scalaz-stream equivalent to Play Framework's Enumerator.fromCallback

fromCallback.scala

  import java.util.concurrent.atomic.AtomicInteger
  import scala.concurrent.ExecutionContext.Implicits.global
  import scala.concurrent.Future
  import scala.concurrent.future
  import scala.util.{Failure, Success}
  import scalaz.concurrent.Task
  import scalaz.stream.Process.End
  import scalaz.stream._
  import scalaz.{-\/, \/-}

  val cnt = new AtomicInteger(0)

  def serviceCall: Future[Option[String]] = future {
    if (cnt.incrementAndGet() <= 10) Some(s"Task #${cnt.get()}") else None
  }

  val task: Task[String] = Task.async(cb => serviceCall onComplete {
    case Success(Some(str)) => cb(\/-(str))
    case Success(None)      => cb(-\/(End))
    case Failure(err)       => cb(-\/(err))
  })

  Process.repeatEval(task).runLog.run.foreach(println)