FastForall

gistfile1.scala

import scalaz.Forall

object FastForall {
  type Not[A] = A => Unit
  type DNE[P[_]] = Not[P[A]] forSome { type A }
  type CPS[P[_]] = Not[DNE[P]]

  def apply[P[_]](p: CPS[P]): Forall[P] = new Forall[P] {
    private var cache: Option[P[_]] = None
    def apply[A]: P[A] = synchronized {
      if (cache.isEmpty) p((arg:P[A]) => cache = Some(arg))
      cache.get.asInstanceOf[P[A]]
    }
  }
}