spell_checker.pl

use v6;

my %dictionary;
slurp("big.txt").comb(/<alpha>+/).map({%dictionary{$_.lc}++});

sub edits($word) {
    my @s = (^$word.chars).map({$word.substr(0, $_), $word.substr($_)});
    my @deletes = @s.map(-> $a, $b { $a ~ $b.substr(1); });
    my @transposes = @s.map(-> $a, $b { $a ~ $b.substr(0, 2).flip ~ $b.substr(2) if $b.chars > 1 });
    my @replaces = @s.map(-> $a, $b {$a ~ ':' ~ $b.substr(1)});
    my @inserts = (@s,$word,"").map(-> $a, $b {$a ~ ':' ~ $b});
    return (@deletes, @transposes, @replaces, @inserts);
}

sub edit_list_to_regex(@el) {
    any(@el.uniq>>.subst(':', '<alpha>', :g).map({ rx/ ^ $_ $ / }));
}

sub correct($word) {
    return $word if (%dictionary{$word});
    my $regex = edit_list_to_regex(edits($word));
    my @candidates = %dictionary.keys.grep($regex);
    if @candidates.elems == 0 {
        $regex = edit_list_to_regex(edits($word).map({edits($_)}));
        @candidates = %dictionary.keys.grep($regex);
    }
    return @candidates.max({%dictionary{$_} // 0});
}

correct("lary").say;