Langton's Ant Music version 2
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Langton-Music Format



The format is based on XML.

The entire document is enclosed in <langton> tags.

Then there can be 4 things inside that:

  • <config> tags: for header configuration values
  • <breed> tags: Defining the ant breeds
  • <ant> tags: instantiating (using) the ant
  • <rle> tags: RLE data to specify the cells on the grid.

Additionally, because it's XML, you can put comments anywhere you like by using <!-- -->.

Header - <config> tags

This is pretty simple. Each tag is formatted like this: <config name="KEY">VALUE</config>

Supported Header Options

Option (name attribute) Function (content)
bpm Controls maximum beats per minute of playback.
stepCount Doesn't really do anything, it just changes the initial step number from the default zero when you press LOAD. Useful for restoring from a dump.
#blah An arbitrary interpolation value (see below).

Ant Breeds - <breed> tag

This is a little complicated. Let's start with an example, classic Langton's Ant:

<breed species="Ant" name="langton">
    <case cell="0">
            <command name="put">1</command>
            <command name="lt"></command>
            <command name="fd"></command>
    <case cell="1">
            <command name="put">0</command>
            <command name="rt"></command>
            <command name="fd"></command>

Each "breed" of ant is enclosed in <breed> tags. The species attribute determines what commands are available, and the name attribute gives the ant breed a name so it can be referred to later on.

Inside the <breed>, there are one or more <case>s. The <case>s each have a cell attribute and a state attribute that determines when the case is applied - state is the internal state that the ant is in, and cell is the external state of the cell the ant is sitting on. Both must be numbers; and if state is omitted it defaults to 1.

If there is no case for a state:cell pair, the ant will halt and do nothing until another ant comes and changes the cell. (Multiple ants can occupy the same cell, and must if an ant is to be re-started in this manner, but if two "active" ants run into each other, the behavior is not defined.)

Within the <case>s there are <action>s that define groups of commands. Each action is queued, and only one action executes per tick. Case lookup only occurs when the queue is exhausted. Within the action group, all commands execute at once.

Each <command> has a name attribute that is the command. In some cases the command needs an argument; this goes inside the tag.

Scroll to the bottom for the list of supported commands and species of ants.


Inside each <command>, the parameter can also include interpolations.

There are two types of interpolations: fixed and expressions.

Fixed Interpolations

These look like #xxx, where xxx is a name. Some names are provided by the ant, which take precedence; the rest are user-defined via <config>s.

Fixed Interpolation Name Value
dir 0, 1, 2, or 3 depending on the ant's direction.
state Whatever state the ant is in.
blah Whatever value #blah is set to in a <config>. (blah can be anything.)

Expression Interpolations

These are similar to fixed interpolations: They look like #xxx; - the only difference is a semicolon at the end and the xxx's are an expression. Expressions are processed after fixed interpolations; so the former can include the latter.

The expression language is a crude stack-based (postfix) language that is somewhat like Befunge; it's not Turing-complete, but it should suffice. The "returned value" is the top of the stack after the expression is executed.

Command/Token Function
0-9 number Pushes the arbitrary number to the stack; only integers are supported.
`string` Pushes the arbitrary string between the backticks.
' No-op. Useful for separating numbers (the parser is greedy so it needs a non-digit character to stop it).
\ Swap top two items on the stack.
$ Drops the top item.
: Duplicates the top item.
? Pushes a random integer from 0 to the top number minus 1.
% Pushes second number mod top number.
* Pushes second number times top number.
/ Pushes second number divided by top number.
+ Pushes second number plus top number.
- Pushes second number minus top number.
~ Pushes negation of top number. Shortcut for ,0\-.
| Pushes second number bitwise or top number.
& Pushes second number bitwise and top number.
^ Pushes second number bitwise xor top number.
< Pushes true or false depending on if second number is less than the top number.
> Pushes true or false depending on if second number is greater than the top number.
= Pushes true or false depending on if second number is equal to the top number.
@ Pushes the third number if the first is true, otherwise the second.

An (incomplete) test suite is available at

Actual Ants - <ant> tag

Ants are simpler and do not have any contents.

A full <ant> looks like this: <ant breed="langton" id="ant1" state="1" dir="1" x="0" y="0"></ant>.

  • breed is the breed of ant, which references a <breed> elsewhere.
  • id is the "name" of the ant as it appears in the "Track Ant" pulldown menu. If this is not supplied. a random one will be generated automatically.
  • state is the initial state of the ant; if omitted it defaults to 1.
  • dir is the direction of the ant; it is 0, 1, 2, or 3.
  • x and y are the position of the ant.

Cell Data - <rle> tag

This is almost like Golly's RLE format, but it has some differences. First, there is no x = N, y = N, rule = N header line per se. The metadata (x- and y-offset) is stored in the offsetx and offsety attributes of the <rle> tag, and default to 0 if omitted.

Otherwise this is just the same as Golly RLE format:

For rules with more than two states, a "." represents a zero state; states 1..24 are represented by "A".."X", states 25..48 by "pA".."pX", states 49..72 by "qA".."qX", and on up to states 241..255 represented by "yA".."yO".

Supported Ant Species and Commands

Ant (base class for all)

(Do note that the parenthesis notation here is used only to save space. foo(bar) would really be written <command name="foo">bar</command>.)

Command What it does
fd(num), bk(num) Moves forward or that many cells. Defaults to 1 if argument is omitted.
rt(num), lt(num) Turn right or left that many steps (step = 90 degrees). Defaults to 1 if argument is omitted.
dir(num) Set the direction to num. Use of this command turns the ant into an absolute turmite.
put(state) Set the cell the ant is sitting on to state (which must be a number).
state(num) Sets the ant's internal state to num. Use of this command turns the ant into an turmite.
spawn(breed:dir:state) Spawn an ant of breed breed here, in state state and facing in dir. dir is relative, meaning 0 = same way as me, 1 = right turn from me, etc.
die Mark this ant as dead, so it will be removed.
alert(text) Shows the text to the user in an alert box. Useful for debugging.
status(text, color) Puts the text in the status bar. Color is optional, defaults to black.

Beetle and Cricket

Command What it does
play(note:pan) Play that note for 1 tick. note can be a number, which is a frequency in hertz, or a note name string such as Bb5 which is converted to the frequency of that piano note. Support for stereo pan is experimental - defaults to 0.

Beetle (think: "beat") uses a Tone.MembraneSynth, whereas Cricket uses a Tone.AMSynth.




Drag Tool

This allows you to pan around the world and zoom in and out. Click and drag to pan in any direction, and scroll up and down to zoom.

If you hold down SHIFT this will disable zoom, and it will instead pan up and down. If you have a mouse that supports left-right scrolling as well (such as a trackpad or Apple Magic Mouse) you can scroll to pan left and right too.

Draw Cells tool

This lets you draw cells under the ants to change what they do. Enter a cell state in the box, and draw it onto the canvas.

If you start drawing by clicking on the same cell state as the one selected in the box, you will begin erasing the cells and setting them to state 0.

If you hold down SHIFT and click on a cell, it will become an eyedropper tool and update the cell state in the box with the one you clicked on instead of drawing.

Draw Ants tool

Like the Draw Cells tool, this tool allows you to place ants. Select a breed, state, and direction, and click on the canvas to place an ant. (You can't drag to place multiple ants at once; I might add this in the future.)

You can't edit the behavior of the ants with this tool; for that, you will have to use the raw XML editor.

If you hold down SHIFT and click on an ant, it become an eyedropper and update the ant value pickers similar to the Draw Cells tool.

If you hold down CTRL and click on an ant, the ant will be removed.

Actions menu

Open Clipboard

This reads your clipboard, and loads it into the world.


This saves the world state into your browser's local storage so that you won't lose it when you close Langton-Music. It will be automatically loaded when you open Langton-Music the next time.

Nothing is ever sent to any server, it is all stored locally on your computer. This also means that if you "save" on one device, you won't be able to load it on another device.


This lets you share the world state through any tool that your browser supports sharing to, such as email, iMessage, Discord, etc. The choices of tools is wholly dependent on your browser and the other apps you have installed -- it may differ between devices.

Copy as XML

This copies the XML-serialized state of the world (what you see when you open the editor) to your clipboard.

Copy as BBCode

This is the same as the Copy as XML option, except it wraps the content in [code][/code] tags for easier pasting into a forums post.


This captures the current contents of the canvas, and downloads it as a PNG image.