Beispiel: Scala

http://scala-lang.org

algebraische Datentypen:

abstract class Tree[A]
case class Leaf[A](key: A) extends Tree[A]
case class Branch[A]
    (left: Tree[A], right: Tree[A]) 
        extends Tree[A]

pattern matching:

def size[A](t: Tree[A]): Int = t match {
    case Leaf(k) => 1
    case Branch(l, r) => size(l) + size(r)
  }