Exercise 3.28

Read Exercise 3.28 ~ Solution

(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)