How will the output look if my program used call by name?

Question

So this is my code and I know the output for call by value is

Here is f
main: z = 15 

What would it be if a language used call by name instead of call by value?

int f() {
    cout << "Here is f" << endl;
    return 5;
}
int g(int a) {
    int x = a;
    int y = 2 * a;
    return x + y;
}
int main() {
    int z = g(f());
    cout << "main: z = " << z << endl;
}

Answer 1

You could do it like this:

#define f(n) (cout << "Here is f" << endl, n)

#define g(n) (n + 2 * n)

int main()
{
    int z = g(f(5));
    cout << "main: z = " << z << endl;
}

The "body" of f() is evaluated twice, because it is used twice in g().

Answer 2

You can simulate call by name with std::function, and adapting the syntax:

int f() {
    std::cout << "Here is f" << std::endl;
    return 5;
}

int g(std::function<int()> a) {
    int x = a();
    int y = 2 * a();
    return x + y;
}
int main() {
    int z = g(f);
    cout << "main: z = " << z << endl;
}

With output:

Here is f
Here is f
main: z = 15

Demo