flatmap.clj

(defn flatmap<
  "Takes a function and a source channel, and returns a channel which
  contains the values in each channel produced by applying f to
  each value taken from the source channel. f must return a
  channel."
  [f in]
  (let [out (a/chan)]
    (a/go-loop []
      (let [item (a/<! in)]
        (if (nil? item)
          (a/close! out)
          (a/pipe (f item) out))))
    out))