In message "[ruby-talk:9078] Re: Regexp for matching Ruby reg exps?"
    on 01/01/11, "Ben Tilly" <ben_tilly / hotmail.com> writes:
>Friedl's solution only handles nesting to a limited depth.
>Enough for parsing email addresses but not a general
>solution.  Not only is handling arbitrary nesting in a

Oh, I misread the book :-<

>    perldoc -q nesting
>
>Yup.  Perl's documentation agrees with me.  Can't be done
>in Perl with a straight regular expression.

I didn't know that document.  Thank you very much.  

Now, I have a question: Any any formal proofs of the impossibleness
known for a extended RE?  In other words, what extension can buil a
stack? 

>Writing negative patterns in any regular expression engine
>tends to be difficult.  I claim that this is a limitation
>inherent in the RE view of the world, and not to any
>specific implementation.

I agree.  

Btw, when I started learning RE of a programming language after had
gotten a unit of language theory, I was confused by the different
between theoretical one and that; They have same name and very
confuging (at least for me :-)

-- Gotoken