Comparison of the straightforward embedding of a basic tenet of category theory in Scala vs Haskell.

Haskell

yonedaLemma = Iso (flip fmap) ($ id)

Scala

def yonedaLemma[F[_]:Functor, A]: F[A] <=> (({type λ[α] = A => α })#λ ~> F) =
  new (F[A] <=> (({type λ[α] = A => α })#λ ~> F)) {
    def to(fa: F[A]) = new (({type λ[α] = A => α })#λ ~> F) {
      def apply[R](f: A => R) = Functor[F].map(fa)(f)
    }
    def from(f: (({type λ[α] = A => α })#λ ~> F)) = f(a => a)
  }