Debugging core.async channels.

debug-chan.clj

(def chan-log (atom []))

(defn debug-chan [pre]
  (let [c (chan)
        lc (chan)]
    (async/tap (async/mult c) lc)
    (go-loop [m (<! lc)]
             (swap! chan-log conj [pre m])
             (recur (<! lc)))
    c))