What is tail recursion?

Question

Whilst starting to learn lisp, I\'ve come across the term tail-recursive. What does it mean exactly?

Answer 1

In Java, here's a possible tail recursive implementation of the Fibonacci function:

public int tailRecursive(final int n) {
    if (n <= 2)
        return 1;
    return tailRecursiveAux(n, 1, 1);
}

private int tailRecursiveAux(int n, int iter, int acc) {
    if (iter == n)
        return acc;
    return tailRecursiveAux(n, ++iter, acc + iter);
}

Contrast this with the standard recursive implementation:

public int recursive(final int n) {
    if (n <= 2)
        return 1;
    return recursive(n - 1) + recursive(n - 2);
}