object Rationals {

  class Rational(x :Int, y: Int) {
    def numer = x
    def denom = y

    def neg = new Rational(-numer, denom)

    def add(that: Rational) =
      new Rational(
        numer * that.denom + that.numer * denom,
        denom * that.denom)

    def sub(that: Rational) = add(that.neg)

    override def toString = numer + "/" + denom

  }

  def run = {
    println("Rationals")
    println(new Rational(2, 3).add(new Rational(3, 4)).toString)
    println(new Rational(1, 3).sub(new Rational(5 ,7)).sub(new Rational(3, 2)).toString)
  }

}