(set! load-noisily? #t)

; Bank account objects in Scheme

(define (newaccount b)
  
   ; local procedures
   (define (withdraw a) (begin (set! b (- b a)) b))
   (define (deposit a) (begin (set! b (+ b a)) b))
   ;   (define (inquiry) b)
   (define inquiry (lambda () b))

   (define (interface method)
      (cond ((equal? method 'withdraw) withdraw)
	    ((equal? method 'deposit) deposit)
	    ((equal? method 'inquiry) (inquiry))  ; subtlety here
	    (else 'error)))

  ; body of newaccount returns the interface
  interface)

(define myaccount (newaccount 100))
(define youraccount (newaccount 200))
(myaccount 'inquiry)
((myaccount 'withdraw) 40)
((youraccount 'deposit) 100)