Appendix D: Glossary

A comprehensive reference of Smalltalk-specific terminology and concepts. All terms are defined in beginner-friendly language with cross-references to relevant chapters.

A

Abstract Class A class designed to be subclassed but not instantiated directly. It defines common behavior for its subclasses but leaves some methods unimplemented. Example: Collection is abstract; you use Array or Set instead. See Chapter 15.

Accessor A method that provides access to an instance variable. There are two types: getters (return the value) and setters (change the value). Example: name and name:. See Chapter 12.

Alan Kay Principal inventor of Smalltalk and the concept of object-oriented programming. Visionary behind the “everything is an object” philosophy. Winner of the Turing Award. See Chapter 1.

Argument A value passed to a method or block when it’s executed. Also called a “parameter.” Example: in 3 + 4, the 4 is an argument. See Chapters 4, 9.

Array A fixed-size, ordered collection that can hold any objects. Created with #( ) literal syntax or Array new:. Example: #(1 2 3). See Chapter 6.

Assignment The act of storing a value in a variable using :=. Example: x := 42. The := is the assignment operator. See Chapter 7.

Automatic Testing See Unit Testing.

B

Bag A collection that holds objects with duplicates allowed, optimized for counting occurrences. Like a multiset in mathematics. See Chapter 6.

Baseline A Metacello configuration that defines package dependencies and load order for a project. Used for managing complex multi-package projects. See Chapter 26.

Binary Message A message using an operator symbol like +, -, *, /, <, >, =. Always takes exactly one argument. Example: 3 + 4. See Chapter 4.

Block A chunk of code enclosed in square brackets [ ] that can be stored, passed around, and executed later. Also called a closure. Example: [ 2 + 2 ]. See Chapter 9.

Block Argument A parameter passed to a block when it executes. Declared with colons. Example: [ :x | x * 2 ] - here :x is the block argument. See Chapter 9.

Boolean An object representing true or false. In Smalltalk, true and false are actual objects (instances of True and False). See Chapter 8.

Browser See System Browser.

C

Cascade A way to send multiple messages to the same receiver using semicolons ;. Example: transcript show: 'Hello'; cr; show: 'World'. Avoids repeating the receiver. See Chapter 4.

Changes File A file (.changes) that logs every change you make to the code in an image. A complete history that allows recovery after crashes. See Chapter 17.

Class A blueprint or template for creating objects. Defines the structure (instance variables) and behavior (methods) of its instances. Example: Point, String, Array. See Chapter 11.

Class-side Method A method defined on the class itself rather than on instances. Used for creating instances or accessing class-level information. Example: Date today. See Chapter 11.

Closure Another name for a block. Called “closure” because it closes over (captures) variables from its surrounding scope. See Chapter 9.

Cog VM The modern, high-performance virtual machine used by Pharo, Squeak, and Cuis. Features JIT compilation. Developed at OpenSmalltalk project. See Chapter 2.

Collection A general term for objects that hold multiple other objects. Includes Array, OrderedCollection, Set, Dictionary, Bag. See Chapter 6.

Comment Explanatory text enclosed in double quotes " ". Ignored by the interpreter. Example: "This is a comment". See Chapter 3.

Compiler The part of Smalltalk that translates source code into bytecode. Accessible as an object - you can customize it! See Chapter 16.

Cuis Smalltalk A minimalist, elegant Smalltalk implementation focused on simplicity and understandability. Created by Juan Vuletich. See Chapter 30.

D

Debugger An interactive tool for examining and fixing code while it’s running. One of Smalltalk’s most powerful features - you can modify code in a paused program! See Chapter 21.

Dictionary A collection that maps keys to values. Like a phone book or hash map. Created with Dictionary new. Example: dict at: 'name' put: 'Alice'. See Chapter 6.

Do It Execute selected code in the current context. Keyboard shortcut: Ctrl+D (or Cmd+D on Mac). Fundamental way to run code in Smalltalk. See Chapter 3.

Dolphin Smalltalk A Windows-only Smalltalk implementation with excellent Windows integration. Open source. See Chapter 30.

Double Dispatch A design pattern using two polymorphic calls to achieve behavior based on two objects’ types. Common in Smalltalk for operations like arithmetic with mixed types. See Chapter 23.

Duck Typing “If it walks like a duck and quacks like a duck, it’s a duck.” In Smalltalk, objects are compatible if they respond to the needed messages, regardless of their class. See Chapter 23.

Dynamic Typing Variables don’t have declared types; any variable can hold any object. Types are checked at runtime, not compile time. Fundamental to Smalltalk’s flexibility. See Chapter 7.

E

Encapsulation Hiding an object’s internal state and requiring interaction through methods. Instance variables are private; access through accessor methods. See Chapter 13.

ESUG European Smalltalk User Group. Organizes the main annual Smalltalk conference. Active community, great conference videos on YouTube. See Chapter 38.

Exception An object representing an error or unusual condition. Can be signaled, caught, handled, resumed, or retried. Example: Error, ZeroDivide. See Chapter 24.

Explorer A tool for navigating object structures, especially nested collections. Like a file browser but for objects. See Chapter 20.

F

Factory Method A design pattern where a class-side method creates and returns instances. Example: Color red, Date today. See Chapter 36.

False The class of the single false object. A singleton. Responds to ifTrue:ifFalse: by executing the false branch. See Chapter 8.

File-in Loading code from a file into the image. Historical term from early Smalltalk days. Modern Smalltalk uses Tonel/Git. See Chapter 17.

File-out Saving code from the image to a file. Historical term. Replaced by modern version control with Tonel. See Chapter 17.

Finder See Method Finder or Spotter.

Fork Create a new process (lightweight thread) that runs concurrently. Example: [ expensive computation ] fork. See Chapter 37.

G

Garbage Collection Automatic memory management. The system finds and reclaims objects no longer referenced. You never manually free memory in Smalltalk. See Chapter 16.

Getter An accessor method that returns an instance variable’s value. Example: person name calls the name getter. See Chapter 12.

Glamorous Toolkit (GT) A revolutionary Smalltalk environment focused on “moldable development” - customizing tools for your domain. Created by Tudor Gîrba. See Chapter 29.

Global Variable A variable accessible from anywhere in the system. Starts with a capital letter. Example: Transcript, Smalltalk. Use sparingly! See Chapter 7.

GNU Smalltalk A command-line Smalltalk implementation following GNU project conventions. File-based rather than image-based. See Chapter 30.

H

Halo In Morphic (Squeak/Pharo UI framework), colored handles around a morph allowing you to resize, move, rotate, etc. Opened with Shift+Click. See Chapter 35.

Heap The memory area where objects are allocated. Managed automatically by garbage collection. See Chapter 16.

Hierarchy Browser A tool showing the class inheritance hierarchy visually as a tree. Useful for understanding relationships between classes. See Chapter 19.

I

Iceberg Pharo’s Git integration tool. Manages code repositories, commits, branches, and remote synchronization. See Chapter 18.

Image A snapshot of all objects in the Smalltalk system - your code, tools, open windows, everything. Saved as a .image file. The heart of Smalltalk development. See Chapter 16.

Implementors A tool that finds all methods with a given name across the entire system. Example: find all implementations of +. Keyboard: Ctrl+M. See Chapter 22.

Inheritance When a class inherits behavior from a parent class (superclass). The subclass gets all methods and instance variables of the superclass. Example: String inherits from Collection. See Chapter 15.

Initialize A conventional method name for setting up a new object’s initial state. Automatically called after new. See Chapter 13.

Inspect It Execute code and open an inspector on the result. Keyboard: Ctrl+I (or Cmd+I). Essential for exploring objects. See Chapter 3.

Inspector A tool for examining an object’s instance variables and evaluating expressions in its context. Like X-ray vision for objects. See Chapter 20.

Instance A specific object created from a class. Example: 'hello' is an instance of String, 42 is an instance of SmallInteger. See Chapter 11.

Instance-side Method A normal method that operates on instances of a class. Contrasts with class-side methods. Example: size is instance-side. See Chapter 12.

Instance Variable A variable that belongs to an object, holding part of its state. Private to the object. Example: a Person might have name and age instance variables. See Chapter 13.

Interval A collection representing a range of numbers. Created with to: or to:by:. Example: 1 to: 10 represents numbers from 1 to 10. See Chapter 10.

Iterate To repeat an operation for each element in a collection. Example: #(1 2 3) do: [ :each | ... ]. See Chapter 10.

J

JIT Compiler Just-In-Time compiler. Part of Cog VM that compiles frequently-executed bytecode into native machine code for speed. See Chapter 2.

K

Keyword Message A message with one or more colons in its name. Example: at:put:, ifTrue:ifFalse:. Each keyword takes an argument. See Chapter 4.

KM (Keymapping) Pharo’s keyboard shortcut system. Accessible via KMRepository. Can be customized. See Appendix B.

L

Lazy Initialization A pattern where an instance variable is created only when first accessed. Saves memory and time. Example: cache ifNil: [ cache := Dictionary new ]. See Chapter 13.

Lepiter Glamorous Toolkit’s notebook system for moldable documentation and development. Combines text, code, and custom views. See Chapter 29.

Literal A value written directly in code. Examples: 42 (number), 'hello' (string), #(1 2 3) (array), #symbol (symbol). See Chapter 5.

Live Coding Modifying and debugging code while the program is running. No compile-run-crash cycle. Fundamental to Smalltalk. See Chapter 16.

Live Object An actual object in memory, not a representation or data structure describing an object. In Smalltalk, you work directly with live objects. See Chapter 20.

M

Message A request sent to an object to perform some behavior. The fundamental mechanism of Smalltalk. Example: 3 + 4 sends message + to object 3. See Chapter 4.

Message Browser A tool showing all messages sent or referenced in selected code. Useful for understanding dependencies. See Chapter 19.

Message Passing The paradigm where computation happens by objects sending messages to each other. Smalltalk is pure message passing. See Chapter 4.

Message Send See Message.

Metacello A package management system for Smalltalk. Handles dependencies, versions, and complex project configurations. See Chapter 26.

Metaclass The class of a class. Every class is an instance of its metaclass. Where class-side methods live. Advanced topic! See Chapter 11.

Method A named piece of code belonging to a class that defines behavior. Called when the corresponding message is sent. See Chapter 12.

Method Finder A tool that finds methods by example behavior. Example: give it 'hello' and 'HELLO', it suggests asUppercase. See Chapter 22.

Method Lookup The process of finding which method to execute when a message is sent. Searches the receiver’s class, then superclasses, up to Object. See Chapter 14.

Monticello An older package management system for Smalltalk. Replaced by Tonel/Git in modern Pharo. See Chapter 17.

Morph A graphical object in the Morphic UI framework. Everything visual is a morph. See Chapter 35.

Morphic The graphics and UI framework used by Pharo and Squeak. Everything is a composable graphical object (morph). See Chapter 35.

N

Nautilus The older System Browser in Pharo versions before Pharo 7. Replaced by Calypso. See Chapter 19.

Nil The object representing “no object” or “nothing.” The only instance of class UndefinedObject. Default value of uninitialized variables. See Chapter 7.

Nesting Placing one structure inside another. Example: blocks within blocks, conditionals within loops. See Chapters 8-10.

O

Object An entity that combines data (instance variables) and behavior (methods). Everything in Smalltalk is an object. See Chapter 4.

OrderedCollection A dynamically-sized, ordered collection. Can grow and shrink. Like ArrayList in Java or list in Python. See Chapter 6.

Override To define a method in a subclass that already exists in a superclass. The subclass version is used for instances of the subclass. See Chapter 15.

P

Package A unit of code organization. A collection of related classes and extensions. Example: Collections-Strings, Kernel-Objects. See Chapter 26.

PARC (Xerox PARC) Palo Alto Research Center. Where Smalltalk was invented in the 1970s. Also created GUIs, ethernet, laser printing, and more. See Chapter 1.

Pharo A modern, open-source Smalltalk implementation. Clean, actively developed, great tools. The recommended Smalltalk for most users. See Chapter 27.

PharoLauncher An application for managing multiple Pharo images and VMs. Simplifies installing and organizing different Pharo versions. See Chapter 27.

Playground The modern name for Workspace in Pharo. A place to write and execute code snippets. See Chapter 3.

Polymorphism When different classes respond to the same message in different ways. Example: size works on strings, arrays, sets, etc. See Chapter 23.

Print It Execute code and print the result after the selection. Keyboard: Ctrl+P (or Cmd+P). See Chapter 3.

Print String The textual representation of an object. Returned by the printString method. What you see in inspectors and print-it results. See Chapter 5.

Process A lightweight thread of execution. Smalltalk supports concurrent processes. Created with fork. See Chapter 37.

Protocol A group of related methods in a class. Used for organization, not enforcement. Example: accessing, testing, private. See Chapter 12.

Protocol (Duck Typing) An informal interface - a set of messages an object understands. If an object responds to the right messages, it conforms to the protocol. See Chapter 23.

R

Receiver The object that receives a message. In 3 + 4, 3 is the receiver. In person name, person is the receiver. See Chapter 4.

Refactoring Changing code structure without changing behavior. Smalltalk has excellent refactoring tools built in. See Chapter 19.

Reflection The ability of a program to examine and modify itself at runtime. Smalltalk is highly reflective - everything is accessible. See Chapter 16.

Return To exit a method and provide a result. Uses the caret ^. Example: ^ 42. Methods without explicit return automatically return self. See Chapter 12.

S

Selector The name of a message/method. Example: size, at:, ifTrue:ifFalse:. Can be represented as a symbol like #size. See Chapter 4.

Self A pseudo-variable referring to the receiver of the current message. “This object.” Example: self name calls the name method on this object. See Chapter 14.

Senders A tool that finds all places where a particular message is sent. Example: find everywhere that sends +. Keyboard: Ctrl+N. See Chapter 22.

Setter An accessor method that changes an instance variable’s value. By convention, ends with colon. Example: name:. See Chapter 12.

Set An unordered collection with no duplicates. Like mathematical sets. Example: Set with: 1 with: 2 with: 2 contains only 1 and 2. See Chapter 6.

Singleton A design pattern where a class has exactly one instance. Example: true, false, and nil are singletons. See Chapter 36.

Smalltalk

  1. The programming language. 2. The global object representing the system (capital S). Example: Smalltalk globals accesses global variables. See Chapter 1.

SmallInteger A class representing small integers that fit in a machine word. Highly optimized. Usually transparent to users. See Chapter 5.

Source Code The text form of programs. In Smalltalk, stored in the changes file and sources file. See Chapter 17.

Sources File A file (.sources) containing the source code for the system classes. Shared among images of the same version. See Chapter 17.

Spec 2 Pharo’s modern UI framework. Declarative, reusable, flexible. Used for building tools and applications. See Chapter 31.

Spotter Pharo’s universal search tool. Opened with Shift+Enter. Searches classes, methods, files, and more. Powerful and fast. See Chapter 22.

Squeak A Smalltalk implementation focused on multimedia and education. Very portable, stable, great for teaching. See Chapter 28.

Stack

  1. The call stack - the chain of method calls currently executing. Visible in the debugger. 2. A data structure (LIFO). See Chapters 21, 36.

String A sequence of characters. Created with single quotes. Example: 'Hello, World!'. Strings are objects! See Chapter 5.

Subclass A class that inherits from another class (its superclass). Example: String is a subclass of Collection. See Chapter 15.

Super A pseudo-variable that sends messages to the superclass’s implementation. Used when overriding methods. Example: super initialize. See Chapter 14.

Superclass The parent class in an inheritance hierarchy. Example: Collection is the superclass of Array, Set, etc. See Chapter 15.

Symbol An immutable, unique string used as an identifier. Created with #. Example: #name. Only one #name symbol exists in memory. See Chapter 5.

System Browser The primary tool for browsing and editing classes and methods. Four or five pane layout. Heart of Smalltalk development. See Chapter 19.

SUnit Smalltalk’s unit testing framework. The original xUnit framework that inspired JUnit, NUnit, etc. See Chapter 25.

T

TDD (Test-Driven Development) A development methodology: write test first (red), make it pass (green), improve code (refactor). Invented by Kent Beck in Smalltalk! See Chapter 25.

Template Method A design pattern where a superclass defines an algorithm’s structure, and subclasses fill in specific steps. Common in Smalltalk. See Chapter 36.

Temporary Variable A variable that exists only within a method or block. Declared with pipes | |. Example: | temp |. See Chapter 7.

TestCase The superclass for all test classes in SUnit. Your tests inherit from this. Provides assertion methods. See Chapter 25.

Tonel A text-based file format for Smalltalk code. One file per class. Designed for version control (Git). Used by Iceberg. See Chapter 18.

Transcript A system-wide output window for displaying messages. Like console output. Example: Transcript show: 'Hello'. See Chapter 3.

True The class of the single true object. A singleton. Responds to ifTrue:ifFalse: by executing the true branch. See Chapter 8.

U

UndefinedObject The class of nil. Has only one instance. See Chapter 7.

Unary Message A message with no arguments. Just a name. Example: 'hello' size, 42 factorial. See Chapter 4.

Unicode Character encoding supporting all writing systems. Smalltalk strings support Unicode. See Chapter 5.

Unit Test A small test that verifies one specific behavior. Written with SUnit framework. See Chapter 25.

V

VA Smalltalk A commercial Smalltalk implementation by Instantiations. Strong in enterprise environments, especially IBM mainframe integration. See Chapter 30.

Variable A named container for an object. Types: temporary, instance, class, global. See Chapter 7.

Virtual Machine (VM) The engine that runs Smalltalk bytecode. Handles memory, graphics, OS interaction. Example: Cog VM. See Chapter 2.

VisualWorks A commercial Smalltalk implementation by Cincom. Highly portable, mature, widely used in industry. See Chapter 30.

W

Workspace A text area for writing and executing code snippets. Called Playground in modern Pharo. See Chapter 3.

X

Xerox PARC See PARC.

Z

ZeroConf A one-line installation script for Pharo. Downloads and sets up everything automatically. See Appendix A.

Common Abbreviations

Special Characters and Syntax

Keyboard Shortcut Abbreviations

See Appendix B for complete keyboard shortcut reference.

Resources

Where to look up terms:

  1. System itself: Select any term and Ctrl+B (Browse it)
  2. Pharo By Example: Free book with clear explanations
  3. Discord: Ask the community at https://discord.gg/QewZMZa
  4. This book: Check the table of contents for relevant chapters

Tips for Using This Glossary

Cross-references: When you see “See Chapter X”, that chapter covers the topic in depth.

Bold terms: Indicate the main entry. Synonyms point to main entries.

Examples: Most entries include code examples showing usage.

Progressive disclosure: Start with basic entries (Object, Message, Class) and build up to advanced concepts (Metaclass, Reflection).

Context matters: Some terms have multiple meanings (like Protocol or Process). Context makes it clear.

Contributing

Found a term missing or unclear? This glossary should grow with the community’s needs. Suggest additions via:

Quick Concept Map

Object
  ├─ has Instance Variables
  ├─ responds to Messages
  ├─ created from Class
  └─ lives in Image

Class
  ├─ defines Instance Variables
  ├─ defines Methods
  ├─ has Superclass (Inheritance)
  └─ creates Instances

Message
  ├─ Unary (no args)
  ├─ Binary (operators)
  └─ Keyword (named args)

Method
  ├─ has Selector (name)
  ├─ has Parameters
  ├─ contains Statements
  └─ returns Object

Image
  ├─ contains all Objects
  ├─ paired with Changes file
  ├─ run by VM
  └─ saved as snapshot
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