Scalaz test bed

MonadImpliesFunctor.scala

import scala.language.higherKinds

trait Monad[M[_]] {
  implicit def `Monad ~> Functor`[M[_]: Monad]: Functor[M] = new Functor[M]{}
}

trait Functor[F[_]] {
}
object Functor {
  implicit val OptionFunctor: Functor[Option] = new Functor[Option]{}
}

case class Foo[A]()
object Foo extends Monad[Foo] {
  implicit val M: Monad[Foo] = new Monad[Foo]{}
}

def requiresFunctor[F[_]: Functor, A](f: F[A]) = 42

requiresFunctor(Foo[Int]())