Problem with the Unzip type family

[Lysxia]

Unzip assumes that in any type of the form f a, where a has kind Type, a is a type of field. But a could also be phantom or a parameter of a data family (or yet something else?).

Related to #42 because this another problem with genericAdaptor, but #42 might be fixed independently in a way that works for most common cases.

The present issue seems to require an overhaul of Unzippable, for which #42 should certainly be taken into account.

[tomjaguarpaw]

I wonder if genericAdaptor is not really a well-defined thing. It seems somewhat challenging to write down a mathematical definition of its behaviour.

[Lysxia]

Right, other than explaining it in terms of sums and products, which is literally what Generic does, I don't know.