code: function readMultiplicativeExpr(walker) {
      var expr = readUnaryExpr(walker);
  
      while (1) {
          walker.goUntil();
  
          var code = walker.currentCode();
          switch (code) {
              case 37: // %
              case 42: // *
              case 47: // /
                  walker.go(1);
                  expr = {
                      type: ExprType.BINARY,
                      operator: code,
                      segs: [expr, readUnaryExpr(walker)]
                  };
                  continue;
          }
  
          break;
      }
  
  
      return expr;
  }
docs: 读取乘法表达式
  
  @param {Walker} walker 源码读取对象
  @return {Object}