Akka strems factorial

factorial.scala

object Factorial extends App {
  implicit val system = ActorSystem("QuickStart")
  implicit val materializer = ActorMaterializer()

  val source: Source[Int, NotUsed] = Source(1 to 100)

  val factorials: Source[BigInt, NotUsed] = source.scan(BigInt(1))((acc, next) => acc * next)

  val result: Future[IOResult] =
    factorials
      .map(num => ByteString(s"$num\n"))
      .runWith(FileIO.toPath(Paths.get("factorials.txt")))
}