Quickstart

Your first program

Create hello.milo:

fn main(): i32 {
    print("hello, world!")
    return 0
}

Every Milo program starts at main, which returns an i32 exit code.

Run it

bun run src/main.ts run hello.milo

The run command compiles and executes in one step — no artifacts left behind.

Build a binary

bun run src/main.ts build hello.milo -o hello
./hello

The binary is standalone — no runtime needed. Typically under 300KB.

Build modes

bun run src/main.ts build app.milo -o app            # default: -O2
bun run src/main.ts build app.milo -o app --release   # -O3
bun run src/main.ts build app.milo -o app --debug     # -O0

See the LLVM IR

bun run src/main.ts emit-ir hello.milo

Useful for understanding what the compiler generates.

Run the test suite

bun test

Something more interesting

Create greet.milo:

struct User {
    name: string,
    age: i32,
}

fn greet(user: &User): string {
    return "hi, " + user.name + "!"
}

fn main(): i32 {
    let u = User { name: "Alice", age: 30 }
    print(greet(u))
    print("age: ", u.age)
    return 0
}

$ bun run src/main.ts run greet.milo
hi, Alice!
age: 30

&User borrows the value without consuming it — u is still usable after the call. Milo auto-borrows at call sites, so you write greet(u) not greet(&u).

Next: IDE Setup → or jump to Variables & Types →