I have the following code in my `.emacs` file, which works as you'd expect:

```lisp
;; Ruby
(global-font-lock-mode 1)
(autoload 'ruby-mode "ruby-mode" "Ruby editing mode." t)
(setq auto-mode-alist (cons '("\\.rb$" . ruby-mode) auto-mode-alist))
(setq auto-mode-alist (cons '("\\.rsel$" . ruby-mode) auto-mode-alist))
(setq auto-mode-alist (cons '("\\.rhtml$" . html-mode) auto-mode-alist))
(setq auto-mode-alist (cons '("\\.erb$" . html-mode) auto-mode-alist))
(setq auto-mode-alist (cons '("\\.prawn$" . html-mode) auto-mode-alist))
(setq auto-mode-alist (cons '("Rakefile$" . ruby-mode) auto-mode-alist))

```

However, my attempts to DRY it up a bit fail:

```lisp
(defun set-mode-for-filename-patterns (mode filename-pattern-list)
  (mapcar
    (lambda (filename-pattern)
      (setq 
        auto-mode-alist 
        (cons '(filename-pattern . mode) auto-mode-alist)))
    filename-pattern-list))

;; Ruby
(global-font-lock-mode 1)
(autoload 'ruby-mode "ruby-mode" "Ruby editing mode." t)
(set-mode-for-filename-patterns 
  ruby-mode
  '("\\.rb$"
    "\\.rsel$"
    "\\.rhtml$"
    "\\.erb$" 
    "\\.prawn$"
    "Rakefile$"
    "Gemfile$"))

```

... with the following error:

```
Debugger entered--Lisp error: (void-variable ruby-mode)
  (set-mode-for-filename-patterns ruby-mode (quote ("\\.rb$" "\\.rsel$" "\\.rhtml$" "\\.erb$" "\\.prawn$" "Rakefile$" "Gemfile$")))
  eval-buffer(#<buffer  *load*> nil "/home/duncan/.emacs" nil t)  ; Reading at buffer position 1768
  load-with-code-conversion("/home/duncan/.emacs" "/home/duncan/.emacs" t t)
  load("~/.emacs" t t)
  #[nil "\205\264

```

I'm a bit confused here ... in particular, I don't understand how `ruby-mode` is void & so can't be passed to a function, but *can* be `cons`ed into a pair?

Any pointers (heh) would be greatly appreciated.