1. Introduction to Clojure
Soligorsk, 26.01.2013
Friedrich Boeckh

2. Clojure rocks & Sam Aaron is badass
Overtone,
http://blip.tv/clojure/sam-aaron-programming-music-with-overtone-5970273

3. ThoughtWorks 2012:
Clojure is on the Radar
http://www.thoughtworks.com/articles
/technology-radar-october-2012
… even Microsoft cares
… as always - it does not make
everybody happy:
http://cafe.elharo.com/programming/java-
programming/why-functional-programming-in-java-is-
dangerous/

4. World singles
Sean Corfield
http://corfield.org/articles/WorldSinglesWeb.pdf
• 3,000,000 members
• 1,000,000 emails / day
• 80,000 logins / day
• 2,000 concurrent users (average)

5. uSwitch.com
http://skillsmatter.com/podcast/home/reviving-the-uswitch-back-office-with-clojure
Ryan Greenhall

6. Clojure at a bank
Malcolm Sparks
http://blog.malcolmsparks.com/?p=17

7. Clojure at another bank
Jon Pither
http://www.pitheringabout.com/?p=693

8. Clojure at yet another bank

9. Clojure at Nokia Entertainment
http://skillsmatter.com/event/clojure/clojure-at-nokia-entertainment

10. Big Data Done Better – Mastodon C
https://www.mastodonc.com/

11. Clojure gives Innovation a Boost
Stuart Halloway Justin Gethland
& Rich Hickey

12. Russian wording in the following
from Alex Ott´s talk at itsea 2012
http://de.slideshare.net/alexott/clojure-lisp-for-the-modern-world
http://alexott.net/ru/clojure/clojure-intro/index.html
http://alexott.net/en/clojure/video.html

13. Что такое Clojure?
• Rich Hickey, 17.10.2007, с v1.4, RC v1.5
• Lisp-ообразный
• Функциональный
• Конкурентное программирование
http://stackoverflow.com/questions/1050222/concurrency-vs-
parallelism-what-is-the-difference
• Многоплатформенный (JVM, .Net, JavaScript, etc.)
• Открытый исходный код и либеральная лицензия
Eclipse Public License 1.0
• Активное сообщество разработчиков
• Коммерческое применение
• Коммерческая поддержка

14. Активное сообщество разработчиков
Sean Corfield
http://corfield.org/articles/WorldSinglesWeb.pdf, mid 2012

15. Почему Lisp?
• Простой синтаксис - code as data structures homoiconic
• Метапрограммирование (макросы)
• Создание доменно-специфических языков DSLs
• Генерация кода во время компиляции
• Возможность избежать повторений
• Генерация и выполнение кода в runtime
• Интерактивная разработка REPL
• Динамически типизированный

16. Lisp? 7 элементов + fn нотация
John McCarthy
1927 - 2011
Lisp Specification, 1958

17. Lisp? 7 элементов + fn нотация
Paul Graham, The Roots of Lisp
http://www.paulgraham.com/rootsoflisp.html
http://www.cse.sc.edu/~mgv/csce531sp07/jmc.pdf
• (quote x) returns x
• (atom x)returns the atom t (true) if the value of x is
an atom or the empty list. Otherwise it returns ().
• (eq x y) returns t if the values of x and y are the
same atom or both the empty list, and () otherwise.
• (car x) expects the value of x to be a list, and returns its first element.
• (cdr x) expects the value of x to be a list, and returns everything after
the first element.
• (cons x y) expects the value of y to be a list, and returns a list
containing the value of x followed by the elements of the value of y.
• (cond (p1 e1) ... (pn en)) is evaluated as follows. The p
expressions are evaluated in order until one returns t (true). When one is
found, the value of the corresponding e expression is returned as the value
of the whole cond expression.
• A function is expressed as (lambda (p1 ... pn) e), where
p1 ... pn are atoms, called parameters, and e is an expression.

