Beefy Boxes and Bandwidth Generously Provided by pair Networks vroom
"be consistent"
 
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 ]> }
}

[download]
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.

Comment on Perl 6 - How to combine two negates charachter classes in a grammar
Select or Download Code
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>>
   .
}

    [download]

    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> }

    [download]

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

    Perl 6 - links to (nearly) everything that is Perl 6.
[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom

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 cooling their heels in the Monastery: (12)
As of 2013-12-19 20:34 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    How do you parse XML?
















    Results (406 votes), past polls