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Diffstat (limited to 'coding-exercises/3/33.rkt')
| -rw-r--r-- | coding-exercises/3/33.rkt | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/coding-exercises/3/33.rkt b/coding-exercises/3/33.rkt new file mode 100644 index 0000000..b8b2f25 --- /dev/null +++ b/coding-exercises/3/33.rkt @@ -0,0 +1,256 @@ +#lang racket + +(define (inform-about-value constraint) (constraint 'I-have-a-value)) +(define (inform-about-no-value constraint) (constraint 'I-lost-my-value)) + +(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 (for-each-except q f list) + (define (loop items) + (cond ((null? items) 'done) + ((eq? q (car items)) (loop (cdr items))) + (else (f (car items)) + (loop (cdr items))))) + (loop list)) + +(define (make-connector) + (let ((value false) + (informant false) + (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 false) + (for-each-except retractor + inform-about-no-value + constraints)) + 'ignored)) + (define (connect new-constraint) + (when (not (memq new-constraint constraints)) + (set! constraints + (cons new-constraint constraints))) + (when (has-value? me) + (inform-about-value new-constraint)) + 'done) + (define (me request) + (cond ((eq? request 'has-value?) + (if informant true false)) + ((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 (constant value connector) + (define (me request) + (error "Unknown request -- CONSTANT" request)) + (connect connector me) + (set-value! connector value me) + me) + +(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 (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 (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 (averager a b c) + (define (process-new-value) + (cond ((and (has-value? a) (has-value? b)) + (set-value! c + (/ (+ (get-value a) (get-value b)) + 2) + me)) + ((and (has-value? a) (has-value? c)) + (set-value! b + (- (* 2 (get-value c)) + (get-value a)) + me)) + ((and (has-value? b) (has-value? c)) + (set-value! a + (- (* 2 (get-value c)) + (get-value b)) + me)))) + (define (process-forget-value) + (forget-value! a me) + (forget-value! b me) + (forget-value! c 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 -- AVERAGER" request)))) + (connect a me) + (connect b me) + (connect c me) + me) + +(let ((a (make-connector)) + (b (make-connector)) + (c (make-connector))) + (probe 'a a) + (probe 'b b) + (probe 'c c) + ;; (define d (constant 6 a)) + (define e (constant 3 b)) + (define avg (averager a b c)) + (newline) + ;;(forget-value! a d) + (newline) + (set-value! c 100 'user)) + +;; using multiplier as squarer only works in one direction +(define (squarer a b) + (define (process-new-value) + (if (has-value? b) + (if (< (get-value b) 0) + (error "square less than 0 -- SQUARER" (get-value b)) + (when (not (has-value? a)) + (set-value! a + (sqrt (get-value b)) + me))) + (when (has-value? a) + (set-value! b + (* (get-value a) (get-value a)) + me)))) + (define (process-forget-value) + (forget-value! a me) + (forget-value! b 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 -- SQUARER" request)))) + (connect a me) + (connect b me) + me) + +;; bidirectional +(let ((a (make-connector)) + (b (make-connector))) + (probe 'a a) + (probe 'b b) + (newline) + (set-value! a 10 'user) + (define s (squarer a b)) + (newline) + (forget-value! a 'user) + (newline) + (set-value! b 100 'user) + (newline)) + +;; expression style (return compound object pointer) +(define (c+ x y) + (let ((z (make-connector))) + (adder x y z) + z)) +(define (c- x y) + (let ((u (make-connector)) + (v (make-connector)) + (w (make-connector))) + (constant -1 u) + (multiplier u y v) + (adder x v w) + w)) +(define (cv a) + (let ((z (make-connector))) + (constant a z) + z)) +(get-value (c+ (cv 5) (cv 6))) +(get-value (c- (cv 5) (cv 6))) |