gistfile1.clj

(defn watch-until [reference pred timeout-ms]
  (let [result    (promise)
        watch-key (random-uuid)]
    (try
      (add-watch reference
                 watch-key
                 (fn [_ _ _ value]
                   (when (pred value)
                     (deliver result true))))
      (or (pred @reference)
          (deref result timeout-ms false))
      (finally
       (remove-watch reference watch-key)))))