thunks

thunk.scala

sealed trait Stream[+A]
case object Empty extends Stream[Nothing]
case class Cons[+A](h: () => A, t: () => Stream[A]) extends Stream[A]
object Stream {
 def cons[A](hd: => A, tl: => Stream[A]): Stream[A] = {
  lazy val head = hd
  lazy val tail = tl
  Cons(() => head, () => tail)
 }
 def empty[A]: Stream[A] = Empty
 def apply[A](as: A*): Stream[A] =
  if (as.isEmpty) empty else cons(as.head, apply(as.tail: _*))
 }
}