Template Haskell doesn't work well with Lexically Scoped Type Variables

[fons]

I don't know if TH is meant to work properly with LSTV. I don't personally need it and I run into this bug by chance, but at least I think that the error should be friendlier in any case. See this (pretty stupid, sorry) example.

Foo.hs

{-# LANGUAGE TemplateHaskell, ScopedTypeVariables #-}
module Foo where


myid :: forall a . a -> a
myid = $([| (\x -> x) :: (a -> a) |])

Ghci shows this user-unfriendly error:

$ ghci Foo.hs 
GHCi, version 6.8.2: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling Foo              ( Foo.hs, interpreted )

Foo.hs:6:12:
    DsMeta: failed binder lookup when desugaring a TH bracket: a
Failed, modules loaded: none.
Prelude>

[simonpj]

Thanks. Fixed by

Wed Jan 16 15:16:12 GMT 2008  simonpj@microsoft.com
  * Complain sensibly if you try to use scoped type variables in Template Haskell

Ian: pls merge this across.

Simon

[igloo]

Merged