Smalltalkfor

Unix & Windows

Dennis Smith

Cherniak Software Development Corporation

Smalltalk

• Smalltalk is …– a computer language

– a development environment

– a philosophy of development

– 100% objects

Where did it come from

• Conceived in the late 1960’s by Alan Kay

• Ideas from Simula, Logo, SketchPad• Concept of communicating “cells”

from his biology background• “Cells” later became “Objects”

• Alan Kay Moved to Xerox Park in 1972 where he worked on Smalltalk as a language for teaching children

Alan Kay

• Developed a number of concepts in the 60’s and 70’s– Objects– GUI interfaces– LapTop Computer– Smalltalk

• Alan Kay is now a “Disney Fellow” doing general Research

Smalltalk Yesterday & Today

• First commercial use– Tektronix, embedded in

oscilloscopes

• Used in many areas today– U.S. Power and Light utilities– Insurance Industry– Volkswagen production line– Swiss banks– Ford, General Motors, Chrysler

(Xtreme Programming)– Active Web Sites

Implementations

• VisualWorks (CINCOM) – Based on Xerox Park work– Binary cross-platform (UNIX,

Linux, Windows, Mac)– Full NC version at

www.cincom.com

• ObjectStudio (CINCOM)– Windows & Mainframes

• IBM VisualAge Smalltalk– Cross-platform via source (UNIX,

Windows, OS/2)

Implementations (2)

• Gemstone/S (Gemstone)– server side, persistent, multi-user, active

ODBMS (Unix, Linux, Windows)

– NC versions available at www.gemstone.com

• Dolphin– was free now commercial

• Squeak– Free - small group started by Alan Kay– Available at www.squeak.org

• MT– compiled, windows-only

• GNU– command line, no GUI

Smalltalk – What Is It

• A pure object language

• Simple syntax (5 lines of BNF)

• No compile-time types– Object’s have types– Variables / parameters do not

• Syntax contains no conditionals

• Syntax contains no loops

• Automatic Garbage Collection

Smalltalk – What is it (2)

• Uses a VM

• Compiles to byte codes

• Byte codes can be interpreted

• Normal execution uses a “cached compile” technique pioneered by Smalltalk in the 1980’s.

• Debugging uses interpreter

The Language

• Data is encapsulated in objects

• Access via sending message to the object

• A message invokes a method

• All method returns a value (default the object)

• Everything is an object– Integer, Float, Character, String– Class, Method, Byte Codes– Other Objects

Classes, Variables, Objects

• A class is a pattern for an object– Defines instance variables

– Defines methods

– May inherit from another class

• An Object is instantiated from a class using “Class new”

• Two kinds of variables– Instance variables in the object

– Temporary variables in the method

Methods and Messages

• Three kinds of messages– Unary (name of method)

• person surname

– Keyword (name and parameters)• person surname: ‘Jones’

– Binary, any single or pair of special characters

• personA = personB

• stringA , stringB

• age + 4

• age + 4 * 2

Constant Values

• Constants– Integers 2, 248– Characters $A $+ $$– Strings ‘this is a string’– Floats 123.45– Fixed Decimal (some) 123.45s– Symbols (canonicalized strings)

#abc #surname– Arrays #(12 ‘string’)

• Comments– “this is a comment”

Arithmetic

• This slide should be empty, there is no such concept

• However, by convention, if you send the message “+” to a numeric value the result is likely the sum

• Note however that “+” could be defined for String, Person etc.

• Note “3 + 4 * 5” results in 35!!

Conditionals

• Code block (its an object)[statements][:parm | statements]

• ConditionalaBoolean ifTrue: […]aBoolean ifTrue: […] ifFalse: […]

(true) ifTrue: aBlockaBlock value

(false) ifTrue: aBlock“do nothing”

Collections

• Many types of collections– Array (fixed size)– OrderedCollection (variable size)– Dictionary (keyed values)

• Simple enumeratoraCollection do: [:obj | …]

• Other enumeratorsselect:block returns boolean

reject:block returns boolean

collect: block returns new values

Sample Code

(PersonHolder)firstPerson

| person |person := self getPerson.spouse := person spouse.spouse > person ifTrue: [^spouse].^person

(Person)> aPerson

^self age > aPerson age

Sample Code (2)

• Find all persons older than some other person:

allOlderThan: aPerson

^personList select: [:p | p > aPerson]

Why Smalltalk

• Its fast

• Its easy to work and think with

• Changes are instantly available

• Debugger is fully interactive

• Its fully reflective, classes, methods, byte codes, compiler all written in Smalltalk

• Automatic garbage collection

Why Smalltalk (2)

• Features– IDE uses single browser (written

in Smalltalk of course)– Fully integrated GUI

development– Image reading (gif, bmp) and

manipulation (grow, shrink, rotate, flip, …)

– Network Support (SMTP, POP, IMAO, SOAP, SSP (JSP), …)

What We doat Cherniak Software

• Tools and Framework for building end-user database applications– Accounting– Payroll– Custom

• VisualWorks and Gemstone

• Business and Framework code runs both on VW and on Gemstone