#14722: Error message points to wrong location -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 Resolution: | Keywords: | TypeApplications Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => TypeApplications Comment: You're right. This is a consequence of the fact that (currently) GHC reports visible-type-application errors "eagerly", as soon as it encounters them, discarding all pending errors. In this case the error you want reported will be pending (in the constraints being gathered) but it never gets a chance to be reported. Richard: it'd be good to find a way to defer the visible-type-application error. But we don't have a way to do that yet. A `HoleCan` isn't right. A constraint `[W] () ~ forall a. ???` doesn't seem right because we have nothing to put for the `??`. I suppose we could invent a new kind of deferred error constraint, perhaps generalising `HoleCan`. See [wiki:TypeApplication] for a list of other VTA-related tickets; I have not checked but I bet that some are like this one. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14722#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler