but basically it’s along C#’s async/await state machine, with strong emphasis on libraries to provide actual processing of steps. Compiler only transforms co-routine into something suspendable and gives control to library functions.

javafx.Toolkit#enterNestedEventLoop()

// scala
val path: Signal[Path] = Signal.flow(new Path) { self =>
  val down = self await mouseDown
  self()= self.previous.moveTo(down.position)
  self.loopUntil(mouseUp) {
    val e = self awaitNext mouseMove
    self()= self.previous.lineTo(e.position)
  }
  self()= self.previous.close()
}

//kotlin
val path: Signal[Path] = Signal.flow(new Path) { self =>
  val down = self await mouseDown
  self()= self.previous.moveTo(down.position)
  self.loopUntil(mouseUp) //co-routine method that enters nested event loop.
  val e = self awaitNext mouseMove
  self() = self.previous.lineTo(e.position)
  self() = self.previous.close()
}

congruity of listeners

var path: Path = null
val moveObserver = { (event: MouseEvent) =>
  path.lineTo(event.position)
  draw(path)
}
control.addMouseDownObserver { event =>
  path = new Path(event.position)
  control.addMouseMoveObserver(moveObserver)
}
control.addMouseUpObserver { event =>
  control.removeMouseMoveObserver(moveObserver)
  path.close()
  draw(path)
}

Iterable<T>.maxBy

valueOf(...)

not sure how can we potentially capture arbitrary listeners though, like addMouseDownObserver. One would probably need to create some kind of adaptor to something awaitable for each such event

inline