linux-kernel - Re: [PATCH] Make checkpatch rant about trailing ; at the end of "if" expr

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Message-ID: <Pine.LNX.4.64.0708221156330.20435@fbirervta.pbzchgretzou.qr>
Date:	Wed, 22 Aug 2007 11:57:24 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Bodo Eggert <7eggert@....de>
cc:	Andy Whitcroft <apw@...dowen.org>,
	Eugene Teo <eugeneteo@...nel.sg>, linux-kernel@...r.kernel.org,
	auke-jan.h.kok@...el.com
Subject: Re: [PATCH] Make checkpatch rant about trailing ; at the end of "if"
  expr


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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