#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 Iceland_jack): I attached an example, I found another need for this: encoding that the opposite category is coercible to the current: {{{#!hs type Cat obj = obj -> obj -> Type class (forall xx yy. Coercible (cat xx yy) (Op cat yy xx)) => Category (cat :: Cat obj) where type Op cat :: Cat obj }}} The use case is similar as the other one but I can elaborate if needed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14333#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler