Naive quasispray directive

SimpleDirective.scala

trait Directive[X <: HList] { self =>
  def happly(f: X => Route): Route
  def apply[F](f: F)(implicit fp: FnToProduct.Aux[F, X => Route]) = {
    happly(fp(f))
  }
  def &[Y <: HList](that: Directive[Y])(implicit prepend: Prepend[X, Y]): Directive[prepend.Out] = new Directive[prepend.Out] {
    override def happly(f: prepend.Out => Route): Route = {
      self.happly( x =>
        that.happly( y =>
          f(prepend(x, y))
        )
      )
    }
  }
}