#9210: "overlapping instances" through FunctionalDependencies -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | 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 diatchki): Here is a simplified version of the example in the ticket: {{{ class Foo a b c | a b -> c instance Foo (x, a) x ((), a) instance Foo (x, a) a (x, ()) }}} These two instances are accepted by GHC 8.0.1, but should be rejected as they violate the FD on the class. Here is the counter example: {{{ Foo (Int,Int) Int ((), Int) Foo (Int,Int) Int (Int, ()) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9210#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler