fn main() {
    {
        macro_rules! def_var1{
            ($varname:ident) => { let $varname = 42; }
        }

        def_var1!(var1);
        println!("{:?}", var1)
    }

    {
        macro_rules! def_var2 {
            () => { let var2 = 42; }
        }

        def_var2!();
        println!("{:?}", var2)
    }
}