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ARO Documentation

Welcome to the ARO programming language documentation.

ARO (Action-Result-Object) is a declarative domain-specific language for expressing business features in a human-readable format. ARO programs describe what should happen using natural language constructs, and the runtime handles how it executes.

About ARO

ARO is designed for building event-driven applications with clear, readable business logic. Key characteristics include:

• Declarative Syntax: Express intent, not implementation details
• Event-Driven Architecture: Feature sets respond to events automatically
• Multi-File Applications: Organize code across files without imports
• Built-in Services: HTTP server/client, file system, sockets out of the box

Documentation

Getting Started

Document	Description
Getting Started	Install ARO and write your first application
A Tour of ARO	A comprehensive introduction to ARO's features

Language Guide

Detailed documentation of ARO language features:

Fundamentals

Chapter	Description
The Basics	Fundamental concepts, syntax, and structure
Feature Sets	Defining and organizing feature sets
Actions	Built-in actions and the ARO statement pattern
Variables and Data Flow	Variable binding, scoping, and publishing
Type System	Primitives, collections, and OpenAPI types
Control Flow	Conditionals, guards, and branching
Error Handling	The "Code Is The Error Message" philosophy
Computations	Calculation and expression evaluation
Dates	Working with date and time values
Concurrency	Async feature sets, sync statements

Runtime & Events

Chapter	Description
Events	Event-driven programming and handlers
Application Lifecycle	Start, run, and shutdown
Services	Built-in service architecture

I/O & Communication

Chapter	Description
HTTP Services	HTTP server operations
HTTP Client	Making HTTP requests
WebSockets	Real-time bidirectional communication
File System	File I/O and directory watching
Sockets	TCP communication
Repositories	Data storage and management

Advanced

Chapter	Description
Data Pipelines	Filter, Map, Reduce for collection processing
Streaming Execution	Process large datasets with constant memory
Context-Aware Responses	Dynamic response generation
System Commands	External command execution

Language Reference

Formal language specification:

Document	Description
Grammar	Complete EBNF grammar specification
Statements	Statement types and syntax
Actions Reference	Complete action verb reference

Extending ARO

Document	Description
Action Developer Guide	Creating custom actions in Swift

Quick Example

(* Application entry point *)
(Application-Start: Hello World) {
    Log "Hello, ARO!" to the <console>.
    Return an <OK: status> for the <startup>.
}

(* Graceful shutdown *)
(Application-End: Success) {
    Log "Goodbye!" to the <console>.
    Return an <OK: status> for the <shutdown>.
}

Run with:

aro run ./HelloWorld

Resources

• Evolution Proposals - Language design proposals
• Examples - Example applications
• GitHub Repository - Source code
• Mastodon - Daily language tips and updates

Version

This documentation covers ARO 1.0.