Macro parse_enum 

macro_rules! parse_enum {
    (
        $ty:ty,
        $(
            ($variant:ident, $text:expr),
        )+
        |$arg:ident| $fallback:expr,
    ) => { ... };
    (
        $ty:ty,
        $(
            ($variant:ident, $text:expr),
        )+
    ) => { ... };
}