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{-# LANGUAGE TypeFamilies, FlexibleContexts #-}
{-# LANGUAGE EmptyDataDecls, FlexibleInstances #-}
module InstContextNorm
where
data EX _x _y (p :: * -> *)
data ANY
class Base p
class Base (Def p) => Prop p where
type Def p
instance Base ()
instance Prop () where
type Def () = ()
instance (Base (Def (p ANY))) => Base (EX _x _y p)
instance (Prop (p ANY)) => Prop (EX _x _y p) where
type Def (EX _x _y p) = EX _x _y p
data FOO x
instance Prop (FOO x) where
type Def (FOO x) = ()
data BAR
instance Prop BAR where
type Def BAR = EX () () FOO
-- Needs Base (Def BAR)
-- And (Def Bar = Ex () () FOO)
-- so we need Base (Def (Foo ANY))
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