This code attempts to show one way asynchronous requests can be batched in a type safe manner.

gistfile1.scala

// This code attempts to show one way asynchronous requests can be batched in a type safe manner.

object BatchableRequests {  

  sealed trait Request[A] {
    def serialize(): String
    def deserialize(s: String): Option[(A, String)]
    def pair[B](b: Request[B]): Request[(A, B)] = RequestPair(this, b)
  }
  case class RequestPair[A, B](a: Request[A], b: Request[B]) extends Request[(A, B)] {
    def serialize() = a.serialize + b.serialize
    def deserialize(s: String) =
      for {
        (av, rest) <- a.deserialize(s)
        (bv, rest2) <- b.deserialize(rest)
      } yield ((av, bv), rest2)
  }
  case class SampleRequest1(a: Int) extends Request[Either[String, Boolean]] {
    def serialize = ???
    def deserialize(s: String) = ???
  }
  case class SampleRequest2(a: String, b: String) extends Request[Int] {
    def serialize = ???
    def deserialize(s: String) = ???
  }

  def call[A](r: Request[A]): Future[Either[String, A]] = {
    def asyncCall(s: String) : Future[String] = ???
    asyncCall(r.serialize()).map(r.deserialize(_)
        .fold[Either[String, A]](Left("Badly formatted response"))(o => Right(o._1)))
  }
 
  val a = call(SampleRequest1(10) pair SampleRequest2("x", "y") pair SampleRequest1(2))
  // a's infered type: Future[Either[String,((Either[String,Boolean], Int), Either[String,Boolean])]]
}