code: function readParenthesizedExpr(walker) {
      walker.go(1);
      var expr = readTertiaryExpr(walker);
      walker.goUntil(41); // )
  
      expr.parenthesized = true;
      return expr;
  }
docs: 读取括号表达式
  
  @param {Walker} walker 源码读取对象
  @return {Object}