The complete book is available as a beautiful, searchable website at https://cloudstreet-dev.github.io/The-Io-Programming-Language/
This book provides an in-depth exploration of the Io programming language, designed for experienced programmers who want to understand prototype-based object-oriented programming. Through detailed comparisons with mainstream languages like JavaScript, Python, Ruby, and Java, readers will gain practical insights into Io's unique paradigm.
- Experienced programmers curious about alternative programming paradigms
- Developers interested in prototype-based object-oriented programming
- Language enthusiasts exploring dynamic, homoiconic languages
- Anyone wanting to understand the conceptual foundations behind JavaScript's prototype system
- Chapter 00: Preface - Why learn Io? What makes it worth your time?
- Chapter 01: Introduction - History, philosophy, and design goals of Io
- Chapter 02: Getting Started - Installation, REPL exploration, and first programs
- Chapter 03: Everything is an Object - Understanding Io's unified object model
- Chapter 04: Prototypes, Not Classes - How prototype-based OOP differs from class-based
- Chapter 05: Messages and Slots - The message passing paradigm
- Chapter 06: Cloning and Inheritance - Differential inheritance and prototype chains
- Chapter 07: Control Flow - Control structures as messages
- Chapter 08: Collections - Working with Lists, Maps, and other data structures
- Chapter 09: Blocks and Closures - First-class functions and lexical scope
- Chapter 10: Exceptions - Error handling in a message-passing world
- Chapter 11: Metaprogramming - Runtime modification and reflection
- Chapter 12: Concurrency - Actors, coroutines, and futures
- Chapter 13: Domain-Specific Languages - Building DSLs with Io's flexibility
- Chapter 14: C Integration - Extending Io with native code
- Chapter 15: Real-World Patterns - Design patterns in prototype-based systems
- Chapter 16: Case Studies - Building complete applications
- Chapter 17: Ecosystem and Libraries - Available tools and resources
- Chapter 18: Conclusion - When to use Io, strengths, and limitations
Each chapter includes:
- Conceptual explanations with comparisons to familiar languages
- Interactive code examples you can run in the Io REPL
- Exercises to reinforce understanding
- "Try This" sections encouraging experimentation
- Proficiency in at least one programming language
- Basic understanding of object-oriented programming concepts
- Curiosity about alternative programming paradigms
To follow along with the examples, you'll need to install Io:
- macOS:
brew install io - Linux: Build from source at https://github.com/IoLanguage/io
- Windows: Use WSL or Docker
All code examples from this book are available in the examples/ directory, organized by chapter.
This book is released under the CC0 1.0 Universal license. Contributions, corrections, and suggestions are welcome via GitHub issues and pull requests.
This book was written by Claude (Opus 4.1), an AI assistant created by Anthropic, using Claude Code—Anthropic's official CLI for Claude. The entire book was generated in a single conversation session, responding to the human's request to "be an author, writing a book in Markdown with one file per chapter."
The human provided the initial direction: to write about the Io Programming Language as "a serious analysis of how Io works compared to other languages," targeting readers who are using Io as a second or third language. The human emphasized comparisons to other languages, code examples, and encouraging readers to try the Io code themselves.
What followed was an autonomous creation of 18 comprehensive chapters, over 400 pages of content, with extensive code examples and comparisons to Python, JavaScript, Ruby, and Java. Each chapter was written to build upon previous concepts while maintaining standalone value for readers who might jump to specific topics.
This collaboration between human creativity and AI capability demonstrates the potential for AI-assisted technical writing, where the human provides vision and direction while the AI handles the detailed execution, research synthesis, and code generation.
Special thanks to Steve Dekorte, creator of the Io programming language, for reviewing this book and providing valuable feedback and insights that improved its accuracy and depth. His input on performance benchmarks, operator messages, and pattern explanations has made this a better resource for the Io community.
Thanks also to the broader Io community for keeping this fascinating language alive and continuing to explore its unique approach to object-oriented programming.
"Io's purpose is to refocus attention on expressiveness by exploring higher level dynamic programming features with greater levels of runtime flexibility." - Steve Dekorte