what's the difference between the two?

gistfile1.clj

;; this one fails with 
;;#<IllegalStateException java.lang.IllegalStateException: Invalid use of SingleClientConnManager: connection still allocated.
;;Make sure to release the connection before allocating another one.>

(defn run-test [num-requests channel-name]
  (let [channel (ChannelAPI.)
        requests (init-requests num-requests channel-name)
        listener (make-listener requests)]
    (connect-at-sim channel channel-name listener)
    (doall (map do-request requests))))

;; this one works the way I want but uses defs

(defn run-test2 [num-requests channel-name]
  (def channel (ChannelAPI.))
  (def requests (init-requests num-requests channel-name))
  (def listener (make-listener requests))
  (connect channel channel-name listener)
  (doall (map do-request requests)))

turns out connect-at-sim had a reference to "channel" which only worked when channel was reset in run-test2. I've corrected the typo. thanks for the help everyone :)