macro_rules! guard {
    ($o:expr) => {
        if let Some(x) = $o { x } else { return; }
    };
    ($o:expr, $body:block) => {
        if let Some(x) = $o { x } else { $body; return; }
    };
}

fn main() {
    let x = Some("hello");
    let y = guard!(x);
    println!("{}", y);

    let x = None;
    let y = guard!(x, {
        println!("Nothing to see here!");
    });
    println!("{:?}", y);
}