Skip to content

Basics

This guide shows you how to run small Lutra programs locally and introduces the core language ideas.

Prerequisite:

Create your first program

Create a file named example.lt:

func main() -> "Hello, world!"

Run it with the interpreter:

$ lutra run --project example.lt --interpreter
const output = "Hello, world!"

Lutra does not have a print function. Instead, you run a function and the CLI prints the returned value.

Use constants and functions

A const defines a value. A func defines a computation.

const greeting = "Hello"

func greet(name: text) -> f"{greeting}, {name}!"

func main() -> greet("Ada")

$ lutra run --project example.lt --interpreter
const output = "Hello, Ada!"

Use const for fixed values. Use func when you need computation, parameters, or reusable logic.

Work with types

Lutra is statically typed. Every expression has a type known at compile time.

const answer: int32 = 42
const title = "Arrival"

func is_large(x: int32) -> x > 10

func main() -> {
  answer,
  title,
  is_large(answer),
}

Common types include:

  • primitive types such as bool, int32, int64, float32, float64, and text
  • tuples such as {id: int32, title: text}
  • arrays such as [text]
  • enums such as enum {draft, published}

Type annotations

Lutra can infer many types, but explicit annotations are useful when they make intent clearer or when the compiler must choose a numeric type.

const movie_id: int32 = 5
const rating = 8.7: float64

func main() -> {movie_id, rating}

Build tuples and arrays

Tuples group values of different types:

const movie = {
  id = 1: int32,
  title = "Arrival",
  released = true,
}

func main() -> {movie.title, movie.released}

Arrays hold many values of the same type:

const titles = [
  "Arrival",
  "Dune",
  "Sicario",
]

func main() -> titles

You will use arrays of tuples often, because they model tabular data naturally.

const movies: [{id: int32, title: text}] = [
  {1, "Arrival"},
  {2, "Dune"},
]

func main() -> movies

Use enums for alternatives

Enums represent one value chosen from named variants.

type Status: enum {
  draft,
  published,
  scheduled: text,
}

const posts: [Status] = [
  .draft,
  .published,
  .scheduled("2026-01-01"),
]

func main() -> posts

Optional values are usually modeled as enum {none, some: T}.

type MovieWithSubtitle: {
  id: int32,
  subtitle: enum {none, some: text},
}

const movie1: MovieWithSubtitle = {1, .none}
const movie2: MovieWithSubtitle = {2, .some("Part Two")}

func main() -> [movie1, movie2]

Keep learning

You now know enough to read and run small Lutra programs.

Next steps:

For exact syntax, use the language reference: