How to customize mode-line-format?

Question

I want to customize mode-line-format using if or cond etc., to let it show different text conditionally.

Here is a demo that I tried:

(setq-default
 mode-line-format
 (quote
  (
   (:eval
    (cond
     (buffer-read-only
      (propertize " ⚑ "
                  'face (:foreground "red" :weight 'bold)
                  'help-echo "buffer is read-only!!!"))
     ;; (overwrite-mode
     ;;  (propertize "??"))
     (buffer-modified-p
      (propertize " ☡ "
                  'face (:foreground "orange")
                  'help-echo "buffer modified."))
     ))

   (:eval (if (or (eq (buffer-local-value 'major-mode (current-buffer)) 'ruby-mode)
                 (eq (buffer-local-value 'major-mode (current-buffer)) 'enh-ruby-mode))
              (:propertize "Ruby"
                           face (:foreground "green"))
            (:propertize "Not Ruby"
                         face (:foreground "orange"))))
   )))

But it does not show anything, I don't know where is wrong. Need help.

BTW:

I googled this, And got two good results:

• http://amitp.blogspot.com/2011/08/emacs-custom-mode-line.html
• http://emacs-fu.blogspot.com/2011/08/customizing-mode-line.html

And I saw two different code:

(setq-default
 mode-line-format
 '(
   (:propertize var
                'face (:foreground "green"))
   ))

(setq-default
 mode-line-format
 (list
   '(:eval (if ...))
   ))

I don't know what's the difference.

---------------- UPDATE ---------------------

I found I can't put multiple (propertize ...) in one (progn ...). Is there any solution to solve this?

(setq-default
 mode-line-format
'(
  (:eval
    (if (memq (buffer-local-value 'major-mode (current-buffer))
              '(ruby-mode enh-ruby-mode))
        (progn
          (propertize " ("
                      'face '(:foreground "#444444"))
          (propertize "Ruby: "
                      'face '(:family "Segoe Print"
                                      :height 80
                                      :foreground "red2"))
          (propertize (rbenv--active-ruby-version) ; `rbenv--modestring'
                      'face '(:foreground "cyan")
                      'help-echo '(concat "\nCurrent Ruby version: " (rbenv--active-ruby-version)
                                          "\nmouse-1: switch Ruby version menu")
                      ;; 'local-map
                      )
          (propertize ")"
                      'face '(:foreground "#444444"))
          )
      ;; (propertize "Not Ruby"
      ;;             'face '(:foreground "red2"))
      ))
))

This is solved, use (list (propertize ...) (propertize ...).

Answer 1

If you want something that changes according to conditions then you pretty much need to use :eval, as in the second borrowed-code snippet.

There are several things wrong with your code. buffer-modified-p is a function, not a variable; you forgot to quote some things; etc. Try this, and then compare it carefully with your code:

(setq-default mode-line-format
              '((:eval
                 (cond
                   (buffer-read-only
                    (propertize " ⚑ "
                                'face '(:foreground "red" :weight 'bold)
                                'help-echo "buffer is read-only!!!"))
                   ((buffer-modified-p)
                    (propertize " ☡ "
                                'face '(:foreground "orange")
                                'help-echo "buffer modified."))))
                (:eval (if (memq (buffer-local-value 'major-mode (current-buffer))
                                 '(ruby-mode enh-ruby-mode))
                           (propertize "Ruby" 'face '(:foreground "green"))
                         (propertize "Not Ruby" 'face '(:foreground "orange"))))))