Rational.scala

object rationals {
    
  val x = new Rational(1,3)                       //> x  : Rational = 1/3
  x.numer                                         //> res0: Int = 1
  x.denom                                         //> res1: Int = 3
  
  val y = new Rational(5,7)                       //> y  : Rational = 5/7
  x.add(y)                                        //> res2: Rational = 22/21
  
  val z = new Rational(3,2)                       //> z  : Rational = 3/2
  //val m = x - y - z
  x.neg                                           //> res3: Rational = -1/3
  x.sub(y).sub(z)                                 //> res4: Rational = -79/42
}

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

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

  //def -(that: Rational) = new Rational(-x, y)
  def neg: Rational = new Rational(-numer, denom)

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

  override def toString = numer + "/" + denom


}