vala

void factorial(uint32 n, out double result)
{
  if ( n <= 1) {
      result = 1.0;
  } else {
     double partial_result;
     uint32 next_n = n - 1;
     factorial(next_n, out partial_result);
     result = n * partial_result;
  }
}

void main()
{
  double result;
  uint32 n = 5;
  factorial(n, out result);
  stdout.printf("%g\n", result);
}