Faking OO in Clojure

September 13, 2012

When programming in a functional language, the often comes a time when we must couple data to functions like in an Object Oriented language. I mostly see this happen in terms of databases and relations.

In my hypothetical application I have users that have many documents. Here’s what their Hyperion protocols might look like.

(ns sample.user.user
  (:require [hyperion.api :refer [defentity]]))

(defentity User
  [name])

(ns sample.document.document
  (:require [hyperion.api :refer [defentity]]))

(defentity Document
  [name]
  [body]
  [user-key :type :key])

What if we wanted to add a method for users to get their corresponding documents? Follow certain conventions we can create a method that looks very OO.

(ns sample.user.user
  (:require [hyperion.api :refer [defentity find-by-kind]]))

;defentity

(defn documents [this]
  (find-by-kind "document" :filters [:= :user-key (:key this)]))

By using this as the name of the argument we are but into the mindset of manipulating User hashes. Every function defined inside this namespace should take a user hash as the first argument.