(define (logistic-map r x cb)
  (let ((xt x))
    (lambda ()
      (set! xt (* r xt (- 1 xt)))
      (cb xt)
      xt)))

(define seed 0.2)

;; Returns a random number generator by initializing r to 4, so that
;; the sequence is chaotic.
(define (mk-rand)
  (logistic-map 4 seed (lambda (x) (set! seed x))))

;; tests

;; The user need not specify a seed, he gets a fully constructed
;; random number generator wrapped up in a procedure.
> (define r1 (mk-rand))
> (r1)
0.6400000000000001
> (r1)
0.9215999999999999

;; New random number generators are independent of the previous ones
> (define r2 (mk-rand))
> (r2)
0.585420538734196
> (r2)
0.970813326249439