The Ξ (Xi) Programming Language

A statically-typed, ahead-of-time compiled language that makes dependency injection, function intent, and refined types first-class - compiled to native binaries through C, and self-hosting.

Get started → GitHub

Xi is self-hosting - its compiler is written in Xi and compiles its own source to a byte-identical fixpoint. The only non-Xi code is a small C runtime (the equivalent of a language's libc/libcore). You don't need any of that to write Xi - install the toolchain and go.

Install

On macOS (Apple Silicon + Intel) and Linux, install with Homebrew:

brew install code-by-sia/xi/xi

Or grab a prebuilt tarball from the releases page and put its bin/ on your PATH. Either way you get xc (compiler) and xi (run tool + REPL); you just need a C compiler (cc) on PATH. Full steps: Getting started.

Highlights

• Refined types - type Age = Number where value >= 0 and value <= 130, checked at construction.
• Eight function kinds - mapper, projector, predicate, consumer, producer, reducer, creator, action: intent is syntactic.
• Dependency injection in the language - deps { ... }, module { bind ... }, App.resolve(Interface), conditional when bindings, singleton/transient.
• where-guarded overloading - multiple functions with one name, selected by a guard.
• Decision tables, interrupts, atoms, machines & events - business rules, resumable conditions, active-state stores, finite state machines, and publish/subscribe with the listener kind, all as language features.
• Error handling - T! result types, ok/err, and ? propagation.
• Serialization - a built-in std/json library.
• Query - reified query chains: query.from<User>("users") .filter { it.age >= 18 }.collect(db) compiles to a typed plan a provider runs in memory or renders to SQL.
• Repository - std/data generic Repository / CrudRepository interfaces bind to any provider: composable reads, provider-backed writes, and overridable entity ↔ model mapping.
• Native output - compiles to a standalone binary via C; no VM, no GC.

A taste

import "std/log.xi"

type Age   = Number where value >= 0 and value <= 130
type User  = { name: String, age: Age }

predicate isAdult(u: User) { return u.age >= 18 }

mapper describe(u: User) -> String {
    return u.name + " (" + u.age + ")"
}

async entry (logger: Logger) main(args: String[]) {
    let u = User { name: "Ada", age: 36 }
    if isAdult(u) { logger.info(describe(u)) }
}

module App {}

$ xc greeting.xi && ./build/greeting

Where to go next

The docs are ordered as a path. If you are new, read down this list; each page assumes the ones above it.

#	Read	To learn
1	Getting started · CLI	install the toolchain, compile and run a file
2	Language guide	types, refined types, the function kinds, interfaces, generics
3	Error handling · Decision tables	T! results, ? propagation, business rules as tables
4	Dependency injection	deps, module, binds and scopes - the heart of how Xi apps are wired
5	Multi-file projects · Config · Testing	modules, imports, typed config, xt
6	Atoms · Machines · Interrupts · Events	state that accumulates, state machines, resumable conditions, pub/sub
7	Threading · Memory	share-nothing threads, channels, how allocation works
8	Standard library	every module, with links to the guides below

The standard library

Module	Guide	What it gives you
std/collections	Collections	List, Set, Map, Stack, sequences, ranges
std/json, yaml, xml	Serialization	a Json tree, derived codecs, as Json
std/query, std/sql	Query	reified query chains that a provider runs or renders to SQL
std/data	Repository	Repository / CrudRepository over any provider
std/web	Web	a REST framework: controllers, routing, HTTPS/HTTP-2
std/events	Events	typed publish/subscribe with listener
std/monitoring	Monitoring	health and metrics, decoupled from what it watches
std/thread	Threading	threads and channels
plus	stdlib reference	math, text, bytes, crypto, fs, net, http, time, io, …

Interop lives in FFI (calling C) and WebAssembly.

Showcase

See Xi in a real application: eXstream is a music-streaming service whose backend is a set of Xi microservices (auth, file storage, playlist) behind an API gateway, with a React front end and Docker deployment - an end-to-end example of modules, dependency injection, the web framework, and JWT auth.

Ready? Head to Getting started.