#14048: Data instances of kind Constraint -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 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: #12369 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Could you elaborate on comment:4? As in, give a program that would benefit from this treatment (inventing syntax as you go). I think `(=>)` should have kind `Constraint -> TYPE r -> Type`, and that's it. Yes, in class and instance heads, the symbol `=>` appears between two types of kind `Constraint`, but that's not properly a use of the `(=>)` operator; it's just a piece of concrete syntax. To clarify my comment:3, I do think this is a possible direction of future travel and would make an appropriate ghc-proposal. I'm not yet convinced about the idea, but my reluctance is based in personal preference/taste, not technical grounds. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14048#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler