Orgmode plain list bullet : change automatically with list depth

[DEBRY.Edouard <edouard.debry@mbda-systems.com>]

When making a plain list in orgmode, I would like to change of bullet
autmatically depending on the list depth.

Currently, I use this to prettify bullets :

(font-lock-add-keywords 'org-mode
                        '(("^ *\\([-]\\) "
                           (0 (prog1
                                  ()
                                (setq bullet "•")
                                (compose-region (match-beginning 1) (match-end 1) bullet))))))

I attempted to this :
(font-lock-add-keywords 'org-mode
                         '(("^ *\\([-]\\) "
                            (0 (let* ((depth (org-list--depth (org-element-at-point)))
                                      (bullet (cond ((= depth 1) "•")
                                                    ((= depth 2) "▸")
                                                    (t "-"))))
                                 (prog1 () (compose-region (match-beginning 1) (match-end 1) bullet)))))))

for the bullet to change with respect to the org list depth, so to have
(e.g.) :
• test
  ▸ test1
  ▸ test2

But it breaks the org file.

How could I achieve this ?

Regards

___________________________________________________________________________________________________________________________________

This email and any attachments are confidential to the intended recipient and may also be privileged.
If you are not the intended recipient please delete it from your system and notify the sender. 
You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person.
 

Ce courriel et ses pieces-jointes sont envoyes de maniere confidentielle et doivent etre traites avec attention.
Si vous n'etes pas le destinataire, merci de le detruire et d'en informer son auteur. 
Vous ne devez pas copier, utiliser, reveler ou diffuser son contenu a quiconque.