this post was submitted on 28 Nov 2023
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Quick pain-saver tip

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It is recommended to not use lambdas in (add-hook) expressions. Is there a better way to do (setq)s for major modes without (add-hook) at all? (alien.top)
submitted 1 year ago by ragnese@alien.top to c/emacs
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For example, let's say I were to change backward-delete-char-untabify-method for prog-mode buffers. Naively, I'd write something like,

(add-hook 'prog-mode-hook (lambda ()
                       (setq-local backward-delete-char-untabify-method 'hungry)))

but the documentation recommends against using lambdas in add-hook calls (which makes sense). I can, of course, just make a named function instead of a lambda and pass that to add-hooks. But, rather than do that, is there any other option for setting variables automatically for modes besides a hook like this?

Also, as a bonus question, if I wanted to also do something like enable show-paren-mode for all prog-mode buffers, which of the following do you consider "better" (assume that this is not something that is likely to change frequently):

;; option 1
(defun my-prog-mode-settings ()
  (setq-local backward-delete-char-untabify-method 'hungry))

(add-hook 'prog-mode-hook #'my-prog-mode-settings)
(add-hook 'prog-mode-hook #'show-paren-mode)

;; option 2
(defun my-prog-mode-settings ()
  (setq-local backward-delete-char-untabify-method 'hungry)
  (show-paren-mode))

(add-hook 'prog-mode-hook #'my-prog-mode-settings)

Obviously, I realize that it's not really important, but I feel like bike-shedding this morning.

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[–] JDRiverRun@alien.top 1 points 1 year ago

You can also use this approach:

(add-hook 'text-mode-hook
          (defalias 'my/fancy-mode-setup
            (let (some-closure-var)
              (lambda () ...))))

Advantage is that there can be only one alias, and it's added by name to the hook. So you can alter and re-run add-hook without duplication, and you can easily remove it by name. Best of all, you can create a closure (the let there) if you need that gives you "local storage in the function" that persists between runs (without cluttering the namespace with global variables).