P6: parsing whitespace

rir has asked for the wisdom of the Perl Monks concerning the following question:

In the below, I don't see why the x matches differently from the * ?

#!/home/rir/rakudo/parrot_install/bin/perl6
use v6;

grammar Calc {
    rule TOP { <term> <op> <term>  }
#    rule TOP { <term>\s?<op>\s?<term>  }   # a fix
    token term { \d+(\.\d*)? }
    token op { '*' | 'x' }
}

my @t = (
    [ 44, " 8.8 * 5.0 " ],
    [ 44, " 8.8 x 5.0 " ],
    [ 44, " 8.8*5.0 " ],
    [ 44, " 8.8x5.0 " ],        # no match
);

for @t -> $i {
    my $m = Calc.parse( $i[1]);
    print $m ?? "  " !! "no";
    say " match: $i[1]"
}
[download]

Be well,
rir

Comment on P6: parsing whitespace Download Code

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Re: P6: parsing whitespace by moritz (Cardinal) on Jun 09, 2010 at 18:01 UTC
If you have whitespace in a `rule`, it is internally replaced by a call to the `ws` token. The default `ws` matches at least one space (\s+) if the left and right are word characters (ie matching \w), and matching zero or more (\s) otherwise. In code: `class Grammar { token ws { <!ww> \s } }` [download] Where `ww` is within word, and could be defined as `token ww { <after \w> <before \w> }` [download] If you want 8.8x5.0 to match, you need to override the `ws` rule in your grammar: `grammar Calc { token ws { \s* } # rest of your code here without any modifications` [download] (Update: fixed `ww` rule after comment from TimToady++) Perl 6 - links to (nearly) everything that is Perl 6.	[reply] [d/l] [select]

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Re: P6: parsing whitespace
by moritz (Cardinal) on Jun 09, 2010 at 18:01 UTC

rule

ws

The default ws matches at least one space (\s+) if the left and right are word characters (ie matching \w), and matching zero or more (\s*) otherwise.

In code:

class Grammar {
   token ws {
       <!ww> \s*
   }
}
[download]

Where ww is within word, and could be defined as

token ww {
    <after  \w>
    <before \w>
}
[download]

If you want 8.8x5.0 to match, you need to override the ws rule in your grammar:

grammar Calc {
    token ws { \s* }
    # rest of your code here without any modifications
[download]

(Update: fixed ww rule after comment from TimToady++)

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