Clojure -统计嵌套map中嵌套键的出现次数？

(defn count-nested-keys [data key]
  (let [counter (atom 0)]
    (defn count-keys [data key]
      (cond
        (map? data) (do
                      (when (contains? data key)
                        (swap! counter inc))
                      (doseq [v (vals data)]
                        (count-keys v key)))
        (coll? data) (doseq [v data]
                      (count-keys v key))
        :else nil))
    (count-keys data key)
    @counter))

(def nested-map {:a {:b {:c 1 :d 2}}})
(count-nested-keys nested-map :c) ; 统计嵌套map中键:c的出现次数