(define make-plane
  (let ((flight 0))
    (lambda (from to flying-time)
      (define (random-number n)
        ;; Generate a random number between 1 and n
        (+ 1 (random n)))
      (let ((ground-time (random-number 4))
            (my-flight-no flight)
            (current-time 0))
        (define (plane message)
          (cond ((eq? message 'install)
                 (lambda (self) ...))
                ((eq? message 'airplane?)
                 (lambda (self) true))
                ((eq? message 'destination)
                 (lambda (self) to))
                ((eq? message 'flight)
                 (lambda (self) my-flight-no))
                ((eq? message 'clock-tick)
                 (lambda (self) ...))
                (else (get-method message ...))))
        (set! flight (+ flight 1))
        plane))))
                     
(define (make&install-plane from to flying-time)
  (make&install-object make-plane from to flying-time))