I had a bit of discussion today on how to handle generic instances for abstract types. It resolved to the following question, in a sense -- what are the laws for the Generic typeclass? Should require that `from` and `to` be an isomorphism of data types (i.e. that `from . to` and `to . from` both be the identity) or should we require only the weaker one-sided retract condition (i.e. that `from . to` be the identity.). If the latter, is it better that `from` be partial (which i prefer) or that it quotient together "equivalent" representations (i.e. representing a map as a `fromList` as syb-generics do). The documentation doesn't seem to provide clear guidance here, and it might be worth discussing if some should be added. Cheers, Gershom