#2256: Incompleteness of type inference: must quantify over implication constraints -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: lowest | Milestone: 7.10.1 Component: Compiler | Version: 6.8.2 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: GHC | Related Tickets: rejects valid program | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by thomie): * failure: None/Unknown => GHC rejects valid program * component: Compiler => Compiler (Type checker) Comment: SPJ: this ticket is not listed on [wiki:Status/SLPJ-Tickets]. The error message with HEAD (ghc-7.9.20141204): {{{ Could not deduce (Eq b) arising from a use of ‘sig’ from the context (Eq c) bound by the type signature for h :: Eq c => c -> () at test.hs:5:26-40 Possible fix: add (Eq b) to the context of the type signature for h :: Eq c => c -> () or the inferred type of g :: b -> () In the expression: sig x y z In an equation for ‘h’: h z = sig x y z In the expression: let h :: Eq c => c -> () h z = sig x y z in () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/2256#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler