code: function readLogicalANDExpr(walker) {
      var expr = readEqualityExpr(walker);
      walker.goUntil();
  
      if (walker.currentCode() === 38) { // &
          if (walker.nextCode() === 38) {
              walker.go(1);
              return {
                  type: ExprType.BINARY,
                  operator: 76,
                  segs: [expr, readLogicalANDExpr(walker)]
              };
          }
  
          walker.go(-1);
      }
  
      return expr;
  }
docs: 读取逻辑与表达式
  
  @param {Walker} walker 源码读取对象
  @return {Object}