#15220: ScopedTypeVariables binds a non-existent variable -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 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: -------------------------------------+------------------------------------- GHC accepts this definition: {{{#!hs f :: (forall a. a -> a) -> () f (x :: b -> b) = x (undefined :: b) `seq` () }}} If a scoped type variable is bound always to a variable, then what variable is `b` bound to? In the desugared Core, it looks like `b` is bound to `Any`. Note that I couldn't find any valid argument for `x` here other than `undefined`. I think this definition should be rejected. In terms of implementation, the `zonkTcTypeToType` function should never encounter a unfilled-in `SigTv`. If it does, error. I don't like putting the error there, but I'm not sure I know another place to do it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15220 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler