Improve RIO async support

core/js/src/main/scala/eu/joaocosta/minart/backend/HtmlCanvas.scala

@@ -38,7 +38,6 @@ class HtmlCanvas() extends LowLevelCanvas {
       "keydown",
       (ev: KeyboardEvent) => {
         JsKeyMapping.getKey(ev.keyCode).foreach(k => keyboardInput = keyboardInput.press(k))
-        println("keydown")
       }
     )
     dom.document.addEventListener[KeyboardEvent](

pure/shared/src/main/scala/eu/joaocosta/minart/pure/CanvasIO.scala

@@ -21,8 +21,9 @@ object CanvasIO {
   /** Store an unsafe canvas operation in a [[CanvasIO]]. */
   def accessCanvas[A](f: Canvas => A): CanvasIO[A] = RIO.access[Canvas, A](f)
 
-  /** Polls a future and optionally returns its result. */
-  def pollFuture[A](future: Future[A]): CanvasIO[Option[Try[A]]] = RIO.pollFuture(future)
+  /** Returns a [[Poll]] from a function that receives a callback */
+  def fromCallback[A](operation: (Try[A] => Unit) => Unit): CanvasIO[Poll[A]] =
+    RIO.fromCallback(operation)
 
   /** Fetches the canvas settings. */
   val getSettings: CanvasIO[Canvas.Settings] = accessCanvas(_.settings)

pure/shared/src/main/scala/eu/joaocosta/minart/pure/Poll.scala

@@ -0,0 +1,73 @@
+package eu.joaocosta.minart.pure
+
+import scala.concurrent._
+import scala.util.{Try, Failure, Success}
+
+import eu.joaocosta.minart.core._
+
+/** Representation of a running asyncronous computation that can be polled.
+  *
+  *  Note that, unlike Futures, operations on an Poll don't require an execution context and
+  *  might be applied sequentially every time `poll` is called.
+  *  While this might be inneficient, this is by design, to simplify multiplatform development.
+  */
+case class Poll[+A](poll: RIO[Any, Option[Try[A]]]) extends AnyVal {
+
+  /** Transforms the result of this operation. */
+  def transform[B](f: Try[A] => Try[B]): Poll[B] =
+    Poll[B](poll.map(_.map(f)))
+
+  /** Maps the result of this operation. */
+  def map[B](f: A => B): Poll[B] =
+    this.transform(_.map(f))
+
+  /** Combines two operations by applying a function to the result of the first operation. */
+  def flatMap[B](f: A => Poll[B]): Poll[B] = Poll[B](
+    poll.flatMap {
+      case Some(Success(x)) => f(x).poll
+      case Some(Failure(t)) => RIO.pure(Some(Failure(t)))
+      case None             => RIO.pure(None)
+    }
+  )
+
+  /** Combines two operations by combining their results with the given function. */
+  def zipWith[B, C](that: Poll[B])(f: (A, B) => C): Poll[C] = this.flatMap(x => that.map(y => f(x, y)))
+
+  /** Combines two operations by combining their results into a tuple. */
+  def zip[B](that: Poll[B]): Poll[(A, B)] = this.zipWith(that)((x, y) => x -> y)
+
+  /** Changes the result of this operation to another value. */
+  def as[B](x: B): Poll[B] = this.map(_ => x)
+
+  /** Changes the result of this operation unit. */
+  def unit: Poll[Unit] = this.as(())
+}
+
+object Poll {
+
+  /** Lifts a value into a successful [[Poll]]. */
+  def successful[A](x: A): Poll[A] = Poll(RIO.pure(Some(Success(x))))
+
+  /** Lifts a value into a failed [[Poll]]. */
+  def failed(t: Throwable): Poll[Nothing] = Poll(RIO.pure(Some(Failure(t))))
+
+  /** Creates an [[Poll]] that never returns a value. */
+  val never: Poll[Nothing] = Poll(RIO.pure(None))
+
+  /** Builds an [[Poll]] from a running future */
+  def fromFuture[A](future: Future[A]): Poll[A] =
+    Poll(RIO.suspend(future.value))
+
+  /** Converts an `Iterable[Poll[A]]` into a `Poll[List[A]]`. */
+  def sequence[A](it: Iterable[Poll[A]]): Poll[List[A]] =
+    it.foldLeft[Poll[List[A]]](Poll.successful(Nil)) { case (acc, next) =>
+      acc.zipWith(next) { case (xs, x) => x :: xs }
+    }.map(_.reverse)
+
+  /** Converts an `Iterable[A]` into a `Poll[List[B]]` by applying an operation to each element. */
+  def traverse[A, B](it: Iterable[A])(f: A => Poll[B]): Poll[List[B]] =
+    it.foldLeft[Poll[List[B]]](Poll.successful(Nil)) { case (acc, next) =>
+      acc.zipWith(f(next)) { case (xs, x) => x :: xs }
+    }.map(_.reverse)
+
+}

pure/shared/src/main/scala/eu/joaocosta/minart/pure/RIO.scala

@@ -65,8 +65,11 @@ object RIO {
   /** Returns a operation that requires some resource. */
   def access[R, A](f: R => A): RIO[R, A] = Suspend[R, A](f)
 
-  /** Polls a future and optionally returns its result. */
-  def pollFuture[A](future: Future[A]): RIO[Any, Option[Try[A]]] = Suspend[Any, Option[Try[A]]](_ => future.value)
+  /** Returns a [[Poll]] from a function that receives a callback */
+  def fromCallback[A](operation: (Try[A] => Unit) => Unit): RIO[Any, Poll[A]] = {
+    val promise = scala.concurrent.Promise[A]()
+    RIO.suspend(operation(promise.complete)).as(Poll.fromFuture(promise.future))
+  }
 
   /** Converts an `Iterable[RIO[R, A]]` into a `RIO[R, List[A]]`. */
   def sequence[R, A](it: Iterable[RIO[R, A]]): RIO[R, List[A]] =

pure/shared/src/test/scala/eu/joaocosta/minart/pure/PollSpec.scala

@@ -0,0 +1,55 @@
+package eu.joaocosta.minart.pure
+
+import scala.concurrent._
+import scala.util.{Success, Failure}
+
+import verify._
+
+import eu.joaocosta.minart.core._
+
+object PollSpec extends BasicTestSuite {
+  test("store pure results") {
+    val error = new Exception("error")
+    assert(Poll.successful(1).poll.run(()) == Some(Success(1)))
+    assert(Poll.failed(error).poll.run(()) == Some(Failure(error)))
+    assert(Poll.never.poll.run(()) == None)
+  }
+
+  test("allow polling Futures") {
+    val promise = Promise[Int]()
+    val io      = Poll.fromFuture(promise.future)
+    assert(io.poll.run(()) == None)
+    promise.complete(scala.util.Success(0))
+    assert(io.poll.run(()) == Some(Success(0)))
+  }
+
+  test("provide a stack-safe transform operation") {
+    val io = (1 to 1000).foldLeft[Poll[Int]](Poll.failed(new Exception("error"))) { case (acc, _) =>
+      acc.transform(_.recover { case _ => 0 }.map(_ + 1))
+    }
+    assert(io.poll.run(()) == Some(Success(1000)))
+  }
+
+  test("provide a stack-safe map operation") {
+    val io = (1 to 1000).foldLeft[Poll[Int]](Poll.successful(0)) { case (acc, _) => acc.map(_ + 1) }
+    assert(io.poll.run(()) == Some(Success(1000)))
+  }
+
+  test("provide a stack-safe flatMap operation") {
+    val io = (1 to 1000).foldLeft[Poll[Int]](Poll.successful(0)) { case (acc, _) =>
+      acc.flatMap(x => Poll.successful(x + 1))
+    }
+    assert(io.poll.run(()) == Some(Success(1000)))
+  }
+
+  test("provide zip/zipWith operations") {
+    assert(Poll.successful(1).zip(Poll.successful(2)).poll.run(()) == Some(Success((1, 2))))
+
+    assert(Poll.successful(1).zipWith(Poll.successful(2))(_ + _).poll.run(()) == Some(Success(3)))
+  }
+
+  test("correctly sequence operations") {
+    val io = Poll.sequence(List(Poll.successful(1), Poll.successful(2), Poll.successful(3)))
+    assert(io.poll.run(()) == Some(Success(List(1, 2, 3))))
+  }
+}

pure/shared/src/test/scala/eu/joaocosta/minart/pure/RIOSpec.scala

@@ -19,12 +19,16 @@ object RIOSpec extends BasicTestSuite {
     assert(hasRun == true)
   }
 
-  test("allow polling Futures") {
-    val promise = Promise[Int]()
-    val io      = RIO.pollFuture(promise.future)
-    assert(io.run(()) == None)
-    promise.complete(scala.util.Success(0))
-    assert(io.run(()) == Some(scala.util.Success(0)))
+  test("allow polling async operations") {
+    var completer: Int => Unit = (_) => ()
+    val io = RIO
+      .fromCallback[Int] { cb =>
+        completer = (x: Int) => cb(scala.util.Success(x))
+      }
+      .run(())
+    assert(io.poll.run(()) == None)
+    completer(0)
+    assert(io.poll.run(()) == Some(scala.util.Success(0)))
   }
 
   test("provide a stack-safe map operation") {