#8185: Change role annotation syntax ----------------------------------------------+---------------------------- Reporter: goldfire | Owner: Type: feature request | goldfire Priority: normal | Status: new Component: Compiler | Milestone: 7.8.1 Keywords: | Version: 7.7 Architecture: Unknown/Multiple | Operating System: Difficulty: Moderate (less than a day) | Unknown/Multiple Blocked By: | Type of failure: Related Tickets: | None/Unknown | Test Case: | Blocking: ----------------------------------------------+---------------------------- Currently, role annotations look like this: {{{ data Foo a@N = ... }}} I've received several criticisms of this syntax: * It is not backward compatible. If a library wishes to use role annotations and remain compilable with earlier versions of GHC, preprocessor commands are necessary. * It is inscrutable for someone not well-versed in roles. * It reminds people of as-patterns, which it is unrelated to. * It is conceivable that it would conflict with type-level as-patterns. For these reasons, I propose the following: {{{ data Foo a {-# ROLE Nominal #-} = ... }}} This syntax, while verbose, eliminates these concerns, considering that the new syntax is easily searchable for someone who doesn't know it. I have proposed something similar on ghc-devs, with no response, so I will implement it shortly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8185 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler