Superclasses of type families returning constraints?

[Alexis King]

> On Jan 6, 2020, at 12:05, Alexis King <lexi.lambda at gmail.com> wrote:
> 
>    type family F a b where
>      F a b = () -- regular (), not (() :: Constraint)

(Err, sorry, this should be `F a a = ()`. But I think you can understand what I’m getting at.)