LWW in Datalog (https://speakerdeck.com/ept/data-structures-as-queries-expressing-crdts-using-datalog?slide=15)

lww-datalog.clj

  ;; LWW Register
  ;; https://speakerdeck.com/ept/data-structures-as-queries-expressing-crdts-using-datalog?slide=15

  (def schema
    {:assign/time  {:db/valueType :Number}
     :assign/key   {:db/valueType :Number}
     :assign/value {:db/valueType :Number}})

  (def rules
    '[[(older ?t1 ?key)
       [?op :assign/key ?key] [?op :assign/time ?t1]
       [?op2 :assign/key ?key] [?op2 :assign/time ?t2]
       [(< ?t1 ?t2)]]

      [(lww ?key ?val)
       [?op :assign/time ?t]
       [?op :assign/key ?key]
       [?op :assign/value ?val]
       (not [(older ?t ?key)])]])

  ;; possible ergonomics improvement
  (def rules
    '[[(older ?t1 ?key)
       #:assign{:key ?key :time ?t1}
       #:assign{:key ?key :time ?t2}
       [(< ?t1 ?t2)]]])