async-mem.cljc

(def lookup-sentinel  #?(:clj ::not-found :cljs (js-obj))
(def pending-sentinel #?(:clj ::pending   :cljs (js-obj))

(defn memoize-async
  [f]
  (let [>in (chan)
        pending (pub >in :args)
        mem (atom {})]
    (letfn
        [(memoized [& args]
           (go
             (let [v (get @mem args lookup-sentinel)]
               (condp identical? v
                 lookup-sentinel
                 (do
                   (swap! mem assoc args pending-sentinel)
                   (go
                     (let [ret (<! (apply f args))]
                       (swap! mem assoc args ret)
                       (put! >in {:args args :ret ret})))
                   (<! (apply memoized args)))
                 pending-sentinel
                 (let [<out (chan 1)]
                   (sub pending args <out)
                   (:ret (<! <out)))
                 v))))]
        memoized)))