#7401: Can't derive instance for Eq when datatype has no constructor, while it is trivial do do so. -------------------------------------+------------------------------------- Reporter: jpbernardy | Owner: (none) Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving, | newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #10577, #13117 | Differential Rev(s): Phab:D4047 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"1317ba625d40fbd51cb0538b3fde28f412f30c01/ghc" 1317ba62/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="1317ba625d40fbd51cb0538b3fde28f412f30c01" Implement the EmptyDataDeriving proposal This implements the `EmptyDataDeriving` proposal put forth in https://github.com/ghc-proposals/ghc- proposals/blob/dbf51608/proposals/0006-deriving-empty.rst. This has two major changes: * The introduction of an `EmptyDataDeriving` extension, which permits directly deriving `Eq`, `Ord`, `Read`, and `Show` instances for empty data types. * An overhaul in the code that is emitted in derived instances for empty data types. To see an overview of the changes brought forth, refer to the changes to the 8.4.1 release notes. Test Plan: ./validate Reviewers: bgamari, dfeuer, austin, hvr, goldfire Reviewed By: bgamari Subscribers: rwbarton, thomie GHC Trac Issues: #7401, #10577, #13117 Differential Revision: https://phabricator.haskell.org/D4047 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7401#comment:53 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler