#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: osa1 Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving, Operating System: Unknown/Multiple | newcomer Type of failure: GHC rejects | Architecture: valid program | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: Phab:D978 -------------------------------------+------------------------------------- Comment (by simonpj): What if the method does not have an `a` argument? `Read` is one example, but there are probably others. `Ix` perhaps. Still, I really don't care myself. What I want is for someone to be able to look in the user manual and correctly predict what derived instance you'll get for an empty data type. If you and osa1 agree, I bet everyone else will too. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7401#comment:31 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler