(use '[datomic.api :only [db q] :as d])

(def schema
  [{:db/doc "A persons name"
    :db/id #db/id[:db.part/db]
    :db/ident :name
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/one
    :db.install/_attribute :db.part/db}
   
   {:db/doc "A persons daughter"
    :db/id #db/id[:db.part/db]
    :db/ident :daughter
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/many
    :db.install/_attribute :db.part/db}

   {:db/doc "A persons son"
    :db/id #db/id[:db.part/db]
    :db/ident :son
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/many
    :db.install/_attribute :db.part/db}])

(def tx-data
  (let [[victor kathleen joseph
         wendy  jeffrey  rosa
         harry  grace    william]
        (repeatedly #(d/tempid :db.part/user))]
    [{:db/id victor :name "Victor"
      :son [joseph harry]
      :daughter [grace]}
     {:db/id joseph :name "Joseph"
      :son [william]
      :daughter [rosa wendy]}
     {:db/id grace :name "Grace"
      :son [jeffrey]}
     {:db/id kathleen :name "Kathleen"}
     {:db/id wendy :name "Wendy"}
     {:db/id jeffrey :name "Jeffrey"}
     {:db/id rosa :name "Rosa"}
     {:db/id harry :name "Harry"}
     {:db/id william :name "William"}]))

(def genealogy
  (let [uri "datomic:mem://genealogy"]
    (d/delete-database uri)
    (d/create-database uri)
    (let [conn (d/connect uri)]
      (d/transact conn schema)
      (d/transact conn tx-data)
      (db conn))))

;; 'child' is derived
(def child
  '[[[child ?parent ?child]
     [?parent :daughter ?child]]
    [[child ?parent ?child]
     [?parent :son ?child]]])

;; Who are the children of Joseph?
(q '[:find ?child-name
     :in $ % ?parent-name
     :where
     [?child :name ?child-name]
     [?parent :name ?parent-name]
     [child ?parent ?child]]
   genealogy
   child
   "Joseph")
;; #<HashSet [["Wendy"], ["Rosa"], ["William"]]>

(def ancestor
  '[[[ancestor ?a ?d]
     [child ?a ?d]]
    [[ancestor ?a ?d]
     [child ?a ?x]
     [ancestor ?x ?d]]])

;; Who are the ancestors of Victor?
(q '[:find ?dname
     :in $ % ?aname
     :where
     [?ae :name ?aname]
     [?d :name ?dname]
     [ancestor ?ae ?d]]
   genealogy
   (concat ancestor child)
   "Victor")
;; #<HashSet [["Joseph"], ["Wendy"], ["Grace"], ["William"],
;;            ["Rosa"], ["Harry"], ["Jeffrey"]]>

;; Exact copy of previous query, but the ?ae variable changed to ?a
(q '[:find ?dname
     :in $ % ?aname
     :where
     [?a :name ?aname]
     [?d :name ?dname]
     [ancestor ?a ?d]]
   genealogy
   (concat ancestor child)
   "Victor")
;; #<HashSet []>