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TextFile

Info file emacs, produced by texinfo-format-buffer   -*-Text-*-
from file emacs.tex

This file documents the GNU Emacs editor.

Copyright (C) 1985, 1986 Richard M. Stallman.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
sections entitled "The GNU Manifesto", "Distribution" and "GNU Emacs
General Public License" are included exactly as in the original, and
provided that the entire resulting derived work is distributed under the
terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the sections entitled "The GNU Manifesto", "Distribution"
and "GNU Emacs General Public License" may be included in a translation
approved by the author instead of in the original English.

▶1f◀
File: emacs  Node: Defuns, Prev: Lists, Up: Programs, Next: Grinding

Defuns
======

  In Emacs, a parenthetical grouping at the top level in the buffer is
called a "defun".  The name derives from the fact that most top-level
lists in a Lisp file are instances of the special form `defun', but
any top-level parenthetical grouping counts as a defun in Emacs parlance
regardless of what its contents are, and regardless of the programming
language in use.  For example, in C, the body of a function definition is a
defun.

`C-M-a'     
     Move to beginning of current or preceding defun
     (`beginning-of-defun').
`C-M-e'     
     Move to end of current or following defun (`end-of-defun').
`C-M-h'     
     Put region around whole current or following defun (`mark-defun').

  The commands to move to the beginning and end of the current defun are
`C-M-a' (`beginning-of-defun') and `C-M-e' (`end-of-defun').

  If you wish to operate on the current defun, use `C-M-h'
(`mark-defun') which puts point at the beginning and mark at the end
of the current or next defun.  For example, this is the easiest way to get
ready to move the defun to a different place in the text.  In C mode,
`C-M-h' runs the function `mark-c-function', which is almost the
same as `mark-defun'; the difference is that it backs up over the
argument declarations, function name and returned data type so that the
entire C function is inside the region.

  Emacs assumes that any open-parenthesis found in the leftmost column is
the start of a defun.  Therefore, never put an open-parenthesis at the
left margin in a Lisp file unless it is the start of a top level list.
Never put an open-brace or other opening delimiter at the beginning of a
line of C code unless it starts the body of a function.  The most likely
problem case is when you want an opening delimiter at the start of a line
inside a string.  To avoid trouble, put an escape character (`\', in C
and Emacs Lisp, `/' in some other Lisp dialects) before the opening
delimiter.  It will not affect the contents of the string.

  In the remotest past, the original Emacs found defuns by moving upward a
level of parentheses until there were no more levels to go up.  This always
required scanning all the way back to the beginning of the buffer, even for
a small function.  To speed up the operation, Emacs was changed to assume
that any `(' (or other character assigned the syntactic class of
opening-delimiter) at the left margin is the start of a defun.  This
heuristic was nearly always right and avoided the costly scan; however,
it mandated the convention described above.

▶1f◀
File: emacs  Node: Grinding, Prev: Defuns, Up: Programs, Next: Matching

Indentation for Programs
========================

  The best way to keep a program properly indented ("ground") is to use
Emacs to re-indent it as you change it.  Emacs has commands to indent
properly either a single line, a specified number of lines, or all of the
lines inside a single parenthetical grouping.

* Menu:

* Basic Indent::
* Multi-line Indent::   Commands to reindent many lines at once.
* Lisp Indent::		Specifying how each Lisp function should be indented.
* C Indent::		Choosing an indentation style for C code.

▶1f◀
File: emacs  Node: Basic Indent, Prev: Grinding, Up: Grinding, Next: Multi-line Indent

Basic Program Indentation Commands
----------------------------------

`TAB'     
     Adjust indentation of current line.
`LFD'     
     Equivalent to RET followed by TAB (`newline-and-indent').

  The basic indentation command is TAB, which gives the current line
the correct indentation as determined from the previous lines.  The
function that TAB runs depends on the major mode; it is `lisp-indent-line'
in Lisp mode, `c-indent-line' in C mode, etc.  These functions
understand different syntaxes for different languages, but they all do
about the same thing.  TAB in any programming language major mode
inserts or deletes whitespace at the beginning of the current line,
independent of where point is in the line.  If point is inside the
whitespace at the beginning of the line, TAB leaves it at the end of
that whitespace; otherwise, TAB leaves point fixed with respect to
the characters around it.

  Use `C-q TAB' to insert a tab at point.

  When entering a large amount of new code, use LFD (`newline-and-indent'),
which is equivalent to a RET followed by a TAB.  LFD creates
a blank line, and then gives it the appropriate indentation.

  TAB indents the second and following lines of the body of an
parenthetical grouping each under the preceding one; therefore, if you
alter one line's indentation to be nonstandard, the lines below will tend
to follow it.  This is the right behavior in cases where the standard
result of TAB is unaesthetic.

  Remember that an open-parenthesis, open-brace or other opening delimiter
at the left margin is assumed by Emacs (including the indentation routines)
to be the start of a function.  Therefore, you must never have an opening
delimiter in column zero that is not the beginning of a function, not even
inside a string.  This restriction is vital for making the indentation
commands fast; you must simply accept it.  *Note Defuns::, for more
information on this.

▶1f◀
File: emacs  Node: Multi-line Indent, Prev: Basic Indent, Up: Grinding, Next: Lisp Indent

Indenting Several Lines
-----------------------

  When you wish to re-indent several lines of code which have been altered
or moved to a different level in the list structure, you have several
commands available.

`C-M-q'     
     Re-indent all the lines within one list (`indent-sexp').
`C-u TAB'     
     Shift an entire list rigidly sideways so that its first line
     is properly indented.
`C-M-\'     
     Re-indent all lines in the region (`indent-region').

  You can re-indent the contents of a single list by positioning point
before the beginning of it and typing `C-M-q' (`indent-sexp' in
Lisp mode, `indent-c-exp' in C mode; also bound to other suitable
functions in other modes).  The indentation of the line the sexp starts on
is not changed; therefore, only the relative indentation within the list,
and not its position, is changed.  To correct the position as well, type a
TAB before the `C-M-q'.

  If the relative indentation within a list is correct but the indentation
of its beginning is not, go to the line the list begins on and type
`C-u TAB'.  When TAB is given a numeric argument, it moves all the
lines in the grouping starting on the current line sideways the same amount
that the current line moves.  It is clever, though, and does not move lines
that start inside strings, or C preprocessor lines when in C mode.

  Another way to specify the range to be re-indented is with point and
mark.  The command `C-M-\' (`indent-region') applies TAB to every line
whose first character is between point and mark.
 
▶1f◀
File: emacs  Node: Lisp Indent, Prev: Multi-line Indent, Up: Grinding, Next: C Indent

Customizing Lisp Indentation
----------------------------

  The indentation pattern for a Lisp expression can depend on the function
called by the expression.  For each Lisp function, you can choose among
several predefined patterns of indentation, or define an arbitrary one with
a Lisp program.

  The standard pattern of indentation is as follows: the second line of the
expression is indented under the first argument, if that is on the same
line as the beginning of the expression; otherwise, the second line is
indented underneath the function name.  Each following line is indented
under the previous line whose nesting depth is the same.

  If the variable `lisp-indent-offset' is non-`nil', it overrides
the usual indentation pattern for the second line of an expression, so that
such lines are always indented `lisp-indent-offset' more columns than
the containing list.

  The standard pattern is overridded for certain functions.  Functions
whose names start with `def' always indent the second line by
`lisp-body-indention' extra columns beyond the open-parenthesis
starting the expression.

  The standard pattern can be overridden in various ways for individual
functions, according to the `lisp-indent-hook' property of the
function name.  There are four possibilities for this property:

`nil'     
     This is the same as no property; the standard indentation pattern is used.
`defun'     
     The pattern used for function names that start with `def' is used for
     this function also.
a number, NUMBER     
     The first NUMBER arguments of the function are
     "distinguished" arguments; the rest are considered the "body"
     of the expression.  A line in the expression is indented according to
     whether the first argument on it is distinguished or not.  If the
     argument is part of the body, the line is indented `lisp-body-indent'
     more columns than the open-parenthesis starting the containing
     expression.  If the argument is distinguished and is either the first
     or second argument, it is indented twice that many extra columns.
     If the argument is distinguished and not the first or second argument,
     the standard pattern is followed for that line.
a symbol, SYMBOL     
     SYMBOL should be a function name; that function is called to
     calculate the indentation of a line within this expression.  The
     function receives two arguments:
     STATE     
          The value returned by `parse-partial-sexp' (a Lisp primitive for
          indentation and nesting computation) when it parses up to the
          beginning of this line.
     POS     
          The position at which the line being indented begins.
     It should return either a number, which is the number of columns of
     indentation for that line, or a list whose car is such a number.  The
     difference between returning a number and returning a list is that a
     number says that all following lines at the same nesting level should
     be indented just like this one; a list says that following lines might
     call for different indentations.  This makes a difference when the
     indentation is being computed by `C-M-q'; if the value is a
     number, `C-M-q' need not recalculate indentation for the following
     lines until the end of the list.

▶1f◀
File: emacs  Node: C Indent, Prev: Lisp Indent, Up: Grinding

Customizing C Indentation
-------------------------

  Two variables control which commands perform C indentation and when.

  If `c-auto-newline' is non-`nil', newlines are inserted both
before and after braces that you insert, and after colons and semicolons.
Correct C indentation is done on all the lines that are made this way.

  If `c-tab-always-indent' is non-`nil', the TAB command
in C mode does indentation only if point is at the left margin or within
the line's indentation.  If there is non-whitespace to the left of point,
then TAB just inserts a tab character in the buffer.  Normally,
this variable is `nil', and TAB always reindents the current line.

  C does not have anything analogous to particular function names for which
special forms of indentation are desirable.  However, it has a different
need for customization facilities: many different styles of C indentation
are in common use.

  There are six variables you can set to control the style that Emacs C
mode will use.

`c-indent-level'     
     Indentation of C statements within surrounding block.  The surrounding
     block's indentation is the indentation of the line on which the
     open-brace appears.
`c-continued-statement-offset'     
     Extra indentation given to a substatement, such as the then-clause of
     an if or body of a while.
`c-brace-offset'     
     Extra indentation for line if it starts with an open brace.
`c-brace-imaginary-offset'     
     An open brace following other text is treated as if it were this far
     to the right of the start of its line.
`c-argdecl-indent'     
     Indentation level of declarations of C function arguments.
`c-label-offset'     
     Extra indentation for line that is a label, or case or default.

  The variable `c-indent-level' controls the indentation for C
statements with respect to the surrounding block.  In the example

         {
           foo ();

the difference in indentation between the lines is `c-indent-level'.
Its standard value is 2.

If the open-brace beginning the compound statement is not at the beginning
of its line, the `c-indent-level' is added to the indentation of the
line, not the column of the open-brace.  For example,

     if (losing) {
       do_this ();

One popular indentation style is that which results from setting
`c-indent-level' to 8 and putting open-braces at the end of a line in
this way.  I prefer to put the open-brace on a separate line.

  In fact, the value of the variable `c-brace-imaginary-offset' is
also added to the indentation of such a statement.  Normally this variable
is zero.  Think of this variable as the imaginary position of the open
brace, relative to the first nonblank character on the line.  By setting
this variable to 4 and `c-indent-level' to 0, you can get this style:

     if (x == y) {
         do_it ();
         }

  When `c-indent-level' is zero, the statements inside most braces
will line up right under the open brace.  But there is an exception made
for braces in column zero, such as surrounding a function's body.  The
statements just inside it do not go at column zero.  Instead,
`c-brace-offset' and `c-continued-statement-offset' (see below)
are added to produce a typical offset between brace levels, and the
statements are indented that far.

  `c-continued-statement-offset' controls the extra indentation for a
line that starts within a statement (but not within parentheses or
brackets).  These lines are usually statements that are within other
statements, such as the then-clauses of `if' statements and the bodies
of `while' statements.  This parameter is the difference in
indentation between the two lines in

     if (x == y)
       do_it ();

Its standard value is 2.  Some popular indentation styles correspond to a
value of zero for `c-continued-statement-offset'.

  `c-brace-offset' is the extra indentation given to a line that
starts with an open-brace.  Its standard value is zero;
compare

     if (x == y)
       {

with

     if (x == y)
       do_it ();

if `c-brace-offset' were set to 4, the first example would become

     if (x == y)
           {

  `c-argdecl-indent' controls the indentation of declarations of the
arguments of a C function.  It is absolute: argument declarations receive
exactly `c-argdecl-indent' spaces.  The standard value is 5, resulting
in code like this:

     char *
     index (string, char)
          char *string;
          int char;

  `c-label-offset' is the extra indentation given to a line that
contains a label, a case statement, or a `default:' statement.  Its
standard value is -2, resulting in code like this

     switch (c)
       {
       case 'x':

If `c-label-offset' were zero, the same code would be indented as

     switch (c)
       {
         case 'x':

This example assumes that the other variables above also have their
standard values.

  I strongly recommend that you try out the indentation style produced by
the standard settings of these variables, together with putting open braces
on separate lines.  You can see how it looks in all the C source files of
GNU Emacs.

▶1f◀
File: emacs  Node: Matching, Prev: Grinding, Up: Programs, Next: Comments

Automatic Display Of Matching Parentheses
=========================================

  The Emacs parenthesis-matching feature is designed to show automatically
how parentheses match in the text.  Whenever a self-inserting character
that is a closing delimiter is typed, the cursor moves momentarily to the
location of the matching opening delimiter, provided that is on the screen.
If it is not on the screen, some text starting with that opening delimiter
is displayed in the echo area.  Either way, you can tell what grouping is
being closed off.

  In Lisp, automatic matching applies only to parentheses.  In C, it
applies to braces and brackets too.  Emacs knows which characters to regard
as matching delimiters based on the syntax table, which is set by the major
mode.  *Note Syntax::.

  If the opening delimiter and closing delimiter are mismatched---such as
in `[x)'---a warning message is displayed in the echo area.  The
correct matches are specified in the syntax table.

  Two variables control parenthesis match display.  `blink-matching-paren'
turns the feature on or off; `nil' turns it off, but the default is
`t' to turn match display on.  `blink-matching-paren-distance'
specifies how many characters back to search to find the matching opening
delimiter.  If the match is not found in that far, scanning stops, and
nothing is displayed.  This is to prevent scanning for the matching
delimiter from wasting lots of time when there is no match.  The default
is 4000.

▶1f◀
File: emacs  Node: Comments, Prev: Matching, Up: Programs, Next: Balanced Editing

Manipulating Comments
=====================

  The comment commands insert, kill and align comments.

`M-;'     
     Insert or align comment (`indent-for-comment').
`C-x ;'     
     Set comment column (`set-comment-column').
`C-u - C-x ;'     
     Kill comment on current line (`kill-comment').
`M-LFD'     
     Like RET followed by inserting and aligning a comment
     (`indent-new-comment-line').

  The command that creates a comment is `Meta-;' (`indent-for-comment').
If there is no comment already on the line, a new comment is created,
aligned at a specific column called the "comment column".  The comment
is created by inserting the string Emacs thinks comments should start with
(the value of `comment-start'; see below).  Point is left after that
string.  If the text of the line extends past the comment column, then the
indentation is done to a suitable boundary (usually, at least one space is
inserted).  If the major mode has specified a string to terminate comments,
that is inserted after point, to keep the syntax valid.

  `Meta-;' can also be used to align an existing comment.  If a line
already contains the string that starts comments, then `M-;' just moves
point after it and re-indents it to the conventional place.  Exception:
comments starting in column 0 are not moved.

  Some major modes have special rules for indenting certain kinds of
comments in certain contexts.  For example, in Lisp code, comments which
start with two semicolons are indented as if they were lines of code,
instead of at the comment column.  Comments which start with three
semicolons are supposed to start at the left margin.  Emacs understands
these conventions by indenting a double-semicolon comment using TAB,
and by not changing the indentation of a triple-semicolon comment at all.

     ;; This function is just an example
     ;;; Here either two or three semicolons are appropriate.
     (defun foo (x)
     ;;; And now, the first part of the function:
       ;; The following line adds one.
       (1+ x))           ; This line adds one.

  In C code, a comment preceded on its line by nothing but whitespace
is indented like a line of code.

  Even when an existing comment is properly aligned, `M-;' is still
useful for moving directly to the start of the comment.

  `C-u - C-x ;' (`kill-comment') kills the comment on the current line,
if there is one.  The indentation before the start of the comment is killed
as well.  If there does not appear to be a comment in the line, nothing is
done.  To reinsert the comment on another line, move to the end of that
line, do `C-y', and then do `M-;' to realign it.  Note that
`C-u - C-x ;' is not a distinct key; it is `C-x ;' (`set-comment-column')
with a negative argument.  That command is programmed so that when it
receives a negative argument it calls `kill-comment'.  However,
`kill-comment' is a valid command which you could bind directly to a
key if you wanted to.


Multiple Lines of Comments
--------------------------

  If you are typing a comment and find that you wish to continue it on
another line, you can use the command `Meta-LFD' (`indent-new-comment-line'),
which terminates the comment you are typing, creates a new blank line
afterward, and begins a new comment indented under the old one.  When Auto
Fill mode is on, going past the fill column while typing a comment causes
the comment to be continued in just this fashion.  If point is not at the
end of the line when `M-LFD' is typed, the text on the rest of
the line becomes part of the new comment line.


Options Controlling Comments
----------------------------

  The comment column is stored in the variable `comment-column'.  You
can set it to a number explicitly.  Alternatively, the command `C-x ;'
(`set-comment-column') sets the comment column to the column point is
at.  `C-u C-x ;' sets the comment column to match the last comment
before point in the buffer, and then does a `Meta-;' to align the
current line's comment under the previous one.  Note that `C-u - C-x ;'
runs the function `kill-comment' as described above.

  `comment-column' is a per-buffer variable; altering the variable
affects only the current buffer, but there is a default value which you can
change as well.  *Note Locals::.  Many major modes initialize this variable
for the current buffer.

  The comment commands recognize comments based on the regular expression
that is the value of the variable `comment-start-skip'.  This regexp
should not match the null string.  It may match more than the comment
starting delimiter in the strictest sense of the word; for example, in C
mode the value of the variable is `"/\\*+ *"', which matches extra
stars and spaces after the `/*' itself.  (Note that `\\' is
needed in Lisp syntax to include a `\' in the string, which is needed
to deny the first star its special meaning in regexp syntax.  *Note Regexps::.)

  When a comment command makes a new comment, it inserts the value of
`comment-start' to begin it.  The value of `comment-end' is
inserted after point, so that it will follow the text that you will insert
into the comment.  In C mode, `comment-start' has the value
`"/* "' and `comment-end' has the value `" */"'.

  `comment-multi-line' controls how `M-LFD' (`indent-new-comment-line')
behaves when used inside a comment.  If `comment-multi-line' is
`nil', as it normally is, then the comment on the starting line is
terminated and a new comment is started on the new following line.  If
`comment-multi-line' is not `nil', then the new following line is
set up as part of the same comment that was found on the starting line.
This is done by not inserting a terminator on the old line, and not
inserting a starter on the new line.  In languages where multi-line comments
work, the choice of value for this variable is a matter of taste.

  The variable `comment-indent-hook' should contain a function that
will be called to compute the indentation for a newly inserted comment or
for aligning an existing comment.  It is set differently by various major
modes.  The function is called with no arguments, but with point at the
beginning of the comment, or at the end of a line if a new comment is to be
inserted.  It should return the column in which the comment ought to start.
For example, in Lisp mode, the indent hook function bases its decision
on how many semicolons begin an existing comment, and on the code in the
preceding lines.

▶1f◀
File: emacs  Node: Balanced Editing, Prev: Comments, Up: Programs, Next: Lisp Completion

Editing Without Unbalanced Parentheses
======================================

`M-('     
     Put parentheses around next sexp(s) (`insert-parentheses').
`M-)'     
     Move past next close parenthesis and re-indent
     (`move-over-close-and-reindent').

  The commands `M-(' (`insert-parentheses') and `M-)'
(`move-over-close-and-reindent') are designed to facilitate a style of
editing which keeps parentheses balanced at all times.  `M-(' inserts a
pair of parentheses, either together as in `()', or, if given an
argument, around the next several sexps, and leaves point after the open
parenthesis.  Instead of typing `( F O O )', you can type `M-( F O
O', which has the same effect except for leaving the cursor before the
close parenthesis.  Then you would type `M-)', which moves past the
close parenthesis, deleting any indentation preceding it (in this example
there is none), and indenting with LFD after it.

▶1f◀
File: emacs  Node: Lisp Completion, Prev: Balanced Editing, Up: Programs, Next: Documentation

Completion for Lisp Symbols
===========================

  Usually completion happens in the minibuffer.  But one kind of completion
is available in all buffers: completion for Lisp symbol names.

  The command `M-TAB' (`lisp-complete-symbol') takes the
partial Lisp symbol before point to be an abbreviation, and compares it
against all nontrivial Lisp symbols currently known to Emacs.  Any
additional characters that they all have in common are inserted at point.
Nontrivial symbols are those that have function definitions, values or
properties.

  If there is an open-parenthesis immediately before the beginning of
the partial symbol, only symbols with function definitions are considered
as completions.

