**scanl** +containers

scanl is similar to foldl, but returns a sequence of reduced values from the left:
> scanl f z (fromList [x1, x2, ...]) = fromList [z, z `f` x1, (z `f` x1) `f` x2, ...]
scanl1 is a variant of scanl that has no starting value argument:
> scanl1 f (fromList [x1, x2, ...]) = fromList [x1, x1 `f` x2, ...]