#13290: Data constructors should not have RULES -------------------------------------+------------------------------------- Reporter: simonpj | Owner: dfeuer Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #7398 | Differential Rev(s): Phab:D3169 Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Implemented by bc332b3159613190a4dc33a067c1ab31039a8434 {{{ Prohibit RULES changing constructors Previously, RULES like {-# RULES "JustNothing" forall x . Just x = Nothing #-} were allowed. Simon Peyton Jones say this seems to have been a mistake, that such rules have never been supported intentionally, and that he doesn't know if they can break in horrible ways. Furthermore, Ben Gamari and Reid Barton are considering trying to detect the presence of "static data" that the simplifier doesn't need to traverse at all. Such rules do not play well with that. So for now, we ban them altogether. In most cases, it's possible to work around the ban using hand-written wrapper functions. Reviewers: austin, simonpj, bgamari Reviewed By: simonpj, bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D3169 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13290#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler