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{-# LANGUAGE RankNTypes, GADTs, DataKinds, PolyKinds, TypeOperators, TypeFamilies #-}
module T9222 where
import Data.Kind
import Data.Proxy
-- Nov 2014: actually the type of Want is ambiguous if we
-- do the full co/contra thing for subtyping,
-- which we now do
-- So this program is erroneous. (But the original ticket was
-- a crash, and that's still fixed!)
-- Apr 2020: with simple subsumption (#17775), the type isn't
-- ambiguous any more
data Want :: (i,j) -> Type where
Want :: (a ~ '(b,c) => Proxy b) -> Want a
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