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{-# LANGUAGE RankNTypes #-}
-- Test silly type synonyms
module ShouldCompile where
type C u a = u -- Note 'a' unused
foo :: (forall a. C u a -> C u a) -> u
foo x = undefined x
bar :: Num u => u
bar = foo (\t -> t + t)
-- The (Num u) should not get trapped inside the
-- /\a-abstraction which the compiler constructs for
-- the arg to foo. But it might because it's Num (C u a)!
-- This test tickles a bizarre corner case documented
-- as [Silly Type Synonym] in GHC.Tc.Utils.TcMType
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