  If the partial name in the buffer has more than one possible completion
and they have no additional characters in common, a list of all possible
completions is displayed in another window.

▶1f◀
File: emacs  Node: Documentation, Prev: Lisp Completion, Up: Programs, Next: Change Log

Documentation Commands
======================

  As you edit Lisp code to be run in Emacs, the commands `C-h f'
(`describe-function') and `C-h v' (`describe-variable') can
be used to print documentation of functions and variables that you want to
call.  These commands use the minibuffer to read the name of a function or
variable to document, and display the documentation in a window.

  For extra convenience, these commands provide default arguments based on
the code in the neighborhood of point.  `C-h f' sets the default to the
function called in the innermost list containing point.  `C-h v' uses
the symbol name around or adjacent to point as its default.

  Documentation on Unix commands, system calls and libraries can be
obtained with the `M-x manual-entry' command.  This reads a topic as an
argument, and displays the text on that topic from the Unix manual.
`manual-entry' always searches all 8 sections of the manual, and
concatenates all the entries that are found.  For example, the topic
`termcap' finds the description of the termcap library from section 3,
followed by the description of the termcap data base from section 5.

▶1f◀
File: emacs  Node: Change Log, Prev: Documentation, Up: Programs, Next: Tags

Change Logs
===========

  The Emacs command `M-x add-change-log-entry' helps you keep a record
of when and why you have changed a program.  It assumes that you have a
file in which you write a chronological sequence of entries describing
individual changes.  The default is to store the change entries in a file
called `ChangeLog' in the same directory as the file you are editing.
The same `ChangeLog' file therefore records changes for all the files
in the directory.

  A change log entry starts with a header line that contains your name and
the current date.  Aside from these header lines, every line in the change
log starts with a tab.  One entry can describe several changes; each change
starts with a line starting with a tab and a star.  `M-x add-change-log-entry'
visits the change log file and creates a new entry unless the most recent
entry is for today's date and your name.  In either case, it adds a new
line to start the description of another change just after the header line
of the entry.  When `M-x add-change-log-entry' is finished, all is
prepared for you to edit in the description of what you changed and how.
You must then save the change log file yourself.

  The change log file is always visited in Indented Text mode, which means
that LFD and auto-filling indent each new line like the previous
line.  This is convenient for entering the contents of an entry, which must
all be indented.  *Note Text Mode::.

  Here is an example of the formatting conventions used in the change log
for Emacs:

     Wed Jun 26 19:29:32 1985  Richard M. Stallman  (rms at mit-prep)
     
             * xdisp.c (try_window_id):
             If C-k is done at end of next-to-last line,
             this fn updates window_end_vpos and cannot leave
             window_end_pos nonnegative (it is zero, in fact).
             If display is preempted before lines are output,
             this is inconsistent.  Fix by setting
             blank_end_of_window to nonzero.
     
     Tue Jun 25 05:25:33 1985  Richard M. Stallman  (rms at mit-prep)
     
             * cmds.c (Fnewline):
             Call the auto fill hook if appropriate.
     
             * xdisp.c (try_window_id):
             If point is found by compute_motion after xp, record that
             permanently.  If display_text_line sets point position wrong
             (case where line is killed, point is at eob and that line is
             not displayed), set it again in final compute_motion.

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File: emacs  Node: Tags, Prev: Change Log, Up: Programs, Next: Fortran

Tag Tables
==========

  A "tag table" is a description of how a multi-file program is broken
up into files.  It lists the names of the component files and the names and
positions of the functions in each file.  Grouping the related files makes
it possible to search or replace through all the files with one command.
Recording the function names and positions makes possible the `Meta-.'
command which you can use to find the definition of a function without
having to know which of the files it is in.

  Tag tables are stored in files called "tag table files".  The
conventional name for a tag table file is `TAGS'.

  Each entry in the tag table records the name of one tag, the name of the
file that the tag is defined in (implicitly), and the position in that file
of the tag's definition.

  Just what names from the described files are recorded in the tag table
depends on the programming language of the described file.  They normally
include all functions and subroutines, and may also include global
variables, data types, and anything else convenient.  In any case, each
name recorded is called a "tag".

* Menu:

* Tag Syntax::
* Create Tag Table::
* Select Tag Table::
* Find Tag::
* Tags Search::
* Tags Stepping::
* List Tags::

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File: emacs  Node: Tag Syntax, Prev: Tags, Up: Tags, Next: Create Tag Table

Source File Tag Syntax
----------------------

  In Lisp code, any function defined with `defun', any variable
defined with `defvar' or `defconst', and in general the first
argument of any expression that starts with `(def' in column zero, is
a tag.

  In C code, any C function is a tag, and so is any typedef if `-t' is
specified when the tag table is constructed.

  In Fortran code, functions and subroutines are tags.

  In LaTeX text, the argument of any of the commands `\chapter',
`\section', `\subsection', `\subsubsection', `\eqno', `\label', `\ref',
`\cite', `\bibitem' and `\typeout' is a tag.

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File: emacs  Node: Create Tag Table, Prev: Tag Syntax, Up: Tags, Next: Select Tag Table

Creating Tag Tables
-------------------

  The `etags' program is used to create a tag table file.  It knows
the syntax of C, Fortran, LaTeX, Scheme and Emacs Lisp/Common Lisp.  To
use `etags', type

     etags INPUTFILES...

as a shell command.  It reads the specified files and writes a tag table
named `TAGS' in the current working directory.  `etags'
recognizes the language used in an input file based on its file name and
contents; there are no switches for specifying the language.  The `-t'
switch tells `etags' to record typedefs in C code as tags.

  If the tag table data become outdated due to changes in the files
described in the table, the way to update the tag table is the same way it
was made in the first place.  It is not necessary to do this often.

  If the tag table fails to record a tag, or records it for the wrong file,
then Emacs cannot possibly find its definition.  However, if the position
recorded in the tag table becomes a little bit wrong (due to some editing
in the file that the tag definition is in), the only consequence is to slow
down finding the tag slightly.  Even if the stored position is very wrong,
Emacs will still find the tag, but it must search the entire file for it.

  So you should update a tag table when you define new tags that you want
to have listed, or when you move tag definitions from one file to another,
or when changes become substantial.  Normally there is no need to update
the tag table after each edit, or even every day.

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File: emacs  Node: Select Tag Table, Prev: Create Tag Table, Up: Tags, Next: Find Tag

Selecting a Tag Table
---------------------

  Emacs has at any time one "selected" tag table, and all the commands
for working with tag tables use the selected one.  To select a tag table,
type `M-x visit-tags-table', which reads the tag table file name as an
argument.  The name `TAGS' in the default directory is used as the
default file name.

  All this command does is store the file name in the variable
`tags-file-name'.  Emacs does not actually read in the tag table
contents until you try to use them.  Setting this variable yourself is just
as good as using `visit-tags-table'.  The variable's initial value is
`nil'; this value tells all the commands for working with tag tables
that they must ask for a tag table file name to use.

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File: emacs  Node: Find Tag, Prev: Select Tag Table, Up: Tags, Next: Tags Search

Finding a Tag
-------------

  The most important thing that a tag table enables you to do is to find
the definition of a specific tag.

`M-. TAG'     
     Find first definition of TAG (`find-tag').
`C-u M-.'     
     Find next alternate definition of last tag specified.
`C-x 4 . TAG'     
     Find first definition of TAG, but display it in another window
     (`find-tag-other-window').

  `M-.' (`find-tag') is the command to find the definition of a
specified tag.  It searches through the tag table for that tag, as a
string, and then uses the tag table info to determine the file that the
definition is in and the approximate character position in the file of the
definition.  Then `find-tag' visits that file, moves point to the
approximate character position, and starts searching ever-increasing
distances away for the the text that should appear at the beginning of the
definition.

  If an empty argument is given (just type RET), the sexp in the
buffer before or around point is used as the name of the tag to find.
*Note Lists::, for info on sexps.

  The argument to `find-tag' need not be the whole tag name; it can be
a substring of a tag name.  However, there can be many tag names containing
the substring you specify.  Since `find-tag' works by searching the
text of the tag table, it finds the first tag in the table that the
specified substring appears in.  The way to find other tags that match the
substring is to give `find-tag' a numeric argument, as in `C-u
M-.'; this does not read a tag name, but continues searching the tag
table's text for another tag containing the same substring last used.  If
you have a real META key, `M-0 M-.' is an easier alternative
to `C-u M-.'.

  Like most commands that can switch buffers, `find-tag' has another
similar command that displays the new buffer in another window.  `C-x 4
.' invokes the function `find-tag-other-window'.  (This key sequence
ends with a period.)

  Emacs comes with a tag table file `TAGS', in the directory
containing Lisp libraries, which includes all the Lisp libraries and all
the C sources of Emacs.  By specifying this file with `visit-tags-table'
and then using `M-.' you can quickly look at the source of any Emacs
function.

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File: emacs  Node: Tags Search, Prev: Find Tag, Up: Tags, Next: Tags Stepping

Searching and Replacing with Tag Tables
---------------------------------------

  The commands in this section visit and search all the files listed in the
selected tag table, one by one.  For these commands, the tag table serves
only to specify a sequence of files to search.  A related command is
`M-x grep' (*Note Compilation::).

`M-x tags-search'     
     Search for the specified regexp through the files in the selected tag
     table.
`M-x tags-query-replace'     
     Perform a `query-replace' on each file in the selected tag table.
`M-,'     
     Restart one of the commands above, from the current location of point
     (`tags-loop-continue').

  `M-x tags-search' reads a regexp using the minibuffer, then visits
the files of the selected tag table one by one, and searches through each
one for that regexp.  It displays the name of the file being searched so
you can follow its progress.  As soon as an occurrence is found,
`tags-search' returns.

  Having found one match, you probably want to find all the rest.  To find
one more match, type `M-,' (`tags-loop-continue') to resume the
`tags-search'.  This searches the rest of the current buffer, followed
by the remaining files of the tag table.

  `M-x tags-query-replace' performs a single `query-replace' through all
the files in the tag table.  It reads a string to search for and a string
to replace with, just like ordinary `M-x query-replace'.  It searches much
like `M-x tags-search' but repeatedly, processing matches according to your
input.  *Note Replace::, for more information on `query-replace'.

  It is possible to get through all the files in the tag table with a
single invocation of `M-x tags-query-replace'.  But since any
unrecognized character causes the command to exit, you may need to continue
where you left off.  `M-,' can be used for this.  It resumes the last
tags search or replace command that you did.

  It may have struck you that `tags-search' is a lot like `grep'.
You can also run `grep' itself as an inferior of Emacs and have Emacs
show you the matching lines one by one.  This works mostly the same as
running a compilation and having Emacs show you where the errors were.
*Note Compilation::.

