Macro def_enum

macro_rules! def_enum {
    (
        $ident:ident ($discriminant_type:ident) {
            $(
                $discriminant:literal = $variant:ident
                $(
                    {
                        $(
                            $field:ident $typ:ident $(<$generics:ident>)?
                        );* $(;)?
                    }
                )?
            ),* $(,)?
        }
    ) => { ... };
}