# File lib/rgl/traversal.rb, line 300
300:     def depth_first_search (vis = DFSVisitor.new(self), &b)
301:       each_vertex do |u|
302:         unless vis.finished_vertex?(u)
303:           vis.handle_start_vertex(u)
304:           depth_first_visit(u, vis, &b)
305:         end
306:       end
307:     end