Perfect binary trees

Perfect

object Perfect {

  sealed trait Perfect[+A] {
    // TODO: Try to implement flatMap.
    // Hint: It can't be done. Why?
  }
  case class Empty extends Perfect[Nothing]
  case class Node[+A](head: A, tail: Perfect[Perfect[A]]) extends Perfect[A]

  sealed trait Square[+A]
  case class Zero[+A](a: A) extends Square[A]
  case class Succ[+A](succ: Square[(A, A)]) extends Square[A]

}