#11796: Warn about unwanted instances in a modular way -------------------------------------+------------------------------------- Reporter: Lemming | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11219 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bergmark): Another notorious instance is `Show (a -> b)` from `base:Text.Show.Functions`. I ran across a bug where this instance was used by mistake because one of my libraries used it thus propagating the instance down to me. My solution was to remove this import from the offending library and also adding an `Unsatisfiable => Show (a -> b)` instance locally to prevent it from being used in the future. The latter does course not scale and shouldn't be used in libraries. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11796#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler