mapcascalog.clj

(def src [[{:name "smeagol"}]
          [{:name "gollum"}]
          [{:tuple "field!"}]])

;; Retrieve some field from a bunch of records:
(??<- [?name]
      (src ?m)
      (get ?m :name :> ?name))
;;=> (["smeagol"] ["gollum"])

;; Using !name keeps the nils around:
(??<- [!name]
      (src ?m)
      (get ?m :name :> !name))
;;=> (["smeagol"] ["gollum"] [nil])

;; Filter based on a map field:
(??<- [?m]
      (src ?m)
      (get ?m :name :> "smeagol"))
;;=> ([{:name "smeagol"}])

;; or on the presence of a key:
(??<- [?m]
      (src ?m)
      (contains? ?m :name)
      (:distinct false))
;;=> ([{:name "smeagol"}]
;;    [{:name "gollum"}])