memoized-fn-map.clj

;; required: the latest master

;; memoized function (for one arg only, without implementing 'apply')
;; which implements IPersistentMap
(deftype MemoizedFn [mem-map f]
  clojure.lang.IFn
  (invoke [this a] (if-let [ret (find @mem-map a)]
                      (.val ret)
                      (let [ret (.invoke f a)]
                        (swap! mem-map assoc a ret)
                        ret)))
  clojure.lang.IPersistentMap
  (valAt [this k] (.invoke this k))
  (containsKey [this k] (boolean (.invoke this k)))
  (seq [this] (seq @mem-map))
  (count [this] (count @mem-map))
  (empty [this] {})
  (equiv [this x] (.equiv @mem-map x))
  ;; how to implement those ?
  (valAt [this k default])
  (without [this k])
  (assoc [this k v]))

(defn memoized-fn-map-hybrid [f]
  (MemoizedFn. (atom {}) f))

(def mem (memoized-fn-map-hybrid #(* 2 %)))

(mem 2)
(mem 100)
(into {} mem)
(keys mem)
(vals mem)