Scala-IDE worksheet with some examples of iteratees, enumerators and enumeratees and how to use and compose them. Originated from a presentation at Dutch Scala Enthusiasts.

iteratees-by-example.scala

import play.api.libs.iteratee._
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent._
import scala.concurrent.duration._
import play.api.libs.concurrent.Promise

object iteratees {

  // Implicit conversion to add 'await' to a Future
  implicit class WFuture[A](val inner: Future[A]) extends AnyVal {
    def await(implicit timeout: Duration) = Await.result(inner, timeout)
  }

  // Default timeout for futures.
  implicit val timeout = 10 second                //> timeout  : scala.concurrent.duration.FiniteDuration = 10 seconds

  // Simple enumerator with pre-known values
  val enumerator = Enumerator(1, 2, 3, 4, 5)      //> enumerator  : play.api.libs.iteratee.Enumerator[Int] = play.api.libs.iterate
                                                  //| e.Enumerator$$anon$21@571a75a2
  // Iteratee that just prints all input
  val printIteratee = Iteratee.foreach[Int] { i => print("[" + i + "]") }
                                                  //> printIteratee  : play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.libs.i
                                                  //| teratee.Cont$$anon$3@6f25844f
  // Apply anumerator to iteratee
  (enumerator |>> printIteratee).await            //> [1][2][3][4][5]res0: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.li
                                                  //| bs.iteratee.Iteratee$$anon$1@148238f4

  // Create an iteratee that just takes the first five elements, by transforming the regular
  // printIteratee with an enumeratee that only takes five elements.
  def printFiveIteratee = Enumeratee.take(5) &>> printIteratee
                                                  //> printFiveIteratee: => play.api.libs.iteratee.Iteratee[Int,Unit]

  // Test whether our printFiveIteratee actually only consumes the
  // first five elements of an enumerator with more chunks
  (Enumerator(1, 2, 3, 4, 5, 6, 7, 8) |>> printFiveIteratee).await
                                                  //> [1][2][3][4][5]res1: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Iteratee$$anon$1@716c9867

  // Now we have the printFiveIteratee, we can make endless enumerators and still show
  // their first chunks, without blowing up.
  val ones = Enumerator.repeat(1)                 //> ones  : play.api.libs.iteratee.Enumerator[Int] = play.api.libs.iteratee.Enu
                                                  //| merator$$anon$15@5982bcde

  // Print the first five chunks from an infinite enumerator
  (ones |>> printFiveIteratee).await              //> [1][1][1][1][1]res2: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Done$$anon$2@4e513d61

  // So far, our enumerators had no internal state.
  // Here we create one with the 'unfold' method that has
  // a state, and uses the state to compute an element and a new state
  val counting = Enumerator.unfold(0)(counter => Some(counter + 1, counter))
                                                  //> counting  : play.api.libs.iteratee.Enumerator[Int] = play.api.libs.iteratee
                                                  //| .Enumerator$$anon$12@2bb5340c
  // Test it
  (counting |>> printFiveIteratee).await          //> [0][1][2][3][4]res3: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Done$$anon$2@71060478

  // Create an enumerator with state, that computes the element
  // and new state asynchronously. The 'Promise' is a play.api.libs.concurrent.Promise,
  // not the scala.concurrent one, because the Play one has a nice 'timeout' method
  // to create a future that will be completed after some time.
  val slowCounting = Enumerator.unfoldM(0) { counter =>
    Promise.timeout(Some(counter + 1, counter), 1 second)
  }                                               //> slowCounting  : play.api.libs.iteratee.Enumerator[Int] = play.api.libs.iter
                                                  //| atee.Enumerator$$anon$12@60491c4c
  // Apply our slow enumerator on the printing iteratee
  // Note that this prints one element every second.
  // Commented out by default, because it's slow
  // (slowCounting |>> printFiveIteratee).await

  // So far, our iteratees were stateless. Here we create
  // an iteratee that maintains state, using the 'fold' method on the
  // Iteratee object. Notice the similarity with the 'fold' method
  // on classes from the collections api.
  val summingIteratee = Iteratee.fold(0)((state, elem: Int) => state + elem)
                                                  //> summingIteratee  : play.api.libs.iteratee.Iteratee[Int,Int] = play.api.libs
                                                  //| .iteratee.Cont$$anon$3@7632efa7
  // With an iteratee that has state, it's actually interesting
  // to look at the iteratee future that the enumerator produces
  // after being applied to the original iteratee.
  // The enumerator returns the iteratee as it is after pushing
  // in all the chunks. So this iteratee will have an internal state
  // of '15'
  val iterateeFuture = (enumerator |>> summingIteratee)
                                                  //> iterateeFuture  : scala.concurrent.Future[play.api.libs.iteratee.Iteratee[I
                                                  //| nt,Int]] = scala.concurrent.impl.Promise$DefaultPromise@a13f991
  // With the 'run' method on an Iteratee, we feed it an EOF
  // and then extract the value.
  Await.result(iterateeFuture.flatMap(_.run), 1 second)
                                                  //> res4: Int = 15

  // An enumeratee that only keeps even numbers
  val evenEnumeratee = Enumeratee.filter[Int](i => i % 2 == 0)
                                                  //> evenEnumeratee  : play.api.libs.iteratee.Enumeratee[Int,Int] = play.api.lib
                                                  //| s.iteratee.Enumeratee$$anon$18@6f878144

  // This transforms (&>>) the iteratee with the enumeratee
  (counting |>> evenEnumeratee &>> printFiveIteratee).await
                                                  //> [0][2][4][6][8]res5: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Done$$anon$2@15f48262
  // Same as the above, but with parentheses to make the operator
  // precedence explicit
  (counting |>> (evenEnumeratee &>> printFiveIteratee)).await
                                                  //> [0][2][4][6][8]res6: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Done$$anon$2@679bfb30

  // This "throughs" the enumerator through the enumerate. Give the
  // same result as the previous two, but this time the enumeratee is
  // composed with the enumerator, and not with the iteratee.
  // So whether you are dealing with an Enumerator or an Iteratee,
  // you can always compose with an Enumeratee.
  (counting &> evenEnumeratee |>> printFiveIteratee).await
                                                  //> [0][2][4][6][8]res7: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Iteratee$$anon$1@7d95d4fe
  // Same as the above
  ((counting &> evenEnumeratee) |>> printFiveIteratee).await
                                                  //> [0][2][4][6][8]res8: play.api.libs.iteratee.Iteratee[Int,Unit] = play.api.l
                                                  //| ibs.iteratee.Iteratee$$anon$1@77d2b01b

}

await can't print value on worksheet.
any idea?