code: function parseCall(source, defaultArgs) {
      var expr = readCall(new Walker(source), defaultArgs);
  
      if (expr.type !== ExprType.CALL) {
          expr = {
              type: ExprType.CALL,
              name: expr,
              args: defaultArgs || []
          };
      }
  
      expr.raw = source;
      return expr;
  }
docs: 解析调用
  
  @param {string} source 源码
  @param {Array=} defaultArgs 默认参数
  @return {Object}