Why changing the value of this variable via add-to-list is not working?

Question

Usually, I do the following to change a variable's value:

1 - I execute the command set-variable

2 - I pick cider-shadow-cljs-command

3 - I tweak the value changing it to be "shadow-cljs"

It works. However, it is painful to do this every time. Thus, I would like to make the changes persist over time.

Hence, I edited my init.el file to have the following snippet:

(add-to-list 'cider-shadow-cljs-command "shadow-cljs")

Unfortunately, if I restart Emacs, an error is retrieved:

Warning (initialization): An error occurred while loading /Users/pedro/.emacs.d/init.el: Wrong type argument: listp, npx shadow-cljs

This is the original value:

(defcustom cider-shadow-cljs-command
  "npx shadow-cljs"
  "The command used to execute shadow-cljs.

By default we favor the project-specific shadow-cljs over the system-wide."
  :type 'string
  :safe #'stringp
  :package-version '(cider . "0.17.0"))

How can I fix this? Should I use a different command than add-to-list?

Answer 1

You're using set-variable interactively, not add-to-list, so I think the corresponding elisp code would be either:

(setq cider-shadow-cljs-command "shadow-cljs")

or

(customize-set-variable 'cider-shadow-cljs-command "shadow-cljs")

The setq only works if you run that after cider is loaded, and the customize-set-variable will work even if you run it before cider is loaded (it is meant for defcustom variables), so I would recommend customize-set-variable in this case.

Answer 2

add-to-list expects the value of its first argument to be a list. You're passing it symbol cider-shadow-cljs-command as first arg, and the value of that variable is a string, not a list.