1. Clojure John Vlachoyiannis @jonromero jon@emotionull.comHttp://jon.is.emotionull.com

2. What is Clojure?

3. Ok, what is Lisp?

4. Lisp is worth learning for the profound enlightenment experience you will havewhen you finally get it; that experience willmake you a better programmer for the restof your days, even if you never actually use Lisp itself a lot." Eric S. Raymond, "How to Become a Hacker".

5. LISP stands for: Lots of Insane Stupid Parentheses Anonymous

6. The Truth about Lisp

7. LISt Processing LIS Second oldest high-level language (first is Fortran) Code as Data (Homoiconic) Perfect for Domain-specific languages (DSL) Exploratory programming

8. Clojure Lisp in JVM Concurrent programming Dynamic Development (REPL) Lazy sequences No side effects (almost)

9. Enter Clojure

10. Everything is code

11. (println "Hello World")function argument

12. Everything is data

13. (println "Hello World")list symbol string

14. Integers 1234567891234 Doubles 3.14. BigDecimals 3.14M Ratios 22/4 Strings foo, Character a b c Symbols foo, Keywords :foo Booleans true false, Null nil Regex patterns #[a-zA-Z0-9]|

15. Data structures Lists (1 2 3 4), (foo bar baz), (list 1 2 3) Vectors [1 2 3], [foo bar], (vector 1 2 3) Maps {:a 1 :b 2 :c 3} Sets #{foo bar}

16. It is better to have 100functions operate on one data structure than to have 10 functions operate on 10 data Structures. Alan J. Perlis

17. clojure might be a better java than java

18. public class StringUtils { public static boolean isBlank(String str) { int strLen; if (str == null || (strLen = str.length()) == 0) { return true; } for (int i = 0; i < strLen; i++) { if ((Character.isWhitespace(str.charAt(i)) ==false)) { return false; } } return true; }}

19. public class StringUtils { public isBlank(str) { if (str == null || (strLen = str.length()) == 0) { return true; } for (i = 0; i < strLen; i++) { if ((Character.isWhitespace(str.charAt(i)) ==false)) { return false; } } return true; }}

20. public isBlank(str) { if (str == null || (strLen = str.length()) == 0) { return true; } for (i = 0; i < strLen; i++) { if ((Character.isWhitespace(str.charAt(i)) == false)) return false; } } return true;}

21. public isBlank(str) { if (str == null || (strLen = str.length()) == 0) { return true; } every (ch in str) { Character.isWhitespace(ch); } return true;}

22. public isBlank(str) { every (ch in str) { Character.isWhitespace(ch); }}

23. (defn blank? [s] (every? #(Character/isWhitespace %) s))

24. Clojure vs Java code Side-effect free Error prone Easy to (unit) test Not so easy Lazy collection Only one element Any element Only with chars Slower Faster Data manipulation If/for/while code Exploratory Design Is Law

25. Clojure is a functional language Functions are first-class objects Data is immutable Functions are pure

26. So what?

27. Simple: no loops, variables or mutable state Thread-safe: no locking Parallelizable: map/reduce anyone? Generic: data is always data Easy to test: same input, same output

28. user=> (println "hello world")| hello world-> nil

29. user=> (defn hello [name] (str "Hello, " name))#user/hello

30. (hello "Clojure")

31. (.toUpperCase hello)

32. (str hello world)

33. (+ 1 3 4 (* 5 6))

34. (defn greeting"Returns a greeting of the form Hello, username."[username](str "Hello, " username))

35. (greeting "world")

36. user=> (doc greeting) ------------------------- exploring/greeting ([username])Returns a greeting of the form Hello, username.

37. (defn is-small? [number] (if (< number 100) "yes" ))

38. (is-small? 50) "yes"

39. (is-small? 50000) nil

40. (defn is-small? [number] (if (< number 100) "yes" "no" ))

41. Solving problems Experiment with the problem Create your data structures Data transformations Write code that writes code for you (macros) Create a mini language (a DSL)

42. Java in Clojure Yeap

43. Clojure in Java Yeap

44. Clojure in Clojure Yeap, yeap

45. Java in Clojurejava new Widget(foo)clojure (Widget. foo)java dialog.show()clojure (.show dialog)

46. Tools Emacs + SLIME ViMClojure Enclojure + Intellij IDEA Counterclockwise + Eclipse Leiningen

47. Clojure is not a just a new language

48. Is another, simplier way to solve problems

49. Thanks! Questions? @jonromero