3.28.rkt

#lang racket
(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)

(define (logical-or a1 a2)
    (cond [(and (= a1 0) (= a2 0))
         0]
        [(or (and (= a1 1) (a2 0))
             (and (= a1 0) (a2 1))
             (and (= a1 1) (a2 1)))
         1]
        [else (error "Invalid Signal")]))