#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. ---------------------------------+------------------------------------------ Reporter: jpbernardy | Owner: Type: feature request | Status: infoneeded Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords: deriving | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: GHC rejects valid program Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by monoidal): I can try to do on this, but let me ask: Allowing "data A deriving (Eq)" is not compatible with Haskell 98 nor 2010 (point 6 at http://www.haskell.org/onlinereport/haskell2010/haskellch11.html#x18-1820001...). Does this mean I should add an add a flag, say `-XEmptyDeriving`, or should GHC allow such declarations by default? -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7401#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler