Demystifying Functional Programming

Transcript

1. Demystifying Demystifying Functional Functional Programming Programming Cristian Spinetta| @cspinetta | Diego Parra | @dpsoft
2. Demystifying Demystifying Functional Functional Programming Programming with some abstractions Cristian Spinetta| @cspinetta | Diego Parra | @dpsoft
3. Disclaimer Disclaimer
4. Typeclass Typeclass trait HtmlWriter[A] { def write(value: A): String } The type class itself is a trait with a single type parameter
5. Typeclass Typeclass trait HtmlWriter[A] { def write(value: A): String } implicit val intWriter:HtmlWriter[Int] = new HtmlWriter[Int] { override def write(value: Int): String = value.toString } implicit val stringWriter:HtmlWriter[String] = new HtmlWriter[String] { override def write(value: String): String = value.replaceAll("<", "&lt;").replaceAll(">", "&gt;") } The type class itself is a trait with a single type parameter Type class instances
6. Typeclass Typeclass trait HtmlWriter[A] { def write(value: A): String } implicit val intWriter:HtmlWriter[Int] = new HtmlWriter[Int] { override def write(value: Int): String = value.toString } implicit val stringWriter:HtmlWriter[String] = new HtmlWriter[String] { override def write(value: String): String = value.replaceAll("<", "&lt;").replaceAll(">", "&gt;") } implicit def boxWriter[A]:HtmlWriter[Box[A]] = new HtmlWriter[Box[A]] { override def write(value: Box[A]): String = ??? } The type class itself is a trait with a single type parameter Type class instances Extra type class instances
7. Typeclass Typeclass trait HtmlWriter[A] { def write(value: A): String } implicit val intWriter:HtmlWriter[Int] = new HtmlWriter[Int] { override def write(value: Int): String = value.toString } implicit val stringWriter:HtmlWriter[String] = new HtmlWriter[String] { override def write(value: String): String = value.replaceAll("<", "&lt;").replaceAll(">", "&gt;") } implicit def boxWriter[A]:HtmlWriter[Box[A]] = new HtmlWriter[Box[A]] { override def write(value: Box[A]): String = ??? } The type class itself is a trait with a single type parameter Type class instances Extra type class instances What are typeclasses? | Scala Haskell
8. Semigroup Semigroup A semigroup is a binary associative operation
9. Semigroup Semigroup A semigroup is a binary associative operation trait Semigroup[A] { /** * Associativity means: * combine(x, combine(y, z)) = combine(combine(x, y), z) */ def combine(x: A, y: A): A // append | compose | whatever } implicit val intAdditionSemigroup: Semigroup[Int] = new Semigroup[Int] { override def combine(x: Int, y: Int): Int = x + y }
10. Semigroup Semigroup A semigroup is a binary associative operation trait Semigroup[A] { /** * Associativity means: * combine(x, combine(y, z)) = combine(combine(x, y), z) */ def combine(x: A, y: A): A // append | compose | whatever } implicit val intAdditionSemigroup: Semigroup[Int] = new Semigroup[Int] { override def combine(x: Int, y: Int): Int = x + y } Semigroup.combineAll[Int](100, 50) //150 def combineAll[A](x: A, y: A)(implicit semigroup: Semigroup[A]): A = semigroup.combine(x, y)
11. Semigroup Semigroup A semigroup is a binary associative operation trait Semigroup[A] { /** * Associativity means: * combine(x, combine(y, z)) = combine(combine(x, y), z) */ def combine(x: A, y: A): A // append | compose | whatever } implicit val intAdditionSemigroup: Semigroup[Int] = new Semigroup[Int] { override def combine(x: Int, y: Int): Int = x + y } Semigroup.combineAll[Int](100, 50) //150 List(1, 2, 3).foldLeft(0)(Semigroup.combineAll) //6 def combineAll[A](x: A, y: A)(implicit semigroup: Semigroup[A]): A = semigroup.combine(x, y)
12. Semigroup Semigroup A semigroup is a binary associative operation trait Semigroup[A] { /** * Associativity means: * combine(x, combine(y, z)) = combine(combine(x, y), z) */ def combine(x: A, y: A): A // append | compose | whatever } implicit val intAdditionSemigroup: Semigroup[Int] = new Semigroup[Int] { override def combine(x: Int, y: Int): Int = x + y } Semigroup.combineAll[Int](100, 50) //150 List(1, 2, 3).foldLeft(0)(Semigroup.combineAll) //6 def reduce[A](as: List[A])(implicit semigroup: Semigroup[A]): A = as.foldLeft(/* ??? */)(semigroup.combine) // We can't generalize the previous function def combineAll[A](x: A, y: A)(implicit semigroup: Semigroup[A]): A = semigroup.combine(x, y)
13. Monoid Monoid A monoid is a binary associative operation with an identity trait Monoid[A] extends Semigroup[A] { /** * Identity means: * combine(x, empty) = combine(empty, x) = x */ def empty: A } implicit val intMonoid:Monoid[Int] = new Monoid[Int] { def combine(x: Int, y: Int): Int = x + y def empty: Int = 0 }
14. Monoid Monoid A monoid is a binary associative operation with an identity trait Monoid[A] extends Semigroup[A] { /** * Identity means: * combine(x, empty) = combine(empty, x) = x */ def empty: A } implicit val intMonoid:Monoid[Int] = new Monoid[Int] { def combine(x: Int, y: Int): Int = x + y def empty: Int = 0 } def combineAll[A](as: List[A])(implicit monoid: Monoid[A]): A = as.foldLeft(monoid.empty)(monoid.combine)
15. Monoid Monoid A monoid is a binary associative operation with an identity trait Monoid[A] extends Semigroup[A] { /** * Identity means: * combine(x, empty) = combine(empty, x) = x */ def empty: A } implicit val intMonoid:Monoid[Int] = new Monoid[Int] { def combine(x: Int, y: Int): Int = x + y def empty: Int = 0 } def combineAll[A](as: List[A])(implicit monoid: Monoid[A]): A = as.foldLeft(monoid.empty)(monoid.combine) Monoid.combineAll(List(1,2,3))
16. Monoid Monoid A monoid is a binary associative operation with an identity trait Monoid[A] extends Semigroup[A] { /** * Identity means: * combine(x, empty) = combine(empty, x) = x */ def empty: A } implicit val intMonoid:Monoid[Int] = new Monoid[Int] { def combine(x: Int, y: Int): Int = x + y def empty: Int = 0 } def combineAll[A](as: List[A])(implicit monoid: Monoid[A]): A = as.foldLeft(monoid.empty)(monoid.combine) Monoid.combineAll(List(1,2,3)) case class Times(data: Map[String, FiniteDuration]) implicit val timesMonoid: Monoid[Times] = new Monoid[Times] { def combine(x: Times, y: Times): Times = Times(x.data ++ y.data) def empty: Times = Times(Map.empty) } Example
17. Functor Functor A functor is a way to apply a function over or around some structure that we don’t want to alter it
18. Functor Functor trait Functor[F[_]] { /** * Identity: Option(identity(1)) == identity(Option(1)) * Composition: F[f o g] = F[f] o F[g] */ def map[A, B](fa: F[A])(f: A => B): F[B] } implicit val optionFunctor: Functor[Option] = new Functor[Option] { def map[A, B](fa: Option[A])(f: A => B): Option[B] = fa match { case None => None case Some(a) => Some(f(a)) } } A functor is a way to apply a function over or around some structure that we don’t want to alter it
19. Functor Functor trait Functor[F[_]] { /** * Identity: Option(identity(1)) == identity(Option(1)) * Composition: F[f o g] = F[f] o F[g] */ def map[A, B](fa: F[A])(f: A => B): F[B] } implicit val optionFunctor: Functor[Option] = new Functor[Option] { def map[A, B](fa: Option[A])(f: A => B): Option[B] = fa match { case None => None case Some(a) => Some(f(a)) } } A functor is a way to apply a function over or around some structure that we don’t want to alter it def mapOption[A, B](as: Option[A]) (f: A => B) (implicit functor: Functor[Option]): Option[B] = functor.map(as)(f)
20. Functor Functor Example
21. Functor Functor Functor.map(Some(5))(_ + 3) Example
22. Functor Functor Functor.map(Some(5))(_ + 3) Example
23. Functor Functor Functor.map(Some(5))(_ + 3) Example
24. Functor Functor Functor.map(Some(5))(_ + 3) Example Functor.map(None)(_ + 3)
25. Functor Functor Functor.map(Some(5))(_ + 3) Example Functor.map(None)(_ + 3)
