tree.scala

trait Tree[A]{
  def map[B](f: A => B):Tree[B]
  def forEach(f: A => Unit):Unit
}
case class Node[A](value:A, left:Tree[A], right:Tree[A]) extends Tree[A] {
  def map[B](f: A => B): Node[B] = Node(f(value), left.map(f), right.map(f))
  def forEach(f: A => Unit): Unit = {
    f(value)
    left.forEach(f)
    right.forEach(f)
  }
}
case class Leaf[A](value:A) extends Tree[A] {
  def map[B](f: A => B): Leaf[B] = Leaf(f(value))
  def forEach(f: A => Unit): Unit = f(value)
}

val tree: Tree[Int] = Node(
  1,
  Node(
    2,
    Leaf(3),
    Node(
      4,
      Leaf(5),
      Leaf(6)
    )
  ),
  Leaf(7)
)

val newTree = tree.map(_.toString())
newTree.forEach(println)