Smalltalk
Aaron Bloomfield
CS 415
Fall 2005
1

Evolution of Smalltalk
• Alan Kay – grad student at Utah
– Dynabook
• Xerox PARC.
• Influenced by Lisp, Simula, Ivan
Sutherland’s Sketchpad, LOGO, Dewey,
Montessori, Piaget
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3

Smalltalk
• Interpreted
• Everything is an object
• Dynamically & Strongly Typed
• Rich programming environment
– Window-oriented display management
– Mouse, Menus
• Example of a pure Object-Oriented
Language
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Smalltalk and Squeak
• Smalltalk – commercial product
• Squeak – free version, used for education
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x <- 3 x <- x + 1
X is bound to 4
Bindings
In Squeak, write <as underscore OR
:=
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Objects and Messages
• Everything is an Object
• Everything is done by sending messages to objects x * 2
• Sends the message *2 to the object x.
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3 + 2 * 5
Other Examples
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Inheritance
• Superclass
• Subclass
• Object
• Overriding
• No multiple Inheritance
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Implementation
• Mostly written in Smalltalk
• Main loop: true whileTrue: [Display put: user run]
Class - userTask run ||
Keyboard read eval print
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Virtual Machine
• Storage Manager
• Interpreter
• Primitive Subroutines
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Storage Manager
• Collects and manages free space
• Handles requests to:
– Create new objects
– Fetch class of an object
– Fetch and store fields of an object
• Uses reference counting
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Concurrency
• Easy to implement
• Handy for simulations
• Each activation record is a Smalltalk object sched map: [:Task | Task run]
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