Clojure & ClojureScript

A presentation at I.T.A.K.E. 2015

Transcript

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. 1 2 3 a a ! (3 2 1)
54. a ! (3 2 1) b ! (conj a 4) (4 3 2 1)
55. 1 2 3 a a ! (3 2 1) b ! (4 3 2 1) 4 b 5 c 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. log32 n
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. Macro Code 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. DSL Domain Specific Languages
102. Transparency
103. (source if-let) (source await)
104. ClojureScript
105. om
106. Very dynamic
107. DEMO
108. REPL Oriented Programming