From the new Template Haskell proposal at
http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal

  A declaration group is the chunk of declarations created by a top-level
  declaration splice, plus those following it, down to but not including the
  next top-level declaration splice. Then the type environment seen by reify
  includes all the declaration up to the end of the immediately preceding
  declaration block, but no more.

This change adds '$(return [])' where necessary to allow following declarations
to see (module-local) top-level definitions.