memoize.rkt

#lang racket

(define (memoize proc)
  (define memo '())
  (λ (x) 
    (cond [(assq x memo) => cdr]
          [else (let ([result (proc x)])
                  (set! memo (cons (cons x result) memo))
                  result)])))

(define fibonacci
  (memoize
   (λ (n)
     (if (< n 2)
         1
         (+ (fibonacci (- n 1))
            (fibonacci (- n 2)))))))

(fibonacci 100) ; => 573147844013817084101

multi_memoize.rkt

(define (memoize proc)
  (define memo '())
  (λ x 
    (cond [(assq x memo) => cdr]
          [else (let ([result (apply proc x)])
                  (set! memo (cons (cons x result) memo))
                  result)])))