#14771: TypeError reported too eagerly -------------------------------------+------------------------------------- Reporter: hsyl20 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.2.2 checker) | Keywords: Resolution: | CustomTypeErrors 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: | -------------------------------------+------------------------------------- Comment (by diatchki): For issue 1: the high-level question is what to do when we encounter an unevaluated type function with an error parameter (e.g., `T x (TypeError ...)`). Currently, we always report such errors, which is simple, but probably too eager in some cases. I guess a better solution, although more complex, would be too look at the available equations for `T` and see if evaluation is "stuck" due to the type error. If so, we report the custom error. Otherwise, we leave the expression as is. Note, however, that if we choose to not report the custom error we'd get a rather ugly "normal" error, as GHC would still print the description of the error (in combinator form) when it is rendering the type. For issue 2: I am not sure I understand 100% what the request is. Could you give a concrete example? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14771#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler