(define (ex1 v1 v2)
  (let ([f (let ([memory 0])
	     (lambda (x)
	       (set! memory (+ memory x))
	       memory))])
    (f v1)
    (f v2)))
(ex1 1 2) '= 3
(ex1 7 3) '= 10

(define (ex2 v1 v2)
  (let ([mk (let ([memory 0])
	      (lambda ()
		(lambda (x)
		  (set! memory (+ memory x))
		  memory)))])
    (let ([f (mk)]
	  [g (mk)])
      (f v1)
      (g v2)
      (g 0))))
(ex2 1 2) '= 3
(ex2 7 3) '= 10

(define (ex3 v1 v2)
  (let ([mk (lambda ()
	      (let ([memory 0])
		(lambda (x)
		  (set! memory (+ memory x))
		  memory)))])
    (let ([f (mk)]
	  [g (mk)])
      (f v1)
      (g v2)
      (g 0))))
(ex3 1 2) '= 2
(ex3 7 3) '= 3

(define (ex4 v1 v2 v3 v4)
  (let ([mk  (let ([shared-memory 0])
	       (lambda ()
		 (let ([unshared-memory 0])
		   (lambda (a b)
		     (set! unshared-memory (+ a unshared-memory))
		     (set! shared-memory (+ b shared-memory))
		     (+ unshared-memory shared-memory)))))])
    (let ([f (mk)]
	  [g (mk)])
      (f v1 v2)
      (g v3 v4)
      (list (f 0 0) (g 0 0)))))
(ex4 1 2 3 4) '= (list 7 9)
(ex4 7 3 1 8) '= (list 18 12)