"Ranga Nathan" <RNathan@baxglobal.com> wrote:
> 
>    I use (?? to create drop in regex. However now there is a need to
> actually execute some code and return a regex pattern. The postponed regex
> operator (?? does not interpolate and does not seem to run any code other
> than take an expression.

Why?

> Anyway to override this? I am looking at the possibility of creating a
> custom regex module for this.

Damian Conway's OO module has a chapter where he creates customized
regular expression objects to do interesting stuff. You could look
there for ideas.  But...

> This is for a project that requires parsing strings that are deeply nested
> to varying degree sometimes delimiters can be used. Mostly the level of
> nesting is identified by a numeric value. Anyone remembering COBOL would
> be able to recall OCCURS DEPENDING ON in COBOL structure definitions. I am
> taking it to the extreme level to create a generic script.

...right there that's your problem.  REGULAR EXPRESSSIONS ARE FOR MATCHING
PATTERNS, NOT FOR PARSING!  (At least not until Perl 6 comes around.)  If
you want to parse, then use the regular expression engine as a tokenizer,
and process tokens in code.  You'll wind up using \G in your patterns
and /cg in the flags a lot.  (\G is described in perlre, /c and /g in
perlop.)

> Any experience / suggestion would be appreciated.

And there is my suggestion.  Rethink your approach.  Don't use a regular
expressions where they don't fit.

Cheers,
Ben