(defmethod interface:components ((graph undirected-graph))
  (do* ((remaining (interface:vertices graph)
                   (set-difference remaining last-seen))
        (interface:components '() (cons last-seen interface:components))
        (last-seen '() '()))
       ((null remaining) interface:components)
    ;; A component is created by recording all the targets in a
    ;; depth-first search.
    (interface:depth-first-search graph
                                  (lambda (_ x)
                                    (declare (ignore _))
                                    (push x last-seen))
                                  ;; Start the component discovery at any vertex from the remaining.
                                  (first remaining))))