#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 | Version: 8.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The technique described in http://www.well-typed.com/blog/2015/07/checked-exceptions/ makes use of a class without any methods, i.e. {{{#!hs class Throws e }}} However, this by definition results in redundant constraints, e.g. {{{#!hs readFoo :: Throws IOError => FilePath -> IO Foo readFoo fn = {- ... -} }}} which GHC 8.0 warns about. I propose to suppress warnings in case a class which has no methods is used as seemingly redundant constraint. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11369 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler