api.someNetworkFunctionThatMayFail()
.retryWhen({ (error) -> Observable<Int> in
    return error.flatMap({ error -> Maybe<Int> in
        return UIAlertController.rx.show(in: self, title: "Error", message: error.localizedDescription, buttonTitles: ["Retry", "Abort"])
            .filter({value in value == 0})
    })
})
.subscribe(onNext, onError, etc)

UIAlertController.rx.show(in: self,
                       title: "Change avatar", 
                     message: "Select source", 
                     buttons: [.default("Take a picture"), .default("Select from gallery"), .cancel("Cancel")],
              preferredStyle: .actionSheet)
    .flatMap({ [unowned self] choice in
        if choice == 0 {
            return self.picker.takePhoto()
        } else {
            return self.picker.selectImage(source: .photoLibrary)
        }
    })
    .map { (original, edited) -> UIImage in
        return original
    }
    .bind(to: imageView.rx.image)
    .disposed(by: disposeBag)