From: Robert Feldt <feldt@...>
Date: 2001-06-14T18:00:12+09:00
Subject: [ruby-talk:16464] Re: Opinion sought: parsing non-regular languages

On Thu, 14 Jun 2001, ts wrote:

> >>>>> "R" == Robert Feldt <feldt@ce.chalmers.se> writes:
> 
> R>    /%q(.)(?while count(\1) != count(balancing(\1)))\1/
> 
>  You are on the road of a P language with this, and there is some madness
> in it :-)))
> 
Thanks for the pointer.

>  See (?{}), (??{}), etc
> 
>  and there are *VERY GOOD* reasons for this (from perlre)
> 
>  ------------------------------------------------------------
>  For reasons of security, this construct is forbidden if the regular
>  expression involves run-time interpolation of variables, unless the
>  perilous C<use re 'eval'> pragma has been used (see L<re>), or the
>  variables contain results of C<qr//> operator (see
>  L<perlop/"qr/STRING/imosx">).  
>  ------------------------------------------------------------
>  
I'm not sure I fully understand what you mean. Is is "mad" only because of
security concerns or is it mad in itself (as in for example leading to
strange regexp behavior)?

Matz: Any plans on including (?{}) constructs in future Ruby regexp
engines?

Regards,

Robert