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File: emacs  Node: Tags Stepping, Prev: Tags Search, Up: Tags, Next: List Tags

Stepping Through a Tag Table
----------------------------

  If you wish to process all the files in the selected tag table, but
`M-x tags-search' and `M-x tags-query-replace' in particular are not what
you want, you can use `M-x next-file'.

`C-u M-x next-file'     
     With a numeric argument, regardless of its value, visit the first
     file in the tag table, and prepare to advance sequentially by files.
`M-x next-file'     
     Visit the next file in the selected tag table.

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File: emacs  Node: List Tags, Prev: Tags Stepping, Up: Tags

Tag Table Inquiries
-------------------

`M-x list-tags'     
     Display a list of the tags defined in a specific program file.
`M-x tags-apropos'     
     Display a list of all tags matching a specified regexp.

  `M-x list-tags' reads the name of one of the files described by the
selected tag table, and displays a list of all the tags defined in that
file.  The "file name" argument is really just a string to compare
against the names recorded in the tag table; it is read as a string rather
than as a file name.  Therefore, completion and defaulting are not
available, and you must enter the string the same way it appears in the tag
table.  Do not include a directory as part of the file name unless the file
name recorded in the tag table includes a directory.

  `M-x tags-apropos' is like `apropos' for tags.  It reads a regexp,
then finds all the tags in the selected tag table whose entries match that
regexp, and displays the tag names found.

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File: emacs  Node: Fortran, Prev: Tags, Up: Programs

Fortran Mode
============

  Fortran mode provides special motion commands for Fortran statements and
subprograms, and indentation commands that understand Fortran conventions
of nesting, line numbers and continuation statements.

  Special commands for comments are provided because Fortran comments are
unlike those of other languages.

  Built-in abbrevs optionally save typing when you insert Fortran keywords.

  Use `M-x fortran-mode' to switch to this major mode.  Doing so calls
the value of `fortran-mode-hook' as a function of no arguments if
that variable has a value that is not `nil'.

* Menu:

* Motion: Fortran Motion.     Moving point by statements or subprograms.
* Indent: Fortran Indent.     Indentation commands for Fortran.
* Comments: Fortran Comments. Inserting and aligning comments.
* Columns: Fortran Columns.   Measuring columns for valid Fortran.
* Abbrev: Fortran Abbrev.     Built-in abbrevs for Fortran keywords.

  Fortran mode was contributed by Michael Prange.

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File: emacs  Node: Fortran Motion, Prev: Fortran, Up: Fortran, Next: Fortran Indent

Motion Commands
---------------

  Fortran mode provides special commands to move by subprograms (functions
and subroutines) and by statements.  There is also a command to put the
region around one subprogram, convenient for killing it or moving it.


`C-M-a'     
     Move to beginning of subprogram
     (`beginning-of-fortran-subprogram').
`C-M-e'     
     Move to end of subprogram (`end-of-fortran-subprogram').
`C-M-h'     
     Put point at beginning of subprogram and mark at end
     (`mark-fortran-subprogram').
`C-c C-n'     
     Move to beginning of current or next statement
     (`fortran-next-statement').
`C-c C-p'     
     Move to beginning of current or previous statement
     (`fortran-previous-statement').

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File: emacs  Node: Fortran Indent, Prev: Fortran Motion, Up: Fortran, Next: Fortran Comments

Fortran Indentation
-------------------

  Special commands and features are needed for indenting Fortran code in
order to make sure various syntactic entities (line numbers, comment line
indicators and continuation line flags) appear in the columns that are
required for standard Fortran.

* Menu:

* Commands: ForIndent Commands. Commands for indenting Fortran.
* Numbers:  ForIndent Num.      How line numbers auto-indent.
* Conv:     ForIndent Conv.     Conventions you must obey to avoid trouble.
* Vars:     ForIndent Vars.     Variables controlling Fortran indent style.

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File: emacs  Node: ForIndent Commands, Prev: Fortran Indent, Up: Fortran Indent, Next: ForIndent Num

Fortran Indentation Commands
............................

`TAB'     
     Indent the current line (`fortran-indent-line').
`M-LFD'     
     Break the current line and set up a continuation line.
`C-M-q'     
     Indent all the lines of the subprogram point is in
     (`fortran-indent-subprogram').

  TAB is redefined by Fortran mode to reindent the current line for
Fortran (`fortran-indent-line').  Line numbers and continuation
markers are indented to their required columns, and the body of the
statement is independently indented based on its nesting in the program.

  The key `C-M-q' is redefined as `fortran-indent-subprogram', a
command to reindent all the lines of the Fortran subprogram (function or
subroutine) containing point.

  The key `M-LFD' is redefined as `fortran-split-line', a
command to split a line in the appropriate fashion for Fortran.  In a
non-comment line, the second half becomes a continuation line and is
indented accordingly.  In a comment line, both halves become separate
comment lines.

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File: emacs  Node: ForIndent Num, Prev: ForIndent Commands, Up: Fortran Indent, Next: ForIndent Conv

Line Numbers and Continuation
.............................

  If a number is the first non-whitespace in the line, it is assumed to be
a line number and is moved to columns 0 through 4.  (Columns are always
counted from 0 in GNU Emacs.)  If the text on the line starts with the
conventional Fortran continuation marker `$', it is moved to column 5.
If the text begins with any non whitespace character in column 5, it is
assumed to be an unconventional continuation marker and remains in column
5.

