datahike_simple_recursion.clj

(require '[datahike.api :as d])

(def uri "datahike:mem://simple_recursion")

(d/delete-database uri)

(d/create-database uri :schema-on-read true)

(def conn (d/connect uri))

(d/transact conn [{:db/id 1
                   :ancestor 2}
                  {:db/id 2
                   :ancestor 3}
                  {:db/id 3
                   :ancestor 4}])

(def rule '[[(ancestor ?e1 ?e2)
             [?e1 :ancestor ?e2]]
            [(ancestor ?e1 ?e2)
             [?e1 :ancestor ?t]
             (ancestor ?t ?e2)]])

(d/q '[:find  ?u1 ?u2
       :in    $ %
       :where (ancestor ?u1 ?u2)]
     @conn
     rule)