grammar;

pub Expression: i64 = {
  <Term>,
  <left:Expression> PLUS <right:Term> => {
    left + right
  },
  <left:Expression> STAR <right:Term> => {
    left * right
  },
};

Term: i64 = {
  NUMBER => {
    <>.parse::<i64>().unwrap()
  },
  LEFT_PARENTHESIS <Expression> RIGHT_PARENTHESIS,
};

pub ExpressionPro: i64 = {
  <Expression2Pro>,
  <left:ExpressionPro> STAR <right:Expression2Pro> => {
    left * right
  },
};

Expression2Pro: i64 = {
  <TermPro>,
  <left:Expression2Pro> PLUS <right:TermPro> => {
    left + right
  },
};

TermPro: i64 = {
  NUMBER => {
    <>.parse::<i64>().unwrap()
  },
  LEFT_PARENTHESIS <ExpressionPro> RIGHT_PARENTHESIS,
};

match {
  r"\p{Zs}+" => { },

  r"[0-9]+" => NUMBER,

  "+" => PLUS,

  "*" => STAR,

  "(" => LEFT_PARENTHESIS,

  ")" => RIGHT_PARENTHESIS,
}