I can not understant a paragraph in Emacs Lisp Reference.

I can not understant a paragraph in Emacs Lisp Reference.

[waterloo]

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As a `\' is not special inside a character alternative, it can never
remove the special meaning of `-' or `]'.  So you should not quote
these characters when they have no special meaning either.  This would
not clarify anything, since backslashes can legitimately precede these
characters where they _have_ special meaning, as in `[^\]' (`"[^\\]"'
for Lisp string syntax), which matches any single character except a
backslash.

`[^\]'  or `"[^\\]"' , which is right ? what is Lisp string syntax for ?

thanks

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Re: I can not understant a paragraph in Emacs Lisp Reference.

[Anselm Helbig]

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Hi!

> As a `\' is not special inside a character alternative, it can never
> remove the special meaning of `-' or `]'.  So you should not quote
> these characters when they have no special meaning either.  This would
> not clarify anything, since backslashes can legitimately precede these
> characters where they _have_ special meaning, as in `[^\]' (`"[^\\]"'
> for Lisp string syntax), which matches any single character except a
> backslash.
> 
> `[^\]'  or `"[^\\]"' , which is right ? what is Lisp string syntax for ?

Seems to be clear to me: the first one is correct, but the second one
also works, you're just specifying the same character twice, like in
`[^aa]'. So the elisp string would be "[^\\]". Do you know about 
M-x re-builder?

Happy hacking!

Anselm


-- 
Anselm Helbig 
mailto:anselm.helbig+news2009@googlemail.com

Re: I can not understant a paragraph in Emacs Lisp Reference.

[waterloo]

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I try with re-builder ,  find that `"[^\\]"' is corrct .
`"[^\]"' can not find anything .
Thanks

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Re: I can not understant a paragraph in Emacs Lisp Reference.

[Teemu Likonen]

On 2009-07-11 22:46 (+0800), waterloo wrote:

> I try with re-builder ,  find that `"[^\\]"' is corrct .
> `"[^\]"' can not find anything .

Please note that in regexp-builder the regexp is built in a Lisp
string--in which you need to backslash-escape all backslashes. It means
that Lisp string "[^\\]" is really regexp [^\] .

RE: I can not understant a paragraph in Emacs Lisp Reference.

[Drew Adams]

>>     `[^\]' (`"[^\\]"' for Lisp string syntax)

>> `[^\]'  or `"[^\\]"' , which is right ?
>> what is Lisp string syntax for ?

> I try with re-builder ,  find that `"[^\\]"' is corrct .
> `"[^\]"' can not find anything .

Lisp string syntax is the syntax used in Lisp code when you write a literal
string (constant). The Lisp reader (part of the Lisp interpreter) reads the
string syntax you enter and constructs a string constant accordingly.

In Lisp string syntax, you need to double each backslash that you want in the
string. So "\\" is Lisp string syntax for the string that has one character, a
backslash. This doubling is needed because Lisp string syntax uses the backslash
for special escape sequences: for example, \" represents a double-quote
character.

See the Elisp manual, node `Syntax for Strings'.

Re: I can not understant a paragraph in Emacs Lisp Reference.

[waterloo]

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Thanks , the explanation is good enough.

2009/7/11 Drew Adams <drew.adams@oracle.com>

> >>     `[^\]' (`"[^\\]"' for Lisp string syntax)
>
> >> `[^\]'  or `"[^\\]"' , which is right ?
> >> what is Lisp string syntax for ?
>
> > I try with re-builder ,  find that `"[^\\]"' is corrct .
> > `"[^\]"' can not find anything .
>
> Lisp string syntax is the syntax used in Lisp code when you write a literal
> string (constant). The Lisp reader (part of the Lisp interpreter) reads the
> string syntax you enter and constructs a string constant accordingly.
>
> In Lisp string syntax, you need to double each backslash that you want in
> the
> string. So "\\" is Lisp string syntax for the string that has one
> character, a
> backslash. This doubling is needed because Lisp string syntax uses the
> backslash
> for special escape sequences: for example, \" represents a double-quote
> character.
>
> See the Elisp manual, node `Syntax for Strings'.
>
>

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