#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. ---------------------------------+------------------------------------------ Reporter: jpbernardy | Owner: monoidal Type: feature request | Status: new 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 simonpj): Thanks for helping. Concerning your question, I think it would be fine for `-XEmptyDataDecls` to imply that we can derive `Eq` etc for them. No need for a second flag. What would be good would be some documentation in the user manual (in the empty data decls section) that says what is derived for the standard build-in classes. Simon -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7401#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler