gistfile1.txt

import scala.language.higherKinds

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

trait Traverse[F[_]] {
  implicit val F: Functor[F]
}

object Traverse {
  type Aux[F[_], FF] = Traverse[F] { val F: FF }
}

trait Monad[F[_]] {
  implicit val F: Functor[F]
}

object Monad {
  type Aux[F[_], FF] = Monad[F] { val F: FF }
}

object List {
  implicit val listFunctor: Functor[List] =
    new Functor[List] {
      def map[A, B](fa: List[A])(f: A => B): List[B] = fa.map(f)
    }

  implicit val listTraverse: Traverse.Aux[List, listFunctor.type] =
    new Traverse[List] {
      val F: listFunctor.type = listFunctor
    }

  implicit val listMonad: Monad.Aux[List, listFunctor.type] =
    new Monad[List] {
      val F: listFunctor.type = listFunctor
    }
}

object Demo {
  import List._

  def foo[F[_]](ff: Functor[F])(implicit M: Monad.Aux[F, ff.type], T: Traverse.Aux[F, ff.type]): F[Int] = ???

  foo(listFunctor)
}