tau.scala

type ∀[F[_]] = scalaz.Forall[F]

/**
 * An unpublished arbitrary type.  May be viewed as a formulation of
 * (∃ α . α).  Thus, we encode a rank-1 universal by means of a rank-2
 * existential.  This encoding is more convenient for our purposes.
 */
sealed trait τ

object τ {

  def skolemize[F[_]](fa: F[τ]): ∀[F] = new ∀[F] {
    def apply[α]: F[α] = fa.asInstanceOf[F[α]]
  }

  def unskolemize[F[_]](fa: ∀[F]): F[τ] = fa[τ]
}