RASExtensions.swift

extension Signal {
    // Turn the producer from a Signal<Result<Value, Error>, NoError> into a Signal<Value, Error>.
    func liftError<T, E>() -> Signal<T, E> where Value == Result<T, E>, Error == NoError {
        return materialize()
            .map { event -> Signal<T, E>.Event in
                switch event {
                case let .value(.success(value)):
                    return .value(value)
                case let .value(.failure(error)):
                    return .failed(error)
                case .failed:
                    fatalError("NoError is impossible to construct")
                case .completed:
                    return .completed
                case .interrupted:
                    return .interrupted
                }
            }
            .dematerialize()
    }
    
    // Turn the producer from a Signal<Value, Error> into a Signal<Result<Value, Error>, NoError>.
    func subdueError() -> Signal<Result<Value, Error>, NoError> {
        return materialize()
            .flatMap(.concat) { event -> SignalProducer<Signal<Result<Value, Error>, NoError>.Event, NoError> in
                switch event {
                case let .value(value):
                    return .init(value: .value(.success(value)))
                case let .failed(error):
                    return .init([ .value(.failure(error)), .completed ])
                case .completed:
                    return .init(value: .completed)
                case .interrupted:
                    return .init(value: .interrupted)
                }
            }
            .dematerialize()
    }
}

extension SignalProducer {
    // Turn the producer from a SignalProducer<Result<Value, Error>, NoError> into a SignalProducer<Value, Error>.
    func liftError<T, E>() -> SignalProducer<T, E> where Value == Result<T, E>, Error == NoError {
        return lift { $0.liftError() }
    }
    
    // Turn the producer from a SignalProducer<Value, Error> into a SignalProducer<Result<Value, Error>, NoError>.
    func subdueError() -> SignalProducer<Result<Value, Error>, NoError> {
        return lift { $0.subdueError() }
    }
}