Newsgroups: comp.lang.perl
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!ukma!usenet.ins.cwru.edu!ncoast!allbery
From: allbery@NCoast.ORG (Brandon S. Allbery KF8NH)
Subject: Re: regular expressions
Reply-To: allbery@ncoast.ORG (Brandon S. Allbery KF8NH)
Organization: North Coast Public Access Un*x (ncoast)
Date: Sat, 8 Jun 1991 14:54:19 GMT
Message-ID: <1991Jun8.145419.22522@NCoast.ORG>
Followup-To: comp.lang.perl
References: <1991Jun4.175023.6509@serval.net.wsu.edu>
Lines: 29

As quoted from <1991Jun4.175023.6509@serval.net.wsu.edu> by hakimian@tek4.eecs.wsu.edu (Karl Hakimian - staff):
+---------------
| I would like to talk with and and all regular expression gurus. It seems that
| the regular expressions that are supported by perl (and unix) do not accept
| any and all regular languages. If this is not true, I would love to learn how
| to do some of the things that I am trying to do.
+---------------

It's true, which is why Perl will never replace, say, Icon for *all*
applications.

+---------------
| For example, how would you write a regular expression that accepts a string
| with "foo" iff "bar" is not also in the string.
+---------------

You don't.

Regexps are most capable in combination with other constructs; so, while you
can't write a regexp that matches /foo/ iff it does not also match /bar/, you
*can* say (in Perl):  (($str !~ /bar/) && ($str =~ /foo/)).  (I could argue
that Perl is nothing more than an extended regexp parser, if I were feeling
whimsical....)

++Brandon
-- 
Me: Brandon S. Allbery			 KF8NH: DC to LIGHT!  [44.70.4.88]
Internet: allbery@NCoast.ORG		 Delphi: ALLBERY
uunet!usenet.ins.cwru.edu!ncoast!allbery