Not Join in datascript

negation.clj

(def conn (d/create-conn {}))

(def data
  [{:a 1 :b 2}
   {:a 2 :b 3 :c true}])

(d/transact! conn data)

(defn not-join
  [db q vars where]
  (let [q+ (assoc q :find vars)
        q- (assoc q+ :where where :in ['$ [vars '...]])
        q-join (assoc q :in ['$ [vars '...]])
        vals+ (d/q q+ db)
        vals- (d/q q- db vals+)
        vals (clojure.set/difference vals+ vals-)]
    (d/q q-join db vals)))

(comment
  {:find [?a ?b]
   :where
   [[?e :a ?a]
    [?e :b ?b]
    (not-join [?e]
              [?e :c true])]})

(println
  (not-join
    (d/db conn)
    '{:find [?a ?b]
      :where
      [[?e :a ?a]
       [?e :b ?b]]}
    '[?e]
    '[[?e :c true]]))