18. Богатство Lisp наследия
• Hal Abelson, Jerry Sussman and Julie Sussman, Structure and
Interpretation of Computer Programs (SICP),
http://mitpress.mit.edu/sicp/,
http://newstar.rinet.ru/~goga/sicp/sicp.pdf (russ.),
http://ocw.mit.edu/courses/electrical-engineering-and-
computer-science/6-001-structure-and-interpretation-of-
computer-programs-spring-2005/video-lectures/
• Peter Seibel, Practical Common Lisp,
http://www.gigamonkeys.com/book/
• Paul Graham, On Lisp, http://www.paulgraham.com/onlisp.html,
http://lib.store.yahoo.net/lib/paulgraham/onlisp.pdf

19. Богатство Lisp наследия
Conrad Barski (M.D.)
http://vimeo.com/9605639

20. Богатство Lisp наследия
• VLSI design, Boeing, US government & military, ITA Software (in
2010 acquired by Google)
• NASA, The Remote Agent Experiment - Debugging code from
60 million miles away, Ron Garret, 14 February 2012
• Paul Graham, Beating the Averages,
http://www.paulgraham.com/avg.html,
http://lib.store.yahoo.net/lib/paulgraham/bbnexcerpts.txt
• Andreas Lehmann, Common Lisp Raytracer, (source code
transcript e. g. here https://github.com/fbmnds/clrt),
videos and PDFs
http://rudairandamacha.blogspot.de/2012/09/writing-simple-
raytracer-in-common-lisp.html

21. Богатство Lisp наследия
• Peter Norvig, Paradigms of Artificial Intelligence Programming:
Case Studies in Common Lisp (PAIP),
http://norvig.com/paip.html
• Daniel P. Friedman, Matthias Felleisen, The Little Schemer,
http://mitpress.mit.edu/books/little-schemer
• Overview by Vsevolod Dyomkin,
http://lisp-univ-etc.blogspot.com/2012/12/lisp-books.html
• Rich Hickey, Books that influenced Clojure,
http://www.amazon.com/gp/richpub/listmania/fullview/R3LG3Z
BZS4GCTH

22. Богатство Lisp наследия – Emacs ??
Marco Baringer's SLIME Tutorial Video:
http://www.youtube.com/watch?v=_B_4vhsmRRI
( underscore)

23. Отличия от других Lisp’ов
• Немного упрощенный синтаксис -- меньше скобочек
• Неизменяемые данные (immutability)
• Добавлено больше базовых структур данных: вектора,
отображения (maps) и т.д.
• Расширяемый reader, но без reader macros
• "Ленивые" коллекции (lazy-seq)
• Мета-информация привязанная к данным и функциям
• Case-sensitive names
• Исключения вместо условий/рестартов
• Полиморфизм: протоколы и мультиметоды
• Software Transactional Memory System (STM)
• Java Interoperation, http://clojure.org/java_interop
( underscore)

24. Полиморфизм на Clojure
• Протоколы, мультиметоды
…
Stuart Sierra, https://www.ibm.com/developerworks/java/library/j-clojure-protocols/

25. Полиморфизм на Clojure
• Протоколы, мультиметоды
http://oredev.org/2012/sessions/expressing-yourself-polymorphism-in-clojure

26. Software Transactional Memory System (STM)
Graig Andera
http://pluralsight.com/training/Courses/TableOfContents/clojure-concurrency-tutorial

27. Почему ФП?
• Функции в математическом смысле
Lambda Calculus
• Функции – объекты первого порядка
first-class objects, higher-order functions (HOF)
• Неизменяемость данных immutability
• Отсутствие побочных эффектов
• Возможность автоматической параллелизации кода
• Меньше проблем с конкурентным выполнением кода

28. Lambda Calculus ~ “effectively programmable”
Alonzo Church Stephen Kleene Alan Turing
1903 - 1995 1909 - 1994 1912 - 1954

29. Lambda Calculus
http://www.infoq.com/presentations/Y-Combinator
(defn Y
[h]
Jim Weirich (Y-rich)
((fn [f] (f f)) (fn [f]
(h (fn [n]
((f f) n))))))
(def fact
(Y (fn [g]
(fn [n]
(if (< n 2) 1 (* n (g (dec n))))))))
transcript by Michael Kohl,
http://citizen428.net/blog/2010/12/14/clojure-deriving-the-y-combinator-in-7-stolen-steps/

30. Почему ФП?
1922 - 1990
You want functions?

