exporting instances: was Using associated data types to create unpacked data structures

[John Lask]

re ...
>
> As I understand it the generated code is not exported from the
> translation unit so there are no collisions at link time. We could do
> the same if we could force the generated type class instance to not be
> exported from the module.

I have encountered several occasions when I wished control over what
instances get imported or exported from a module.

I have wondered and perhaps someone can explain: what are the issues in
explicit control of instance export and import? (apart from defining an 
appropriate syntax)

John