Slides used to present Clojure for students in Trondheim. Tasks can be found here: https://github.com/andreaja/clojure-workshop

1. Clojure workshop
Alf Kristian Støyle
Andreas Jacobsen

2. Agenda
• Introduksjon - hvorfor er Clojure viktig
• Basic syntax
• Oppgaver
• Gjennomgang av oppgaver
• JSON over HTTP
• Oppgaver
• Gjennomgang
• Oppsummering

3. Kontoeksempelet

4. public class Account {
private long balance;
public final int accountNo;
public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}
public void debit(long debitAmount) {
this.balance -= debitAmount;
}
public void credit(long creditAmount) {
this.balance += creditAmount;
}
public long getBalance() {
return this.balance;
}
}

5. public class Account {
private long balance;
public final int accountNo;
public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}
public synchronized void debit(long debitAmount) {
this.balance -= debitAmount;
}
public synchronized void credit(long creditAmount) {
this.balance += creditAmount;
}
public long getBalance() {
return this.balance;
}
}

6. public class Account {
private long balance;
public final int accountNo;
public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}
public synchronized void debit(long debitAmount) {
this.balance -= debitAmount;
}
public synchronized void credit(long creditAmount) {
this.balance += creditAmount;
}
public synchronized long getBalance() {
return this.balance;
}
}

7. public class Account {
private volatile long balance;
public final int accountNo;
public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}
public synchronized void debit(long debitAmount) {
this.balance -= debitAmount;
}
public synchronized void credit(long creditAmount) {
this.balance += creditAmount;
}
public synchronized long getBalance() {
return this.balance;
}
}

8. public void transfer(Account fromAccount, Account toAccount,
long amount) throws Exception {
if (fromAccount.getBalance() < amount) {
throw new Exception("Not enough money!");
}
fromAccount.debit(amount);
toAccount.credit(amount);
}

9. public void transfer(Account fromAccount, Account toAccount,
long amount) throws Exception {
synchronized (fromAccount) {
synchronized (toAccount) {
if (fromAccount.getBalance() < amount) {
throw new Exception("Not enough money!");
}
fromAccount.debit(amount);
toAccount.credit(amount);
}
}
}

10. public void transfer(Account fromAccount, Account toAccount,
long amount) throws Exception {
Object mutex1 = toAccount;
Object mutex2 = fromAccount;
if (fromAccount.accountNo < toAccount.accountNo) {
mutex1 = fromAccount;
mutex2 = toAccount;
}
synchronized (mutex1) {
synchronized (mutex2) {
if (fromAccount.getBalance() < amount) {
throw new Exception("Not enough money!");
}
fromAccount.debit(amount);
toAccount.credit(amount);
}
}
}

11. public void transfer(Account fromAccount, Account toAccount,
long amount) throws Exception {
Object mutex1 = toAccount;
Object mutex2 = fromAccount;
if (fromAccount.accountNo < toAccount.accountNo) {
mutex1 = fromAccount;
mutex2 = toAccount;
?
}
synchronized (mutex1) {
synchronized (mutex2) {
if (fromAccount.getBalance() < amount) {
throw new Exception("Not enough money!");
}
fromAccount.debit(amount);
toAccount.credit(amount);
}
}
}
public class Account {
private volatile long balance;
public final int accountNo;
public Account(long balance, int accountNo){
this.balance = balance; this.accountNo = accountNo;
}
public synchronized void debit(long debitAmount) {
this.balance -= debitAmount;
}
public synchronized void credit(long creditAmount) {
this.balance += creditAmount;
}
public synchronized long getBalance() {
return this.balance;
}
}

12. (defn transfer [from-account to-account amount]
(dosync
(if (> amount @from-account)
(throw (new Exception "Not enough money!")))
(alter from-account - amount)
(alter to-account + amount)))

13. (defn transfer [from-account to-account amount]
(dosync
(if (> amount @from-account)
(throw (new Exception "Not enough money!")))
(alter from-account - amount)
(alter to-account + amount)))
(def account-a (ref 1000))
(def account-b (ref 800))

14. (defn transfer [from-account to-account amount]
(dosync
(if (> amount @from-account)
(throw (new Exception "Not enough money!")))
(alter from-account - amount)
(alter to-account + amount)))
(def account-a (ref 1000))
(def account-b (ref 800))
(transfer account-a account-b 300)
@account-a
; => 700

15. http://www.dehne.carleton.ca/research/multi-core

16. Concurrency
dreier som om å gjøre flere oppgaver
omtrent samtidig
Parallelism
dreier seg om å dele en oppgave i mange
deloppgaver som kan gjøres concurrent

17. Clojure

18. Accidental complexity

19. Clojure
• General purpose
• Lisp (List Processing)
• Funksjonelt
• Kompilert
• Dynamisk typet
• Tett knyttet til JVM’en

20. 1
; => 1
"Hello World"
; => "Hello World"

21. 1
; => 1
"Hello World"
; => "Hello World"
(class 1)
; => java.lang.Integer
(class "Hello world")
; => java.lang.String

22. (println "Hello " "world")
; “Hello world”
; => nil

23. Funksjonsnavn
(println "Hello " "world")
; “Hello world”
; => nil

24. Funksjonsnavn Parametere
(println "Hello " "world")
; “Hello world”
; => nil

25. Funksjonsnavn Parametere
(println "Hello " "world")
,
; “Hello world”
; => nil

26. Prefiks notasjon
Funksjonsnavn Parametere
(println "Hello " "world")
,
; “Hello world”
; => nil

27. Methods.callStatic();
methods.callInstance();
callStatic();
callInstance();
this.callInstance();
methods.callStatic();
Methods.this.callInstance();
Methods.this.callStatic();

28. (println "Hello world")
; Hello world
; => nil

29. (println "Hello world")
; Hello world
; => nil
(sum 1 2 3)
; => 6

30. (println "Hello world")
; Hello world
; => nil
(sum 1 2 3)
; => 6
(+ 1 2)
; => 3

31. (println "Hello world")
; Hello world
; => nil
(sum 1 2 3)
; => 6
(+ 1 2)
; => 3
(+ 1 2 3)
; => 6

32. (println "Hello world")
; Hello world
; => nil
(sum 1 2 3)
; => 6
(+ 1 2)
; => 3
(+ 1 2 3)
; => 6
(+)
; => 0

33. 1 + 2 * 3

34. 1 + 2 * 3
1 + (2 * 3)

35. 1 + 2 * 3
1 + (2 * 3)
(+ 1 (* 2 3))

36. Funksjoner
(fn [& nums]
(apply + nums))

37. Funksjoner
(def sum
(fn [& nums]
(apply + nums)))

38. Funksjoner
(def sum
)

39. Funksjoner
(def sum
(fn [& nums]
(apply + nums)))

40. Funksjoner
(def sum
(fn [& nums]
(apply + nums)))
(defn sum
[& nums] (apply + nums))

41. Lister!
'(3 2 1)
; => (3 2 1)
(+ 3 2 1)
; => 6

42. Lister!
'(3 2 1)
; => (3 2 1)
(+ 3 2 1)
; => 6
(defn iterate
[f x] (cons x (lazy-seq (iterate f (f x)))))

43. Immutable collections
; List
'(3 2 1)
; Vector
[1 2 3]
; Set
#{1 2 3}
; Map
{1 "one", 2 "two"‚ 3 "three"}

44. Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)

45. Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)

46. Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)
(def my-other-list (cons 4 my-list))
; => (4 3 2 1)

47. Persistent data
structures
(def my-list '(3 2 1))
; => (3 2 1)
(def my-other-list (cons 4 my-list))
; => (4 3 2 1)

48. Immutable records
(defrecord Person [fname lname])
; => user.Person
(Person. "Alf" "Støyle")
; => #:user.Person{:fname "Alf", :lname "Støyle"}

49. Immutable objects are always thread-safe.

50. Ren funksjonell
programmering
f(x) = x + 1

51. Clojures filosofi
Verdier
Immutable/uforanderlig, primitiv eller sammensatt

52. Clojures filosofi
Verdier
Immutable/uforanderlig, primitiv eller sammensatt
Identitet
En observert entitet som vi assosierer med en serie
relaterte tilstander (verdier) over tid

53. Clojures filosofi
Verdier
Immutable/uforanderlig, primitiv eller sammensatt
Identitet
En observert entitet som vi assosierer med en serie
relaterte tilstander (verdier) over tid
Tilstand
Verdien til en identitet i på et gitt tidspunkt

54. Clojures filosofi
Verdier
Immutable/uforanderlig, primitiv eller sammensatt
Identitet
En observert entitet som vi assosierer med en serie
relaterte tilstander (verdier) over tid
Tilstand
Verdien til en identitet i på et gitt tidspunkt
Tid
Relativ før/etter endring av identitet

55. Perception

56. Perception

57. Perception

58. Perception

59. Perception

60. Perception

61. Fra Rich Hickeys
“Are we there yet”

62. Reference types
• Atoms - synkron og ukoordinert oppdatering
• Agents - asynkron og ukoordinert oppdatering
• Refs - synkron og koordinert oppdatering

63. Reference types
• Atoms - synkron og ukoordinert oppdatering
• Agents - asynkron og ukoordinert oppdatering
• Refs - synkron og koordinert oppdatering
• Synkron perception

64. Atoms
(def an-atom (atom 0))
; => #'user/an-atom

65. Atoms
(def an-atom (atom 0))
; => #'user/an-atom
(swap! an-atom inc)
; => 1

66. Atoms
(def an-atom (atom 0))
; => #'user/an-atom
(swap! an-atom inc)
; => 1
(deref an-atom)
; => 1

67. Atoms
(def an-atom (atom 0))
; => #'user/an-atom
(swap! an-atom inc)
; => 1
(deref an-atom)
; => 1
@an-atom
; => 1

68. Agents
(def an-agent (agent 0))
; => #'user/an-atom

69. Agents
(def an-agent (agent 0))
; => #'user/an-atom
(send an-agent inc)
; => #<Agent@9b7c63f: 0>

70. Agents
(def an-agent (agent 0))
; => #'user/an-atom
(send an-agent inc)
; => #<Agent@9b7c63f: 0>
@an-agent
; => ; 0 eller 1 ??

71. Agents
(def an-agent (agent 0))
; => #'user/an-atom
(send an-agent inc)
; => #<Agent@9b7c63f: 0>
@an-agent (await an-agent)
; => ; 0 eller 1 ?? ; => nil
@an-agent
; => 1

72. Refs
(def ref-1 (ref 0))
; => #'user/ref-1
(def ref-2 (ref 0))
; => #'user/ref-2

73. Refs
(def ref-1 (ref 0))
; => #'user/ref-1
(def ref-2 (ref 0))
; => #'user/ref-2
(alter ref-1 inc)

74. Refs
(def ref-1 (ref 0))
; => #'user/ref-1
(def ref-2 (ref 0))
; => #'user/ref-2
(alter ref-1 inc)
; java.lang.IllegalStateException:
; No transaction running

75. Refs
(def ref-1 (ref 0))
; => #'user/ref-1
(def ref-2 (ref 0))
; => #'user/ref-2
(alter ref-1 inc)
; java.lang.IllegalStateException:
; No transaction running
(dosync (alter ref-1 inc))
; => 1

76. Refs
(dosync
(alter ref-1 inc)
(alter ref-2 dec))
; => -1

77. Refs
(dosync
(alter ref-1 inc)
(alter ref-2 dec))
; => -1
@ref-1
; => 2
@ref-2
; => -1

78. Refs
(dosync
(alter ref-1 inc)
(dosync
(alter ref-2 dec)))
; => -2
@ref-1
; => 3
@ref-2
; => -2

79. Software transactional
memory

80. Software transactional
memory

81. Software transactional
memory
Transactional memory is to
shared-memory concurrency
as
garbage collection is to
memory management

82. Software transactional
memory

83. Software transactional
memory
Atomic
Consistent
Isolated
Durable

85. (defn transfer [from-account to-account amount]
(dosync
(if (> amount @from-account)
(throw (new Exception "Not enough money!")))
(alter from-account - amount)
(alter to-account + amount)))
(def account-a (ref 1000))
(def account-b (ref 800))
(transfer account-a account-b 300)
@account-a
; => 700

86. Oppsummering
• Skiller tilstand og identitet
• Ingen mutable tilstand
• Ingenting blokkerer
• Clojure hjelper langt på vei med concurrency

