Functor.scala

trait Functor[T[_]]{
  def fmap[A,B](f:A=>B)(ta:T[A]):T[B]
}

trait Applicative[T[_]] extends Functor[T]{
  def pure[A](a:A):T[A]
  def <*>[A,B](tf:T[A=>B])(ta:T[A]):T[B]
}

trait Monad[M[_]] extends Applicative[M]{
  def >>=[A,B](ma:M[A])(f:A=>M[B]):M[B]
}

functors.hs

-- from "Learn you a Haskell for great good"

class Functor f where  
    fmap :: (a -> b) -> f a -> f b  

class (Functor f) => Applicative f where  
    pure :: a -> f a  
    (<*>) :: f (a -> b) -> f a -> f b  

class (Applicative m) = > Monad m where 
    (>>=) :: m a -> (a -> m b) -> m b