Maintaining State in Clojure

example.clj

(defn ^:private progress-input-stream
  [^java.io.InputStream input-stream size]
  (let [total-read (atom 0)]
    (proxy [java.io.InputStream] []
      (available []
        (.available input-stream))
      (close []
        (.close input-stream))
      (read 
        ([]
         (let [data (.read input-stream)]
           (when (> data -1)
             (reset! total-read (report-progress 1 @total-read size)))
           data))
        ([b]
         (let [bytes-read (.read input-stream b)]
           (when (pos? bytes-read)
             (reset! total-read (report-progress bytes-read @total-read size)))
           bytes-read))
        ([b off len]
         (let [bytes-read (.read input-stream b off len)]
           (when (pos? bytes-read)
             (reset! total-read (report-progress bytes-read @total-read size)))
           bytes-read)))
      (skip [n]
        (let [bytes-skipped (.skip input-stream n)]
          (when (pos? bytes-skipped)
            (reset! total-read (report-progress bytes-skipped @total-read size)))
          bytes-skipped)))))

refactored_example.clj

(def total-bytes-read (atom 0))

(defn- update-bytes-read
  [bytes-read-atom new-bytes-read]
  (swap! bytes-read-atom + new-bytes-read))

(defn- reset-bytes-read
  [bytes-read-atom]
  (reset! bytes-read-atom 0))

(defn- progress-input-stream
  [^java.io.InputStream input-stream]
    (proxy [java.io.InputStream] []
      (available
      	[]
        (.available input-stream))
      (close
      	[]
        (.close input-stream))
      (read
        ([]
         (let [data (.read input-stream)]
           (when (> data -1)
             (update-bytes-read total-bytes-read 1))
           data))
        ([b]
         (let [bytes-read (.read input-stream b)]
           (when (pos? bytes-read)
              (update-bytes-read total-bytes-read bytes-read))
           bytes-read))
        ([b off len]
         (let [bytes-read (.read input-stream b off len)]
           (when (pos? bytes-read)
             (update-bytes-read total-bytes-read bytes-read))
           bytes-read)))
      (skip
        [n]
        (let [bytes-skipped (.skip input-stream n)]
          (when (pos? bytes-skipped)
          	(update-bytes-read total-bytes-read bytes-skipped))
          bytes-skipped)))))