lux

lux is a small language built to be a great first language and then to be outgrown. Every feature is the simplest honest version of something shared by Rust, Swift, and Go, so what you learn here carries straight over when you move on to one of those. The few hard ideas lux leaves out — ownership, classes, goroutines — are the lessons those bigger languages exist to teach.

The full language fits on one page. Read learn-lux.md: it is the reference, the tutorial, and the test corpus all at once — the suite runs every example in it. The same material is built into the binary, so once lux is installed you can read it in your terminal with lux learn.

Installing

On macOS or Linux, install a prebuilt lux with one command:

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/anderix/lux/releases/latest/download/lux-installer.sh | sh

To remove it again:

curl --proto '=https' --tlsv1.2 -LsSf https://raw.githubusercontent.com/anderix/lux/main/uninstall.sh | sh

Running a program

lux run examples/tour.lux

lux run interprets a program directly. lux convert <rust|swift|go> <file.lux> prints your program as real source in that language, and lux build <file.lux> runs the Rust translation through rustc to a native binary.

Playing a crawl

lux crawl

lux crawl writes a small, playable text adventure into a crawl/ folder and tells you how to play it. The whole world is the world.lux it leaves you — open it, and the rooms, doors, and the torch in the cellar are all there in plain lux, yours to change. lux learn crawl walks through how one is built.

Learning the language

The reference travels inside the binary. lux learn opens a menu of short topics and guided lessons. Each topic is a one-screen card — lux learn match prints the idea, a runnable example, and an experiment to try; add more for the deeper why, the universal name for the concept, and where it goes in Rust, Swift, and Go. lux learn basics lays out the handful of shapes every procedural language shares, so the next language is mostly new spelling, and lux learn tour reads the whole thing top to bottom. Every example is real lux you can paste into a file and run. And when a program hits an error, the diagnostic points you at the topic that explains it — a non-exhaustive match ends with help: run lux learn match — so you learn the idea at the moment you need it.

lux learn               # the menu
lux learn enums         # one topic, as a card
lux learn enums more    # the deeper level
lux learn basics        # the shapes every language shares
lux learn tour          # the whole language

Building from source

lux is written in Rust with no dependencies.

cargo build --release
./target/release/lux run examples/hello.lux

Status

Early, and growing in milestones. lux run now covers the core (print, let/var, the four basic types, arithmetic, strings, if/else, while), functions with recursion, for ... in, ranges, and arrays, your own types (structs, enums with associated values, and exhaustive match), and no null — Option<T> and Result<T, E> instead. All three transpiler backends are live: lux convert turns any of these into idiomatic Rust, Swift, or Go, each leaning on what that language already has — Swift's enums and Optional, Go's interfaces and (value, error) returns — and lux build compiles the Rust to a binary. That completes the teaching surface: every feature is runnable and translatable to all three. The milestones since have gone into lux learn — the built-in reference, now a two-level card-and-more system cross-referenced from error messages — and into the outside world: readFile, writeFile, args, readLine, and print/eprint across stdout and stderr, fallible I/O modeled as the same Option and Result lux already teaches. The latest milestone runs other programs: run(program, [args]) returns Result<Output, string>, where Output — status, stdout, stderr — is the first built-in struct, and the two-layer result keeps "did it launch" and "did it succeed" apart. The latest milestone turns the error messages themselves into part of the reference: when a program trips on an idea, the diagnostic ends with a trail to the lux learn topic that teaches it, and a new lux learn errors covers how to read one, and a closing lux learn beyond names what carries past lux once it is outgrown. The latest milestone turns the language on itself: lux crawl drops a small text adventure in your folder whose whole world is one lux file — you play it by running it and change it by editing it, the first step from using a program to building one. The latest milestone draws the line between converting and parsing: int, float, and string are total conversions that cannot fail, while reading a number out of text — which can — moves to parseInt and parseFloat, each handing back the same Option lux already teaches instead of crashing on bad input. The same milestone adds lux magic: task-indexed spells (read a line, read a number, loop until done, carry a list, save to a file, read launch arguments, run another program) that already work and carry a trail to the lux learn topics behind them — a working shape now for a reader still climbing the ladder, honest about where the trick is explained. See the scope notes at the bottom of learn-lux.md, or CHANGELOG.md for the version history.

License

MIT. Written by David M. Anderson with AI assistance.