core.clj

(ns core
  (:require [mount.core :as mount]
            [user-finder :refer [user-finder user-finder-2]]
            [users-db :refer [db]))
          
(mount/start)
(user-finder 2)  ; finds user with id = 2

; when I stop users-db it still works (althought db state is stopped)
; this is because state is partially applied fn that resolves db during state's start I guess
(mount/stop #'users-db/db)
(user-finder 2)  ; finds user with id = 2

; if there is no partial application it works as expected, but requires db state 
(user-finder-2 db 2)  ; throws ex that there is no db state

; is there a way to have benefits of this partially applied version (no need for passing db everywhere)
; as well as having behavior of the seconduser-finder-2 - have "live-link" to db state?

finders.clj

(ns finders)

(defn find-user [users id]
  (some #(if (= (:id %) id) %) users))

user-finder.clj

(ns user-finder
  (:require [mount.core :refer [defstate]]
            [finders :as finders]
            [users-db :refer [db]]))

(defstate user-finder :start (partial finders/find-user db))

(defstate user-finder-2 :start finders/find-user)

users-db.clj

(ns users-db
  (:require [mount.core :refer [defstate]]))

(def users #{{:id 1 :name "foo"}
             {:id 2 :name "bar"}})

(defstate db :start users)