gistfile1.clj

(defn a-star [get-options calc-distance from to]
  (let [add-node (fn [queue node]
                     (if (> (calc-distance (:pos (first queue)) to) (calc-distance (:pos node) to))
                       (cons node queue)
                       (cons (first queue) (add-node (rest queue) node))))
        process (fn [[node & queue] visited]
                (if (= (:pos node) to) node
                  (if (and (get visited (:pos node)) (< (:cost (get visited (:pos node))) (:cost node)))
                    (process queue visited)
                    (let [new-nodes (for [new-pos (get-options (:pos node))]
                                      {:pos new-pos :cost (inc (:cost node)) :from node})
                          new-queue (reduce add-node queue new-nodes)
                          new-visited (assoc visited (:pos node) node)]
                      (if (nil? new-nodes) nil (process new-queue new-visited))))))
        extract-path (fn [node path] 
                       (if (nil? node) path
                         (extract-path (:from node) (cons (:pos node) path))))]
    (extract-path (process '({:pos from :cost 0 :from nil}) {}) nil)))