Re: [boost] [regex] specify parenthesis

From: Lorenzo Bettini (bettini_at_[hidden])
Date: 2007-05-01 11:36:16

Phil Endecott wrote:
> Lorenzo wrote:
>> is there a way to specify open and closed parenthesis with a
>> regular expression syntax?  For instance, if I'd want to specify a
>> single regular expression that matches both (foo) and [foo] and {foo}?
> 
> Lorenzo,
> 
> Matching parentheses to arbitrary depth is, like matching palindromes, 
> a textbook example of something that cannot be done with a regular 
> language and instead needs a context-free language.  Google for 
> "chomsky hierarchy palindrome" for some background material.  Of 
> course, it's possible that some regexp library somewhere has a hack to 
> add this functionality.  But fundamentally, you need a more 
> sophisticated parser.
> 

Hi Phil

yes I know about that, but since regex supports backreferences and
conditionals, I thought that this might be implemented by a combination
of these two mechanisms...  indeed John Maddock answered to this thread
right with a manual solution using backreferences and conditionals...

so I thought a regular expression syntax could already be provided to
match these...

I'm using regular expressions for this software
http://www.gnu.org/software/src-highlite that highlights programs, and
it assumes that the program itself is correct.  Thus, I assume that
parenthesis (and brackets - sorry, in Italian both (, [ and { are called
parenthesis :-) are balanced, and with greedy regular expressions,
nested parenthesis are already handled...

Lorenzo

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