From: Noah Easterly <noah.easterly@...>
Date: 2007-11-19T22:25:02+09:00
Subject: Re: Regexp for parsing?

On Nov 18, 8:50 pm, Wayne Magor <Wayne.Ma...@gmail.com> wrote:
> I understand regular expressions, but can someone please explain this:
>
> re = %r/((?<pg>\((?:\\[()]|[^()]|\g<pg>)*\)))/
>
> By the way, this only works with the Oniguruma engine (Ruby 1.9).
>
> So, now that there is the capability to match balanced parens and so
> forth, does this mean that the new regular expression engine can be
> used to construct simple parsers (matching language constructs)?

%r/ ... /
-- regexp delimter (why they didn't just use / ... /, I don't know)
( ... )
-- non-capturing group - (normally would be capturing, but see
http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt, part 10, case 3)
-- seems rather useless, given that the only contained item is a
capturing group
(?<pg> ... )
-- capturing named group (see http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt,
part 7)
\( .. \)
-- literal parentheses surrounding pattern
(?: ... | ... | ... )*
-- non-capturing group of 3 alternatives, repeated 0 or more times
\\[()]
-- escaped literal parens
[^()]
-- anything except parens
\g<pg>
-- match the pg-named pattern here (recursive sub-exp - see
http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt, part 9)