#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 rwbarton): I agree with jpbernardy that generating an empty case on (or equivalently forcing) the first argument would be more correct than producing a new error. However, it seems that in this case the "blame" could be assigned to jpbernardy, who wrote the original report with `instance Eq D where (==) = undefined` :) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7401#comment:34 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler