Boxed lazy values

gistfile1.scala

// Is this even faintly novel? The closest I've seen is
//
// http://stackoverflow.com/questions/2618891/using-lazy-evaluation-functions-in-varargs
//
// which is a bit clunky by comparison. But this is so trivial someone must have
// done it this way before.

// UPDATE:
// Thanks to the Twittersphere (@etorreborre, @pchiusano and @loverdos) for a few sightings of related things,
//
// https://github.com/etorreborre/specs2/blob/1.5/src/main/scala/org/specs2/control/LazyParameter.scala
// https://github.com/scalaz/scalaz/blob/master/core/src/main/scala/scalaz/Name.scala (Need at the bottom)
// http://blog.ckkloverdos.com/2008/07/24/implementing-lazy-values-in-scala-at-the-language-level/

object Lazy extends App {
  class Lazy[T](t0 : => T) {
    private lazy val t = t0
    def force : T = t
  }
  
  implicit def mkLazy[T](t : => T) = new Lazy(t)
  implicit def mkEager[T](l : Lazy[T]) : T = l.force
  
  def obs[T](t : T) = { println("Observing: "+t) ; t }
  
  def lazySeq[T](ts : Lazy[T]*) = ts
  
  val ls = lazySeq(obs(1), obs(2), obs(3))
  
  println("Head:")
  val e1 = ls.head+1
  println(e1)
  
  println("Map:")
  val s = ls.map(_ + 1)
  println(s)
}

This kind of Lazy type is very useful, because by-name parameter is not a first-class type.

https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/Name.scala#L33

(Latest and greatest and least buggiest)

And of course, it's a Monad :)