#11451: Inconsistent warnings for unused binders -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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 goldfire): Good point. They shouldn't be different. It's just that it seems so natural to say `instance C (Maybe a)`. But perhaps it shouldn't. In any case, this discovery subtly redefines the goal of the warning: 1. Warn when a type variable is bound explicitly but never used. 2. Warn when a type variable is bound implicitly but used in only one place. Refining the goal with point (2) clarifies why there should be no warning in `type instance Equals x x = True`. What do we think about `length :: [_] -> Int`? According to my goals above, that should be the correct type signature, as opposed to `length :: [a] -> Int` which should emit a warning. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11451#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler