3.1-3.4

 

;CHAPTER 3

;3.1
(define (make-accumulator x)
  (lambda (y) (begin (set! x (+ x y))
                     x)))

(define A (make-accumulator 5))

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

(define s (make-monitored sqrt))

;3.3 3.4
(define (make-account balance password)
  (define 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 (dispatch pas m)
    (if (eq? pas password)
        (cond ((eq? m 'withdraw) withdraw)
              ((eq? m 'deposit) deposit)
              (else "Unknow request -- MAKE-ACCOUNT"))
        (begin (set! count (+ 1 count))
               (if (> count 7)
                   call-the-cops
                   do-nothing))))
    
  dispatch)

(define acc (make-account 100 'secret-password))


(define do-nothing (lambda (x) '()))
(define call-the-cops (lambda (x) 'call-the-cops))