this chapter.
@end ifinfo
- Under XEmacs 20, a syntax table is a particular subtype of the
+ Under XEmacs 20 and later, a syntax table is a particular subtype of the
primitive char table type (@pxref{Char Tables}), and each element of the
char table is an integer that encodes the syntax of the character in
question, or a cons of such an integer and a matching character (for
their meanings, and examples of their use.
@deffn {Syntax class} @w{whitespace character}
-@dfn{Whitespace characters} (designated with @w{@samp{@ }} or @samp{-})
+@dfn{Whitespace characters} (designated with @samp{-})
separate symbols and words from each other. Typically, whitespace
characters have no other syntactic significance, and multiple whitespace
characters are syntactically equivalent to a single one. Space, tab,
-newline and formfeed are almost always classified as whitespace.
+newline and formfeed are almost always classified as whitespace. (The
+designator @w{@samp{@ }} is accepted for backwards compatibility with
+older versions of XEmacs, but is deprecated. It is invalid in GNU Emacs.)
@end deffn
@deffn {Syntax class} @w{word constituent}
@subsection Syntax Flags
@cindex syntax flags
+@c This is a bit inaccurate, the ``a'' and ``b'' flags actually don't
+@c exist in the internal implementation. AFAICT it doesn't affect the
+@c semantics as perceived by the LISP programmer.
In addition to the classes, entries for characters in a syntax table
-can include flags. There are six possible flags, represented by the
-characters @samp{1}, @samp{2}, @samp{3}, @samp{4}, @samp{b} and
-@samp{p}.
-
- All the flags except @samp{p} are used to describe multi-character
-comment delimiters. The digit flags indicate that a character can
-@emph{also} be part of a comment sequence, in addition to the syntactic
-properties associated with its character class. The flags are
+can include flags. There are eleven possible flags, represented by the
+digits @samp{1}--@samp{8}, and the lowercase letters @samp{a}, @samp{b},
+and @samp{p}.
+
+ All the flags except @samp{p} are used to describe comment delimiters.
+The digit flags indicate that a character can @emph{also} be part of a
+multi-character comment sequence, in addition to the syntactic
+properties associated with its character class. The flags must be
independent of the class and each other for the sake of characters such
as @samp{*} in C mode, which is a punctuation character, @emph{and} the
second character of a start-of-comment sequence (@samp{/*}), @emph{and}
the first character of an end-of-comment sequence (@samp{*/}).
+Emacs supports two comment styles simultaneously in any one syntax
+table. This is for the sake of C++. Each style of comment syntax has
+its own comment-start sequence and its own comment-end sequence. Each
+comment must stick to one style or the other; thus, if it starts with
+the comment-start sequence of style ``b'', it must also end with the
+comment-end sequence of style ``b''.
+
+@c #### Compatibility note; index here.
+As an extension to GNU Emacs 19 and 20, XEmacs supports two arbitrary
+comment-start sequences and two arbitrary comment-end sequences. (Thus
+the need for 8 flags.) GNU Emacs restricts the comment-start sequences
+to start with the same character, XEmacs does not. This means that for
+two-character sequences, where GNU Emacs uses the @samp{b} flag, XEmacs
+uses the digit flags @samp{5}--@samp{8}.
+
+A one character comment-end sequence applies to the ``b'' style if its
+first character has the @samp{b} flag set; otherwise, it applies to the
+``a'' style. The @samp{a} flag is optional. These flags have no effect
+on non-comment characters; two-character styles are determined by the
+digit flags.
+
The flags for a character @var{c} are:
@itemize @bullet
@item
@samp{1} means @var{c} is the start of a two-character comment-start
-sequence.
+sequence of style ``a''.
@item
@samp{2} means @var{c} is the second character of such a sequence.
@item
@samp{3} means @var{c} is the start of a two-character comment-end
-sequence.
+sequence of style ``a''.
@item
@samp{4} means @var{c} is the second character of such a sequence.
@item
+@samp{5} means @var{c} is the start of a two-character comment-start
+sequence of style ``b''.
+
+@item
+@samp{6} means @var{c} is the second character of such a sequence.
+
+@item
+@samp{7} means @var{c} is the start of a two-character comment-end
+sequence of style ``b''.
+
+@item
+@samp{8} means @var{c} is the second character of such a sequence.
+
+@item
+@samp{a} means that @var{c} as a comment delimiter belongs to the
+default ``a'' comment style. (This flag is optional.)
+
+@item
@c Emacs 19 feature
@samp{b} means that @var{c} as a comment delimiter belongs to the
-alternative ``b'' comment style.
+alternate ``b'' comment style.
-Emacs supports two comment styles simultaneously in any one syntax
-table. This is for the sake of C++. Each style of comment syntax has
-its own comment-start sequence and its own comment-end sequence. Each
-comment must stick to one style or the other; thus, if it starts with
-the comment-start sequence of style ``b'', it must also end with the
-comment-end sequence of style ``b''.
+@item
+@c Emacs 19 feature
+@samp{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 @code{backward-prefix-chars} moves back over these
+characters, as well as over characters whose primary syntax class is
+prefix (@samp{'}). @xref{Motion and Syntax}.
+@end itemize
+
+Lisp (as you would expect) has a simple comment syntax.
+
+@table @asis
+@item @samp{;}
+@samp{<}
+@item newline
+@samp{>}
+@end table
+
+Note that no flags are used.
+This defines two comment-delimiting sequences:
-The two comment-start sequences must begin with the same character; only
-the second character may differ. Mark the second character of the
-``b''-style comment-start sequence with the @samp{b} flag.
+@table @asis
+@item @samp{;}
+This is a single-character comment-start sequence because the syntax
+class is @samp{<}.
-A comment-end sequence (one or two characters) applies to the ``b''
-style if its first character has the @samp{b} flag set; otherwise, it
-applies to the ``a'' style.
+@item newline
+This is a single character comment-end sequence because the syntax class
+is @samp{>} and the @samp{b} flag is not set.
+@end table
-The appropriate comment syntax settings for C++ are as follows:
+C++ (again, as you would expect) has a baroque, overrich, and
+excessively complex comment syntax.
@table @asis
@item @samp{/}
-@samp{124b}
+@samp{1456}
@item @samp{*}
@samp{23}
@item newline
@samp{>b}
@end table
-This defines four comment-delimiting sequences:
+Note that the ``b'' style mixes one-character and two-character
+sequences. The table above defines four comment-delimiting sequences:
@table @asis
@item @samp{/*}
-This is a comment-start sequence for ``a'' style because the
-second character, @samp{*}, does not have the @samp{b} flag.
+This is a comment-start sequence for ``a'' style because the @samp{1}
+flag is set on @samp{/} and the @samp{2} flag is set on @samp{*}.
@item @samp{//}
-This is a comment-start sequence for ``b'' style because the second
-character, @samp{/}, does have the @samp{b} flag.
+This is a comment-start sequence for ``b'' style because both the @samp{5}
+and the @samp{6} flags are set on @samp{/}.
@item @samp{*/}
-This is a comment-end sequence for ``a'' style because the first
-character, @samp{*}, does not have the @samp{b} flag
+This is a comment-end sequence for ``a'' style because the @samp{3}
+flag is set on @samp{*} and the @samp{4} flag is set on @samp{/}.
@item newline
This is a comment-end sequence for ``b'' style, because the newline
character has the @samp{b} flag.
@end table
-@item
-@c Emacs 19 feature
-@samp{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 @code{backward-prefix-chars} moves back over these
-characters, as well as over characters whose primary syntax class is
-prefix (@samp{'}). @xref{Motion and Syntax}.
-@end itemize
@node Syntax Table Functions
@section Syntax Table Functions
You can use @code{forward-comment} to move forward or backward over
one comment or several comments.
-@defun forward-comment count &optional buffer
+@defun forward-comment &optional count buffer
This function moves point forward across @var{count} comments (backward,
if @var{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 @var{count}.
+It also stops after satisfying @var{count}. @var{count} defaults to @code{1}.
- Optional argument @var{buffer} defaults to the current buffer.
+Optional argument @var{buffer} defaults to the current buffer.
@end defun
To move forward over all comments and whitespace following point, use
projects / chise / xemacs-chise.git.1 / blobdiff