Continuation Monad in Scala

continuation-monad.scala

case class M[+A](in: (A => Any) => Any);

def unit[A](x: A) = M { k: (A => Any) => k(x) }

def bind[A, B](m: M[A], f: A => M[B]): M[B] =
  M { k: (B => Any) =>
    m.in { x: A =>
      f(x).in(k)
    }
  }