3.03.scm

(define (make-account balance account-password)
  (define (withdraw amount)
    (if (<= amount balance)
        (begin (set! balance (- balance amount))
               balance)
        (error "Insufficient funds")))

  (define (deposit amount)
    (set! balance (+ balance amount))
    balance)

  (define (dispatch password m)
    (if (eq? password account-password)
        (cond ((eq? m 'withdraw) withdraw)
              ((eq? m 'deposit) deposit)
              (else (error "Unknown request: MAKE-ACCOUNT" m)))
        (error "Incorrect password")))

  dispatch)