tag table after each edit, or even every day.
1092
1093 @node Select Tag Table, Find Tag, Create Tag Table, Tags
1094 @subsection Selecting a Tag Table
1095
1096 @vindex tag-table-alist
1097 At any time Emacs has one @dfn{selected} tag table, and all the commands
1098 for working with tag tables use the selected one. To select a tag table,
1099 use the variable @code{tag-table-alist}.
1100
1101 The value of @code{tag-table-alist} is a list that determines which
1102 @code{TAGS} files should be active for a given buffer. This is not
1103 really an association list, in that all elements are checked. The car
1104 of each element of this list is a pattern against which the buffers file
1105 name is compared; if it matches, then the cdr of the list should be the
1106 name of the tags table to use. If more than one element of this list
1107 matches the buffers file name, all of the associated tags tables are
1108 used. Earlier ones are searched first.
1109
1110 If the car of elements of this list are strings, they are treated
1111 as regular-expressions against which the file is compared (like the
1112 @code{auto-mode-alist}). If they are not strings, they are evaluated.
1113 If they evaluate to non-@code{nil}, the current buffer is considered to
1114 match.
1115
1116 If the cdr of the elements of this list are strings, they are
1117 assumed to name a tags file. If they name a directory, the string
1118 @file{tags} is appended to them to get the file name. If they are not
1119 strings, they are evaluated and must return an appropriate string.
1120
1121 For example:
1122
1123 @example
1124 (setq tag-table-alist
1125 '(("/usr/src/public/perl/" . "/usr/src/public/perl/perl-3.0/")
1126 ("\\.el$" . "/usr/local/emacs/src/")
1127 ("/jbw/gnu/" . "/usr15/degree/stud/jbw/gnu/")
1128 ("" . "/usr/local/emacs/src/")
1129 ))
1130 @end example
1131
1132 The example defines the tag table alist in the following way:
1133
1134 @itemize @bullet
1135 @item
1136 Anything in the directory @file{/usr/src/public/perl/}
1137 should use the @file{TAGS} file @file{/usr/src/public/perl/perl-3.0/TAGS}.
1138 @item
1139 Files ending in @file{.el} should use the @file{TAGS} file
1140 @file{/usr/local/emacs/src/TAGS}.
1141 @item
1142 Anything in or below the directory @file{/jbw/gnu/} should use the
1143 @file{TAGS} file @file{/usr15/degree/stud/jbw/gnu/TAGS}.
1144 @end itemize
1145
1146 If you had a file called @file{/usr/jbw/foo.el}, it would use both
1147 @file{TAGS} files, @* @file{/usr/local/emacs/src/TAGS} and
1148 @file{/usr15/degree/stud/jbw/gnu/TAGS} (in that order), because it
1149 matches both patterns.
1150
1151 If the buffer-local variable @code{buffer-tag-table} is set, it names a
1152 tags table that is searched before all others when @code{find-tag} is
1153 executed from this buffer.
1154
1155 If there is a file called @file{TAGS} in the same directory as the file
1156 in question, then that tags file will always be used as well (after the
1157 @code{buffer-tag-table} but before the tables specified by this list).
1158
1159 If the variable @code{tags-file-name} is set, the @file{TAGS} file it names
1160 will apply to all buffers (for backwards compatibility.) It is searched
1161 first.
1162
1163 @vindex tags-always-build-completion-table
1164 If the value of the variable @code{tags-always-build-completion-table}
1165 is @code{t}, the tags file will always be added to the completion table
1166 without asking first, regardless of the size of the tags file.
1167
1168 @vindex tags-file-name
1169 @findex visit-tags-table
1170 The function @kbd{M-x visit-tags-table}, is largely made obsolete by
1171 the variable @code{tag-table-alist}, tells tags commands to use the tags
1172 table file @var{file} first. The @var{file} should be the name of a
1173 file created with the @code{etags} program. A directory name is also
1174 acceptable; it means the file @file{TAGS} in that directory. The
1175 function only stores the file name you provide in the variable
1176 @code{tags-file-name}. Emacs does not actually read in the tag table
1177 contents until you try to use them. You can set the variable explicitly
1178 instead of using @code{visit-tags-table}. The value of the variable
1179 @code{tags-file-name} is the name of the tags table used by all buffers.
1180 This is for backward compatibility, and is largely supplanted by the
1181 variable @code{tag-table-alist}.
1182
1183 @node Find Tag, Tags Search, Select Tag Table, Tags
1184 @subsection Finding a Tag
1185
1186 The most important thing that a tag table enables you to do is to find
1187 the definition of a specific tag.
1188
1189 @table @kbd
1190 @item M-.@: @var{tag &optional other-window}
1191 Find first definition of @var{tag} (@code{find-tag}).
1192 @item C-u M-.
1193 Find next alternate definition of last tag specified.
1194 @item C-x 4 . @var{tag}
1195 Find first definition of @var{tag}, but display it in another window
1196 (@code{find-tag-other-window}).
1197 @end table
1198
1199 @kindex M-.
1200 @findex find-tag
1201 @kbd{M-.}@: (@code{find-tag}) is the command to find the definition of
1202 a specified tag. It searches through the tag table for that tag, as a
1203 string, then uses the tag table information to determine the file in
1204 which the definition is used and the approximate character position of
1205 the definition in the file. Then @code{find-tag} visits the file,
1206 moves point to the approximate character position, and starts searching
1207 ever-increasing distances away for the text that should appear at
1208 the beginning of the definition.
1209
1210 If an empty argument is given (by typing @key{RET}), the sexp in the
1211 buffer before or around point is used as the name of the tag to find.
1212 @xref{Lists}, for information on sexps.
1213
1214 The argument to @code{find-tag} need not be the whole tag name; it can
1215 be a substring of a tag name. However, there can be many tag names
1216 containing the substring you specify. Since @code{find-tag} works by
1217 searching the text of the tag table, it finds the first tag in the table
1218 that the specified substring appears in. To find other tags that match
1219 the substring, give @code{find-tag} a numeric argument, as in @kbd{C-u
1220 M-.}. This does not read a tag name, but continues searching the tag
1221 table's text for another tag containing the same substring last used.
1222 If your keyboard has a real @key{META} key, @kbd{M-0 M-.}@: is an easier
1223 alternative to @kbd{C-u M-.}.
1224
1225 If the optional second argument @var{other-window} is non-@code{nil}, it uses
1226 another window to display the tag.
1227 Multiple active tags tables and completion are supported.
1228
1229 Variables of note include the following:
1230
1231 @vindex tag-table-alist
1232 @vindex tags-file-name
1233 @vindex tags-build-completion-table
1234 @vindex buffer-tag-table
1235 @vindex make-tags-files-invisible
1236 @vindex tag-mark-stack-max
1237
1238 @table @kbd
1239 @item tag-table-alist
1240 Controls which tables apply to which buffers.
1241 @item tags-file-name
1242 Stores a default tags table.
1243 @item tags-build-completion-table
1244 Controls completion behavior.
1245 @item buffer-tag-table
1246 Specifies a buffer-local table.
1247 @item make-tags-files-invisible
1248 Sets whether tags tables should be very hidden.
1249 @item tag-mark-stack-max
1250 Specifies how many tags-based hops to remember.
1251 @end table
1252
1253 @kindex C-x 4 .
1254 @findex find-tag-other-window
1255 Like most commands that can switch buffers, @code{find-tag} has another
1256 similar command that displays the new buffer in another window. @kbd{C-x 4
1257 .}@: invokes the function @code{find-tag-other-window}. (This key sequence
1258 ends with a period.)
1259
1260 Emacs comes with a tag table file @file{TAGS} (in the directory
1261 containing Lisp libraries) that includes all the Lisp libraries and all
1262 the C sources of Emacs. By specifying this file with @code{visit-tags-table}
1263 and then using @kbd{M-.}@: you can quickly look at the source of any Emacs
1264 function.
1265
1266 @node Tags Search, Tags Stepping, Find Tag, Tags
1267 @subsection Searching and Replacing with Tag Tables
1268
1269 The commands in this section visit and search all the files listed in the
1270 selected tag table, one by one. For these commands, the tag table serves
1271 only to specify a sequence of files to search. A related command is
1272 @kbd{M-x grep} (@pxref{Compilation}).
1273
1274 @table @kbd
1275 @item M-x tags-search
1276 Search for the specified regexp through the files in the selected tag
1277 table.
1278 @item M-x tags-query-replace
1279 Perform a @code{query-replace} on each file in the selected tag table.
1280 @item M-,
1281 Restart one of the commands above, from the current location of point
1282 (@code{tags-loop-continue}).
1283 @end table
1284
1285 @findex tags-search
1286 @kbd{M-x tags-search} reads a regexp using the minibuffer, then visits
1287 the files of the selected tag table one by one, and searches through each
1288 file for that regexp. It displays the name of the file being searched so
1289 you can follow its progress. As soon as an occurrence is found,
1290 @code{tags-search} returns.
1291
1292 @kindex M-,
1293 @findex tags-loop-continue
1294 After you have found one match, you probably want to find all the rest.
1295 To find one more match, type @kbd{M-,} (@code{tags-loop-continue}) to
1296 resume the @code{tags-search}. This searches the rest of the current
1297 buffer, followed by the remaining files of the tag table.
1298
1299 @findex tags-query-replace
1300 @kbd{M-x tags-query-replace} performs a single @code{query-replace}
1301 through all the files in the tag table. It reads a string to search for
1302 and a string to replace with, just like ordinary @kbd{M-x query-replace}.
1303 It searches much like @kbd{M-x tags-search} but repeatedly, processing
1304 matches according to your input. @xref{Replace}, for more information on
1305 @code{query-replace}.@refill
1306
1307 It is possible to get through all the files in the tag table with a
1308 single invocation of @kbd{M-x tags-query-replace}. But since any
1309 unrecognized character causes the command to exit, you may need to continue
1310 from where you left off. You can use @kbd{M-,} to do this. It resumes
1311 the last tags search or replace command that you did.
1312
1313 It may have struck you that @code{tags-search} is a lot like @code{grep}.
1314 You can also run @code{grep} itself as an inferior of Emacs and have Emacs
1315 show you the matching lines one by one. This works mostly the same as
1316 running a compilation and having Emacs show you where the errors were.
1317 @xref{Compilation}.
1318
1319 @node Tags Stepping, List Tags, Tags Search, Tags
1320 @subsection Stepping Through a Tag Table
1321 @findex next-file
1322
1323 If you wish to process all the files in a selected tag table, but
1324 @kbd{M-x tags-search} and @kbd{M-x tags-query-replace} are not giving
1325 you the desired result, you can use @kbd{M-x next-file}.
1326
1327 @table @kbd
1328 @item C-u M-x next-file
1329 With a numeric argument, regardless of its value, visit the first
1330 file in the tag table and prepare to advance sequentially by files.
1331 @item M-x next-file
1332 Visit the next file in the selected tag table.
1333 @end table
1334
1335 @node List Tags,, Tags Stepping, Tags
1336 @subsection Tag Table Inquiries
1337
1338 @table @kbd
1339 @item M-x list-tags
1340 Display a list of the tags defined in a specific program file.
1341 @item M-x tags-apropos
1342 Display a list of all tags matching a specified regexp.
1343 @end table
1344
1345 @findex list-tags
1346 @kbd{M-x list-tags} reads the name of one of the files described by the
1347 selected tag table, and displays a list of all the tags defined in that
1348 file. The ``file name'' argument is really just a string to compare
1349 against the names recorded in the tag table; it is read as a string rather
1350 than a file name. Therefore, completion and defaulting are not
1351 available, and you must enter the string the same way it appears in the tag
1352 table. Do not include a directory as part of the file name unless the file
1353 name recorded in the tag table contains that directory.
1354
1355 @findex tags-apropos
1356 @kbd{M-x tags-apropos} is like @code{apropos} for tags. It reads a regexp,
1357 then finds all the tags in the selected tag table whose entries match that
1358 regexp, and displays the tag names found.
