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Academic Scala implementations of Functional Reactive Programming -- different Signal[A] and foldp[A, B] implementations as examples
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| // Haskell Signal and foldp implementation. | |
| // foldp := (Signal<A>, (B, A) => B, B) => Signal<B> | |
| class Signal[A](initial: A) { | |
| type Listener = Function[A, Unit] | |
| val value = Ref(initial) | |
| val listeners = Ref(Seq[Listener]()) | |
| def set(newValue: A): Unit = { | |
| // Atomically change the value, blocks the thread, but a not an issue since it's a simple operation. | |
| // Finally return the current state/set of listeners. | |
| atomic { implicit txn => | |
| value() = newValue | |
| listeners() | |
| }.foreach(_(newValue)) | |
| } | |
| def get: A = atomic { implicit txn => | |
| value() | |
| } | |
| def listen(listener: Listener): Unit = atomic { implicit txn => | |
| listeners() = listeners() :+ listener | |
| } | |
| } | |
| object Foo extends App { | |
| val slot = new Signal(0) | |
| slot.listen({ value => | |
| println(value) // hooray! | |
| }) | |
| slot.set(5) | |
| } |
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| case class SignalImmutable[A](value: A, listeners: Seq[Function[A, Unit]] = Seq()) | |
| object SignalImmutable { | |
| def set[A](newValue: A)(signal: SignalImmutable[A]): SignalImmutable[A] = { | |
| signal.listeners.foreach(_(newValue)) | |
| signal.copy(value = newValue) | |
| } | |
| def get[A](signal: SignalImmutable[A]): A = signal.value | |
| def listen[A](listener: Function[A, Unit])(signal: SignalImmutable[A]): SignalImmutable[A] = { | |
| signal.copy(listeners = signal.listeners :+ listener) | |
| } | |
| } | |
| object Foo extends App { | |
| val sig = SignalImmutable(1) | |
| val sig2 = SignalImmutable.listen({v: Int => println(v)})(sig) | |
| val sig3 = SignalImmutable.set(5)(sig2) | |
| } |
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