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Scalawags #14

Scalawags #14: Shapelessless

in which Shapeless is only threatened to be discussed.

music and dancing (0:00)

Scala 2.10.4 and 2.11.0-RC3, Java 8 (2:30)

  • Josh & co have 900,000 lines of open source Scala code compiling on 2.11.0-RC3
  • does 2.10.4 support Java 8? as far as we know. (Daniel had bytecode validation problems with 2.10.1)
  • scalac can't handle Java 8 sources yet
  • have we tried Java 8 language features? no, that would require us to use Java
  • no more PermGen! (= thrash and fail later, instead of fail early?) the world needs more PermGen.
  • Seth likes using Nashorn to test his CoffeeScript and JavaScript code without leaving the Scala ecosystem
  • Josh says the Play framework guys are hooking up different JS engines (including Nashorn and V8) to sbt

sbt 0.13.2-RC1, 0.13.5 (16:35)

  • name-hashing (Grzegorz Kossakowski) in 0.13.2 should “dramatically improve” performance on incremental compilation, says Josh
  • except for Daniel
  • sbt 0.13.5 (previewing sbt 1.0) will fragment sbt so everything will be a plugin
  • binary compatible with existing 0.13 plugins and projects

Northeast Scala Symposium 2014 (20:50)

  • only Dick didn’t go but next year will be at Dick’s house and we’ll drink all his wine
  • love from Daniel for nescala audiences willing to follow him into crazyland

Free monads & scalaz-stream (25:40)

  • Daniel’s nescala day 2 conversation with Lars H, Paul C, Rúnar B, Brian M, Tim P, et al debating the future of Scalaz’s IO monad
  • IO being replaced with Task. IO falls out as a special case
  • trampolined computations are suspendable and resumable
  • not just for avoiding stack overflow
  • comparison with Future (Task doesn't start running right away)
  • free generalizes trampolining
  • build up computations as graphs to be evaluated later. your program writes a program
  • tasks can run sequentially or in parallel
  • in what sense is this nondeterminism?
  • (tpolecat on IRC: “parallel applicative composition is nondeterministic if your actions are side-effecting, which they are in IO. that's the whole point”)
  • Dick gave a talk at Bay Area Scala about scalaz-stream
  • He worked on a project (with Rúnar et al) supporting bioinformaticians
  • Providing them with a high-level API similar to the Scala collections
  • Hit a bug where some tasks were evaluated too eagerly during cleanup and fallback
  • Difficulties debugging code where execution is dispersed across multiple threads
  • Except Josh, he never has any trouble
  • Josh: Iulian Dragos’s work on debugging in an asychronous world
  • Daniel’s pie-in-the-sky ideal debugger

Scalive & REPLs (49:10)

  • Scalive — attach a Scala REPL to any already-running JVM “without any prior setup”
  • by Ngoc Dao, https://twitter.com/ngocdaothanh
  • https://github.com/ngocdaothanh/scalive
  • discussion on tech details
  • limitation re: classloaders
  • Dick sheds a tear for Smalltalk
  • Seth sheds a tear for Macintosh Common Lisp
  • Daniel hearts JRebel
  • Seth: Scala REPL as tool for exploring code fails if anything in your code isn’t public
  • if the REPL could switch packages, that would help
  • or even switch into a specific class?
  • Josh: you can do setAccessible(true)
  • mpilquist on IRC: “would be straightforward to give access to private methods using Dynamic that sets accessible and invokes reflectively”)
  • “public by default” and “binary compatibility” are enemies
  • Josh: don't make access impossible, just make it feel evil
  • making everything public can restrict freedom for an API to change
  • on sbt Josh uses private[sbt] to mark code that may change. people are free to do package sbt to get in there.

Mythbusters: Scalacheck revisited (1:07:05)

  • Dick is unrepentant about ScalaCheck
  • Seth invites ScalaCheck lovers to publish their experience reports on the typelevel.org blog
  • (Lars H said at NE Scala that their blog seeks case studies and experience reports from users of typelevel libraries)
  • Daniel: ScalaCheck is great for testing a codec (serialization/deserialization)
  • Josh runs a miiiiiiiiillion ScalaCheck cases
  • shhhhh, the partiality monad is the same as the trampoline monad, but don't tell anyone Daniel said so
  • Daniel: don't just generate random cases from nothing; randomly fuzz your handwritten cases
  • Josh (& Daniel): if ScalaCheck regression testing is too slow, segregate it from your fast unit tests. save it for PR validation

The end (1:17:00)

  • let's talk about Shapeless next time?
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