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{-# LANGUAGE TypeFamilies, FlexibleContexts, FlexibleInstances #-}
module T6161 where
data family Fam a
data instance Fam Float = FamFloat Float
class Super a where
testSup :: a -> Float
class Super a => Duper a where
testDup :: a -> Float
--class ( Super (Fam a) ) => Foo a where
class Duper (Fam a) => Foo a where
testFoo :: Fam a -> Float
instance Foo a => Duper (Fam a) where
testDup x = testFoo x + testSup x
--instance Super (Fam Float) where
-- testSup (FamFloat x) = x
instance Foo Float where
testFoo (FamFloat _) = 5.0
testProg :: Float
testProg = testDup (FamFloat 3.0)
{- Reasoning:
dfDuperFam :: Foo a -> Duper (Fam a)
dfDuperFam d = Duper (sc (sc d)) (...testDup...)
dfFooFloat :: Foo Float
dfFooFloat = Foo (dfDuperFloat dx) ...
dx :: Foo Float
dx = dfFooFloat
[W] d1 :: Duper (Fam Float)
-- Use Duper instnance
d1 = dfDuperFam d2
[W] d2 :: Foo Float
-}
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