87. Oppsummering
• Skiller tilstand og identitet
• Ingen mutable tilstand
• Ingenting blokkerer
• Clojure hjelper langt på vei med concurrency
• Mindre “accidental complexity”

88. Clojure syntaks
(Masse paranteser)

89. • REPL
• Syntaks
• Data strukturer
• Funksjoner
• Hvordan fylle ut oppgavene
• Hvordan finne hjelp

91. clojure-workshop/$ lein repl

92. Dette er en form

93. Dette er også en liste

94. Et uttrykk (expression)

97. Dette er en liste

98. Akkurat samme, skrevet litt lenger

99. Noen som klarer å gjette hva dette blir?

100. En funksjon er også bare data

101. Dette er en funksjon (uten navn)

102. Lost in Stupid Parentheses?

103. let lar deg binde lokale variable

104. Oppgaver!
Disse ligger under
clojure-workshop/test/
clojure-workshop/test/
(Dere ser ikke dobbelt)

105. Start med core.clj

106. c-w/$ lein test
c-w/$ lein test clojure-workshop.test.core

107. To streker: __ => En funksjon
Tre streker: ___ => En verdi

110. Alle testene er kommentert ut, flytt
(comment
nedover for å kommentere inn tester

111. • http://clojuredocs.org
• http://clojure.org/cheatsheet
• Repl har innebygget hjelp
• (doc first)
• (find-doc “Returns the first item”)
• (apropos ‘first)
• (source first)

112. JSON over HTTP

113. JSON
• JavaScript Object Notation
• http://www.json.org/
• It is easy for humans to read and write.
• It is easy for machines to parse and generate

114. {
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address":
{
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": "10021"
},
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}
http://en.wikipedia.org/wiki/JSON

115. {
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address":
{
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
map },
"postalCode": "10021"
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}
http://en.wikipedia.org/wiki/JSON

116. {
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address":
{
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
map },
"postalCode": "10021"
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
vector {
"type": "fax",
"number": "646 555-4567"
}
]
}
http://en.wikipedia.org/wiki/JSON

117. (clojure.data.json/read-json "...")

118. {
:firstName John,
:lastName Smith,
:age 25,
:address
{
:streetAddress 21 2nd Street,
:city New York,
:state NY,
:postalCode 10021
},
:phoneNumber
[
{
:type home,
:number 212 555-1234
}
{
:type fax,
:number 646 555-4567
}
]
}

119. {
"firstName": "John",
"lastName": "Smith",
"age": 25,
"address":
{
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": "10021"
},
"phoneNumber":
[
{
"type": "home",
"number": "212 555-1234"
},
{
"type": "fax",
"number": "646 555-4567"
}
]
}

120. (get {:one 1 :two 2 :three 3} :one)
;=> 1

121. (get {:one 1 :two 2 :three 3} :one)
;=> 1
(:one {:one 1 :two 2 :three 3})
;=> 1

122. (get {:one 1 :two 2 :three 3} :one)
;=> 1
(:one {:one 1 :two 2 :three 3})
;=> 1
({:one 1 :two 2 :three 3} :one)
;=> 1

123. clj-http
(client/get "http://google.com")
=> {:status 200
:headers {"date" "Sun, 01 Aug 2010 07:03:49 GMT"
"cache-control" "private, max-age=0"
"content-type" "text/html; charset=ISO-8859-1"
...}
:body "<!doctype html>..."}
https://github.com/dakrone/clj-http

124. Oppgave
• Eksempel på twitter json i “twitter-java-search-json.txt”
• Skrive ut “tweet-text” fra live twitter søk
• Skriv ut encodings benyttet i resultat av live twitter søk
• twitter-java-search-json.txt
• Finn antall unike encodings
• Skriv ut tweets fra “world_finance”
• Skriv ut tweets som er replies
• API’er
• https://github.com/dakrone/clj-http
• http://clojure.github.com/clojure-contrib/json-api.html

125. Lyst til å lære mer?
• clojure.org
• 4clojure.com
• github.com/functional-koans/clojure-koans

126. Takk for oss :)
• Spørsmål:
• aks@knowit.no
• aja@knowit.no
• Oppgaver: github.com/andreaja/clojure-workshop
• Løsninger: github.com/andreaja/clojure-workshop/tree/solutions