Flatten a clojure map

flatten.clj

(defn map-flatten
  ([m] (map-flatten m [] []))
  ([todo keys collection]
   (if (empty? todo)
    collection
    (let [[k v] (first todo)]
      (if (map? v)
        (concat (map-flatten v
                             (conj keys k)
                             collection)
                (map-flatten (into {} (rest todo))
                             keys
                             collection))
        (map-flatten (into {} (rest todo))
                              keys
                              (conj collection (conj keys k v))))))))