gistfile1.txt

```Haskell
upload :: Async FilePath -> Async (Either () ())
upload files =
  asyncly
  $ maxThreads 10
  $ S.concatMap S.fromList
  |$ serially
  $ S.mapM finalizeUploads
  |$ asyncly
  $ S.chunksOf 1000 FL.toList
  |$ S.mapM uploadFile
  |$ S.filterM needUpload
  |$ files
  where
    -- at most about 10 in parallel (filesystem bound)
    needUpload :: FilePath -> IO Bool
    needUpload fp = return True
    -- at most about 10 in parallel (network bound)
    uploadFile :: FilePath -> IO FilePath
    uploadFile fp = return fp
    -- at most one at a time (must be called serially)
    finalizeUploads :: [FilePath] -> IO [Either () ()]
    finalizeUploads fps = return $ fmap (\_ -> Right ()) fps
```