Annotated Examples

[Veykril]

The old book had an annotated examples section which basically was meant to show some more complex real world macros with comments explaining it more in-depth.

See https://danielkeep.github.io/tlborm/book/aeg-README.html

[guigo613]

in section 2.2 there is a good example of a macro
playing a little I created a simpler macro and would like to share it in case it is useful

use std::iter::from_fn;

macro_rules! recur {
    ($x:ident[$y:ident]: $t:ty = $($a:literal),+, ..., $b:expr) => {
        {
            let mut $x = [$($a),+];
            let mut $y = 0;
            let len = $x.len();
            from_fn::<$t, _>(move || {
                if $y < len {
                    let b = Some($x[$y]);
                    $y += 1;
                    
                    b
                } else if len > 1 {
                    let b = $b;
                    $x.copy_within(1.., 0);
                    $x[len - 1] = b;
                    Some(b)
                } else {
                    $x[0] = $b;
                    Some($x[0])
                }
            })
        }
    }
}

let re = recur!(a[n]: usize = 0, 1, 1, 2, 3, 5, ..., a[n-2] + a[n-1]);
    
for r in re.skip(3).take(10) {
    println!("{r}");
}