#11594: closed empty type families fully applied get reduced lazily when in a constraint tuple and fully applied -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9636 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by adamgundry): * cc: adamgundry (added) * related: => #9636 Comment: Replying to [comment:3 goldfire]:
To paraphrase, you want GHC to recognize that an empty closed type family is insoluble.
Note that empty closed type families are not necessarily insoluble in the presence of type-checker plugins. Indeed, the whole point of adding empty CTFs was to allow them to be given special reduction behaviour by plugins. So I think the implementation should be left alone (but for some contrasting views see the discussion on #9636). Documentation improvements are welcome, of course. :-) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11594#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler