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Created January 4, 2019 17:55
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typeable28.hs
data AppResult t where
App :: TypeRep a -> TypeRep b -> AppResult (a b)
splitApp :: TypeRep a -> Maybe (AppResult a)
splitApp (TrApp _ ra rb) = Just $ App ra rb
splitApp _ = Nothing
dynFst :: Dynamic -> Maybe Dynamic
dynFst (Dyn rpab x) = do
App rpa rb <- splitApp rpab
App rp ra <- splitApp rpa
Refl <- eqT rp (typeRep :: TypeRep (,))
return $ Dyn ra (fst x)
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