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Task/Draw-a-clock/Racket/draw-a-clock.rkt

@@ -0,0 +1,55 @@
+#lang racket/gui
+
+(require racket/date slideshow/pict)
+
+(define (clock h m s [r 100])
+  (define (draw-hand length angle
+                     #:width [width 1]
+                     #:color [color "black"])
+    (dc (λ (dc dx dy)
+          (define old-pen (send dc get-pen))
+          (send dc set-pen (new pen% [width width] [color color]))
+          (send dc draw-line
+                (+ dx r) (+ dy r)
+                (+ dx r (* length (sin angle)))
+                (+ dy r (* length (cos angle))))
+          (send dc set-pen old-pen))
+      (* 2 r) (* 2 r)))
+  (cc-superimpose
+   (for/fold ([pict (circle (* 2 r))])
+             ([angle (in-range 0 (* 2 pi) (/ pi 6))]
+              [hour (cons 12 (range 1 12))])
+     (define angle* angle)
+     (define r* (* r 0.8))
+     (define txt (text (number->string hour) '(bold . "Helvetica")))
+     (define x (- (* r* (sin angle*)) (/ (pict-width txt) 2)))
+     (define y (+ (* r* (cos angle*)) (/ (pict-height txt) 2)))
+     (pin-over pict (+ r x) (- r y) txt))
+   (draw-hand (* r 0.7) (+ pi (* (modulo h 12) (- (/ pi 6))))
+              #:width 3)
+   (draw-hand (* r 0.5) (+ pi (* m (- (/ pi 30))))
+              #:width 2)
+   (draw-hand (* r 0.7) (+ pi (* s (- (/ pi 30))))
+              #:color "red")
+   (disk (* r 0.1))))
+
+(define f (new frame% [label "Clock"] [width 300] [height 300]))
+
+(define c
+  (new canvas%
+       [parent f]
+       [paint-callback
+        (λ (c dc)
+          (define date (current-date))
+          (draw-pict (clock (date-hour date)
+                            (date-minute date)
+                            (date-second date)
+                            (/ (send c get-width) 2))
+                     dc 0 0))]))
+
+(define t
+  (new timer%
+       [notify-callback (λ () (send c refresh-now))]
+       [interval 1000]))
+
+(send f show #t)