연습문제 3.1 ~ 3.4

[M.TVLLI.CICERO]

;;; 3.1
(define (make-accumulator value)
(lambda (n)
(begin
(set! value (+ value n))
value)))

(define A (make-accumulator 5))

(A 10)

(A 10)

;; 3.2
(define (make-monitored f)
(let ((rc 0))
(lambda (m)
(cond ((eq? m 'reset-count) (set! rc 0))
((eq? m 'how-many-calls?) rc)
(else (begin (set! rc (+ 1 rc)) (f m)))))))

(define s (make-monitored sqrt))

(s 100)
(s 65536)
(s 'how-many-calls?)
(s 4294967296)
(s 'how-many-calls?)

;; 3.3 & 3.4
(define (make-account password balance)
(let ((incorrect-count 0))
(define (withdraw amount)
(if (>= balance amount)
(begin (set! balance (- balance amount))
balance)
"Insufficient funds"))
(define (deposit amount)
(set! balance (+ balance amount))
balance)
(define (call-the-cops)
"Call the cops!")
(define (incorrect-password amount)
(begin (set! incorrect-count (+ incorrect-count 1))
(if (> incorrect-count 7)
(call-the-cops)
"Incorrect password")))
(define (dispatch p m)
(if(eq? p password)
(cond ((eq? m 'withdraw) withdraw)
((eq? m 'deposit) deposit)
(else (error "Unknown request -- MAKE-ACCOUNT"
m)))
incorrect-password))
dispatch))

(define acc (make-account 'break 100))
((acc 'break 'withdraw) 50)
((acc 'lock 'withdraw) 60)
((acc 'break 'deposit) 40)
((acc 'break 'withdraw) 60)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)
((acc 'lock 'withdraw) 1000)