#13262: Allow type synonym family application in instance head if it has no free variables -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 12680 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ezyang): This seems to be more complicated than just lifting the restriction, because whenever we have a wanted Show (F T) (where F is the type family), we always flatten this into Show a, a ~ F T; and of course, there is never an instance of Show for a in the top-level. I'm not entirely sure how the solver solves this when Show (F T) is a local constraint; some guidance here would be appreciated. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13262#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler