[Haskell-beginners] Problems with parsing in attoparsec

[Michel Kuhlmann]

Hi,
I couldn't figure out, why I'm failing with attoparsec.
I have the follwing code (https://github.com/michelk/devsurf/tree/readNet)

    import           Data.Attoparsec.Text
    import qualified Data.Text as T
    import           Language.DevSurf.Readers.SpringNet
    import Prelude hiding (takeWhile, take)

    data IndexedFace 
        = IndexedFaceTriangle Int Int Int
        | IndexedFaceQuad     Int Int Int Int
        deriving (Show)

    -- | block of faces-lines
    faces :: Parser [[(Int, IndexedFace)]]
    faces = faceLine `sepBy` endOfLine
    
    -- | Line containing up to two indexed faces
    faceLine :: Parser [(Int, IndexedFace)]
    faceLine = face `sepBy` (take 6)
    
    -- | single indexed-face
    face :: Parser (Int, IndexedFace)
    face = do
      i  <- index
      v1 <- index
      v2 <- index
      v3 <- index
      v4 <- index
      case v4 of
        0  -> return (i, IndexedFaceTriangle v1 v2 v3)
        _  -> return (i, IndexedFaceQuad     v1 v2 v3 v4)
    
    -- | node or face index 6 wide
    index :: Parser Int
    index = do
      i <- take 6
      return . read . T.unpack $ i

When testing, the follwing is working: 

    testEleL2 = do
      let ele = T.pack    "     1    10     1     9     0           2     1     2     9     0\n"
          r    =  parse faceLine ele
      case r of
           Partial _ -> print $ feed r (T.pack "")
           _         -> print r

    testEles = do
      let eles = T.pack $ concat ["     1    10     1     9     0           2     1     2     9     0\n"
                                 --,"     3    11     9     2     0\n"
                                 ,"     4    12     8     1     0\n"
                                 ]
          r    =  parse faces eles
      case r of
           Partial _ -> print $ feed r (T.pack "")
           _         -> print r

    testEles = do
      let eles = T.pack $ concat ["     1    10     1     9     0           2     1     2     9     0\n"
                                 ,"     3    11     9     2     0\n"
                                 --,"     4    12     8     1     0\n"
                                 ]
          r    =  parse faces eles
      case r of
           Partial _ -> print $ feed r (T.pack "")
           _         -> print r

But this is not working

    testEles = do
      let eles = T.pack $ concat ["     1    10     1     9     0           2     1     2     9     0\n"
                                 ,"     3    11     9     2     0\n"
                                 ,"     4    12     8     1     0\n"
                                 ]
          r    =  parse faces eles
      case r of
           Partial _ -> print $ feed r (T.pack "")
           _         -> print r


    testEles = do
      let eles = T.pack $ concat ["     1    10     1     9     0           2     1     2     9     0\n"
                                 ,"     3    11     9     2     0           4    12     8     1     0\n"
                                 ]
          r    =  parse faces eles
      case r of
           Partial _ -> print $ feed r (T.pack "")
           _         -> print r

Please help.
Thanks, Michel