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README.adoc

RattleScript

Python-syntax AffineScript. Write code that looks like Python. Get affine resource guarantees, algebraic effects, and typed WASM out.

Table of Contents

What it is

RattleScript is AffineScript with its Python face pre-selected. If you write Python, you already know most of the syntax. The compiler checks that your resources (files, sockets, tokens) are used exactly as many times as you say — and proves it at compile time.

def greet(name: String) -> String:
    "Hello, " + name + "!"

def main() -> ():
    let msg = greet("world")
    IO.println(msg)

That’s a valid .rattle file. Run it:

rattle eval hello.rattle

Why Python syntax?

Because Python programmers deserve a sound type system. RattleScript is Python’s more dangerous cousin — same comfortable whitespace- delimited blocks, but with teeth: no null pointer exceptions, no use-after-free, no data races, and no runtime surprises that the type checker already knows about.

The mascot is a rattlesnake. Python’s more dangerous cousin.

Surface mappings

Python surface AffineScript equivalent

def f(x: T) → R:

fn f(x: T) → R { …​ }

True / False

true / false

None

()

and / or / not

&& / || / !

class Name:

type Name

pass

()

import a.b

use a::b;

from a import b

use a::b;

if cond: / else:

if cond { …​ } else { …​ }

for x in e:

for x in e { …​ }

match e:

match e { …​ }

# comment

// comment

See rattle preview-python-transform <file> to inspect the full transform for any file.

Installation

From source (monorepo dev)

# From nextgen-languages/affinescript root — build affinescript first:
dune build

# Then build the rattle wrapper:
cd distributions/rattlescript
just build
# Binary at: target/debug/rattle

Installed release

just install
# Installs rattle to ~/.cargo/bin

Standalone GitHub repo

The standalone hyperpolymath/rattlescript repo contains a pre-configured distribution with affinescript as a git submodule. Use that for a self-contained checkout.

Usage

# Type-check a file
rattle check hello.rattle

# Evaluate
rattle eval hello.rattle

# Compile to WASM
rattle compile hello.rattle

# See the canonical AffineScript generated by the preprocessor
rattle preview-python-transform hello.rattle

# All affinescript subcommands work — --face python is pre-injected
rattle lint hello.rattle
rattle fmt hello.rattle

Relationship to AffineScript

RattleScript is AffineScript — same compiler, same type system, same WASM output. The only difference is --face python is the default.

The Python face lives in lib/python_face.ml and the error vocabulary in lib/face.ml. No compiler internals change when the face changes.

Sync strategy

This directory (distributions/rattlescript/) lives inside the affinescript monorepo. The standalone rattlescript GitHub repo uses affinescript as a git submodule and contains only:

  • This distributions/rattlescript/ content (copied at release time)

  • Branding assets

  • CI workflows

just update-affinescript advances the submodule pointer after each affinescript release. All language changes, face changes, and bug fixes come through that single submodule bump — no duplication.