8 - OOP - Smalltalk Syntax

Stéphane Ducasse
Stéphane Ducasse
stephane.ducasse@inria.fr
http://stephane.ducasse.free.fr/
1
A Little Journey in the
Smalltalk Syntax

S.Ducasse 2
Goal
Lower your stress :)
Show you that this is simple

S.Ducasse 5
Yeah!
Smalltalk is a dynamically typed
language

S.Ducasse 6
ArrayList<String> strings= new ArrayList<String>();
strings := ArrayList new.

S.Ducasse 7
Shorter
Thread regThread = new Thread(new Runnable() {public void run() {this.doSomething();}});regThread.start();
[self doSomething] fork.

S.Ducasse 8
Smalltalk = Objects + Messages + (...)

S.Ducasse 9
Roadmap
Fun with numbers

S.Ducasse 11
1 class
>SmallInteger

S.Ducasse 13
1 class maxVal
>1073741823

S.Ducasse 14
1 class maxVal + 1

S.Ducasse 15
1 class maxVal + 1
>1073741824

S.Ducasse 16
(1 class maxVal + 1) class

S.Ducasse 17
(1 class maxVal + 1) class
>LargePositiveInteger

S.Ducasse 23
1000 factorial
40238726007709377354370243392300398571937486421071463254379991042993851239862902059204420848696
94048004799886101971960586316668729948085589013238296699445909974245040870737599188236277271887
32519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783
64784997701247663288983595573543251318532395846307555740911426241747434934755342864657661166779
73966688202912073791438537195882498081268678383745597317461360853795345242215865932019280908782
97308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426
23613141250878020800026168315102734182797770478463586817016436502415369139828126481021309276124
489635992870511496497541990934222156683257208082133318611681155361583654698404670897560290095053
76164758477284218896796462449451607653534081989013854424879849599533191017233555566021394503997
36280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178
11419454525722386554146106289218796022383897147608850627686296714667469756291123408243920816015
37808898939645182632436716167621791689097799119037540312746222899880051954444142820121873617459
92642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265
17048330422614397428693306169089796848259012545832716822645806652676995865268227280707578139185
81788896522081643483448259932660433676601769996128318607883861502794659551311565520360939881806
12138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470
93519062092902313649327349756551395872055965422874977401141334696271542284586237738753823048386
56889764619273838149001407673104466402598994902222217659043399018860185665264850617997023561938
970178600408118897299183110211712298459016419210688843871218556461249607987229085192968193723886
42614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344
82801505139969429015348307764456909907315243327828826986460278986432113908350621709500259738986
35542771967428222487575867657523442202075736305694988250879689281627538488633969099598262809561
21450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742
17358240106367740459574178516082923013535808184009699637252423056085590370062427124341690900415
36901059339838357779394109700277534720000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

S.Ducasse 24
1000 factorial / 999 factorial

S.Ducasse 25
1000 factorial / 999 factorial
> 1000

S.Ducasse 27
10 @ 100
(10 @ 100) x

S.Ducasse 28
10 @ 100
(10 @ 100) x
> 10

S.Ducasse 29
10 @ 100
(10 @ 100) x
> 10
(10 @ 100) y

S.Ducasse 30
10 @ 100
(10 @ 100) x
> 10
(10 @ 100) y
>100

S.Ducasse 31
Points!
Points are created using @

S.Ducasse 32
Puzzle
(10@100) + (20@100)

S.Ducasse 33
Puzzle
(10@100) + (20@100)
>30@200

S.Ducasse 34
Puzzle
(10@100) + (20@100)
>30@200

S.Ducasse 35
Roadmap
Fun with characters, strings, arrays

S.Ducasse 36
$C $h $a $r $a $c $t $e $r
$F, $Q $U $E $N $T $i $N

S.Ducasse 37
space tab?!
Character space
Character tab
Character cr

S.Ducasse 38
‘Strings’
‘Tiramisu’

S.Ducasse 39
Characters
12 printString
> ’12’

S.Ducasse 40
Strings are collections of chars
‘Tiramisu’ at: 1

S.Ducasse 41
Strings are collections of chars
‘Tiramisu’ at: 1
> $T

S.Ducasse 42
A program! -- finding the last char

S.Ducasse 43
A program!
| str |

S.Ducasse 44
A program!
| str | local variable

S.Ducasse 45
A program!
str := ‘Tiramisu’.

