#11369: Suppress redundant-constraint warnings in case of empty classes -------------------------------------+------------------------------------- Reporter: hvr | Owner: simonpj Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.1 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 ekmett): Note: Suppressing only in the absence of superclasses means that any class constraint that just gives you a law will **always** spring this warning. {{{#!hs class Bifunctor p => Braided p where braid :: p a b -> p b a -- | @braid . braid = id@ class Braided p => Symmetric p swap :: Symmetric p => p a b -> p b a swap = braid }}} (This code is slightly simplified from http://hackage.haskell.org/package/categories-1.0.7/docs/Control-Category- Braided.html) One "solution" here is to move `swap` into the `Symmetric` class, but then you need to worry about it being overridden to be different than `braid`, which operationally can't happen in the current approach. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11369#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler