#10675: GHC does not check the functional dependency consistency condition correctly -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: FunDeps 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 simonpj): Let me note that the commit in comment:5 added this note {{{ Note [Bogus consistency check] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In checkFunDeps we check that a new ClsInst is consistent with all the ClsInsts in the environment. The bogus aspect is discussed in Trac #10675. Currenty it if the two types are *contradicatory*, using (isNothing . tcUnifyTys). But all the papers say we should check if the two types are *equal* thus not (substTys subst rtys1 `eqTypes` substTys subst rtys2) For now I'm leaving the bogus form because that's the way it has been for years. }}} Would someone like to fix the bogus-ness as suggested, and check what, if anything, goes wrong. (See #9210 comment:4 for some possible testsuite failures. Maybe they SHOULD fail.) It'd be worth checking what Hackage libraries build before, but fail to build after. This has been wrong for a long time. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10675#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler