core.async example from https://github.com/clojure/core.async/tree/master/examples

google.clj

(require '[clojure.core.async
            :as async
            :refer [<! >! <!! timeout chan alt! go]])

(defn fake-search [kind]
  (fn [c query]
    (go
     (<! (timeout (rand-int 100)))
     (>! c [kind query]))))

(def web1 (fake-search :web1))
(def web2 (fake-search :web2))
(def image1 (fake-search :image1))
(def image2 (fake-search :image2))
(def video1 (fake-search :video1))
(def video2 (fake-search :video2))

(defn fastest [query & replicas]
  (let [c (chan)]
    (doseq [replica replicas]
      (replica c query))
    c))

(defn google [query]
  (let [c (chan)
        t (timeout 80)]
    (go (>! c (<! (fastest query web1 web2))))
    (go (>! c (<! (fastest query image1 image2))))
    (go (>! c (<! (fastest query video1 video2))))
    (go (loop [i 0 ret []]
          (if (= i 3)
            ret
            (recur (inc i)
                   (conj ret
                        (alt! [c t] ([v] v)))))))))

(<!! (google "clojure"))