Macro gen_command 

macro_rules! gen_command {
    ($ctx_type:ty, [ $( ($native_name:tt, $native_func:expr $(,)?) ),* $(,)?], [ $( ($embedded_name:tt, $embedded_space:tt, $embedded_func:expr, $embedded_help:tt $(,)?) ),* $(,)?] $(,)?) => { ... };
}