#9948: Recommend class constraint instead of instance constraint -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by adamgundry): I think the message ought to keep saying `No instance for (Num a)` because that is exactly what is logically missing, as Richard says. There is an instance for `Foo a`, and it would be very confusing if GHC claimed there wasn't. I'd be open to the `Possible fix` line saying `(Num a) or (Foo a)`, but I suspect the work required to change it may outweigh the benefit. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9948#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler