'&$%CSE 341:Programming LanguagesDan GrossmanSpring 2004Lecture 19— Introduction to SmalltalkDan Grossman CSE341 Spring 2004, Lecture 19 1'&$%TodayWhy Smalltalk?Some basics of smalltalk programs• Syntax• Messages• Blocks• Classes and Methods• Dynamic Dispatch• self and superSection: The Squeak environment (projects, saving your work, etc.)Dan Grossman CSE341 Spring 2004, Lecture 19 2'&$%Smalltalk• Pure object-oriented• Class-based• Dynamically typedA good starting point for discussing what each of these means andwhat other languages look like.The language has been quite stable since 1980.Other points:• A tiny language; easy to learn almost all of it• A complete commitment to dynamic changes; little abstractionsupportDan Grossman CSE341 Spring 2004, Lecture 19 3'&$%Overview of Smalltalk1. All values are objects• Even numbers, code, and classes2. Objects communicate via messages (i.e., methods)3. Objects have their own state4. Every object is an instance of a class5. A class provides behavior for its instancesThis sounds a lot like Java, but smaller.It’s also much more like Scheme than it seems; we’ll return to “whatreally makes something OO”But first we need to get “the feel for Smalltalk”Dan Grossman CSE341 Spring 2004, Lecture 19 4'&$%Syntaxexp ::= atom | assign| unarySend | infixSend | keywordSend| ( exp ) | exp . exp | ^ expatom ::= ID | literal | blockliteral ::= INTEGER | STRING | ...block ::= [:ID1 ... :IDn | exp] | [ exp ]assign ::= name := exp | name _ expunarySend ::= exp IDinfixSend ::= exp OPERATOR expkeywordSend ::= exp ID1: exp ... IDn: expDan Grossman CSE341 Spring 2004, Lecture 19 5'&$%Some key ideas• Really, everything is an object• Blocks are lambdas• Return (↑) is special• Everything is “dynamic” – evaluation can add/remove classes,add/remove methods, etc.• Dynamic typing• Dynamic dispatch• Sends to self (a special identifier; Java’s this)Dan Grossman CSE341 Spring 2004, Lecture 19 6'&$%Protection?• Fields are inaccessible outside of instance• All classes and methods are available to everyone• No namespace management; category has no semantic significanceDan Grossman CSE341 Spring 2004, Lecture 19
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