Re: balanced parens regexp hangs

Your code does not hang on my machine, with perl-5.10.0.

(?:[^{}]+?|\{(??{$parens})\})*

Such a regex with nested quantifiers is potentially dangerous, because the outer quantifier can force the inner quantifier to backtrack. Use a non-backtracking group (?>...)* instead. (Oh, and why are you using non-greed +? on the [^{}] group? I see no reason for that).

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Re^2: balanced parens regexp hangs by grizzley (Chaplain) on Mar 27, 2009 at 08:32 UTC
I run it on WinXP with ActiveState Perl v5.10.0. (build 1004). Localizing helped solving my problem, but I removed non-greed and tried to use `(?>...)` but I must admit I don't fully understand documentation of this construct yet. Did you think about something like this? `local $parens = qr{(?:(?>[^{}])\|\{(??{$parens})\})*}x;` [download]	[reply] [d/l] [select]
Re^3: balanced parens regexp hangs by moritz (Cardinal) on Mar 27, 2009 at 09:07 UTC
Actually I meant `(?>(?>[^{}])\|\{(??{$parens})\})`, since I don't see a reason why any of these groups should ever give up something that they successfully matched. For an explanation of `(?>...)` see How backtracking works in regular expressions and Avoiding regex backtracking.	[reply] [d/l] [select]
Re^4: balanced parens regexp hangs by grizzley (Chaplain) on Mar 27, 2009 at 10:10 UTC
I agree. Thanks again!	[reply]