On Fri, 31 Mar 2017, Sven Panne wrote:
So a reluctant +1 for b), but only *after* we have a flag/pragma. A strong -1 for adding the instances before such a flag/pragma.
Generally we should first have a way to limit damage before adding more type unsafety. Currently re-adding safety belts lags years behind reduction of type safety. Btw. the ticket is https://ghc.haskell.org/trac/ghc/ticket/11796
Next battle: What will be the default for the flag/pragma? >:-)
I'd prefer that this warning is enabled by default. Next best solution is to integrate the warning in Wall. There are people who even find that too annoying. Using the new selective conversion of warnings to errors we can also get back type errors: https://ghc.haskell.org/trac/ghc/ticket/11219