#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 diatchki): I think that rwbarton's comments above explain quite well why danilo2's program is incorrect, and GHC correctly rejects it. No matter which rule we use to ''implement'' the consistency check for the functional- dependency, it is crucial that the rule is ''sound''. No sound rule will accept that program, because it violates the ''specification'' for functional dependencies. As for `DysfunctoinalDependencies`: I have no idea what that means, or how it is supposed to work. Is there a write-up or a spec that explains the extension? I'll refrain from commenting further until I understand the concept, but I do think that if it gets implemented, it should use a different syntax from FDs. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8634#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler