Make sure 7.6 modifications stil compile with 7.4

Database/MongoDB/Query.hs

@@ -1,6 +1,6 @@
 -- | Query and update documents
 
-{-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, TypeFamilies #-}
+{-# LANGUAGE OverloadedStrings, RecordWildCards, NamedFieldPuns, TupleSections, FlexibleContexts, FlexibleInstances, UndecidableInstances, MultiParamTypeClasses, GeneralizedNewtypeDeriving, StandaloneDeriving, TypeSynonymInstances, TypeFamilies, CPP #-}
 
 module Database.MongoDB.Query (
 	-- * Monad
@@ -47,8 +47,13 @@ import Data.Int (Int32)
 import Data.Maybe (listToMaybe, catMaybes)
 import Data.Word (Word32)
 
+#if MIN_VERSION_base(4,6,0)
 import Control.Concurrent.MVar.Lifted (MVar, newMVar, mkWeakMVar,
                                        readMVar, modifyMVar)
+#else
+import Control.Concurrent.MVar.Lifted (MVar, newMVar, addMVarFinalizer,
+                                         readMVar, modifyMVar)
+#endif
 import Control.Monad.Base (MonadBase(liftBase))
 import Control.Monad.Error (ErrorT, Error(..), MonadError, runErrorT,
                             throwError)
@@ -78,6 +83,10 @@ import Database.MongoDB.Internal.Protocol (Reply(..), QueryOption(..),
 import Database.MongoDB.Internal.Util (MonadIO', loop, liftIOE, true1, (<.>))
 import qualified Database.MongoDB.Internal.Protocol as P
 
+#if !MIN_VERSION_base(4,6,0)
+--mkWeakMVar = addMVarFinalizer
+#endif
+
 -- * Monad
 
 newtype Action m a = Action {unAction :: ErrorT Failure (ReaderT Context m) a}
@@ -511,6 +520,9 @@ newCursor db col batchSize dBatch = do
 	let cursor = Cursor (db <.> col) batchSize var
 	mkWeakMVar var (closeCursor cursor)
 	return cursor
+#if !MIN_VERSION_base(4,6,0)
+  where mkWeakMVar = addMVarFinalizer
+#endif
 
 nextBatch :: (MonadIO m, MonadBaseControl IO m) => Cursor -> Action m [Document]
 -- ^ Return next batch of documents in query result, which will be empty if finished.

System/IO/Pipeline.hs

@@ -3,6 +3,7 @@
 A pipeline closes itself when a read or write causes an error, so you can detect a broken pipeline by checking isClosed.  It also closes itself when garbage collected, or you can close it explicitly. -}
 
 {-# LANGUAGE DoRec, RecordWildCards, NamedFieldPuns, ScopedTypeVariables #-}
+{-# LANGUAGE CPP #-}
 
 module System.IO.Pipeline (
 	IOE,
@@ -19,10 +20,20 @@ import Control.Monad (forever)
 import GHC.Conc (ThreadStatus(..), threadStatus)
 
 import Control.Monad.Trans (liftIO)
+#if MIN_VERSION_base(4,6,0)
 import Control.Concurrent.MVar.Lifted (MVar, newEmptyMVar, newMVar, withMVar,
                                        putMVar, readMVar, mkWeakMVar)
+#else
+import Control.Concurrent.MVar.Lifted (MVar, newEmptyMVar, newMVar, withMVar,
+                                         putMVar, readMVar, addMVarFinalizer)
+#endif
 import Control.Monad.Error (ErrorT(ErrorT), runErrorT)
 
+#if !MIN_VERSION_base(4,6,0)
+mkWeakMVar :: MVar a -> IO () -> IO ()
+mkWeakMVar = addMVarFinalizer
+#endif
+
 onException :: (Monad m) => ErrorT e m a -> m () -> ErrorT e m a
 -- ^ If first action throws an exception then run second action then re-throw
 onException (ErrorT action) releaser = ErrorT $ do