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Re: RFC: Perl regex to validate arithmetic expressions

by mellon85 (Monk)
on Feb 21, 2011 at 18:53 UTC ( #889463=note: print w/replies, xml ) Need Help??

in reply to RFC: Perl regex to validate arithmetic expressions

You actually can parse an arithmetic expression with a "regular" expression if it uses a stack automata. Just think that a regular language can't even check if there is a correct number of parenthesis if the maximum depth is undefined, as such, strictly speaking that is not so much regular...
  • Comment on Re: RFC: Perl regex to validate arithmetic expressions

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Re^2: RFC: Perl regex to validate arithmetic expressions
by JavaFan (Canon) on Feb 22, 2011 at 09:58 UTC
    Since 5.10, Perl regular expressions can match anything that's matched by a context-free grammar - and then some (backreferences add even more power). Matching balanced parenthesis is easy in 5.10 and later: /^(\((?1)*\))$/.

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[1nickt]: hippo lately I can tell just by the fact that Anonymous posts a reply after some hours that it is more than likely That Monk.
[virtualsue]: weird. my p6 simple web spider fails to extract anchor tags from
[holli]: Nice. Turns out I don't have to remove Sweet home Alabama from my playlist ;)
[Corion]: virtualsue: We have some links with a newline between <a and the attributes, maybe your extractor fails to handle that?
[virtualsue]: It's not getting any at all, which seems quite broken

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