(defn long-inc [x]
  (do
    (println "Calculating...")
    (inc x)))

(long-inc 8)
;; Calculating...
;; 9

(long-inc 8)
;; Calculating...
;; 9

(def memoized-long-inc (memoize long-inc))

(memoized-long-inc 8)
;; Calculating...
;; 9

(memoized-long-inc 8)
;; 9

(memoized-long-inc 1815)
;; Calculating...
;; 1816