Move static doc from Arrow Docs to arrow-docs module

arrow-docs/docs/docs/arrow-fx/async/README.md

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+---
+layout: docs-fx
+title: Async
+permalink: /effects/async/
+---
+
+## Async
+
+
+
+
+Being able to run code in a different context of execution (i.e., thread) than the current one implies that, even if it's part of a sequence, the code will have to be asynchronous.
+Running asynchronous code always requires a callback after completion on error capable of returning to the current thread.
+
+The same way the typeclass [`Monad`]({{ '/arrow/typeclasses/monad' | relative_url }}) represents a sequence of events, and [`MonadError`]({{ '/arrow/typeclasses/monaderror' | relative_url }}) a sequence that can fail, the typeclass `Async` represents asynchronous code with a callback.
+Examples that can run code asynchronously are typically datatypes that can suspend effects and delay evaluation.
+
+```kotlin:ank
+import arrow.*
+import arrow.core.*
+import arrow.fx.*
+import arrow.fx.extensions.io.async.*
+
+IO.async()
+  .async { callback: (Either<Throwable, Int>) -> Unit ->
+    callback(1.right())
+  }.fix().attempt().unsafeRunSync()
+```
+
+```kotlin:ank
+IO.async()
+  .async { callback: (Either<Throwable, Int>) -> Unit ->
+    callback(RuntimeException().left())
+  }.fix().attempt().unsafeRunSync()
+```
+
+`Async` includes all combinators present in [`MonadDefer`]({{ '/effects/monaddefer/' | relative_url }}).
+
+### Main Combinators
+
+#### async
+
+Receives a function returning `Unit` with a callback as a parameter.
+The function is responsible for calling the callback once it obtains a result.
+The callback accepts `Either<Throwable, A>` as the return, where the left side of the [`Either`]({{ '/apidocs/arrow-core-data/arrow.core/-either/' | relative_url }}) represents an error in the execution, and the right side is the completion value of the operation.
+
+```kotlin
+IO.async()
+  .async { callback: (Either<Throwable, Int>) -> Unit ->
+    userFetcherWithCallback("1").startAsync({ user: User ->
+      callback(user.left())
+    }, { error: Exception ->
+      callback(error.right())
+    })
+  }
+```
+
+```kotlin
+IO.async()
+  .async { callback: (Either<Throwable, Int>) -> Unit ->
+    userFromDatabaseObservable().subscribe({ user: User ->
+      callback(user.left())
+    }, { error: Exception ->
+      callback(error.right())
+    })
+  }
+```
+
+#### continueOn
+
+It makes the rest of the operator chain execute on a separate `CoroutineContext`, effectively jumping threads if necessary.
+
+```kotlin
+IO.async().run {
+  // In current thread
+  just(createUserFromId(123))
+    .continueOn(CommonPool)
+    // In CommonPool
+    .flatMap { request(it) }
+    .continueOn(Ui)
+    // In Ui
+    .flatMap { showResult(it) }
+}
+```
+
+Behind the scenes, `continueOn()` starts a new coroutine and passes the rest of the chain as the block to execute.
+
+The function `continueOn()` is also available inside [`Monad Comprehensions`]({{ '/patterns/monad_comprehensions' | relative_url }}).
+
+#### effect
+
+Similar to `MonadDefer`'s `later`, this constructor takes a single suspended function and, optionally, the `CoroutineContext` it has to be run on.
+
+```kotlin
+IO.async().run {
+  // In current thread
+  effect(CommonPool) {
+    // In CommonPool
+    requestSuspend(createUserFromId(123))
+  }
+}
+```
+
+#### invoke with CoroutineContext
+
+Similar to `MonadDefer`'s `later`, this constructor takes a single generator function and the `CoroutineContext` it has to be run on.
+
+```kotlin
+IO.async().run {
+  // In current thread
+  invoke(CommonPool) {
+    // In CommonPool
+    requestSync(createUserFromId(123))
+  }
+}
+```
+
+#### defer with CoroutineContext
+
+Similar to `MonadDefer`'s `defer`, this constructor takes a single function returning a `Kind<F, A>` and the `CoroutineContext` it has to be run on.
+
+```kotlin
+IO.async().run {
+  // In current thread
+  defer(CommonPool) {
+    // In CommonPool
+    async { cb ->
+      requestAsync(createUserFromId(123), cb)
+    }
+  }
+}
+```
+
+#### never
+
+Creates an object using `async()` whose callback is never called.
+
+Depending on how the datatype is implemented, this may cause unexpected errors like awaiting forever for a result.
+
+Use with *SEVERE CAUTION*.
+
+```kotlin
+IO.async()
+  .never()
+  .unsafeRunSync()
+// ERROR!! The program blocks the current thread forever.
+```
+
+> never() exists to test datatypes that can handle non-termination.
+For example, IO has unsafeRunTimed that runs never() safely.
+
+### Laws
+
+Arrow provides `AsyncLaws` in the form of test cases for internal verification of lawful instances and third party apps creating their own `Async` instances.
+
+### Data types
+
+```kotlin:ank:replace
+import arrow.reflect.*
+import arrow.fx.typeclasses.*
+
+TypeClass(Async::class).dtMarkdownList()
+```
+
+ank_macro_hierarchy(arrow.fx.typeclasses.Async)

arrow-docs/docs/docs/arrow-fx/effect/README.md

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+---
+layout: docs-fx
+title: Effect
+permalink: /effects/effect/
+---
+
+## Effect
+
+
+
+
+<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">But can I use callback? I love callbacks. Christmas tree style. with the lights and all....</p>&mdash; Hadi Hariri (@hhariri) <a href="https://twitter.com/hhariri/status/986652337543491586?ref_src=twsrc%5Etfw">April 18, 2018</a></blockquote>
+<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
+
+If you want to use callbacks or run suspended datatypes, then `Effect` is the typeclass to use. It contains a single function `runAsync` that takes a callback and returns a new instance of the datatype. The operation will not yield a result immediately; to start running the suspended computation, you have to evaluate that new instance using its own start operator: `unsafeRunAsync` or `unsafeRunSync` for `IO`, `subscribe` or `blocking` for `Observable`, and `await` or `runBlocking` for `Deferred`.
+
+TODO. Meanwhile you can find a short description in the [intro to typeclasses]({{ '/typeclasses/intro/' | relative_url }}).
+
+### Data types
+
+```kotlin:ank:replace
+import arrow.reflect.*
+import arrow.fx.typeclasses.*
+
+TypeClass(Effect::class).dtMarkdownList()
+```
+
+ank_macro_hierarchy(arrow.fx.typeclasses.Effect)

arrow-docs/docs/docs/arrow-fx/fiber/README.md

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+---
+layout: docs-fx
+title: Fiber
+permalink: /effects/fiber/
+---
+
+## Fiber
+
+
+A `Fiber` is a concurrency primitive for describing parallel operations or multi-tasking.
+Concurrently started tasks can either be joined or canceled, and these are the only two operators available on `Fiber`.
+
+Using `Fiber`, we can describe parallel operations such as `parallelMap` relatively easily.
+**Note** the operation written below does not support proper cancellation.
+When the resulting `IO` is canceled, it does not propagate this cancellation back to the underlying `IO`.
+
+```kotlin:ank
+import arrow.fx.*
+import kotlinx.coroutines.Dispatchers.Default
+import arrow.fx.extensions.fx
+import arrow.fx.typeclasses.Fiber
+import arrow.fx.IO
+
+fun <A, B, C> parallelMap(first: IO<A>,
+                     second: IO<B>,
+                     f: (A, B) -> C): IO<C> =
+  IO.fx {
+    val (fiberOne: Fiber<ForIO, A>) = first.fork(Default)
+    val (fiberTwo: Fiber<ForIO, B>) = second.fork(Default)
+    f(!fiberOne.join(), !fiberTwo.join())
+  }
+
+val first = IO<Unit> { Thread.sleep(5000) }.map {
+  println("Hi, I am first")
+  1
+}
+
+val second = IO<Unit> { Thread.sleep(5000) }.map {
+  println("Hi, I am second")
+  2
+}
+```
+
+```kotlin
+parallelMap(first, second, Int::plus).await()
+
+//Hi, I am second
+//Hi, I am first
+//3
+```
+
+We could fix this snippet to support proper cancellation by using `bracket` instead of `flatMap`,
+which allows us to register an operation to run on cancellation, error, or completion.
+
+```kotlin:ank
+import arrow.fx.extensions.io.monad.flatMap
+import arrow.fx.extensions.io.monad.map
+
+fun <A, B, C> parallelMap2(first: IO<A>,
+                          second: IO<B>,
+                          f: (A, B) -> C): IO<C> =
+      first.fork(Default).bracket(use = { (joinA, _) ->
+          second.fork(Default).bracket(use = { (joinB, _) ->
+            joinA.flatMap { a ->
+              joinB.map { b -> f(a, b) }
+            }
+          }, release = { (_, cancelB) -> cancelB })
+        }, release = { (_, cancelA) -> cancelA })
+```