Monad Error with Cats/monad-error-with-cats

catsによるMonadErrorの説明資料です。

Transcript

1. .POBE&SSPS
   XJUIDBUT
   
   

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2. ࿩͢͜ͱ
   w .POBE&SSPSͱ͸
   w DBUTΛ༻͍ͨ.POBE&SSPSͷ࣮૷
   

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3. .POBE&SSPSͱ͸
   .POBEͰந৅ԽΛߦ͏ࡍʹɺ
   ΤϥʔϋϯυϦϯάΛิॿ͢Δ΋ͷ
   

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4. ந৅Խ
   def authF(name: String, password: String): Future[User]
   def authT(name: String, password: String): Try[User]
   def authE(name: String, password: String): Either[String, User]
   def auth[F[_]](name: String, password: String): F[User]
   5BHMFTT'JOBMͰ
   ྑ͘ग़ͯ͘Δ΍ͭ
   

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5. ΤϥʔϋϯυϦϯά
   'VUVSF
   &JUIFS
   5SZ
   Τϥʔʹର͢Δॲཧ
   Future {
   ???
   throw new RuntimeException
   } recoverWith {
   case e: IllegalArgumentException => Future.successful(0)
   }
   Try {
   ???
   throw new RuntimeException
   } match {
   case Success(result) => result
   case Failure(e) => println(s"failure :${e.getMessage}")
   }
   Either {
   ???
   Left("Error")
   } match {
   case Right(success) => success
   case Left(e) => println(s"failure: $e")
   }
   

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6. .POBEͰந৅Խ͕೉͍͠ྫ
   'VUVSF
   &JUIFS
   5SZ
   def program(value: Either[String, Int], e: => String): Either[String, Int] = for {
   n result else Right(n * 2)
   } yield result
   def program(value: Future[Int], e: => String)(implicit ec: ExecutionContext): Future[Int] = for {
   n result else Future.successful(n*2)
   } yield result
   def program(value: Try[Int], e: => String): Try[Int] = for {
   n result else Success(n*2)
   } yield result
   

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7. 'VUVSF
   &JUIFS
   5SZ
   def program(value: Either[String, Int], e: => String): Either[String, Int] = for {
   n result else Right(n * 2)
   } yield result
   .POBEʹΑͬͯ
   ΤϥʔϋϯυϦϯά
   ͕ҟͳΔ
   .POBEͰந৅Խ͕೉͍͠ྫ
   def program(value: Future[Int], e: => String)(implicit ec: ExecutionContext): Future[Int] = for {
   n result else Future.successful(n*2)
   } yield result
   def program(value: Try[Int], e: => String): Try[Int] = for {
   n result else Success(n*2)
   } yield result
   

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8. Ϟνϕʔγϣϯ
   def program[F[_], E](value: F[Int], e: => E)(implicit ME: MonadError[F, E]): F[Int]
   def program(value: Either[String, Int], e: => String): Either[String, Int]
   def program(value: Future[Int], e: => String)(implicit ec: ExecutionContext): Future[Int]
   def program(value: Try[Int], e: => String): Try[Int]
   

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9. ࿩͢͜ͱ
   w .POBE&SSPSͱ͸
   w DBUTΛ༻͍ͨ.POBE&SSPSͷ࣮૷
   

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10. $BUT
    4DBMB[ͷ಺෦෼྾ʹΑͬͯੜ·Εͨ
    ؔ਺ܕϓϩάϥϛϯά༻ͷ4DBMBϥΠϒϥϦ
    ɾ೥ࠒ஀ੜ
    ɾʹWϦϦʔε ݱࡏͷ࠷৽͸W
    
