Iteratees/Enumerators in Play
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The document discusses Iteratees and Enumerators in Play Framework. It provides an overview of the important concepts - Enumerator produces values, Enumeratee transforms values, and Iteratee consumes input. It also summarizes the APIs for Enumerator, Enumeratee and Iteratee, including common patterns for building Iteratees. Links are provided for additional documentation and examples.
![THE IMPORTANT BITS
ENUMERATOR[A]
PRODUCES VALUES OF TYPE A
MONAD (COMPOSABLE WITH A CONTEXT)
MANY UTILITIES IN COMPANION OBJECT
SMART
!](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-7-320.jpg)
 : Enumerator[A]
Enumerator.enumerate[A](a: TraversableOnce[A]) : Enumerator[A]
Enumerator.generateM[A](e : => Future[Option[A]]) : Enumerator[A]
ALL THE FLATMAP GOODIES + GIVEN AN ENUMERATOR[E]
|>>[A](i: Iteratee[E, A]): Future[Iteratee[E, A]]
|>>>[A](i: Iteratee[E, A]): Future[A]
&>[To](enumeratee: Enumeratee[E, To]): Enumerator[To]](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-8-320.jpg)
![THE IMPORTANT BITS
ENUMERATEE[A,B]
TRANSFORMS VALUES FROM A => B
!
MANY UTILITIES IN COMPANION OBJECT
!
NOT AS DUMP AS I THOUGHT](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-9-320.jpg)
![THE IMPORTANT BITS
ITERATEE[A,B]
CONSUMES INPUT ELEMENTS OF TYPE A AND OUTPUTS B
MONAD (COMPOSABLE WITH A CONTEXT)
SUPER SMART
!
!
!
INPUT IS EITHER:
A.EMPTY: INPUT.EMPTY
B.EOF: INPUT.EOF
C.OR CONTAINS AN A: INPUT.EL(A)
!
ITERATEE STATE IS EITHER:
A. DONE CONSUMING WITH A RESULT
B. READY TO CONSUME MORE CONT
C. OR IN ERROR STATE](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-10-320.jpg)
![ITERATEE API
ALL THE FLATMAP GOODIES + GIVEN AN ITERATEE[E,A]
run: Future[A]
COMMON PATTERN TO BUILD AN ITERATEE:
def myIteratee(x: AllTheStateINeed,
oForNothing: O) : Iterator[I,O] = Cont {
case Input.EOF => Done(oForNothing, Input.EOF)
case Input.Empty => myIterator(x, oForNothing)
case in@Input(i) => // be done with o || change state and recurse
// create an Error with Error(message, in)
!](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-11-320.jpg)
![val processElement: Iteratee[Byte, Element] = for {
_ <- findLeftBrace
string <- consumeUntilRightBrace
element <- {
safeParse(string) match {
case Success(element) => Done[Byte, Element](element)
case Failure(_) => Error[Byte](s"$string not a valid element", Input.EOF)
}
}
} yield element
COMPOSE
ITERATEES & ENUMERATORS
USING FOR
COMPREHENSIONS](https://image.slidesharecdn.com/iteratees-141006145008-conversion-gate02/85/Iteratees-Enumerators-in-Play-15-320.jpg)
Iteratees/Enumerators in Play
- 1. ENUMERATOR &> PLAY |>>> ITERATEE PLAY MEETUP HAMBURG, 6.10.2014 MARKUS.KLINK@INO.IO @JOHEINZ
- 2. GIT CLONE HTTPS:// GITHUB.COM/INOIO/ ITERATEE-TALK ! ! ! SBT ~RUN
- 3. SOME LINKS: PLAY DOCUMENTATION (MORE OR LESS INCOMPREHENSIBLE) HTTP://MANDUBIAN.COM/2012/08/27/UNDERSTANDING-PLAY2-ITERATEES-FOR-NORMAL-HUMANS/ (ADDRESSES SOME OF THE SHORTCOMINGS) HTTPS://JAZZY.ID.AU/2012/11/06/ITERATEES_FOR_IMPERATIVE_PROGRAMMERS.HTML (YEAH, MORE INFO) ACTIVATOR TEMPLATE (SEARCH FOR ITERATEES) HTTPS://GITHUB.COM/JROPER/PLAY-ITERATEES-EXTRAS HTTPS://WWW.PLAYFRAMEWORK.COM/DOCUMENTATION/2.3.X/API/SCALA/INDEX.HTML#PLAY.API.LIBS.3
- 4. DATA PROCESSING PIPELINE HARPER & CHRISTY DOING IT PURELY FUNCTIONAL
- 5. REACTIVE STREAMS ARE TWO WAY, IT'S NOT JUST YOU, THE STREAM CONSUMER THAT IS REACTING TO INPUT, THE STREAM PRODUCER MUST REACT TO YOU BEING READY FOR INPUT. James Roper
- 6. OTHER IMPLEMENTATIONS SCALAZ STREAM SCALAZ ITERATEES (OUTDATED)
- 7. THE IMPORTANT BITS ENUMERATOR[A] PRODUCES VALUES OF TYPE A MONAD (COMPOSABLE WITH A CONTEXT) MANY UTILITIES IN COMPANION OBJECT SMART !
- 8. ENUMERATOR API Enumerator.apply[A](a: A*) : Enumerator[A] Enumerator.enumerate[A](a: TraversableOnce[A]) : Enumerator[A] Enumerator.generateM[A](e : => Future[Option[A]]) : Enumerator[A] ALL THE FLATMAP GOODIES + GIVEN AN ENUMERATOR[E] |>>[A](i: Iteratee[E, A]): Future[Iteratee[E, A]] |>>>[A](i: Iteratee[E, A]): Future[A] &>[To](enumeratee: Enumeratee[E, To]): Enumerator[To]
- 9. THE IMPORTANT BITS ENUMERATEE[A,B] TRANSFORMS VALUES FROM A => B ! MANY UTILITIES IN COMPANION OBJECT ! NOT AS DUMP AS I THOUGHT
- 10. THE IMPORTANT BITS ITERATEE[A,B] CONSUMES INPUT ELEMENTS OF TYPE A AND OUTPUTS B MONAD (COMPOSABLE WITH A CONTEXT) SUPER SMART ! ! ! INPUT IS EITHER: A.EMPTY: INPUT.EMPTY B.EOF: INPUT.EOF C.OR CONTAINS AN A: INPUT.EL(A) ! ITERATEE STATE IS EITHER: A. DONE CONSUMING WITH A RESULT B. READY TO CONSUME MORE CONT C. OR IN ERROR STATE
- 11. ITERATEE API ALL THE FLATMAP GOODIES + GIVEN AN ITERATEE[E,A] run: Future[A] COMMON PATTERN TO BUILD AN ITERATEE: def myIteratee(x: AllTheStateINeed, oForNothing: O) : Iterator[I,O] = Cont { case Input.EOF => Done(oForNothing, Input.EOF) case Input.Empty => myIterator(x, oForNothing) case in@Input(i) => // be done with o || change state and recurse // create an Error with Error(message, in) !
- 12. HINT WHEN USING DONE, ALWAYS SPECIFY THE NEXT INPUT EXPLICITLY (DEFAULTS TO INPUT.EMPTY)
- 13. ENUMERATEE ><> ENUMERATOR ENUMERATEE ITERATEE &> &>> ENUMERATOR ITERATEE ENUMERATEE API
- 14. ENUMERATEE API THINK OF AN ENUMERATOR AS A KIND OF TRANSFORMER, ADAPTER AND COLLECTION: TAKE, TAKEWHILE, GROUPED, DROP, DROPWHILE, FILTER, FILTERNOT, MAP,
- 15. val processElement: Iteratee[Byte, Element] = for { _ <- findLeftBrace string <- consumeUntilRightBrace element <- { safeParse(string) match { case Success(element) => Done[Byte, Element](element) case Failure(_) => Error[Byte](s"$string not a valid element", Input.EOF) } } } yield element COMPOSE ITERATEES & ENUMERATORS USING FOR COMPREHENSIONS
- 16. IN PRINCIPLE ITS EASY, IT IS JUST POWERFUL CODE