Depth first search

dfs.clj

(defn dfs [g]
  (let [visited (atom #{})]
    (letfn
	[(search_tree [v]
		      (if (not (@visited v))
			(do
			  (swap! visited conj v)
			  (cons v (search (g v))))))
	 (search [vs]
		 (if (seq vs)
		   (mapcat search_tree vs)))]
      (search (keys g)))))

;===============================================================================

(def graph {:a [:b :c :g]
	    :b [:e :g]
	    :c []
	    :d []
	    :e [:a]
	    :f [:c :d]
	    :g [:e]})

(def vertex_order [:a :b :e :g :c :d :f])

(assert (= (dfs graph) vertex_order))