"Programming Scala" Chapter 6

Rational.scala

class Rational(n: Int, d: Int) {

  require(d != 0)

  private val g = gcd(n.abs, d.abs)
  val numer: Int = n / g
  val denom: Int = d / g

  def this(n: Int) = this(n, 1)

  override def toString() = numer + "/" + denom

  private def gcd(a: Int, b: Int): Int = 
    if (b == 0) a else gcd(b, a % b)

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

  def + (i: Int) = 
    new Rational(numer + i * denom, denom)

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

  def * (i: Int) =
    new Rational(numer * i, denom)

  def lessThan(that: Rational) =
    numer * that.denom < that.numer * denom

  def max(that: Rational) = 
    if (this.lessThan(that)) that else this

}