perflatten2.hs

parFlatten2 :: [[a]] -> [a]
parFlatten2 lst = result
  where
    (result, tmp)                  =  parFlattenLoop tmp lst
    parFlattenLoop y []            =  (r, [])
      where
        (r, t)
          | null y     =  ([], undefined)
          | otherwise  =  parFlattenLoop t y
    parFlattenLoop y ([]:xss)      =  parFlattenLoop y xss
    parFlattenLoop y ((x:[]):xss)  =  (x:r, t)
      where
        (r, t) = parFlattenLoop y xss
    parFlattenLoop y ((x:xs):xss)  =  (x:r, xs:t)
      where
        (r, t) = parFlattenLoop y xss