2008/2/4, Ashish Agarwal <agarwal1975@gmail.com>:
> > but then I must append at the end of a list, that is something time
> consuming. I do not known about more options.
>
> Append to the beginning of the list during the recursion, producing the list
> in reverse. Then do a List.rev at the end.

If you don't need persistence, you can also use a stream. That way,
the stream will be consumed only as needed, and you'll have a constant
space usage, (both heap and stack).