foldl' :: (r -> a -> r) -> r -> Node a -> r
foldl' f z (Node _ n) = V.foldl' f z n
foldl' :: (r -> a -> r) -> r -> Node a -> r
foldl' f z (Node _ n) = V.foldl' f z n
foldl' f z (Node _ n) = V.foldl' f z n