Simple demo of type construction from Datomic with core.typed and a little glue

core.clj

(defn create-type
  "Extract a type from provided field idents stored in Datomic database at uri."
  [uri type-name overrides]
  (let [c (d/connect uri)
        d (d/db c)
        datomic-type-map {:db.type/string 'String
                          :db.type/ref 'Any}
        mt (dt/q> :- [EntityID]
              '[:find ?e
                :in $ ?t-name
                :where [?e :type/name ?t-name]]
                d
                type-name)
        t-e (->> (ffirst mt) (d/entity d) d/touch)
        man-attrs (:type/mandatory t-e)
        opt-attrs (:type/optional t-e)
        get-type
          (fn [kw]
            (->>
              (dt/q> :- [Keyword]
                '[:find ?v
                  :in $ ?a
                  :where [?e :db/ident ?a]
                         [?e :db/valueType ?v]]
                  d
                  kw)
              ffirst
              (d/ident d)
              datomic-type-map))
        t-map (fn [m] (apply merge
                        (map (fn [k] { k (get-type k) }) m)))
        man-t (merge (t-map man-attrs) overrides)
        opt-t (t-map opt-attrs)]
    `(~'HMap :mandatory ~man-t :optional ~opt-t :complete? true)))

(defmacro create-typer [n uri]
  `(defmacro ~n
    ([n# type-name#]
      `(def-alias ~n# ~(create-type ~uri type-name# {})))
    ([n# type-name# overrides#]
      `(def-alias ~n# ~(create-type ~uri type-name# overrides#)))))

datomic-types.clj

; Create a type extractor for this database.
(dat/create-typer create-type "datomic:mem://jelp")

; Use to reify a User type
(create-type User "User")

; Create Admin type from User, with a fixed :user/group
; Lets Admins be used wherever a User is, and be statically checked.
(create-type Admin "User" {:user/group (Value "admin")})

(ann my-admin Admin)
(def my-admin {:user/id "my-id"
               :user/email "[email protected]"
               :user/password "my-pass"
               :user/group "admin"})

(ann my-user User)
(def my-user {:user/id "my-id"
              :user/email "[email protected]"
              :user/password "my-pass"
              :user/group "user"})

;; Failing cases

(ann my-not-admin Admin)
(def my-not-admin {:user/id "my-id"
                   :user/email "[email protected]"
                   :user/password "my-pass"
                   :user/group "user"}) ; this isn't the admin group

(ann my-invalid-user User)
(def my-invalid-user {:user/id 10 ; should be string
                      :user/email "[email protected]"
                      :user/password "my-pass"
                      :user/group "admin"})

;; Storing the optional/mandatory inside the database like so:

  { :db/id #db/id[:db.part/types]
    :type/name "User"
    :type/mandatory [:user/id
                     :user/email
                     :user/password
                     :user/group]
    :type/optional  [:user/forename
                     :user/surname] }