From: Ilya Zakharevich <nospam-abuse@ilyaz.org>
To: help-gnu-emacs@gnu.org
Subject: Re: will we ever have zero width assertions in regexps?
Date: Fri, 28 Jan 2011 23:49:57 +0000 (UTC) [thread overview]
Message-ID: <slrnik6lh5.rji.nospam-abuse@powdermilk.math.berkeley.edu> (raw)
In-Reply-To: jwv7hdql4ea.fsf-monnier+gnu.emacs.help@gnu.org
On 2011-01-27, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>>> similar to Lua's Lpeg. I myself would also be more interested in
>>> replacing the backtracking matcher with a non-backtracking one (for the
>>> cases where backtracking is not required by backrefs).
>> What for? [After my final round of backtracking-optimizations for
>> Perl REx engine, I do not recollect people (loudly) wanting anything
>> like this for Perl anymore...]
>
> To get rid of the occasional pathological case where matching takes
> forever and Emacs appears to be frozen. Programmers who are used to
> backtracking matchers will usually intuitively stay away from regexps
> that can show such behaviors, but not all programmers do, and even if
> you're careful there are cases that are hard to avoid.
Did you try it with Perl recently (last 10 years or so)? As I said, I
put some optimizations which in most (AFAIK) practical senses remove
such pathologies. (The underlying problems remain; the optimizations
are only "heuristic"; but one needs to be extra inventive to
circumvent the optimizations.)
> Another minor reason is that it can be handy to have an incremental
> matching primitive, so you can match over a long string one chunk at
> a time. I'm not sure how often this would be useful, but I've come
> across a few cases where it seemed like it could be put to good use
> (tho, for lack of experience with it, I can't sweat that it would turn
> out to be a good idea).
Do not know what you mean by this...
Ilya
next prev parent reply other threads:[~2011-01-28 23:49 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.1.1296054361.23496.help-gnu-emacs@gnu.org>
2011-01-26 15:58 ` will we ever have zero width assertions in regexps? Stefan Monnier
2011-01-27 1:45 ` Le Wang
[not found] ` <mailman.6.1296092730.6982.help-gnu-emacs@gnu.org>
2011-01-27 2:21 ` Stefan Monnier
2011-01-27 6:34 ` Ilya Zakharevich
2011-01-27 16:10 ` Stefan Monnier
2011-01-28 23:49 ` Ilya Zakharevich [this message]
2011-01-29 2:51 ` Stefan Monnier
2011-01-29 22:28 ` Ilya Zakharevich
2011-01-31 16:08 ` Stefan Monnier
2011-01-31 17:10 ` Ilya Zakharevich
2011-01-31 21:29 ` Stefan Monnier
2011-02-02 15:09 ` Ilya Zakharevich
2011-02-07 20:30 ` Stefan Monnier
2011-02-08 22:41 ` Ilya Zakharevich
2011-01-26 14:55 Le Wang
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