[elisp新手历险] 在function里add-hook ... lambda ...

Emacs-Lisp
1

我需要给不同的major mode设置不同的company-backends，自然想到用个函数wrap一下，省略掉

(add-hook 'web-mode-hook (lambda ()
(setq-local company-backends (append '(company-web-html company-css) company-backends))))

这里的lambda setq-local append部分。

一开始写出来是这样的：

(defun jester/set-company-backends-for-mode (mode backends)
    "append `BACKENDS' to the head of default `company-backends',
use the result for `MODE'\'s local `company-backends'."
    (add-hook (intern (format "%s\-hook" mode))
              (lambda () (setq-local company-backends (append backends company-backends)))))

结果一直显示backends是个void variable。想了很久，明明这是个普通的function啊，backends作为参数不是会被eval吗，哪里出了问题。

终于灵光乍现：lambda里面的内容不会被eval！怎么办呢，要eval它再构造lambda，只能用macro了，试着写了下，测试下来是对的：

(defmacro jester/set-company-backends-for-mode (mode backends)
    "append `BACKENDS' to the head of default `company-backends',
use the result for `MODE'\'s local `company-backends'."
    `(add-hook (intern (format "%s\-hook" ,mode))
              (lambda () (setq-local company-backends (append ,backends company-backends)))))
1 个赞
2 
(setq lexical-binding t)

开启lexical binding就可以用函数啦

3

我是把这个过程直接写在各个mode-hook里……

不过现在其实就设一个company-backends也没什么关系，因为backends会自行判断要不要加载

2 个赞
4

变量作用域的问题，跟这个帖子一样：如何定义函数来嵌入after-make-frame-functions

5

真的！随便看了下company-css里有

(or (derived-mode-p 'css-mode)
    (and (derived-mode-p 'web-mode)
         (string= (web-mode-language-at-pos) "css")))
6

还有lexical-binding下lambda自动成为closure