Programming in Emacs Lisp笔记（十）Yanking Text Back

kill ring是被删除字符串的列表。例如：

("some text" "a different piece of text" "yet more text")

yank命令也可以用于复制文本。复制文本而不从缓冲区剪切文本，文本被复制一份放到kill ring中。

有三个函数可以将文本从kill ring上恢复：yank，通常被绑定在C-y上；yank-pop，通常绑定在M-y；rotate-yank-pointer它使用了另外两个函数。

这些函数通过变量kill-ring-yank-pointer指向kill ring。实际上yank和yank-pop插入文本的代码都是：

(insert (car kill-ring-yank-pointer))

kill-ring-yank-pointer是与kill-ring类似的变量。

如果kill ring的内容如下：

("some text" "a different piece of text" "yet more text")

("a different piece of text" "yet more text")

kill-ring     kill-ring-yank-pointer
    |               |
    |      ___ ___  |     ___ ___      ___ ___
     ---> |   |   |  --> |   |   |    |   |   |
          |___|___|----> |___|___|--> |___|___|--> nil
            |              |            |
            |              |            |
            |              |             --> "yet more text"
            |              |
            |               --> "a different piece of text
            |
             --> "some text"

rotate-yank-pointer函数修改kill-ring-yank-pointer指向的元素；当指针指向元素的第二个元素为kill ring的结束位置时，它将自动指向kill ring的第一个元素。这也展示了如何将一个list转变为ring。rotate-yank-pointer函数虽然看起来不复杂，但它实际包含了很多 细节。