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-- Exercise 7.1-iii
-- Write the `Show` instance for `HasShow` in terms of `elimHasShow`.
data HasShow where
HasShow :: Show t => t -> HasShow
elimHasShow :: (forall a. Show a => a -> r) -> HasShow -> r
elimHasShow f (HasShow a) = f a
-- This version also prepends the `HasShow` name to the result of `show`:
instance Show HasShow where
show = mappend "HasShow " . elimHasShow show
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