26. Functor Functor Using a List
27. Functor Functor Using a List implicit val listFunctor: Functor[List] = new Functor[List] { def map[A, B](fa: List[A])(f: A => B): List[B] = fa match { case Nil => Nil case a :: as => f(a) :: map(as)(f) } }
28. Functor Functor Functor.map(List(2, 8, 12))(_ + 3) Using a List implicit val listFunctor: Functor[List] = new Functor[List] { def map[A, B](fa: List[A])(f: A => B): List[B] = fa match { case Nil => Nil case a :: as => f(a) :: map(as)(f) } } Example
29. Functor Functor Functor.map(List(2, 8, 12))(_ + 3) Using a List implicit val listFunctor: Functor[List] = new Functor[List] { def map[A, B](fa: List[A])(f: A => B): List[B] = fa match { case Nil => Nil case a :: as => f(a) :: map(as)(f) } } Example
30. Applicative Applicative Applicative is a way to apply a wrapped function over or around some structure that we don’t want to alter it
31. Applicative Applicative Applicative is a way to apply a wrapped function over or around some structure that we don’t want to alter it trait Applicative[F[_]] extends Functor[F] { def ap[A, B](ff: F[A => B])(fa: F[A]): F[B] def pure[A](a: A): F[A] def map[A, B](fa: F[A])(f: A => B): F[B] = ap(pure(f))(fa) }
32. Applicative Applicative Applicative is a way to apply a wrapped function over or around some structure that we don’t want to alter it trait Applicative[F[_]] extends Functor[F] { def ap[A, B](ff: F[A => B])(fa: F[A]): F[B] def pure[A](a: A): F[A] def map[A, B](fa: F[A])(f: A => B): F[B] = ap(pure(f))(fa) } implicit val optionApplicative = new Applicative[Option] { def ap[A, B](ff: Option[A => B])(fa: Option[A]): Option[B] = (ff, fa) match { case (Some(f), Some(a)) => Some(f(a)) case _ => None } def pure[A](a: A): Option[A] = Option(a) }
33. Applicative Applicative Applicative is a way to apply a wrapped function over or around some structure that we don’t want to alter it trait Applicative[F[_]] extends Functor[F] { def ap[A, B](ff: F[A => B])(fa: F[A]): F[B] def pure[A](a: A): F[A] def map[A, B](fa: F[A])(f: A => B): F[B] = ap(pure(f))(fa) } implicit val optionApplicative = new Applicative[Option] { def ap[A, B](ff: Option[A => B])(fa: Option[A]): Option[B] = (ff, fa) match { case (Some(f), Some(a)) => Some(f(a)) case _ => None } def pure[A](a: A): Option[A] = Option(a) } def apOption[A, B](opt: Option[A]) (f: Option[A => B]) (implicit functor: Applicative[Option]): Option[ optionApplicative.ap(f)(opt)
34. Applicative Applicative Example
35. Applicative Applicative apOption(Some(2))(Some(i => s"The number is: ${i.toString}")) // Some(The number is: 2) Example
36. Applicative Applicative apOption(Some(2))(Some(i => s"The number is: ${i.toString}")) // Some(The number is: 2) Example
37. Applicative Applicative apOption(Some(2))(Some(i => s"The number is: ${i.toString}")) // Some(The number is: 2) Example
38. Applicative Applicative apOption(Some(2))(Some(i => s"The number is: ${i.toString}")) // Some(The number is: 2) Example apOption(None)(Some(i => s"The number is: ${i.toString}")) // None
39. Applicative Applicative apOption(Some(2))(Some(i => s"The number is: ${i.toString}")) // Some(The number is: 2) Example apOption(None)(Some(i => s"The number is: ${i.toString}")) // None
40. Monad Monad Monad introduces a way to append two structure sequentially and the results of previous computations may influence what computations to run next
41. Monad Monad Monad introduces a way to append two structure sequentially and the results of previous computations may influence what computations to run next trait Monad[F[_]] extends Applicative[F] { def flatMap[A, B](fa: F[A])(f: A => F[B]): F[B] def ap[A, B](ff: F[A => B])(fa: F[A]): F[B] = flatMap(ff)(x => map(fa)(x)) }
