#11503: TypeError woes (incl. pattern match checker) -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: | PatternMatchWarnings, | CustomTypeErrors Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #14141 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): I ran into this issue a few days ago, and it really is annoying. We're forced to choose between a constraint the pattern checker will work with properly (`'True ~ 'False`) and a constraint that will give a good error message when accidentally matching against `MkT2` (`TypeError ...`). There's a sort of workaround, but it's really horrible: instead of `'True ~ 'False`, use something like `"" ~ "This is an error message!"`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11503#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler