scratch.clj

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

(defn find-paths [graph from to]
  (let [children (fn [[path visited node]]
                   (map (fn [child]
                          [(conj path child)
                           (conj visited child)
                           child])
                        (remove visited (graph node))))]
    (map first (filter (comp #{to} peek)
                       (tree-seq children children [[from] #{from} from])))))

(comment
  user> (find-paths graph :a :e)
  ([:a :b :e] [:a :b :g :e] [:a :g :e])

  user> (find-paths graph :g :d)
  ()

  user> (find-paths graph :g :a)
  ([:g :e :a]))

I’ve finally found the time to fully understand your code and it’s really elegant and taught me a lot. Thanks.