sub ret_permute_iter {
  if (@_ < 2) {
    my @vals = ("garbage", @_);
    return sub {
      shift @vals;
      return @vals;
    };
  }
  else {
    my ($cur, @left) = @_;
    my @done;
    my $iter = ret_permute_iter(@left);
    return sub {
      my @res = $iter->();
      if (@res) {
        return ($cur, @res);
      }
      elsif (@left) {
        push @done, $cur;
        $cur = shift @left;
        $iter = ret_permute_iter(@done, @left);
        @res = $iter->();
        return ($cur, @res);
      }
      else {
        return;
      }
    };
  }
}

my $demo_iterator = ret_permute_iter(1..5);
foreach (1..120) {
  print $demo_iterator->(), "\n";
}