Parameterizing Stock instance deriving
See the original request on haskell-cafe ML: https://mail.haskell.org/pipermail/haskell-cafe/2019-September/131503.html
Allow this syntax:
data E = ... deriving stock Eq via myTransformer myTransformer :: E -> E myTransformer = ...
This would mean that
myTransformer is applied to the values before they are passed to the derived class functions (
This extension would require a GHC proposal.