Async.scala

trait Async[F[_]] {
  def pure[A](value: => A): F[A]
  def promise[A]: Async.Promise[F, A]
  def flatMap[A, B](m: F[A])(f: A => F[B]): F[B]
  def map[A, B](m: F[A])(f: A => B): F[B]
  def run[A, U](m: F[A])(f: Try[A] => U): Unit
}

object Async {
  case class Promise[F[_], A](future: F[A], complete: Try[A] => Unit)
}