Examples Overview

This section provides practical examples of Onion programs, demonstrating various language features and programming patterns.

Example Programs

All examples can be found in the run/ directory of the Onion repository.

Basic Programs

• Hello World - Simple output
• Arrays - Array manipulation
• User Input - Reading input

Object-Oriented Examples

• Classes and Objects - Basic OOP
• Inheritance - Extending classes
• Interfaces - Interface implementation

Functional Programming

• Lambda Expressions - Anonymous functions
• Closures - Capturing variables
• Recursion - Recursive algorithms

Practical Use-Cases

• Scripting & CLI - Command-line arguments, process execution, file I/O
• JSON & HTTP - JSON/YAML parsing, HTTP client basics
• Async & Concurrency - Futures, async composition, do-notation
• Error Handling - Option, Result, validation patterns

Running Examples

Using the Script Runner

cd run
onion Hello.on

Compiling and Running

onionc Hello.on
java Hello

Example Index

File	Description	Topics Covered
Hello.on	Hello World	Basic I/O
Array.on	Array operations	Arrays, loops
StringCat.on	String concatenation	Strings, arrays
ReadLine.on	User input	I/O, strings
List.on	Dynamic lists	ArrayList, << operator
Foreach.on	Foreach loop	Iteration, collections
Select.on	Pattern matching	Select expression
LineFilter.on	Lambda filtering	Lambdas, closures
LineCounter.on	File processing	Recursion, I/O
Factorial.on	Recursion	Recursive functions
Delegation.on	Delegation pattern	Interfaces, forward
Calculator.on	GUI calculator	Swing, event handling
Bean.on	JavaBean pattern	Serialization, getters/setters
OrderReport.on	Larger data pipeline	Records, enums, collection pipelines
ExprEval.on	Expression evaluator	Interfaces, polymorphism
StatsApp.on	Statistics processing	Generics, extension methods
TodoManager.on	Task manager	Records, enums, extension methods
ShapeProcessor.on	Geometry shapes	Inheritance, extension methods
TextAnalyzer.on	Text statistics	String/List extension methods
ConfigApp.on	CLI + config file	Args, YAML, derive!(Yaml)
JsonApiClient.on	JSON + HTTP client	Http, Json, records
AsyncDownloader.on	Concurrent futures	Future, do-notation
ShellPipeline.on	Shell process pipeline	Proc, file I/O
ResultValidation.on	Validation with errors	Option, Result
StaticImports.on	Static method imports	import { Class::method }
UnitConverter.on	CLI unit converter	Extension methods, Args

Learning Path

Beginner

1. Start with Hello.on - Basic syntax
2. Try Array.on - Data structures
3. Explore Foreach.on - Iteration

Intermediate

1. Study Factorial.on - Recursion
2. Learn LineFilter.on - Lambdas
3. Review Bean.on - OOP patterns
4. Try UnitConverter.on - Extension methods and CLI args

Advanced

1. Analyze Calculator.on - GUI programming
2. Understand Delegation.on - Design patterns
3. Examine LineCounter.on - File processing

Practical

1. ConfigApp.on - Build a CLI-driven config loader
2. JsonApiClient.on - Parse JSON and call HTTP APIs
3. AsyncDownloader.on - Run tasks concurrently
4. ShellPipeline.on - Orchestrate shell commands
5. ResultValidation.on - Handle errors functionally

Next Steps

• Basic Examples - Simple programs
• OOP Examples - Object-oriented code
• Functional Examples - Functional programming
• Scripting Examples - CLI and process automation
• JSON & HTTP Examples - Network and data formats
• Async Examples - Concurrent programming
• Error Handling Examples - Validation and errors