1. Aaron Bloomfield CS 415 Fall 2005
Smalltalk
Aaron Bloomfield
CS 415
Fall 2005

2. Evolution of Smalltalk
Alan Kay – grad student at Utah
Dynabook
Xerox PARC.
Influenced by Lisp, Simula, Ivan Sutherland’s Sketchpad, LOGO, Dewey, Montessori, Piaget
Alan Kay at Utah in late 60s

4. 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

5. Smalltalk and Squeak Smalltalk – commercial product
Squeak – free version, used for education
Smalltalk-80 was developed at Xerox (PARC in the 1970s. )
-VM written in assembly
Apple obtained a license in A team at (Apple developed Squeak in 1996), and have made it available free under license.
Squeak – VM is written in smalltalk, highly portable implementation of Smalltalk-80
(current developers are at Disney – Alan Kay is still part of that. but it is free and anyone can modify it.)
Folks – Mark Guzdial at GA Tech

6. Bindings x <- 3 x <- x + 1
In Squeak, write <-as underscore OR :=
X is bound to 4

7. 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.

8. Other Examples 3 + 2 * 5 25 is answer (use parenthesis if you want 13)
Precedence is left to right within same message type.
Unary-> binary-> keyword
(new) (math ops) (newAt:)
[This example uses all binary operators.]
Parenthesis override
UNDERSCORE is the <- assignment in Squeak
Alt-P to execute
“this is a comment”
Transcript show: ‘Hello World’

9. Inheritance Superclass Subclass Object Overriding
No multiple Inheritance
Object is the class that everything inherits from
If you create a new class it will be a subclass of Object.
Simulation is the mode of programming

10. Implementation Mostly written in Smalltalk Main loop:
true whileTrue: [Display put: user run]
Class - userTask
run ||
Keyboard read eval print
(Compiler, debugger, decompiler, editor, file system = 97% of code.)
Even activation records are smalltalk objects.
Smalltalk-80 – VM – written in assembly (except for Squeak – written in Smalltalk, with an translator into C)
Infinite loop – executes stuff in block. Sends the run mesg to user task.

11. Virtual Machine Storage Manager Interpreter Primitive Subroutines
Interpreter – operates on an intermediate language (the operations of the smalltalk virtual machine)
Prim. Subroutines – collection of methods that for performance reasons are impelemented in assembly.
(I/O, integer arithemtic)

12. 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

13. Concurrency Easy to implement Handy for simulations
Each activation record is a Smalltalk object
sched map: [:Task | Task run]
If sched is a set of tasks, then map will map the block [] to sched.
[] needs to be something that will take a task and send it the run message.
Like map in Scheme