#10991: Don't permit type variables in the context unless they are in the type -------------------------------------+------------------------------------- Reporter: bernalex | Owner: bernalex Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC accepts the following: {{{ f :: Eq a => b -> b f b = b }}} This is not valid Haskell 2010[0], so we should not permit it. [0] «The context cx must only contain type variables referenced in t», https://www.haskell.org/report/node/2010/haskellch4.html#x10-660004.1.3 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10991 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler