this version is useful for side-effects only (like printing)

first_one_wins_side_effects.clj

(defn first-out [& fns]
  (let [fs (atom [])
        terminate (fn [] (println "cancling..") (doall (map future-cancel @fs)))]
    (reset! fs (doall
                (map (fn [x] (future-call #((x) (terminate)))) fns )))))

(defn wait-for [n s]
  (fn [] (print "start...") (flush) (Thread/sleep n) (print s) (flush)))

(first-out (wait-for 1000 "long") (wait-for 500 "short"))