code: function readNumber(walker) {
      var match = walker.match(/\s*(-?[0-9]+(\.[0-9]+)?)/g, 1);
  
      if (match) {
          return {
              type: ExprType.NUMBER,
              value: +match[1]
          };
      }
      else if (walker.currentCode() === 45) {
          walker.go(1);
          return {
              type: ExprType.UNARY,
              expr: readUnaryExpr(walker),
              operator: 45
          };
      }
  }
docs: 读取数字
  
  @inner
  @param {Walker} walker 源码读取对象
  @return {Object}