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Created January 4, 2019 17:55
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typeable25.hs
dynFst :: Dynamic -> Maybe Dynamic
dynFst (Dyn (TrApp _ rpa rb) x)
= case rpa of
TrApp rp ra -> case eqT rp (typeRep :: TypeRep (,)) of
Just Refl -> Just $ Dyn ra (fst x)
Nothing -> Nothing
_ -> Nothing
dynFst _ = Nothing
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