Unlocking the Power of Arrow 2.0

We’ll dive into Arrow 2.0, a transformative update to Kotlin's functional programming landscape. Join the maintainer for an enlightening tour of Arrow 2.0's advancements, including typed error handling for safer code, seamless integration with Kotlin Coroutines for concurrent programming, resilient programming techniques, and elegant approaches to working with immutable data structures. Arrow 2.0 represents a significant milestone in our journey to make Functional Programming in Kotlin truly idiomatic, simple, and elegant to empower developers to write expressive, efficient, and reliable code. Whether you're a seasoned functional programmer or a Kotlin enthusiast, this session promises practical insights into mastering Arrow 2.0 and navigating the functional frontier in Kotlin.

Transcript

1. Unlocking the Power of Arrow 2.0 Simon Vergauwen @vergauwen_simon
2. ΛRROW Who am I? nomisRev vergauwen_simon vergauwensimon arrow-kt.io
3. ΛRROW
4. ΛRROW AutoClose
5. AutoClose DataSource(config).use { dataSource - > Tracing().use { tracing - > / / use dataSource & tracing } } Why? ΛRROW
6. AutoClose DataSource(config).use { dataSource > Tracing().use { tracing > / } } autoCloseScope { val dataSource = install(DataSource(config)) val tracing = install(Tracing()) // use dataSource & tracing } Why? ΛRROW
7. AutoClose fun <A> runBlocking( block: suspend CoroutineScope.() -> A ): A How? ΛRROW
8. AutoClose fun <A> runBlocking( block: suspend CoroutineScope.() > ): A How? inline fun <A> autoCloseScope( block: AutoCloseScope.() -> A ): A ΛRROW
9. AutoCloseScope interface AutoCloseScope { fun <A : AutoCloseable> install(autoCloseable: A): A } How? ΛRROW
10. AutoCloseScope interface AutoCloseScope { fun <A : AutoCloseable> install(autoCloseable: A): A } ΛRROW Bring your own types!
11. AutoCloseScope interface AutoCloseScope { fun <A : AutoCloseable> install(autoCloseable: A): A } ‣Success: null ‣Cancelled: CancellationException ‣Failed: Throwable Bring your own types! ΛRROW fun <A> autoClose( acquire: () -> A, release: (A, Throwable?) -> Unit ): A
12. AutoCloseScope autoCloseScope { val dataSource = install(DataSource(config)) val database = install(Tracing()) // use database & tracing } DSL ΛRROW
13. AutoCloseScope Same guarantees as AutoCloseable.use Imperative code, no nesting Bring your own types! Conclusion ΛRROW
14. ΛRROW ‣ Raise ‣ Either ‣ NonEmptyList & Set ‣ Ior ‣ Tuple (4-9) ‣ Option AutoClose
15. ΛRROW by CashApp AutoClose
16. Typed Error Handling ΛRROW Why? class UserExists(message: String): RuntimeException(message) fun insertUser(username: String): User = throw UserExists("User $username already exists.”)
17. Typed Error Handling ΛRROW Why? try { insertUser(1) } catch (e: UserExists) { recover(e) }
18. Typed Error Handling ΛRROW Why? try { insertUser(1) } catch (e: UserExists) { recover(e) }
19. Typed Error Handling interface Raise<in Error> { fun raise(r: Error): Nothing / / bind, ensure, ensureNotNull, etc. } ΛRROW DSL
20. Typed Error Handling ΛRROW How? data class UserExists(val username: String) fun Raise<UserExists>.insertUser(username: String): User = raise(UserExists(username))
21. Typed Error Handling ΛRROW Context Parameters data class UserExists(val username: String) context(Raise<UserExists>) fun insertUser(username: String): User = raise(UserExists(username))
22. Typed Error Handling inline fun <Error, A> recover( block: Raise<Error>.() -> A, recover: (error: Error) -> A, ): A ΛRROW DSL
23. Typed Error Handling fun Raise<UserExists>.insertUser(username: String): User = raise(UserExists(username)) ΛRROW recover({ // Raise<UserExists>.() -> User insertUser(“nomisrev") }) { error: UserExists -> null } DSL
24. When truly exceptional Fatal exception ( ThreadDeath, VirtualMachineError, …) Unexpected exception, non-business related Type-safety helps protect what you care about Prevent forgetting about business errors Typed Error Handling ΛRROW FAQ : Exception vs Typed Errors?
