Milo

A memory-safe systems language. Ownership without lifetimes, contracts the compiler checks, native binaries via LLVM.

Milo keeps ownership — single owner, moves, borrowed references — and drops the machinery that makes it hard: no lifetime annotations, no borrow-checker puzzles, no unsafe in everyday code. Small enough to hold in your head; proven by shipping, not theory — game-console emulators, terminal apps, an HTTP/TLS/JSON standard library, a package manager, and the compiler itself are all written in Milo. Even the contract prover behind milo prove is a Milo program, and it discharges the contracts in Milo's own standard library on every test run.

from "std/http" import { Request, Response, serve }

fn main(): i32 {
    serve(8080, (req: &Request) => {
        return Response.Html("<h1>hello from milo</h1>")
    })!
    return 0
}

Docs & Playground · Demos — NES, Genesis, and SNES emulators written in Milo, playable in your browser.

Install

Prebuilt binary:

curl -fsSL https://raw.githubusercontent.com/cs01/milo/main/install.sh | sh
milo run examples/hello.milo

From source (needs Bun + LLVM): clone the repo and use the ./milo wrapper — it's just bun run src/main.ts <args>:

git clone https://github.com/cs01/milo.git && cd milo
./milo run examples/hello.milo
./milo build examples/hello.milo -o hello

See Installation for details.

Self-hosting

Milo compiles itself. milo0 — the compiler written in Milo (src-milo/, ~8.2K lines) — compiles its own source to a byte-identical fixed point at -O2: stage1 == stage2 == stage3, 161K-line IR identical, manifest-wide 212/339 fixtures emitting identical IR across stages with zero divergences.

sh scripts/selfhost.sh            # oracle builds stage1 (stage1 binary is gitignored)
bun test tests/selfhost.test.ts   # smoke + manifest convergence gate

See docs/self-hosting.md for the milestone log and the eight compiler miscompiles the self-compile exposed and fixed.