package examples object patterns { trait Tree case class Branch(left: Tree, right: Tree) extends Tree case class Leaf(x: Int) extends Tree val tree1 = Branch(Branch(Leaf(1), Leaf(2)), Branch(Leaf(3), Leaf(4))) def sumLeaves(t: Tree): Int = t match { case Branch(l, r) => sumLeaves(l) + sumLeaves(r) case Leaf(x) => x } def find[a,b](it: Iterator[Pair[a, b]], x: a): Option[b] = { var result: Option[b] = None var found = false while (it.hasNext && !found) { val Pair(x1, y) = it.next if (x == x1) { found = true; result = Some(y) } } result } def printFinds[a](xs: List[Pair[a, String]], x: a) = find(xs.iterator, x) match { case Some(y) => System.out.println(y) case None => System.out.println("no match") } def main(args: Array[String]) { println("sum of leafs=" + sumLeaves(tree1)) printFinds(List(Pair(3, "three"), Pair(4, "four")), 4) } }