42. Monad Monad Monad introduces a way to append two structure sequentially and the results of previous computations may influence what computations to run next trait Monad[F[_]] extends Applicative[F] { def flatMap[A, B](fa: F[A])(f: A => F[B]): F[B] def ap[A, B](ff: F[A => B])(fa: F[A]): F[B] = flatMap(ff)(x => map(fa)(x)) } val optionMonad = new Monad[Option] { def flatMap[A, B](fa: Option[A])(f: A => Option[B]): Option[B] = fa match { case None => None case Some(a) => f(a) } def pure[A](a: A): Option[A] = Some(a) }
43. Monad Monad Example
44. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example
45. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None }
46. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None }
47. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
48. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
49. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
50. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
51. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
52. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
53. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
54. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
55. Monad Monad implicit class OptionMonad[A](opt: Option[A]) { def flatMap[B](f: A => Option[B]): Option[B] = optionMonad.flatMap(opt)(f) } Example def half(number: Int): Option[Int] = { if (number % 2 == 0) Some(number / 2) else None } val result = Some(6) .flatMap(half) .flatMap(half) .flatMap(half)
56. Monads Everywhere Monads Everywhere
57. Monads Everywhere Monads Everywhere
58. Monads Everywhere Monads Everywhere Option Future List Try Either
59. Monad Transformers Monad Transformers
60. Monad Transformers Monad Transformers def compose[M[_]: Monad, N[_]: Monad]: Monad[M[N[_]]] = Monads do not compose
61. Monad Transformers Monad Transformers def compose[M[_]: Monad, N[_]: Monad]: Monad[M[N[_]]] = Monads do not compose val greeting: Option[String] = Some("Hello") val firstName: Option[String] = Some("John") val lastName: Option[String] = Some("Doe") for { g <- greetingOption f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" Same monads
62. Monad Transformers Monad Transformers def compose[M[_]: Monad, N[_]: Monad]: Monad[M[N[_]]] = Monads do not compose val greetingFuture: Future[String] = Future.successful("Hello") val firstNameOption: Option[String] = Some("John") val lastNameOption: Option[String] = Some("Doe") for { g <- greetingFuture f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" val greeting: Option[String] = Some("Hello") val firstName: Option[String] = Some("John") val lastName: Option[String] = Some("Doe") for { g <- greetingOption f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" Same monads Different monads
63. Monad Transformers Monad Transformers def compose[M[_]: Monad, N[_]: Monad]: Monad[M[N[_]]] = Monads do not compose val greetingFuture: Future[String] = Future.successful("Hello") val firstNameOption: Option[String] = Some("John") val lastNameOption: Option[String] = Some("Doe") for { g <- greetingFuture f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" val greeting: Option[String] = Some("Hello") val firstName: Option[String] = Some("John") val lastName: Option[String] = Some("Doe") for { g <- greetingOption f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" Same monads Different monads
64. Monad Transformers Monad Transformers def compose[M[_]: Monad, N[_]: Monad]: Monad[M[N[_]]] = Monads do not compose val greetingFuture: Future[String] = Future.successful("Hello") val firstNameOption: Option[String] = Some("John") val lastNameOption: Option[String] = Some("Doe") for { g <- greetingFuture f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" val greeting: Option[String] = Some("Hello") val firstName: Option[String] = Some("John") val lastName: Option[String] = Some("Doe") for { g <- greetingOption f <- firstNameOption l <- lastNameOption } yield s"$g $f $l" Same monads Monads (in general) do not compose Different monads
