On Aug 22 2007 11:21, Bodo Eggert wrote:
>
>> >> But. The above regex does not seem to handle
>> >>
>> >> if ((a = b));
>> >> oops;
>> >>
>> >> I have tried to come up with a superduper regex that handles multiple
>> >> (), but my regex fu seems to stop above two pairs of ().
>> >
>> >This is because you can't do that using finite regular expressions.
>> >
>> >Regular expressions are Type-3 grammars, but you'd need a Type-2
>> >grammar to express the Dyck language (and you need to parse a Dyck
>> >Language, ignoring the non-dyck-parts).
>>
>> So what about this then...
>>
>> $s = shift @ARGV;
>> $r = qr/a(??{ $r })?b/;
>
>This is not a regular expression, because it can't be parsed by a
>finite state machine (DFA/NFA) without a stack.
>http://en.wikipedia.org/wiki/Deterministic_finite_state_machine
>
>Obviously perl does allow non-regular expressions.
Exactly, and which is why my idea was to use a (??{ }) block to match if((()));
but for some reason, it did not fly, and I do not know either why.
Jan
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