1 665c255d 2023-08-04 jrmu (define (exchange account1 account2)
 2 665c255d 2023-08-04 jrmu   (let ((difference (- (account1 'balance)
 3 665c255d 2023-08-04 jrmu 		       (account2 'balance))))
 4 665c255d 2023-08-04 jrmu     ((account1 'withdraw) difference)
 5 665c255d 2023-08-04 jrmu     ((account2 'deposit) difference)))
 6 665c255d 2023-08-04 jrmu 
 7 665c255d 2023-08-04 jrmu (define (make-account-and-serializer balance)
 8 665c255d 2023-08-04 jrmu   (define (withdraw amount)
 9 665c255d 2023-08-04 jrmu     (if (>= balance amount)
10 665c255d 2023-08-04 jrmu 	(begin (set! balance (- balance amount))
11 665c255d 2023-08-04 jrmu 	       balance)
12 665c255d 2023-08-04 jrmu 	"Insufficient funds"))
13 665c255d 2023-08-04 jrmu   (define (deposit amount)
14 665c255d 2023-08-04 jrmu     (set! balance (+ balance amount))
15 665c255d 2023-08-04 jrmu     balance)
16 665c255d 2023-08-04 jrmu   (let ((balance-serializer (make-serializer)))
17 665c255d 2023-08-04 jrmu     (define (dispatch m)
18 665c255d 2023-08-04 jrmu       (cond ((eq? m 'withdraw) withdraw)
19 665c255d 2023-08-04 jrmu 	    ((eq? m 'deposit) deposit)
20 665c255d 2023-08-04 jrmu 	    ((eq? m 'balance) balance)
21 665c255d 2023-08-04 jrmu 	    ((eq? m 'serializer) balance-serializer)
22 665c255d 2023-08-04 jrmu 	    (else (error "Unknown request -- MAKE-ACCOUT"
23 665c255d 2023-08-04 jrmu 			 m))))
24 665c255d 2023-08-04 jrmu     dispatch))
25 665c255d 2023-08-04 jrmu 
26 665c255d 2023-08-04 jrmu (define (deposit account amount)
27 665c255d 2023-08-04 jrmu   (let ((s (account 'serializer))
28 665c255d 2023-08-04 jrmu 	(d (account 'deposit)))
29 665c255d 2023-08-04 jrmu     ((s d) amount)))
30 665c255d 2023-08-04 jrmu 
31 665c255d 2023-08-04 jrmu (define (serialized-exchange account1 account2)
32 665c255d 2023-08-04 jrmu   (let ((serializer1 (account1 'serializer))
33 665c255d 2023-08-04 jrmu 	(serializer2 (account2 'serializer)))
34 665c255d 2023-08-04 jrmu     ((serializer1 (serializer2 exchange))
35 665c255d 2023-08-04 jrmu      account1
36 665c255d 2023-08-04 jrmu      account2)))