31. Почему ФП?
Get some:

32. Clojure / ФП - Namespaces
http://clojure.org/namespaces
• Namespaces are mappings from simple (unqualified) symbols
to Vars and/or Classes.
• Namespaces are first-class, they can be enumerated etc.
• Namespaces are also dynamic, they can be created, removed
and modified at runtime, at the Repl etc.
• The best way to set up a new namespace at the top of a Clojure
source file is to use the ns macro.
• The current namespace, *ns* can and should be set only with
a call to in-ns or the ns macro, both of which create the
namespace if it doesn't exist.

33. Clojure / ФП - Namespaces
• clojure.core - Fundamental library of the Clojure language
• clojure.data - Non-core data functions.
• clojure.inspector - Graphical object inspector for Clojure data
structures.
• clojure.java.browse - Start a web browser from Clojure
• clojure.java.io
• clojure.java.javadoc - A repl helper to quickly open javadocs.
• clojure.java.shell
• clojure.main
• clojure.pprint - A Pretty Printer for Clojure
• clojure.reflect - Reflection on Host Types
• clojure.repl - Utilities meant to be used interactively at the REPL

34. Clojure / ФП - Namespaces
• clojure.set
• clojure.stacktrace - Print stack traces oriented towards Clojure, not
Java.
• clojure.string
• clojure.template - Macros that expand to repeated copies of a
template expression.
• clojure.test - A unit testing framework.
• clojure.walk
• clojure.xml - XML reading/writing.
• clojure.zip - Functional hierarchical zipper, with navigation, editing,
and enumeration. See Huet

35. Базовый синтаксис
• Код – структуры данных
• Выражение – список, первый элемент бывает:
• Функция
• Макрос
• Специальная форма
• Примеры:
(def a 1) (defn square [x] (* x x))
(+ 1 2) (defmacro when [x & body]
`(if ~x (do ~@body)))

36. Базовые типы данных
• Числа (целые, рациональные, вещественные):
42, 1/3, 12345678901234567N, 4.2, 42.2M
• Строки: "string... "
• Знаки (characters): a, newline, …
• Регулярные выражения: #"d+"
• Логические значения: true, false
• как null в Java nil
• Симбол (symbol): name
• keyword: :name,
(:name {:name "test"})

37. Коллекции
• Разные коллекции:
• Списки: '(1 2 3 "abc") (quoting)
• Вектора: [1 2 3] (no quoting)
• Отображения (maps): {:k1 1234 :k2 "value"}
• Множества: #{:val1 "text" 1 2 10}
• persistent & transient коллекции
• Вектора, отображения и множества сами являются
функциями:
([1 2 3] 2) ({:a 1 :b 2 :c 3} :b)
=> 3 => 2
(no quoting) (no quoting)

38. Persistent collections
• Новая копия данных при
изменении
• Затрагивается только
измененная часть
• Производительность
сравнима с коллекциями
Java
Rich Hickey to the Western Mass.
Developers Group on Clojure and
concurrency.
(2,5h – well invested time!)
http://blip.tv/clojure/clojure-concurrency-819147
http://www.youtube.com/user/ClojureTV

39. Последовательности
• Последовательности (sequences):
• Коллекции Clojure & Java, массивы, iterable, …
• "Ленивые" операции над последовательностями
• Могут быть бесконечными
• Один набор операций над последовательностями:
map, reduce / reductions, filter, …
http://www.infoq.com/presentations/Clojure-Reducers
Tim McCormack, http://www.brainonfire.net/files/seqs-and-colls/main.html

40. Google Lectures on MapReduce
http://www.youtube.com/watch?v=yjPBkvYh-ss
http://www.youtube.com/watch?v=-vD6PUdf3Js
http://www.youtube.com/watch?v=5Eib_H_zCEY
http://www.youtube.com/watch?v=1ZDybXl212Q
Aaron Kimball http://www.youtube.com/watch?v=BT-piFBP4fE

41. Clojure Destructuring
http://blog.jayfields.com/2010/07/clojure-destructuring.html
(def indexes [1 2 3])
; #'user/indexes
(let [[x & more :as full-list] indexes]
(println "x:" x "more:" more "full list:"
full-list))
; x: 1 more: (2 3) full list: [1 2 3]
(def point {:x 5 :y 7})
; #'user/point
(let [{the-x :x the-y :y} point]
(println "x:" the-x "y:" the-y))
; x: 5 y: 7 Jay Fields

42. Clojure core.logic
Prolog
Dan Friedman
William Byrd
https://www.youtube.com/watch?v=A7de6pC-tnU

43. Clojure core.logic
http://www.vimeo.com/45128721
Prolog

44. IDE & средства сборки кода
• Поддержка в IDE/редакторах:
– Eclipse (Counterclockwise)
– Netbeans (Enclojure)
– IntelliJ IDEA (La Clojure)
– Emacs + SLIME (depricated) или nRepl / ritz-repl
• Ubuntu: https://launchpad.net/~cassou/+archive/emacs
• Windows: ftp://ftp.gnu.org/gnu/emacs/windows/, cygwin.com
– VimClojure
– LightTable, Textmate, Sublime Text 2, Jedit
• Средства сборки кода:
– Поддержка Clojure в Maven, Ant, Cake, Gradle
– самый популярный: Leiningen (спасибо, Phil)
Phil Hagelberg

45. Библиотеки и репозитории
• Простой доступ к библиотекам JVM
• Библиотеки написанные на Clojure:
– Web-разработка: Compojure, Ring, Scriptjure
– RDBMS: ClojureQL, clojure.java.jdbc, Korma
– NoSQL: Monger, Clouch, …
– GUI: Seesaw
http://darevay.com/talks/clojurewest2012/#/title-slide
– Логическое программирование: core.logic
• Репозитории: Maven Central, Clojars.org

46. Clojure + Leiningen + Emacs 24/emacs-live
on Windows 8
Caveat: emacs-live does not yet collaborate on Windows with ritz-repl,
i.e.emacs-live provides not the full SLIME functionality as per mid Jan. 2013
• Install Java JDK from http://www.java.com
• Install cygwin, use defaults; use cygwin package manager to install git
• Install Leiningen 2.0 in cygwin, this includes Clojure:
– $ cd; git clone
https://raw.github.com/technomancy/leiningen/preview/bin/lein
– Place it on your $PATH, preferably use ~/bin
– $ chmod 755 ~/bin/lein
– $ lein self-install
• Install Emacs 24 + emacs-live in Windows:
• Download Emacs 24 from ftp://ftp.gnu.org/gnu/emacs/windows/
• Download emacs-live from https://github.com/overtone/emacs-live
• Move directory emacs-live to
C:Users%your user name%AppDataRoaming.emacs.d

47. Let´s start: 4clojure.com
See also:
http://www.lisperati.com/clojure-spels/casting.html
https://github.com/relevance/labrepl
http://clojurekoans.com/
http://tryclj.com/

48. Lazy Searching
;;;; 4clojure #108
;; find f satisfying:
;
(= 64 (f (map #(* % % %) (range)) ;; perfect cubes
(filter #(zero? (bit-and % (dec %))) (range)) ;; powers of 2
(iterate inc 20))) ;; at least as large as 20
;; caution: the function for powers of 2 becomes
;; highly inefficient for n > 28:
;
(time (last (take 28 (filter #(zero? (bit-and % (dec %))) (range)))))
;"Elapsed time: 25954.456087 msecs"
;67108864

49. Lazy Searching
;; define predicate on ordered, infinite seqs:
;
(defn in? [coll x]
(cond (empty? coll) false
(= x (first coll)) true
(< x (first coll)) false
:else (in? (rest coll) x)))
;; for convenience:
;
(def inf-seq-1 (map #(* % % %) (range)))
(def inf-seq-2 (filter #(zero? (bit-and % (dec %))) (range)))
(def inf-seq-3 (iterate inc 20))

50. Lazy Searching
;; predicate in? can be used on a finite list of infinite seqs:
;
(take 10
(for [i (range)]
[i (map #(in? % i) (list inf-seq-1 inf-seq-2 inf-seq-3))]))
;([0 (true true false)] [1 (true true false)] [2 (false true false)]
[3 (false false false)] [4 (false true false)] [5 (false false false)]
[6 (false false false)] [7 (false false false)] [8 (true true false)]
[9 (false false false)])
(first (drop 64
(for [i (range)]
[i (map #(in? % i) (list inf-seq-1 inf-seq-2 inf-seq-3))])))
;[64 (true true true)]

51. Lazy Searching
;; for convenience:
;
(def three-infinite-seqs (list inf-seq-1 inf-seq-2 inf-seq-3))
;; predicate in? can be reduced on a finite list
;; of infinite seqs;
;; for convenience define in-seqs?:
;
(defn in-seqs? [x & colls]
(reduce #(and %1 %2) (map #(in? % x) colls)))
(apply in-seqs? 4 three-infinite-seqs)
;false
(apply in-seqs? 64 three-infinite-seqs)
;true

52. Lazy Searching
;; in-seqs? can be used to build a vector tuple in a for loop:
(take 10
(for [i (range)]
[i (apply in-seqs? i three-infinite-seqs)]))
;([0 false] [1 false] [2 false] [3 false] [4 false] [5 false]
[6 false] [7 false] [8 false] [9 false])
;; hence, filtering on the infinite seq of tuples is possible:
;
(first
(filter #(true? (% 1))
(for [i (range)]
[i (apply in-seqs? i three-infinite-seqs)]))
;[64 true]

53. Lazy Searching
;; finally, pick the solution from the right tupel:
;
((first
(filter #(true? (% 1))
(for [i (range)]
[i (apply in-seqs? i three-infinite-seqs)]))) 0)
;64
;; Remark:
;;
;; optimize the solution by using -> / ->>
;; http://kotka.de/blog/2010/04/Did_you_know_II.html

54. Balanced Primes – 1st
;;;; 4clojure #116 (Prime Sandwich)
(= 1103 (nth (filter balanced? (range)) 15))
(defn prime? [n]
(cond (< n 2) false
(= n 2) true
:else (= '(1)
(filter #(zero? (rem n %)) (range 1 (inc (Math/sqrt n)))))))
(defn p-before [p] (last (filter prime? (range p))))
(defn p-after [p] (first (filter prime? (drop (inc p) (range)))))
(defn balanced? [p]
(cond (< p 4) false
(prime? p) (= p (/ (+ (p-before p) (p-after p)) 2))
:else false))

55. Balanced Primes – 2nd
(= 1103 (nth (filter balanced? (range)) 15))
;; prime?, balanced? as before
;; balanced? needs to be refreshed
;; and (take 10 primes)
;;
(def primes (filter prime? (range)))
(defn p-before [p] (last (filter #(< % p) primes)))
(defn p-after [p] (first (filter #(> % p) primes)))

56. Balanced Primes – 3rd
(= 1103 (nth (filter balanced? (range)) 15))
;; prime?, primes, in? as before
(def partitioned-primes
(map #(vector (second %)
(= (second %) (/ (+ (first %) (last %)) 2)))
(partition 3 1 primes)))
(def balanced-primes
(map #(% 0) (filter #(true? (% 1)) partitioned-primes)))
(defn balanced? [p]
(in? balanced-primes p)))

57. Вопросы?
Спасибо за внимание.