S.Ducasse 46
A program!
str := ‘Tiramisu’. assignment

S.Ducasse 47
A program!
str at: str length

S.Ducasse 48
A program!
str at: str length message send
> $u

S.Ducasse 49
double ‘ to get one
‘L’’Idiot’
> one string

S.Ducasse 50
For concatenation use ,
‘Calvin’ , ‘ & ‘, ‘Hobbes’

S.Ducasse 51
> ‘Calvin & Hobbes’

S.Ducasse 52
> ‘Calvin & Hobbes’

S.Ducasse 53
Symbols: #Pharo
#Something is a symbol
Symbol is a unique string in the system
#Something == #Something
> true

S.Ducasse 54
“Comment”
“what a fun language lecture.
I really liked the desserts”

S.Ducasse 55
#(Array)
#(‘Calvin’ ‘hates’ ‘Suzie’)

S.Ducasse 56
#(Array)
#(‘Calvin’ ‘hates’ ‘Suzie’) size

S.Ducasse 57
#(Array)
#(‘Calvin’ ‘hates’ ‘Suzie’) size
> 3

S.Ducasse 58
First element starts at 1
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2

S.Ducasse 59
First element starts at 1
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2
> ‘hates’

S.Ducasse 60
at: to access, at:put: to set
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’

S.Ducasse 61
#(Array)
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put: ‘loves’
> #(‘Calvin’ ‘loves’ ‘Suzie’)

S.Ducasse 62
Syntax Summary
comment: “a comment”
character: $c $h $a $r $a $c $t $e $r $s $#
$@
string: ‘a nice string’ ‘lulu’ ‘l’’idiot’
symbol: #mac #+
array: #(1 2 3 (1 3) $a 4)
byte array: #[1 2 3]
integer: 1, 2r101
real: 1.5, 6.03e-34,4, 2.4e7
fraction: 1/33
boolean: true, false
point: 10@120

S.Ducasse 63
Roadmap
Fun with keywords-based messages

S.Ducasse 64
Keyword-based messages
arr at:2 put: ‘loves’

S.Ducasse 65
Keyword-based messages
arr at:2 put: ‘loves’
somehow like arr.atput(2,‘loves’)

S.Ducasse 66
From Java to Smalltalk
postman.send(mail,recipient);

S.Ducasse 67
Removing

S.Ducasse 68
Removing unnecessary
postman send mail recipient

S.Ducasse 69
But without losing information
postman send mail to recipient

S.Ducasse 70
postman send: mail to: recipient

S.Ducasse 71
postman send: mail to: recipient
The message is send:to:

S.Ducasse 72
Roadmap
Fun with variables

S.Ducasse 73
Shared or Global starts with Uppercase
Transcript cr .
Transcript show: ‘hello world’.
Transcript cr .

S.Ducasse 74
local or temps starts with lowercase
| str |
str := ‘Tiramisu’

S.Ducasse 75
self, super, true, false, nil
self = this
super
true, false are for Booleans
nil is UndefinedObject instance

S.Ducasse 76
self, super, true, false, nil
self = this in Java
super
true, false are for Booleans
nil is UndefinedObject instance

S.Ducasse 77
Roadmap
Fun with classes

S.Ducasse 78
A class definition!
Superclass subclass: #Class
instanceVariableNames: 'a b c'
...
category: 'Package name'

S.Ducasse 79
A class definition!
Object subclass: #Point
instanceVariableNames: 'x y'
classVariableNames: ''
poolDictionaries: ''
category: 'Graphics-Primitives'

S.Ducasse 80
A class definition!
Object subclass: #Point
instanceVariableNames: 'x y'
classVariableNames: ''
poolDictionaries: ''
category: 'Graphics-Primitives'

S.Ducasse 81
Roadmap
Fun with methods

S.Ducasse 82
On Integer
asComplex
"Answer a Complex number that represents value of
the the receiver."
^ Complex real: self imaginary: 0

S.Ducasse 83
On Boolean
xor: aBoolean
"Exclusive OR. Answer true if the receiver is not
equivalent to aBoolean."
^(self == aBoolean) not

