stage restriction for instances in quotations

LibTest.hs

{-# LANGUAGE TemplateHaskell #-}
module LibTest where

import Language.Haskell.TH.Ppr (pprint)
import Language.Haskell.TH.Syntax (runQ, Lit(StringL), reify)
import Language.Haskell.TH.Lib (litE)
import Monad (liftM)
import Data.Typeable (typeOf)

import Language.Haskell.TH.Syntax (Q, Exp)

testEqIO :: Q Exp -> Q Exp -> Q Exp
testEqIO expr1 expr2 = do
  e1 <- expr1
  e2 <- expr2
  let
    q :: Q Exp -> Q Exp
    q = (\e -> e >>= (litE . StringL . pprint))
  [|do
      v1 <- $(expr1)
      v2 <- $(expr2)
      print (typeOf v1)
      print (typeOf v2)
      if (v1 == v2)
        then putStr "."
        else do
          putStrLn ($(q expr1) ++ " == " ++ $(q expr2) ++ " failed:")
          putStrLn ("First: " ++ show v1)
          putStrLn ("Second: " ++ show v2)
    |]

TestA.hs

{-# LANGUAGE TemplateHaskell, DeriveDataTypeable #-}
-- just run $ghc TestA.hs -e main
-- I have ghc=7.0.4
module TestA where

import LibTest

import Data.Typeable (Typeable)
import List (find)
import Maybe (fromJust)

class A a where
  runA :: a -> Integer

findA l = fromJust (find ((/= 0) . runA) l)

newtype TestA = TestA Integer deriving (Eq, Show, Typeable)

instance A TestA where
  runA (TestA v) = v

main = $(testEqIO [|return $ findA ([]{- :: [TestA] -})|] -- if uncomment the (correct) type - compilation fails due to stage restriction, otherwise it works
                  [|return $ TestA 1|])