#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): I'm losing the will to live on this one!

Please, consider forcing the arguments in all these instances, before failing.

Not necessarily easy, if the argument is `[a]`, say rather than `a`. This is so much a corner case that what osa1 has implemented seems fine to me. On (3) I suppose that either you can make the `TcDeriv` code check for `isEnumerationOrEmpty` (simplest), or fix the table-generation stuff. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7401#comment:29 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler