#14845: TypeInType, index GADT by constraint witness -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.5 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13895 | Differential Rev(s): Phab:D4728 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => patch * differential: => Phab:D4728 Comment: Phab:D4728 attempts to provide a better error message when promoting a data constructor with an unpromotable context. Note that I didn't attempt to change `checkValidType` in this patch, since that would require a significant amount of plumbing to check whether `checkValidType` was being called on a type or a kind. I felt that the existing error message from `tcInstBinder` (which I tweaked slightly in this Diff to say "kind" instead of "type") was sufficient. This patch also doesn't check for type synonyms, as suggested in comment:15, since that would require changing the checks in `tcInstBinder` accordingly, and I don't know how to do that. But in any case, this is a solid improvement over the status quo. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14845#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler