gistfile1.scala

import scala.concurrent.{Future, Promise}
import scala.concurrent.duration.{Duration, FiniteDuration}
import scala.concurrent.{Await, Promise}
import scala.util.{Failure, Success}
import scala.concurrent.ExecutionContext.Implicits.global
  
  
  def performSequentially[A](items: Seq[A])(f: A => Future[Unit]): Future[Unit] = {
    items.headOption match {
      case Some(nextItem) =>
        val fut = f(nextItem)
        fut.flatMap { _ =>
            performSequentially(items.tail)(f)
        }
      case None =>
        // nothing left to process
        Future.successful(())
    }
  }
  
val items = 0 to 5

val seqFuture = performSequentially(items) { i => Future { Thread.sleep(1000); println("hello " + i) } }
Await.result(seqFuture, Duration.Inf)