package greeter

object Chapter6 {

  println("Classes and Objects")                  //> Classes and Objects

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

    private def gcd(x: Int, y: Int): Int = {

      if (x == 0) y

      else if (x < 0) gcd(-x, y)

      else if (y < 0) -gcd(x, -y)

      else gcd(y % x, x)

    }

    private val g = gcd(n, d)

    val numer: Int = n / g

    val denom: Int = d / g

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

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

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

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

    //Inheritance and Overriding

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

    //Parameterless Methods

    def square = new Rational(numer * numer, denom * denom)

  }

  //Inheritance and Overriding

  var i = 1                                       //> i  : Int = 1

  var x = new Rational(0, 1)                      //> x  : greeter.Chapter6.Rational = 0/1

  while (i <= 10) {

    x += new Rational(1, i)

    i += 1

  }

  println("" + x.numer + "/" + x.denom)           //> 7381/2520

  //Parameterless Methods

  val r = new Rational(3, 4)                      //> r  : greeter.Chapter6.Rational = 3/4

  println(r.square)                               //> 9/16

  //Abstract Classes

  abstract class IntSet {

    def incl(x: Int): IntSet

    def contains(x: Int): Boolean

  }

  //Triats

  trait IntSett {

    def incl(x: Int): IntSet

    def contains(x: Int): Boolean

  }

  //Implementing abstract class

  class EmptySet extends IntSet {

    def contains(x: Int): Boolean = false

    def incl(x: Int): IntSet = new NonEmptySet(x, new EmptySet, new EmptySet)

  }

  class NonEmptySet(elem: Int, left: IntSet, right: IntSet) extends IntSet {

    def contains(x: Int): Boolean =

      if (x < elem) left contains x

      else if (x > elem) right contains x

      else true

    def incl(x: Int): IntSet =

      if (x < elem) new NonEmptySet(elem, left incl x, right)

      else if (x > elem) new NonEmptySet(elem, left, right incl x)

      else this

  }

}