(defmethod interface:components ((graph undirected-graph))
  (iterate (for remaining = (interface:vertices graph)
                then (set-difference remaining last-seen))
    (as last-seen = nil)                ; last-seen is reset to nil every time?
    (while remaining)
    (with components)
    (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))
    ;; this returns a list of last-seen sets, which I think is what the original does, but if you
    ;; want a single set, then this should be "appending"
    (collecting last-seen)))