From: David Alan Black <dblack@...>
Date: 2002-05-07T23:54:23+09:00
Subject: Re: RegExp zero-width negative lookahead

Hello --

On Tue, 7 May 2002, Lars Christensen wrote:

>
> Hi,
>
> I'm puzzled why this doesn't work the way I expect it to.
>
> "xxoxxxoxx" =~ /(?!x)ox+o(?!x)/      #=> nil (ok)
> "xx oxxxoxx" =~ /(?!x)ox+o(?!x)/     #=> nil (ok)
> "xx oxxxo xx" =~ /(?!x)ox+o(?!x)/    #=> 3 (ok)
> "xxoxxxo xx" =~ /(?!x)ox+o(?!x)/     #=> 2 (huh!?)
>
> Why is the string matched in the last case?

Because the first 'o' (or really the zero-width point just to its
left) satisfies (?!x), but without being consumed.  Then that same
'o' satisfies /o/, and is consumed.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav