Immutable cycles (as seen in "Case classes a la carte with shapeless, now!" at scalax2014 by @milessabin)

gistfile1.scala

// immutable cycle
class Node[T]( val value: T, _next: => Node[T] ){
  lazy val next = _next
}
val cycle: Node[Int] = new Node( 1, new Node( 2, cycle ) )

// prints List(1, 2, 1, 2, 1, 2, 1, 2, 1, 2)
println(cycle.iterator.take(10).map(_.value).toList)

implicit class NodeIterator[T](node: Node[T]){
  def iterator = new Iterator[Node[T]]{
    var current = node
    def next = {
      val previous = current
      current = current.next
      previous
    }
    val hasNext = true
  }
}