[Haskell-beginners] foldM with tuple and maybe

Hi, please can you help me with following? I have a following function: f1 :: (String, String) -> IO (Maybe String) which I would like to apply to a list of tuples.I have defined the function like this, but that gives me error (below): f2 :: [(String, String)] -> IO (Maybe String) f2 x = foldM f1 0 x error: Couldn't match expected type `IO (Maybe String)' with actual type `[b0] -> m0 (String, String)' In the return type of a call of `foldM' thanks, m.