Mandatory definitions for State Monad

gistfile1.scala

  implicit def stateFunctor[S]() = new Functor[({type λ[α] = State[α,S]})#λ] {
    def map[T, P >: T, U](source: State[T, S])(f: P => U): State[U, S] = new State[U, S]((s: S) => {
      val (value, state) = source(s)
      (f(value), state)
    })
  }

  implicit def stateMonad[S]() =  new Monad[({type λ[α] = State[α,S]})#λ]{

    def apply[T](data: T) = new State((s: S) => (data, s))

    def flatten[T](m: State[State[T, S], S]): State[T, S] = new State[T, S]((s: S) => {
      val (mp, sp) = m(s)
      mp(sp)
    })
  }