Completion to set style

Question

I have the following function, where I would like to use completion to set the style. But the way I have done does not reset the style using M-x rk-bracemk-companion.

    (defcustom rk-bracemk-companion-style
      '("parenthesis" "expression" "mixed")
      "Set bracemk-companion-style."
      :type '(repeat string)
      :group 'convenience)
    
    (defun rk-bracemk-companion (style)
      "Indicates counterpart character when matching bracketing pairs."
    
      (interactive
       (list
        (completing-read "bracemk-companion, Sel Style: "
                 rk-bracemk-companion-style)))
    
      (show-paren-mode 1)
      (setq show-paren-delay 1.3)
    
      ;; Options: Style | `parenthesis', `expression', `mixed'
      (setq show-paren-style style)
      (setq show-paren-when-point-inside-paren t))

Answer 1

Your code has a couple of problems.

1. Option show-paren-style expects a symbol, not a string. So (a) change your defcustom to use symbols, and (b) use intern on the value returned by completing-read (which is a string).

2. Don't use setq with user options, as a general rule (good habit). Why? Because some defcustoms use :set functions, and just changing the value with setq won't do the right thing in that case.

3. You probably want a non-nil REQUIRE-MATCH arg for completing-read.

(defcustom rk-bracemk-companion-style
  '(parenthesis expression mixed)
  "Completion candidates for `rk-bracemk-companion'."
  :type '(repeat symbol)
  :group 'convenience)

(defun rk-bracemk-companion (style)
  "Choose a `show-paren-style' and use it."
  (interactive
   (list (completing-read "Style: " rk-bracemk-companion-style nil t)))
  (customize-set-variable 'show-paren-delay 1.3)
  (customize-set-variable 'show-paren-style (intern style))
  (customize-set-variable 'show-paren-when-point-inside-paren t)
  (show-paren-mode -1)
  (show-paren-mode 1))