RxSwift recursive flatMap

recursive_flatMap.swift

func recursive(observable: Observable<Int>) -> Observable<Int> {
    return observable.flatMap { value -> Observable<Int> in
        guard value < 10 else {
            return Variable(-1).asObservable()
        }
        
        print(value)
        return recursive(Variable(value + 1).asObservable())
    }
}
recursive(Variable(0).asObservable()).subscribeNext { _ in }

it's so nice.