#8264: Canonical way to prevent manual instances -------------------------------------------+------------------------------- Reporter: nomeata | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- For some classes (Typeable) the user must not provide hand-written instances, for other no hand-written instances in Safe mode (old Typeable) and for others no instances at all (Coercible). Currently the Typeable checks are in tcInstDecls1 in [source:compiler/typecheck/TcInstDcls.lhs]; but a more proper place would be in checkValidInstHead in [source:compiler/typecheck/TcValidity.lhs]. Why file a ticket and not just do it? The latter source location does not know whether the instance is a (stand-alone) deriving instance or a hand- written one, so this needs a bit of refactoring. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8264 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler