#13415: Instance declarations don't recognize named wildcards -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.4.1 Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: #13324 | Differential Rev(s): Phab:D3332 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): OK so there are two separate things * Error messages. You say "_x is a named wildcard and GHC is not detecting it". So perhaps, with `NamedWildCards` we should complain about `_x` in any `LHsSigType`, rather than treating it as an ordinary type variable. Good plan: that would nail the error message issue. * Extending instance declarations to support wildcards. You want to do this in two steps. I'd prefer to take the second step (getting the payoff) before committing the first. Step 2 may turn out to influence Step 1. (E.g. the only wildcard we want to allow is in the context.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13415#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler