RE: Can an RPG module call another RPG module?

where I'm using recursion though, it would have been nearly impossible to
duplicate the process without it.

Recursion removal is quite common.  For example, here is a bit of C code to
traverse a binary tree (using recursion)

traverse( struct node *t)  {
    if (t != z)  {
        visit(t);
        traverse(t->left);
        traverse(t->right);
    }
}

By replacing the recursion code with a stack, the following non-recursive
implementation can be made:
traverse(struct node *t) {
        push(t);
        while (!stackempty()) {
            t = pop();
            visit(t);
           if (t->right != z) push(t->right);
           if (t->left != z) push(t->left);
        }
}

If you are interested in reading all the gory details, this bit is from
'Algorithms in C' by Robert Sedgewick.  I use code similar to the above to
traverse nodes in an XML document.