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Re: Patch for lookaround assertion in regexp

From: Stefan Monnier
Subject: Re: Patch for lookaround assertion in regexp
Date: Tue, 24 Jan 2012 09:40:38 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.92 (gnu/linux)

>>> In 2009, Tomohiro Matsuyama sent a message to this list with a patch
>>> to add lookahead/lookbehind assertions to Emacs regular expressions
>>> (regexps).  Is there any plan to incorporate this useful feature into
>>> an official release?
>> I'd like to replace the current regexp engine with one that does not
>> suffer from exponential blowup (i.e. using "Thompson's NFA").
>> OTOH, noone has submitted code to replace the current regexp engine, and
>> I don't forsee I'll have the time to write it myself, so maybe I should
>> just give up on this plan.
> As an alternative to PCRE, which, as has already been pointed out,
> doesn’t match any of these requirements, how about RE2?
> http://code.google.com/p/re2/
> It’s written in C++, which is a minus, but it should be simple enough
> to extend it with \c and \s.

That might work, indeed (tho someone still has to write the
corresponding code).
Note that it does not support lookaround assertions.


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