How to find inheritance of modes?

Question

As an example, let's use latex-mode, that inherits from tex-mode, that inherits from text-mode. Is there a command, that would take as input latex-mode and give me parent and grand-parent? Or, other way around, is there a command that would take text-mode as input, and give me children and grand-children?

Answer 1

Property derived-mode-parent of a mode symbol gives you the parent mode it is derived from.

(get 'latex-mode 'derived-mode-parent)
(get 'tex-mode 'derived-mode-parent)

This will give you a list of the hierarchy:

(defun derived-modes (mode)
  "Return a list of the ancestor modes that MODE is derived from."
  (let ((modes   ())
        (parent  nil))
    (while (setq parent (get mode 'derived-mode-parent))
      (push parent modes)
      (setq mode parent))
    (setq modes  (nreverse modes))))

Answer 2

I have a version based on recursion

(defun my/derived-modes (mode)
  (interactive (list major-mode))
  (defun iter (mode)
    (and mode
         (cons mode
               (iter (get mode 'derived-mode-parent)))))
  (message "%s" (iter mode)))