[Haskell-cafe] Partially applied type synonyms

[Ttt Mmm]

I was surprised to find the below code doesn't typecheck even with -XLiberalTypeSynonyms. Am I missing something or is this really not possible?

Thanks,
Tom

---

{-# LANGUAGE FlexibleInstances, KindSignatures, LiberalTypeSynonyms, StandaloneDeriving #-}
-- This works:
data Foo s x = Foo (s x) x
deriving (Eq)
-- This replacement doesn't:
{-
data Foo' sx x = Foo' sx x
deriving (Eq)
type Foo (s :: * -> *) (x :: *) = Foo' (s x) x
-}
data Bar (m :: * -> *) = Bar (m Int)

-- Neither of these typecheck:
x :: Bar (Foo Maybe)
x = undefined
deriving instance Eq (Bar (Foo Maybe))

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