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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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[Discipulus]: i invented also 'gired'
[Lady_Aleena]: Discipulus, then that is a problem. I wanted to find total seconds of my entire .mp3 collection to do some math on it to see how many days of continuous music i have.
[LanX]: darn. .. I wanted to see Marine and Melonchon go to next round, just for fun xD
[Discipulus]: LA use Perl: traversing a dir tree is simple; foreach file mp3 $sec+= use Mp3::Info
[Lady_Aleena]: Discipulus, I was able to get the sum of the seconds on the command line using awk. Then I ran the result through a perl script and got the result. It came bach with 4 days, 9 hours, 56 minutes, 43 seconds.
[Lady_Aleena]: s/bach/back/;
[Discipulus]: gired anyway is the intermediate state between hired and fired (and vice versa;)
[Lady_Aleena]: Discipuluis, I don't know if I want to fight with File::Find. File::Find and I are not friends.
[Discipulus]: 4 day Bach is too muche even for me
[Discipulus]: LA you know who is paco?

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