Using Eta for what you don't like writing in Scala

The integration of Scala with a lazy-by-default, modern and statically-typed functional language could lead to some interesting language-heterogeneous implementations despite the fact that the Eta programming language is missing a comprehensive documentation, robust concurrency support and an interactive REPL.

This talk aims to cover some of those interaction patterns to help both people already working or struggling with Haskell, and through that to also motivate the use of Eta for those still unfamiliar with this "end of the FP spectrum".

Transcript

1. May 2017
   @filippovitale
   Using for what you
   don't like writing in .
   

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7. What is Eta?
   

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8. https://jaxenter.com/pirates-of-the-jvm-the-infographic-132524.html
   

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9. https://jaxenter.com/pirates-of-the-jvm-the-infographic-132524.html
   

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10. Modern Haskell on the JVM
    - Rahul Muttineni
    - github.com/typelead/eta
    - github.com/typelead/etlas
    - github.com/typelead/eta-hackage
    - Objectives
    - JVM + Haskell Ecosystems
    - Accessibility for beginners
    It is GHC 7.10.3
    

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11. Modern Haskell on the JVM
    - Rahul Muttineni
    - github.com/typelead/eta
    - github.com/typelead/etlas
    - github.com/typelead/eta-hackage
    - Objectives
    - JVM + Haskell Ecosystems
    - Accessibility for beginners
    forked from haskell/cabal
    It is GHC 7.10.3
    

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12. Modern Haskell on the JVM
    - Rahul Muttineni
    - github.com/typelead/eta
    - github.com/typelead/etlas
    - github.com/typelead/eta-hackage
    - Objectives
    - JVM + Haskell Ecosystems
    - Accessibility for beginners
    forked from haskell/cabal
    set of patches for
    particular packages from
    Hackage that cannot be
    built out-of-the-box
    It is GHC 7.10.3
    

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13. What does Eta compile?
    

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14. module Main where
    import System.CPUTime
    main :: IO ()
    main = getCPUTime >>= print
    object Main extends App {
    println(System.nanoTime() * 1000)
    }
    https://github.com/filippovitale/eta-playground/tree/master/simplest-ghc-program
    

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15. module Main where
    import System.CPUTime
    main :: IO ()
    main = getCPUTime >>= print
    object Main extends App {
    println(System.nanoTime() * 1000)
    }
    λ> :t getCPUTime
    getCPUTime :: IO Integer
    

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16. module Main where
    import System.CPUTime
    main :: IO ()
    main = getCPUTime >>= print
    object Main extends App {
    println(System.nanoTime() * 1000)
    }
    λ> :t print
    print :: Show a => a -> IO ()
    λ> :t getCPUTime
    getCPUTime :: IO Integer
    λ> :i Integer
    …
    instance Show Integer
    

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17. module Main where
    import System.CPUTime
    main :: IO ()
    main = getCPUTime >>= print
    object Main extends App {
    println(System.nanoTime() * 1000)
    }
    

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18. module Main where
    import System.CPUTime
    main :: IO ()
    main = getCPUTime >>= print
    object Main extends App {
    nanoTime() * 1000 |> println
    }
    

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19. $ cat > Main.hs
    stack ghc Main.hs && ./Main
    

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20. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    

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21. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    $ java -jar RunMain.jar
    422227000000
    

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22. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    Driver
    .hs
    ghc
    Core STG
    https://www.microsoft.com/en-us/research/wp-content/uploads/1992/04/spineless-tagless-gmachine.pdf
    

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23. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    Driver
    Parser
    Typechecker
    Desugarer
    Optimizer
    Simplifier
    Code
    Generator
    .hs
    Core STG
    ghc
    http://www.aosabook.org/en/ghc.html
    

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24. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    Driver
    Parser
    Typechecker
    Desugarer
    Optimizer
    Simplifier
    Code
    Generator
    .hs
    Core STG
    .jar
    

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25. $ cat > Main.hs
    $ eta Main.hs
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    $ ls -lh
    -rw-r--r-- 711B Main.hi
    -rw-r--r-- 84B Main.hs
    -rw-r--r-- 3.3K Main.jar
    -rw-r--r-- 18M RunMain.jar
    - Main.jar content
    - all the dependencies
    - GHC runtime-system
    https://github.com/filippovitale/eta-playground/tree/master/simplest-ghc-program
    

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26. How can we use libs from
    the JVM ecosystem?
    

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28. {-# LANGUAGE MagicHash #-}
    module Main where
    import Java
    -- foreign import declaration
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeIO :: IO Int64
    main :: IO ()
    main = nanoTimeIO >>= print
    $ eta Main.hs && java -jar RunMain.jar
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    149320110727531
    IO Monad
    https://github.com/filippovitale/eta-playground/blob/master/java-static-import
    

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29. {-# LANGUAGE MagicHash #-}
    module Main where
    import Java
    -- foreign import declaration
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeJava :: Java a Int64
    main :: IO ()
    main = java nanoTimeJava >>= print
    $ eta Main.hs && java -jar RunMain.jar
    [1 of 1] Compiling Main ( Main.hs, Main.jar )
    Linking RunMain.jar ...
    149319575014401
    java :: Java c a -> IO a
    Java Monad
    

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30. {-# LANGUAGE MagicHash #-}
    module Main where
    import Java
    -- foreign import declarations
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeJava :: Java a Int64
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeIO :: IO Int64
    forall a. Java a b
    -- isomorphic to --
    IO b
    https://github.com/typelead/eta/issues/255#issuecomment-290937594
    

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31. {-# LANGUAGE MagicHash #-}
    module Main where
    import Java
    -- foreign import declarations
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeJava :: Java a Int64
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeIO :: IO Int64
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimePlain :: Int64
    main :: IO ()
    main = do
    java nanoTimeJava >>= print
    java nanoTimeJava >>= print
    nanoTimeIO >>= print
    nanoTimeIO >>= print
    print nanoTimePlain
    print nanoTimePlain
    

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32. {-# LANGUAGE MagicHash #-}
    module Main where
    import Java
    -- foreign import declarations
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeJava :: Java a Int64
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimeIO :: IO Int64
    foreign import java unsafe "@static java.lang.System.nanoTime" nanoTimePlain :: Int64
    main :: IO ()
    main = do
    java nanoTimeJava >>= print
    java nanoTimeJava >>= print
    nanoTimeIO >>= print
    nanoTimeIO >>= print
    print nanoTimePlain
    print nanoTimePlain
    $ java -jar RunMain.jar
    149319575014401
    149320109787317
    149320110727531
    149320111517553
    149320112027191
    149320112027191
    https://github.com/filippovitale/eta-playground/blob/master/java-static-import
    

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33. From Java static methods
    to full libraries
    

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34. https://github.com/filippovitale/eta-playground/tree/master/javafx-canvas-grid
    

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35. $ mkdir javafx-canvas-grid && cd "$_"
    $ etlas init && tree
    .
    ├── LICENSE
    ├── Setup.hs
    ├── javafx-canvas-grid.cabal
    

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36. $ mkdir javafx-canvas-grid && cd "$_"
    $ etlas init && tree
    .
    ├── LICENSE
    ├── Setup.hs
    ├── javafx-canvas-grid.cabal
    └── src
    ├── CanvasGridApp.hs
    ├── JavaFX
    │ ├──
    │ ├──
    │ └──
    ├── JavaFX.hs
    └── Main.hs
    

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37. $ mkdir javafx-canvas-grid && cd "$_"
    $ etlas init && tree
    .
    ├── LICENSE
    ├── Setup.hs
    ├── javafx-canvas-grid.cabal
    └── src
    ├── CanvasGridApp.hs
    ├── JavaFX
    │ ├── Core.hs
    │ ├── Methods.hs
    │ └── Types.hs
    ├── JavaFX.hs
    └── Main.hs
    

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38. module JavaFX.Types where
    import Java
    data {-# CLASS "javafx.stage.Stage" #-} Stage = Stage (Object# Stage) deriving Class
    data {-# CLASS "javafx.scene.Scene" #-} Scene = Scene (Object# Scene) deriving Class
    data {-# CLASS "javafx.scene.Group" #-} Group = Group (Object# Group) deriving Class
    -- There is a default instance for “object arrays”
    data {-# CLASS "javafx.scene.canvas.Canvas" #-} Canvas = Canvas (Object# Canvas) deriving Class
    data {-# CLASS "javafx.scene.canvas.Canvas[]" #-} Canvases = Canvases (Object# Canvases) der...
    instance JArray Canvas Canvases
    src/JavaFX/Types.hs
    

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39. module JavaFX.Methods where
    import Java
    import JavaFX.Types
    -- Stage methods
    foreign import java unsafe "show" show :: Java Stage ()
    foreign import java unsafe "setTitle" setTitle :: String -> Java Stage ()
    foreign import java unsafe "setScene" setScene :: Scene -> Java Stage ()
    -- GraphicsContext methods
    foreign import java unsafe "fillOval" fillOval ::
    Double -> Double -> Double -> Double -> Java GraphicsContext ()
    src/JavaFX/Methods.hs
    

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40. import javafx.application.Application
    import javafx.stage.Stage
    class CanvasGridApp extends Application {
    override def start(primaryStage: Stage): Unit = {
    ???
    }
    }
    

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41. module CanvasGridApp where
    import Java
    data {-# CLASS "org.eta.CanvasGridApp extends javafx.application.Application" #-}
    CanvasGridApp = CanvasGridApp (Object# CanvasGridApp)
    start :: Stage -> Java CanvasGridApp ()
    start primaryStage = undefined
    foreign export java "start" start :: Stage -> Java CanvasGridApp ()
    src/CanvasGridApp.hs
    class CanvasGridApp extends Application {
    override def start(primaryStage: Stage): Unit = {
    ???
    }
    }
    

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42. start :: Stage -> Java CanvasGridApp ()
    start primaryStage = do
    c <- newCanvas w h
    gc <- c <.> getGraphicsContext2D
    src/CanvasGridApp.hs
    -- Execute a Java action in the Java monad of another class
    -- with respect to the given object.
    (<.>) :: (Class c) => c -> Java c a -> Java b a
    

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43. start :: Stage -> Java CanvasGridApp ()
    start primaryStage = do
    c <- newCanvas w h
    gc <- c <.> getGraphicsContext2D
    forM_ [(i, j) | i <- [0..(n-1)], j <- [0..(n-1)]]
    $ \(i, j) -> gc <.> fillOval (u*i) (u*j) (u*r) (u*r)
    src/CanvasGridApp.hs
    

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44. start :: Stage -> Java CanvasGridApp ()
    start primaryStage = do
    c <- newCanvas w h
    gc <- c <.> getGraphicsContext2D
    forM_ [(i, j) | i <- [0..(n-1)], j <- [0..(n-1)]]
    $ \(i, j) -> gc <.> fillOval (u*i) (u*j) (u*r) (u*r)
    s <- (newGroup c) >>= newScene
    primaryStage <.> (setScene s >> setTitle "Eta-JavaFX CanvasGrid" >> show)
    where w = 320
    h = 320
    n = 8
    u = (min w h) / n
    r = 0.9
    src/CanvasGridApp.hs
    

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45. $ etlas run
    Resolving dependencies...
    Configuring javafx-canvas-grid-0.1.0.0...
    Preprocessing executable 'javafx-canvas-grid'
    Building executable 'javafx-canvas-grid'
    [1 of 6] Compiling JavaFX.Types
    [2 of 6] Compiling JavaFX.Methods
    [3 of 6] Compiling JavaFX.Core
    [4 of 6] Compiling JavaFX
    [5 of 6] Compiling CanvasGridApp
    [6 of 6] Compiling Main
    Linking dist/build/javafx-canvas-grid/javafx-canvas-grid.jar ...
    Running javafx-canvas-grid...
    https://github.com/filippovitale/eta-playground/tree/master/javafx-canvas-grid
    

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46. Old school Demoscene
    

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47. https://pouet.net/
    

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48. http://www.p01.org/
    

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49. http://jamie-wong.com/2016/07/15/ray-marching-signed-distance-functions/
    http://www.iquilezles.org/www/material/nvscene2008/rwwtt.pdf
    Signed Distance Function
    http://www.p01.org/tea_storm/
    Here be
    Dragons
    

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50. start :: Stage -> Java TeaStormApp ()
    start primaryStage = do
    t0 <- nanoTime
    c <- newCanvas w h
    s <- (newGroup c) >>= newScene
    loop <- newAnimationLoop c t0 n u m
    loop <.> startAnimation
    primaryStage <.> (setTitle "Eta-JavaFX TeaStorm" >> setScene s >> show)
    where n = 96
    m = 10
    w = n * m
    h = n * m
    u = (min w h) / n
    src/TeaStormApp.hs
    https://github.com/filippovitale/eta-playground/tree/master/javafx-teastorm
    

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51. start :: Stage -> Java TeaStormApp ()
    start primaryStage = do
    t0 <- nanoTime
    c <- newCanvas w h
    s <- (newGroup c) >>= newScene
    loop <- newAnimationLoop c t0 n u m
    loop <.> startAnimation
    primaryStage <.> (setTitle "Eta-JavaFX TeaStorm" >> setScene s >> show)
    where n = 96
    m = 10
    w = n * m
    h = n * m
    u = (min w h) / n
    src/TeaStormApp.hs
    

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52. name: javafx-teastorm
    version: 0.1.0.0
    homepage: https://github.com/filippovitale/eta-playground/javafx-teastorm
    executable javafx-teastorm
    main-is: Main.hs
    java-sources: java/teastorm/AnimationLoop.java
    build-depends: base >=4.8 && <4.9
    hs-source-dirs: src
    default-language: Haskell2010
    javafx-teastorm.cabal
    

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53. public class AnimationLoop extends AnimationTimer {
    public AnimationLoop(Canvas c, long t0, double n, double u, double m) {...}
    private static double computeIntensity(final double x, final double y, final double s, final double t) {
    double intensity = 1;
    for (double d = intensity * 4, df = 1; .025 < df * intensity; intensity -= .025) {
    double X = d * x / s - d / 2;
    double Y = d * y / s - d / 2;
    double Z = d / 2 - 9;
    df = (X * X +
    Y * Y * Math.cos(t/6 + Math.cos(d - X - Y)) +
    Z * Z) / 12
    - 1 + Math.cos(X + t) * Math.cos(Y - t);
    d += df;
    }
    return intensity;
    }
    @Override
    public void handle(long currentNanoTime) {
    double t = (currentNanoTime - t0) / (500 * oneMillisecondInNanoTime);
    gc.clearRect(0, 0, w, h); // clear the Canvas
    for (int x = 0; x < n; x++) {
    for (int y = 0; y < n; y++) {
    double i = computeIntensity(x, y, n, t);
    gc.setGlobalAlpha(i);
    gc.fillOval(x * u, y * u, i * m * 1.4, i * m * 1.4);
    }
    }
    }
    }
    

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54. $ etlas run
    Resolving dependencies...
    Configuring javafx-teastorm-0.1.0.0...
    Preprocessing executable 'javafx-teastorm' for
    javafx-teastorm-0.1.0.0..
    Building executable 'javafx-teastorm' for javafx-teastorm-0.1.0.0..
    [1 of 6] Compiling JavaFX.Types
    [2 of 6] Compiling JavaFX.Methods
    [3 of 6] Compiling TeaStormApp
    [4 of 6] Compiling JavaFX.Core
    [5 of 6] Compiling JavaFX
    [6 of 6] Compiling Main
    Linking dist/build/javafx-teastorm/javafx-teastorm.jar ...
    Running javafx-teastorm...
    https://github.com/filippovitale/eta-playground/tree/master/javafx-teastorm
    

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55. Eta is embeddable:
    you can export Haskell
    functions to the JVM
    

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56. Source
    Sink
    

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57. Boba Fett
    WARAWHWHAHOR
    

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58. FileIO.fromPath(jsonPath)
    .via(gunzip())
    .via(lineSplitter)
    .map(_.utf8String)
    .via(extractNameFlow)
    .via(wookieeFlow)
    .runWith(Sink.foreach(println))
    extractNameFlow
    wookieeFlow
    https://github.com/filippovitale/eta-playground/tree/master/scala-akka-stream-eta-wookiee
    

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59. name: scala-akka-stream-eta-wookiee
    version: 0.1.0.0
    cabal-version: >=1.10
    executable scala-akka-stream-eta-wookiee
    main-is: Main.hs
    build-depends: base >=4.8 && <4.9,
    bytestring,
    containers,
    aeson
    hs-source-dirs: src
    default-language: Haskell2010
    -- java-sources: lib/manually-downloaded-akka-stream-uber.jar
    

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60. name: scala-akka-stream-eta-wookiee
    version: 0.1.0.0
    cabal-version: >=1.10
    executable scala-akka-stream-eta-wookiee
    main-is: Main.hs
    build-depends: base >=4.8 && <4.9,
    bytestring,
    containers,
    aeson
    hs-source-dirs: src
    default-language: Haskell2010
    maven-depends: com.typesafe.akka:akka-stream_2.12:2.4.17
    

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61. name: scala-akka-stream-eta-wookiee
    version: 0.1.0.0
    cabal-version: >=1.10
    executable scala-akka-stream-eta-wookiee
    main-is: Main.hs
    build-depends: base >=4.8 && <4.9,
    bytestring,
    containers,
    aeson
    hs-source-dirs: src
    default-language: Haskell2010
    maven-depends: com.typesafe.akka:akka-stream_2.12:2.4.17
    

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62. src/AkkaStream/Exports.hs
    data {-# CLASS "stream.Example" #-} Example = Example (Object# Example)
    type JStringFlow = Flow JString JString NotUsed
    extractNameFlow :: Java Example JStringFlow
    extractNameFlow = undefined
    wookieeFlow :: Java Example JStringFlow
    wookieeFlow = undefined
    foreign export java extractNameFlow :: Java Example JStringFlow
    foreign export java wookieeFlow :: Java Example JStringFlow
    

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63. src/AkkaStream/Exports.hs
    data {-# CLASS "stream.Example" #-} Example = Example (Object# Example)
    type JStringFlow = Flow JString JString NotUsed
    extractNameFlow :: Java Example JStringFlow
    extractNameFlow = flowFromFunction $ applyFunction f
    where
    f js = undefined
    wookieeFlow :: Java Example JStringFlow
    wookieeFlow = flowFromFunction $ applyFunction f
    where
    f js = undefined
    foreign export java extractNameFlow :: Java Example JStringFlow
    foreign export java wookieeFlow :: Java Example JStringFlow
    akka.stream.javadsl.Flow.fromFunction
    static Flow fromFunction(Function f)
    

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64. src/AkkaStream/Exports.hs
    data {-# CLASS "stream.Example" #-} Example = Example (Object# Example)
    type JStringFlow = Flow JString JString NotUsed
    extractNameFlow :: Java Example JStringFlow
    extractNameFlow = flowFromFunction $ applyFunction f
    where
    f js = undefined
    wookieeFlow :: Java Example JStringFlow
    wookieeFlow = flowFromFunction $ applyFunction f
    where
    f js = undefined
    foreign export java extractNameFlow :: Java Example JStringFlow
    foreign export java wookieeFlow :: Java Example JStringFlow
    akka.japi.function.Function
    trait Function[-T, +R] { def apply(param: T): R }
    

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65. src/AkkaStream/Exports.hs
    data {-# CLASS "stream.Example" #-} Example = Example (Object# Example)
    type JStringFlow = Flow JString JString NotUsed
    extractNameFlow :: Java Example JStringFlow
    extractNameFlow = flowFromFunction $ applyFunction f
    where
    f js = return (toJava $ g $ pack (fromJava js :: [Char]))
    g s = (fromMaybe empty (decode s :: Maybe (Map String String))) ! "name"
    wookieeFlow :: Java Example JStringFlow
    wookieeFlow = flowFromFunction $ applyFunction f
    where
    f js = return (toJava $ (fromJava js :: [Char]) >>= wookiee)
    foreign export java extractNameFlow :: Java Example JStringFlow
    foreign export java wookieeFlow :: Java Example JStringFlow
    

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66. src/main/scala/stream/Main.scala
    object Main extends App {
    val e = new Example()
    val extractNameFlow = e.extractNameFlow()
    val wookieeFlow = e.wookieeFlow()
    val jsonURL = getClass.getResource("/all_characters.json-stream.gz")
    val jsonPath = Paths.get(jsonURL.toURI)
    val lineSplitter = Framing.delimiter(ByteString("\n"), Int.MaxValue)
    FileIO.fromPath(jsonPath)
    .via(gunzip())
    .via(lineSplitter)
    .map(_.utf8String)
    .via(extractNameFlow)
    .via(wookieeFlow)
    .runWith(Sink.foreach(println))
    .onComplete(_ => system.terminate())
    }
    

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67. https://github.com/filippovitale/eta-playground/tree/master/scala-akka-stream-eta-wookiee
    

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68. Where Eta is going?
    

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69. - Interactive REPL
    - Java FFI imports aid / helpers
    - Hot-code reloading as JVM has “built-in dynamism”
    - GraalVM on JDK9
    - New JIT Compiler and
    - Polyglot Runtime for the JVM
    - Stability
    - Support for the fundamental Hackage libraries
    Eta active development areas
    

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70. May 2017
    @filippovitale
    Thanks!
    

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71. May 2017
    @filippovitale
    $ tail -f questions
    

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