135 lines
3.4 KiB
Racket
135 lines
3.4 KiB
Racket
#lang sicp
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(define (inverter input output)
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(define (invert-input)
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(let ((new-value (logical-not (get-signal input))))
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(after-delay inverter-delay
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(lambda ()
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(set-signal! output new-value)))))
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(add-action! input invert-input)
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'ok)
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(define (logical-not s)
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(cond ((= s 0) 1)
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((= s 1) 0)
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(else (error "Invalid signal" s))))
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;; *following uses logical-and -- see ch3support.scm
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(define (logical-and x y)
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(cond ((and (= x 1) (= y 1)) 1)
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((or
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(and (= x 0) (= y 1))
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(and (= x 1) (= y 0))
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(and (= x 0) (= y 0)))
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0)
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(else
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(error "Invalid signal"))))
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(define (and-gate a1 a2 output)
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(define (and-action-procedure)
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(let ((new-value
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(logical-and (get-signal a1) (get-signal a2))))
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(after-delay and-gate-delay
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(lambda ()
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(set-signal! output new-value)))))
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(add-action! a1 and-action-procedure)
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(add-action! a2 and-action-procedure)
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'ok)
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(define (logical-or x y)
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(cond ((and (= x 0) (= y 0)) 0)
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((or
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(and (= x 0) (= y 1))
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(and (= x 1) (= y 0))
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(and (= x 1) (= y 1)))
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1)
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(else
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(error "Invalid signals" x y))))
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(define (or-gate a1 a2 output)
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(define (or-action-procedure)
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(let ((new-value
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(logical-or (get-signal a1) (get-signal a2))))
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(after-delay or-gate-delay
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(lambda ()
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(set-signal! output new-value)))))
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(add-action! a1 or-action-procedure)
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(add-action! a2 or-action-procedure)
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'ok)
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(define (half-adder a b s c)
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(let ((d (make-wire)) (e (make-wire)))
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(or-gate a b d)
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(and-gate a b c)
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(inverter c e)
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(and-gate d e s)
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'ok))
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(define (full-adder a b c-in sum c-out)
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(let ((s (make-wire))
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(c1 (make-wire))
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(c2 (make-wire)))
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(half-adder b c-in s c1)
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(half-adder a s sum c2)
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(or-gate c1 c2 c-out)
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'ok))
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(define (ripple-carry-adder a b s c)
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(define (add-full-adder a b s c)
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(if (and (pair? a)
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(pair? b)
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(pair? s))
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(let ((ci (make-wire)))
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(full-adder (car a)
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(car b)
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c
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(car s)
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ci)
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(add-full-adder (cdr a)
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(cdr b)
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(cdr s)
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ci))))
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(if (= (length a)
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(length b)
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(length s))
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(add-full-adder a b s c)))
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;; Support procedures
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(define (make-wire)
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(let ((signal-value 0) (action-procedures '()))
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(define (set-my-signal! new-value)
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(if (not (= signal-value new-value))
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(begin (set! signal-value new-value)
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(call-each action-procedures))
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'done))
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(define (accept-action-procedure! proc)
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(set! action-procedures (cons proc action-procedures))
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(proc))
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(define (dispatch m)
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(cond ((eq? m 'get-signal) signal-value)
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((eq? m 'set-signal!) set-my-signal!)
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((eq? m 'add-action!) accept-action-procedure!)
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(else (error "Unknown operation -- WIRE" m))))
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dispatch))
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(define (call-each procedures)
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(if (null? procedures)
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'done
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(begin
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((car procedures))
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(call-each (cdr procedures)))))
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(define (get-signal wire)
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(wire 'get-signal))
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(define (set-signal! wire new-value)
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((wire 'set-signal!) new-value))
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(define (add-action! wire action-procedure)
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((wire 'add-action!) action-procedure))
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