1359
1360 @node Fortran, Asm Mode, Tags, Programs
1361 @section Fortran Mode
1362 @cindex Fortran mode
1363
1364 Fortran mode provides special motion commands for Fortran statements and
1365 subprograms, and indentation commands that understand Fortran conventions
1366 of nesting, line numbers, and continuation statements.
1367
1368 Special commands for comments are provided because Fortran comments are
1369 unlike those of other languages.
1370
1371 Built-in abbrevs optionally save typing when you insert Fortran keywords.
1372
1373 @findex fortran-mode
1374 Use @kbd{M-x fortran-mode} to switch to this major mode. Doing so calls
1375 the value of @code{fortran-mode-hook} as a function of no arguments if
1376 that variable has a non-@code{nil} value.
1377
1378 @menu
1379 * Motion: Fortran Motion. Moving point by statements or subprograms.
1380 * Indent: Fortran Indent. Indentation commands for Fortran.
1381 * Comments: Fortran Comments. Inserting and aligning comments.
1382 * Columns: Fortran Columns. Measuring columns for valid Fortran.
1383 * Abbrev: Fortran Abbrev. Built-in abbrevs for Fortran keywords.
1384 @end menu
1385
1386 Fortran mode was contributed by Michael Prange.
1387
1388 @node Fortran Motion, Fortran Indent, Fortran, Fortran
1389 @subsection Motion Commands
1390
1391 Fortran mode provides special commands to move by subprograms (functions
1392 and subroutines) and by statements. There is also a command to put the
1393 region around one subprogram, which is convenient for killing it or moving it.
1394
1395 @kindex C-M-a (Fortran mode)
1396 @kindex C-M-e (Fortran mode)
1397 @kindex C-M-h (Fortran mode)
1398 @kindex C-c C-p (Fortran mode)
1399 @kindex C-c C-n (Fortran mode)
1400 @findex beginning-of-fortran-subprogram
1401 @findex end-of-fortran-subprogram
1402 @findex mark-fortran-subprogram
1403 @findex fortran-previous-statement
1404 @findex fortran-next-statement
1405
1406 @table @kbd
1407 @item C-M-a
1408 Move to beginning of subprogram@*
1409 (@code{beginning-of-fortran-subprogram}).
1410 @item C-M-e
1411 Move to end of subprogram (@code{end-of-fortran-subprogram}).
1412 @item C-M-h
1413 Put point at beginning of subprogram and mark at end
1414 (@code{mark-fortran-subprogram}).
1415 @item C-c C-n
1416 Move to beginning of current or next statement
1417 (@code{fortran-next-@*statement}).
1418 @item C-c C-p
1419 Move to beginning of current or previous statement
1420 (@code{fortran-@*previous-statement}).
1421 @end table
1422
1423 @node Fortran Indent, Fortran Comments, Fortran Motion, Fortran
1424 @subsection Fortran Indentation
1425
1426 Special commands and features are available for indenting Fortran
1427 code. They make sure various syntactic entities (line numbers, comment line
1428 indicators, and continuation line flags) appear in the columns that are
1429 required for standard Fortran.
1430
1431 @menu
1432 * Commands: ForIndent Commands. Commands for indenting Fortran.
1433 * Numbers: ForIndent Num. How line numbers auto-indent.
1434 * Conv: ForIndent Conv. Conventions you must obey to avoid trouble.
1435 * Vars: ForIndent Vars. Variables controlling Fortran indent style.
1436 @end menu
1437
1438 @node ForIndent Commands, ForIndent Num, Fortran Indent, Fortran Indent
1439 @subsubsection Fortran Indentation Commands
1440
1441 @table @kbd
1442 @item @key{TAB}
1443 Indent the current line (@code{fortran-indent-line}).
1444 @item M-@key{LFD}
1445 Break the current line and set up a continuation line.
1446 @item C-M-q
1447 Indent all the lines of the subprogram point is in
1448 (@code{fortran-indent-subprogram}).
