From: "Rob Pike" <robpike@gmail.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@9fans.net>
Subject: Re: [9fans] non greedy regular expressions
Date: Fri, 24 Oct 2008 10:15:51 -0700 [thread overview]
Message-ID: <7359f0490810241015s4d3107dagfef90e3fb463b173@mail.gmail.com> (raw)
In-Reply-To: <20081024170237.68ED28DE7@okapi.maths.tcd.ie>
Backreferences within the pattern (such as in /(.*)\1/) make the
matcher non-regular and exponentially hard. It was a deliberate
decision not to implement them in sam and I'd make the same decision
today.
As far as greedy/non-greedy operators go, they have more utility but I
believe they have become popular primarily to deal with the problems
with Perl and PCRE doing greedy implementations badly in order to
avoid the exponential cost of their backtracking matchers. These
matchers can give crazy results.
Sam etc. are O(length of string * length of pattern) at all times and
their leftmost-longest properties work throughout.
Again, Russ has most of this in his analysis.
-rob
next prev parent reply other threads:[~2008-10-24 17:15 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-23 18:58 Rudolf Sykora
2008-10-23 19:05 ` erik quanstrom
2008-10-24 8:08 ` Rudolf Sykora
2008-10-24 12:23 ` erik quanstrom
2008-10-24 16:11 ` Rudolf Sykora
2008-10-24 16:54 ` erik quanstrom
2008-10-24 17:02 ` John Stalker
2008-10-24 17:15 ` Rob Pike [this message]
2008-10-24 17:41 ` Rudolf Sykora
2008-10-24 18:01 ` Russ Cox
2008-10-24 19:56 ` Rudolf Sykora
2008-10-24 21:10 ` Russ Cox
2008-10-24 21:40 ` Rudolf Sykora
2008-10-24 21:47 ` erik quanstrom
2008-10-24 22:04 ` Rudolf Sykora
2008-10-24 22:38 ` Gabriel Diaz Lopez de la Llave
2008-10-24 22:54 ` Charles Forsyth
2008-10-24 22:59 ` Charles Forsyth
2008-10-24 23:52 ` Tom Simons
2008-10-25 22:35 ` Rudolf Sykora
2008-10-25 23:02 ` Steve Simon
2008-10-26 8:57 ` John Stalker
2008-10-26 18:36 ` Eris Discordia
2008-10-27 4:55 ` Russ Cox
2008-10-27 8:28 ` Rudolf Sykora
2008-10-27 10:18 ` Charles Forsyth
2008-10-27 13:13 ` Eris Discordia
2008-10-27 13:23 ` erik quanstrom
2008-10-27 19:42 ` Eris Discordia
2008-10-27 16:13 ` Brian L. Stuart
2008-11-30 8:29 ` Yard Ape
2008-12-11 16:32 ` Rudolf Sykora
2008-10-24 18:02 ` John Stalker
2008-10-24 17:10 ` Uriel
2008-10-24 19:56 ` Charles Forsyth
2008-10-24 19:56 ` Rudolf Sykora
2008-10-26 21:23 ` Rob Pike
2008-10-24 11:27 Aharon Robbins
2008-10-27 19:23 Aharon Robbins
2008-10-27 20:15 ` Eris Discordia
2008-10-27 20:00 Eris Discordia
2008-10-28 14:51 ` Brian L. Stuart
2008-10-28 15:07 ` Eris Discordia
2008-10-27 21:08 Aharon Robbins
2008-10-28 14:53 ` Eris Discordia
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