gistfile1.txt

(def-map-type MapLayer [hm dissoced m mta]
  (get [_ k default-value]
       (let [v (get m k ::none)]
         (if (= v ::none)
           (if (contains? dissoced k)
             default-value
             (get hm k default-value))
           v)))
  (assoc [_ k v]
         (MapLayer. hm (disj dissoced k) (assoc m k v) mta))
  (dissoc [_ k]
          (MapLayer. hm (conj dissoced k) (dissoc m k) mta))
  (keys [_]
        (vec (set/union (set/difference (set (keys hm)) dissoced) (set (keys m)))))
  (meta [_] mta)
  (with-meta [_ mta]
    (MapLayer. hm dissoced m mta)))

(defn map-layer
  "Civilizes java.util.Maps"
  [java-hashmap]
  (MapLayer. java-hashmap #{} {} {}))