#14333: GHC doesn't use the fact that Coercible is symmetric -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeFamilies, | Roles 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 Simon Peyton Jones <simonpj@…>): In [changeset:"5a66d574890ed09859ca912c9e0969dba72f4a23/ghc" 5a66d57/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="5a66d574890ed09859ca912c9e0969dba72f4a23" Better solving for representational equalities This patch adds a bit of extra solving power for representational equality constraints to fix Trac #14333 The main changes: * Fix a buglet in TcType.isInsolubleOccursCheck which wrongly reported a definite occurs-check error for (a ~R# b a) * Get rid of TcSMonad.emitInsolubles. It had an ad-hoc duplicate-removal piece that is better handled in interactIrred, now that insolubles are Irreds. We need a little care to keep inert_count (which does not include insolubles) accurate. * Refactor TcInteract.solveOneFromTheOther, to return a much simpler type. It was just over-complicated before. * Make TcInteract.interactIrred look for constraints that match either way around, in TcInteract.findMatchingIrreds This wasn't hard and it cleaned up quite a bit of code. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14333#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler