my $ones;
$ones = ll_new(1, memoize(sub { $ones }));

my $integers;
$integers = ll_new(0,
                   memoize(sub { ll_add($ones,
                                        $integers) }));

sub multiples {
  my $n = shift;
  return ll_map( sub { $n * $_[0] }, $integers );
}

sub challenge {
  return [] unless @_;
  my $x = shift;
  my $out;
  $out = merge( multiples($x), challenge(@_) );
  return $out;
}

my @first_200 = take( 200, challenge(2, 3, 5) );
print "@first_200\n";