which is better?

gistfile1.clj

;; vanilla version

(defn make-lock []
  (atom nil)) 

(defn has-lock? [lock id]
  (= id @lock))

(defn set-lock! [lock id new-id]
  (let [lock-id @lock]
    (if (or (nil? lock-id) (= lock-id id))
      (compare-and-set! lock lock-id new-id))))


(def a-lock (make-lock))
(has-lock? a-lock 12) ; >> false
(set-lock! a-lock 12) ; >> true


;; closure version (is this bad form?)

(defn make-lock []
  (let [lock (atom nil)]
    (fn [cmd & args]
      (apply 
        (condp = cmd
          :is? (fn [id] (= id @lock))
          :set! (fn [id new-id] 
                  (let [lock-id @lock]
                    (if (or (nil? lock-id) (= lock-id id))
                      (compare-and-set! lock lock-id new-id))))
        args)))))

(def a-lock (make-lock))
(a-lock :is? 12)  ; >> false
(a-lock :set! 12) ; >> true