gistfile1.scala

  trait Run[F[_]] {
    def apply[I](request: F[I]): (I, Run[F])
    def unit[I](i: I): F[I] // needed to be able to implement Monad[F]
  }

  def runnerMonad[F[_]](requestRunner: Run[F]) = new Monad[F] {
    // keep the current state of the runner here
    var runner = requestRunner

    def unit[A](a: => A): F[A] = runner.unit(a)
    def flatMap[A, B](ma: F[A])(f: A => F[B]): F[B] = {
      runner.apply(ma) match { case (a, ma1) => runner = ma1; f(a) }
    }
  }