;;          Object Oriented Programming Style in Scheme


(define (make-account password balance)
  (lambda (op)
    (let ((passwd (begin (display "Enter Password")
                         (newline) (read))))
      (cond ((not (eq? password passwd))
             (display "Incorrect Password") (newline))
            (else
             (cond ((eq? op 'balance)
                    (display "Balance is ") (display balance)
                    (newline))
                   ((eq? op 'withdraw)
                    (let ((amount (begin (display "Enter Amount") 
                                        (newline) (read))))
                      (cond ((<= amount balance) 
                             (set! balance (- balance amount))
                             'done)
                            (else (display "Amount exceeds balance")
                                  (newline)))))
                   ((eq? op 'deposit)
                    (let ((amount (begin (display "Enter Amount") 
                                        (newline) (read))))
                      (set! balance (+ balance amount))
                      'done))
                   (else (display "Incorrect Operation")
                         (newline))
                   )))
      )))
 

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;;;   Sample Session

==> (define account (make-account 'ben 1000))
ACCOUNT

==> (account 'balance)
Enter Password
ben
Balance is 1000
#T

==> (account 'withdraw)
Enter Password
ben
Enter Amount
1500
Amount exceeds balance
#T

==> (account 'withdraw)
Enter Password
ben
Enter Amount
140
DONE

==> (account 'balance)
Enter Password
ben
Balance is 860
#T

==> (account 'deposit)
Enter Password
ben
Enter Amount
400
DONE

==> (account 'balance)
Enter Password
ben
Balance is 1260
#T

==> (account 'balance)
Enter Password
foo
Incorrect Password
#T