Assignment_07/src/main/scala/Main.scala

   1 object Main {
   2
   3   // Question 1.
   4   trait Stack[+A] {
   5     def push[B >: A](elem: B): Stack[B]
   6     def top: A
   7     def pop: Stack[A]
   8   }
   9
  10   case class EmptyStack[A]() extends Stack[A] {
  11     def push[B >: A](elem: B): Stack[B] = ElemStack(elem, this)
  12     def top: A = throw new Exception
  13     def pop: Stack[A] = throw new Exception
  14   }
  15
  16   case class ElemStack[A](top: A, rest: Stack[A]) extends Stack[A] {
  17     def push[B >: A](elem: B): Stack[B] = ElemStack(elem, this)
  18     def pop: Stack[A] = rest
  19     override def toString = s"${top.toString()},${rest.toString()}"
  20   }
  21
  22   def question1 = {
  23     println("Question 1")
  24     // Construction, pop and toString.
  25     val a = EmptyStack().push("hello").push("world").push("it's fun").pop
  26     println(s"a: ${a}")
  27     assert(a.toString() == "world,hello,EmptyStack()")
  28
  29     // Getting top.
  30     val b = EmptyStack().push(1).push(3)
  31     println(s"b.top: ${b.top}")
  32     assert(b.top == 3)
  33
  34     // Variance checks.
  35     class Foo
  36     class Bar extends Foo
  37     val c: Stack[Bar] = EmptyStack().push(new Bar()).push(new Bar())
  38     assert(c.top.isInstanceOf[Bar])
  39     assert(c.top.isInstanceOf[Foo])
  40
  41     // Variance check 2.
  42     val d: Stack[Foo] = EmptyStack().push(new Bar()).push(new Bar())
  43     assert(d.top.isInstanceOf[Foo])
  44   }
  45
  46   // Question 2.
  47   abstract sealed class Temperature {
  48     val temp: Double
  49   }
  50
  51   case class Celsius(v: Double) extends Temperature {
  52     val temp = v
  53     override def toString = s"$v° C"
  54   }
  55
  56   case class Kelvin(v: Double) extends Temperature {
  57     val temp = v
  58     override def toString = s"$v° K"
  59   }
  60
  61   object Temperature {
  62     implicit def toCelsius(temp: Kelvin): Celsius = new Celsius(temp.v + 273.15)
  63     implicit def toCelsius(temp: Int): Celsius = new Celsius(temp)
  64     implicit def toKelvin(temp: Celsius): Kelvin = new Kelvin(temp.v - 273.15)
  65     implicit def toKelvin(temp: Int): Kelvin = new Kelvin(temp)
  66   }
  67
  68   def question2 = {
  69     println("Question 2")
  70     val a: Celsius = 30
  71     val b: Kelvin = 30
  72     val c: Kelvin = Celsius(10)
  73     val d: Celsius = c
  74     val e: Temperature = d
  75     println(a)
  76     println(b)
  77     println(e)
  78   }
  79
  80   // Question 3.
  81   def addStream(s1: Stream[Int], s2: Stream[Int]): Stream[Int] =
  82     (s1.head + s2.head) #:: addStream(s1.tail, s2.tail)
  83
  84   lazy val fib: Stream[Int] = 0 #:: 1 #:: addStream(fib, fib.tail)
  85
  86   def question3 = {
  87     println(fib.take(30).toList)
  88   }
  89
  90   def main(args: Array[String]): Unit = {
  91     question1
  92     question2
  93     question3
  94   }
  95 }