Stefan Kanev: Clojure, ClojureScript and Why They're Awesome at I T.A.K.E. Unconference 2015

1. http://xkcd.com/{224,297}

2. Clojure & ClojureScript
Stefan Kanev
http://skanev.com/
@skanev
I.T.A.K.E. Unconf
26 May 2015
Sofia

4. twitter: @skanev
github: skanev
blog: http://skanev.com/

5. Clojure from 10,000 feet

6. A modern LISP, hosted
in the JVM, with a
focus on concurrency

7. A modern LISP, hosted
in the JVM, with a
focus on concurrency

8. LISP:“that language with
the parentheses”
also: a subculture

9. “LISP is too
hip, even for
me”
– a hipster

10. LISP

12. a * b + c * d
(+ (* a b) (* c d))

13. homoiconicity
data is code, code is
data

15. A modern LISP, hosted
in the JVM, with a
focus on concurrency

16. Sans the antiquities:
car cdr lambda

17. Way better design

18. Less parentheses

19. A modern LISP, hosted
in the JVM, with a
focus on concurrency

20. Stable platform

21. Access to full
Java ecosystem

22. Occasionally a huge P.I.T.A.

23. A modern LISP, hosted
in the JVM, with a
focus on concurrency

24. parallelism vs.
concurrency

25. parallelism
Breaking a problem down to
smaller parts that can be
computed at the same time

26. concurrency
Synchronising a number of
independent processes that are
fighting for the same resources

27. Syntax

28. (func arg-1 arg-2 …)

29. (println "Hello world")

30. (+ 1 2)
(< x y)

31. (+ 1 2 3 4 5 6)
(< u v w x y z)

32. (+ (* a b) (* c d))
(+ (* a b)
(* c d))

33. (defn say-hello [who]
(println "Hello" who "!"))
(say-hello "Doctor")

34. OMG Parentheses!
Or should I say:
((o) ((m)) (g) ( (( (( (( )) )) )) ))

35. Parentheses in LISP are
not unlike metric time

36. (defn classify [age]
(if (<= 13 age 19)
"Teenager"
"A normal person"))
(classify 18) ; "Teenager"

37. (defn factorial [n]
(if (= n 1)
1
(* n (factorial (- n 1)))))

38. (defn fib [n]
(cond (= n 0) 1
(= n 1) 1
:else (+ (fib (- n 1))
(fib (- n 2)))))

39. (fn [x] (* x 2))

40. (map (fn [n] (str "Mr. " n))
["Anderson"
"Bond"
"Bean"])
; ("Mr. Anderson”
; "Mr. Bond"
; "Mr. Bean")

41. (filter prime? (range 2 100))
; (2 3 5 7 11 13 17 19 23 29 31 37 41
; 43 47 53 59 61 67 71 73 79 83 89 97)

42. (defn prime? [n]
(not-any? (fn [x] (zero? (rem n x)))
(range 2 (inc (Math/sqrt n)))))

43. Data Structures

44. maps (hashes)
vectors (arrays)
sets

45. immutable

46. “Modifying” a structure creates
a copy containing the change.
The original remains unmodified.

47. Y

48. simplicity

49. multicore ❤
immutable

50. persistent

51. The “originals” are
maximally reused

52. a ! (3 2 1)

53. 123
a
a ! (3 2 1)

54. a ! (3 2 1)
b ! (conj a 4)
(4 3 2 1)

55. 123
a
a ! (3 2 1)
b ! (4 3 2 1)
4b
5c
c ! (conj a 5)

56. Hash Table
1020394597
1020205863
{:foo first, :bar second}
first
second

57. Hash Table
1020394597
1020205863
Hash Table
1020394597
1020205863
1021027443
(conj table :qux 1024)

58. not that simple

59. Vectors
(“arrays” in other langs)

60. Vectors are represented by trees
Each node has 32 children

61. log32
…
…

62. …
… ⨯

63. O(?)

64. log32n

65. 325 = 33 554 432
326 = 1 073 741 824

66. “essentially constant
time”

68. Software Transactional Memory

69. concurrency 101

70. 100 € +50 € ⨯2
How much money will the account have?

71. 300 €250 €

72. 100 €
+50 € = 150 €
x2 = 300 €

73. 100 €
x2 = 200 €
+50 € = 250 €

74. 100 €
200 €
150 €
x2
+50
100 €
100 €

75. 100 €
150 €
200 €
x2
+50
100 €
100 €

76. ref

77. state mutation is
modelled as a
transaction

78. if two transactions
“get in each others’
way”, one of them will
restart

79. (def account (ref 100))
; Thread 1 - Uncle Scrooge
(dosync
(alter account (fn [n] (* n 2)))
(println "Scrooge: set to " @account))
; Thread 2 - Donald Duck
(dosync
(alter account (fn [n] (+ n 50)))
(println "Donald: set to " @account))

80. 100 €
300 €
150 €
x2
+50
100 €
100 €
X
x2
150 €

81. Y

82. familiar

83. safe, easy, no
deadlocks

84. Macros

85. Powerful instrument
allowing expressive code

86. Also known as:
the mother of all
metaprogramming

87. MacroCode
Some other
code

89. doStuff();

90. Outputs on STDOUT.
We want to have the
result in a string
instead.

91. PrintStream original = System.out;
ByteArrayOutputStream output = new ByteArrayOutputStream();
try {
PrintStream fileStream = new PrintStream(output);
orgStream = System.out;
System.setOut(fileStream);
doStuff();
} finally {
System.setOut(original);
}
String output = output.toString();

92. (do-stuff)

93. (with-out-str
(do-stuff))

94. (with-out-str (do-stuff))

95. String output = withOutStr {
doStuff();
}

96. unless

97. (unless (hungry?)
(sleep)
(eat))
(if (not (hungry?))
(sleep)
(eat))

98. (defmacro unless [condition consequent alternative]
`(if (not ~condition)
~consequent
~alternative))

99. unless (isHungry()) {
sleep();
} else {
eat();
}

100. (cond (= n 0) 1
(= n 1) 1
:else (+ (fib (- n 2))
(fib (- n 1))))
(if (= n 0)
1
(if (= n 1)
1
(+ (fib (- n 2))
(fib (- n 1)))))

101. DSLDomain Specific Languages

102. Transparency

103. (source if-let)
(source await)

104. ClojureScript

105. om

106. Very dynamic

107. DEMO

108. REPL Oriented Programming