memoize.clj

(defmacro defmem
  [name parms & body]
  (let [fname (gensym) memname (gensym)]
    `(do (declare ~name)
         (letfn [(~fname ~parms ~@body)]
           (let [~memname (atom {})]
             (defn ~name ~parms
               (if (contains? @~memname ~parms)
                 (get @~memname ~parms)
                 (do (swap! ~memname assoc ~parms (~fname ~@parms))
                     (get @~memname ~parms)))))))))
(defmem fib
  [x]
  (if (<= x 1)
    x
    (+' (fib (- x 1)) (fib (- x 2)))))