Reactor Integration (arrow-kt#706)

* Starting Reactor integration

* Adding some tests

* Adding instances for MonoK

* Including arrow-effects-reactor in settings.gradle

* Updating FluxK

* Updating MonoK

* Fixing tests

* Adding another test for FluxK

* Adding tests for MonoK

* Removing duplicated laws for MonoK

* Adding docs for reactor integration

* Including missing dependencies

* Fixing typo in package name

* Adding reactor dependency line to the root README

README.md

@@ -51,6 +51,7 @@ dependencies {
     compile 'io.arrow-kt:arrow-mtl:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects-rx2:0.7.2' //optional
+    compile 'io.arrow-kt:arrow-effects-reactor:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects-kotlinx-coroutines:0.7.2' //optional
     compile 'io.arrow-kt:arrow-optics:0.7.2' //optional
     compile 'io.arrow-kt:arrow-generic:0.7.2' //optional

modules/docs/arrow-docs/build.gradle

@@ -12,6 +12,7 @@ dependencies {
     compile project(':arrow-instances-data')
     compile project(':arrow-effects')
     compile project(':arrow-effects-rx2')
+    compile project(':arrow-effects-reactor')
     compile project(':arrow-effects-kotlinx-coroutines')
     compile project(':arrow-optics')
     compile project(':arrow-recursion')
@@ -27,6 +28,7 @@ dependencies {
 
     compile "org.jetbrains.kotlinx:kotlinx-coroutines-core:$kotlinxCoroutinesVersion"
     compile "io.reactivex.rxjava2:rxjava:2.1.13"
+    compile "io.projectreactor:reactor-core:3.1.3.RELEASE"
 }
 
 task printcp {

modules/docs/arrow-docs/docs/_data/menu.yml

@@ -276,6 +276,9 @@ options:
       - title: Rx2
         url: /docs/integrations/rx2/
 
+      - title: Reactor
+        url: /docs/integrations/reactor/
+
       - title: kotlinx.coroutines
         url: /docs/integrations/kotlinxcoroutines/
 

modules/docs/arrow-docs/docs/docs/README.md

@@ -56,6 +56,7 @@ dependencies {
     compile 'io.arrow-kt:arrow-mtl:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects-rx2:0.7.2' //optional
+    compile 'io.arrow-kt:arrow-effects-reactor:0.7.2' //optional
     compile 'io.arrow-kt:arrow-effects-kotlinx-coroutines:0.7.2' //optional
     compile 'io.arrow-kt:arrow-optics:0.7.2' //optional
     compile 'io.arrow-kt:arrow-generic:0.7.2' //optional

