(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 credential m)
    (if (not (eq? credential password))
        (error "Incorrect password"))
    (cond ((eq? m 'withdraw) withdraw)
          ((eq? m 'deposit) deposit)
          (else (error "Unknown request -- MAKE-ACCOUNT" m))))
  dispatch)

; 1 ]=> (define acc (make-account 100 'secret-password))
; 
; ;Value: acc
; 
; 1 ]=> ((acc 'secret-password 'withdraw) 40)
; 
; ;Value: 60
; 
; 1 ]=> ((acc 'some-other-password 'deposit) 50)
; 
; ;Incorrect password