Some simple primitives for inverting control in FS2

inversion-of-control.scala

trait Ack[+W]
object Ack {
  case class Accept(unprocessedSize: Int) extends Ack[Nothing]
  case class Halt(unprocessed: Seq[W]) extends Ack[W]
  case class Fail(err: Throwable, unprocessed: Seq[W]) extends Ack[W]
}

trait Input[+W]
object Input {
  case class Send[W](chunk: Chunk[W]) extends Input[W]
  case object Done extends Input[Nothing]
  case class Fail(err: Throwable) extends Input[Nothing]
}

def asyncs[W](register: (Input[W] => Ack[W]) => Unit): Task[Stream[Task,W]] = ???

def signal[W](w: W)(register: (Input[W] => Ack[W]) => Unit): Task[Stream[Task,W]] = ???

Might want asyncs and signal to take a Strategy.

To convert result of signal to a continuous version:

def hold[F[_]:Async,A](p: Stream[F,A]): Stream[F,A]

Not sure about the names asyncs and signal.