blog_practical_cats_05.scala

def getUser(id: Int): Future[Either[String, User]] = ???
def getCity(user: User): Future[Either[String, City]] = ???
def getCountry(city: City): Future[Either[String, Country]] = ???

def getCountryByUserId(id: Int): Future[Either[String, Country]] = {
  getUser(id) flatMap {
    case Left(err) => Future.successful(Left(err))
    case Right(user) => 
      getCity(user) flatMap {
        case Left(err) => Future.successful(Left(err))
        case Right(city) => getCountry(city)
      }
  }
}