Snippet from .emacs for LESS auto-compilation

less-compilation.el

(add-to-list 'auto-mode-alist '("\\.less$" . css-mode))
(setq-default compile-less nil)
(add-hook 'css-mode-hook
          (lambda ()
            (when (string-match "\\.less$" buffer-file-name)
              (add-hook 'after-save-hook
                        (lambda ()
                          (when compile-less
                            (funcall compile-less)))))))