a live execution environment for large Codea projects
Python Lua Shell
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A live coding environment for large Codea projects.


xCodea lets you seamlessly switch working on your Codea project from your iPad to your laptop/desktop (and back), to take advantage of

  • a proper keyboard! :)
  • extended screen estate thanks to your 4 monitors
  • your favourite text editor/IDE, with powerful features such as
    • autocompletion
    • refactoring
    • advanced code navigation with fast keyboard shortcuts
  • inline or external documentation always visible
  • being able to easily find and integrate code snippets (or whole libraries) from the internet without interrupting your workflow
  • git (or your favourite SCM) for versioning, experimentation, and team collaboration, integrated into your workflow
  • powerful tools for managing large projects with lots of files and dependencies
  • ...

And most importantly:

  • your project runs live (on your iPad) - you see the effect of changes in the code in (almost) realtime
  • your project runs in a sandbox - whenever you make a mistake only that part of the code is affected, while the rest of the project keeps running; fix the error and you're right back in the program flow without restarting anything


Assuming your computer's IP is, you will keep your projects in a folder named CodeaProjects (this folder is generally referred to as projectsRoot) and you'll work on a Codea project called MyCoolGame:

Command line

  • git clone http://github.com/lowne/xCodea.git CodeaProjects; cd CodeaProjects - or download the ZIP and extract its contents into CodeaProjects
  • nano xCodea/EDIT_THIS.lua - or open EDIT_THIS.lua inside the xCodea subfolder with a text editor
  • put in the (static) IP address or hostname (spaces and apostrophes will likely cause trouble, though) of your computer, as in xCodea_server = "" then save
  • start the server: ./xcodeaserver.py MyCoolGame (I suggest adding -lcsn for remote logging, colour output, sound and notifications on errors)


Grab the .dmg file from the latest release. Usual caveats apply for Gatekeeper (right-click, open) and firewall (the server requires inbound connections, eh?) It'll ask for your projectsRoot at first launch, type it in. Then Project->New Project->MyCoolGame, then Start server.

on the iPad (both GUI and cmdline)

  • point Safari to the server: type in the location bar
  • select the entire text and copy it
  • launch Codea, long-press the Add New Project button then tap Paste into project; call it xCodea
  • tap the right-pointing triangle to run xCodea :p

Running the server

[ TODO command line options etc]

Connection and syncing

When xCodea on the iPad connects to the xCodea server any changes (files or dependencies that were updated, added or removed from either side) are synced. In practice almost always you'll have been working on your project on the iPad while away from the computer. When you connect to xCodea it'll sync these changes back to the computer. In case of changes from both sides on the same file, the iPad version wins by default, overwriting the file on your computer.

  • In special circumstances (such as having two iPads, or calamitous corruption on your computer) you can manually force the sync direction with the --push and --pull options on the server [ TODO not yet implemented in the GUI]

You can disconnect (stop xCodea, quit Codea altogether, put the iPad to sleep, take the iPad on a long trip) whenever you want; the next time xCodea connects it'll sync any intervening changes and restart the project. There's no need to ever stop and restart the server unless you want to work on a different project (to stop the command line server, press ctrl-C in its terminal window).

Live coding

Whenever a project file is changed on disk (i.e. on save) its contents are sent to the client.

  • If the file is not a valid lua chunk (meaning, there's a syntax error) you'll immediately see an error (with filename and line number).
  • Otherwise the file will be evaluated inside xCodea's sandbox, updating your functions etc., and letting you see the effects of the changes almost immediately.
  • Whenever a runtime error happens you'll see the stack trace (with filename and line number of the offending code).
    • If the error happens outside of the draw() event (see below for useful tips), your project will keep drawing in the background.
  • Errors are displayed both on your iPad and in the server log.

Moreover the server watches for a special eval.luac file in your projectsRoot folder. As soon as this file is created, the server sends its contents to be evaluated inside xCodea's sandbox, then deletes the file.

  • You can use this as a live REPL to control and alter your project at runtime.
  • You can send xCodea.restart() to safely reset the sandbox and restart the project execution

Finally, if you're using LDT (or some other Eclipse-based IDE) xCodea monitors the .buildpath file for your project to detect dependency changes (when a change occurs the project is automatically restarted).

Taking advantage of xCodea

  • When defining new classes or containers, use the idiom myClass = myClass or class() or myObj = myObj or {}. If you use myClass = class() myClass will be recreated every time the file is evaluated (which is every time the file is saved), destroying its state. Similarly, you should avoid initialising variables in the main chunk of a file - use setup functions (called in turn by the main setup())
  • During execution of a Codea project there is normally a single entry point for your code - the draw() function. xCodea gives you another entry point: update(). Take advantage of it to separate program-state updates and actual drawing; this improves a lot feedback during live coding as runtime errors in update() won't affect drawing.

    • In order to take advantage of this, you must have a global function update() ... end somewhere in your project (usually in your Main.lua), and you must call update() as the first statement inside your draw() (or any other function in your draw call chain - xCodea should be able to hunt it down and set the hook). Simple example:
    function update()
        -- update the program state here
    function draw()
        -- do your drawing here
    • As an aside, a similar technique is used to separate Codea's tween.update from your draw loop - e.g. runtime errors in callbacks from tween(..., callback,args) won't affect the draw loop (but the callback will be terminated)
  • LDT is a powerful Eclipse-based IDE for Lua projects (if a bit rough on the edges, but it's possible with some effort to make it behave). I prepared an execution environment (explanation) that will get you code assist and in-place documentation for the Codea API; if you use LDT get it here
  • Set up keyboard shortcuts to take advantage of eval.luac for a REPL-like experience. For example I use BetterTouchTool to intercept some key combinations while in LDT:
    • ⌘⏎: sends ⌘C, then executes pbpaste > path/to/projectsRoot/eval.luac (eval the current selection)
    • ⌘⌥⏎: executes echo "xCodea.restart()" > path/to/projectsRoot/eval.luac (restart the project)
    • ⌘\: navigates to the file and linenumber of the last error - xCodea allows this via non-default pasteboards but the macro is a bit more complex
  • If you want to see the value of a variable or expression you can send it "naked" to eval.luac, xCodea will do the required print() wrapping (and sending to the server log) for you.


xCodea was inspired by, and strives to improve upon, the excellent LiveCodea, which begot AirCode in Codea itself, whose limitations xCodea attempts to overcome. Some ideas were taken from the also excellent AirCodea


  • complete this readme :)
  • push, pull commands [DONE in cmdline, more testing needed]
  • update() hook [DONE]
  • if possible (almost certainly not), hijack tween() to use the update() hook [DONE, it even has its own update loop; on error it'll kill the offending callback to let the sandbox keep running]
  • warn about files deleted server-side
  • extend the sandbox coverage to 100%; loadstring() is fully sandboxed, but dofile() and require() currently (probably) break it
  • asset management
  • project discovery (and creation server-side) (possibly available in a future Codea 2.x update)