#10431: EqualityConstraints extension? -------------------------------------+------------------------------------- Reporter: adamgundry | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler (Type | Version: 7.11 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 AntC): However this gets resolved, please doco which extensions enable the `(~)` syntax. Currently at 8.0.1: * Section 10.14.1 'Equality Constraints' tells how to use `(~)`, but not how to enable it. * Section 10.8.3.3 'Relaxed rules for instance contexts' mentions -XGADTs or -XTypeFamilies, as an aside.\\I'd call that a less than obvious place to look. It's not too bad: if you use `(~)` without either of those switched on, GHC's error message is very clear. (See this post https://mail.haskell.org/pipermail/glasgow-haskell- users/2017-April/026521.html.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10431#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler