Macro native_function

macro_rules! native_function {
    ( $func_name:tt, $env:expr $( , this ( $self_name:tt ) )? $( , vm ( $vm_name:tt ) )? $( , params ( $( $required:tt ),+ ) )? $( , defaults ( $( $default:tt = $default_value:expr ),+ ) )? $( , variadic ( $variadic:tt ) )? => $body:expr ) => { ... };
}