ZIO from Home

ZIO provides a variety of features for building synchronous, asynchronous and concurrent applications.

In this talk, I will show how to use functional effects and data types built on ZIO how to manage errors and recover from them, how to manage resources and how to make concurrent tasks.

Transcript

1. ZIO from
   Home
   Wiem Zine Elabidine
   @WiemZin
   Stay Safe
   

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2. Functional Effects
   

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3. Functional Programming
   Pure functions
   Referential
   transparency.
   Composability
   Combine functions
   together to build
   new data.
   Immutability
   Values couldn’t be
   changed.
   Data & Functionality
   Pass data through
   functions to
   change its
   behaviors.
   

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4. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   

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5. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   def toInt(str: String): Try[Int] =
   Try(str.toInt)
   

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6. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   def toInt(str: String): Try[Int] =
   Try(str.toInt)
   toInt("One")
   

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7. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   def toInt(str: String): Try[Int] =
   Try(str.toInt)
   toInt("One")
   Failure(java.lang.NumberFormatException: For input string: "One")
   

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8. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   def nextDay(day: DayOfWeek): String =
   day.plus(1) .toString
   assert(nextDay(THURSDAY)))(equalTo("FRIDAY"))
   

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9. Stay home safe and
   use what you have
   No Side effects
   Pure Function
   Trust your types
   Total
   Test your functions
   Deterministic
   def nextDay(day: DayOfWeek): String =
   day.plus(1) .toString
   assert(nextDay(THURSDAY)))(equalTo("FRIDAY"))
   

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10. Stay home safe and
    use what you have
    No Side effects
    Pure Function
    Trust your types
    Total
    Test your functions
    Deterministic
    def add(pasta: Pasta, sauce: Sauce,
    water: Water): Cooked[Pasta] = {
    val p = water.boil.map(_.put(pasta))
    p.addSauce(sauce)
    }
    

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11. Stay home safe and
    use what you have
    No Side effects
    Pure Function
    Trust your types
    Total
    Test your functions
    Deterministic
    

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12. Effects are useful
    ❏ handle events
    ❏ Send messages
    ❏ read from the DataBase
    ❏ persist information
    ❏ print out the result
    ❏ retry in event of errors
    ❏ send result to other
    services
    ❏ ...
    Real World Applications
    

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13. Abstract your programs!
    Describe everything in
    immutable data type!
    Functional Effects
    Effects as values?
    

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14. Functional Effects
    case class IO[A](unsafeRun: () => A) {
    def map[B](f: A => B): IO[B] = ???
    def flatMap[B](f: A => IO[B]): IO[B] = ???
    }
    object IO {
    def effect[A](a: => A): IO[A] = new IO[A](() => a)
    }
    

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15. Functional Program
    val program: IO[Unit] = for {
    event <- IO.effect(handleEvent)
    user <- IO.effect(getUser(event.userId))
    _ <- IO.effect(logInfo(user))
    ...
    } yield ()
    

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16. Functional Program
    val program: IO[Unit] = for {
    event <- IO.effect(handleEvent)
    user <- IO.effect(getUser(event.userId))
    _ <- IO.effect(logInfo(user))
    ...
    } yield ()
    program.unsafeRun()
    

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17. Execution
    Just do it!
    Description
    Make a plan A - Z
    Be prepared!
    

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18. ● Control over all type of interactions
    ● Testability
    ● Refactoring
    Why Functional Effects?
    

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19. Functional Effects
    case class IO[A](unsafeRun: () => A) {
    def map[B](f: A => B): IO[B] = ???
    def flatMap[B](f: A => IO[B]): IO[B] = ???
    }
    object IO {
    def effect[A](a: => A): IO[A] = new IO[A](() => a)
    }
    

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20. ZIO
    Zero dependency Scala library for asynchronous and concurrent
    programming using purely functional code.
    

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21. Functional Effects in ZIO
    ZIO[R, E, A]
    Description of a program
    R
    E A
    Dependencies
    Error Success
    

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22. Functional Effects in ZIO
    RIO[R, A]
    Description of a program
    R
    Throwable
    A
    Dependencies
    Error Success
    

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23. Functional Effects in ZIO
    URIO[R, A]
    Description of a program
    R
    A
    Dependencies
    Success
    

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24. Functional Effects in ZIO
    Task[A]
    Description of a program
    Throwable
    A
    Error Success
    

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25. Functional Effects in ZIO
    IO[E, A]
    Description of a program
    E
    A
    Error Success
    

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26. Functional Effects in ZIO
    UIO[A]
    Description of a program
    A
    Success
    

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27. Run Effects
    object Main extends zio.App {
    override def run(args: List[String]): IO[Nothing, Int] =
    program.fold(_ => 1, _ => 0)
    }
    OR
    object Main {
    Runtime.default.unsafeRun(program)
    }
    

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28. Error
    Management
    

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29. Error Management
    Throwable
    def divideM(a: Int, b: Int): Task[Int] =
    Task(divide(a, b))
    Task[Int]
    Throwable Int
    

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30. Error Management
    Throwable
    val throwException: Task[Nothing] =
    Task(throw new Exception("sorry"))
    Task[Nothing]
    Throwable
    

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31. Error Management
    String
    val failedIO: IO[String, Nothing] = IO.fail("sorry again")
    IO[String, Nothing]
    String
    

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32. Error Management
    Customized Errors
    sealed trait Error
    object Error {
    case class UserNotFound(id: UserId) extends Error
    case class InternalServer(t: Throwable) extends Error
    ...
    }
    val program: IO[Error, Unit] = ???
    

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33. Error Management
    Customized Errors
    val program: IO[Error, Unit] =
    for {
    userId <- requestListener // IO[InternalServer, UserId]
    user <- getUser(userId) // IO[UserNotFound, User]
    _ <- logInfo(user) // IO[ Nothing, Unit]
    _ <- sendResponse(user) // IO[InternalServer, Unit]
    } yield ()
    

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34. Error Management
    The state of the program
    val program: IO[Error, Unit] = ???
    val programState: IO[Nothing, Exit[Error, Unit]] = program.run
    

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35. Error Management
    Exit[E, A]
    Success[A]
    Failure[E]
    

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36. Error Management
    Exit[E, A]
    Success[A]
    Failure[E]
    

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37. Error Management
    Exit[E, A]
    Success[A]
    Failure[E]
    Cause[E]
    

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38. Cause[E]
    Die
    Expected Error
    Unexpected Error, Exception
    Fail[E]
    Interrupted effect
    Interrupt
    

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39. Many causes?
    Both(left, right)
    Both(Fail(e1),
    Then(Both(Fail(e2), Die(t)), Interrupt)
    Then(left, right)
    

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40. Example: Cause.Both
    IO.fail("error1")
    .zipPar(
    IO.succeed(throw new Exception(" surprise!"))
    )
    

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41. Example: Cause.Both
    IO.fail("error1") // Cause.Fail("error1")
    .zipPar(
    IO.succeed(throw new Exception(" surprise!"))
    )
    

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42. Example: Cause.Both
    IO.fail("error1") // Cause.Fail("error1")
    .zipPar(
    IO.succeed(throw new Exception(" surprise!")) // Cause.Die(...)
    )
    

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43. Example: Cause.Both
    IO.fail("error1") // Cause.Fail("error1")
    .zipPar(
    IO.succeed(throw new Exception(" surprise!")) // Cause.Die(...)
    )
    ⇒ Both(Cause.Fail("error1"), Cause.Die(java.lang.Exception: surprise!)))
    

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44. Example: Cause.Then
    IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
    

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45. Example: Cause.Then
    IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
    Fail("error")
    

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46. Example: Cause.Then
    IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
    Fail("error") Die(java.lang.Exception Don’t try this at Home)
    

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47. Example: Cause.Then
    IO.fail("error").ensuring(IO.die(new Exception("Don't try this at Home")))
    Fail("error") Die(java.lang.Exception Don’t try this at Home)
    ⇒ Then(Cause.Fail("error"), Cause.Die(java.lang.Exception: Don’t try this at Home))
    

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48. Error Management
    Expose all causes:
    def divide(a: Int, b: Int): IO[Cause[Throwable], Int] =
    Task(a / b).sandbox
    

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49. Error Management
    Catch Errors:
    def divide(a: Int, b: Int): Task[Int] =
    Task(a / b)
    .catchSome{
    case _: ArithmeticException => UIO(0)
    }
    

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50. Error Management
    Peek at the errors:
    def divide(a: Int, b: Int): Task[Int] =
    Task(a / b)
    .tapError{
    error => UIO(println(s"failed with: $e"))
    }
    

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51. Error Management
    Fallback:
    val io1: IO[Error, Int] = ???
    val io2: IO[String, Int] = ???
    val result: IO[String, Int] = io1.orElse(io2)
    

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52. Error Management
    Fallback:
    val loginUser: IO[Error, Profile] = ???
    val loginAnonymous: IO[Throwable, LimitedProfile] = ???
    val result: IO[Throwable, Either[Profile, LimitedProfile]] =
    loginUser.orElseEither(loginAnonymous)
    

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53. Error Management
    Recover:
    def divide(a: Int, b: Int): UIO[Int] =
    Task(a / b).foldM(_ => UIO(0), n => UIO(n))
    

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54. Error Management
    Crash it:
    def divide(a: Int, b: Int): UIO[Int] =
    Task(a / b).orDie
    

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55. Error Management
    Make defects as expected errors:
    val io: IO[String, Nothing] =
    IO.succeed(throw new Exception(""))
    .unrefine(e => s"The error is: $e")
    

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56. Error Management
    What about fatal Errors?
    

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57. Error Management
    def simpleName[A](c: Class[A]) = c.getSimpleName
    object Example
    Task(simpleName(Example.getClass))
    

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58. Error Management
    def simpleName[A](c: Class[A]) = c.getSimpleName
    object Example
    Task(simpleName(Example.getClass))
    [error] java.lang.InternalError: Malformed class name
    [error] at java.lang.Class.getSimpleName(Class.java:1330)
    

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59. Error Management
    object Main extends zio.App {
    override val platform: Platform =
    Platform.default.withFatal (_ => false)
    override def run(args: List[String]): ZIO[zio.ZEnv, Nothing, Int] = {
    Task(simpleName(Example.getClass)).fold(_ =>1, _ => 0)
    }
    }
    

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60. Error Management
    override val platform: Platform = new Platform {
    val executor = Executor.makeDefault(2)
    val tracing = Tracing.disabled
    def fatal(t: Throwable): Boolean =
    !t.isInstanceOf[InternalError] && t.isInstanceOf[VirtualMachineError]
    def reportFatal(t: Throwable): Nothing = {
    t.printStackTrace()
    throw t
    }
    def reportFailure(cause: Cause[Any]): Unit = {
    if (cause.died)
    System.err.println(cause.prettyPrint)
    }
    ...
    }
    

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61. Build concurrent
    programs
    

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62. ZIO Fibers
    Fibers are lightweight mechanism of concurrency.
    OS Thread
    ZIO Fiber
    Task1 Task2 Task3 ... ..
    

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63. How ZIO runs Effects?
    ZIO[R, E, A]
    

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64. How ZIO runs Effects?
    ZIO[R, E, A]
    R => IO[E, A]
    

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65. How ZIO runs Effects?
    ZIO[R, E, A]
    R => IO[E, A]
    

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66. How ZIO runs Effects?
    ZIO[R, E, A]
    R => IO[E, A]
    

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67. How ZIO runs Effects?
    IO[E, A]
    

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68. How ZIO runs Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    

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69. How ZIO runs Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    

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70. How ZIO runs Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    

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71. How ZIO runs concurrent Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    IO[Nothing,Fiber[E, A]]
    fork
    

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72. How ZIO runs concurrent Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    IO[Nothing,Fiber[E, A]]
    fork
    

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73. How ZIO runs concurrent Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    IO[Nothing,Fiber[E, A]]
    fork
    Fiber[E, A]
    unsafeRun
    

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74. How ZIO runs concurrent Effects?
    IO[E, A]
    Fiber[E, A]
    unsafeRun
    IO[Nothing,Fiber[E, A]]
    fork
    Fiber[E, A]
    unsafeRun
    

