Create Iterator which traverse binary tree nodes.

BinTreeIterator.scala

object BinTreeIterator {
  sealed trait Tree
  case class Node(v: Int, l: Tree, r: Tree) extends Tree
  case object Leaf extends Tree

  def toIterator(node: Tree): Iterator[Int] = {
    def toStream(n: Tree): Stream[Int] = n match {
      case Node(v, l, r) => v #:: toStream(l) #::: toStream(r)
      case Leaf => Stream.empty
    }
    toStream(node).iterator
  }

  def main(args: Array[String]) {
    var it = toIterator(Node(1, Node(2, Leaf, Leaf), Node(3, Leaf, Leaf)))
    for(e <- it) {
      println(e)
    }
//  val e: Int = 0
//  while(it.hasNext) {
//    println(it.next) //こっちももちろん動く
//  }
  }
}