Haskell Quiz/Maximum Sub-Array/Solution Kristof

This solution uses a left fold to find the maximum sum. It keeps track of the maximum sublist found so far (the list max and it's sum sum), and the maximum sublist that contains the current position (r and rsum).

max_sublist l = reverse $ fst $ foldl find_max ([],(0,[],0)) l where
  find_max (max, (sum, r, rsum)) x = (max', (sum', r', rsum'))
    where
    (r', rsum')  = if (rsum > 0)
                   then (x:r, rsum+x)
                   else ([x], x)
    (max', sum') = if (rsum' > sum)
                   then (r', rsum')
                   else (max, sum)