modules/docs/arrow-docs/docs/docs/integrations/reactor/README.md

@@ -0,0 +1,157 @@
+---
+layout: docs
+title: Reactor
+permalink: /docs/integrations/reactor/
+---
+
+## Project Reactor
+
+Arrow aims to enhance the user experience when using Project Reactor. While providing other datatypes that are capable of handling effects, like IO, the style of programming encouraged by the library allows users to generify behavior for any existing abstractions.
+
+One of such abstractions is Project Reactor, a library that, like RxJava, offers reactive streams.
+
+```kotlin
+val flux = Flux.just(7, 4, 11 ,3)
+    .map { it + 1 }
+    .filter { it % 2 == 0 }
+    .scan { acc, value -> acc + value }
+    .collectList()
+    .subscribeOn(Schedulers.parallel())
+    .block()
+//[8, 20, 24]
+```
+
+### Integration with your existing Flux chains
+
+The largest quality of life improvement when using Flux streams in Arrow is the introduction of the [Monad Comprehension]({{ '/docs/patterns/monad_comprehensions' | relative_url }}). This library construct allows expressing asynchronous Flux sequences as synchronous code using binding/bind.
+
+#### Arrow Wrapper
+
+To wrap any existing Flux in its Arrow Wrapper counterpart you can use the extension function `k()`.
+
+```kotlin:ank
+import arrow.effects.*
+import reactor.core.publisher.*
+
+val flux = Flux.just(1, 2, 3, 4, 5).k()
+flux
+```
+
+```kotlin:ank
+val mono = Mono.just(1).k()
+mono
+```
+
+You can return to their regular forms using the function `value()`.
+
+```kotlin:ank
+flux.value()
+```
+
+```kotlin:ank
+mono.value()
+```
+
+### Observable comprehensions
+
+The library provides instances of [`MonadError`]({{ '/docs/typeclasses/monaderror' | relative_url }}) and [`MonadDefer`]({{ '/docs/effects/monaddefer' | relative_url }}).
+
+[`MonadDefer`]({{ '/docs/effects/async' | relative_url }}) allows you to generify over datatypes that can run asynchronous code. You can use it with `FluxK` or `MonoK`.
+
+```kotlin
+fun <F> getSongUrlAsync(MS: MonadDefer<F>) =
+  MS { getSongUrl() }
+
+val songFlux: FluxKOf<Url> = getSongUrlAsync(FluxK.monadDefer())
+val songMono: MonoKOf<Url> = getSongUrlAsync(MonoK.monadDefer())
+```
+
+[`MonadError`]({{ '/docs/typeclasses/monaderror' | relative_url }}) can be used to start a [Monad Comprehension]({{ '/docs/patterns/monad_comprehensions' | relative_url }}) using the method `bindingCatch`, with all its benefits.
+
+Let's take an example and convert it to a comprehension. We'll create an observable that loads a song from a remote location, and then reports the current play % every 100 milliseconds until the percentage reaches 100%:
+
+```kotlin
+getSongUrlAsync()
+  .map { songUrl -> MediaPlayer.load(songUrl) }
+  .flatMap {
+    val totalTime = musicPlayer.getTotaltime()
+    Flux.interval(Duration.ofMillis(100))
+      .flatMap {
+        Flux.create { musicPlayer.getCurrentTime() }
+          .map { tick -> (tick / totalTime * 100).toInt() }
+      }
+      .takeUntil { percent -> percent >= 100 }
+  }
+```
+
+When rewritten using `bindingCatch` it becomes:
+
+```kotlin
+import arrow.effects.*
+import arrow.typeclasses.*
+
+ForFluxK extensions {
+  bindingCatch {
+    val songUrl = getSongUrlAsync().bind()
+    val musicPlayer = MediaPlayer.load(songUrl)
+    val totalTime = musicPlayer.getTotaltime()
+
+    val end = DirectProcessor.create<Unit>()
+    Flux.interval(Duration.ofMillis(100)).takeUntilOther(end).bind()
+
+    val tick = musicPlayer.getCurrentTime().bind()
+    val percent = (tick / totalTime * 100).toInt()
+    if (percent >= 100) {
+      end.onNext(Unit)
+    }
+
+    percent
+  }.fix()
+}
+```
+
+Note that any unexpected exception, like `AritmeticException` when `totalTime` is 0, is automatically caught and wrapped inside the flux.
+
+### Subscription and cancellation
+
+Flux streams created with comprehensions like `bindingCatch` behave the same way regular flux streams do, including cancellation by disposing the subscription.
+
+```kotlin
+val disposable =
+  songFlux.value()
+    .subscribe({ println("Song $it") }, { System.err.println("Error $it") })
+
+disposable.dispose()
+```
+Note that [`MonadDefer`]({{ '/docs/effects/monaddefer' | relative_url }}) provides an alternative to `bindingCatch` called `bindingCancellable` returning a `arrow.Disposable`.
+Invoking this `Disposable` causes an `BindingCancellationException` in the chain which needs to be handled by the subscriber, similarly to what `Deferred` does.
+
+```kotlin
+val (flux, disposable) =
+  FluxK.monadDefer().bindingCancellable {
+    val userProfile = Flux.create { getUserProfile("123") }
+    val friendProfiles = userProfile.friends().map { friend ->
+        bindDefer { getProfile(friend.id) }
+    }
+    listOf(userProfile) + friendProfiles
+  }
+
+flux.value()
+    .subscribe({ println("User $it") }, { System.err.println("Boom! caused by $it") })
+
+disposable()
+// Boom! caused by BindingCancellationException
+```
+
+## Available Instances
+
+* [Applicative]({{ '/docs/typeclasses/applicative' | relative_url }})
+* [ApplicativeError]({{ '/docs/typeclasses/applicativeerror' | relative_url }})
+* [Functor]({{ '/docs/typeclasses/functor' | relative_url }})
+* [Monad]({{ '/docs/typeclasses/monad' | relative_url }})
+* [MonadError]({{ '/docs/typeclasses/monaderror' | relative_url }})
+* [MonadDefer]({{ '/docs/effects/monaddefer' | relative_url }})
+* [Async]({{ '/docs/effects/async' | relative_url }})
+* [Effect]({{ '/docs/effects/effect' | relative_url }})
+* [Foldable]({{ '/docs/typeclasses/foldable' | relative_url }})
+* [Traverse]({{ '/docs/typeclasses/traverse' | relative_url }})

modules/effects/arrow-effects-reactor/build.gradle

@@ -0,0 +1,19 @@
+dependencies {
+    compile project(':arrow-data')
+    compile project(':arrow-effects')
+    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlinVersion"
+    compile project(':arrow-annotations')
+    kapt project(':arrow-annotations-processor')
+    kaptTest project(':arrow-annotations-processor')
+    compileOnly project(':arrow-annotations-processor')
+    testCompileOnly project(':arrow-annotations-processor')
+    testCompile "io.kotlintest:kotlintest:$kotlinTestVersion"
+    testCompile project(':arrow-test')
+
+    compile "io.projectreactor:reactor-core:3.1.3.RELEASE"
+    testCompile "io.projectreactor:reactor-test:3.1.3.RELEASE"
+}
+
+apply from: rootProject.file('gradle/gradle-mvn-push.gradle')
+apply from: rootProject.file('gradle/generated-kotlin-sources.gradle')
+apply plugin: 'kotlin-kapt'

modules/effects/arrow-effects-reactor/gradle.properties

@@ -0,0 +1,4 @@
+# Maven publishing configuration
+POM_NAME=Arrow-Effects-Reactor
+POM_ARTIFACT_ID=arrow-effects-reactor
+POM_PACKAGING=jar

modules/effects/arrow-effects-reactor/src/main/kotlin/arrow/effects/FluxK.kt

@@ -0,0 +1,120 @@
+package arrow.effects
+
+import arrow.Kind
+import arrow.core.Either
+import arrow.core.Eval
+import arrow.core.Left
+import arrow.core.Right
+import arrow.core.identity
+import arrow.effects.typeclasses.Proc
+import arrow.higherkind
+import arrow.typeclasses.Applicative
+import reactor.core.publisher.Flux
+import reactor.core.publisher.FluxSink
+
+fun <A> Flux<A>.k(): FluxK<A> = FluxK(this)
+
+fun <A> FluxKOf<A>.value(): Flux<A> =
+    this.fix().flux
+
+@higherkind
+data class FluxK<A>(val flux: Flux<A>) : FluxKOf<A>, FluxKKindedJ<A> {
+  fun <B> map(f: (A) -> B): FluxK<B> =
+      flux.map(f).k()
+
+  fun <B> ap(fa: FluxKOf<(A) -> B>): FluxK<B> =
+      flatMap { a -> fa.fix().map { ff -> ff(a) } }
+
+  fun <B> flatMap(f: (A) -> FluxKOf<B>): FluxK<B> =
+      flux.flatMap { f(it).fix().flux }.k()
+
+  fun <B> concatMap(f: (A) -> FluxKOf<B>): FluxK<B> =
+      flux.concatMap { f(it).fix().flux }.k()
+
+  fun <B> switchMap(f: (A) -> FluxKOf<B>): FluxK<B> =
+      flux.switchMap { f(it).fix().flux }.k()
+
+  fun <B> foldLeft(b: B, f: (B, A) -> B): B = flux.reduce(b, f).block()
+
+  fun <B> foldRight(lb: Eval<B>, f: (A, Eval<B>) -> Eval<B>): Eval<B> {
+    fun loop(fa_p: FluxK<A>): Eval<B> = when {
+      fa_p.flux.hasElements().map { !it }.block() -> lb
+      else -> f(fa_p.flux.blockFirst(), Eval.defer { loop(fa_p.flux.skip(1).k()) })
+    }
+
+    return Eval.defer { loop(this) }
+  }
+
+  fun <G, B> traverse(GA: Applicative<G>, f: (A) -> Kind<G, B>): Kind<G, FluxK<B>> = GA.run {
+    foldRight(Eval.always { GA.just(Flux.empty<B>().k()) }) { a, eval ->
+      f(a).map2Eval(eval) { Flux.concat(Flux.just<B>(it.a), it.b.flux).k() }
+    }.value()
+  }
+
+  fun handleErrorWith(function: (Throwable) -> FluxK<A>): FluxK<A> =
+      this.fix().flux.onErrorResume { t: Throwable -> function(t).flux }.k()
+
+  fun runAsync(cb: (Either<Throwable, A>) -> FluxKOf<Unit>): FluxK<Unit> =
+      flux.flatMap { cb(Right(it)).value() }.onErrorResume { cb(Left(it)).value() }.k()
+
+  companion object {
+    fun <A> just(a: A): FluxK<A> =
+        Flux.just(a).k()
+
+    fun <A> raiseError(t: Throwable): FluxK<A> =
+        Flux.error<A>(t).k()
+
+    operator fun <A> invoke(fa: () -> A): FluxK<A> =
+        defer { just(fa()) }
+
+    fun <A> defer(fa: () -> FluxKOf<A>): FluxK<A> =
+        Flux.defer { fa().value() }.k()
+
+    fun <A> runAsync(fa: Proc<A>): FluxK<A> =
+        Flux.create { emitter: FluxSink<A> ->
+          fa { either: Either<Throwable, A> ->
+            either.fold({
+              emitter.error(it)
+            }, {
+              emitter.next(it)
+              emitter.complete()
+            })
+          }
+        }.k()
+
+    tailrec fun <A, B> tailRecM(a: A, f: (A) -> FluxKOf<Either<A, B>>): FluxK<B> {
+      val either = f(a).fix().value().blockFirst()
+      return when (either) {
+        is Either.Left -> tailRecM(either.a, f)
+        is Either.Right -> Flux.just(either.b).k()
+      }
+    }
+
+    fun monadFlat(): FluxKMonadInstance = monad()
+
+    fun monadConcat(): FluxKMonadInstance = object : FluxKMonadInstance {
+      override fun <A, B> Kind<ForFluxK, A>.flatMap(f: (A) -> Kind<ForFluxK, B>): FluxK<B> =
+          fix().concatMap { f(it).fix() }
+    }
+
+    fun monadSwitch(): FluxKMonadInstance = object : FluxKMonadErrorInstance {
+      override fun <A, B> Kind<ForFluxK, A>.flatMap(f: (A) -> Kind<ForFluxK, B>): FluxK<B> =
+          fix().switchMap { f(it).fix() }
+    }
+
+    fun monadErrorFlat(): FluxKMonadErrorInstance = monadError()
+
+    fun monadErrorConcat(): FluxKMonadErrorInstance = object : FluxKMonadErrorInstance {
+      override fun <A, B> Kind<ForFluxK, A>.flatMap(f: (A) -> Kind<ForFluxK, B>): FluxK<B> =
+          fix().concatMap { f(it).fix() }
+    }
+
+    fun monadErrorSwitch(): FluxKMonadErrorInstance = object : FluxKMonadErrorInstance {
+      override fun <A, B> Kind<ForFluxK, A>.flatMap(f: (A) -> Kind<ForFluxK, B>): FluxK<B> =
+          fix().switchMap { f(it).fix() }
+    }
+  }
+}
+
+inline fun <A, G> FluxKOf<Kind<G, A>>.sequence(GA: Applicative<G>): Kind<G, FluxK<A>> =
+    fix().traverse(GA, ::identity)