(defprotocol AProtocol
  (say-hello [this])
  (location [this]))

(defrecord Place [name])

(extend-protocol AProtocol
  Object
  (say-hello [this] (str "Hello " (location this)))
  Place
  (location [this] (str (:name this))))

(defrecord HappyPlace [name])

(extend-protocol AProtocol
  HappyPlace
  (say-hello [this] (str "HELLO " (location this) "!"))
  (location [this] (str (:name this))))

(say-hello (Place. "World"))

;; No implementation of method: :say-hello of protocol: #'user/AProtocol found for class: user.Place
;;  [Thrown class java.lang.IllegalArgumentException]