2. "Fails instances", which are of the form `instance Num Char fails`;
#9334: Implement "instance chains" -------------------------------------+------------------------------------- Reporter: diatchki | Owner: diatchki Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.9 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Replying to [comment:6 diatchki]: they enable programmers to state explicitly that an instance should never exits. Interestingly, I just found a very related ticket asking for the same sort of thing (#7775). Using `Any` as a superclass we can effectively [https://gist.github.com/Icelandjack/5afdaa32f41adf3204ef9025d9da2a70 #hackage-no-instances-allowed forbid instances], of course the compiler is not privy to this. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9334#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler