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Adapt Lisp reference to reader changes

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The reader now warns about some unescaped character literals, but
still allows them for compatibility reasons.  Slightly adapt the
manual to forbid them officially.

* doc/lispref/objects.texi (Basic Char Syntax): Document that
backslashes are now required before some characters.
This commit is contained in:
Philipp Stephani 2017-07-02 12:31:12 +02:00
parent 4383ff87a1
commit 95343daa79
1 changed files with 18 additions and 17 deletions
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doc/lispref/objects.texi
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@ -283,11 +283,11 @@ character @kbd{a}.
?Q @result{} 81 ?q @result{} 113
@end example
You can use the same syntax for punctuation characters, but it is
often a good idea to add a @samp{\} so that the Emacs commands for
editing Lisp code don't get confused. For example, @samp{?\(} is the
way to write the open-paren character. If the character is @samp{\},
you @emph{must} use a second @samp{\} to quote it: @samp{?\\}.
You can use the same syntax for punctuation characters. However, if
the punctuation character has a special syntactic meaning in Lisp, you
must quote it with a @samp{\}. For example, @samp{?\(} is the way to
write the open-paren character. Likewise, if the character is
@samp{\}, you must use a second @samp{\} to quote it: @samp{?\\}.
@cindex whitespace
@cindex bell character
@ -336,18 +336,19 @@ escape character; this has nothing to do with the
character @key{ESC}. @samp{\s} is meant for use in character
constants; in string constants, just write the space.
A backslash is allowed, and harmless, preceding any character without
a special escape meaning; thus, @samp{?\+} is equivalent to @samp{?+}.
There is no reason to add a backslash before most characters. However,
you should add a backslash before any of the characters
@samp{()\|;'`"#.,} to avoid confusing the Emacs commands for editing
Lisp code. You can also add a backslash before whitespace characters such as
space, tab, newline and formfeed. However, it is cleaner to use one of
the easily readable escape sequences, such as @samp{\t} or @samp{\s},
instead of an actual whitespace character such as a tab or a space.
(If you do write backslash followed by a space, you should write
an extra space after the character constant to separate it from the
following text.)
A backslash is allowed, and harmless, preceding any character
without a special escape meaning; thus, @samp{?\+} is equivalent to
@samp{?+}. There is no reason to add a backslash before most
characters. However, you must add a backslash before any of the
characters @samp{()[]\;"}, and you should add a backslash before any
of the characters @samp{|'`#.,} to avoid confusing the Emacs commands
for editing Lisp code. You can also add a backslash before whitespace
characters such as space, tab, newline and formfeed. However, it is
cleaner to use one of the easily readable escape sequences, such as
@samp{\t} or @samp{\s}, instead of an actual whitespace character such
as a tab or a space. (If you do write backslash followed by a space,
you should write an extra space after the character constant to
separate it from the following text.)
@node General Escape Syntax
@subsubsection General Escape Syntax