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Re: Patch for lookaround assertion in regexp

From: Stefan Monnier
Subject: Re: Patch for lookaround assertion in regexp
Date: Mon, 23 Jan 2012 09:11:09 -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?
> [IMHO, it is incredibly useful. The only responses to Matsuyama-san's
> message were positive.]

I'd like to replace the current regexp engine with one that does not
suffer from exponential blowup (i.e. using "Thompson's NFA").
Every feature added to the current regexp engine will make it more
difficult to switch, so I'm not too thrilled at the idea of adding
lookaround operators.
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.


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