This document summarizes a presentation about Clojure and ClojureScript. It describes Clojure as a modern Lisp dialect that runs on the JVM with a focus on concurrency. It notes advantages like stable platforms, access to Java libraries, and immutable persistent data structures that facilitate parallelism. The document discusses Clojure concepts like homoiconicity, concurrency vs parallelism, syntax using s-expressions, macros for metaprogramming, and data structures like maps, vectors, and sets. It also mentions ClojureScript and domain-specific languages.

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