Return values

start:        die  /^\Z/

die:          'd' number
            | number 'd' number

number:       /\d+/

• A rule returns the value of the production that matched; undefined if no production matched.
• If a production matches, it will return the return value of the last non-comment item. (This is not always true!).
• Items return:
  • Subrule: what the subrule matches.
  • Token: the substring of the literal or regex match.
  • Action: the value of the last statement of the block.
  • Directive: we'll come back to that.
  • Comment: doesn't return anything.