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{-# LANGUAGE TypeFamilies, PolyKinds, DataKinds #-}
-- {-# LANGUAGE CUSKs #-} -- enabled by default
module CuskFam where
type family F a -- non-injective
type family X :: F a
-- Used to fail with:
--
-- • Couldn't match expected kind ‘F a1’ with actual kind ‘F a’
-- NB: ‘F’ is a non-injective type family
-- The type variable ‘a1’ is ambiguous
-- • In the type family declaration for ‘X’
--
-- See Note [Unifying implicit CUSK variables] in GHC.Tc.Gen.HsType
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