Beefy Boxes and Bandwidth Generously Provided by pair Networks
XP is just a number
 
PerlMonks  

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
?


holli

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

Replies are listed 'Best First'.
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.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://830548]
Approved by rovf
Front-paged by Arunbear
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others examining the Monastery: (8)
As of 2016-06-29 21:11 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My preferred method of making French fries (chips) is in a ...











    Results (387 votes). Check out past polls.