#12860: GeneralizedNewtypeDeriving + MultiParamTypeClasses sends typechecker into an infinite loop -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: FunDeps, Resolution: | deriving Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Well I'm not sure what to do. 1 You don't want 'deriving' to loop 2 If the fundep coverage condition isn't satisfied, instance resolution can go into a loop, 3 But comment:18 says that you want 'deriving' to work when fundep coverage doesn't hold. Perhaps (2) is over-conservative, somehow? Presumably there is something special about (3) that makes it terminate, despite (2) not holding. If you can identify what that is, you can make that into a new (more expressive) fundep coverage condition. Iavor is the fundep expert. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12860#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler