conc.erl

(defn slow [] 
    (do (. Thread (sleep 700)) "slow call"))

(defn fast []
    (do (. Thread (sleep 100)) "fast call"))

(defn thread-deliver [fun prom]
    (.start (Thread. (fn [] (deliver prom (fun))))))

(defn main [a aw b overall default]
    (let [p (promise)]
        (thread-deliver a p)
        (let [r (deref p aw nil)]
            (cond r r
            :else (do 
                (thread-deliver b p)
                (deref p (- overall aw) default))))))