gistfile1.txt

constant target = "Hello world!";
constant mutate_chance = .08;
constant alphabet = map &chr, ^128;  # ASCII characters
constant C = 100;
 
sub mutate {
    $^code.comb.map(
	{ (rand < mutate_chance ?? alphabet.pick !! $_) x (1 xx 10, 0, 2).pick }
    ).join
}
sub fitness($code) {
    my $string = .Str given try {
	EVAL $code;
	CATCH { return 0 }
    }
    ( [+] $string.comb Zeq state @ = target.comb )
    / [+] 1, grep * > 1, $code.comb.BagHash.values;
}
 
loop (
    my $parent = "say 'Hello world!'";
    $parent ne target;
    $parent = max :by(&fitness), mutate($parent) xx C
) { printf "%6d: '%s'\n", (state $)++, $parent }