atom.clj

(defn memoize [f]
  (let [mem (atom {})]
    (fn [& args]
      (if-let [e (find @mem args)]
        (val e)
        (let [ret (apply f args)]
          (swap! mem assoc args ret)
          (prn @mem)
          ret)))))

(defn fibb [n]
  (if (<= n 1)
    n
    (+ (fibb (dec n)) (fibb (- n 2)))))


(def fibb (memoize fibb))

(time (fibb 100))
;; java.lang.ArithmeticException: integer overflow until 92