macro_rules! string {
    ($x:ident) => {
        stringify!($x).to_owned()
    };
}

macro_rules! make_grammar {
    (
        // comma-separated grammar rules
        $(
            $lhs:ident
            ->
            $(
                $($arg:ident)*
             )|* $(|)?
         ),* $(,)?

        // backslash for terminals
        $(
            %
            $(
                $lhs_:ident
                ->
                $re:expr
             ),* $(,)?
         )?
    ) => {
        crate::grammar::Grammar {
            start: hashset!{ $(string!($lhs),)* },
            productions: hashmap!{
                $(string!($lhs) => vec![
                    $(vec![
                        $(string!($arg),)*
                    ],)*
                ],)*
            },
            terminals: hashmap!{
                $(
                    $(string!($lhs_) => regex::Regex::new($re).unwrap(),)*
                 )?
            },
            first_sets: crate::utils::MapOfSet::default(),
        }
    };
}