3.3.rkt

#lang scheme

(define (make-account balance password)
  (define (withdraw amount)
    (if (>= balance amount) 
        (begin (set! balance (- balance amount)) balance)
	      "Insufficient funds"))
  (define (deposit amount)
    (set! balance (+ balance amount)) 
    balance)
  (define (dispatch pw m)
    (cond ((not (eq? pw password)) (error "Incorrect password"))
      	  ((eq? m 'withdraw) withdraw)
          ((eq? m 'deposit) deposit)
          (else (error "Unknown request: MAKE-ACCOUNT"
                m))))
  dispatch)

; test
(define acc (make-account 100 'secret-password))
((acc 'secret-password 'withdraw) 40)
((acc 'some-other-password 'deposit) 50)