module List where

mapAccumL               :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])
mapAccumL f s []        =  (s, [])
mapAccumL f s (x:xs)    =  (s'',y:ys)
                           where (s', y ) = f s x
                                 (s'',ys) = mapAccumL f s' xs