Macro define_lang 

macro_rules! define_lang {
    (
        $suffix:ident,
        $( ($const:ident, $id:expr, $str:expr, $kind:expr $(, $block:expr)? ) ),* $(,)?
    ) => { ... };
    (@unwrap_block $block:expr) => { ... };
    (@unwrap_block) => { ... };
}