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Iota is a source-to-source compiler which accepts Io language code and outputs JavaScript. It was written as an experiment for CodeCombat's parser challenge and is currently being used in CodeCombat through Aether.

The project is very much still in its infancy: only a minimal subset of Io is implemented. A number of core constructs and much of the standard library are not yet done.

Try it out here.


  • JavaScript interoperability
  • messages, objects, methods
  • prototype chain
  • global and local contexts
  • infix operators (supporting different precedence levels)
  • assignment operator
  • primitives: strings, numbers, boolean values, nil

Still to come

  • self
  • first-class primitive methods
  • primitives: lists
  • call introspection
  • library methods
  • prototype tree
  • proper scope chain
  • proper lazy argument evaluation
  • defining operators of custom precedence
  • defining assignment operators
  • concurrency



The AST constructed by the parser complies with the Mozilla Parser API specification.


npm install [-g] iota-compiler

Installing globally gives you easy access to the command-line interface.



var iota = require('iota-compiler');

var ioProgram = 'fact := method(n, if (n == 0, 1, n * fact (n - 1))); fact(5)';
// => 120

// Lower-level API:

var _io = iota.lib; // make runtime library available
var result = eval(iota.compile(ioProgram));
// => 120
// => Number


A demo of Iota running in a web page may be found in ./demos/browser.

Simply include iota-browser.js and lib.js in your web page. Usage is the same as with node (complete with require, courtesy of Browserify), except that the _io binding isn't required.


iota ./demos/node/

You'll have to install Iota globally for this to work. Installing locally will place the executable at node_modules/.bin/iota intead.


iota.parse(code[, options]);

Parses a string of Io code and returns a JavaScript object representing the resulting AST.

iota.compile(code[, options]);

Parses, then outputs ready-to-run JavaScript.

options is a JavaScript object that allows you to tweak the behaviour of the parser:

  • wrapWithFunction If true, the compiled output will be wrapped in a function to facilitate interaction with the outside world. Defaults to false.
  • useProxy If true, messages sent to Lobby will be directed instead to a special proxy object, which converts these messages into JavaScript method invocations. Meant to be used with wrapWithFunction, so the wrapped function can be invoked with a dynamic this. Defaults to false.
  • functionName The name given to the wrapper function if wrapWithFunction is true. You can also pass a string such as, in which case the function will be bound to the corresponding property on the object in the current scope (this way you can eval the compiled code without the function being bound globally). Defaults to io.
  • self The name of object that the wrapper function is being invoked with. Defaults to self.
  • runtimeLib The name of the runtime library binding that Iota will look for. Defaults to _io.

Convenience method that evalutes a string of Io code, then unwraps and returns the result.

JavaScript Interop


A number of Io primitives are bound to their JavaScript equivalents. For example, writeln invokes console.log.

Executing Io code from JavaScript

The simplest way is to use iota.eval as shown above.

iota.compile gives a greater level of control, with provisions for wrapping the generated code in a function and executing it in the context of an arbitrary object. An example of the former:

var jsCode = iota.compile(ioCode, {
    wrapWithFunction: true,
    functionName: 'ioFromJS'


Calling eval will make a function named ioFromJS available in the global scope (see the functionName option if this is undesirable; more sophisticated sandboxing can also be used). It will implicitly return the value of the last Io statement.

Executing JavaScript code from Io

An additional option, useProxy, should be set:

var jsCode = iota.compile(ioCode, {
    wrapWithFunction: true,
    functionName: 'jsFromIo',
    useProxy: true
eval(jsCode);{a: 24601, b: function() {return 'one day more';}});

The function may then be invoked using call, apply, or bind on a JavaScript object. Properties of the object will be made available as Io objects in the Io scope chain (right before Lobby). Messages passed to them will be translated into property accesses or method invocations, and arguments will be relayed appropriately. The value of the last Io statement will be returned.