History

• How:
  • Smalltalk was created by Alan Kay, Dan Ingalls, and Adele Goldberg at Xerox PARC in the 1970s.
  • It was designed as a complete software environment and OS, pioneering graphical user interfaces (GUIs), mouse-driven windowing, and the Model-View-Controller (MVC) design pattern.
  • Standardized across major releases: Smalltalk-72, Smalltalk-76, and the famous Smalltalk-80, which was open-sourced and influenced all modern Object-Oriented languages (such as Ruby, Objective-C, Java, and Python).
  • Smalltalk established the concept of “pure Object-Oriented Programming” where everything (including numbers, boolean structures, classes, and compile scopes) is a first-class object, communicating solely via message passing.
• Who:
  • Alan Kay (conceived the actor/object concepts), Dan Ingalls (implemented the code virtual machines), and Adele Goldberg (led the documentation and design team).
• Why:
  • Created to design a user-centric computing environment where software can be dynamically composed, debugged, and modified live during execution.

Introduction

Advantages

• Pure Object Orientation — Absolute consistency. No raw primitives; numbers like 5 and boolean states like true are regular objects with methods.
• Dynamic Live Debugging (The Image Model) — Code runs in a persistent memory state (“The Image”). Execution can be paused, edited, and resumed mid-crash without restarting the process.
• Elegant, Minimalist Syntax — The syntax is incredibly small, fitting on a post-card. Message sending rules govern all logic.
• First-Class Blocks (Closures) — Code blocks are objects, enabling powerful, custom control flow architectures (like custom loops or error checks).

Disadvantages

• Non-traditional File Layout — Standard Smalltalk tools store code in a binary image rather than text files, which can make git versioning and command-line deployments challenging.
• Small Modern Ecosystem — Limited catalog of libraries for web development or cloud integrations compared to languages like Python or JavaScript.
• Dynamic Execution Overhead — Dynamic message dispatching is slower than statically compiled function calls.

Remember Points

• Messages, Not Methods — You do not call methods; you send messages to objects. The object decides how to process the selector.
• Message Precedence Rules — Unary messages evaluate first, then binary, then keyword messages. Parentheses override order.
• Return Expression — The caret ^ returns values from methods. Without ^, the method implicitly returns self.

Basics

Hello World & Output

"This is a comment in Smalltalk (wrapped in double quotes)"
 
"Transcript is the standard output logging window"
Transcript show: 'Hello, World!'; cr.

• Single quotes 'hello' declare literal string objects.
• Semicolon ; cascades multiple messages to the same receiver object.

Variables and Assignments

"1. Declaring Local Variables (enclosed in vertical pipes |)"
| name age |
 
"2. Assignment (:=)"
name := 'VR Rathod'.
age := 25.
 
"3. Literal Objects:"
"Numbers:"
10. "Integer"
3.14. "Float"
(2/3). "Fractional object representing exactly two-thirds"
 
"Array literal:"
#( 1 2 3 'four' )

Message Passing Types

Unary Messages (No Arguments)

"Syntax: receiver selector"
5 negated. -- Returns -5
'hello' size. -- Returns 5

Binary Messages (Operators)

"Syntax: receiver operator argument"
3 + 4. -- Returns 7
'hello', ' world'. -- Concatenation returns 'hello world'

Keyword Messages (Multi-Arguments)

"Syntax: receiver key1: arg1 key2: arg2"
"at:put: is a single selector taking two arguments"
myArray at: 1 put: 'first'. 
 
'hello' copyFrom: 1 to: 3. -- Returns 'hel'

Precedence and Cascades

"1. Precedence: Unary > Binary > Keyword (evaluated left to right)"
2 + 3 raisedTo: 2 negated. 
"Evaluated as:"
"  2 negated -> -2"
"  2 + 3 -> 5"
"  5 raisedTo: -2 -> 0.04"
 
"2. Cascades (;): Send multiple messages to the same receiver"
Transcript 
  show: 'Line 1';
  cr;
  show: 'Line 2'. -- sends show:, cr, and show: to Transcript

Control Flow via Messages

Conditionals

• In Smalltalk, conditionals are regular keyword messages sent to Boolean objects (true/false):

"ifTrue:ifFalse: is a message sent to (score >= 90)"
(score >= 90)
    ifTrue: [ Transcript show: 'Grade A' ]
    ifFalse: [ Transcript show: 'Grade F' ].

Loops

• Loops are also implemented by sending messages to numbers or blocks:

"1. Times Loop"
5 timesRepeat: [ Transcript show: 'Looping'; cr ].
 
"2. Counter Loop (to:do:)"
1 to: 5 do: [ :i |
    Transcript show: i printString; cr.
].
 
"3. While Loop (whileTrue: sent to condition block)"
[ counter < 3 ] whileTrue: [
    counter := counter + 1.
].

Blocks (Closures)

Code Block Evaluations

• Blocks are deferred execution closure objects:

"1. Block definition: [ :args | expressions ]"
| addBlock |
addBlock := [ :a :b | a + b ].
 
"2. Evaluate using value: selector"
result := addBlock value: 10 value: 20. -- returns 30
 
"3. Caret Return (exits containing method, not just block scope)"
myMethod
    [ ^ 'Early Exit' ] value.
    ^ 'Default Return' -- Never reached if block evaluates

Class Definitions

Creating Classes & Methods

• Classes are created dynamically by sending messages to parent classes:

"1. Class Declaration"
Object subclass: #Person
    instanceVariableNames: 'name age'
    classVariableNames: ''
    package: 'App-Model'
 
"2. Method Definition (Accessors)"
name: aString
    name := aString.
    
name
    ^ name.

Runtimes & Environments

Image-based concept

• The Image: A binary snapshot of memory containing all active objects, classes, and execution state. Saved dynamically to disk (.image).
• Pharo: Modern, open-source Smalltalk IDE and virtual machine.
• Squeak: Multimedia-rich open-source Smalltalk dialect.

# Run Pharo image headlessly from terminal executing script file
pharo Pharo.image eval "Transcript show: 'CLI Smalltalk'; cr"

More Learn

Explore valuable resources for Smalltalk:

• Pharo.org (Modern Smalltalk ecosystem)
• Pharo by Example (Free PDF book)
• Squeak.org
• GNU Smalltalk