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Task/Polymorphism/EchoLisp/polymorphism.echolisp

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+(struct Point ((real:x 0) (real:y 0)))
+(struct Circle ((real:x 0) (real:y 0) (real:r 1)))
+
+(define-method (print Point:p) (printf "📌 [%d %d]" p.x p.y))
+(define-method (print Circle:c) (printf "⭕️ center:[%d %d] radius:%d" c.x c.y c.r))
+
+(print (Point 5 6))
+    → 📌 [5 6]
+(print (Circle 2 3 4))
+    → ⭕️ center:[2 3] radius:4
+
+;; Accessors :
+;; (Point-x p), (Point-y p) or p.x, p.y
+;; (Circle-x c), c.x , etc.
+;; Setters :
+;; (set-Point-x! p value), (set-Circle-r!  c value)  etc.
+
+;; Constructors
+;; (Point) (Point x) (Point x y)
+;; (Circle) (circle x) (Circle x y) (Circle x y r)
+
+;;Copy
+(print (copy (Circle 3 3 )))
+    →  ⭕️ center:[3 3] radius:1
+
+;;Assignment (to a variable)
+(define my-point (Point 7 8))
+
+;;Destructor : none. Points and Circles are garbage collected.
+
+;;Type checking
+(Point "here" "there")
+    💣 error: Real : type-check failure : here → 'Point:x'
+
+;;Initializer procedure
+(struct Circle ((x 0) (y 0) (r 1) d) #:initialize circle-init)
+(define (circle-init Circle:c) (set-Circle-d! c (* 2 PI c.r)))
+(define-method (print Circle:c)
+    (printf "⭕️ center:[%d %d] radius:%d diameter:%d" c.x c.y c.r c.d))
+
+(print (Circle 0 0 10))
+    → ⭕️ center:[0 0] radius:10 diameter:62.83185307179586