needtocombine.hs

foo :: Rules UrlPairs
 foo = preprocess $ do
    xs <- loadUrlMap "redirectLinks.tsv"
    case xs of
      Left err -> do print err
                     pure ([] :: UrlPairs)
      Right m -> pure m

 bar :: Rules ()
 bar =  do
    xs <- foo
    let f = arr fromFilePath
        ys = fmap (Arrow.first f) xs
    createRedirects ys

blop :: Rules ()
blop = do
    xs <- preprocess $ do
      xs <- loadUrlMap "redirectLinks.tsv"
      case xs of
        Left err -> do print err
                       pure ([] :: UrlPairs)
        Right m -> pure m
    let f = arr fromFilePath
        ys = fmap (Arrow.first f) xs
    createRedirects ys