decrement.clj

(defn decrement! [[from-str from-chan] [to-str to-chan] & [start-value]]
  (go-loop [n (or start-value (<! from-chan))]
    (println from-str "sends" n "to" to-str)
    (>! to-chan n)
    (when-let [reply (<! from-chan)]
      (println from-str "gets" reply)
      (if (pos? reply)
        (recur (dec reply))
        (do
          (close! from-chan)
          (close! to-chan)
          (println "Finished"))))))