.emacs loop to assign some minor mode to some major modes

Question

I want to hook {whitespace and yas/minor-mode} minor modes to some major modes. Of course that could be done, manually, but I want a loop. So I tried to write it:

(progn 
(setq modes-to-be-hooked '(lisp-mode-hook rst-mode-hook python-mode-hook emacs-lisp-mode-hook text-mode-hook tcl-mode-hook c-mode-hook fortran-mode-hook))
  (while modes-to-be-hooked
    (setq my-hooks '( yas/minor-mode whitespace-mode ))
      (while my-hooks
         (add-hook '(pop modes-to-be-hooked) '(pop my-hooks)))
  )
)

The problem with this loop is that the last element of list is "nil" and (add-hook 'nil 'nil) gives an error. Then I tried to escape nils with if, but it doesn't work:

(progn 
  (setq mylist '(a b c))
  (while mylist
        (progn
          (setq temp (pop mylist))
          (if temp (message "%s" temp) (message "It's nil!") )
          (sleep-for 1)
        )
  )
)

prints nil :(

phils phils · Accepted Answer · 2011-06-18T16:32:59

Well I can see a couple of problems with your code. Firstly, you are popping from your major mode list every time you pop from your minor mode list. Secondly, you are quoting your (pop) calls, which means you are not passing the values you want into (add-hook).

A while loop does not execute its body when the loop value is nil, so your second block of code doesn't produce nil via your (message) because it doesn't get that far. nil is simply the final value produced in that (progn), being the eventual return value of the while loop when it encounters nil.

You might want to check out the interactive debugging support in Emacs so that you can figure out what is actually happening if your code isn't behaving the way you expected. See:
M-: (info "(elisp) debugging") RET

However, I would suggest using lhui's solution rather than fixing what you have.

For an alternative syntax, I use this approach:

(defun my-coding-config ()
  (whitespace-mode 1)
  (yas/minor-mode 1))

(mapc
 (lambda (language-mode-hook)
   (add-hook language-mode-hook 'my-coding-config))
 '(lisp-mode-hook
   rst-mode-hook
   python-mode-hook
   emacs-lisp-mode-hook
   text-mode-hook
   tcl-mode-hook
   c-mode-hook
   fortran-mode-hook))

Defining a named function like my-coding-config simplifies things if you decide to include some new functionality later (such as including another minor mode) as you can make the change take immediate effect simply by re-evaluating that one function, rather than removing/adding items to all those hook variables.

.emacs loop to assign some minor mode to some major modes

2 Answers