scala - 重复 eval T => scala.concurrent.Future[T] 到 Process[?, T]

Question

我有一个函数get: T => scala.concurrent.Future[T]

我想像这样迭代它:

   val futs: Iterator[Future[T]] = Iterator.iterate(get(init)){
        _.flatMap(prev => get(prev))
   }

但是Iterator的类型是Future[T]，处理这个迭代器并不容易。

How could I transfer that to Process[?, T]

(也许T => Future[T]作为上下文类型F)。

Answer 1

不是很好的解决方案，但有效

  import scala.concurrent.ExecutionContext.Implicits.global
  import scala.concurrent.{Future => SFuture}
  import scala.language.implicitConversions
  import scalaz.concurrent.Task
  import scalaz.stream._

  implicit class Transformer[+T](fut: => SFuture[T]) {
    def toTask(implicit ec: scala.concurrent.ExecutionContext): Task[T] = {
      import scala.util.{Success, Failure}
      import scalaz.syntax.either._
      Task.async {
        register =>
          fut.onComplete {
            case Success(v) => register(v.right)
            case Failure(ex) => register(ex.left)
          }
      }
    }
  }

  val init: Int = 0

  def f(i: Int): SFuture[Int] = SFuture(i + 1)

  val p = Process.repeatEval[Task, Int] {
    var prev = init
    f(prev).toTask.map(next => {prev = next; next})
  }

  println(p.take(10).runLog.run)