Unlifted class method rejected

If I say

class C a where
  meth :: Array# a

I get

    • Expecting a lifted type, but ‘Array# a’ is unlifted
    • In the type signature: meth :: Array# a
      In the class declaration for ‘C’

This definition looks OK to me. I don't see why we can't have an unlifted member of a class.

(As @oerjan points out in ticket:12708#comment:128807, we can't have a levity-polymorphic class member, but this is solidly levity-monomorphic.)

I'm happy to lift this restriction in ongoing work in this area, but I wanted to double-check before doing so.

For the record, the same error occurs even when the class has more than one member, so it's not the no-unlifted-newtypes restriction.

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