Ah, I see.  OK, it's probably best to avoid the `lens` dependency for `vector-space-points`.  I agree `Diagrams.Core.Points` is a good place, in which case let's do `Iso' (Point v) v`.  Then it's easy to read the type without knowing anything about `AffineSpace`.  It's hard to imagine any users of diagrams wanting the extra generality (and it's super easy to write your own if you do).