Are programs in functional languages more likely to have stack overflows?

Question

I am starting to learn ocaml, and am really appreciating the power of recursion in the language. However, one thing that I am worried about is stack overflows.

If ocaml uses the stack for function calls, won't it eventually overflow the stack? For example, if I have the following function:

let rec sum x =
  if x > 1 then f(x - 1) + x
  else x;;

it must eventually cause a stack-overflow. If I was to do the equivalent thing in c++ (using recursion), I know that it would overflow.

So my question is, is there built in safeguards to prevent functional languages from overflowing the stack? If not, are they not less useful like this, since the above summing algorithm, written in a procedural style with a for loop, could handle any number (dis-regarding integer overflow)?

Answer 1

All (decent implementations of;-) functional languages optimize tail recursion, but that's not what you're doing here, since the recursive call is not the LAST operation (it needs to be followed by the addition).

So, one soon learns to use an auxiliary function that IS tail recursive (and takes the current total being accumulated as an argument) so the optimizer can do its job, i.e., net of possible O'Caml syntax in which I'm rusty:

let sum x =
  aux(x)(0);;

let rec aux x accum =
  if x > 1 then aux(x - 1)(accum + x)
  else (accum + x);;

Here, the sum happens as an ARGUMENT to the recursive call, i.e., BEFORE the recursion itself, and so tail optimization can kick in (because the recursion IS the last thing that needs to happen!).