I gave a talk about an excellent Clojure/ClojureScript rule engine library at Ichigaya Geek Night September 22 2017. https://ichigayageek.connpass.com/event/65356/

2. - Cybozu Startups, inc
- Write web apps with
Clojure/ClojureScript
- Since May 2016

3. - http://qiita.com/iku000888
- http://github.com/iku000888
- https://twitter.com/iku000888

4. - Rule Engines
- About
- Are good
- Clara-rules
- Facts
- defrule & defquery
- session
- serialization
- Use from Java
- RETE
- Application in UI dev

5. - http://www.clara-rules.org/
- [com.cerner/clara-rules "0.16.0"]
- Clojure(JVM)
- ClojureScript(Browser etc)

6. - Historical:
- Shortage of devs
- Let non devs code
domain logic
- Lisp!
- Prolog!
- Branch of AI!
- Failed or not
debate
App
Domain
Logic
Domain
Logic

7. - ANA case
- JBoss BRMS
- https://japan.zdnet.com/article/35107193/
- ‘作業時間を20〜40%削減’!!
- ‘スクラッチ開発と比較すると約3分の1の低コスト’!!

8. Layers of functions!
- Responsibility of each layer?
- Border line case?
- Change in function params?
- Brittle!
- Spaghetti!
Controller
DB View
External
Service

9. Controller
DB View
External
Service

10. Controller
DB
View
External
Service
session
QueriesRules
Insert Facts
Fire!
Q
u
e
r
y
Q
u
e
r
y

11. - Anything
- Typically record or Java Class
;; Clojure
(defrecord Item [item-name id price])
//Java
public Class Item{
String itemName etc...
}

12. - Match with fact(s) in session
- LFS => RHS
- Bind variables (LFS)
- Join with other facts (LFS)
- Create new facts (RHS)
(r/defrule tax-item
[Item (= ?n item-name) (= ?id id) (= ?p price)]
[Tax (= id ?id) (= ?t tax)]
=> (r/insert! (->TaxedItem ?n ?id (+ ?p (* ?p ?t)))))

13. - Can take parameter
- Accumulators
- Cator to result consumers

14. (require '[clara.rules.accumulators :as acc])
(r/defquery total
[] ;; Can accept parameter
[?total <- (acc/sum :taxed-price) :from [TaxedItem]])

15. - App interface
- Immutable: ops return new sessions
- Insert facts
- Fire
- Query Results

16. (-> (r/mk-session);;defsession also
(r/insert (->Item "fish" "001" 200))
(r/insert (->Tax "001" 0.08))
(r/insert (->Item "milk" "002" 150))
(r/insert (->Tax "002" 0.28))
(r/fire-rules)
(r/query total))

17. - Advanced
- e.g. Hot load rules from a remote
server
- e.g. Store working session in DB
- e.g. Validate rules with hash

18. Still write rules/queries in Clojure
Official website:

19. - Used by many rule engines
- Allows clara-rules to be fast
- RETEII, RETEIII
- ‘Dramatically faster’ for
complex problems
- Proprietary!
- Bummer!

20. - Makes code clean
- Query -> View(React)
- Events -> Facts
- Instances
- Precept
- Fact UI

21. clara-rules:
1. Helps keep your code clean
2. Can be used to build cool stuff
3. Compelling excuse to introduce
Clojure for Java/Scala/etc users

22. http://qiita.com/iku000888/items/72525cd34cd3c0b44b31

23. Talks:
Clarifying Rules Engines with Clara Rules - Mike Rodriguez
- https://www.youtube.com/watch?v=Q_k5MkZmd-o
"Retaking Rules for Developers" by Ryan Brush
- https://www.youtube.com/watch?v=Z6oVuYmRgkk
Midwest.io 2014 - Rules as a Control Structure - Ryan Brush
- https://www.youtube.com/watch?v=zs5Rueo42TA