Scala Next SF Scala meetup Dec 8 th , 2011

1. Scala Next SF Scala meetup Dec 8th, 2011

2. Scala Today

3. Some adoption vectors: • Web platforms • Trading platforms • Financial modeling • Simulation • Fast to first product, scalable afterwards

4. Github vs. Stack Overflow RedMonk: “Revisiting the Dataists Programming Language Rankings” Typesafe Confidential

5. Commercial Adoption • Scala jobs tripled in last year • Now at estimated 100,000 developers Typesafe Confidential

6. (Only 17 months ago!) • New collections • Package objects • Context bounds • Better implicits • ... Scala 2.8:

7. Parallel collections • DelayedInit and App • Faster REPL • Progress on IDEs: Eclipse, IntelliJ, Neatbeans, ENSIME • Better docs • Lots of bug fixes Scala 2.9:

8. Parallel Collections • Use Java 7 Fork Join framework • Split work by number of Processors • Each Thread has a work queue that is split exponentially. Largest on end of queue • Granularity balance against scheduling overhead • On completion threads “work steals” from end of other thread queues

9. ... and its usage import java.util.ArrayList; ... Person[] people; Person[] minors; Person[] adults; { ArrayList<Person> minorsList = new ArrayList<Person>(); ArrayList<Person> adultsList = new ArrayList<Person>(); for (int i = 0; i < people.length; i++) (people[i].age < 18 ? minorsList : adultsList) .add(people[i]); minors = minorsList.toArray(people); adults = adultsList.toArray(people); } ... in Java: A function value An infix method call ... in Scala: val people: Array[Person] val(minors, adults) = people partition (_.age < 18) A simple pattern match

10. Going Parallel ? ... in Java: ... in Scala: val people: Array[Person] val(minors, adults) = people.par partition (_.age < 18)

11. General Collection Hierarchy Remove this layer in 2.10? GenTraversable GenIterable Traversable GenSeq Iterable ParIterable Seq ParSeq

12. Going Distributed • Can we get the power of parallel collections to work on 10’000s of computers? • Hot technologies: MapReduce (Google’s and Hadoop) • But not everything is easy to fit into that mold • Sometimes 100’s of map-reduce steps are needed. • Distributed collections retain most operations, provide a powerful frontend for MapReduce computations. • Scala’s uniform collection model is designed to also accommodate parallel and distributed. • Projects at Google (Cascade), Berkeley (Spark), EPFL.

13. Scala next: Eclipse IDE Play web framework 2.0 Akka 2.0 Scala 2.10

14. Scala Eclipse IDE Now in RC2 Final expected before the end of the year.

15. Goals reliable (no crashes/lock ups) responsive (never wait when typing) work with large projects/files • Scala compiler (80k LOC), 4-5000 LOC/file • advanced use of the type system: path-dependent types, self-types, mix-ins

16. Features Keep it simple • highlight errors as you type • completions (including implicits) • hyperlinking • project builder (+ dependent projects) Support mixed Java-Scala projects • all features should work between Java/Scala sources JUnit Test Runner should pick up tests More stuff based on external libraries • (some) refactoring, code formatter, mark occurrences, structured selections, show inferred semi-colons

17. Features (3) based on external libraries • (some) refactoring • code formatter • mark occurrences • structured selections • show inferred semi-colons

18. @jonifreeman Joni Freeman Latest Scala Eclipse plugin works surprisingly well! Even manages our mixed Java/Scala project. Kudos to the team! #scala @esorribas Eduardo Sorribas The latest beta of the Scala IDE for eclipse is much better. I'm starting to like it. @jannehietamaki Janne Hietamäki After years of misery, the Eclipse Scala plugin actually seems to work quite well.

19. Architecture • Use the full-blown Scala compiler for: • interactive error highlight, completion, hyperlinking • turning Scala symbols into Java model elements • Weave the JDT compiler when it needs help • JDT was NOT meant to be extended

20. Why rely on scalac? • reuse (type-checker == 1-2 person years) • consistency • compiler plugins Why not? • SPEED • (very) tight dependency on the Scala version

21. Presentation Compiler asynchronous interruptible targeted stop after type-checking

24. Result is communicated through a SyncVar

25. All compiler activity happens on PC thread • compile loaded files when work queue is empty (in the background) • Check work queue when type checker reaches “safe-points” in the AST • Drop everything when a file is changed (AskReload)

26. Implementation

27. 1 type-checker run / instance --> 100sof type-check runs / minute • memory leaks • side-effects/state • out-of-order and targeted type-checking needed to improve the compiler • 2.9.x, 2.10 (trunk) • what about 2.8? 2.8.2, 2.8.3-SNAPSHOT

28. New: Play Framework 2.0 • Play Framework is an open source web application framework, inspired by Ruby on Rails, for Java and Scala • Play Framework 2.0 retains full Java support while moving to a Scala core and builds on key pieces of the Typesafe Stack, including Akka middleware and SBT • Play will be integrated in TypeSafe stack 2.0 • Typesafe will contribute to development and provide commercial support and maintenance.

29. Roadmap May 2011 Oct 2011 Q1 2012 Q3 2012 Typesafe Stack 1.0 Typesafe Stack 1.1 Typesafe Stack 2.0 Typesafe Stack 2.x Scala 2.9.0 Akka 1.1 Scala 2.9.1 Akka 1.2 Scala 2.9.x Akka 2.0 Play 2.0 Scala 2.10 Akka 2.x Play 2.x Slick (DB)

30. Scala 2.10: New reflection framework Reification type Dynamic More IDE improvements: find-references, debugger, worksheet. Faster builds SIPs: string interpolation, simpler implicits. ETA: Early 2012.

31. New in Scala 2.10: Dynamic Type Dynamic bridges the gap between static and dynamic typing. Method calls get translated to applyDynamic Great for interfacing with dynamic languages (e.g. JavaScript) class JS extends Dynamic { def applyDynamic(methName: String, args: Any*): Any = { println("apply dynamic "+methName+args.mkString("(", ",", ")")) } } val x = new JS x.foo(1) //  x.applyDynamic(“foo”, 1) x.bar //  x.applyDynamic(“bar”)

32. Proposed for Scala 2.10: SIP 11: String interpolation Idea: Instead of “Bob is ” + n + “years old” write: s“Bob is $n years old” which gets translated to new StringContext(“Bob is”, “years old”).s(n) Here, s is a library-defined method for string interpolation.

33. This can be generalized to other string processors besides s: xml””” <body> <a href = “some link”> ${linktext} </a> </body> ””” scala””” scala.concurrent.transaction.withinTransaction { (implicit currentTransaction: Transaction) => $expr } ”””

34. Proposed for Scala 2.10: SIP 12: Uncluttering control Should be able to write: if x < 0 then –x else x while x > 0 do { println(x); x -= 1 } for x <- xs do println(x) for x <- xs yield x * x

35. Proposed for Scala 2.10: SIP 13: Implicit classes Variation: Add @inline to class def to get speed of extension methods.

36. New in Scala 2.10: Reflection Previously: Needed to use Java reflection, no runtime info available on Scala’s types. Now you can do:

37. (Bare-Bones) Reflection in Java Why not add some meaningful operations? Need to write essential parts of a compiler (hard). Need to ensure that both compilers agree (almost impossible). Want to know whether type A conforms to B? Write your own Java compiler!

38. How to do Better? • Problem is managing dependencies between compiler and reflection. • Time to look at DI again. Dependency Injection • Idea: Avoid hard dependencies to specific classes. • Instead of calling specific classes with new, have someone else do the wiring.

39. Using Guice for Dependency Injection (Example by Jan Kriesten)

40. ... plus some Boilerplate

41. Dependency Injection in Scala Components are classes or traits Requirements are abstract values Wiring by implementing requirement values But what about cyclic dependencies?

42. The Cake Pattern Components are traits Wiring by mixin composition Requirements are types of this

43. Cake Pattern in the Compiler The Scala compiler uses the cake pattern for everything Here’s a schema: (In reality there are about ~20 slices in the cake.)

44. Towards Better Reflection Can we unify the core parts of the compiler and reflection? Compiler Reflection Different requirements: Error diagnostics, file access, classpath handling - but we are close!

45. Compiler Architecture Problem: This exposes way too much detail! reflect.internal.Universe nsc.Global(scalac) reflect.runtime.Mirror

46. Complete Reflection Architecture Cleaned-up facade: Full implementation: reflect.api.Universe /reflect.mirror reflect.internal.Universe nsc.Global(scalac) reflect.runtime.Mirror

47. How to Make a Facade The Facade Interfaces are not enough! The Implementation

48. Conclusion Scala is a very regular language when it comes to composition: • Everything can be nested: • classes, methods, objects, types • Everything can be abstract: • methods, values, types • The type of thiscan be declared freely, can thus express dependencies • This gives great flexibility for SW architecture, allows us to attack previously unsolvable problems.

49. Going further: Parallel DSLs Mid term, research project: How do we keep tomorrow’s computers loaded? • How to find and deal with 10000+ threads in an application? • Parallel collections and actors are necessary but not sufficient for this. Our bet for the mid term future: parallel embedded DSLs. • Find parallelism in domains: physics simulation, machine learning, statistics, ... Joint work with Kunle Olukuton, Pat Hanrahan @ Stanford. EPFL side funded by ERC.

50. EPFL / Stanford Research Scientific Engineering Virtual Worlds Personal Robotics Data informatics Rendering Physics (Liszt) Scripting Probabilistic (RandomT) Machine Learning (OptiML) Applications Domain Specific Languages Domain Embedding Language (Scala) Static Domain Specific Opt. Polymorphic Embedding Staging DSL Infrastructure Parallel Runtime (Delite, Sequoia, GRAMPS) Dynamic Domain Spec. Opt. Task & Data Parallelism Locality Aware Scheduling Hardware Architecture Heterogeneous Hardware SIMD Cores OOO Cores Threaded Cores Specialized Cores Programmable Hierarchies Scalable Coherence Isolation & Atomicity On-chip Networks Pervasive Monitoring