Retry on exception, returning either accumulated failures or first successful value. Based on http://stackoverflow.com/questions/1879885/clojure-how-to-to-recur-upon-exception

try-times.clj

(defn try-times-wait-millis* [times wait-millis thunk]
  (let [attempts (repeatedly times
                            #(try (thunk)
                                  (catch Exception ex (do
                                                        (Thread/sleep wait-millis)
                                                        {::failure ex}))))
        successes (drop-while #(contains? % ::failure) attempts)]

    (if (not (empty? successes))
        {:success (first successes)}
        {:failures (map #(get % ::failure) attempts)})))

(defmacro try-times-wait-millis
  "Executes body. If an exception is thrown, will retry after wait-millis. At
  most n tries are done. Returns union with either :success value or :failures
  with a list of encountered exceptions."
  [times wait-millis & thunk]
  `(try-times-wait-millis* ~times ~wait-millis (fn [] ~@thunk)))