How to use evil-next-line in a function when being in a visually selected mode?

Question

Good day,

I wanted to use evil to move a few lines down or up at once, less than with evil-scroll-down/up, but more than one line. I made a brief function:

defun  go-up-few-lines ()
  "Insert a todo-subheading"
  (interactive)
  (evil-previous-line 4)

It works, however when I enter a visual mode it stops working. Even usual previous line doesn't work if I try to execute it with M-x. When I press the shortcut button previous line works, but go up a few lines command. I am using doom emacs on a MacOS. How can I make go up few lines work in visual mode also?

Answer 1

EDIT in response to comment

Interestingly, the command in the answer below seems to work only when invoked from a keyboard shortcut; you could bind it (e.g. to, capital, 'K') as follows:

(evil-global-set-key 'motion (kbd "K") #'my-evil-go-up-few-lines)

Due to how marking a line is implemented by evil, it is not obvious to me how to use evil commands for this programmatically, however, it anyway is preferable to use 'native emacs' functions, if possible, in 'programs'.

END EDIT

I am not sure how evil works exactly, but it is (somewhat) documented here. It mentions that using evil-declare-motion 'ensures that it behaves correctly in visual state'.

However, for this tiny modification, I would first inspect the evil-previous-line function itself, and conclude it is easiest to just adapt it to a custom version as follows:

(evil-define-motion my-evil-go-up-few-lines (count)
  "Move the cursor 4 times COUNT lines up."
  :type line
  (let (line-move-visual)
    (evil-line-move (- (* (or count 1) 4)))))