65. Monad Transformers Monad Transformers
66. Monad Transformers Monad Transformers Monads do not compose generically.
67. Monad Transformers Monad Transformers Monads do not compose generically. Gives us a way to stack two monads on top of each other and have them act a single monad.
68. Monad Transformers Monad Transformers Monads do not compose generically. Gives us a way to stack two monads on top of each other and have them act a single monad. EitherT[F[_], A, B] ^ |__ ANY MONAD!
69. Monad Transformers Monad Transformers Monads do not compose generically. Gives us a way to stack two monads on top of each other and have them act a single monad. Future[Either[Throwable, String]] => EitherT[Future, Throwable, String] EitherT[F[_], A, B] ^ |__ ANY MONAD!
70. Monad Transformers Monad Transformers Monads do not compose generically. Instead of nesting Gives us a way to stack two monads on top of each other and have them act a single monad. Future[Either[Throwable, String]] => EitherT[Future, Throwable, String] EitherT[F[_], A, B] ^ |__ ANY MONAD!
71. Monad Transformers Monad Transformers Monads do not compose generically. Instead of nesting We have a stack Gives us a way to stack two monads on top of each other and have them act a single monad. Future[Either[Throwable, String]] => EitherT[Future, Throwable, String] EitherT[F[_], A, B] ^ |__ ANY MONAD!
72. Monad Transformers Monad Transformers Monads do not compose generically. Instead of nesting We have a stack Gives us a way to stack two monads on top of each other and have them act a single monad. Future[Either[Throwable, String]] => EitherT[Future, Throwable, String] There exists a transformer equivalent for every monad instance Monad Transformers Monad Transformers | | Scala Scala Haskell Haskell EitherT[F[_], A, B] ^ |__ ANY MONAD!
73. Monad Transformers Monad Transformers
74. Monad Transformers Monad Transformers Example val greetingEither: Future[Either[Throwable, String]] = Future.successful(Either.right("Hello")) val firstNameFuture: Future[String] = Future.successful("Jane") val lastNameOption: Option[String] = Some("Doe") def greet: Future[Either[Throwable, String]] = { val result: EitherT[Future, Throwable, String] = for { g <- EitherT(greetingEither) f <- EitherT.liftF(firstNameFuture) l <- EitherT.fromOption[Future](lastNameOption, new RuntimeException("lastName not found")) } yield s"$g $f $l" result.value // => EitherT[Future, Throwable, String] => Future[Either[Throwable, String]] }
75. Monad Transformers Monad Transformers Example val greetingEither: Future[Either[Throwable, String]] = Future.successful(Either.right("Hello")) val firstNameFuture: Future[String] = Future.successful("Jane") val lastNameOption: Option[String] = Some("Doe") def greet: Future[Either[Throwable, String]] = { val result: EitherT[Future, Throwable, String] = for { g <- EitherT(greetingEither) f <- EitherT.liftF(firstNameFuture) l <- EitherT.fromOption[Future](lastNameOption, new RuntimeException("lastName not found")) } yield s"$g $f $l" result.value // => EitherT[Future, Throwable, String] => Future[Either[Throwable, String]] }
76. Monad Transformers Monad Transformers Example val greetingEither: Future[Either[Throwable, String]] = Future.successful(Either.right("Hello")) val firstNameFuture: Future[String] = Future.successful("Jane") val lastNameOption: Option[String] = Some("Doe") def greet: Future[Either[Throwable, String]] = { val result: EitherT[Future, Throwable, String] = for { g <- EitherT(greetingEither) f <- EitherT.liftF(firstNameFuture) l <- EitherT.fromOption[Future](lastNameOption, new RuntimeException("lastName not found")) } yield s"$g $f $l" result.value // => EitherT[Future, Throwable, String] => Future[Either[Throwable, String]] } case class AwesomeError(msg: String) type ResultT[F[_], A] = EitherT[F, AwesomeError, A] type FutureResult[A] = ResultT[Future, A]
