Munich Clojure Workshop - 01 - Introduction

Copyright © 2012-2014 Clojure Workshop Team: Maximilian Karasz, Jan Stępień, Marek Kubica, Oleksandr Petrov

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Transcript

1. Introduction to Clojure Friday, October 11, 13
2. Clojure, the language Friday, October 11, 13
3. • Extremely expressive • First-class functions • Awesome Java Interoperability • Power of lisp (macros, function composition) • FUNctional Friday, October 11, 13
4. What are we looking for? Friday, October 11, 13
5. • sane development environment, integrated with a language • ability to develop and evaluate things on the fly • ease maintenance production • scalability • integration with well-known / existing tools • good, stable runtime • runtime debugging toolkit • performance Friday, October 11, 13
6. • Leiningen, Clojure build tool https://github.com/technomancy/leiningen • repl just run `lein repl` in your console • emacs (it’s written in lisp, you know?) excellent nrepl and (older thing) clojure-swank, paredit-mode, formatting • nrepl get to the guts of runtime • VisualVm and the rest of Java goodness like jmap, jstack, jstat etc etc etc Friday, October 11, 13
7. • JMX java management extensions • nrepl • JVM configuration/tuning • No shared mutable state • No locks • Pure functions -> same input -> same output • Easy composition and pipelining Friday, October 11, 13
8. • Good baseline performance • Utilization of all processor resources anyone can eat out all the memory, right? • Painless parallel execution • Memory efficiency as far as it is possible with lisps, of course. in my mind that was mostly about structural sharing & persistent DS • JIT / inlining Friday, October 11, 13
9. • Very, very good Java interop options • Most of libraries are either ported to Clojure, or use Java library underneath • Your favorite Java application container / web server • Jar packaging / public / private Maven repositories • Not to replace, but to complement your existing JVM toolkit Friday, October 11, 13
10. Primer Friday, October 11, 13
11. Functions Friday, October 11, 13
12. function () { return 5; } JS Function Friday, October 11, 13
13. (function () return 5) Add parentheses Friday, October 11, 13
14. (fn [] return 5) function -> fn Friday, October 11, 13
15. (fn [] 5) Ditch return Friday, October 11, 13
16. Prefix notation, function calls Friday, October 11, 13
17. (+ 1 1) Function Arguments Friday, October 11, 13
18. Everything is an expression Friday, October 11, 13
19. 5 ; 㱺 5 Friday, October 11, 13
20. (+ 1 1) ; 㱺 2 Friday, October 11, 13
21. (if true "yes" "no") ; 㱺 “yes” Friday, October 11, 13
22. Language Primitives Friday, October 11, 13
23. "this is a string" String Friday, October 11, 13
24. :key Keyword Friday, October 11, 13
25. 'key Symbol Friday, October 11, 13
26. [1 2 3] [:key 1 "value"] Vector Friday, October 11, 13
27. {:key "value" :key2 "value2"} Hash Friday, October 11, 13
28. Syntactic Sugar Friday, October 11, 13
29. #() => (fn []) Function Friday, October 11, 13
30. #{} => (set ..) Set Friday, October 11, 13
31. #inst "2013-10-04T13:32:41.008-00:00" Date Friday, October 11, 13
32. Definitions Friday, October 11, 13
33. (def a 1) Friday, October 11, 13
34. (def a (+ 1 (* 2 2))) Friday, October 11, 13
35. Functions Friday, October 11, 13
36. (fn [number] (- number 1)) Function Definition Argument (s) Function Body Friday, October 11, 13
37. (defn square "Returns a square of a number" [x] (* x x)) Function Definition Argument (s) Function Body Docstring Friday, October 11, 13
38. Destructuring basics Friday, October 11, 13
39. [1 2 3 ] [first second third] Friday, October 11, 13
40. Passing functions as arguments to functions Friday, October 11, 13
41. (map inc [1 2 3]) Function call Passed function Friday, October 11, 13
42. (map (fn [i] (+ i 1)) [1 2 3]) Function call Passed (anonymous) function Friday, October 11, 13
43. Getting help Friday, October 11, 13
44. (clojure.repl/doc defn) Friday, October 11, 13
45. (clojure.repl/source defn) Friday, October 11, 13
46. Let Friday, October 11, 13
47. function (a, b, c) { var sum = a + b + c; var count = 3; return sum / count; } Friday, October 11, 13
48. (fn [a b c] (let [sum (+ a b c) count 3] (/ sum count)) Friday, October 11, 13
49. Control structures Friday, October 11, 13
50. Conditionals Friday, October 11, 13
51. • Sometimes referred as “control structures” • Expressions, often implemented as macros • Used to delay evaluation of certain code blocks Friday, October 11, 13
52. if Friday, October 11, 13
53. Imagine “if” were a function for a minute: (if-fn (even? 2) (println "even!") (println "odd!")) Both “even!” and “odd!” are printed. Friday, October 11, 13
54. `if` structure/usage: (if (predicate) (truthy-expression) (falsy-expression)) Friday, October 11, 13
55. Multi-expression & do blocks (if (predicate) (do (truthy-expression) (another-truthy-expression)) (falsy-expression)) Friday, October 11, 13
56. when Friday, October 11, 13
57. (when (predicate) (expression-1) (expression-2)) Friday, October 11, 13
58. • Useful when you don’t have “false” part • You can write more than one expression within `where` block Friday, October 11, 13
59. if-let Friday, October 11, 13
60. (def user {:name "Alex"}) (if-let [name (:name user)] (println "Hello " name) (println "Name is empty")) Friday, October 11, 13
61. • Useful when you need to check an expression and reuse the expression result in “truth” block • As the name itself states, if-let behaves as let wrapped over if Friday, October 11, 13
62. cond Friday, October 11, 13
63. (cond (< n 0) "negative" (> n 0) "positive" :else "zero") Friday, October 11, 13
64. • Useful when you want to avoid multiple nested ifs • `:else` here is arbitrary, you can use any expression that evaluates to something truthful Friday, October 11, 13
65. Composition Friday, October 11, 13
66. (fn [c] (first (rest c))) (comp first rest) Friday, October 11, 13
67. Application Friday, October 11, 13
68. (apply max [1 2 3]) (max 1 2 3) Friday, October 11, 13
69. Namespaces Friday, October 11, 13
70. (ns superlib.core) Friday, October 11, 13
71. (:require ...) Friday, October 11, 13
72. (:import ...) Friday, October 11, 13
73. (:use ...) Friday, October 11, 13
74. (:gen-class ...) Friday, October 11, 13
75. Practical excercises Friday, October 11, 13
76. • arrange into groups of 2-3 people • you’ll be given a function name and parameters vector • tests are located under `test/workshop_tasks/*-test.clj • write a function, run the tests • submit results to exercise server Friday, October 11, 13