[GHC] #15147: Type checker plugin receives Wanteds that are not completely unflattened
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Mon Jun 4 20:24:50 UTC 2018
#15147: Type checker plugin receives Wanteds that are not completely unflattened
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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: |
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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>
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