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75. Concurrent Tasks
    trait ZIO[R, E, A] {
    def race(that: ZIO[R, E, A]): ZIO[R, E, A]
    def raceAll(ios: Iterable[ZIO[R, E, A]]): ZIO[R, E, A]
    def zipPar(that: ZIO[R, E, B]): ZIO[R, E, (A, B)]
    def on(ec: ExecutionContext): ZIO[R, E, A]
    ...
    }
    object ZIO {
    def foreachPar(as: Iterable[A])(fn: A => ZIO[R, E, B]): ZIO[R, E, List[B]]
    ...
    }
    

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76. Concurrent Tasks
    def getUserInfo(id: Id): Task[(User, Profile)] =
    fetchUser(id).zipPar(fetchProfile(id))
    Task 1 Task 2
    (User, Profile)
    

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77. Example
    case class IlForno(queue: Queue[Request], currentIngredients: Ref[Ingredients]) {
    def handleRequests(p: Promise[Nothing, Unit]): ZIO[Clock, MissingIngredient, Unit] =
    (for {
    request <- queue.take
    rest <- currentIngredients.update(preparePizza(request, _))
    _ <- evaluate(rest)
    } yield ())
    .tapError(_ => p.succeed(()))
    .repeat(Schedule.duration(8.hours) && Schedule.spaced(10.minutes))
    .unit
    val listenRequests: IO[Error, Unit] = ???
    }
    

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78. val program: ZIO[Clock, Error, Unit] = for {
    ilForno <- IlForno(initialIngredient)
    f1 <- ilForno.listenRequests.fork
    p <- Promise.make[Nothing, Unit]
    f2 <- ilForno.handleRequests(p).fork
    _ <- p.await
    _ <- f1.interrupt.zipPar(f2.interrupt)
    } yield ()
    Example
    

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79. Example
    val program: ZIO[Clock, Error, Unit] = for {
    ilForno <- IlForno(initialIngredient)
    f1 <- ilForno.listenRequests.fork
    p <- Promise.make[Nothing, Unit]
    f2 <- ilForno.handleRequests(p).fork
    _ <- p.await
    _ <- f1.interrupt.zipPar(f2.interrupt)
    } yield ()
    

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80. Example
    val program: ZIO[Clock, Error, Unit] = for {
    ilForno <- IlForno(initialIngredient)
    f1 <- ilForno.listenRequests.fork
    p <- Promise.make[Nothing, Unit]
    f2 <- ilForno.handleRequests(p).fork
    _ <- p.await
    _ <- f1.interrupt.zipPar(f2.interrupt)
    } yield ()
    

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81. Example
    val program: ZIO[Clock, Error, Unit] = for {
    ilForno <- IlForno(initialIngredient)
    f1 <- ilForno.listenRequests.fork
    p <- Promise.make[Nothing, Unit]
    f2 <- ilForno.handleRequests(p).fork
    _ <- p.await
    _ <- f1.interrupt.zipPar(f2.interrupt)
    } yield ()
    

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82. Resource
    Management
    

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83. Resource Management
    File Connection
    Open / close / use = Acquire / release / use
    Database Clients
    

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84. Resource Management
    IO.effect(startApp)
    .ensuring(
    console.putStr("Shutdown ..."))
    ensuring
    01
    

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85. Resource Management
    IO.effect(startApp)
    .ensuring(
    console.putStr("Shutdown ..."))
    createClient(config)
    .bracket(_.close)(c =>
    processEvents(c))
    ensuring bracket
    01 02
    

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86. Resource Management
    IO.effect(startApp)
    .ensuring(
    console.putStr("Shutdown ..."))
    ensuring
    val resource =
    Managed.make(openFile(file))(_.close)
    ...
    resource.use(computeLines)
    Management
    bracket
    01 03
    02
    createClient(config)
    .bracket(_.close)(c =>
    processEvents(c))
    

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87. Resource Management
    ● You can use the methods provided by the dependencies in your
    program.
    ● once you provide a layer or an environment, the implementation
    will be acquired and used then released at the end.
    ZIO Environment & ZLayer[R, E, A]
    

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88. ZIO
    is Awesome
    

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89. WrapUp
    documentation
    https://github.com/zio/zio
    zio.dev
    ZIO projects
    Blog post
    https://medium.com/@wiemzin
    

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90. CREDITS: This presentation template was
    created by Slidesgo, including icons by Flaticon,
    and infographics & images by Freepik
    THANKS
    Follow me: @WiemZin
    Please keep this slide for attribution
    

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