fun fun fun

journalmap.clj

(defprotocol IJournalMap
  (journal [_]))

(deftype JournalMap [journal data]
  IJournalMap
  (journal [_] journal)
  
  clojure.lang.ILookup
  (valAt [this key] (get data key))
  (valAt [this key nf] (get data key nf))

  clojure.lang.IPersistentMap
  (assoc [this k v]
    (JournalMap. (conj journal k) (assoc data k v)))
  (without [this k]
    (JournalMap. journal (dissoc data k)))

  clojure.lang.Associative
  (containsKey [this k]
    (some? (get data k)))
  (entryAt [this k]
    (get data k))

  clojure.lang.Counted
  (count [this]
    (count data))
  
  clojure.lang.Seqable
  (seq [_]
    (seq data))
  
  Object
  (toString [this] (str "JournalMap" this)))

;;user> ((juxt class identity journal) (-> (->JournalMap [] {}) 
;;                                         (assoc :x 6 :y 5) 
;;                                         (dissoc :y) 
;;                                         (update :x inc)))
;;[JournalMap {:x 7} [:x :y :x]]