Print channel, a channel that prints whatever is in the input and puts it back to output.

print-channel.clj

(require '[clojure.core.async :refer [chan, go, <!, >!, >!!, <!!]])
;=> nil
(defn print-channel
  [channel-msg in]
  (let [out (chan 1)]
    (go (let [msg (<! in)]
                ((println channel-msg msg)
                 (>! out msg))))
    out
    ))
(def in (chan))
(def out (print-channel "in-channel message: " in))
(>!! in "hello")
; => true
; in-channel message:  hello
(<!! out)
; => "hello"