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Perl 6 - How to combine two negates charachter classes in a grammar

by holli (Monsignor)
on Mar 24, 2010 at 12:57 UTC ( #830548=perlquestion: print w/replies, xml ) Need Help??
holli has asked for the wisdom of the Perl Monks concerning the following question:

Suppose I have
use v6; grammar G { token not_a { <-[ a ]> } token not_b { <-[ b ]> } }
How do i implement a token neither_a_nor_b
as a composition of not_a
and not_b


You can lead your users to water, but alas, you cannot drown them.

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Re: Perl 6 - How to combine two negates charachter classes in a grammar
by moritz (Cardinal) on Mar 24, 2010 at 13:17 UTC

    Just like in Perl 5 you can use look-aheads:

    token neither_a_nor_b { <?before <not_a>> <?before <not_b>> . }

    If you define your define your character classes positively, you can also combine them directly:

    token a { <[ a ]> } token b { <[ b ]> } token neither_a_nor_b { <-a-b> }

    (don't know if anybody implements that, though.

    Perl 6 - links to (nearly) everything that is Perl 6.

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[LanX]: Yeah option a doesn't go into history
[LanX]: probably I need to teach the app to restart after C-c Kill
[Corion]: LanX: Maybe have an infinite-loop cmd file? Much easier than trying to manage that from within Perl IMO
[Corion]: Alternatively, relaunch the application from cron (or a Windows cron) every minute
[LanX]: will try infinite loop ...
[Corion]: :START ... goto START
[LanX]: oh .bat you mean?
[LanX]: obscure cult ...
[Corion]: LanX: cmd.exe is just another way to launch Perl

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