1 
2 
3 Exercise 3.45.  Louis Reasoner thinks our bank-account system is unnecessarily complex and error-prone now that deposits and withdrawals aren't automatically serialized. He suggests that make-account-and-serializer should have exported the serializer (for use by such procedures as serialized-exchange) in addition to (rather than instead of) using it to serialize accounts and deposits as make-account did. He proposes to redefine accounts as follows:
4 
5 (define (make-account-and-serializer balance)
6   (define (withdraw amount)
7     (if (>= balance amount)
8         (begin (set! balance (- balance amount))
9                balance)
10         "Insufficient funds"))
11   (define (deposit amount)
12     (set! balance (+ balance amount))
13     balance)
14   (let ((balance-serializer (make-serializer)))
15     (define (dispatch m)
16       (cond ((eq? m 'withdraw) (balance-serializer withdraw))
17             ((eq? m 'deposit) (balance-serializer deposit))
18             ((eq? m 'balance) balance)
19             ((eq? m 'serializer) balance-serializer)
20             (else (error "Unknown request -- MAKE-ACCOUNT"
21                          m))))
22     dispatch))
23 
24 Then deposits are handled as with the original make-account:
25 
26 (define (deposit account amount)
27  ((account 'deposit) amount))
28 
29 Explain what is wrong with Louis's reasoning. In particular, consider what happens when serialized-exchange is called.