Questions about rust macro

help
1

Hi,

I constructed the following macro and it could pass the compilation. But I'm wondering how to use this or whether it's legal in syntax.

macro_rules! foo {
   (aa$e:expr) => { println!(stringify!($e)); }
}
2

It is legal: Rust Playground

fn main() {
    foo!(aa 1 + 1);
}
3

oh, thx a lot