Attempt to get the coproduct of natural transformations working.

NaturalTransformation.scala

trait NaturalTransformation[-F[_], +G[_]] {
  self =>
  def apply[A](fa: F[A]): G[A]

  def compose[E[_]](f: E ~> F): E ~> G = new (E ~> G) {
    def apply[A](ea: E[A]) = self(f(ea))
  }

  def or[H[_]](f: H ~> G): ({type f[x] = Coproduct[F, H, x]})#f ~> G =
    new (({type f[x] = Coproduct[F, H, x]})#f ~> G) {
      def apply[A](c: Coproduct[F, H, A]): G[A] = c.run match {
        case -\/(fa) => self(fa)
        case \/-(ha) => f(ha)
      }
    }
}