#9262: Allow free variables in reifyInstances ------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE TemplateHaskell #-} module Bug where import Language.Haskell.TH $( do insts <- reifyInstances ''Eq [ListT `AppT` VarT (mkName "a")] runIO $ putStrLn $ pprint insts return [] ) }}} I get {{{ Bug.hs:7:4: Not in scope: type variable ‘a’ In the argument of reifyInstances: GHC.Classes.Eq [a] }}} But, I wanted the declaration for `instance Eq a => Eq [a]`. The error message isn't wrong, exactly -- `a` really isn't in scope -- but I think we can do better by just treating variables as fresh. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9262 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler