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Re: Negate a regexp

From: Thierry Volpiatto
Subject: Re: Negate a regexp
Date: Mon, 19 Apr 2010 19:54:46 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

Leo <> writes:

> On 2010-04-19 16:51 +0100, Drew Adams wrote:
>>> How to negate a regexp? For example this one: \(?:\sw\|\s_\|\s\\).
>> You cannot express a complement using (real) regexps. Regular expressions are
>> just not that expressive (powerful).
>> However, Emacs Lisp is that powerful; its use of regexps is not limited to 
>> real
>> regular expressions; and you can bathe your use of regexps in a more powerful
>> sauce.
>> In Emacs Lisp, you can in some cases use complementary syntax: \W as 
>> complement
>> of \w, \S_ as complement of \s_, etc. And you can use ^ at the beginning of a
>> [...] character set to complement that set (what the manual calls a
>> "complemented character alternative"). See node `Syntax of Regexps' in the 
>> Elisp
>> manual.
>> Another thing you can do is to use a regexp to determine a set of matches -
>> those elements you do not want, and then, assuming you know the overall 
>> domain
>> explicitly (extensively), subtract those matches to get the complement (those
>> elements of the domain that do not match).
> I need to provide a regexp to an abbrev table so that the match in group
> 1 (which is the abbrev name) can contain word symbol or \. The match is
> done through (looking-back ...) with the GREEDY arg omitted. For example
> in a buffer with text \coor-!-, where -!- indicates point, (looking-back
> REGEXP) (match-string 1) should return \coor. Any idea how to construct
> such a REGEXP?
It will return \\coor because \ have to be escaped.

(save-excursion (when (looking-back "^\\(\\\\[a-z]*\\)") (match-string 0)))

It match on 1 also.

> I am not entirely sure the way the :regexp to abbrev table should be
> provided is well thought-out. See my question to emacs-devel:
> Cheers,
> Leo

Thierry Volpiatto
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