Computing value from list lengths

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I have the following code and want to determine maxdepth
automatically from the length of the dark-theme-colours and
light-theme-colours (and changing the ahrd coded (dotimes (i 8)).

What would be the strategy?


(defcustom maxdepth 8
  "Number of faces defined for colouring brace marks.
Determines depth at which to cycle through faces again."
  :type 'integer
  :group 'test)
(eval-when-compile
  (defmacro colour-typeface ()

    ( let ( (faces '())
            (dark-theme-colours
             [ "#ff62d4" "#3fdfd0" "#fba849" "#9f80ff"
           "#4fe42f" "#fe6060" "#4fafff" "#f0dd60" ])
        (light-theme-colours
             [ "#a8007f" "#005f88" "#904200" "#7f10d0"
           "#006800" "#b60000" "#1f1fce" "#605b00" ]) )

      (dotimes (i 8)
        (push
         `( defface ,(intern (format "depth-%d-face" (1+ i)))
            '( (default (:inherit richerenkov-base-face))
               ( ((class color) (background dark))
                 :foreground ,(aref dark-theme-colours  i) )
               ( ((class color) (background light))
                 :foreground ,(aref light-theme-colours i) ))
            ,(format "Nested delimiter face, depth %d." (1+ i) )
            :group 'colour-faces )
         faces))

      `(progn ,@faces) ) ))

(colour-typeface)