10. Smalltalk and Closures

Programmierung 2, SS 2007

Adrian Kuhn, PhD candidate

Software Composition Group

University of Bern

Beyond Java

Beyond is the future

Beyond Java 6.0 is Java 7.0

Beyond, also, is the past

Beyond Java is Smalltalk

Developed in the 70ies

Smalltalk-80 since 1980

For example, Closures

Planned for Java 7.0 in 2008

Featured in Smalltalk since 1980

Get winner I

public boolean hasWinner() { for (Player each : players) { if (each.isWinner()) { return true; } } return false;}

Get winner II

public boolean hasWinner() { return players.contains({ Player each | each.isWinner() });}

Get winner III

hasWinner ^players contains: [ :each | each isWinner ]

Handler I

Jbutton button = new JButton(“Save”);button.addActionListener( new ActionListener() { public void actionPerformed (ActionEvent e) { this.saveAndClose(); } });

Handler II

Jbutton button = new JButton(“Save”);button.addActionListener({ ActionEvent e | this.saveAndClose() });

Handler III

button = Button new: ‘Save’.Button addActionListener: [ :event | self saveAndClose ].

Closure

• A code block as first-class object

• Developed in the 60ies

• First implemented in Scheme, ie LISP

• Smalltalk-80, Ruby, Python, etc…

• In discussion for Java 7

Smalltalk

• An object oriented language

• Everything is an object– including primitive values

• Everything is a message send– including the control flow

Syntax

How to format it?

Smalltalk Syntax IAlbum album = new Album();album.play();album.playTrack(1);album.playTrack(1,5);

Album = Album new. album play.album playTrack: 1.album playFromTrack: 1 to: 5.

Smalltak Syntax IIalbum.setName(“Fat of the Land”);String str = album.getName();char ch = str.charAt(0); //starts at 0assert ch == ‘F’;

album name: ‘Fat of the Land’.str := album name.ch := str at: 1. “starts at 1, not 0!”[ ch == $F ] assert.

Semantics

What does it mean?

Smalltak Semantics// Semantics of = is assignment// Semantics of “…” defines a string literal

variable = “Foobar”; assert variable == null; //blahblah

“Semantics of = is comparison”“Semantics of “…” defines a comment”

variable := ‘Foobar’.[ variable = nil ] assert. “blahblah”

Closure, more examples

Closure syntaxdiff := [ :a :b | Transcript show: a. Transcript show: b. (a - b) abs “closure return the result “of the last expression.” ].

x := 23;y := 42;Z := diff value: x value: y.

Sort I

List<String> list = /* some code here */;Collections.sort(list, new Comparable<String>() { public int compare(String a, String b) { return o1.length() - o2.length();

}); }

Sort II

List<String> list = /* some code here */;Collections.sort(list, { String a, String b | return o1.length() - o2.length() });

Sort III

list = “some code here”. List sort: [ :a :b | a size <= b size ].

Iterate collectionfor (Object each : list) { System.out.println(each);}

list.do({ Object each | System.out.println(each) });

list do: [ :each | Transcript show: each ].

Sequence Diagram:Client a :Arrayb :Closure

b value: a1

a do: b

b value: a2

b value: a3

b value: an

Times repeatfor (Integer n = 0; n < 10; n++) { System.out.println(“foo”);}

10.timesRepeat({ System.out.println(“foo”) });

10 timesRepeat: [ Transcript show: ‘foo’ ].

For loopfor (Integer n = 0; n < 10; n++) { System.out.println(n+1);}

0.loop(10,{ int each | System.out.println(each+1) });

1 to: 10 do: [ :each | Transcript show: each ].

Branchingif (game.hasWinner()) { System.out.prinrtln(game.getWinner());}

game.hasWinner().ifTrue({ System.out.println(game.getWinner()) });

game hasWinner ifTrue: [ Transcript show: game winner ].

Class Diagram

TrueifTrue: aClosure ^aClosure value

FalseifTrue: aClosure ^nil

BooleanifTrue: aClosure “abstract”

For loopint sum = 1;for (int each : numbers) { sum += each;}

numbers.map(0,{ int sum, int each | sum + each });

numbers inject: 0 into: [ :sum :each | sum + each ].

Closures and Collections

Collection >> do:

Collection >> allSatisfy:Collection >> anySatisfy:Collection >> contains:Collection >> inject:into: Collection >> detect:Collection >> select:Collection >> reject:

ArrayedCollection >> sort:

Closures and Flow Control

Boolean >> ifTrue:Boolean >> ifFalse:Boolean >> ifTrue:ifFalse:

Integer >> timesRepeat:Integer >> to:do:

BlockClosure >> whileTrue:BlockClosure >> whileFalse:

More Smalltalk

Smalltalk’s family tree

Family tree

Objects, Garbage Collection, Byte code, etc…

Bit Blitting

Overlapping windows

Model-View-Controller

Design Patterns

Refactoring Browser

Unit Testing

Collection framework

Extreme programming

JIT compilation

1st Apple Prototype

Eclipse IDE

Java, Self, JavaScript

1st wiki community

And some name dropping

• Alan Kay• Dan Ingalls• Adele Goldberg• Ted Kaehler• Scott Wallance• John Brandt• Don Roberts

• Kent Beck• Gilad Bracha• Ward Cunningham• Erich Gamma• Ron Jeffries• Martin Fowler• Ralph Johnson

Pure Object-Orientation

• Pure object oriented language

• Everything is an object– including primitive values

• Everything is a message send– including the control flow

Persistent Object Memory

• Smalltalk is language and environment

• Everything inside the image– persistent objects– fully reflective system– incremental compilation– “hot debugging”

Virtual machine

• Compiled code, ie byte code• Source code• Objects• Classes• IDE• Application

*.im file, the image

Squeak

Open-source Smalltalk

www.squeak.org

Squeak ScreenshotQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Hands-on demo

Postoffice exercise in Smalltalk

More see P2 wiki

smallwiki.unibe.ch/p22007smallwiki