Macro rules 

macro_rules! rules {
    (
        $(
            $v:vis $name:ident $( ($id:expr) )? = ($symbol:ident,$rules:ident) => $b:block
        )*
    ) => { ... };
    (@I $v:vis $name:ident($id:expr) = ($symbol:ident,$rules:ident) => $b:block) => { ... };
    (@I $v:vis $name:ident = ($symbol:ident,$rules:ident) => $b:block) => { ... };
}