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First Steps

This page jumps into downloading and using Clara. Some new users may be interested in learning more about Clara’s approach to rules.

Let’s get started! The first thing you’ll need to do is bring Clara into your project. You can do this in Leiningen:

[com.cerner/clara-rules "0.21.1"]

or, for tools.deps, in deps.edn:

com.cerner/clara-rules {:mvn/version "0.21.1"}

or to your Maven POM:

<dependency>
  <groupId>com.cerner</groupId>
  <artifactId>clara-rules</artifactId>
  <version>0.21.1</version>
</dependency>

Your first rules

Clara rules live in a Clojure namespace and can be treated like any other code.

Let’s look at a simple, complete example using Clara:

(ns clara.example
  (:require [clara.rules :refer :all]))

(defrecord SupportRequest [client level])

(defrecord ClientRepresentative [name client])

(defrule is-important
  "Find important support requests."
  [SupportRequest (= :high level)]
  =>
  (println "High support requested!"))

(defrule notify-client-rep
  "Find the client representative and request support."
  [SupportRequest (= ?client client)]
  [ClientRepresentative (= ?client client) (= ?name name)]
  =>
  (println "Notify" ?name "that"  
          ?client "has a new support request!"))

Now let’s run those rules! We can do so from Clojure:

(-> (mk-session 'clara.example)
    (insert (->ClientRepresentative "Alice" "Acme")
            (->SupportRequest "Acme" :high))
    (fire-rules))

Or from Java:

// In Java, our facts would typically be JavaBeans.
List<Object> facts = ...;

RuleLoader.loadRules("clara.example")
  .insert(facts)
  .fireRules();

This program will simply print the following:

High support requested!
Notify Alice that Acme has a new support request!

What’s next?

Of course, a real rule set would infer new knowledge and offer ways to query it.