Aaron Bloomfield CS 415 Fall 2005 Smalltalk Aaron Bloomfield CS 415 Fall 2005

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

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

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 1980. 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

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

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.

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’

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

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.

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)

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

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