Joy of Clojure

A very brief introduction to Clojure delivered at Barcamp Shanghai on March 3, 2012.

Transcript

1. The Joy of Clojure Clojure之乐 John Biesnecker twitter: @biesnecker 新浪微博: @岳撼 Barcamp Shanghai, 03 March 2012
2. Quick show of hands. Clojure junkies? LISP hackers? Functional Programming aficionados? Java nerds? How many of you are ...
3. (= :clojure [:lisp :functional :jvm])
4. (= :clojure [:lisp :functional :jvm])
5. http://xkcd.com/297/
6. (= :data :code) (= :code :data) homoiconicity
7. (+ 1 2) ;; => 3
8. (eval (list (symbol “+”) 1 2)) ;; => 3
9. macros extend the language seamlessly
10. (defmacro unless [condition & body] `(if (not ~condition) (do ~@body))) ;; (unless (= true false) ;; (println “You don’t understand booleans, do you?”))
11. (= :clojure [:lisp :functional :jvm])
12. functional, but not pedantic about it (sorry Haskell... we can still be friends though, right?)
13. immutable by default (with managed mutability when you need it)
14. easier to reason about
15. expressive
16. ;; sum of multiples of 27 under one million (reduce + (filter #(zero? (mod % 27)) (range 0 1e6))) ;; 18518981481
17. composable (small pieces, loosely joined)
18. ;; functions are first-class object (defn increment-by-three [x] (+ x 3)) (defn contrived-example [avector afunction] (map afunction avector) ;; (contrived-example [1 2 3] increment-by-three) ;; => (4 5 6)
19. ;; anonymous functions are easy (defn contrived-example [avector afunction] (map afunction avector) ;; (contrived-example [1 2 3] #(+ % 3)) ;; => (4 5 6)
20. (= :clojure [:lisp :functional :jvm])
21. (almost) seamless interop with Java
22. (BigInteger. “12345678900987654321”) ;; returns a java.math.BigInteger object
23. most new languages have poor library support
24. Clojure has every library ever written in Java
25. ;; writing a high-performance thread-safe cache is hard (import ‘com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap) (import ‘com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap$Builder) (-> (ConcurrentLinkedHashMap$Builder.) (.maximumWeightedCapacity 1000) (.build)) ;; thanks, Google ;-)
26. (= :clojure [:lisp :functional :jvm])
27. did I mention killer concurrency support?
28. questions?
29. 谢谢 Thank you