Darcs + Emacs

Aha, I've found it:

 ;;David's Advanced Revision Control System
(if (executable-find "darcs")
    (progn (add-to-list 'vc-handled-backends 'DARCS)
           (autoload 'vc-darcs-find-file-hook "vc-darcs")
           (add-hook 'find-file-hooks 'vc-darcs-find-file-hook)))

Since not on every computer there is/is needed darcs I've wrapped in config darcs support in order not to receive annoying error messages on every file opening.

I was lazy to write checking for the presence of executable file in PATH. It turned out that everything already exists. M-x apropos is great :)