1449 @end table
1450
1451 @findex fortran-indent-line
1452 @key{TAB} is redefined by Fortran mode to reindent the current line for
1453 Fortran (@code{fortran-indent-line}). Line numbers and continuation
1454 markers are indented to their required columns, and the body of the
1455 statement is independently indented, based on its nesting in the program.
1456
1457 @kindex C-M-q (Fortran mode)
1458 @findex fortran-indent-subprogram
1459 The key @kbd{C-M-q} is redefined as @code{fortran-indent-subprogram}, a
1460 command that reindents all the lines of the Fortran subprogram (function or
1461 subroutine) containing point.
1462
1463 @kindex M-LFD (Fortran mode)
1464 @findex fortran-split-line
1465 The key @kbd{M-@key{LFD}} is redefined as @code{fortran-split-line}, a
1466 command to split a line in the appropriate fashion for Fortran. In a
1467 non-comment line, the second half becomes a continuation line and is
1468 indented accordingly. In a comment line, both halves become separate
1469 comment lines.
1470
1471 @node ForIndent Num, ForIndent Conv, ForIndent Commands, Fortran Indent
1472 @subsubsection Line Numbers and Continuation
1473
1474 If a number is the first non-whitespace in the line, it is assumed to be
1475 a line number and is moved to columns 0 through 4. (Columns are always
1476 counted from 0 in XEmacs.) If the text on the line starts with the
1477 conventional Fortran continuation marker @samp{$}, it is moved to column 5.
1478 If the text begins with any non whitespace character in column 5, it is
1479 assumed to be an unconventional continuation marker and remains in column
1480 5.
1481
1482 @vindex fortran-line-number-indent
1483 Line numbers of four digits or less are normally indented one space.
1484 This amount is controlled by the variable @code{fortran-line-number-indent},
1485 which is the maximum indentation a line number can have. Line numbers
1486 are indented to right-justify them to end in column 4 unless that would
1487 require more than the maximum indentation. The default value of the
1488 variable is 1.
1489
1490 @vindex fortran-electric-line-number
1491 Simply inserting a line number is enough to indent it according to these
1492 rules. As each digit is inserted, the indentation is recomputed. To turn
1493 off this feature, set the variable @code{fortran-electric-line-number} to
1494 @code{nil}. Then inserting line numbers is like inserting anything else.
1495
1496 @node ForIndent Conv, ForIndent Vars, ForIndent Num, Fortran Indent
1497 @subsubsection Syntactic Conventions
1498
1499 Fortran mode assumes that you follow certain conventions that simplify
1500 the task of understanding a Fortran program well enough to indent it
1501 properly:
1502
1503 @vindex fortran-continuation-char
1504 @itemize @bullet
1505 @item
1506 Two nested @samp{do} loops never share a @samp{continue} statement.
1507
1508 @item
1509 The same character appears in column 5 of all continuation lines. It
1510 is the value of the variable @code{fortran-continuation-char}.
1511 By default, this character is @samp{$}.
1512 @end itemize
1513
1514 @noindent
1515 If you fail to follow these conventions, the indentation commands may
1516 indent some lines unaesthetically. However, a correct Fortran program will
1517 retain its meaning when reindented even if the conventions are not
1518 followed.
1519
1520 @node ForIndent Vars,, ForIndent Conv, Fortran Indent
1521 @subsubsection Variables for Fortran Indentation
1522
1523 @vindex fortran-do-indent
1524 @vindex fortran-if-indent
1525 @vindex fortran-continuation-indent
1526 @vindex fortran-check-all-num-for-matching-do
1527 @vindex fortran-minimum-statement-indent
1528 Several additional variables control how Fortran indentation works.
1529
1530 @table @code
1531 @item fortran-do-indent
1532 Extra indentation within each level of @samp{do} statement (the default is 3).
1533
1534 @item fortran-if-indent
1535 Extra indentation within each level of @samp{if} statement (the default is 3).
1536
1537 @item fortran-continuation-indent
1538 Extra indentation for bodies of continuation lines (the default is 5).
1539
1540 @item fortran-check-all-num-for-matching-do
1541 If this is @code{nil}, indentation assumes that each @samp{do}
1542 statement ends on a @samp{continue} statement. Therefore, when
1543 computing indentation for a statement other than @samp{continue}, it
1544 can save time by not checking for a @samp{do} statement ending there.
