#14245: Make ScopedTypedVariables be effective for any type signature -------------------------------------+------------------------------------- Reporter: jeltsch | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 (Type checker) | 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: -------------------------------------+------------------------------------- At the moment, `ScopedTypeVariables` does not have an effect for type signatures without an explicit `forall`. Therefore, you are forced to explicitly quantify type variables if you want the type variables of your type signature to be visible outside the type signature. When defining global variables, this means that you have to change part of the interface (the type signature) because of a change in the implementation. Of course, the change is only syntactical, but there is still a change. This is particularly problematic, because Haddock will follow the source code when deciding whether to include a top-level `forall` in the generated documentation or not. Your Haddock-generated documentation will include spurious `forall`s just because of the way your implementation works. You could say that this is just a Haddock issue. However, problems do not stop here. There is also an inconsistency between scoped type variables in variable definitions and scoped type variables in instance declarations. In instance declarations, you do not have to use an explicit `forall`. Type variables in the instance declaration head are visible in the body as soon as `ScopedTypeVariables` is enabled. I propose to change the semantics of `ScopedTypeVariables` such that as soon as it is enabled, the feature is in effect for all rank-1 type variables in any type signature. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14245 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler