Example of memoization use in Clojure

memoization.clj

; First we create a function. Let's try Fibonacci

(defn fib [n] 
  (if  (or (zero? n) (= n 1)) 
    1 
    (+  (fib (dec n) )  (fib (- n 2))))) 

; Se let's measure the time needed to run the function

(do
  (time (fib 30))
  (time (fib 30))
  (time (fib 30)))

; "Elapsed time: 398.613 msecs"
; "Elapsed time: 397.204 msecs"
; "Elapsed time: 398.835 msecs"
; 1346269

; Now let's memoize fib and store the result in fib-memo. Let's measure the time again

(let [fib-memo (memoize fib)]
  (time (fib-memo 30))
  (time (fib-memo 30))
  (time (fib-memo 30)))

; "Elapsed time: 398.870 msecs"
; "Elapsed time: 0.007 msecs"
; "Elapsed time: 0.005 msecs"
; 1346269

; 57000x ~ 79000x faster is good enough for you?

; Anyway don't expect miracles:
(let [fib-memo (memoize fib)]
  (time (fib-memo 30))
  (time (fib-memo 31))
  (time (fib-memo 32)))

; "Elapsed time: 399.709 msecs"
; "Elapsed time: 647.915 msecs"
; "Elapsed time: 1052.429 msecs"