jerzy.karczmarczuk@info.unicaen.fr wrote:
> Data with where?
> You haven't heard about GADTs?

To avoid clashing with GADT's "where", I propose to rename ok's keyword
to "wherein", or "wheretype", or something

data B k v = E | F b b wherein type b = B k v

data B k v = E | F b b wheretype b = B k v