> For the complete documentation index, see [llms.txt](https://trizen.gitbook.io/perl6-rosettacode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://trizen.gitbook.io/perl6-rosettacode/programming_tasks/e/evolutionary_algorithm.md).

# Evolutionary algorithm

```perl
constant target = "METHINKS IT IS LIKE A WEASEL";
constant @alphabet = flat 'A'..'Z',' ';
constant C = 10;

sub mutate(Str $string, Real $mutate-chance where 0 ≤ * < 1) {
  $string.subst: /<?{ rand < $mutate-chance }> . /, @alphabet.pick, :global
}
sub fitness(Str $string) { [+] $string.comb Zeq target.comb }

printf "\r%6d: '%s'", $++, $_ for
  @alphabet.roll(target.chars).join,
  { max :by(&fitness), mutate($_, .001) xx C } ... target;
print "\n";
```