Evaluation of hooks

[Sebastian Tennant]

Hi all,

I would like to add a function to my emacs-lisp-mode-hook so that whenever I
visit emacs source files, view-mode minor mode is enabled.

  (add-hook 'emacs-lisp-mode-hook
          (lambda ()
            (when (>= (compare-strings
               (buffer-file-name) 1 nil "/usr/share/emacs/" 1 nil) 17)
              (view-mode-enable))))

With the above code in my ~/.emacs, I get the following message at startup:

  >: Wrong type argument: stringp, nil

but apart from this the startup process is unaffected, and the function is
successfully added to my emacs-lisp-mode-hook, as you can see:

((lambda nil
   (when
       (>
        (compare-strings
         (buffer-file-name)
         0 nil "/usr/share/emacs/" 0 nil)
        18)
     (view-mode-enable))))

Needless to say the hook doesn't work, i.e., view-mode is not enabled when I
visit files whose full name begins /usr/share/emacs/.

The condition itself works fine, but just not as a hook.  I have tried quoting
the function (buffer-file-name) but this did not improve things.

Any help much appreciated.

TIA

sdt