Tree.scala

    case class Tree[A](datum:A, children:List[Tree[A]]) {
            def map[B](fn: A => B): Tree[B] = {
                new Tree[B](fn(datum),children.map(_.map(fn)))
            }
 
            def foreach(fn: A => Unit) {
                fn(datum)
                children.foreach(_.foreach(fn))
            }

            def exists(a: A): Boolean = {
                datum.equals(a) || children.exists(_.exists(a))
            }
        }

        //  create:
        //     1
        //    / \
        //   2   3

        val tree = Tree(1,List(Tree(2,Nil),Tree(3,Nil)))
        val squareTree = tree.map(a => a*a)
        assertTrue(tree.exists(3))
        assertTrue(squareTree.exists(9))