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Re: RFC: Parsing with perl - Regexes and beyond

by pKai (Priest)
on Apr 03, 2008 at 21:21 UTC ( #678271=note: print w/replies, xml ) Need Help??


in reply to RFC: Parsing with perl - Regexes and beyond

The first two definitions are recursive, so they are not "regular" any more.

You can argue that the first production is "tail recursive" which does not pose a problem with respect to regularity. Like a tail recursive function can be transformed into a loop.

The non-regularity comes with the 2nd production.

term        -> '(' term ')'

The point is that term can grow to arbitrary length and we still should keep the correspondence between the two parentheses, which is not possible with (CS)-Regexes ("pumping lemma").

This last observation is the border where you need a CFL-parser and would be lost with Regexes alone.

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[LanX]: ... but this part is already in production for a year now
[Corion]: LanX: The "good" approach here would be to use the appropriate DBI parameters to make the driver decode strings properly. But that will have a ripple-on effect of messing up all the places where manual decoding happens ;)
[LanX]: which means albeit being broken UTF8 it'll be handled correctly
[LanX]: and the problem only occurs since we changed the emails to base64
[LanX]: my main problem will be to cnvince my colleagues that our productive code is broken oO ... so in the end I will just make a workaround :-/
LanX hates UTF8 for causing knots in his brain and stomach
[Corion]: LanX: Yes, that's the main problem - you have lots (and lots) of workarounds in various places and stages of the processing, and to clean that mess up requires action across the complete codebase. And it's almost impossible to do it piece-by-piece

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