Data commit

Task/Active-object/Racket/active-object.rkt

@@ -0,0 +1,30 @@
+#lang racket
+
+(require (only-in racket/gui sleep/yield timer%))
+
+(define active%
+  (class object%
+    (super-new)
+    (init-field k) ; input function
+    (field [s 0])  ; state
+    (define t_0 0)
+
+    (define/public (input new-k) (set! k new-k))
+    (define/public (output) s)
+
+    (define (callback)
+      (define t_1 (/ (- (current-inexact-milliseconds) start) 1000))
+      (set! s (+ s (* (+ (k t_0) (k t_1))
+                      (/ (- t_1 t_0) 2))))
+      (set! t_0 t_1))
+
+    (define start (current-inexact-milliseconds))
+    (new timer%
+         [interval 1000]
+         [notify-callback callback])))
+
+(define active (new active% [k (λ (t) (sin (* 2 pi 0.5 t)))]))
+(sleep/yield 2)
+(send active input (λ _ 0))
+(sleep/yield 0.5)
+(displayln (send active output))