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This is Info file elisp, produced by Makeinfo-1.55 from the input file
elisp.texi.
This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 19.
Published by the Free Software Foundation, 675 Massachusetts Avenue,
Cambridge, MA 02139 USA
Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
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 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 this permission notice may be stated in a
translation approved by the Foundation.
File: elisp, Node: Regexp Search, Next: Replacement, Prev: Regular Expressions, Up: Searching and Matching
Regular Expression Searching
============================
In GNU Emacs, you can search for the next match for a regexp either
incrementally or not. Incremental search commands are described in the
`The GNU Emacs Manual'. *Note Regular Expression Search: (emacs)Regexp
Search. Here we describe only the search functions useful in programs.
The principal one is `re-search-forward'.
- Command: re-search-forward REGEXP &optional LIMIT NOERROR REPEAT
This function searches forward in the current buffer for a string
of text that is matched by the regular expression REGEXP. The
function skips over any amount of text that is not matched by
REGEXP, and leaves point at the end of the first string found that
does match.
If the search is successful (i.e., if text matching REGEXP is
found), then point moves to the end of that text, and the function
returns the new value of point.
What happens when the search fails depends on the value of
NOERROR. If NOERROR is `nil', a `search-failed' error is
signaled. If NOERROR is `t', `re-search-forward' does nothing and
returns `nil'. If NOERROR is neither `nil' nor `t', then
`re-search-forward' moves point to LIMIT (or the end of the
buffer) and returns `nil'.
If LIMIT is non-`nil' (it must be a position in the current
buffer), then it is the upper bound to the search. No match
extending after that position is accepted.
If REPEAT is supplied (it must be a positive number), then the
search is repeated that many times (each time starting at the end
of the previous time's match). The call succeeds if all these
searches succeeded, and point is left at the end of the match
found by the last search. Otherwise the search fails.
In the following example, point is initially located directly
before the `T'. After evaluating the form, point is located at
the end of that line (between the `t' of `hat' and before the
newline).
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(re-search-forward "[a-z]+" nil t 5)
=> t
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
- Command: re-search-backward REGEXP &optional LIMIT NOERROR REPEAT
This function searches backward in the current buffer for a string
of text that is matched by the regular expression REGEXP, leaving
point at the beginning of the first text found.
This function is analogous to `re-search-forward', but they are
not simple mirror images. `re-search-forward' finds the match
whose beginning is as close as possible. If `re-search-backward'
were a perfect mirror image, it would find the match whose end is
as close as possible. However, in fact it finds the match whose
beginning is as close as possible. The reason is that matching a
regular expression at a given spot always works from beginning to
end, and is done at a specified beginning position. Thus, true
mirror-image behavior would require a special feature for matching
regexps from end to beginning.
- Function: string-match REGEXP STRING &optional START
This function returns the index of the start of the first match for
the regular expression REGEXP in STRING, or `nil' if there is no
match. If START is non-`nil', the search starts at that index in
STRING.
For example,
(string-match
"quick" "The quick brown fox jumped quickly.")
=> 4
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
The index of the first character of the string is 0, the index of
the second character is 1, and so on.
After this function returns, the index of the first character
beyond the match is available as `(match-end 0)'. *Note Match
Data::.
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
(match-end 0)
=> 32
The `match-beginning' and `match-end' functions are described
together; see *Note Match Data::.
- Function: looking-at REGEXP
This function determines whether the text in the current buffer
directly following point matches the regular expression REGEXP.
"Directly following" means precisely that: the search is
"anchored" and it must succeed starting with the first character
following point. The result is `t' if so, `nil' otherwise.
This function does not move point, but it updates the match data,
which you can access using `match-beginning' or `match-end'.
*Note Match Data::.
In this example, point is located directly before the `T'. If it
were anywhere else, the result would be `nil'.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(looking-at "The cat in the hat$")
=> t
File: elisp, Node: Replacement, Next: Match Data, Prev: Regexp Search, Up: Searching and Matching
Replacement
===========
- Function: perform-replace FROM-STRING REPLACEMENTS QUERY-FLAG
REGEXP-FLAG DELIMITED-FLAG &optional REPEAT-COUNT MAP
This function is the guts of `query-replace' and related commands.
It searches for occurrences of FROM-STRING and replaces some or
all of them. If QUERY-FLAG is `nil', it replaces all occurrences;
otherwise, it asks the user what to do about each one.
If REGEXP-FLAG is non-`nil', then FROM-STRING is considered a
regular expression; otherwise, it must match literally. If
DELIMITED-FLAG is non-`nil', then only replacements surrounded by
word boundaries are considered.
