How can I pass arguments to a Perl 6 grammar? - grammar

Question

In Edit distance: Ignore start/end, I offered a Perl 6 solution to a fuzzy fuzzy matching problem. I had a grammar like this (although maybe I've improved it after Edit #3):
grammar NString {
regex n-chars { [<.ignore>* \w]**4 }
regex ignore { \s }
}
The literal 4 itself was the length of the target string in the example. But the next problem might be some other length. So how can I tell the grammar how long I want that match to be?

Answer 1

Although the docs don't show an example or using the $args parameter, I found one in S05-grammar/example.t in roast.
Specify the arguments in :args and give the regex an appropriate signature. Inside the regex, access the arguments in a code block:
grammar NString {
regex n-chars ($length) { [<.ignore>* \w]**{ $length } }
regex ignore { \s }
}
class NString::Actions {
method n-chars ($/) {
put "Found $/";
}
}
my $string = 'The quick, brown butterfly';
loop {
state $from = 0;
my $match = NString.subparse(
$string,
:rule('n-chars'),
:actions(NString::Actions),
:c($from++),
:args( \(5) )
);
last unless ?$match;
}
I'm still not sure about the rules for passing the arguments though. This doesn't work:
:args( 5 )
I get:
Too few positionals passed; expected 2 arguments but got 1
This works:
:args( 5, )
But that's enough thinking about this for one night.