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Zero to Clojure in 90 minutes

Zero to Clojure in 90 minutes

A presentation/workshop at Agile 2010

Colin Jones

August 11, 2010
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  1. Zero to Clojure in 90 Minutes Colin Jones Software Craftsman

    at 8th Light @trptcolin Thursday, August 12, 2010
  2. More String “go to the” Character \p \a \r \k

    Regex #”\d+” Nil nil Boolean true false Keyword :really/soon Symbol some-time Thursday, August 12, 2010
  3. Collections List (1 2 3 4 5) Vector [1 2

    3 4 5] Map {:first-name “colin”, :last-name “jones”} Set #{a b c d e} Thursday, August 12, 2010
  4. java -jar /path/to/clojure.jar (+ JRE functional-koans) => WIN! From Functional

    Koans directory: Mac / Linux: ./repl.sh Windows: repl From anywhere: Thursday, August 12, 2010
  5. clojure.test user=> (is (= 1 2)) FAIL in clojure.lang.PersistentList$EmptyList@1 15)

    expected: (= 1 2) actual: (not (= 1 2)) false user=> (use ‘clojure.test) nil user=> (is (= 1 1)) true Thursday, August 12, 2010
  6. Equality user=> (is (= “Colin” “Colin”)) true user=> (is (=

    nil nil)) true user=> (is (= ‘(1 2 3) [1 2 3])) true user=> (is (= 1.0 1 4/4)) true Thursday, August 12, 2010
  7. Math fun(ctions) user=> (is (= 15 (+ 1 2 3

    4 5))) true user=> (is (< 1 2 3)) true Thursday, August 12, 2010
  8. Hide and seq? user=> (is (= :a (first [:a :b

    :c]))) true user=> (is (= [:c :b :a] (reverse [:a :b :c]))) true user=> (is (= [:b :c] (rest [:a :b :c]))) true Thursday, August 12, 2010
  9. Defining our own functions user=> (def square-1 (fn [x] (*

    x x))) #‘user/square-1 user=> (defn square-3 [x] (* x x)) #‘user/square-3 user=> (def square-2 #(* % %)) #‘user/square-2 user=> (is (= 9 (square-1 3))) true user=> (is (= 9 (square-2 3))) true user=> (is (= 9 (square-3 3))) true Thursday, August 12, 2010
  10. map user=> (defn square [x] (* x x)) #‘user/square user=>

    (is (= ‘(1 4 9 16 25) (map square ‘(1 2 3 4 5)))) true Thursday, August 12, 2010
  11. apply user=> (is (= “dog” (str \d \o \g))) true

    user=> (is (= “dog” (str dog-letters))) FAIL in clojure.lang.PersistentList$EmptyList expected: (= “dog” (str dog-letters)) actual: (not (= “dog” “[\\d \\o \\g]”)) false user=> (def dog-letters [\d \o \g]) true user=> (is (= “dog” (apply str dog-letters))) true Thursday, August 12, 2010
  12. The whole numbers user=> (def whole-numbers (iterate inc 0)) #‘user/whole-numbers

    user=> (is (= (range 20 40) (take 20 (drop 20 whole-numbers)))) true user=> (is (= (range 0 20) (take 20 whole-numbers))) true Thursday, August 12, 2010
  13. Let’s try it in the REPL user=> (def whole-numbers (iterate

    inc 0)) #‘user/whole-numbers user=> whole-numbers (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 OH NOEZ!!! Thursday, August 12, 2010
  14. Don’t hold onto your head user=> (def whole-numbers (iterate inc

    0)) #‘user/whole-numbers user=> (first (drop 10000000 whole-numbers)) Exception in thread "main" java.lang.OutOfMemoryError: Java heap space user=> (defn whole-numbers [] (iterate inc 0)) #'user/whole-numbers user=> (first (drop 10000000 (whole-numbers))) 10000000 Thursday, August 12, 2010
  15. vars user=> (def x 42) #‘user/x user=> (let [x :foo]

    x) :foo user=> x 42 user=> x 42 Thursday, August 12, 2010
  16. refs user=> (def attendees (ref 30)) #‘user/attendees user=> attendees #<Ref@343aff84:

    30> user=> @attendees 30 user=> (alter attendees dec) java.lang.IllegalStateException: No transaction running user=> (dosync (alter attendees dec)) 29 user=> @attendees 29 Thursday, August 12, 2010
  17. refs (defn transfer [amount a b] (dosync (alter a -

    amount) (alter b + amount))) (def checking (ref 10)) (def savings (ref 50)) Bank Accounts Branch (transfer 25 checking savings) snapshot (checking=10, savings=50) checking = 60, savings=0 ATM (transfer 25 checking savings) snapshot (checking=10, savings=50) commit (checking=35, savings=25) Conflict discovered! (transfer 25 checking savings) Automatic Retry: commit (checking=60, savings=0) snapshot (checking=35, savings=25) Thursday, August 12, 2010
  18. The Internets Functional Koans http://github.com/relevance/functional-koans/tree/clojure Web docs http://clojure.org/ Google Group

    http://groups.google.com/group/clojure IRC #clojure on freenode.net Thursday, August 12, 2010
  19. Uncle Bob Martin, Corey Haines, Dave Astels, Ken Auer, Chad

    Fowler, Keavy McMinn, Michael Feathers, Doug Bradbury, Enrique Comba Riepenhausen, and more... Thursday, August 12, 2010