persistent.clj

(defonce persisted-frames (atom {}))

(defn persist [k v]
  (swap! persisted-frames assoc k v)
  v)

(defn split-until [f s]
  (let [[a b] (split-with #(not (f %)) s)]
    [(concat a (take 1 b)) (rest b)]))

(defmacro with-persists2 [df done todo]
  (let [
         [to-persist todo] (split-until #(= '.persist %) todo)
         persist-statement `(-> ~df ~@to-persist)
         k (concat done to-persist)
         ]
    (if (not= '.persist (last to-persist))
      persist-statement
      `(let [
              persisted-frame# (or
                                 (@persisted-frames '~k)
                                 (persist '~k ~persist-statement))
              ]
         (with-persists2 persisted-frame# ~k ~todo)))))

(defmacro with-persists [df & statements]
  `(with-persists2 ~df [~df] ~statements))