Clojure for Non-Clojurians

A presentation given at the #kansaifp meetup in Kyoto on Dec 6, 2014

http://kansaifp.doorkeeper.jp/events/17206

Transcript

1. Clojure for Non-Clojurians Takahiro Noda @tnoda_ Kansai Kansugata Dojo [2014-12-06 Sat]
2. Outline Clojure? . . . The Good Parts . . . The Bad Parts . . . Applications . . .
3. Clojure? Clojure
4. Clojure? Clojure Java
5. Hello World! Example (Java) $ curl -O http :// repo1.maven.org/maven2/org/clojure/ clojure /1.6.0/ clojure -1.6.0. zip $ unzip clojure -1.6.0. zip $ cd clojure -1.6.0/ $ java -cp clojure -1.6.0. jar clojure.main -e ’(println " Hello␣World!")’ Hello World!
6. Nyampass Co., Ltd. Figure : http://nyampass.com/ They have been using Clojure to develop their mobile BaaS services.
7. Non non biyori (2013)
8. Hello World! (recap) Example (Java) $ java -cp clojure -1.6.0. jar clojure.main \ -e ’(println "Hello␣World!")’
9. Sudden Jar ＿人人人人人人人人人人＿ ＞ clojure-1.6.0.jar　＜ ￣ＹＹＹＹＹＹＹＹＹＹ￣
10. Java SE !"# javac $%%&'&()*+,-)''.'
11. Clojure (Java) !"# javac $%%&'&()*+,-)''.' clojure-x.y.z.jar
12. cloure-x.y.z.jar !"# javac $%%&'&()*+,-)''.' clojure-x.y.z.jar clojure.core ,%/*0-.(
13. Syntax (Clojure) new ClassName(arg0 , arg1 , ...); ClassName.staticMethod(arg0 , arg1 , ...); obj.method(arg0 , arg1 , ...); Syntax (Java interop) (ClassName. arg0 arg1 ...) (ClassName/staticMethod arg0 arg1 ...) (. method obj arg0 arg1 ...) Syntax (Clojure) (func arg0 arg1 … )
14. Type Inference Example (Java) ArrayList list = new ArrayList (); list.add (1); list.add (2); list.add (3);
15. Type Inference Example (Java) ArrayList list = new ArrayList (); list.add (1); list.add (2); list.add (3); Example (Clojure) (let [alist (ArrayList .)] (.add alist 1) (.add alist 2) (.add alist 3))
16. Macro Example (Plain Clojure) (let [alist (ArrayList .)] (.add alist 1) (.add alist 2) (.add alist 3))
17. Macro Example (Plain Clojure) (let [alist (ArrayList .)] (.add alist 1) (.add alist 2) (.add alist 3)) Example (Macro) (doto (ArrayList .) (.add 1) (.add 2) (.add 3))
18. clojure-x.y.z.jar !"# javac $%%&'&()*+,-)''.' clojure-x.y.z.jar clojure.core ,%/*0-.(
19. clojure.core Java (JVM, Bootstrap classes) • Primitives, classes, methods, objects clojure.core • Immutable/Persistent data structures • Collections • Lazy sequences • Stream (Java) • List (Lisp)
20. Built-in collection List • (1 2 3 4) Vector (Stack) • [1 2 3 4] Map • {:a 1, :b 2, :c 3} or {:a 1 :b 2 :c 3} Set • #{1 2 3}
21. Clojure Programming !"##$%&'"( )*+,-. /$01$(%$ !"##$%&'"( )*+,-. /$01$(%$
22. Clojure Programming !"##$%&'"( )*+,-. /$01$(%$ !"##$%&'"( )*+,-. /$01$(%$
23. Conj Conjoin col and x (conj col x) Example (Built-in collections) • (conj [1 2 3 4] 5) • [1 2 3 4 5] • (conj {:a 1 :b 2 :c 3} [:d 4]) • {:a 1 :b 2 :c 3 :d 4} • (conj #{1 2 3} 4) • #{1 2 3 4} • (conj clojure.lang.PersistentQueue/EMPTY 1)
24. Map-filter-reduce map (map inc [1 2]) ;=> (2 3) filter (filter #{1 2} [1 2 3 4]) ;=> (2) reduce (reduce + [1 2 3]) ;=> 6
25. Clojure Programming !"##$%&'"( )*+,-. /$01$(%$ !"##$%&'"( )*+,-. /$01$(%$
26. Checkpoint 1 • Java • clojure-x.y.z.jar • Syntax • Type inference • Macro • Immutable/Persistent data structures • Lazy sequences
27. The Good Parts (1/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
28. Dynamic Development • REPL • Dynamic compilation • Automatically compiled to JVM bytecode on the fly.
29. REPL $ java -cp clojure -1.6.0. jar clojure.main
30. The Good Parts (2/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
31. Functional Programming • First-class functions • fn • defn = def + fn • Immutable data structures • Extensible absraction • seq • Constant-space recursive looping • recur
32. The Good Parts (3/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
33. Lisp • Macro
34. Macro C, C++, Scala String or AST Clojure (Lisp) Sequence
35. The Good Parts (4/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
36. Runtime Polymorphism • Java Interface • Protocol • Type, Record, Protocol • Multimethod
37. Implementing Java Interface (reify java.util.Comparator (compare [this x y] (- y x)) (equals [this x] (= this x))
38. Multimethod (defmulti zoo (fn [x y] [(: diet x) (:diet y)])) (defmethod zoo [: carnivorous :herbivorous] [x y] :eat) (defmethod zoo [: herbivorous :carnivorous] [x y] : run-away) (defmethod zoo [: carnivorous :carnivorous] [x y] :fight) (defmethod zoo [: herbivorous :herbivorous] [x y] :mate)
39. The Good Parts (5/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
40. Concurrent programming • Multithreaded programming • Concurrent operations • JSR-166y (Fork/Join)
41. Multithreaded programming Functions Callable, Runnable public interface Callable <V> { V call (); } Collections Thread-safe Immutability Immutable variables
42. Concurrent Operations • Atomic updates • atom • Asynchronous agents • agent
43. Atomic updates Example (atom) (def a (atom 0)) (swap! a inc) (compare-and-set! a 1 10) (reset! a 20) Java java.util.concurrent.atomic
44. Asynchronous agents Example (agent) (def a (agent 5000)) (send a inc) (senf-off a #( Thread/sleep %)) (await a b) Java • ExecutorService • Fixed-size thread pool (send) • Unbounded thread pool (send-off)
45. Reducers (Fork/Join) Plain Old Clojure (->> s (map ->heptagonal) (filter triangular ?) (reduce +)) Reducer Version (->> s (map ->heptagonal) (r/filter triangular ?) (r/fold +)) http://tnoda-clojure.tumblr.com/post/60197800824/reducers
46. The Good Parts (6/6) • Dynamic development • Functional programming • Lisp • Runtime polymorphism • Concurrent programming • Hosted on JVM
47. Hosted on JVM • Type system • GC • Threads • JVM bytecode • Basic classes • java.util.*, Regular expressions • java.lang.Math • java.io.*
48. Type System Combining static and dynamic type-checking Example (IFn) public interface IFn extends Callable , Runnable { public Object invoke (); public Object invoke(Object arg1); public Object invoke(Object arg1 , Object arg2); ; ... }
49. Checkpoint 2 Dynamic development • REPL • dynamic compilation Functional programming • First-class functions • Immutable data structures • Extensible absraction • Constant-space recursive looping Lisp • Macro
50. Checkpoint 2 Runtime polymorphism • Java Interface • Protocol • Multimethod Concurrent programming • Multithreaded programming • Concurrent operations • JSR-166y (Fork/Join) Hosted on JVM • Type system
51. The Bad Parts • Arrays
52. Type Hinting Example (Java) int x = a[i][j][k]; Example (Clojure) (aget a i j k) ; extremely slow (aget ^ints (aget ^objects (aget a i) j ) k)
53. Remedy http://tnoda-clojure.tumblr.com/post/28996774133/arrays-as-funcions Macro (definline a [i j] (let [larray (gensym "larray")] ‘(let [~ larray (aget ~( with-meta ‘-a {:tag ’objects }) ~i)] (aget ~( with-meta larray {:tag ’longs }) ~j)))) (definline a= [i j x] (let [larray (gensym "larray")] ‘(let [~ larray (aget ~( with-meta ‘-a {:tag ’objects }) ~i)] (aset ~( with-meta larray {:tag ’longs }) ~j (long ~x))))) a, a=
54. Checkpoint 3 Do not use mulitdimensional arrays in Clojure.
55. Applications Middleware • Storm • TrapperKeeper • Datomic Products • Puppet Server • Netflix’s internal services
56. Conclusion Clojure? Java The Good Parts Dynamic development, functional programming, lisp, runtime polymorphism concurrent programming, hosted on JVM The Bad Parts Multidimensinal arrays Applications Storm, Puppet Server