    ɾݍ DBUFHPSZ
    ʹ༝དྷ
    

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11. .POBE&SSPSJODBUT
    trait MonadError[F[_], E] extends ApplicativeError[F, E] with Monad[F] {
    def ensure[A](fa: F[A])(error: => E)(predicate: A => Boolean): F[A]
    def raiseError[A](e: E): F[A]
    def handleError[A](fa: F[A])(f: E => A): F[A]
    …
    }
    .POBEͷܕ 'ʹؚ·ΕΔ
    Τϥʔͷܕ
    .POBEΛܧঝ
    

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12. w SBJTF&SSPS
    w FOTVSF
    w IBOEMF&SSPS
    ˞.POBEͳͷͰɺQVSFɺNBQɺqBU.BQ΋ؚΜͰ͍·͢
    ୅දతͳϝιου
    .POBE&SSPSJODBUT
    

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13. QVSF
    def pure[A](x: A): F[A]
    "Λ'ʹ্࣋ͪ͛Δ.POBEͰ͓ͳ͡Έͷؔ਺
    def pure[B](b: B): Either[A, B] = Right(b)
    'VUVSF
    &JUIFS
    def pure[A](x: A): Future[A] = Future.successful(x)
    

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14. SBJTF&SSPS
    Τϥʔͷத਎Λ'ʹ্࣋ͪ͛Δ
    def raiseError[A](e: E): F[A]
    def raiseError[B](e: A): Either[A, B] = Left(e)
    def raiseError[A](e: Throwable): Future[A] = Future.failed(e)
    'VUVSF
    &JUIFS
    

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15. IBOEMF&SSPS
    def handleError[A](fa: F[A])(f: E => A): F[A]
    ΤϥʔΛ࢖ͬͯ੒ޭʹม׵͢Δɻ
    'VUVSFͷSFDPWFS8JUIΈ͍ͨͳ΍ͭ
    monadError.handleError(value) {
    case failure: E =>
    "It's Ok"
    }
    override def handleError[A](fea: Future[A])(f: Throwable => A): Future[A] =
    fea.recover { case t => f(t) }
    'VUVSF
    def handleErrorWith[A](fa: F[A])(f: E => F[A]): F[A]
    monadError.handleErrorWith(value) {
    case failure: E =>
    monadError.pure("It's Ok")
    case _ =>
    monadError.raiseError(failure)
    }
    

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16. FOTVSF
    def ensure[A](fa: F[A])(error: => E)(predicate: A => Boolean): F[A]
    MonadError[({type E[A] = Either[String, A]})#E, String].ensure(Right(42))("Error")(_ > 0) // Right(42)
    MonadError[({type E[A] = Either[String, A]})#E, String].ensure(Right(-42))(“Error”)(_ > 0) // Left(Error)
    def ensure[A](fa: F[A])(error: => E)(predicate: A => Boolean): F[A] =
    flatMap(fa)(a => if (predicate(a)) pure(a) else raiseError(error))
    ৚݅ࣜ QSFEJDBUF
    Λ͔͚ͯɺ
    USVFͳΒ੒ޭɺGBMTFͳΒΤϥʔ FSSPS
    Λฦؔ͢਺
    

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17. Ϟνϕʔγϣϯ
    def program[F[_], E](value: F[Int], e: => E)(implicit ME: MonadError[F, E]): F[Int]
    def program(value: Either[String, Int], e: => String): Either[String, Int]
    def program(value: Future[Int], e: => String)(implicit ec: ExecutionContext): Future[Int]
    def program(value: Try[Int], e: => String): Try[Int]
    

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18. .POBE&SSPSʹΑΔந৅Խ
    ΤϥʔॲཧΛந৅Խ
    trait MonadError[F[_], E] extends ApplicativeError[F, E] with Monad[F] {
    def ensure[A](fa: F[A])(error: => E)(predicate: A => Boolean): F[A] =
    flatMap(fa)(a => if (predicate(a)) pure(a) else raiseError(error))
    }
    ؆ܿͳදݱ͕Մೳ
    def program(value: Either[String, Int], e: => String): Either[String, Int] = for {
    n result else Right(n * 2)
    } yield result
    def program[F[_], E](value: F[Int], e: => E)(implicit monadError: MonadError[F, E]): F[Int] = for {
    n result else monadError.pure(n * 2)
    } yield result
    def program[F[_], E](value: F[Int], e: => E)(implicit monadError: MonadError[F, E]): F[Int] =
    monadError.ensure(value)(e)(_ >= 0).map(_*2)
    

