#11066: Inacessible branch should be warning - otherwise breaks type soundness? -------------------------------------+------------------------------------- Reporter: rrnewton | Owner: Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #8128, #8740 | Differential Rev(s): Phab:D1454 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): * Concerning the original ticket: I'd be perfectly happy if it became a warning. I agree that it's a bit odd if a program is accepted, but then after one beta-step it is rejected. (I'm not sure I'd call it type- unsound, which to me means that it's not rejected at all, but crashes at runtime.) * Concerning comment:15, good point. I think it might be quite tricky to make the 'deriving' mechanism predict which branches would be inaccessible; but perhaps possible. A significant advantage of making the error into a warning is that we could then ignore the warning in deriving code (we already ignore others). Happy to advise if someone would like to take this up. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11066#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler