1. CS 331 Principles of Programming Languages
A Smidgen of Smalltalk
CS 331
Principles of Programming Languages

2. Overview
Sethi’s book
Section 7.7 and 7.8
Section 15.4
For an overview of Smalltalk, see Kaehler and Patterson’s “A Taste of Smalltalk”
There are numerous Smalltalk resources on the Web
We’ll be using Squeak to demonstrate

3. Fundamental Concepts
The big idea: everything happens as a result of messages sent to objects
Smalltalk code is written in the context of the Smalltalk development environment
The Smalltalk system provides lots of classes which you can use and study

5. Message keywords Class instances are created by class methods
Most classes understand the “new” message
Some messages have keyword arguments which end with a colon, e.g. aStack push:10
A message may have two or more keywords, e.g. moveTower fromPin:1 toPin:3

6. Smalltalk Syntax Values to be returned are indicated by ^
e.g. ^ lastObject
Conditionals and blocks
e.g. x > y ifTrue: [max := x] ifFalse: [max:=y]
Objects can send themselves messages
e.g. Self isEmpty
The name super accesses an overridden method

7. More Syntax The character $a, the string ‘foo’
Assignment operator is the left arrow
e.g. index <- self find: oldObject.
Using arrays and array elements
e.g. A at: I put: x
e.g. y <- A at: I
e.g. A <- #(1 2 3)

8. Example testVar is 1 arrayTest "See if we can access array elements"
testVar <- A at: 1.
Transcript cr.
Transcript show:('testVar is ', testVar printString).
" (Object new) arrayTest "
testVar is 1