S.Ducasse 84
Summary
self, super
can access instance variables
can define local variable | ... |
Do not need to define argument types
^ to return

S.Ducasse 85
Roadmap
Fun with unary messages

S.Ducasse 87
1 class
> SmallInteger

S.Ducasse 91
Date today
> 24 May 2009

S.Ducasse 93
Time now
> 6:50:13 pm

S.Ducasse 95
Float pi
> 3.141592653589793

S.Ducasse 96
We sent messages to objects or
classes!
1 class
Date today

S.Ducasse 97
We sent messages to objects or
classes!
1 class
Date today

S.Ducasse 98
Fun with binary messages
Roadmap

S.Ducasse 99
aReceiver aSelector anArgument
Used for arithmetic, comparison and logical
operations
One or two characters taken from:
+ - / * ~ < > = @ % | & ! ? ,

S.Ducasse 105
‘Black chocolate’ , ‘ is good’

S.Ducasse 106
Roadmap
Fun with keyword-based messages

S.Ducasse 107
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put:
‘loves’

S.Ducasse 108
#(‘Calvin’ ‘hates’ ‘Suzie’) at: 2 put:
‘loves’
> #(‘Calvin’ ‘loves’ ‘Suzie’)

S.Ducasse 110
10@20 setX: 2
> 2@20

S.Ducasse 111
12 between: 10 and: 20

S.Ducasse 112
12 between: 10 and: 20
> true

S.Ducasse 113
receiver
keyword1: argument1
keyword2: argument2
equivalent to
receiver.keyword1keyword2(argument
1, argument2)

S.Ducasse 114
receiver
keyword1: argument1
keyword2: argument2
equivalent to
receiver.keyword1keyword2(argument
1, argument2)

S.Ducasse 115
Browser newOnClass: Point
Roadmap

S.Ducasse 116

S.Ducasse 117

S.Ducasse 118
Yes there is a difference between
doing (side effect)
and returning an object

S.Ducasse 119
> a Browser

S.Ducasse 120
Doing and do not care of the returned
result

S.Ducasse 121
Doing and really want to see the result!
10@20 setX: 2
> 2@20

S.Ducasse 122
Doing vs printing (doing + print result)

S.Ducasse 123
Doing vs printing (doing + print result)

S.Ducasse 124
Roadmap
Messages messages
messages
again messages
....

S.Ducasse 125
Yes there are only messages
unary
binary
keywords

S.Ducasse 126
Composition: from left to right!
69 class inspect
69 class superclass superclass inspect

S.Ducasse 127
Unary> Binary> Keywords
Precedence

S.Ducasse 129
2 + 3 squared
> 2 + 9

S.Ducasse 130
2 + 3 squared
> 2 + 9
> 11

S.Ducasse 131
Color gray - Color white = Color black

S.Ducasse 132
> aColor = Color black

S.Ducasse 133
> aColor = Color black
> true

S.Ducasse 134
2 raisedTo: 3 + 2

S.Ducasse 135
2 raisedTo: 3 + 2
> 2 raisedTo: 5

S.Ducasse 136
2 raisedTo: 3 + 2
> 2 raisedTo: 5
> 32

S.Ducasse 137
1/3 + 2/3
No mathematical precedence

S.Ducasse 138
1/3 + 2/3
>7/3 /3

S.Ducasse 139
Parenthesized takes precedence!
(Msg) > Unary> Binary> Keywords

S.Ducasse 140
(0@0 extent: 100@100) bottomRight

S.Ducasse 141
> (aPoint extent: anotherPoint)
bottomRight

S.Ducasse 142
bottomRight
> aRectangle bottomRight

S.Ducasse 143
bottomRight
> aRectangle bottomRight
> 100@100

S.Ducasse 144
0@0 extent: 100@100 bottomRight

S.Ducasse 145
0@0 extent: 100@100 bottomRight
> Message not understood
> 100 does not understand
bottomRight

S.Ducasse 146
3 + 2 * 10

S.Ducasse 147
3 + 2 * 10
> 5 * 10

S.Ducasse 148
3 + 2 * 10
> 5 * 10
> 50
argh!

S.Ducasse 149
3 + (2 * 10)

S.Ducasse 150
3 + (2 * 10)
> 3 + 20

S.Ducasse 151
3 + (2 * 10)
> 3 + 20
> 23

S.Ducasse 152
1/3 + 2/3
> 7/3 /3

S.Ducasse 153
1/3 + 2/3
> (7/3) /3
> 7/9

S.Ducasse 154
(1/3) + (2/3)

S.Ducasse 155
(1/3) + (2/3)
> 1

S.Ducasse 156
(Msg) > Unary > Binary > Keywords
from left to right
Only Messages

S.Ducasse 157
(Msg) > Unary > Binary > Keywords
from left to right
Only Messages

S.Ducasse 158
Roadmap
Fun with blocks

S.Ducasse 159
Function definition
fct(x) = x * x + x

S.Ducasse 160
Function Application
fct (2) = 6
fct (20) = 420

S.Ducasse 161
Function definition
fct(x) = x * x + x
|fct|
fct:= [:x | x * x + x].

S.Ducasse 162
Function Application
fct (2) = 6
fct (20) = 420
fct value: 2
> 6
fct value: 20
> 420

S.Ducasse 163
Other examples
[2 + 3 + 4 + 5] value
[:x | x + 3 + 4 + 5 ] value: 2
[:x :y | x + y + 4 + 5] value: 2 value: 3

S.Ducasse 164
Block
anonymous method
[ :variable1 :variable2 |
| tmp |
expression1.
...variable1 ... ]
value: ...

S.Ducasse 165
Block
anonymous method
Really really cool!
Can be passed to methods, stored in instance
variables
[ :variable1 :variable2 |
| tmp |
expression1.
...variable1 ... ]
value: ...

S.Ducasse 166
Roadmap
Fun with conditional

S.Ducasse 167
Example
3 > 0
ifTrue:['positive']
ifFalse:['negative']

S.Ducasse 168
Example
3 > 0
ifTrue:['positive']
ifFalse:['negative']
> ‘positive’

S.Ducasse 169
Yes ifTrue:ifFalse: is a message!
Weather isRaining
ifTrue: [self takeMyUmbrella]
ifFalse: [self takeMySunglasses]
ifTrue:ifFalse is sent to an object: a boolean!

S.Ducasse 170
Booleans
& | not
or: and: (lazy)
xor:
ifTrue:ifFalse:
ifFalse:ifTrue:
...

S.Ducasse 171
Yes! ifTrue:ifFalse: is a message send
to a Boolean.
But optimized by the compiler :)

S.Ducasse 172
10 timesRepeat: [ Transcript show:
'hello'; cr]

S.Ducasse 173
10 timesRepeat: [ Transcript show:
'hello'; cr]

S.Ducasse 174
[x<y] whileTrue: [x := x + 3]

S.Ducasse 175
aBlockTest whileTrue
aBlockTest whileFalse
aBlockTest whileTrue: aBlockBody
aBlockTest whileFalse: aBlockBody
anInteger timesRepeat: aBlockBody

S.Ducasse 176
Confused with () and [] ?

S.Ducasse 177
Only put [ ] when you do not the
number of times something may be
executed
(x isBlue) ifTrue: [ x schroumph ]
10 timesRepeat: [ self shout ]

S.Ducasse 178
Conditions are messages sent to
boolean
(x isBlue) ifTrue: [ ]

S.Ducasse 179
Fun with loops
Roadmap

S.Ducasse 180
1 to: 100 do:
[ :i | Transcript show: i ; space]

S.Ducasse 181
1 to: 100 do:

S.Ducasse 182
1 to: 100 by: 3 do:

S.Ducasse 183
1 to: 100 by: 3 do:

S.Ducasse 184
So yes there are real loops in
Smalltalk!
to:do:
to:by:do:
are just messages send to integers

S.Ducasse 185
So yes there are real loops in
Smalltalk!
to:do:
to:by:do:
are just messages send to integers

S.Ducasse 186
Roadmap
Fun with iterators

S.Ducasse 187
ArrayList<String> strings
= new ArrayList<String>();
for(Person person: persons)
strings.add(person.name());
strings :=
persons collect [:person | person name].

S.Ducasse 188
#(2 -3 4 -35 4) collect: [ :each| each
abs]

S.Ducasse 189
#(2 -3 4 -35 4) collect: [ :each| each
abs]
> #(2 3 4 35 4)

S.Ducasse 190
#(15 10 19 68) collect: [:i | i odd ]

S.Ducasse 191
#(15 10 19 68) collect: [:i | i odd ]
> #(true false true false)

S.Ducasse 192
#(15 10 19 68) collect: [:i | i odd ]
We can also do it that way!
|result|
aCol := #( 2 -3 4 -35 4).
result := aCol species new: aCol size.
1 to: aCollection size do:
[ :each | result at: each put: (aCol at: each) odd].
result

S.Ducasse 193
#(15 10 19 68) do:
[:i | Transcript show: i ; cr ]

S.Ducasse 194
#(15 10 19 68) do:
[:i | Transcript show: i ; cr ]

S.Ducasse 195
#(1 2 3)
with: #(10 20 30)
do: [:x :y| Transcript show: (y ** x) ;
cr ]

S.Ducasse 196
#(1 2 3)
with: #(10 20 30)
do: [:x :y| Transcript show: (y ** x) ;
cr ]

S.Ducasse 197
How do: is implemented?

S.Ducasse 198
How do: is implemented?
SequenceableCollection>>do: aBlock
"Evaluate aBlock with each of the receiver's elements as
the argument."
1 to: self size do: [:i | aBlock value: (self at: i)]

S.Ducasse 199
Some others... friends
#(15 10 19 68) select: [:i|i odd]
#(15 10 19 68) reject: [:i|i odd]
#(12 10 19 68 21) detect: [:i|i odd]
#(12 10 12 68) detect: [:i|i odd] ifNone:[1]

S.Ducasse 200
#(15 10 19 68) select: [:i|i odd]
> #(15 19)
#(15 10 19 68) reject: [:i|i odd]
#(12 10 19 68 21) detect: [:i|i odd]

S.Ducasse 201
#(15 10 19 68) select: [:i|i odd]
> #(15 19)
#(15 10 19 68) reject: [:i|i odd]
> #(10 68)
#(12 10 19 68 21) detect: [:i|i odd]

S.Ducasse 202
#(15 10 19 68) select: [:i|i odd]
> #(15 19)
#(15 10 19 68) reject: [:i|i odd]
> #(10 68)
#(12 10 19 68 21) detect: [:i|i odd]
> 19

S.Ducasse 203
#(15 10 19 68) select: [:i|i odd]
> #(15 19)
#(15 10 19 68) reject: [:i|i odd]
> #(10 68)
#(12 10 19 68 21) detect: [:i|i odd]
> 19
> 1

S.Ducasse 204
Iterators are your best friends
compact
nice abstraction
Just messages sent to collections

S.Ducasse 205
Iterators are your best friends
compact
nice abstraction
Just messages sent to collections

S.Ducasse 206
A simple exercise
How do you define the method that does that?
#() -> ‘’
#(a) ->’a’
#(a b c) -> ‘a, b, c’

S.Ducasse 207
#(a b c)
do: [:each | Transcript show: each
printString]
separatedBy: [Transcript show: ‘,’]

S.Ducasse 208
#(a b c)
do: [:each | Transcript show: each
printString]
separatedBy: [Transcript show: ‘,’]

S.Ducasse 210
Messages Sequence
• message1 .
• message2 .
• message3
• . is a separator, not a terminator
•
• | macNode pcNode node1 printerNode |
• macNode := Workstation withName: #mac.
• Transcript cr.
• Transcript show: 1 printString.
• Transcript cr.
• Transcript show: 2 printString

S.Ducasse 211
Multiple messages to an objects ;
To send multiple messages to the same object
Transcript show: 1 printString.
Transcript cr
is equivalent to:
Transcript show: 1 printString ;
cr

S.Ducasse 212
Hints ...
x isNil ifTrue: [...]
x includes: 3 ifTrue: [...]
is read as the message includes:ifTrue:
(x includes: 3) ifTrue: [...]

S.Ducasse 214
Smalltalk is fun
Pure simple powerful
www.seaside.st
(www.dabbledb.com)
www.pharo-project.org

8 - OOP - Smalltalk Syntax

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8 - OOP - Smalltalk Syntax