#11732: Deriving Generic1 interacts poorly with TypeInType -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: TypeInType, | Generics 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 RyanGlScott): Replying to [comment:4 goldfire]:
But
{{{ data Proxy k (a :: k) deriving Functor }}}
would try `instance Functor (Proxy k)`, which is ill-kinded. GHC is surely clever enough to figure out that it should really do `instance Functor (Proxy *)`, but I think it should refrain from doing this.
More to the point of this ticket: I have a bad feeling my fix for #11357 is utterly broken, in that it uses the `tc_args` from the instance tycon despite using visibilities from the parent tycon. Of course, the `tc_args` don't match up. I suppose a `mkFamilyTyConApp` would work nicely here.
But you seem to know much more about generics in GHC than I do. Do you
Right, that's what I mean by "instantiation check". Currently, GHC [http://git.haskell.org/ghc.git/blob/685398ebc5c8377597714cd8c3e97439d32e3a02... unifies the kind of the typeclass] with the kind of the datatype. If, in this process, it ends up instantiating a visible `TyBinder` in the datatype with something other than a type variable, it should be rejected. think you could make this fix? I really do think we just need to use `mkFamilyTyConApp` in the right spot here. I'm not sure what help `mkFamilyTyConApp` would provide, to be honest. Are you saying to do something like this: {{{#!hs let (tc', tc_args') = splitTyConApp (mkFamilyTyConApp tc tc_args) }}} If so, wouldn't you'd end up with the data //family// tycon and arguments? I tried this, and while it seemed to fix the above issue, it comically broke something else: {{{#!hs data family URec p a data instance URec Char a = UChar }}} Since it mistakenly believes that `URec Char a` is too instantiated (it shouldn't even be considering `Char` at all, which is normally the case when you get your type arguments from [http://git.haskell.org/ghc.git/blob/685398ebc5c8377597714cd8c3e97439d32e3a02... tcLookupDataFamInst]). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11732#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler