Luna

Luna embeds a Lua interpreter and adds a standard library and IO access, so a script can reach the outside world — today an HTTP client, SQLite and interactive terminal prompts, with more of the surface below planned — without additional setup.

luna file.lua   # run a script
luna            # start an interactive REPL

Run luna with a script path to execute it, or with no arguments to start an interactive REPL.

The REPL

Running luna with no arguments starts a read-eval-print loop in the same sandboxed environment used for scripts, with the full standard library available. It is convenient for trying out the library or exploring data.

• Bare expressions print their value (1 + 1 → 2); tables are pretty-printed with utils.dump.
• Statements that span several lines (a for loop, a function body) are detected as incomplete and keep reading until they parse.
• Async calls such as os.sleep, http.get, and task.join suspend and resume just as they do in a script — each entry runs on the async executor.
• Line editing and history are provided, with history persisted to ~/.luna_history. Press Ctrl-D to exit (os.exit is not available in the sandbox).

Each entry is compiled as its own chunk, so a local declared on one line is not visible on the next — assign to a global (drop the local) to keep a value across entries.

What it is

Luna is not a Lua implementation; it embeds Lua 5.5 (via mlua) and adds the parts stock Lua omits. Plain Lua ships almost no standard library and no way to reach the outside world without C modules and a build toolchain. Luna provides a standard library written partly in Rust and partly in Lua, together with IO access.

The result is a single binary that runs a .lua file. There is no package manager, build step, or project scaffolding.

The standard library

The standard library is the main purpose of Luna. Available today:

• Networking — HTTP client (WebSocket and MQTT are planned), guarded by a per-script, per-origin permission system (--allow-net and --no-net override it).
• SQLite — access to embedded SQLite databases.
• Filesystem — whole-file read/write and directory listing via fs, guarded by the same permission system per folder (--allow-fs and --no-fs override it; interactive grants are recorded in access.json, and --sandbox denies both files and network).
• Terminal UI — interactive prompts (confirm, text, select, password, number, date), styled/colored output, and terminal control (cursor addressing, alternate screen, scroll regions) via tui.
• Core helpers — math, table, and utils extensions, structured log, os time helpers, and task.join concurrency.

Planned:

• Filesystem ergonomics — glob/walk on top of the existing fs core.
• TUI widgets & input — progress bars, tables, and raw key/mouse events on top of the existing terminal control.

The intent is for the common case to be a single call rather than a multi-step setup.

How it works

• Embeds Lua 5.5 via mlua, on an async core (tokio) so IO-heavy scripts don't block.
• A single self-contained binary. No LuaRocks, no make, no virtualenv.
• Scripts run in a sandboxed environment modeled on Luau's safe environment: io, package, and debug are not loaded; os is trimmed to its time functions; the bytecode/chunk-loading escape hatches (load, loadfile, dofile, string.dump) are removed. The library Luna provides is the supported way to reach the outside world.
• A leading #! shebang line is skipped (after an optional UTF-8 BOM), so scripts can be made executable directly. Script files need not be valid UTF-8 — Lua source is byte-oriented.
• Scripts can be split into files with a sandboxed require: modules are looked up next to the main script (symlinks resolved, so an executable script symlinked into ~/.local/bin finds its files) and in $LUNA_INCLUDE_PATHS, which can also be set in a .env beside the script.

Building

cargo build --release
# binary at target/release/luna

cargo run -- lua/demo/test.lua   # run a script during development

Requires a Rust toolchain (2024 edition). Lua is vendored and built from source, so no system Lua is needed.