#16115: Missing associated type instance not reported with error -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler (Type | Version: 8.6.3 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Yes, that's true. But it's generally reasonable for errors to suppress warnings. And the error isn't too bad. The user thinks "Why doesn't `Item Nat` equal `()`? Oh, I'd better look in `instance FromList Nat`, since `Item` is an associate type of `FromList`; and sure enough there is no `type instance`. So it's not too bad. If we wanted to change, I can imagine various things we could do: * Never suppress warnings, even if there are errors. * Make it compulsory to give an instance for an associated type, if there is no default in the class. That'd be a language change. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16115#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler