settings.clj

  (require '[clojure.spec.alpha :as s])
  (require '[spec-tools.spec :as spec])
  (require '[spec.settings :as ss])

  ;; declare your configuration
  (def settings-config
    {:debug {:spec spec/boolean?
             :doc "When true, debug options are turned on."
             :default false}
     :num-processes {:spec spec/integer?
                     :doc "Number of processes to map over"
                     :default 4}
     :fav-color {:spec spec/string?
                 :doc "Your favorite color."}
     :foo  {:spec spec/string?
            :doc "Foo; not Bar, Baz, or Qux"
            :default "foo"}})
  
  ;; specify your config
  (s/def ::settings (ss/settings-spec ::settings settings-config))

  ;; you'd normally set these via environment or at app startup
  (System/setProperty "sampleapp.debug" "true")
  (System/setProperty "sampleapp.num.processes" "2")
  (System/setProperty "sampleapp.fav.color" "blue")

  ;; validate your settings
  (= (ss/validate-settings! ::settings (ss/all-settings settings-config "sampleapp"))
     {:debug true
      :num-processes 2
      :fav-color "blue"
      :foo "foo"})