syncWithC :: MVar CInt -> CInt -> IO () 
syncWithC m x = do 
              putMVar m x
              return ()

foreign import ccall "wrapper"
  syncWithCWrap :: (CInt -> IO ()) -> IO (FunPtr (CInt  -> IO ()))

main = do
    m <- newEmptyMVar
    -- create a partial function with mvar m already applied. Pass to C. C will back with CInt
    f <- syncWithCWrap $ syncWithC m