prio.scala

package leopards {

  trait Functor[F[_]] {
    def (fa: F[A]) map[A, B](f: A => B): F[B]
    def (fa: F[A]) void[A]: F[Unit] = fa.map(_ => ())
  }

  delegate for Functor[List] {
    def (fa: List[A]) map[A, B](f: A => B): List[B] =
      fa.map(f)
  }

  delegate [T] for Functor[[X] =>> T => X] {
    def (fa: T => A) map[A, B](f: A => B): T => B =
      fa.andThen(f)
  }
}

package usage {
  import delegate leopards._
  val ex1 = List(1, 2, 3).void
}
/*
-- [E007] Type Mismatch Error: prio.scala:21:16 --------------------------------
21 |  val ex1 = List(1, 2, 3).void
   |            ^^^^^^^^^^^^^
   |Found:    List[Int]
   |Required: ?{ void: ? }
   |Note that implicit extension methods cannot be applied because they are ambiguous;
   |both object Functor_List_instance in package leopards and method Functor_Function_instance in package leopards provide an extension method `void` on List[Int]
one error found
*/