25. Typed Error Handling ΛRROW Example: Exception & Typed context(Raise<UserExists>) suspend fun insertUser(username: String): User = try { queries.insert(username) } catch (e: SQLException) { }
26. Typed Error Handling ΛRROW Example: Exception & Typed context(Raise<UserExists>) suspend fun insertUser(username: String): User = try { queries.insert(username) } catch (e: SQLException) { if (e.isUniqueViolation()) raise(UserExists(username)) else throw e }
27. Custom models (sealed hierarchies) Use case Layering Context Parameters Typed Error Handling ΛRROW FAQ : How to model errors
28. Modelling errors: Sealed hierarchy sealed interface UserError data class UserExists(val username: String): UserError data object UsernameMissing : UserError ΛRROW Use-case
29. Modelling errors: Sealed hierarchy sealed interface UserError data class UserExists(val username: String): UserError data object UsernameMissing : UserError ΛRROW Use-case context(Raise<UsernameMissing>) fun HttpRequest.username(): String
30. Modelling errors: Sealed hierarchy sealed interface PaymentError data object ExpiredCard : PaymentError data object InsufficientFunds : PaymentError ΛRROW Use-case
31. Modelling errors: Sealed hierarchy sealed interface PaymentError data object ExpiredCard : PaymentError data object InsufficientFunds : PaymentError ΛRROW Use-case context(Raise<PaymentError>) fun User.receivePayment(): Unit
32. Modelling errors: Sealed hierarchy sealed interface UserRegistrationError sealed interface UserError: UserRegistrationError sealed interface PaymentError : UserRegistrationError ΛRROW ( Service) Layering
33. Context Parameters suspend fun Raise<UserRegistrationError>.route( request: HttpRequest ): HttpResponse { } ΛRROW ( Service) Layering
34. Context Parameters suspend fun Raise<UserRegistrationError>.route( request: HttpRequest ): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED } ΛRROW ( Service) Layering
35. Context Parameters context(Raise<UserExists>, Raise<PaymentError>) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED } ΛRROW Independent errors
36. Typed Error Handling ΛRROW Why Raise DSL? A? ≈ Option<A > suspend () -> A ≈ Mono<A > , Single<A > , … suspend FlowCollector<A > .() -> Unit Context Parameters ( KEEP - 367 )
37. Typed Error Handling suspend fun refresh(redis: Redis, azure: Azure, custom: Custom) { val message = azure.reactor().awaitSingle() val cache = redis.future().await() delay(100) val res = custom.async().value() TODO() } ΛRROW Combine all the things!
38. Typed Error Handling context(Raise<String>) fun everything() { val x = 1.right().bind() val y = ensureNotNull(2) { "Value was null" } ensure(y >= 0) { "y should be >= 0" } val z = quiverOutcome().value() TODO() } ΛRROW Combine all the things!
39. context(Raise<UserExists>) fun transaction(): User = transaction { queries.insertUser("nomisrev") } ΛRROW Typed Error Handling Raise = CancellationException
40. Typed Error Handling ΛRROW Compile-time check unhappy path Bring your own types! Automatic interoperability with ecosystem Elegantly fits into language Many different error handling strategies Conclusion
41. ΛRROW
42. ΛRROW Resilience Fx Coroutines Collectors STM Resource
43. Schedule var count = 0 var user: User? = null while (isActive) { try { result = insertUser(name) break } catch (e: SQLException) { if (count >= MAX_RETRIES) throw e else delay(BASE_DELAY * 2.0.pow(count ++ )) } } return user ! ! ΛRROW Why?
44. Schedule Schedule.exponential<SQLException>(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .retry { insertUser(name) } ΛRROW How?
45. Schedule Schedule.exponential<SQLException>(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .retry { insertUser(name) } ΛRROW Avoid overlapping retries
46. Schedule Schedule.exponential<SQLException>(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .doWhile { e: SQLException, _ -> e.isRetryable() } .retry { insertUser(name) } ΛRROW Retry while error is retryable
47. Schedule Schedule.exponential<PaymentError>(BASE_DELAY) .and(Schedule.recurs(MAX_RETRIES)) .jittered() .doWhile { e: PaymentError, _ -> e.isRetryable() } .retryRaise { raise(ExpiredCard) } ΛRROW Retrying Raise
48. Schedule Schedule.recurs<HttpResponse>(5) .doUntil { response, _ -> response.isCorrect() } .repeat { client.get("my-url") } ΛRROW Repeat 5 times, or until correct result
49. Schedule Split Schedule from logic Allows easily building complex Schedules Reuse for repeating, and retrying BONUS : Easy to replace with testing ΛRROW Conclusion
50. SagaScope ΛRROW Why? context(Raise<UserRegistrationError>) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED }
51. SagaScope ΛRROW Why? context(Raise<UserExists>, SagaScope) suspend fun insertUserOrRollback( username: String ): User
52. SagaScope ΛRROW Why? context(Raise<UserExists>, SagaScope) suspend fun insertUserOrRollback( username: String ): User = saga({ insertUser(username) }) { user -> deleteUser(user) }
53. SagaScope ΛRROW Why? context(Raise<UserRegistrationError>) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUserOrRollback(name) user.receivePayment() return HttpResponse.OK }
54. SagaScope ΛRROW Why? context(Raise<UserRegistrationError>) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() saga { val user = insertUserOrRollback(name) user.receivePayment() }.transact() return HttpResponse.OK }
55. SagaScope ΛRROW Why? context(Raise<UserRegistration>, Transaction) suspend fun route(request: HttpRequest): HttpResponse { val name = request.username() val user = insertUser(name) user.receivePayment() return HttpResponse.CREATED }
56. SagaScope ΛRROW Why? fun Routing.premiumUser() = post("/premiumuser/{username}") { recover({ / / Raise<UserRegistrationError>.() - > newSuspendedTransaction { // Transaction.() -> route(call) } }) { error -> handleError(error) } }
57. SagaScope Saga pattern DSL Avoid distributed transactions Builder for transactional systems ΛRROW Conclusion
58. ΛRROW
59. ΛRROW Compose KSP Reflect
60. Optics data class Product(val id: Long, val price: Double) data class OrderItem(val product: Product, val quantity: Int) Why? ΛRROW
61. Optics val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy( product = item.product.copy( price = item.product.price * 0.9 ) ) Why? ΛRROW
62. Optics val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy( product = item.product.copy( price = item.product.price * 0.9 ) ) Why? ΛRROW OrderItem.product.price.modify(item) { it * 1.1 }
63. Optics How? ΛRROW data class Inventory(val items: List<Product>) inventory.copy( items = inventory.items.map { product -> product.copy(price = product.price * 1.1) } )
64. Optics How? ΛRROW Inventory.items.every.price.modify(inventory) { it * 1.1 } data class Inventory(val items: List<Product>) inventory.copy( items = inventory.items.map { product > product.copy(price = product.price * 1.1) } )
65. Optics How? ΛRROW sealed interface ErrorOrProduct data class Success(val product: Product) : ErrorOrProduct data class Failed(val error: Throwable) : ErrorOrProduct when(errorOrProduct) { is Failed -> errorOrProduct is Success - > Success( errorOrProduct.product .copy(price = errorOrProduct.product.price * 0.9) ) }
66. sealed interface ErrorOrProduct data class Success(val product: Product) : ErrorOrProduct data class Failed(val error: Throwable) : ErrorOrProduct when(errorOrProduct) { is Failed > is Success > errorOrProduct.product .copy(price = errorOrProduct.product.price * 1.1) ) } Optics How? ΛRROW ErrorOrProduct.success.product.price.modify(errorOrProduct) { it * 1.1 }
67. Optics Multiple fields ΛRROW val item = OrderItem(Product(id = 1, price = 1.5), quantity = 1) item.copy { OrderItem.product.price.transform { it * 1.1 } OrderItem.quantity.set(5) }
68. Optics Focus on business logic, and paths Simplify complex immutable transformations KEEP - 237 : Immutability and value classes KT - 44653 by Roman Elisarov “Nicer data transformation with KopyKat and Optics” by Alejandro Serrano ΛRROW Conclusion
69. Conclusion What did we learn? ΛRROW Kotlin ❤ DSLs Arrow ❤ Kotlin Small feature specific modules Plug-n-Play: What you want, when you want Much more to learn!
70. ΛRROW slack-chats.kotlinlang.org/c/arrow arrow-kt.io github.com/arrow-kt github.com/nomisRev/KotlinConf2024Example Resources Much more to learn!
72. Thank you, and don’t forget to vote @vergauwen_simon