  Line numbers of four digits or less are normally indented one space.
This amount is controlled by the variable `fortran-line-number-indent'
which is the maximum indentation a line number can have.  Line numbers
are indented to right-justify them to end in column 4 unless that would
require more than this maximum indentation.  The default value of the
variable is 1.

  Simply inserting a line number is enough to indent it according to these
rules.  As each digit is inserted, the indentation is recomputed.  To turn
off this feature, set the variable `fortran-electric-line-number' to
`nil'.  Then inserting line numbers is like inserting anything else.

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File: emacs  Node: ForIndent Conv, Prev: ForIndent Num, Up: Fortran Indent, Next: ForIndent Vars

Syntactic Conventions
.....................

  Fortran mode assumes that you follow certain conventions that simplify
the task of understanding a Fortran program well enough to indent it
properly:

   * Two nested `do' loops never share a `continue' statement.
     
   * The same character appears in column 5 of all continuation lines, and
     this character is the value of the variable `fortran-continuation-char'.
     By default, this character is `$'.

If you fail to follow these conventions, the indentation commands may
indent some lines unaesthetically.  However, a correct Fortran program will
retain its meaning when reindented even if the conventions are not
followed.

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File: emacs  Node: ForIndent Vars, Prev: ForIndent Conv, Up: Fortran Indent

Variables for Fortran Indentation
.................................

  Several additional variables control how Fortran indentation works.

`fortran-do-indent'     
     Extra indentation within each level of `do' statement (default 3).
     
`fortran-if-indent'     
     Extra indentation within each level of `if' statement (default 3).
     
`fortran-continuation-indent'     
     Extra indentation for bodies of continuation lines (default 5).
     
`fortran-check-all-num-for-matching-do'     
     If this is `nil', indentation assumes that each `do'
     statement ends on a `continue' statement.  Therefore, when
     computing indentation for a statement other than `continue', it
     can save time by not checking for a `do' statement ending there.
     If this is non-`nil', indenting any numbered statement must check
     for a `do' that ends there.  The default is `nil'.
     
`fortran-minimum-statement-indent'     
     Minimum indentation for fortran statements.  For standard Fortran,
     this is 6.  Statement bodies will never be indented less than this
     much.

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File: emacs  Node: Fortran Comments, Prev: Fortran Indent, Up: Fortran, Next: Fortran Columns

Comments
--------

  The usual Emacs comment commands assume that a comment can follow a line
of code.  In Fortran, the standard comment syntax requires an entire line
to be just a comment.  Therefore, Fortran mode replaces the standard Emacs
comment commands and defines some new variables.

  Fortran mode can also handle a nonstandard comment syntax where comments
start with `!' and can follow other text.  Because only some Fortran
compilers accept this syntax, Fortran mode will not insert such comments
unless you have said in advance to do so.  To do this, set the variable
`comment-start' to `"!"' (*Note Variables::).

`M-;'     
     Align comment or insert new comment (`fortran-comment-indent').
     
`C-x ;'     
     Applies to nonstandard `!' comments only.
     
`C-c ;'     
     Turn all lines of the region into comments, or (with arg)
     turn them back into real code (`fortran-comment-region').

  `M-;' in Fortran mode is redefined as the command
`fortran-comment-indent'.  Like the usual `M-;' command, this
recognizes any kind of existing comment and aligns its text appropriately;
if there is no existing comment, a comment is inserted and aligned.  But
inserting and aligning comments are not the same in Fortran mode as in
other modes.

  When a new comment must be inserted, if the current line is blank, a
full-line comment is inserted.  On a non-blank line, a nonstandard `!'
comment is inserted if you have said you want to use them.  Otherwise a
full-line comment is inserted on a new line before the current line.

  Nonstandard `!' comments are aligned like comments in other
languages, but full-line comments are different.  In a standard full-line
comment, the comment delimiter itself must always appear in column zero.
What can be aligned is the text within the comment.  You can choose from
three styles of alignment by setting the variable
`fortran-comment-indent-style' to one of these values:

`fixed'     
     The text is aligned at a fixed column, which is the value of
     `fortran-comment-line-column'.  This is the default.
`relative'     
     The text is aligned as if it were a line of code, but with an
     additional `fortran-comment-line-column' columns of indentation.
`nil'     
     Text in full-line columns is not moved automatically.

  In addition, you can specify the character to be used to indent within
full-line comments by setting the variable `fortran-comment-indent-char'
to the character you want to use.

  Fortran mode introduces two variables `comment-line-start' and
`comment-line-start-skip' which play for full-line comments the same
roles played by `comment-start' and `comment-start-skip' for
ordinary text-following comments.  Normally these are set properly by
Fortran mode so you do not need to change them.

  The normal Emacs comment command `C-x ;' has not been redefined.
If you use `!' comments, this command can be used with them.  Otherwise
it is useless in Fortran mode.

  The command `C-c ;' (`fortran-comment-region') turns all the
lines of the region into comments by inserting the string `C$$$' at
the front of each one.  With a numeric arg, the region is turned back into
live code by deleting `C$$$' from the front of each line in it.  The
string used for these comments can be controlled by setting the variable
`fortran-comment-region'.  Note that here we have an example of a
command and a variable with the same name; these two uses of the name never
conflict because in Lisp and in Emacs it is always clear from the context
which one is meant.

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