#9757: Warn about derivable instances -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: closed request | Milestone: Priority: normal | Version: 7.9 Component: Compiler | Keywords: Resolution: wontfix | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by NeilMitchell): Indeed, I'm certainly happy to discuss this on the HLint issue tracker. I think GHC warnings are generally general-purpose and clear issues (e.g. patterns are inexhaustive) while HLint ones can be more style-based and instance-specific (e.g. use notElem instead of not and elem). My guess is that it's probably impossible in any remotely general way to detect instances that would be better off done with generalised newtype deriving (and obviously actually impossible in the general case), but if anyone can come up with ideas/code I'd certainly consider it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9757#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler