Higher Rank existential types

HigherRankPolymorphism.scala

package sun.flower.higher

/**
 * 
 * User: sunflower
 * Date: 13-1-20
 * Time: 下午11:44
 * 
 */
object HigherRankPolymorphism {

  trait ~>[F[_],G[_]]{
    def apply[A](a : F[A]) : G[A]
  }

  type Id[A] = A

  def apply[B](f: Id ~> List,b : B,s : String ) : (List[B],List[String]) = (f(b):List[B], f(s))


}