core.clj

(defn ^:internal ^:no-doc delayed
  "Creates an timeout-derefable delay around any function taking a timeout"
  [f]
  (let [val (atom ::unrealized)
        realized? #(not= ::unrealized @val)
        rcv (fn [timeout] (reset! val (f timeout)))]
    (proxy [clojure.lang.Delay clojure.lang.IBlockingDeref] [nil]
      (deref
        ([]
           (if (realized?) @val (rcv 0)))
        ([timeout-ms timeout-val]
           (if (realized?)
             @val
             (let [r (rcv timeout-ms)]
               (if (nil? r) timeout-val r)))))
      (isRealized []
        (or (realized?)
          (not (nil? (rcv -1))))))))