Earlier quoted context omitted.
Try extending this approach to, say, a Polygon datatype and see how far you get :)
Hard to please some people :)
In my 3D CL system [0], I have so far kept all geometric data as naive CLOS classes as the intent of the system is to provide a sandbox for experimentation. I have thought of, perhaps one day, representing the geometry as a foreign library for efficient passing to the GPU.