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.
It would be good to know that this is an O(N^2) algorithm.
--
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
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Never fight an inanimate object
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You've achieved success in your field when you don't know whether what
you're doing is work or play
On Sun, Sep 28, 2008 at 2:15 PM, Liam Quin <liam(_at_)w3(_dot_)org> wrote:
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/
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