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Colony, a JavaScript-to-Lua Source Compiler

Colony compiles JavaScript to Lua 5.1 source code, that requires only a small support library. Colony can be used in any Lua application supporting the debug library (enabled in Lua 5.1 by default).

Colony is experimental. It will run all of the examples in the demo/ directory. It will take some time to fully support ECMAScript 5 or support large codebases (like colony-js itself). If you're interested in its development, get involved with its development here or contact me by email.

What it does

Colony lets you use the Lua runtime with JS's familiar syntax. Let's start with the hello world example:

print(["Hello", "world."].concat(["Welcome", "to", "colony"]).join(" "))

Compiled with Colony to Lua:

local _JS = require('colony-js');
local string, math = nil, nil;
local this, Object, Array, String, Math, require, print = _JS.this, _JS.Object, _JS.Array, _JS.String, _JS.Math, _JS.require, _JS.print;
local _exports = {}; local exports = _exports;

(print)(this, _JS._arr({[0]=("Hello"), ("world.")}):concat(_JS._arr({[0]=("Welcome"), ("to"), ("colony")})):join((" ")));

return _exports;

Verbose? Let's break down the output: the first segment loads colony-js.lua, our JavaScript support library. Then we set up our global aliases and our exports object. The next block is our compiled code: we use the JavaScript built-in print function (with an implicit this variable), construct a few 0-indexed arrays, concatenate and join just as we could in any JavaScript implementation.

Larger examples are provided in the demo/ directory, courtesy the Language Benchmarks Game.

Getting Started

Ensure CoffeeScript and Lua 5.1.x are both installed on the commandline.

git clone git://github.com/timcameronryan/colony-js.git
cd colony-js
npm install jast@0.2.1
coffee colonize.coffee demo/binarytrees.js > demo/binarytrees.lua
lua -e 'package.path=package.path..";lib/?.lua"' demo/binarytrees.lua

Requirements

Requirements to run the compiler:

Node.js/CoffeeScript runtime (npm install coffee-script)
jast library from npm

Requirements for compiled code:

Lua 5.1, the bitop package, and the "debug" library
"lib/colony-js.lua" must be included with compiled scripts

Mixing languages

JavaScript (Colony) Interop

Interop with other JavaScript modules works a la CommonJS through the global require function. Note that any JavaScript modules that are required must also have been compiled with Colony before running.

Lua Interop

Interop between JavaScript and Lua works seamlessly, as Colony compiles to Lua source code. Be aware of language caveats:

JavaScript methods compiled to Lua require a this argument as the first parameter.
- Lua functions which call JavaScript function should pass a this object (which may be nil) as the first parameter.
- Inversely, JavaScript calling Lua must pass the first argument as the this parameter; the most logical way to do this is using the .call() method: func.call(arg0, arg1, arg2)
- object.method(arg0, arg1) in JavaScript maps to object:method(arg0, arg1) in Lua.
Arrays in JavaScript are indexed from 0, and Lua arrays are indexed from 1. Make sure to either push a dummy element using .shift() when calling Lua from JavaScript, and to explicitly assign the first array element in Lua to the 0 index (eg. in Lua: {[0]='first element', 'second element', 'third...'})

The debug library: Colony uses the debug library to replace the intrinsic metatables of functions, strings, booleans, and numbers. This probably will not cause issues (functions, booleans, and numbers in Lua have no default metatables), except if a Lua module expects the built-in string object to be the metatable of string literals (eg. ("apples"):len()). The workaround is to ensure all included code explicitly calls the methods of the string object (eg. string.len("apples")). Unfortunately, this limitation extends to all code that runs in conjunction with Colony scripts (for now).

Roadmap

Rough guidelines that will be followed as development continues.

Complete ECMAScript 5 support
Become self-hosting
Enable easier sharing between JavaScript/Lua modules.
Avoid the overriding of built-in metatables using the debug library (if possible)

And of course, bug fixes by the handful.