blog_practical_cats_03.scala

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

def getCountryByUserId(id: Int): Future[Option[Country]] = {
  getUser(id) flatMap {
    case None => Future.successful(None)
    case Some(user) => 
      getCity(user) flatMap {
        case None => Future.successful(None)
        case Some(city) => getCountry(city)
      }
  }
}