Rex Programming Language

Ownership-aware native programming with a Lua front-end, a C backend, and a practical project workflow.

Getting Started · Syntax · Standard Library · CLI Reference · Package Workflow

Website · Book · Releases

What Rex Is

Rex is a systems-style language built around explicit control of values, ownership, borrowing, and runtime behavior. The compiler front-end is written in Lua. Generated programs target C and link against the runtime in rex/runtime_c.

The repository contains the compiler, runtime, examples, language docs, and the current project/package workflow used to build real Rex programs.

Why Rex

• Keep ownership and borrowing explicit without turning the language into a maze.
• Compile through a small, inspectable pipeline instead of a large opaque toolchain.
• Ship practical runtime modules for files, time, JSON, HTTP, UI, and native apps.
• Build real projects with rex.toml, rex.lock, local dependencies, and pinned git dependencies.

Core Capabilities

• Structs, enums, methods (impl), and type aliases
• Generic functions and generic types
• Result and ? for error propagation
• Ownership and borrow checking with & and &mut
• defer for scope-based cleanup
• bond / commit / rollback for transaction-style flows
• Concurrency primitives including spawn and channels
• Runtime modules for io, fs, time, json, http, ui, and more
• Manifest-aware projects with rex.toml and rex.lock

Quick Start

Prerequisites

• Lua 5.4+ or a compatible Lua runtime
• A C compiler: cc, clang, or gcc

Run from the Windows Installer

rex run "C:\rex-lang\rex\examples\hello.rex"

PowerShell fallback:

& "C:\Program Files\RexLang\bin\rex.cmd" run "C:\rex-lang\rex\examples\hello.rex"

If Windows reports C compiler not found:

winget install -e --id LLVM.LLVM
setx CC clang

Run from Source

cd rex
lua compiler/cli/rex.lua run examples/hello.rex

Check a file without building a native binary:

cd rex
lua compiler/cli/rex.lua check examples/hello.rex

Build the example suite to generated C:

cd rex
lua compiler/cli/rex.lua test

Small Example

use rex::io
use rex::fmt
use rex::text

fn main() {
    let title = "Hello World Example"
    let priority: i32 = 42
    let zero = "0"

    let id = text.initials(&title)
    let padded = fmt.pad_left(priority, 4, &zero)
    let raw = id + ":" + padded
    let result = text.lower_ascii(&raw)

    println(result)
}

Output:

hwe:0042

First Project

Create a new project:

rex init my-app

This writes:

• my-app/rex.toml
• my-app/src/main.rex

Then build or run from the project root:

cd my-app
rex build
rex run
rex check

These commands resolve the program entry from entry in rex.toml.

Package Workflow

Rex now supports a project/package workflow built around local and pinned dependencies.

Add a local package:

rex add utils --path ../utils
rex install

Add a git-pinned package:

rex add jsonx --git https://github.com/example/jsonx --rev 4e2d9f1
rex install

Inspect the current dependency graph:

rex deps

Current import surface from packages:

• pub fn via pkg.fn()
• pub struct via pkg.Type.new(...)
• pub enum via pkg.Enum.Variant(...)
• pub type in type positions via pkg::Alias

The full design notes live in docs/package-manager-v1.md.

Minimal manifest:

name = "my-app"
version = "0.1.0"
entry = "src/main.rex"

Here version is the project/package version for my-app. It is separate from the Rex CLI/language release version reported by rex version.

Documentation Map

• docs/getting-started.md - shortest path from checkout to running code
• docs/syntax.md - syntax and core forms
• docs/spec.md - language overview and design baseline
• docs/ownership.md - ownership and borrowing model
• docs/bonds_system.md - bond, commit, and rollback behavior
• docs/stdlib.md - standard library coverage
• docs/cli-reference.md - command surface
• docs/examples-index.md - example guide
• docs/troubleshooting.md - common errors and fixes
• docs/roadmap.md - planned work

Repository Layout

Path	Purpose
rex/compiler	Lexer, parser, typechecker, and C code generator
rex/runtime_c	Runtime used by generated programs
rex/examples	Sample Rex programs
docs	Language and tooling documentation
tools	Editor and packaging support

Current Focus

The current branch of Rex is focused on four things:

• freezing a clear v1.0 stability contract before large syntax additions
• keeping the core language explicit and inspectable
• making the standard library practical for daily work
• stabilizing project and package management before taking on package hosting

Releases

GitHub releases are built through .github/workflows/release.yml. Use rex version to inspect the CLI release line. Use rex check-update to compare the installed CLI version against the latest published release. Project manifests keep their own package version in rex.toml.

Published Windows artifacts:

• rex-<version>-windows-setup.exe
• rex-<version>-windows-portable.zip