77. Monad Transformers Monad Transformers Example val greetingEither: Future[Either[Throwable, String]] = Future.successful(Either.right("Hello")) val firstNameFuture: Future[String] = Future.successful("Jane") val lastNameOption: Option[String] = Some("Doe") def greet: Future[Either[Throwable, String]] = { val result: EitherT[Future, Throwable, String] = for { g <- EitherT(greetingEither) f <- EitherT.liftF(firstNameFuture) l <- EitherT.fromOption[Future](lastNameOption, new RuntimeException("lastName not found")) } yield s"$g $f $l" result.value // => EitherT[Future, Throwable, String] => Future[Either[Throwable, String]] } case class AwesomeError(msg: String) type ResultT[F[_], A] = EitherT[F, AwesomeError, A] type FutureResult[A] = ResultT[Future, A] def getUser(id:String):FutureResult[User] def canBeUpdated(user:User):FutureResult[User] def update(user:User):FutureResult[User]
78. Monad Transformers Monad Transformers Example val greetingEither: Future[Either[Throwable, String]] = Future.successful(Either.right("Hello")) val firstNameFuture: Future[String] = Future.successful("Jane") val lastNameOption: Option[String] = Some("Doe") def greet: Future[Either[Throwable, String]] = { val result: EitherT[Future, Throwable, String] = for { g <- EitherT(greetingEither) f <- EitherT.liftF(firstNameFuture) l <- EitherT.fromOption[Future](lastNameOption, new RuntimeException("lastName not found")) } yield s"$g $f $l" result.value // => EitherT[Future, Throwable, String] => Future[Either[Throwable, String]] } case class AwesomeError(msg: String) type ResultT[F[_], A] = EitherT[F, AwesomeError, A] type FutureResult[A] = ResultT[Future, A] def getUser(id:String):FutureResult[User] def canBeUpdated(user:User):FutureResult[User] def update(user:User):FutureResult[User] def updateUser(user: User):FutureResult[User] = for { u <- getUser(user.id) _ <- canBeUpdated(u) updatedUser <- updateUser(u) } yield updatedUser Better?
79. Show me the Money! Show me the Money!
80. Show me the Money! Show me the Money! Monad! Monad!
81. Show me the Money! Show me the Money! Monad! Monad! trait UserStore { def findUser(id: Long): Future[Either[Throwable, User]] def canBeUpdated(user: User): Future[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): Future[Either[Throwable, User]] } class LoyaltyPoints(store: UserStore) { def addPoints(userId: Long, pointsToAdd: Int): Future[Either[Throwable, User]] = { val result: Future[Either[Throwable, User]] = for { user <- store.findUser(userId) _ <- user.right.map(store.canBeUpdated).left.map(Future.failed).merge updatedUser <- user.right.map(store.updateUser(_)(pointsToAdd)).left.map(Future.failed). } yield updatedUser result } } Api V0
82. Show me the Money! Show me the Money! Monad! Monad! trait UserStore { def findUser(id: Long): Future[Either[Throwable, User]] def canBeUpdated(user: User): Future[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): Future[Either[Throwable, User]] } class LoyaltyPoints(store: UserStore) { def addPoints(userId: Long, pointsToAdd: Int): Future[Either[Throwable, User]] = { val result: Future[Either[Throwable, User]] = for { user <- store.findUser(userId) _ <- user.right.map(store.canBeUpdated).left.map(Future.failed).merge updatedUser <- user.right.map(store.updateUser(_)(pointsToAdd)).left.map(Future.failed). } yield updatedUser result } } Api V0
83. Show me the Monad! Show me the Monad!
84. Show me the Monad! Show me the Monad! trait UserStore { def findUser(id: Long): Future[Either[Throwable, User]] def canBeUpdated(user: User): Future[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): Future[Either[Throwable, User]] } class LoyaltyPoints(store: UserStore) { def addPoints(userId: Long, pointsToAdd: Int): Future[Either[Throwable, User]] = { val result: EitherT[Future, Throwable, User] = for { user <- EitherT(store.findUser(userId)) _ <- EitherT(store.canBeUpdated(user)) updatedUser <- EitherT(store.updateUser(user)(pointsToAdd)) } yield updatedUser result.value // EitherT[Future, Throwable, User] => Future[Either[Throwable, User]] } } Api V1
85. Show me the Monad! Show me the Monad! trait UserStore { def findUser(id: Long): Future[Either[Throwable, User]] def canBeUpdated(user: User): Future[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): Future[Either[Throwable, User]] } class LoyaltyPoints(store: UserStore) { def addPoints(userId: Long, pointsToAdd: Int): Future[Either[Throwable, User]] = { val result: EitherT[Future, Throwable, User] = for { user <- EitherT(store.findUser(userId)) _ <- EitherT(store.canBeUpdated(user)) updatedUser <- EitherT(store.updateUser(user)(pointsToAdd)) } yield updatedUser result.value // EitherT[Future, Throwable, User] => Future[Either[Throwable, User]] } } Api V1 So far so good, but what about description and interpretation?
86. Show me the Monad! Show me the Monad!
87. Show me the Monad! Show me the Monad! trait UserStoreAlg[F[_]] { def findUser(id: Long): F[Either[Throwable, User]] def canBeUpdated(user: User): F[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): F[Either[Throwable, User]] } class LoyaltyPoints[F[_]](store: UserStoreAlg[F])(implicit M: Monad[F]) { def addPoints(userId: Long, pointsToAdd: Int): F[Either[Throwable, User]] = { val result: EitherT[F, Throwable, User] = for { user <- EitherT(store.findUser(userId)) _ <- EitherT(store.canBeUpdated(user)) updatedUser <- EitherT(store.updateUser(user)(pointsToAdd)) } yield updatedUser result.value // EitherT[F, Throwable, User] => F[Either[Throwable, User]] } } Api v2
88. Show me the Monad! Show me the Monad! trait UserStoreAlg[F[_]] { def findUser(id: Long): F[Either[Throwable, User]] def canBeUpdated(user: User): F[Either[Throwable, Boolean]] def updateUser(user: User)(pointsToAdd: Int): F[Either[Throwable, User]] } class LoyaltyPoints[F[_]](store: UserStoreAlg[F])(implicit M: Monad[F]) { def addPoints(userId: Long, pointsToAdd: Int): F[Either[Throwable, User]] = { val result: EitherT[F, Throwable, User] = for { user <- EitherT(store.findUser(userId)) _ <- EitherT(store.canBeUpdated(user)) updatedUser <- EitherT(store.updateUser(user)(pointsToAdd)) } yield updatedUser result.value // EitherT[F, Throwable, User] => F[Either[Throwable, User]] } } Api v2 so, it smells like we have to put EitherT everywhere, doesn't it?
