code: function() {
          index++;
          var node = gobbleExpression();
          gobbleSpaces();
          if (exprICode(index) === CPAREN_CODE) {
            index++;
            return node;
          } else {
            throwError("Unclosed (", index);
          }
        }
docs: `index` stores the character number we are currently at while `length` is a constant All of the gobbles below will modify `index` as we move along