# Powerset: the set of all subsets -- (for illustration only, not used below)
sub powerset {
  my ($car, @cdr) = @_;
  my @cdr_powerset = @cdr ? powerset(@cdr) : ();
  return ([$car], map([$car, @$_], @cdr_powerset), @cdr_powerset);
}

sub iter_powerset {
  my ($car, @cdr) = @_;
  my $cdr_power_iter = @cdr ? iter_powerset(@cdr) : ();
  my $mode = 0;
  return sub {
    if ($mode == 0) {
      ++$mode;
      return [$car];
    }
    elsif ($mode == 1) {
      my $tail = $cdr_power_iter ? $cdr_power_iter->() : [];
      if (@$tail) {
        return [$car, @$tail];
      }
      else {
        ++$mode;
      }
    }
    my $tail = $cdr_power_iter ? $cdr_power_iter->() : [];
    if (@$tail) {
      return [@$tail];
    }
    else {
      $mode = 0;
      return [];
    }
  }
}

my $iter = iter_powerset(2,3,5,7,11);
print "@$_\n" while (@{$_ = $iter->()});