ex 3.28 3.29

わからないところは飛ばす！
悩んでたってしょうがない！
というわけで3.28と3.29の解答

;; ex 3.28
(define (or-gate a1 a2 output)
  (define (or-action-procedure)
    (let ((new-value
           (logical-or (get-signal a1) (get-signal a2))))
      (after-delay or-gate-delay
                   (lambda ()
                     (set-signal! output new-value)))))
  (add-action! a1 or-action-procedure)
  (add-action! a2 or-action-procedure)
  'ok)

;; ex 3.29
(define (or-gate a1 a2 output)
  (let ((c (make-wire))
        (d (make-wire))
        (e (make-wire)))
    (inverter a1 c)
    (inverter a2 d)
    (and-gate c d e)
    (inverter e output)))