This is a basic introduction.

1. THE IDEAS OF CLOJURE
JCConf 2015/12/04
Randy Lien
Things I learn from Clojure

2. About me
@randylien
UI Engineer
#WebAppsRocks
#JavaScriptIsNotSoJavaScript
#WhenIsNextReactJS.TwMeetup
#clojurians.tw@facebook

3. Survey!
• Heard Clojure?
• Clojure developer?
• Enjoy Java development?

4. “I don’t know Java.”
– Speaker

6. History of programming languages

7. LISP

8. Clojure ?

9. React.js Conf 2015

10. Tapestry Dude - https://goo.gl/R5m3am (CC BY-SA 2.0)
The Creator of Clojure
Rich Hickey

11. "Hickey is the new Messiah of software development. Watch
and listen to his talks, and you will understand."
– http://bepsays.com/2014/07/08/how-rich-is-rich-hickey/

12. Few ideas I want to share

13. Philosophy

14. Philosophy
Focus
Simplicity
Empowerment
Pure functions
Expressive Practical
Clarity
Consistency
Separation
of
concerns
Concise
Direct
Interop
- The Joy of Clojure

15. Philosophy - Simplicity
• Pure functions
• Immutable
• Simple abstractions
• defprotocol
• deftype

16. Philosophy - Focus
• Syntax will not bother you
• Consistency
• Dynamic System
• Almost everything defined in Clojure can be
redefined (Even while program is running)
• Use Macro you can build anything you want to do

17. Philosophy - Empowerment
• Use Java Virtual Machine
• Java is mature and has many libraries
• JavaScript is everywhere (ClojureScript)

18. Consistency

19. Syntax does matter

20. Java + Python + JavaScript ?

21. JaPythonScript?

22. Data Types
• Integers - 123
• Doubles - 1.23
• Ratios - 1/23
• Strings - "JCConf"
• "Double Quotes Only"
• Characters - J C

23. Data Types (cont.)
• Symbols - bar
• Keywords - :foo
• Booleans - true false
• Null - nil
• Regex - #"[A-Z0-9._%+-]+@[A-Z0-9.-]+.[A-Z]+"

24. Data Structure
• Lists - (1 2 3)
• Prepend
• Vectors - [1 2 3]
• Zero indexed. Append
• Maps - {:a 1, :b 2, :c "3"}
• Key-value pair
• Comma will be ignored
• Sets - #{1 2 3}
• Unique. Unordered

25. function definition

26. function definition
doc string

27. Clojure
• (+ 1 2)
• (+ 1 2 3)
• (into [] 2)
General
• 1 + 2
• 1 + 2 + 3
• [].push(2)

29. Use host libraries - Java

30. Use host libraries - JavaScript

31. DEMO

32. functions & composition

33. functions & composition
• map, reduce, filter
• partial, comp
• iterate
• repeat, repeatedly
• Many built-in functions and you don’t need to create.
Just compose it!

34. DEMO

35. Values

36. Values should be…
• Value!
• operated by functions
• time-relative
• Immutable

37. Why Immutable?

38. Why mutable?

39. Why mutable?
• Limitations of early computers: Small RAM and disk
• New information replaces old

40. Why
immutable?
• No resource limitation
• Persistent data structure
• Record - Share the same data
• Key to do functional programming
• No side effect
• atom is mutable

41. REPL Driven Development

42. REPL ?
• Read–Eval–Print Loop
• nREPL (network REPL)
• Good for doing TDD
• clojure.test
• ClojureScript - Browser can connect to nREPL

43. REPL
DEMO - ClojureScript

44. REPL
DEMO - Clojure

45. Tooling Eco-system

46. Clojars
emacs
LightTable

47. Leiningen

48. Summary

49. Summary
• Clojure is a practical functional programming language
• Java and JavaScript are two major languages and
Clojure and ClojureScript can run on them
• Using REPL in your TDD practices would be helpful
• Pure functions and Immutable data structure can make
your system stable and easy to reason about

50. Summary (cont.)
• Clojure has much better tooling and keep improving it
• ClojureScript is hotter than Clojure!
• Many companies are using Clojure
• booking.com, Yahoo, Puppet, Walmart, twitter,
heroku, nubank…etc
• STM, transducer, core.asyn

51. If you want to know more…
• Living Clojure
• The Joy of Clojure
• ClojureScript Unraveled
• Clojure Applied
• Clojure for the Brave and True

52. Online resource
• http://www.tryclj.com/
• http://www.4clojure.com/

54. Worth to watch
• Simple Made Easy
• Clojure Made Simple
• The Value of Values
• The Language of the System

55. Thanks