[GHC] #9123: Need for higher kinded roles
GHC
ghc-devs at haskell.org
Tue Dec 16 13:46:14 UTC 2014
#9123: Need for higher kinded roles
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Reporter: simonpj | Owner: goldfire
Type: bug | Status: new
Priority: normal | Milestone: 7.12.1
Component: Compiler | Version: 7.8.2
Resolution: | Keywords:
Operating System: | Architecture: Unknown/Multiple
Unknown/Multiple | Difficulty: Project (more
Type of failure: | than a week)
None/Unknown | Blocked By:
Test Case: | Related Tickets:
Blocking: |
Differential Revisions: |
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Comment (by simonpj):
Replying to [comment:31 goldfire]:
> If, instead, we quantified over the leftover implication, we'd be done,
with an inferred implication constraint.
Not a good plan. I'm sure you can't be saying
* Reject a constraint `C a Int` as "exotic"
* Accept a constraint `forall a. C a Int` as fine
When would an implication be "exotic"?
I think it'd be much better to ask the user to use standalone deriving and
write the constraint; but that's going to be jolly scary for users who
just want `deriving( Monad )`. Your point that it only affects monad
transformers is a good one though.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9123#comment:32>
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