SICP 3.3.5 制約の拡散
3.34~3.37はスキップします。 これはやらなくても別に困らないというか、もういいかなって。
(define (for-each-except exception procedure list) (define (loop items) (cond ((null? items) 'done) ((eq? (car items) exception) (loop (cdr items))) (else (procedure (car items)) (loop (cdr items))))) (loop list)) (define (has-value? connector) (connector 'has-value?)) (define (get-value connector) (connector 'value)) (define (set-value! connector new-value informant) ((connector 'set-value!) new-value informant)) (define (forget-value! connector retractor) ((connector 'forget) retractor)) (define (connect connector new-constraint) ((connector 'connect) new-constraint)) (define (make-connector) (let ((value #f) (informant #f) (constraints '())) (define (set-my-value newval setter) (cond ((not (has-value? me)) (set! value newval) (set! informant setter) (for-each-except setter inform-about-value constraints)) ((not (= value newval)) (error "Contradiction" (list value newval))) (else 'ignored))) (define (forget-my-value retractor) (if (eq? retractor informant) (begin (set! informant #f) (for-each-except retractor inform-about-no-value constraints)) 'ignored)) (define (connect new-constraint) (if (not (memq new-constraint constraints)) (set! constraints (cons new-constraint constraints))) (if (has-value? me) (inform-about-value new-constraint)) 'done) (define (me request) (cond ((eq? request 'has-value?) (if informant #t #f)) ((eq? request 'value) value) ((eq? request 'set-value!) set-my-value) ((eq? request 'forget) forget-my-value) ((eq? request 'connect) connect) (else (error "Unknown operation - - CONNECTOR" request)))) me)) (define (adder a1 a2 sum) (define (process-new-value) (cond ((and (has-value? a1) (has-value? a2)) (set-value! sum (+ (get-value a1) (get-value a2)) me)) ((and (has-value? a1) (has-value? sum)) (set-value! a2 (- (get-value sum) (get-value a1)) me)) ((and (has-value? a2) (has-value? sum)) (set-value! a1 (- (get-value sum) (get-value a2)) me)))) (define (process-forget-value) (forget-value! sum me) (forget-value! a1 me) (forget-value! a2 me) (process-new-value)) (define (me request) (cond ((eq? request 'I-have-a-value) (process-new-value)) ((eq? request 'I-lost-my-value) (process-forget-value)) (else (error "Unknown request - - ADDER" request)))) (connect a1 me) (connect a2 me) (connect sum me) me) (define (multiplier m1 m2 product) (define (process-new-value) (cond ((or (and (has-value? m1) (= (get-value m1) 0)) (and (has-value? m2) (= (get-value m2) 0))) (set-value! product 0 me)) ((and (has-value? m1) (has-value? m2)) (set-value! product (* (get-value m1) (get-value m2)) me)) ((and (has-value? product) (has-value? m1)) (set-value! m2 (/ (get-value product) (get-value m1)) me)) ((and (has-value? product) (has-value? m2)) (set-value! m1 (/ (get-value product) (get-value m2)) me)))) (define (process-forget-value) (forget-value! product me) (forget-value! m1 me) (forget-value! m2 me) (process-new-value)) (define (me request) (cond ((eq? request 'I-have-a-value) (process-new-value)) ((eq? request 'I-lost-my-value) (process-forget-value)) (else (error "Unknown request - - MULTIPLIER" request)))) (connect m1 me) (connect m2 me) (connect product me) me) (define (constant value connector) (define (me request) (error "Unknown request - - CONSTANT" request)) (connect connector me) (set-value! connector value me) me) (define (celsius-fahrenheit-converter c f) (let ((u (make-connector)) (v (make-connector)) (w (make-connector)) (x (make-connector)) (y (make-connector))) (multiplier c w u) (multiplier v x u) (adder v y f) (constant 9 w) (constant 5 x) (constant 32 y) 'ok)) (define (inform-about-value constraint) (constraint 'I-have-a-value)) (define (inform-about-no-value constraint) (constraint 'I-lost-my-value)) (define (probe name connector) (define (print-probe value) (newline) (display "Probe: ") (display name) (display " = ") (display value)) (define (process-new-value) (print-probe (get-value connector))) (define (process-forget-value) (print-probe "?")) (define (me request) (cond ((eq? request 'I-have-a-value) (process-new-value)) ((eq? request 'I-lost-my-value) (process-forget-value)) (else (error "Unknown request - - PROBE" request)))) (connect connector me) me) (define C (make-connector)) (define F (make-connector)) (celsius-fahrenheit-converter C F) (probe "Celsius temp" C) (probe "Fahrenheit temp" F) (set-value! C 25 'user) (set-value! F 212 'user) (forget-value! C 'user) (set-value! F 212 'user) ; ex-3.33 (define (averager a b c) (let ((u (make-connector)) (x (make-connector))) (adder a b u) (multiplier c x u) (constant 2 x) 'ok)) (define A (make-connector)) (define B (make-connector)) (define C (make-connector)) (averager A B C) (probe "A" A) (probe "B" B) (probe "C" C)