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))