#12810: -Wredundant-constraints doesn't factor in associated type families -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): Well type families are allowed to not reduce. For example {{{ *M> :t undefined :: T Int undefined :: T Int :: T Int }}} there's nothing stopping you from writing `T Int`, regardless of whether there is an instance `C Int`. So GHC's warning is consistent with that. In your comment, the problem doesn't seem to be the type family, but rather the lack of any methods. An empty class body gives the same warning. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12810#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler