Haskell Simplification 1.hs

data Query     = Query
data SomeObj   = SomeObj
data IoOnlyObj = IoOnlyObj
data Err       = Err

-- There's a decoder function that makes some object from String
decodeFn :: String -> Either Err SomeObj
decodeFn = undefined

-- There's a query, that runs against DB and returns array of strings
fetchFn :: Query -> IO [String]
fetchFn = undefined

-- there's some additional "context initializer", that also has IO
-- side-effects
makeIoOnlyObj :: [SomeObj] -> IO [(SomeObj, IoOnlyObj)]
makeIoOnlyObj = undefined

-- and now, there's a pipeline function, that takes query,
-- decodes results, and then runs another IO operation with the 
-- results of query. And it seems to me that there are much much
-- better ways of implementing such things. 
--
-- `makeIoOnlyObj` returns IO-wrapped result, and we need
-- return IO Either-wrapped. 
-- 
-- So far what I've got is as follows. How do I improve it?
pipelineFn :: Query
              -> IO (Either Err [(SomeObj, IoOnlyObj)])
pipelineFn query = do
  a <- fetchFn query
  case sequence (map decodeFn a) of
    (Left  err)  -> return $ Left $ err
    (Right res) -> do
      a <- makeIoOnlyObj res
      return $ Right a