tail recursion

[Stephen Bloch]

Are there any Java compilers out there that optimize tail-recursion into a loop using constant memory?

I'm running Java 1.4.1 on my Mac, and tried running the following three methods to see whether the compiler was making this optimization, and it wasn't: tailRecursiveSum crashed with a stack overflow around num=6445. I would have expected the recursiveSum method to stack-overflow, but if the compiler were optimizing tail-recursion (as is specified in Scheme), tailRecursiveSum would not stack-overflow, no matter how large a positive number I gave it.

static int iterativeSum (int num) {
int answer = 0;
while (num > 0) {
answer += num;
--num;
}
return answer;
}

static int recursiveSum (int num) {
if (num <= 0) {
return 0;
}
else {
return num + recursiveSum (num-1);
}
}
 
static int tailRecursiveSum (int num) {
return trsHelper (num, 0);
}
private static int trsHelper (int num, int soFar) {
if (num <= 0) {
return soFar;
}
else {
return trsHelper (num-1, num+soFar);
}
}

[Ilja Preuss]

Have you tried the -server option when running your test?

Googling for "java tail recursion" also gives a bunch of interesting hits...