RattleScript

Python-syntax AffineScript. Write code that looks like Python, get affine resource guarantees and typed-wasm output.

Table of Contents

• What it is
• Hello
• Install
• Use
• Different faces, same cube
• Why RattleScript
• Status
• License

What it is

RattleScript is AffineScript with its rattle face pre-selected. If you write Python, you already know most of the syntax. The compiler checks that your resources (files, sockets, tokens, handles) are used exactly as many times as you declare — and proves it at compile time. No null pointer exceptions. No use-after-free. No silent data races. No GC overhead.

This repo is a brand surface only. The compiler, type checker, borrow checker, and codegen all live in affinescript. This repo carries:

• Examples idiomatic to Python developers

• Documentation aimed at the Python community

• A rattle shim CLI that aliases affinescript --face rattle

• Tutorial and migration guides for moving Python code into a strongly-typed, affine-typed, WASM-targeting world

Hello

examples/hello.affine:

# face: rattlescript

effect IO:
    fn println(s: String) -> ();

def main() -{IO}-> ():
    let greeting = "Hello, RattleScript!"
    println(greeting)

Same logical program, written in Python style. Compiles to the same canonical AST and the same typed-wasm output as every other face.

Install

opam install affinescript
git clone https://github.com/hyperpolymath/rattlescript
cd rattlescript

The affinescript binary does the work. The bin/rattle shim in this repo just defaults the --face flag.

Use

# Direct, via affinescript:
affinescript eval --face rattle examples/hello.affine
affinescript compile --face rattle examples/hello.affine -o hello.wasm

# Or via the rattle shim (same thing):
./bin/rattle eval examples/hello.affine
./bin/rattle compile examples/hello.affine -o hello.wasm

# Or via the justfile:
just run examples/hello.affine
just preview examples/hello.affine    # show the canonical lowering

Source files use the canonical .affine extension. The face is selected by the # face: rattlescript pragma on the first comment line, or by the --face rattle flag.

Different faces, same cube

RattleScript is one of six established faces over the AffineScript core:

• AffineScript — the canonical face

• RattleScript — Python-style (this repo)

• JaffaScript — JavaScript / TypeScript-style

• LucidScript — PureScript / Haskell-style

• CafeScripto — CoffeeScript-style

• PseudoScript — pseudocode-style

All six share the canonical .affine extension and lower to the same AST. Errors are reported in face-appropriate vocabulary.

Why RattleScript

Python is the most popular programming language and has the largest scientific / data / web community on Earth. It also has well-documented limits: dynamic typing, packaging hell, the GIL, performance ceiling for browser deployment, no ownership semantics. RattleScript is a Python-shaped on-ramp to a language that fixes those limits without making you learn an alien syntax first.

For a Python developer, the migration path looks like:

1. Rename your .py files to .affine and add # face: rattlescript at the top.

2. Type-annotate your function signatures (Python’s optional type hints become required, but you can usually copy them over).

3. Add let to bare variable assignments.

4. Replace import a.b with explicit imports.

5. Compile to typed-wasm, ship to browsers / WASI runtimes / native via the same build.

Status

Alpha. The face transformer is implemented in affinescript/lib/python_face.ml. Known limitations are tracked in the affinescript faces README under "Known transformer gaps".

License

AGPL-3.0-or-later. See LICENSE.