1545 If this is non-@code{nil}, indenting any numbered statement must check
1546 for a @samp{do} that ends there. The default is @code{nil}.
1547
1548 @item fortran-minimum-statement-indent
1549 Minimum indentation for Fortran statements. For standard Fortran,
1550 this is 6. Statement bodies are always indented at least this much.
1551 @end table
1552
1553 @node Fortran Comments, Fortran Columns, Fortran Indent, Fortran
1554 @subsection Comments
1555
1556 The usual Emacs comment commands assume that a comment can follow a line
1557 of code. In Fortran, the standard comment syntax requires an entire line
1558 to be just a comment. Therefore, Fortran mode replaces the standard Emacs
1559 comment commands and defines some new variables.
1560
1561 Fortran mode can also handle a non-standard comment syntax where comments
1562 start with @samp{!} and can follow other text. Because only some Fortran
1563 compilers accept this syntax, Fortran mode will not insert such comments
1564 unless you have specified to do so in advance by setting the variable
1565 @code{comment-start} to @samp{"!"} (@pxref{Variables}).
1566
1567 @table @kbd
1568 @item M-;
1569 Align comment or insert new comment (@code{fortran-comment-indent}).
1570
1571 @item C-x ;
1572 Applies to nonstandard @samp{!} comments only.
1573
1574 @item C-c ;
1575 Turn all lines of the region into comments, or (with arg)
1576 turn them back into real code (@code{fortran-comment-region}).
1577 @end table
1578
1579 @kbd{M-;} in Fortran mode is redefined as the command
1580 @code{fortran-comment-indent}. Like the usual @kbd{M-;} command,
1581 it recognizes an existing comment and aligns its text appropriately.
1582 If there is no existing comment, a comment is inserted and aligned.
1583
1584 Inserting and aligning comments is not the same in Fortran mode as in
1585 other modes. When a new comment must be inserted, a full-line comment is
1586 inserted if the current line is blank. On a non-blank line, a
1587 non-standard @samp{!} comment is inserted if you previously specified
1588 you wanted to use them. Otherwise a full-line comment is inserted on a
1589 new line before the current line.
1590
1591 Non-standard @samp{!} comments are aligned like comments in other
1592 languages, but full-line comments are aligned differently. In a
1593 standard full-line comment, the comment delimiter itself must always
1594 appear in column zero. What can be aligned is the text within the
1595 comment. You can choose from three styles of alignment by setting the
1596 variable @code{fortran-comment-indent-style} to one of these values:
1597
1598 @vindex fortran-comment-indent-style
1599 @vindex fortran-comment-line-column
1600 @table @code
1601 @item fixed
1602 The text is aligned at a fixed column, which is the value of
1603 @code{fortran-comment-line-column}. This is the default.
1604 @item relative
1605 The text is aligned as if it were a line of code, but with an
1606 additional @code{fortran-comment-line-column} columns of indentation.
1607 @item nil
1608 Text in full-line columns is not moved automatically.
1609 @end table
1610
1611 @vindex fortran-comment-indent-char
1612 You can also specify the character to be used to indent within
1613 full-line comments by setting the variable @code{fortran-comment-indent-char}
1614 to the character you want to use.
1615
1616 @vindex comment-line-start
1617 @vindex comment-line-start-skip
1618 Fortran mode introduces two variables @code{comment-line-start} and
1619 @code{comment-line-start-skip}, which do for full-line comments what
1620 @code{comment-start} and @code{comment-start-skip} do for
1621 ordinary text-following comments. Normally these are set properly by
1622 Fortran mode, so you do not need to change them.
1623
1624 The normal Emacs comment command @kbd{C-x ;} has not been redefined.
1625 It can therefore be used if you use @samp{!} comments, but is useless in
1626 Fortran mode otherwise.
1627
1628 @kindex C-c ; (Fortran mode)
1629 @findex fortran-comment-region
1630 @vindex fortran-comment-region
1631 The command @kbd{C-c ;} (@code{fortran-comment-region}) turns all the
1632 lines of the region into comments by inserting the string @samp{C$$$} at
1633 the front of each one. With a numeric arg, the region is turned back into
1634 live code by deleting @samp{C$$$} from the front of each line. You can
1635 control the string used for the comments by setting the variable
1636 @code{fortran-comment-region}. Note that here we have an example of a
1637 command and a variable with the same name; the two uses of the name never
1638 conflict because in Lisp and in Emacs it is always clear from the context
1639 which one is referred to.
