Flux

Flux is a small, statically typed language with reactive values built in. Write ordinary functions, structs, and enums, and when some values depend on others, declare that once: Flux keeps them up to date, the way cells in a spreadsheet do.

import io { println }

event Deposit(amount: Int)

let mut balance = 0

let doubled = balance * 2

on Deposit { amount ->
    balance = balance + amount
}

watch balance {
    println("balance={balance} doubled={doubled}")
}

fn main() {
    emit Deposit(50)
}

balance=0 doubled=0
balance=50 doubled=100

Types are checked before anything runs, expected failures are values (Result, Option, ?), and bugs stop the program with a trace that gives the file, line, and column. There is a virtual machine, which defines what programs mean, and an experimental JIT that must match it.

Quick start

You need a recent Rust toolchain.

cargo build --release -p flux_cli
target/release/flux init my_app
cd my_app
../target/release/flux run

Command	What it does
flux run [file]	compile and run
flux check [file]	check without running
flux test [filter]	run every fn test_*() in the project
flux fmt file --write	format a file
flux lock [--check]	manage flux.lock for path dependencies
flux repl	interactive shell
flux lsp-server	language server for editors; see the VS Code extension

Documentation

• The book, in docs/flux, teaches the language. Read it there, or build it with mdBook: mdbook serve docs/flux. The test suite runs every example in it.
• SPEC.md is the exact reference for the language.
• CHANGELOG.md lists what changed.
• ARCHITECTURE.md explains how the compiler is put together.
• PERFORMANCE.md records measurements and how to reproduce them.
• RELEASE.md gives the release gate and the versioning policy.

Status

Version 0.1. The language surface is stable on Linux and macOS, while the JIT, flux wasm, and flux migrate are experimental. There is no package registry yet, only local path dependencies. See Status and limits.

Working on Flux

cargo test --workspace --all-targets --locked
cargo fmt --all -- --check
cargo clippy --workspace --all-targets --locked -- -D warnings

cargo build --profile dist -p flux_cli builds the binary to distribute, with link-time optimization. It takes several minutes, so use --release day to day.

License

Apache-2.0. See LICENSE and NOTICE.