An easy way of suggesting ScopedTypeVariables just came to mind: pretend
#9244: Compiler could warn about type variable shadowing, and hint about ScopedTypeVariables -------------------------------------+------------------------------------- Reporter: stusmith | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #1316, #3691, | Differential Rev(s): #11438 | Wiki Page: | -------------------------------------+------------------------------------- Changes (by thomie): * related: => #1316, #3691, #11438 * milestone: => 8.2.1 Comment: Also reported as #1316, #3691, #11438 and maybe others. @goldfire writes in ticket:11438#comment:1 (I'm moving the discussion here): the extension is always on. When looking up a type variable, if the extension is off but the variable would be in scope otherwise, suggest the extension, while returning a lookup failure (because the variable really isn't in scope!). Getting caught on ScopedTypeVariables is a fairly common occurrence in my experience, so I think it's worth putting in a bit of effort to do better here. (Even better would be to look for type variables in a signature that's missing a forall to suggest adding the forall, but that can be a separate task.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9244#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler