set.scala

package set
object main extends App {
  def power[A](t: Set[A]): Set[Set[A]] = {
    @annotation.tailrec
    def pwr(t: Set[A], ps: Set[Set[A]]): Set[Set[A]] =
      if (t.isEmpty) ps
      else pwr(t.tail, ps ++ (ps map (_ + t.head)))
    pwr(t, Set(Set.empty[A])) //Powerset of ∅ is {∅}
  }

  val a = Set(1,2,3)
  val b = Set(3,4,5,6)

  println("|a| = "+a.size)
  println("|b| = "+b.size)
  println("a ∪ b = "+(a union b))
  println("a ∩ b = "+(a intersect b))
  println("a \\ b = "+(a diff b))
  println(power(Set(1,2,3)))
}