Re: parsing parens in the park

On Sun, Sep 28, 2008 at 09:15:45PM +0100, David Carlisle wrote:
> You can not match nested brackets with regular expressions. (That's more
> or less the defining restriction which is implied by "regular").

Agreed...

> To match brackets you need to use, in addition to regular expressions, a
> language that can either count or (equivalently) has a unbounded stack.
> (Eg recursive function calls).

Actually if all you need to do is test to see if they match or not,
you can do easier things.  In an iterative language,
    while (string has parens) {
        remove all occurrences of "()"
	if there were none, signal an error
    }
    if you get here without error, it's OK.

The XSLT implementaion of this would be recursive though.

Perl regexps can mach parens, and there's an example in the
"perldoc perlre" or, "man perlre" documentation.

Liam

-- 
Liam Quin, W3C XML Activity Lead, http://www.w3.org/People/Quin/
http://www.holoweb.net/~liam/ * http://www.fromoldbooks.org/