#lang racket

(define (make-lazy+ i)
  (lambda ()
    (apply + (build-list (* 500 i) values))))


(define long-big-list (build-list 5000 make-lazy+))


(define (compute-every-1000th l)
  (for/list ([thunk l]
             [i (in-naturals)]
             #:when (zero? (remainder i 1000)))
    (thunk)))


(define (memoize.v2 suspended-c)
  (define (hidden)
    (define the-value (suspended-c))
    (set! hidden (lambda () the-value))
    the-value)
  (lambda () (hidden)))