89. Show me the Monad! Show me the Monad!
90. Show me the Monad! Show me the Monad! case class ServiceError(msg: String) type ResultOrError[F[_], A] = EitherT[F, ServiceError, A] trait UserStoreAlg[F[_]] { def findUser(id: Long): ResultOrError[F, User] def canBeUpdated(user: User): ResultOrError[F, Boolean] def updateUser(user: User)(pointsToAdd: Int): ResultOrError[F, User] } class LoyaltyPoints[F[_]](store: UserStoreAlg[F])(implicit M: Monad[F]) { def addPoints(userId: Long, pointsToAdd: Int): F[Either[ServiceError, User]] = { val result: ResultOrError[F, User] = for { user <- store.findUser(userId) _ <- store.canBeUpdated(user) updatedUser <- store.updateUser(user)(pointsToAdd) } yield updatedUser result.value // EitherT[F, ServiceError, User] => F[Either[ServiceError, User]] } } Api v3
91. Show me the Monad! Show me the Monad! case class ServiceError(msg: String) type ResultOrError[F[_], A] = EitherT[F, ServiceError, A] trait UserStoreAlg[F[_]] { def findUser(id: Long): ResultOrError[F, User] def canBeUpdated(user: User): ResultOrError[F, Boolean] def updateUser(user: User)(pointsToAdd: Int): ResultOrError[F, User] } class LoyaltyPoints[F[_]](store: UserStoreAlg[F])(implicit M: Monad[F]) { def addPoints(userId: Long, pointsToAdd: Int): F[Either[ServiceError, User]] = { val result: ResultOrError[F, User] = for { user <- store.findUser(userId) _ <- store.canBeUpdated(user) updatedUser <- store.updateUser(user)(pointsToAdd) } yield updatedUser result.value // EitherT[F, ServiceError, User] => F[Either[ServiceError, User]] } } Api v3 and now to run the code...
92. Show me the Monad! Show me the Monad!
93. Show me the Monad! Show me the Monad! trait FutureInterpreter extends UserStoreAlg[Future] { override def findUser(id: Long): EitherT[Future, ServiceError, User] = EitherT(Future.successful(Either.right(User(1L, "awesome@fp.com", 1000)))) override def canBeUpdated(user: User): ResultOrError[Future, Boolean] = EitherT(Future.successful(Either.right(true))) override def updateUser(user: User)(pointsToAdd: Int): ResultOrError[Future, User] = EitherT(Future.successful( Either.right(user.copy(loyaltyPoints = user.loyaltyPoints + pointsToAdd)))) } The Interpreter
94. Show me the Monad! Show me the Monad! trait FutureInterpreter extends UserStoreAlg[Future] { override def findUser(id: Long): EitherT[Future, ServiceError, User] = EitherT(Future.successful(Either.right(User(1L, "awesome@fp.com", 1000)))) override def canBeUpdated(user: User): ResultOrError[Future, Boolean] = EitherT(Future.successful(Either.right(true))) override def updateUser(user: User)(pointsToAdd: Int): ResultOrError[Future, User] = EitherT(Future.successful( Either.right(user.copy(loyaltyPoints = user.loyaltyPoints + pointsToAdd)))) } The Interpreter val interpreter:FutureInterpreter = new FutureInterpreter{} val result: Future[Either[ServiceError, User]] = new LoyaltyPoints(interpreter) .addPoints(1, 100) // wait the future Await.result(result, 1 second).foreach(println) // User(1,awesome@fp.com,1100)
95. FP in the JVM FP in the JVM Scalaz - scala Cats- scala Arrow- kotlin Cyclops-react - java vavr.io - java
96. Resources Resources Functors, Applicatives and Monads In Pictures Functional Programming in Scala Learn You a Haskell for Great Good! Haskell Programming from first principles Cats Scalaz Category Theory for Programmers Demystifying Functional Programming (code examples)
97. Questions? Questions?