トークンの正規表現にはパラメータも可

Parse::RecDescent everyday parser 
#!/usr/bin/env perl

use strict;
use Parse::RecDescent;
use Data::Dumper;

my $grammar =
q{
    inputs : /[a-z]/i { print Data::Dumper::Dumper($item[1]); }
};

my $parse = new Parse::RecDescent ($grammar);

while (<>)
{
    defined $parse->inputs($_) or print "Bad text!\n";
}

で、

a
$VAR1 = 'a';
A
$VAR1 = 'A';