#8634: Relax functional dependency coherence check ("liberal coverage condition") -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: feature | Status: new request | Milestone: 7.10.1 Priority: high | Version: 7.7 Component: Compiler | Keywords: Resolution: | Operating System: Unknown/Multiple Differential Revisions: Phab:D69 | Type of failure: None/Unknown Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: #1241, | #2247, #8356, #9103, #9227 | -------------------------------------+------------------------------------- Comment (by danilo2): Replying to [comment:39 simonpj]: 1) Of course - you are right - with `-XScopedTypeVariables` it does compile and works well - please forgot me, I overlooked the flag. 2) Yes this example satisfies the Coverage Condition, but as I described before it is just another simplification of some problem and in general we got instances which satisfy and which does not the condition. 3) There is other problem with providing such types by hand - we are generating the code and it would be very hard to generate such annotations in general. @rwbarton: Thank you again for your example - of course it works as you described. Still, while it needs some type signatures, they are hard for us to generate (while we are generating the Haskell's code). I think introducing optional `-XDysfunctionalDependencies` flag even as a local flag or using `~>` symbol, as Simon suggested above, would be a great thing - allowing to play with type system and creating easier some "hackish" things if user wishesh to. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8634#comment:40 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler