# 12.1 全局变量

最简单粗暴的变量是全局变量。这意味着这个变量在同一时间只有一个值，而且这个值在通常情况下会贯穿整个 Lisp 程序。直到你定义一个新的全局变量重载掉原来的变量。而旧的值就会永远消失。

你可以使用 setq 来给一个符号声明值 (value)，比如：

```
(setq x '(a b))
```

将 value (a b) 赋值给 变量 x 。注意， setq 是一个特殊表达式，而不是函数（详情查阅 特殊表达式）；Lisp 不会对第一个参数求值，而是对第二个参数求值，并将求值结果作为这个符号的值。

一旦一个变量拥有了 值(value)，你就可以将对应的符号作为表达式求值，进而引用这个值，就像这样，

```
x => (a b)
```

如果你重复赋值，那么新值会覆盖掉旧值：

```
x
    => (a b)
(setq x 4)
    => 4
x
    => 4
```

·\`


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