1640
1641 @node Fortran Columns, Fortran Abbrev, Fortran Comments, Fortran
1642 @subsection Columns
1643
1644 @table @kbd
1645 @item C-c C-r
1646 Displays a ``column ruler'' momentarily above the current line
1647 (@code{fortran-column-ruler}).
1648 @item C-c C-w
1649 Splits the current window horizontally so that it is 72 columns wide.
1650 This may help you avoid going over that limit (@code{fortran-window-create}).
1651 @end table
1652
1653 @kindex C-c C-r (Fortran mode)
1654 @findex fortran-column-ruler
1655 The command @kbd{C-c C-r} (@code{fortran-column-ruler}) shows a column
1656 ruler above the current line. The comment ruler consists of two lines
1657 of text that show you the locations of columns with special significance
1658 in Fortran programs. Square brackets show the limits of the columns for
1659 line numbers, and curly brackets show the limits of the columns for the
1660 statement body. Column numbers appear above them.
1661
1662 Note that the column numbers count from zero, as always in XEmacs. As
1663 a result, the numbers may not be those you are familiar with; but the
1664 actual positions in the line are standard Fortran.
1665
1666 The text used to display the column ruler is the value of the variable
1667 @code{fortran-comment-ruler}. By changing this variable, you can change
1668 the display.
1669
1670 @kindex C-c C-w (Fortran mode)
1671 @findex fortran-window-create
1672 For even more help, use @kbd{C-c C-w} (@code{fortran-window-create}), a
1673 command which splits the current window horizontally, resulting in a window 72
1674 columns wide. When you edit in this window, you can immediately see
1675 when a line gets too wide to be correct Fortran.
1676
1677 @node Fortran Abbrev,, Fortran Columns, Fortran
1678 @subsection Fortran Keyword Abbrevs
1679
1680 Fortran mode provides many built-in abbrevs for common keywords and
1681 declarations. These are the same sort of abbrevs that you can define
1682 yourself. To use them, you must turn on Abbrev mode. @pxref{Abbrevs}.
1683
1684 The built-in abbrevs are unusual in one way: they all start with a
1685 semicolon. You cannot normally use semicolon in an abbrev, but Fortran
1686 mode makes this possible by changing the syntax of semicolon to ``word
1687 constituent''.
1688
1689 For example, one built-in Fortran abbrev is @samp{;c} for
1690 @samp{continue}. If you insert @samp{;c} and then insert a punctuation
1691 character such as a space or a newline, the @samp{;c} changes
1692 automatically to @samp{continue}, provided Abbrev mode is enabled.@refill
1693
1694 Type @samp{;?} or @samp{;C-h} to display a list of all built-in
1695 Fortran abbrevs and what they stand for.
1696
1697 @node Asm Mode,, Fortran, Programs
1698 @section Asm Mode
1699
1700 @cindex Asm mode
1701 Asm mode is a major mode for editing files of assembler code. It
1702 defines these commands:
1703
1704 @table @kbd
1705 @item @key{TAB}
1706 @code{tab-to-tab-stop}.
1707 @item @key{LFD}
1708 Insert a newline and then indent using @code{tab-to-tab-stop}.
1709 @item :
1710 Insert a colon and then remove the indentation from before the label
1711 preceding colon. Then do @code{tab-to-tab-stop}.
1712 @item ;
1713 Insert or align a comment.
1714 @end table
1715
1716 The variable @code{asm-comment-char} specifies which character
1717 starts comments in assembler syntax.