(define (make-account balance)
      (define (withdraw amount)
        (if (>= balance amount)
            (begin (set! balance (- balance amount))
                      balance)
            "Insufficient funds"))
      (define (deposit amount)
        (set! balance (+ balance amount))
        balance)
      (define (dispatch m)
        (cond ((eq? m 'withdraw) withdraw)
              ((eq? m 'deposit) deposit)
              (else (error "Unknown request -- make-account" m))))
      dispatch)