Is there a way to count with macros?

Question

I want to create a macro that prints \"Hello\" a specified number of times. It\'s used like:

many_greetings!(3);  // expands to three `println!(\"Hello\");`          


        

Answer 1

As far as I know, no. The macro language is based on pattern matching and variable substitution, and only evaluates macros.

Now, you can implement counting with evaluation: it just is boring... see the playpen

macro_rules! many_greetings {
    (3) => {{
        println!("Hello");
        many_greetings!(2);
    }};
    (2) => {{
        println!("Hello");
        many_greetings!(1);
    }};
    (1) => {{
        println!("Hello");
        many_greetings!(0);
    }};
    (0) => ();
}

Based on this, I am pretty sure one could invent a set of macro to "count" and invoke various operations at each step (with the count).