disable instance MonadPlus CoreM for GHC <= 6.6

diff --git a/compiler/simplCore/CoreMonad.lhs b/compiler/simplCore/CoreMonad.lhs
index ae45ba4..90b062f 100644 (file)
--- a/compiler/simplCore/CoreMonad.lhs
+++ b/compiler/simplCore/CoreMonad.lhs
@@ -125,9 +125,12 @@ instance Applicative CoreM where
 
 -- For use if the user has imported Control.Monad.Error from MTL
 -- Requires UndecidableInstances
+#if __GLASGOW_HASKELL__ > 606
+-- see instance MonadPlus IOEnv
 instance MonadPlus IO => MonadPlus CoreM where
     mzero = CoreM (const mzero)
     m `mplus` n = CoreM (\rs -> unCoreM m rs `mplus` unCoreM n rs)
+#endif
 
 instance MonadUnique CoreM where
     getUniqueSupplyM = do