This document provides an introduction to Clojure, a Lisp dialect that runs on the Java Virtual Machine. It discusses key Clojure concepts like immutable data structures, functional programming with first-class functions, and macros. Examples are given of using Clojure for list processing, building applications with frameworks like Cascalog for logic programming and Compojure for web development. Garbage collection in Clojure is also briefly mentioned.

1. Clojure: from ground up
R君

2. Agenda
• Lisp & Clojure intro (GC, FP, immutable)
• macro
• application

3. Clojure
Yet Another JVM Programming Language, a Lisp dialect.

4. (defn concat [xs ys]!
(if (empty? xs)!
ys!
(let [[h & t] xs]!
(cons h (concat t ys)))))
Lots of Irritating Stupid Parentheses

5. (defn concat [xs ys]!
(if (empty? xs)!
ys!
(let [[h & t] xs]!
(cons h (concat t ys)))))
LISt Processing

6. S-expression
http://norvig.com/lispy.html

7. GC
mark compact

8. GC
mark and sweep
http://atlas.cs.virginia.edu/~weimer/2008-415/reading/bacon-garbage.pdf

9. Functional Programming
• function as first-class citizen
• work by arguments and returning value
(defn make-adder [base]
(let [ref (atom base)]
(fn [delta]
(swap! ref (partial + delta)))))

10. Immutable
m = new HashMap();
m.put(1, “a”);
m.put(2, “b”);
m = new PersistentHashMap();
m = m.assoc(1, “a”);
m = m.assoc(2, “b”);

11. macro
(defmacro when [pred & body]
`(if ~pred (do ~@body) nil))
(when (> x 2)
(* x 4))
(if (> x 2)
(* x 4)
nil)

12. macro
(gen-from-tpl "exception {ex} at {line}")
(defmacro gen-from-tpl
[tpl-str]
(let [partitions (re-partition #"{((?:w|-)+)}" tpl-str)
string-and-symbol (map (fn [{:keys [match? result]}]
(if match?
(-> result second symbol)
result))
partitions)]
`(str ~@string-and-symbol)))
(str "exception" ex "at" line)

13. application
• strom
• cascalog
• compojure

14. application
cascalog
(?- (stdout)
(<- [?word ?count]
(sentence :> ?line)
(tokenise :< ?line :> ?word)
(c/count :> ?count)))
SELECT word, COUNT(*)
FROM words
GROUP BY word

15. application
compojure
(defroutes user-routes
(POST “/login" [username password] users/login)
(GET "/user/:id" [id] users/get-by-id))
(context "/user/current" []
(GET "/" [] …)
(POST "/profile" [phone location] ...)
(GET "/posts" [text] ...)))

16. Why Clojure
Java interop
java.lang.Math/PI => 3.141592653589793
(.exists (java.io.File. "t1.clj")) => true
(.toUpperCase "foo") => "FOO"

17. Q & A

18. Thanks