use strict;
use warnings;
use Parse::RecDescent;

my $grammar = q/
  startrule: choice  "a"
  choice:   "a" "a" <score: -2>
	      | "a" <score: -1>
	/;
my $parser  = Parse::RecDescent->new($grammar);

while (<DATA>) {
	chomp($_);
	print defined($parser->startrule($_)) ? "Good!\n" : "Bad!\n";
}

__DATA__
a a a
a a