Re: RFC: major change to argument processing.

[Marius Vollmer]

Rob Browning <address@hidden> writes:

> More seriously, I'll have to think about this.  If recursion, even
> when tail recursive, really is that much more expensive than other
> approaches, then I should probably start adjusting my assumptions and
> coding practices.

Ahh, no.  I only meant non-tail-recursion.  Tail-recursing is fine.

> In the long run, if there are things we can to do make recursion
> faster/more efficient, then I think they're probably important.

I don't think recursion is particularly expensive with Guile.  No need
to avoid recursion if it is otherwise a natural way to express an
algorithm.

If your algorithm makes use of a stack-like data-structure, you can
just as well use the call stack for it.  Like tree-walking: you have
to code your own stack if you want to avoid recursion.  Unlike
computing the factorial: the algorithm does not need a stack, and
coding it recursively (which might seem natural at first) will use
space linear with the argument, while the iterative version
(i.e. tail-recursing) runs in constant space.

In our case, consing up a list, we already need space linear with the
number of recursions (or iterations), so we can only gain a constant
factor when not using the stack.  Sometimes this is worth it,
sometimes not.