Datafy and Nav

Datafy and Nav are extension points defined in clojure to support user defined logic for transforming anything into clojure data and how to traverse it.

For a great overview of datafy and nav, I recommend reading Clojure 1.10's Datafy and Nav by Sean Corfield.

The below will demonstrate the power of datafy and nav by allowing you to traverse the hacker news api! It will produce data tagged with metadata on how to get more data!

(require '[examples.hacker-news :as hn])

(tap> hn/stories)

An interesting use case for nav is allowing users to nav into keywords to produce documentation for that keyword. This really highlights the power behind datafy and nav. It becomes very easy to tailor a browser into the perfect development environment!

Below is an example of extending the Datafiable protocol to java files:

(require '[clojure.core.protocols :refer [Datafiable]])

(extend-protocol Datafiable
  java.io.File
  (datafy [^java.io.File this]
    {:name          (.getName this)
     :absolute-path (.getAbsolutePath this)
     :flags         (cond-> #{}
                      (.canRead this)     (conj :read)
                      (.canExecute this)  (conj :execute)
                      (.canWrite this)    (conj :write)
                      (.exists this)      (conj :exists)
                      (.isAbsolute this)  (conj :absolute)
                      (.isFile this)      (conj :file)
                      (.isDirectory this) (conj :directory)
                      (.isHidden this)    (conj :hidden))
     :size          (.length this)
     :last-modified (.lastModified this)
     :uri           (.toURI this)
     :files         (seq (.listFiles this))
     :parent        (.getParentFile this)}))

Tips

If you would like to automatically datafy all tapped values, try the following:

(require '[clojure.datafy :as d])
(require '[portal.api :as p])

(def submit (comp p/submit d/datafy))
(add-tap #'submit)

(tap> *ns*)