Macro define_symbols

macro_rules! define_symbols {
    (
            $(
                $(#[no_error $(@ $no_error:tt)?])?
                $(#[optional $(@ $optional:tt)?])?
                $(unsafe $(@ $unsafe:tt)?)? fn $name:ident($($arg:ident: $t:ty),* $(,)?) -> $ret:ty {}
            )*
        ) => { ... };
}