Ah. Now I see a bit more of what you're getting at. We want as if the type synonym were an associated type family with a most-general instance

    class Num a => CPoint a  where

      type Point a

    instance Num a => CPoint a  where

      type Point a = (a, a)

The semantics to be as the PTC paper, such that expanding `Point a` always requires a `CPoint a` instance, which will in turn want a `Num a`.

And the expansion to be immediate (as with type synonyms) so that the client can put `Point a` in instance heads, for example.

> But I really don't know what it means to expand without adding parens. ... what about

>    pointX :: Point a -> a

> ... We don't want that type to expand to (Num a => (a, a)) -> a

Ok, it was your using fancy type operators that put me off. We can represent the AST (and show the need for parens) by reverting to prefix syntax, within H98:

    pointX :: (->) (Point a) a     -- needs parens around (Point a)

And yes my naieve syntactic expansion would give the type you show, wot we do not want.

AntC