protocol-util.clj

(in-ns 'clojure.core)

(defrecord PIP [:protocol :impl])

(defn pip? [x] (instance? clojure.core.PIP x))

(defn extract-pair [p m]
  (if (pip? p)
    [(:protocol p) (merge (:impl p) m)]
    [p m]))

(defn pip [p m]
  (if (or (protocol? p) (pip? p))
    (let [[extracted-p extracted-m] (extract-pair p m)]
      (PIP. extracted-p extracted-m))
    (throw (Exception. "Protocol not provided"))))
       
(defn merge-pip
  [& pips]
  (let [pips (map #(pip % {}) pips)]
    (if (not (apply = (map :protocol pips)))
      (throw (Exception. "Trying to merge different protocols."))
      (pip (:protocol (first pips)) (apply merge (map :impl pips))))))

(defmacro extend+ [atype & proto+maps]
  `(extend ~atype
	   ~(apply concat
		   (map extract-pair
			(partition 2 proto+maps)))))