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# A brief introduction to scalaz-stream

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### A brief introduction to scalaz-stream

1. 1. A brief introduction to scalaz-stream Frank S. Thomas September 18, 2013
2. 2. What is it? scalaz-stream is a library for stream processing and incremental I/O resource safe composable functional: stream transformations are pure values
3. 3. Imperative I/O def linesGt40k1(filename: String): Boolean = { val src = scala.io.Source.fromFile(filename) try { var count = 0 val lines: Iterator[String] = src.getLines while (count <= 40000 && lines.hasNext) { lines.next count += 1 } count > 40000 } finally src.close }
4. 4. I/0 with scalaz-stream def linesGt40k2(filename: String): Boolean = scalaz.stream.io.linesR(filename). drop(40000). once. runLast. run. nonEmpty
5. 5. Stream transformations with Process trait Process[I,O] case class Emit[I,O]( head: Seq[O], tail: Process[I,O] = Halt[I,O]()) extends Process[I,O] case class Await[I,O]( recv: I => Process[I,O], finalizer: Process[I,O] = Halt[I,O]()) extends Process[I,O] case class Halt[I,O]() extends Process[I,O] Process is a state machine with three possible states these must be interpreted by a driver for eﬀects to occur
6. 6. Combinators Modify and compose processes: def map[O2](f: O => O2): Process[I,O2] def flatMap[O2](f: O => Process[I,O2]): Process[I,O2] def append(p: => Process[I,O]): Process[I,O] def filter(f: I => Boolean): Process[I,I] def take(n: Int): Process[I,I] def takeWhile(f: I => Boolean): Process[I,I] ... and many more Feed the output of this to the input of p2: def pipe[O2](p2: Process[O,O2]): Process[I,O2]
7. 7. Another Example import scalaz.stream._ import scalaz.concurrent.Task val converter: Task[Unit] = io.linesR("testdata/fahrenheit.txt"). filter(s => !s.trim.isEmpty && !s.startsWith("//")). map(line => fahrenheitToCelsius(line.toDouble).toString). intersperse("n"). pipe(process1.utf8Encode). to(io.fileChunkW("testdata/celsius.txt")). run val u: Unit = converter.run
8. 8. References https://github.com/scalaz/scalaz-stream Chapter 15 of Functional Programming in Scala http://manning.com/bjarnason/ Advanced Stream Processing in Scala http://www.youtube.com/watch?v=8fC2V9HX_m8