The argument REPLACEMENTS specifies what to replace occurrences
with. If it is a string, that string is used. It can also be a
list of strings, to be used in cyclic order.
If REPEAT-COUNT is non-`nil', it should be an integer, the number
of occurrences to consider. In this case, `perform-replace'
returns after considering that many occurrences.
Normally, the keymap `query-replace-map' defines the possible user
responses. The argument MAP, if non-`nil', is a keymap to use
instead of `query-replace-map'.
- Variable: query-replace-map
This variable holds a special keymap that defines the valid user
responses for `query-replace' and related functions, as well as
`y-or-n-p' and `map-y-or-n-p'. It is special in two ways:
* The "key bindings" are not commands, just symbols that are
meaningful to the functions that use this map.
* Prefix keys are not supported; each key binding must be for a
single event key sequence. This is because the functions
don't use read key sequence to get the input; instead, they
read a single event and look it up "by hand."
Here are the meaningful "bindings" for `query-replace-map'. Several
of them are meaningful only for `query-replace' and friends.
`act'
Do take the action. The action being considered--in other words,
"yes."
`skip'
Do not take action for this question--in other words, "no."
`exit'
Answer this question "no," and don't ask any more.
`act-and-exit'
Answer this question "yes," and don't ask any more.
`act-and-show'
Answer this question "yes," but show the results--don't advance
yet.
`automatic'
Answer this question and all subsequent questions in the series
with "yes," without further user interaction.
`backup'
Move back to the previous place that a question was asked about.
`edit'
Enter a recursive edit to deal with this item--instead of any
other answer.
`delete-and-edit'
Delete the text being considered, then enter a recursive edit to
replace it.
`recenter'
Redisplay and center the window, then ask the same question again.
`quit'
Perform a quit right away. Only the `y-or-n-p' functions use this
answer.
`help'
Display some help, then ask again.
File: elisp, Node: Match Data, Next: Standard Regexps, Prev: Replacement, Up: Searching and Matching
The Match Data
==============
Emacs keeps track of the positions of the start and end of segments
of text found during a regular expression search. This means, for
example, that you can search for a complex pattern, such as a date in
an Rmail message, and extract parts of it.
Because the match data normally describe the most recent search only,
you must be careful not to do another search inadvertently between the
search you wish to refer back to and the use of the match data. If you
can't avoid another intervening search, you must save and restore the
match data around it, to prevent it from being overwritten.
* Menu:
* Simple Match Data:: Accessing single items of match data,
such as where a particular subexpression started.
* Replacing Match:: Replacing a substring that was matched.
* Entire Match Data:: Accessing the entire match data at once, as a list.
* Saving Match Data:: Saving and restoring the match data.
File: elisp, Node: Simple Match Data, Next: Replacing Match, Up: Match Data
Simple Match Data Access
------------------------
This section explains how to use the match data to find the starting
point or ending point of the text that was matched by a particular
search, or by a particular parenthetical subexpression of a regular
expression.
- Function: match-beginning COUNT
This function returns the position of the start of text matched by
the last regular expression searched for. COUNT, a number,
specifies a subexpression whose start position is the value. If
COUNT is zero, then the value is the position of the text matched
by the whole regexp. If COUNT is greater than zero, then the
value is the position of the beginning of the text matched by the
COUNTth subexpression, regardless of whether it was used in the
final match.
Subexpressions of a regular expression are those expressions
grouped inside of parentheses, `\(...\)'. The COUNTth
subexpression is found by counting occurrences of `\(' from the
beginning of the whole regular expression. The first
subexpression is numbered 1, the second 2, and so on.
The value is `nil' for a parenthetical grouping inside of a `\|'
alternative that wasn't used in the match.
The `match-end' function is similar to the `match-beginning'
function except that it returns the position of the end of the
matched text.
Here is an example, with a comment showing the numbers of the
positions in the text:
(string-match
"\\(qu\\)\\(ick\\)" "The quick fox jumped quickly.")
=> 4 ;^^^^^^^^^^
;0123456789
(match-beginning 1) ; The beginning of the match
=> 4 ; with `qu' is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with `ick' is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with `qu' is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with `ick' is at index 9.
Here is another example. Before the form is evaluated, point is
located at the beginning of the line. After evaluating the search
form, point is located on the line between the space and the word
`in'. The beginning of the entire match is at the 9th character
of the buffer (`T'), and the beginning of the match for the first
subexpression is at the 13th character (`c').
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (t 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(Note that in this case, the index returned is a buffer position;
the first character of the buffer counts as 1.)
- Function: match-end COUNT
This function returns the position of the end of text matched by
the last regular expression searched for. This function is
otherwise similar to `match-beginning'.
File: elisp, Node: Replacing Match, Next: Entire Match Data, Prev: Simple Match Data, Up: Match Data
Replacing the Text That Matched
-------------------------------
- Function: replace-match REPLACEMENT &optional FIXEDCASE LITERAL
This function replaces the text matched by the last search with
REPLACEMENT.
If FIXEDCASE is non-`nil', then the case of the replacement text
is not changed; otherwise, the replacement text is converted to a
different case depending upon the capitalization of the text to be
replaced. If the original text is all upper case, the replacement
text is converted to upper case, except when all of the words in
the original text are only one character long. In that event, the
replacement text is capitalized. If *all* of the words in the
original text are capitalized, then all of the words in the
replacement text are capitalized.
If LITERAL is non-`nil', then REPLACEMENT is inserted exactly as
it is, the only alterations being case changes as needed. If it
is `nil' (the default), then the character `\' is treated
specially. If a `\' appears in REPLACEMENT, then it must be part
of one of the following sequences:
`\&'
`\&' stands for the entire text being replaced.
`\N'
`\N' stands for the Nth subexpression in the original regexp.
Subexpressions are those expressions grouped inside of
`\(...\)'. N is a digit.
`\\'
`\\' stands for a single `\' in the replacement text.
`replace-match' leaves point at the end of the replacement text,
and returns `t'.
File: elisp, Node: Entire Match Data, Next: Saving Match Data, Prev: Replacing Match, Up: Match Data
Accessing the Entire Match Data
-------------------------------
The functions `match-data' and `store-match-data' let you read or
write the entire match data, all at once.
- Function: match-data
This function returns a new list containing all the information on
what text the last search matched. Element zero is the position
of the beginning of the match for the whole expression; element
one is the position of the end of the match for the expression.
The next two elements are the positions of the beginning and end
of the match for the first subexpression. In general, element
number 2N corresponds to `(match-beginning N)'; and element number
2N + 1 corresponds to `(match-end N)'.
All the elements are markers or `nil' if matching was done on a
buffer, and all are integers or `nil' if matching was done on a
string with `string-match'. (In Emacs 18 and earlier versions,
markers were used even for matching on a string, except in the case
of the integer 0.)
As always, there must be no possibility of intervening searches
between the call to a search function and the call to `match-data'
that is intended to access the match-data for that search.
(match-data)
=> (#<marker at 9 in foo>
#<marker at 17 in foo>
#<marker at 13 in foo>
#<marker at 17 in foo>)
- Function: store-match-data MATCH-LIST
This function sets the match data from the elements of MATCH-LIST,
which should be a list that was the value of a previous call to
`match-data'.
If MATCH-LIST refers to a buffer that doesn't exist, you don't get
an error; that sets the match data in a meaningless but harmless
way.
File: elisp, Node: Saving Match Data, Prev: Entire Match Data, Up: Match Data
Saving and Restoring the Match Data
-----------------------------------
All asynchronous process functions (filters and sentinels) and
functions that use `recursive-edit' should save and restore the match
data if they do a search or if they let the user type arbitrary
commands. Saving the match data is useful in other cases as
well--whenever you want to access the match data resulting from an
earlier search, notwithstanding another intervening search.
This example shows the problem that can arise if you fail to attend
to this requirement:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; Perhaps `foo' does
; more searching.
(match-end 0)
=> 61 ; Unexpected result---not 48!
In Emacs versions 19 and later, you can save and restore the match
data with `save-match-data':
- Special Form: save-match-data BODY...
This special form executes BODY, saving and restoring the match
data around it. This is useful if you wish to do a search without
altering the match data that resulted from an earlier search.
You can use `store-match-data' together with `match-data' to imitate
the effect of the special form `save-match-data'. This is useful for
writing code that can run in Emacs 18. Here is how:
(let ((data (match-data)))
(unwind-protect
... ; May change the original match data.
(store-match-data data)))
File: elisp, Node: Standard Regexps, Next: Searching and Case, Prev: Match Data, Up: Searching and Matching
Standard Regular Expressions Used in Editing
============================================
Here are the regular expressions standardly used in editing:
- Variable: page-delimiter
This is the regexp describing line-beginnings that separate pages.
The default value is `"^\014"' (i.e., `"^^L"' or `"^\C-l"').
- Variable: paragraph-separate
This is the regular expression for recognizing the beginning of a
line that separates paragraphs. (If you change this, you may have
to change `paragraph-start' also.) The default value is `"^[
\t\f]*$"', which is a line that consists entirely of spaces, tabs,
and form feeds.
- Variable: paragraph-start
This is the regular expression for recognizing the beginning of a
line that starts *or* separates paragraphs. The default value is
`"^[ \t\n\f]"', which matches a line starting with a space, tab,
newline, or form feed.
- Variable: sentence-end
This is the regular expression describing the end of a sentence.
(All paragraph boundaries also end sentences, regardless.) The
default value is:
"[.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]*"
This means a period, question mark or exclamation mark, followed
by a closing brace, followed by tabs, spaces or new lines.
For a detailed explanation of this regular expression, see *Note
Regexp Example::.
File: elisp, Node: Searching and Case, Prev: Standard Regexps, Up: Searching and Matching
Searching and Case
==================
By default, searches in Emacs ignore the case of the text they are
searching through; if you specify searching for `FOO', then `Foo' or
`foo' is also considered a match. Regexps, and in particular character
sets, are included: thus, `[aB]' would match `a' or `A' or `b' or `B'.
If you do not want this feature, set the variable `case-fold-search'
to `nil'. Then all letters must match exactly, including case. This
is a per-buffer-local variable; altering the variable affects only the
current buffer. (*Note Intro to Buffer-Local::.) Alternatively, you
may change the value of `default-case-fold-search', which is the
default value of `case-fold-search' for buffers that do not override it.
- User Option: case-replace
This variable determines whether `query-replace' should preserve
case in replacements. If the variable is `nil', then case need
not be preserved.
- User Option: case-fold-search
This buffer-local variable determines whether searches should
ignore case. If the variable is `nil' they do not ignore case;
otherwise they do ignore case.
- Variable: default-case-fold-search
The value of this variable is the default value for
`case-fold-search' in buffers that do not override it. This is the
same as `(default-value 'case-fold-search)'.
File: elisp, Node: Syntax Tables, Next: Abbrevs, Prev: Searching and Matching, Up: Top
Syntax Tables
*************
A "syntax table" provides Emacs with the information that determines
the syntactic use of each character in a buffer. This information is
used by the parsing commands, the complex movement commands, and others
to determine where words, symbols, and other syntactic constructs begin
and end. The current syntax table controls the meaning of the word
motion functions (*note Word Motion::.) and the list motion functions
(*note List Motion::.) as well as the functions in this chapter.
A syntax table is a vector of 256 elements; it contains one entry for
each of the 256 ASCII characters of an 8-bit byte. Each element is an
integer that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the GNU
Emacs Lisp reader. GNU Emacs Lisp uses built-in syntactic rules when
reading Lisp expressions, and these rules cannot be changed.
Each buffer has its own major mode, and each major mode has its own
idea of the syntactic class of various characters. For example, in Lisp
mode, the character `;' begins a comment, but in C mode, it terminates
a statement. To support these variations, Emacs makes the choice of
syntax table local to each buffer. Typically, each major mode has its
own syntax table and installs that table in each buffer which uses that
mode. Changing this table alters the syntax in all those buffers as
well as in any buffers subsequently put in that mode. Occasionally
several similar modes share one syntax table. *Note Example Major
Modes::, for an example of how to set up a syntax table.
- Function: syntax-table-p OBJECT
This function returns `t' if OBJECT is a vector of length 256
elements. This means that the vector may be a syntax table.
However, according to this test, any vector of length 256 is
considered to be a syntax table, no matter what its contents.
* Menu:
* Syntax Descriptors:: How characters are classified.
* Syntax Table Functions:: How to create, examine and alter syntax tables.
* Motion and Syntax:: Moving over characters with certain syntaxes.
* Parsing Expressions:: Parsing balanced expressions
using the syntax table.
* Standard Syntax Tables:: Syntax tables used by various major modes.
* Syntax Table Internals:: How syntax table information is stored.
File: elisp, Node: Syntax Descriptors, Next: Syntax Table Functions, Up: Syntax Tables
Syntax Descriptors
==================
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a "syntax
descriptor", which is a Lisp string that you pass to
`modify-syntax-entry' to specify the desired syntax.
Emacs defines twelve "syntax classes". Each syntax table puts each
character into one class. There is no necessary relationship between
the class of a character in one syntax table and its class in any other
table.
Each class is designated by a mnemonic character which serves as the
name of the class when you need to specify a class. Usually the
designator character is one which is frequently put in that class;
however, its meaning as a designator is unvarying and independent of how
it is actually classified.
A syntax descriptor is a Lisp string which specifies a syntax class,
a matching character (unused except for parenthesis classes) and flags.
The first character is the designator for a syntax class. The second
character is the character to match; if it is unused, put a space there.
Then come the characters for any desired flags. If no matching
character or flags are needed, one character is sufficient.
Thus, the descriptor for the character `*' in C mode is `. 23'
(i.e., punctuation, matching character slot unused, second character of
a comment-starter, first character of an comment-ender), and the entry
for `/' is `. 14' (i.e., punctuation, matching character slot unused,
first character of a comment-starter, second character of a
comment-ender).
* Menu:
* Syntax Class Table:: Table of syntax classes.
* Syntax Flags:: Additional flags each character can have.
File: elisp, Node: Syntax Class Table, Next: Syntax Flags, Up: Syntax Descriptors
Table of Syntax Classes
-----------------------
Here is a summary of the classes, the characters that stand for them,
their meanings, and examples of their use.
- Syntax class: whitespace character
"Whitespace characters" (designated with ` ' or `-') separate
symbols and words from each other. Typically, whitespace
characters have no other syntactic use, and multiple whitespace
characters are syntactically equivalent to a single one. Space,
tab, newline and formfeed are almost always considered whitespace.
- Syntax class: word constituent
"Word constituents" (designated with `w') are parts of normal
English words and are typically used in variable and command names
in programs. All upper and lower case letters and the digits are
typically word constituents.
- Syntax class: symbol constituent
"Symbol constituents" (designated with `_') are the extra
characters that are used in variable and command names along with
word constituents. For example, the symbol constituents class is
used in Lisp mode to indicate that certain characters may be part
of symbol names even though they are not part of English words.
These characters are `$&*+-_<>'. In standard C, the only
non-word-constituent character that is valid in symbols is
underscore (`_').
- Syntax class: punctuation character
"Punctuation characters" (`.') are those characters that are used
as punctuation in English, or are used in some way in a programming
language to separate symbols from one another. Most programming
language modes, including Emacs Lisp mode, have no characters in
this class since the few characters that are not symbol or word
constituents all have other uses.
- Syntax class: open parenthesis character
- Syntax class: close parenthesis character
Open and close "parenthesis characters" are characters used in
dissimilar pairs to surround sentences or expressions. Such a
grouping is begun with an open parenthesis character and
terminated with a close. Each open parenthesis character matches
a particular close parenthesis character, and vice versa.
Normally, Emacs indicates momentarily the matching open
parenthesis when you insert a close parenthesis. *Note Blinking::.
The class of open parentheses is designated with `(', and that of
close parentheses with `)'.
In English text, and in C code, the parenthesis pairs are `()',
`[]', and `{}'. In Emacs Lisp, the delimiters for lists and
vectors (`()' and `[]') are classified as parenthesis characters.
- Syntax class: string quote
"String quote characters" (designated with `"') is used to delimit
string constants in many languages, including Lisp and C. The
same string quote character appears at the beginning and the end
of a string. Such quoted strings do not nest.
The parsing facilities of Emacs consider a string as a single
token. The usual syntactic meanings of the characters in the
string are suppressed.
The Lisp modes have two string quote characters: double-quote (`"')
and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is
used in Common Lisp. C also has two string quote characters:
double-quote for strings, and single-quote (`'') for character
constants.
English text has no string quote characters because English is not
a programming language. Although quotation marks are used in
English, we do not want them to turn off the usual syntactic
properties of other characters in the quotation.
- Syntax class: escape
An "escape character" (designated with `\') starts an escape
sequence such as is used in C string and character constants. The
character `\' belongs to this class in both C and Lisp. (In C, it
is used thus only inside strings, but it turns out to cause no
trouble to treat it this way throughout C code.)
Characters in this class count as part of words if
`words-include-escapes' is non-`nil'. *Note Word Motion::.
- Syntax class: character quote
A "character quote character" (designated with `/') quotes the
following character so that it loses its normal syntactic meaning.
This differs from an escape character in that only the character
immediately following is ever affected.
Characters in this class count as part of words if
`words-include-escapes' is non-`nil'. *Note Word Motion::.
This class is not currently used in any standard Emacs modes.
- Syntax class: paired delimiter
"Paired delimiter characters" (designated with `$') are like
string quote characters except that the syntactic properties of the
characters between the delimiters are not suppressed. Only TeX
mode uses a paired identical delimiter presently--the `$' that
begins and ends math mode.
- Syntax class: expression prefix
An "expression prefix operator" (designated with `'') is used for
syntactic operators that are part of an expression if they appear
next to one but are not part of an adjoining symbol. These
characters in Lisp include the apostrophe, `'' (used for quoting),
the comma, `,' (used in macros), and `#' (used in the read syntax
for certain data types).
- Syntax class: comment starter
- Syntax class: comment ender
The "comment starter" and "comment ender" characters are used in
different languages to delimit comments. These classes are
designated with `<' and `>', respectively.
English text has no comment characters. In Lisp, the semicolon
(`;') starts a comment and a newline or formfeed ends one.
File: elisp, Node: Syntax Flags, Prev: Syntax Class Table, Up: Syntax Descriptors
Syntax Flags
------------
In addition to the classes, entries for characters in a syntax table
can include flags. There are six possible flags, represented by the
characters `1', `2', `3', `4', `b' and `p'.
All the flags except `p' are used to describe multi-character
comment delimiters. The digit flags indicate that a character can
*also* be part of a comment sequence, in addition to the syntactic
properties associated with its character class. The flags are
independent of the class and each other for the sake of characters such
as `*' in C mode, which is a punctuation character, *and* the second
character of a start-of-comment sequence (`/*'), *and* the first
character of an end-of-comment sequence (`*/').
The flags for a character C are:
* `1' means C is the start of a two-character comment start sequence.
* `2' means C is the second character of such a sequence.
* `3' means C is the start of a two-character comment end sequence.
* `4' means C is the second character of such a sequence.
* `b' means that C as a comment delimiter belongs to the alternative
"b" comment style.
Emacs can now supports two comment styles simultaneously. (This
is for the sake of C++.) More specifically, it can recognize two
different comment-start sequences. Both must share the same first
character; only the second character may differ. Mark the second
character of the "b"-style comment start sequence with the `b'
flag.
The two styles of comment can have different comment-end
sequences. A comment-end sequence (one or two characters) applies
to the "b" style if its first character has the `b' flag set;
otherwise, it applies to the "a" style.
The appropriate comment syntax settings for C++ are as follows:
`/'
`124b'
`*'
`23'
newline
`>b'
Thus `/*' is a comment-start sequence for "a" style, `//' is a
comment-start sequence for "b" style, `*/' is a comment-end
sequence for "a" style, and newline is a comment-end sequence for
"b" style.
* `p' identifies an additional "prefix character" for Lisp syntax.
These characters are treated as whitespace when they appear between
expressions. When they appear within an expression, they are
handled according to their usual syntax codes.
The function `backward-prefix-chars' moves back over these
characters, as well as over characters whose primary syntax class
is prefix (`'').
File: elisp, Node: Syntax Table Functions, Next: Motion and Syntax, Prev: Syntax Descriptors, Up: Syntax Tables
Syntax Table Functions
======================
In this section we describe functions for creating, accessing and
altering syntax tables.
- Function: make-syntax-table &optional TABLE
This function constructs a copy of TABLE and returns it. If TABLE
is not supplied (or is `nil'), it returns a copy of the current
syntax table. Otherwise, an error is signaled if TABLE is not a
syntax table.
- Function: copy-syntax-table &optional TABLE
This function is identical to `make-syntax-table'.
- Command: modify-syntax-entry CHAR SYNTAX-DESCRIPTOR &optional TABLE
This function sets the syntax entry for CHAR according to
SYNTAX-DESCRIPTOR. The syntax is changed only for TABLE, which
defaults to the current buffer's syntax table, and not in any
other syntax table. The argument SYNTAX-DESCRIPTOR specifies the
desired syntax; this is a string beginning with a class designator
character, and optionally containing a matching character and
flags as well. *Note Syntax Descriptors::.
This function always returns `nil'. The old syntax information in
the table for this character is discarded.
An error is signaled if the first character of the syntax
descriptor is not one of the twelve syntax class designator
characters. An error is also signaled if CHAR is not a character.
Examples:
;; Put the space character in class whitespace.
(modify-syntax-entry ?\ " ")
=> nil
;; Make `$' an open parenthesis character,
;; with `^' as its matching close.
(modify-syntax-entry ?$ "(^")
=> nil
;; Make `^' a close parenthesis character,
;; with `$' as its matching open.
(modify-syntax-entry ?^ ")$")
=> nil
;; Make `/' a punctuation character,
;; the first character of a start-comment sequence,
;; and the second character of an end-comment sequence.
;; This is used in C mode.
(modify-syntax-entry ?/ ".13")
=> nil
- Function: char-syntax CHARACTER
This function returns the syntax class of CHARACTER, represented
by its mnemonic designator character. This *only* returns the
class, not any matching parenthesis or flags.
An error is signaled if CHAR is not a character.
The first example shows that the syntax class of space is
whitespace (represented by a space). The second example shows
that the syntax of `/' is punctuation in C-mode. This does not
show the fact that it is also a comment sequence character. The
third example shows that open parenthesis is in the class of open
parentheses. This does not show the fact that it has a matching
character, `)'.
(char-to-string (char-syntax ?\ ))
=> " "
(char-to-string (char-syntax ?/))
=> "."
(char-to-string (char-syntax ?\())
=> "("
- Function: set-syntax-table TABLE
This function makes TABLE the syntax table for the current buffer.
It returns TABLE.
- Function: syntax-table
This function returns the current syntax table, which is the table
for the current buffer.
File: elisp, Node: Motion and Syntax, Next: Parsing Expressions, Prev: Syntax Table Functions, Up: Syntax Tables
Motion and Syntax
=================
This section describes functions for moving across characters in
certain syntax classes. None of these functions exists in Emacs
version 18 or earlier.
- Function: skip-syntax-forward SYNTAXES &optional LIMIT
This function moves point forward across characters whose syntax
classes are mentioned in SYNTAXES. It stops when it encounters
the end of the buffer, or position LIM (if specified), or a
character it is not supposed to skip.
The return value is the distance traveled, which is a nonnegative
integer.
- Function: skip-syntax-backward SYNTAXES &optional LIMIT
This function moves point backward across characters whose syntax
classes are mentioned in SYNTAXES. It stops when it encounters
the beginning of the buffer, or position LIM (if specified), or a
character it is not supposed to skip.
The return value indicates the distance traveled. It is an
integer that is zero or less.
- Function: backward-prefix-chars
This function moves point backward over any number of chars with
expression prefix syntax. This includes both characters in the
expression prefix syntax class, and characters with the `p' flag.
File: elisp, Node: Parsing Expressions, Next: Standard Syntax Tables, Prev: Motion and Syntax, Up: Syntax Tables
Parsing Balanced Expressions
============================
Here are several functions for parsing and scanning balanced
expressions. The syntax table controls the interpretation of
characters, so these functions can be used for Lisp expressions when in
Lisp mode and for C expressions when in C mode. *Note List Motion::,
for convenient higher-level functions for moving over balanced
expressions.
- Function: parse-partial-sexp START LIMIT &optional TARGET-DEPTH
STOP-BEFORE STATE STOP-COMMENT
This function parses an expression in the current buffer starting
at START, not scanning past LIMIT. Parsing stops at LIMIT or when
certain criteria described below are met; point is set to the
location where parsing stops. The value returned is a description
of the status of the parse at the point where it stops.
Normally, START is assumed to be the top level of an expression to
be parsed, such as the beginning of a function definition.
Alternatively, you might wish to resume parsing in the middle of an
expression. To do this, you must provide a STATE argument that
describes the initial status of parsing. If STATE is omitted (or
`nil'), parsing assumes that START is the beginning of a new parse
at level 0.
If the third argument TARGET-DEPTH is non-`nil', parsing stops if
the depth in parentheses becomes equal to TARGET-DEPTH. The depth
starts at 0, or at whatever is given in STATE.
If the fourth argument STOP-BEFORE is non-`nil', parsing stops
when it comes to any character that starts a sexp. If
STOP-COMMENT is non-`nil', parsing stops when it comes to the
start of a comment.
The fifth argument STATE is a seven-element list of the same form
as the value of this function, described below. The return value
of one call may be used to initialize the state of the parse on
another call to `parse-partial-sexp'.
The result is a list of seven elements describing the final state
of the parse:
0. The depth in parentheses, starting at 0.
1. The character position of the start of the innermost
containing parenthetical grouping; `nil' if none.
2. The character position of the start of the last complete
subexpression terminated; `nil' if none.
3. Non-`nil' if inside a string. (It is the character that will
terminate the string.)
4. `t' if inside a comment.
5. `t' if point is just after a quote character.
6. The minimum parenthesis depth encountered during this scan.
Elements 1, 4, 5, and 6 are significant in the argument STATE.
This function is used to determine how to indent lines in programs
written in languages that have nested parentheses.
- Function: scan-lists FROM COUNT DEPTH
This function scans forward COUNT balanced parenthetical groupings
from character number FROM. It returns the character number of
the position thus found.
If DEPTH is nonzero, parenthesis depth counting begins from that
value. The only candidates for stopping are places where the
depth in parentheses becomes zero; `scan-lists' counts COUNT such
places and then stops. Thus, a positive value for DEPTH means go
out levels of parenthesis.
Comments are ignored if `parse-sexp-ignore-comments' is non-`nil'.
If the beginning or end of the buffer (or its accessible portion)
is reached and the depth is not zero, an error is signaled. If
the depth is zero but the count is not used up, `nil' is returned.
- Function: scan-sexps FROM COUNT
Scan from character number FROM by COUNT balanced expressions. It
returns the character number of the position thus found.
Comments are ignored if `parse-sexp-ignore-comments' is non-`nil'.
If the beginning or end of (the accessible part of) the buffer is
reached in the middle of a parenthetical grouping, an error is
signaled. If the beginning or end is reached between groupings but
before count is used up, `nil' is returned.
- Variable: parse-sexp-ignore-comments
If the value is non-`nil', then comments are treated as whitespace
by the functions in this section and by `forward-sexp'.
In older Emacs versions, this feature worked only when the comment
terminator is something like `*/', and appears only to end a
comment. In languages where newlines terminate comments, it was
necessary make this variable `nil', since not every newline is the
end of a comment. This limitation no longer exists.
You can use `forward-comment' to move forward or backward over one
comment or several comments.
- Function: forward-comment COUNT
This function moves point forward across COUNT comments (backward,
if COUNT is negative). If it finds anything other than a comment
or whitespace, it stops, leaving point at the place where it
stopped. It also stops after satisfying COUNT.
To move forward over all comments and whitespace following point, use
`(forward-comment (buffer-size))'. `(buffer-size)' is a good argument
to use, because the number of comments to skip cannot exceed that many.
File: elisp, Node: Standard Syntax Tables, Next: Syntax Table Internals, Prev: Parsing Expressions, Up: Syntax Tables
Some Standard Syntax Tables
===========================
Each of the major modes in Emacs has its own syntax table. Here are
several of them:
- Function: standard-syntax-table
This function returns the standard syntax table, which is the
syntax table used in Fundamental mode.
- Variable: text-mode-syntax-table
The value of this variable is the syntax table used in Text mode.
- Variable: c-mode-syntax-table
The value of this variable is the syntax table in use in C-mode
buffers.
- Variable: emacs-lisp-mode-syntax-table
The value of this variable is the syntax table used in Emacs Lisp
mode by editing commands. (It has no effect on the Lisp `read'
function.)
File: elisp, Node: Syntax Table Internals, Prev: Standard Syntax Tables, Up: Syntax Tables
Syntax Table Internals
======================
Each element of a syntax table is an integer that translates into the
full meaning of the entry: class, possible matching character, and
flags. However, it is not common for a programmer to work with the
entries directly in this form since the Lisp-level syntax table
functions usually work with syntax descriptors (*note Syntax
Descriptors::.).
The low 8 bits of each element of a syntax table indicates the
syntax class.
Integer
Class
whitespace
punctuation
word
symbol
open parenthesis
close parenthesis
expression prefix
string quote
paired delimiter
escape
character quote
comment-start
comment-end
The next 8 bits are the matching opposite parenthesis (if the
character has parenthesis syntax); otherwise, they are not meaningful.
The next 6 bits are the flags.
File: elisp, Node: Abbrevs, Next: Processes, Prev: Syntax Tables, Up: Top
Abbrevs And Abbrev Expansion
****************************
An abbreviation or "abbrev" is a string of characters that may be
expanded to a longer string. The user can insert the abbrev string and
find it replaced automatically with the expansion of the abbrev. This
saves typing.
The set of abbrevs currently in effect is recorded in an "abbrev
table". Each buffer has a local abbrev table, but normally all buffers
in the same major mode share one abbrev table. There is also a global
abbrev table. Normally both are used.
An abbrev table is represented as an obarray containing a symbol for
each abbreviation. The symbol's name is the abbreviation. Its value is
the expansion; its function definition is the hook; its property list
cell contains the use count, the number of times the abbreviation has
been expanded. Because these symbols are not interned in the usual
obarray, they will never appear as the result of reading a Lisp
expression; in fact, they will never be used except by the code that
handles abbrevs. Therefore, it is safe to use them in an extremely
nonstandard way. *Note Creating Symbols::.
For the user-level commands for abbrevs, see *Note Abbrev Mode:
(emacs)Abbrevs.
* Menu:
* Abbrev Mode:: Setting up Emacs for abbreviation.
* Tables: Abbrev Tables. Creating and working with abbrev tables.
* Defining Abbrevs:: Specifying abbreviations and their expansions.
* Files: Abbrev Files. Saving abbrevs in files.
* Expansion: Abbrev Expansion. Controlling expansion; expansion subroutines.
* Standard Abbrev Tables:: Abbrev tables used by various major modes.
File: elisp, Node: Abbrev Mode, Next: Abbrev Tables, Prev: Abbrevs, Up: Abbrevs
Setting Up Abbrev Mode
======================
Abbrev mode is a minor mode controlled by the value of the variable
`abbrev-mode'.
- Variable: abbrev-mode
A non-`nil' value of this variable turns on the automatic expansion
of abbrevs when their abbreviations are inserted into a buffer.
If the value is `nil', abbrevs may be defined, but they are not
expanded automatically.
This variable automatically becomes local when set in any fashion.
- Variable: default-abbrev-mode
This is the value `abbrev-mode' for buffers that do not override
it. This is the same as `(default-value 'abbrev-mode)'.