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((lambda () (set-signal! output 0)) (lambda () (set-signal! output 1)))
If the execution order of the above action list changed, the final result of output will be different.
If two or more input-events trigger an output-event simultaneously; we stop the clock.
And do following,
1)change the output-event for input-event1
2)change the output-event for input-event2 (note that this new output-event is calculated with new input-event1).
3)....and so on.
This has to be done in FIFO order. Otherwise, affecting change for input-event2 will not be correct because output-event would then not reflect the changed input-event1.
For and-gate: both a1 a2 have and-action-procedure which contains after-delay
the point here is that new-value is calculated before delay
if the segments' list has LIFO, and the first wire a1 change first, then the result will be incorrect
(0, 1) initial
(1, 1) a1 0 -> 1, then a1's and-action-procedure called, a1's new-value = 1, lambda procedure inserted into segment
(1, 0) a2 1 -> 0, then a2's and-action-procedure called, a2's new-value = 0, lambda procedure inserted into segment
a2's (lambda() (set-signal! output new-value)) called, set output = 0
a1's (lambda() (set-signal! output new-value)) called, set output = 1
so after this propogation we got output = 1, which is not correct