# EK9 Programming Language

> EK9 is an AI-native, statically-typed programming language whose compiler enforces quality, security, and safety as hard errors — if it compiles, it meets the bar. It fuses object-oriented and functional styles, removes whole classes of bug from the grammar (no break/continue/return/null), models every value as tri-state (absent/unset/set), and compiles to JVM bytecode (LLVM native planned).

This file follows the llmstxt.org convention. The full language reference is at [llms-full.txt](https://ek9.io/llms-full.txt); the structured, machine-readable reference is [forAI.json](https://ek9.io/forAI.json).

## Critical paradigm shifts (read first)

- No `break`, `continue`, `return`, or `null` — use stream pipelines, guard expressions, and tri-state `?`.
- `<-` declares a new variable, `:=` assigns to an existing one, `:=?` assigns only if currently unset.
- `$` converts a value to String (it is not interpolation); backtick strings interpolate with `${...}`.
- Types are closed by default (like Kotlin `final`) — use `as open` or composition.
- Records have public fields and operators only; classes have private fields and methods.
- Banned identifiers are compile errors: temp, tmp, value, val, flag, flg, data, dat, buffer, buf, object, obj.

## Documentation

### Getting Started
_Introduction and basics for new developers_

- [About EK9](https://ek9.io/index.html): Overview and philosophy
- [Introduction](https://ek9.io/introduction.html): Getting started guide
- [Structure](https://ek9.io/structure.html): Module structure, indentation syntax
- [Basics](https://ek9.io/basics.html): Variables, types, tri-state semantics

### Core Language
_Core language constructs and syntax_

- [Operators](https://ek9.io/operators.html): All EK9 operators including ?. :=?, ==, <=>
- [Flow Control](https://ek9.io/flowControl.html): Guards, conditionals, loops (NO break/continue/return)
- [Exceptions](https://ek9.io/exceptions.html): Error handling with try/catch
- [Constants](https://ek9.io/constants.html): Constant definitions
- [Programs](https://ek9.io/programs.html): Entry points and program structure

### Types
_Type system and built-in types_

- [Built-in Types](https://ek9.io/builtInTypes.html): String, Integer, Boolean, etc. (NO null)
- [Collection Types](https://ek9.io/collectionTypes.html): List, Dict, Optional, Result
- [Standard Types](https://ek9.io/standardTypes.html): Date, Time, Duration, etc.
- [Network Types](https://ek9.io/networkTypes.html): HTTP, TCP, UDP types
- [Input Sanitization](https://ek9.io/sanitized.html): Sanitized types for security
- [Enumerations](https://ek9.io/enumerations.html): Enum definitions
- [Records](https://ek9.io/records.html): Data-focused aggregates (mutable — immutability via 'pure')
- [Generics/Templates](https://ek9.io/generics.html): Generic type parameters

### Object Oriented
_Object-oriented programming constructs_

- [Classes](https://ek9.io/classes.html): Class definitions (closed by default)
- [Methods](https://ek9.io/methods.html): Method definitions and dispatchers
- [Traits](https://ek9.io/traits.html): Interface-like abstractions
- [Composition](https://ek9.io/composition.html): Extension by composition with 'by'
- [Inheritance](https://ek9.io/inheritance.html): Type inheritance (use 'as open')
- [Advanced Methods](https://ek9.io/advancedClassMethods.html): Advanced class method patterns

### Functional
_Functional programming features_

- [Functions](https://ek9.io/functions.html): Function definitions (NO return statement)
- [Dynamic Functions](https://ek9.io/dynamicFunctions.html): First-class functions
- [Dynamic Classes](https://ek9.io/dynamicClasses.html): Runtime class creation
- [Streams/Pipelines](https://ek9.io/streamsAndPipelines.html): Stream processing (replaces break/continue)

### Enterprise
_Enterprise and application features_

- [Components](https://ek9.io/components.html): Component definitions
- [Dependency Injection](https://ek9.io/dependencyInjection.html): DI patterns
- [Web Services](https://ek9.io/webServices.html): REST services
- [Design Patterns](https://ek9.io/commonDesignPatterns.html): Common EK9 patterns
- [Text/Properties](https://ek9.io/textProperties.html): I18n and configuration

### Tooling
_Development tools and compiler_

- [Command Line](https://ek9.io/commandline.html): Compiler options including -E3/-E5 for AI
- [Testing](https://ek9.io/testing.html): Test framework and coverage
- [Code Quality](https://ek9.io/quality.html): Metrics and thresholds
- [Packaging](https://ek9.io/packaging.html): Building and distributing
- [REPL](https://ek9.io/repl.html): Interactive evaluation

### Reference
_Reference documentation_

- [Error Index](https://ek9.io/errors.html): All compiler errors with fixes
- [For AI Assistants](https://ek9.io/forAI.html): AI-specific guidance (HTML version)

## For AI assistants

- [For AI Assistants (HTML)](https://ek9.io/forAI.html): guide to EK9 for coding assistants.
- [forAI.json](https://ek9.io/forAI.json): structured machine-readable reference (error codes, type APIs, examples).
- [llms-full.txt](https://ek9.io/llms-full.txt): the full language reference in one file.
- [Q&A corpus](https://ek9.io/qa/): compiler-validated question-and-answer examples (machine-readable: https://ek9.io/qa/qa.jsonl).