@vergauwen_simon KotlinConf’23 Amsterdam Arrow’s 2.0 Trajectory Simon Vergauwen Xebia Functional 

ΛRROW Who am I? @vergauwen_simon 

Arrow’s 2.0 Trajectory Arrow’s history Complexity of FP Evolving (OSS) APIs Embracing Language Eco-system ΛRROW 

Arrow’s History Oct 2017 March 2017 FineCinnamon/Katz Dec 2017 arrow-kt June 2017 Kategory March 2013 MarioAriasC/funKTionale Sept 2017 nomisRev/optikal ΛRROW 

ΛRROW Arrow’s History Typeclasses & Higher Kinded Types < 0.12.x 

Complexity of Higher-Kinded Types interface GistsApi { fun publicGistsForUser(username: String): Kind > } interface Logger { fun log(msg: String): Kind } ΛRROW 

Complexity of Higher-Kinded Types fun main() { GistsApi(MonoK.async(), MonoKLogger, HttpClient.newHttpClient()) .publicGistsForUser("nomisRev") .fix() .mono .block() .let( :: println) } ΛRROW 

Complexity of Higher-Kinded Types fun main() { GistsApi(IO.async(), ... ) // Arrow Fx IO GistsApi(DeferredK.async(), ... ) // KotlinX Coroutines Deferred GistsApi(SingleK.async(), ... ) // RxJava Single } ΛRROW 

Arrow’s History Typeclasses & Higher Kinded Types Rehaul of Arrow < 0.12.x 0.12.x ΛRROW 

Complexity of FP Steep learning curve Non-idiomatic Foreign concepts, no language support ΛRROW 

Suspend to the rescue interface GistsApi { suspend fun publicGistsForUser(username: String): List } interface Logger { suspend fun log(msg: String): Unit } ΛRROW 

Suspend to the rescue fun main() { val api = GistApi(Logger.Default, HttpClient.newHttpClient()) runBlocking { api.publicGistsForUser("nomisRev") } mono { api.publicGistsForUser("raulraja") } scope.future { api.publicGistsForUser("serras") } 
 // ... } ΛRROW 

Arrow’s History Typeclasses & Higher Kinded Types Rehaul of Arrow < 0.12.x 0.12.x Suspend & Kotlin Idiomatic 1.x.x ΛRROW 

Wrapper specific code fun GithubUser.process(): Either = if (login.isNotEmpty()) ProcessedUser(this).right() else ProcessingFailed.left() ΛRROW 

Embracing DSLs fun GithubUser.process(): Either = either.eager { ensure(login.isNotEmpty()) { ProcessingFailed } ProcessedUser(this@process) } ΛRROW 

Traverse & co fun List.processAll(): Either> = traverse(GithubUser :: process) ΛRROW 

Traverse = map + bind fun List.processAll(): Either> = either.eager { map { it.process().bind() } } ΛRROW 

Arrow’s History Typeclasses & Higher Kinded Types Rehaul of Arrow < 0.12.x 0.12.x Suspend & Kotlin Idiomatic Small Uniform APIs & learning curve 1.x.x 2.x.x ΛRROW 

DSLs and smart-contracts val res: Either = either { val x: Int? = null ensureNotNull(x) { "X was zero" } x + 1 } ΛRROW 

Idiomatic API names inline fun Either.getOrElse(default: (A) -> B): B 
 
 fun Either.getOrNull(): B? inline fun Either.onRight(action: (right: B) - > Unit): Either fun Either.leftOrNull(): A? inline fun Either.onLeft(action: (left: A) -> Unit): Either ΛRROW 

Context receivers context(Raise) fun GithubUser.process(): ProcessedUser { ensure(login.isNotEmpty()) { ProcessingFailed } return ProcessedUser(this) } 
 context(Raise) fun List.processAll(): List = map { it.process() } ΛRROW 

DSLs everywhere suspend fun ResourceScope.dataSource(): HikariDataSource = closeable { HikariDataSource(HikariConfig()) } suspend fun SagaScope.example(): String = saga({ "Update user" }) { println("Rollback user") } ΛRROW 

Binary Size Arrow 0.11.0 Arrow 1.0.0 Arrow 2.0.0 5000 4000 3000 2000 1000 0 ΛRROW 4,1 MB 3,1 MB 429 KB 

Evolving APIs Community feedback Iteration makes perfect Breaking Changes ΛRROW 

IntelliJ @Deprecated( RedundantAPI + "Prefer the new recover API", ReplaceWith("recover { a -> f(a).bind() }", "arrow.core.recover") ) inline fun Either.handleErrorWith(f: (A) -> Either): Either ΛRROW 

IntelliJ ΛRROW 

OpenRewrite ΛRROW 

OpenRewrite plugins { kotlin("jvm") id("org.openrewrite.rewrite") version "5.39.3" } dependencies { rewrite(“io.arrow-kt:rewrite-arrow:1.0.0-RC3“) } rewrite { activeRecipe("arrow.RaiseRefactor") } ΛRROW 

OpenRewrite ./gradlew :sample:rewriteRun > Task :sample:rewriteRun Validating active recipes Parsing sources from project sample All sources parsed, running active recipes: arrow.RaiseRefactor Changes have been made to sample/src/main/kotlin/org/example/example.kt by: arrow.RaiseRefactor org.openrewrite.java.ChangeMethodName: .. . org.openrewrite.java.ChangeType: . .. Please review and commit the results. ΛRROW 

ΛRROW Large-scale automated refactoring Experimental Kotlin Support Support JVM & commonMain Friendly & helpful community First Arrow recipe OpenRewrite 

Documentation ΛRROW 

Migration Guide ΛRROW 

Eco System ΛRROW 

Community ΛRROW 

Community https://slack-chats.kotlinlang.org/c/arrow https://github.com/arrow-kt ΛRROW 

Visit us at the booth to talk to Arrow contributors & Xebia Functional and get discount on courses.
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Thank you,
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 to vote @vergauwen_simon KotlinConf’23 Amsterdam