Data commit

Task/Classes/TXR/classes.txr

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+(defstruct shape ()
+  cached-area
+
+  (:init (self)
+    (put-line `@self is born!`))
+
+  (:fini (self)
+    (put-line `@self says goodbye!`))
+
+  (:method area (self)
+    (or self.cached-area
+        (set self.cached-area self.(calc-area)))))
+
+(defstruct circle shape
+  (radius 1.0)
+
+  (:method calc-area (self)
+    (* %pi% self.radius self.radius)))
+
+(defstruct square shape
+  (length 1.0)
+
+  (:method calc-area (self)
+    (* self.length self.length)))