#12201: Wrong instance selection with overlapping instances and local bindings -------------------------------------+------------------------------------- Reporter: kanetw | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: 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 kanetw): Still present on latest HEAD: {{{ GHCi, version 8.1.20160616: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Bug ( /home/kane/ghc8-instance-bug/Bug.hs, interpreted ) /home/kane/ghc8-instance-bug/Bug.hs:22:1: warning: [-Wsimplifiable-class- constraints] The constraint ‘A (Foo s Bool)’ matches an instance declaration instance A (Foo s a) -- Defined at /home/kane/ghc8-instance-bug/Bug.hs:9:10 This makes type inference very fragile; try simplifying it using the instance Ok, modules loaded: Bug. *Bug> :t test test :: A (Foo s Bool) => s -> Int *Bug> :t test2 test2 :: s -> Int }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12201#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler