gistfile1.swift

func loginProducer(username:String, password:String) -> SignalProducer<UserState, LoginError> {
    return SignalProducer { sink, disposable in
        Alamofire.DO_ALAMOFIRE_THINGS { data, response, error in
            // do error checking and nil checking and send errors.
            
            // if all is good, send next and complete.
        }
    } |> tryMap(validateServerError) |> tryMap(validateLogin) |> tryMap(parseLogin)
}