Video and slides synchronized, mp3 and slide download available at URL https://bit.ly/2Jq8Jb2. Jearvon Dharrie discusses Clojure, a language that's taking some older ideas and solving 21st-century problems. Topics that are discussed: Clojure's answer to types, clojure.spec, the ability to write and reason about parallelism and concurrency with core.async, and more. Filmed at qconnewyork.com. Jearvon Dharrie is a software engineer at Comcast. He spends his day working with Javascript, Ruby, and Python. In his free time he enjoys toying with programming languages. He is currently interested in Clojure and ClojureScript.

1. Fun With Clojure

2. InfoQ.com: News & Community Site
• 750,000 unique visitors/month
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Portuguese)
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Watch the video with slide
synchronization on InfoQ.com!
https://www.infoq.com/presentations/
clojure

3. Presented at QCon New York
www.qconnewyork.com
Purpose of QCon
- to empower software development by facilitating the spread of
knowledge and innovation
Strategy
- practitioner-driven conference designed for YOU: influencers of
change and innovation in your teams
- speakers and topics driving the evolution and innovation
- connecting and catalyzing the influencers and innovators
Highlights
- attended by more than 12,000 delegates since 2007
- held in 9 cities worldwide

4. History

5. 21st Century
January 1 2001

6. Clojure
Clojure first appeared in 2007

7. Lisp
Lisp was first specified in 1958

8. CSP
First described in 1978

9. JVM
JVM was introduced in 1994

10. JavaScript
Appeared in 1995

11. Clojure

12. 21st Century Problems

13. Evolvable Systems
— Quickly add new features for customers
— Refactor with Confidence

14. Resilient
— Open System - Handles large amounts of inputs that
you have no control over
— Low response times

15. Something that involves
JavaScript

16. Our Journey

17. Agenda
— Specifying our problems
— Concurrency / Parallelism
— ClojureScript

18. (whoami)
{
:name "Jearvon Dharrie"
:day-to-day "Developer Advocate @ Comcast"
:twitter "@jearvon"
:repo "https://github.com/iamjarvo/qconnyc_2018"
}

19. Clojure

20. Just Enough Clojure

21. (function arg)

22. (+ 1 2)

23. (ns qcon.spec.core
(:require [clojure.spec.alpha :as s]))
(s/valid? string? "1")

24. clojure.spec

25. Spec Anatomy
(spec-function predicate value)

26. (s/valid? int? 3000)
!" true

27. Predicate
(x) !" boolean

28. Builtin Predicates
uri? true?
even? pos-int?
odd? any?

29. Custom Predicates
(fn [value] (!" value 18))

30. Named Specs
(s/def !"port int?)

31. (s/valid? !"port 3000)

32. Spec Registry

33. Spec Maps
(s/def !"config
(s/keys :req-un [!"port !"env]))

34. Compose Specs
(s/def !"valid-port-range
!$and (> % 1023)
(!% % 65535)))
(s/def !"port
(s/and int? !"valid-port-range))

35. What Can You Do With Spec?

36. Validate
(s/valid? !"port "3000")
!# false
(s/valid? !"port 3000)
!# true

37. Conform
(s/conform !"port 3000)
!# 3000

38. (s/def !"building !#re-find #"[0-9]+" %))
(s/def !"address
(s/cat
:building-num !"building
:street string?))
(s/conform !"address ["1701" "JFK Blvd"])

39. Explain
(s/explain !"port "3000")
!# val: "3000" fails spec: :qcon.core/port predicate: int?
(s/explain !"port 400)
!# val: 400 fails spec: :qcon.core/valid-port-range predicate: (and (> % 1023) (!% % 65535))

40. Doc
(doc !"port)
!# Spec
!# (and int? :qcon.core/valid-port-range)

41. Together

42. Spec Functions
(s/fdef find-by-id
:args (s/cat map? "#valid-id)
:ret map?)

43. (defn find-by-id
[db id]
(first
(filter "#= id (:id %)) db)))

44. (doc !"find-by-id)

45. Exploring
(gen/sample (s/gen !"config))

46. Instrument
(stest/instrument `find-by-id)

47. Test Check
(stest/check `find-by-id)

48. Concurrency & Parallelism
The future belongs to languages that can automatically
leverage more cores as they become available
— Clojure Applied

49. Host Platform
— Thread
— java.util.concurrent

50. Pure Functions
(defn add [x y]
(+ x y))

51. Immutable Data
(assoc {:first "Jearvon"} :last "Dharrie")
(let [m {:first "Jearvon"}]
(assoc m :last "Dharrie")
m)

52. Atom
(def qcon (atom 0))
@qcon
!" 0
(swap! @qcon inc)
!" 1

53. pmap
(pmap expensive-call collection)

54. Futures

55. Reducers

56. core.async
https://en.wikipedia.org/wiki/
Communicating_sequential_processes

57. chan
(chan)

58. Put/Take
>!" <!"

59. go

60. Put/Take
>! <!

61. Token Bucket Filter
A token is added to the bucket every 1/r seconds.

62. Token Bucket Filter
The bucket can hold at the most b tokens. If a token
arrives when the bucket is full, it is discarded.

63. Token Bucket Filter
When a packet (network layer PDU) of n bytes arrives, n
tokens are removed from the bucket, and the packet is
sent to the network.

64. Token Bucket Filter
If fewer than n tokens are available, no tokens are
removed from the bucket, and the packet is considered to
be non-conformant.

65. ClojureScript

66. Targets
— Node.js
— The Browser
— Anywhere that JavaScript runs

67. Language

68. Tools

69. Clojure Goodies
— Immutable Data Structures
— clojure.spec!
— core.async
— Libraries

70. Share Code

71. CLJC - Reader Conditionals
!"(:cljs (defn upcase [s] (.toLowerCase s)))
!"(:clj (defn upcase [s] (clojure.string/upper-case s)))

72. React Wrappers
— Reframe
— Om
— React Native

73. Browser REPL

74. Interactive Development

75. Source Maps

76. Differences
https://clojurescript.org/about/differences

77. Some Points
— Learning the language is easy
— Learning how to do things is difficult
— I am always learning and being challenged
— Need to accept the Clojure way - Simple
— Compose libraries instead of frameworks

78. Conclusion
— Clojure supports simplicity, pure functions and
immutable data
— clojure.spec helps you define and validate the shape of
your data
— Concurrency and parallelism are first class citizens in
Clojure
— Clojure compiles to JavaScript and allows you to take
advantage of working in the browser and with nodejs

79. Thanks

80. Watch the video with slide
synchronization on InfoQ.com!
https://www.infoq.com/presentations/
clojure