Iterated Prisoner's Dilemma in Perl 6

prisoners.pl

use v6;

# by convention, True means cooperate, False means defect

my %scoring =
    'True True'   => [4, 4],
    'True False'  => [0, 6],
    'False True'  => [6, 0],
    'False False' => [1, 1],
    ;

# basic, well-known strategies

my %strategies =
    good                => -> *% { True  },
    bad                 => -> *% { False },
    random              => -> *% { Bool.pick },
    tit-for-tat         => -> :@theirs, *% { @theirs[*-1] // True },
    evil-tit-for-tat    => -> :@theirs, *% { @theirs[*-1] // False },
    ;

sub compete(&a, &b, :$count = 20) {
    my @a;
    my @b;
    my @scores = (0, 0);
    for 1..$count {
        my $current-a = a(:theirs(@b), :mine(@a), :total($count));
        my $current-b = b(:theirs(@a), :mine(@b), :total($count));
        @a.push: $current-a;
        @b.push: $current-b;
        @scores = @scores Z+ %scoring{"$current-a $current-b"}.list;
    }
    return @scores;
}



sub tournament($count = 50) {
    my %results;
    my @names = %strategies.keys.sort;
    for @names.keys -> $idx-a {
        for $idx-a .. @names.end -> $idx-b {
            my $a = @names[$idx-a];
            my $b = @names[$idx-b];
            my @r = compete(|%strategies{$a, $b}.list, :$count);
            # say "$a : $b     @r[0] : @r[1]";
            %results{$a} //= 0;
            %results{$b} //= 0;
            %results{$a} += @r[0];
            %results{$b} += @r[1];
        }
    }
    %results;
}

sub MAIN($laps = 50) {
    my %results =  tournament($laps);
    say 'SUMMARY';
    for %results.sort(-*.value) -> $p {
        say $p.value, "\t", $p.key;
    }
}