gistfile1.txt

sub combinations(@items, $count) is export {
    my $size = +@items;
    gather for ^(2 ** $size) -> $i {
        my $gray = $i +^ ($i +> 1);
        my @a = @items.grep({ my $result = $gray +& 1; $gray +>= 1; $result });
        next if @a != $count;
        take [@a];
    }
}