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let levelsSpin = Spinner
    .initialState(Levels(left: 10, right: 20))
    .feedback(Feedback(effect: leftEffect))
    .feedback(Feedback(effect: rightEffect))
    .reducer(Reducer(levelsReducer))

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func leftEffect(inputLevels: Levels) -> AnyPublisher<Event, Never> {
    // this is the stop condition to our Spin
    guard inputLevels.left != inputLevels.right else { return Empty().eraseToAnyPublisher() }

    // this is the regulation for the left level
    if inputLevels.left < inputLevels.right {
        return Just(.increaseLeft).eraseToAnyPublisher()
    }  else {
        return Just(.decreaseLeft).eraseToAnyPublisher()
    }

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func leftEffect(inputLevels: Levels) -> SignalProducer<Event, Never> {
    // this is the stop condition to our Spin
    guard inputLevels.left != inputLevels.right else { return .empty }

    // this is the regulation for the left level
    if inputLevels.left < inputLevels.right {
        return SignalProducer(value: .increaseLeft)
    }  else {
        return SignalProducer(value: .decreaseLeft)
    }

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func leftEffect(inputLevels: Levels) -> Observable<Event> {
    // this is the stop condition to our Spin
    guard inputLevels.left != inputLevels.right else { return .empty() }

    // this is the regulation for the left level
    if inputLevels.left < inputLevels.right {
        return .just(.increaseLeft)
    }  else {
        return .just(.decreaseLeft)
    }

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func levelsReducer(currentLevels: Levels, event: Event) -> Levels {

	guard currentLevels.left != currentLevels.right else { return currentLevels }

	switch event {
	    case .decreaseLeft:
	        return Levels(left: currentLevels.left-1, right: currentLevels.right)
	    case .increaseLeft:
	        return Levels(left: currentLevels.left+1, right: currentLevels.right)
	    case .decreaseRight:

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enum Event {
    case increaseLeft
    case decreaseLeft 
    case increaseRight
    case decreaseRight
}

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struct Levels {
    let left: Int
    let right: Int
}

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// the State of the feedback loop
struct Levels {
    let left: Int
    let right: Int
}

// the transition requests of the feedback loop
enum Event {
    case increaseLeft
    case decreaseLeft 

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// the State of the feedback loop
struct Levels {
    let left: Int
    let right: Int
}

// the transition requests of the feedback loop
enum Event {
    case increaseLeft
    case decreaseLeft 

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import Combine

// When wrapping a value, we take advantage of the setter
// to feed a PassthroughSubject
@propertyWrapper
struct Published<T> {
    
    private var innerValue: T
    private let innerSubject = PassthroughSubject<T, Never>()