class Factorial {

  // Recursive definition
  def factorial1(x: Int): Int = {
    var res: Int = 1;
    if (x > 0) set res = x * this.factorial1(x - 1);
    return res
  };

  // Tail-recursive definition
  def factorial2_aux(x: Int, acc: Int): Int = {
    var res: Int = acc;
    if (x > 0) set res = this.factorial2_aux(x - 1, acc * x);
    return res
  };

  def factorial2(x: Int): Int = this.factorial2_aux(x, 1);

  // Iterative definition
  def factorial3(x: Int): Int = {
    var p: Int = 1;
    while (x > 0) {
      set p = p * x;
      set x = x - 1;
    }
    return p
  };

}

{
  var fac: Factorial = new Factorial();
  var x: Int = 5;
  printInt(fac.factorial1(x));
  printChar(10);
  printInt(fac.factorial2(x));
  printChar(10);
  printInt(fac.factorial3(x));
  printChar(10);
}