an other attempt at improving permutations, using the third method in http://rosettacode.org/wiki/Permutations#Perl_6

permutations.p6

sub permutations(int $n) {
    Seq.new:
    class :: does Iterator {
        has int $!n;
        submethod BUILD { $!n = $n; self }
        method pull-one {
            return (^$!n).List unless (state $i = 0)++;
            return IterationEnd if $i >= self.count-only;
            return map { |(state @ = ^$!n).splice($_, 1) }, $i.polymod($!n ... 2);
        }
        method count-only { state $ = [*] 1 .. $!n }
    }.new(:$n);
}
.say for permutations(3);