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{-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
module Simpl020_A where
class GUIValue a
class GUIObject w where
toGUIObject :: w -> ()
cset :: GUIValue a => a -> w
instance GUIValue Int
class GUIObject w => HasSize w where
width :: Int -> w
class HasSize w => HasGeometry w where
geometry :: Int -> w
class GUIObject w => Window w where
instance (GUIObject w, Window w) => HasSize w where
width w = geometry w
instance Window w => HasGeometry w where
geometry g = cset g
instance GUIObject ()
instance Window ()
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