Macro check_args 

macro_rules! check_args {
    (@AS_EXPR $e:expr) => { ... };
    (@ARGS_CHECK ($(,)?) -> ($($args:tt)*) ()) => { ... };
    (@ARGS_CHECK (, *) -> ($($args:tt)*) ()) => { ... };
    (@ARGS_CHECK (, $arg:tt $($ty:tt)*) -> ($($args:tt)*) ()) => { ... };
    (@ARGS_CHECK (| $($ty:tt)*) -> ($($args:tt)*) ()) => { ... };
    (@ARGS_CHECK ($(,)?) -> ($args:expr) ($($opt_args:tt)+)) => { ... };
    (@ARGS_CHECK (, *) -> ($args:expr) ($($opt_args:tt)+)) => { ... };
    (@ARGS_CHECK (, $arg:tt $($ty:tt)*) -> ($args:expr) ($($opt_args:tt)+)) => { ... };
    (@BUILD_TUPLE $args_iter:ident, $is_opt:tt ($(,)?) -> ($($body:tt)*)) => { ... };
    (@BUILD_TUPLE $args_iter:ident, $is_opt:tt (, *) -> ($($body:tt)*)) => { ... };
    (@BUILD_TUPLE $args_iter:ident, $is_opt:tt (| $($ty:tt)*) -> ($($body:tt)*)) => { ... };
    (@BUILD_TUPLE $args_iter:ident, $is_opt:tt (, $arg:tt $($ty:tt)*) -> ($($body:tt)*)) => { ... };
    (@PARSE_ARG $args_iter:ident, Value) => { ... };
    (@PARSE_ARG_OPT $args_iter:ident, Value) => { ... };
    (@PARSE_ARG $args_iter:ident, $ty:tt) => { ... };
    (@PARSE_ARG_OPT $args_iter:ident, $ty:tt) => { ... };
    (@AS_VALUE_TYPE $value:ident, $ty:tt) => { ... };
    ($args:ident $(,)?) => { ... };
    ($args:ident $($cont:tt)*) => { ... };
}