maxsubseq :: (Ord a, Num a) => [a] -> (a, [a]) 
maxsubseq = snd . foldl f ((0,[]),(0,[])) where
  f ((maxToHere,witnessToHere),(maxSoFar, witnessSoFar) x = (a,b) where
    a = max (0,[]) (fst x + maxToHere, x:witnessToHere)
    b = max sofar a