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19. ࢖͏ଆ͸.POBE&SSPSͷ࣮૷Λࠩ͠ࠐΉ
    // MonadErrorͷEitherͷ࣮૷
    implicit val monadErrorForEither = new MonadError[Either[String, Int], String] {
    ???
    }
    val resEitherSuccess = program[({type E[A] = Either[String, A]})#E, String](43.asRight[String], "Error")
    // Right(86)
    val resEitherFailure = program[({type E[A] = Either[String, A]})#E, String](-43.asRight[String], "Error")
    // Left("Error")
    .POBE&SSPSʹΑΔந৅Խ
    def program[F[_], E](value: F[Int], e: => E)(implicit monadError: MonadError[F, E]): F[Int] =
    monadError.ensure(value)(e)(_ >= 0).map(_*2)
    

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20. new MonadError[Either[A, ?], A] with Traverse[Either[A, ?]] {
    def pure[B](b: B): Either[A, B] = Right(b)
    def flatMap[B, C](fa: Either[A, B])(f: B => Either[A, C]): Either[A, C] =
    fa.right.flatMap(f)
    def raiseError[B](e: A): Either[A, B] = Left(e)
    …
    }
    new FutureCoflatMap with MonadError[Future, Throwable] with Monad[Future] with StackSafeMonad[Future] {
    def pure[A](x: A): Future[A] = Future.successful(x)
    def flatMap[A, B](fa: Future[A])(f: A => Future[B]): Future[B] = fa.flatMap(f)
    def raiseError[A](e: Throwable): Future[A] = Future.failed(e)
    …
    }
    'VUVSF
    &JUIFS
    5SZ 'VUVSF &JUIFS 0QUJPO *0ͷ࣮૷͕طʹ͋Δ
    .POBE&SSPS*OTUBODFJODBUT
    

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21. ͦΕͧΕͷ.POBE&SSPSͷ࣮૷Λࠩ͠ࠐΉ͚ͩ
    import cats.instances.try_._
    val resTrySuccess = program[Try, Throwable](Success(43), new RuntimeException(“Error"))
    // = Success(43)
    val resTryFailure = program[Try, Throwable](Success(-43), new RuntimeException("Error"))
    // = Failure(RuntimeException("Error"))
    import cats.instances.future._
    val resFutureSuccess = program[Future, Throwable](Future(43), new RuntimeException(“Error"))
    // = onComplete => Success(43)
    val resFutureFailure = program[Future, Throwable](Future(-43), new RuntimeException(“Error"))
    // = onComplete => Failure(RuntimeException("Error"))
    'VUVSF
    &JUIFS
    5SZ
    import cats.syntax.either._
    import cats.instances.either._
    val resEitherSuccess = program[({type E[A] = Either[String, A]})#E, String](43.asRight[String], "Error")
    // Right(86)
    val resEitherFailure = program[({type E[A] = Either[String, A]})#E, String](-43.asRight[String], "Error")
    // Left("Error")
    def program[F[_], E](value: F[Int], e: => E)(implicit ME: MonadError[F, E]): F[Int] =
    ME.ensure(value)(e)(_ >= 0).map(_*2)
    .POBE&SSPS*OTUBODFJODBUT
    

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22. ·ͱΊ
    .POBE&SSPS͸.POBEʹΤϥʔϋϯυϦϯάͷ
    ৼΔ෣͍͕௥Ճ͞Εͨ΋ͷ
    5BHMFTT'JOBMΛڧԽͯ͘͠ΕΔ͔΋
    

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