#15147: Type checker plugin receives Wanteds that are not completely unflattened -------------------------------------+------------------------------------- Reporter: nfrisby | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.4.1 checker) | Keywords: Resolution: | TypeCheckerPlugins Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by adamgundry): Replying to [comment:10 nfrisby]:
My plugin is responsible for reducing some type families. Receiving flattened Wanteds appeals to me because all of the tyfam applications (except those under forall? hmmm) would be FunEq constraints, so I wouldn't have to seek them out in the types.
So perhaps if there were a separate mechanism for the plugin to declare a custom "reducer" for a type family, that might eliminate my interest in flattened Wanteds.
I've wanted such a thing as well ([wiki:Plugins/TypeChecker#Underdiscussion:Definingtypefamilies some discussion here]). It's not completely obvious what the right design is, though, because GHC's current type family reduction implementation is pure so it doesn't fit nicely with `TcPluginM`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15147#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler