/tg/ Station 13 - Modules - Types



DM datums are treated as lua userdata, and can be stored in fields. Due to fundamental limitations in lua, userdata is inherently truthy. Since datum userdata can correspond to a deleted datum, which would evaluate to null in DM, the function datum:is_null() is provided to offer a truthiness test consistent with DM.

Keep in mind that BYOND can't see that a datum is referenced in a lua field, and will garbage collect it if it is not referenced anywhere in DM.


Equivalent to DM's datum.var

datum:set_var(var, value)

Equivalent to DM's datum.var = value

datum:call_proc(procName, ...)

Equivalent to DM's datum.procName(...)


This function is used to evaluate the truthiness of a DM var. The lua statement if datum:is_null() then is equivalent to the DM statement if(datum).


Returns a userdatum that allows you to access and modifiy the vars of a DM datum by index. datum.vars.foo is equivalent to datum:get_var("foo"), while datum.vars.foo = bar is equivalent to datum:set_var("foo", bar)


In order to allow lists to be modified in-place across the DM-to-lua language barrier, lists are treated as userdata. Whenever running code that expects a DM value, auxlua will attempt to convert tables into lists.

List references are subject to the same limitations as datum userdata, but you are less likely to encounter these limitations for regular lists.

Some lists (vars, contents, overlays, underlays, vis_contents, and vis_locs) are inherently attached to datums, and as such, their corresponding userdata contains a weak reference to the containing datum. Use list:is_null to validate these types of lists.


Equivalent to DM's list.len


Equivalent to DM's list[index]

list:set(index, value)

Equivalent to DM's list[index] = value


Equivalent to DM's list.Add(value)


Equivalent to DM's list.Remove(value)


Converts a DM list into a lua table.


Will extract only values of type type_path.


A similar truthiness test to datum:is_null(). This function only has the possibility of returning false for lists that are inherently attached to a datum (vars, contents, overlays, underlays, vis_contents, and vis_locs).


Returns a userdatum that allows you to access and modifiy the entries of the list by index. list.entries.foo is equivalent to list:get("foo"), while list.entries.foo = bar is equivalent to list:set("foo", bar)

The dm table

The dm table consists of the basic hooks into the DM language.


The address of the lua state in memory. This is a copy of the internal value used by auxlua to locate the lua state in a global hash map. state_id is a registry value that is indirectly obtained using the dm table's __index metamethod.

dm.global_proc(proc, ...)

Calls the global proc /proc/[proc] with ... as its arguments.


A reference to DM's world, in the form of datum userdata. This reference is always valid, since world always exists.

Due to limitations inherent in the wrapper functions used on tgstation, world:set_var and world:call_proc will raise an error.


A reference to DM's global, in the form of datum userdata. Subject to the same limitations as dm.world


A weak reference to DM's usr. As a rule of thumb, this is a reference to the mob of the client who triggered the chain of procs leading to the execution of Lua code. The following is a list of what usr is for the most common ways of executing Lua code:

  • For resumes and awakens, which are generally executed by the MC, usr is (most likely) null.
  • SS13.wait queues a resume, which gets executed by the MC. Therefore, usr is null after SS13.wait finishes.
  • For chunk loads, usr is generally the current mob of the admin that loaded that chunk.
  • For function calls done from the Lua editor, usr is the current mob of the admin calling the function.
  • SS13.register_signal creates a /datum/callback that gets executed by the SEND_SIGNAL macro for the corresponding signal. As such, usr is the mob that triggered the chain of procs leading to the invocation of SEND_SIGNAL.

Execution Limit

In order to prevent freezing the server with infinite loops, auxlua enforces an execution limit, defaulting to 100ms. When a single lua state has been executing for longer than this limit, it will eventually stop and produce an error.

To avoid exceeding the execution limit, call sleep() or coroutine.yield() before the execution limit is reached.

over_exec_usage(fraction = 0.95)

This function returns whether the current run of the Lua VM has executed for longer than the specified fraction of the execution limit. You can use this function to branch to a call to sleep() or coroutine.yield() to maximize the amount of work done in a single run of the Lua VM. If nil, fraction will default to 0.95, otherwise, it will be clamped to the range [0, 1].

Task management

The Lua Scripting subsystem manages the execution of tasks for each Lua state. A single fire of the subsystem behaves as follows:

  • All tasks that slept since the last fire are resumed in the order they slept.
  • For each queued resume, the corresponding task is resumed.

Yields the current thread, scheduling it to be resumed during the next fire of SSlua. Use this function to prevent your Lua code from exceeding its allowed execution duration. Under the hood, sleep performs the following:

  • Sets the sleep_flag
  • Calls coroutine.yield()
  • Clears the sleep flag when determining whether the task slept or yielded
  • Ignores the return values of coroutine.yield() once resumed

The SS13 package

The SS13 package contains various helper functions that use code specific to tgstation.


A reference to the state datum (/datum/lua_state) handling this Lua state.


The ckey of the user who ran the lua script in the current context. Can be unreliable if accessed after sleeping.


Returns the client of the user who ran the lua script in the current context. Can be unreliable if accessed after sleeping.


A wrapper for the magic string used to tell WrapAdminProcCall to call a global proc. For instance, /datum/callback must be instantiated with SS13.global_proc as its first argument to specify that it will be invoking a global proc. The following example declares a callback which will execute the global proc to_chat:

local callback = SS13.new("/datum/callback", SS13.global_proc, "to_chat", dm.world, "Hello World")
SS13.istype(thing, type)

Equivalent to the DM statement istype(thing, text2path(type)).

SS13.new(type, ...)

Instantiates a datum of type type with ... as the arguments passed to /proc/_new The following example spawns a singularity at the caller's current turf:

SS13.new("/obj/singularity", dm.global_proc("_get_step", dm.usr, 0))
SS13.new_untracked(type, ...)

Works exactly like SS13.new but it does not store the value to the lua state's references list variable. This means that the variable could end up deleted if nothing holds a reference to it.


Can be used to determine if the datum passed is not nil, not undefined and not qdel'd all in one. A helper function that allows you to check the validity from only one function. Example usage:

local datum = SS13.new("/datum")
dm.global_proc("qdel", datum)
print(SS13.is_valid(datum)) -- false

local null = nil
print(SS13.is_valid(null)) -- false

local datum = SS13.new("/datum")
print(SS13.is_valid(datum)) -- true

Converts a string into a type. Equivalent to doing dm.global_proc("_text2path", "/path/to/type")


Deletes a datum. You shouldn't try to reference it after calling this function. Equivalent to doing dm.global_proc("qdel", datum)

SS13.await(thing_to_call, proc_to_call, ...)

Calls proc_to_call on thing_to_call, with ... as its arguments, and sleeps until that proc returns. Returns two return values - the first is the return value of the proc, and the second is the message of any runtime exception thrown by the called proc. The following example calls and awaits the return of poll_ghost_candidates:

local ghosts, runtime = SS13.await(SS13.global_proc, "poll_ghost_candidates", "Would you like to be considered for something?")
SS13.wait(time, timer)

Waits for a number of seconds specified with the time argument. You can optionally specify a timer subsystem using the timer argument.

Internally, this function creates a timer that will resume the current task after time seconds, then yields the current task by calling coroutine.yield with no arguments and ignores the return values. If the task is prematurely resumed, the timer will be safely deleted.

SS13.register_signal(datum, signal, func, make_easy_clear_function)

Registers the Lua function func as a handler for signal on datum.

Like with signal handlers written in DM, Lua signal handlers should not sleep (either by calling sleep or coroutine.yield).

If make_easy_clear_function is truthy, a member function taking no arguments will be created in the SS13 table to easily unregister the signal handler.

This function returns the /datum/callback created to call func from DM.

The following example defines a function which will register a signal that makes target make a honking sound any time it moves:

function honk(target)
	SS13.register_signal(target, "movable_moved", function(source)
		dm.global_proc("playsound", target, "sound/items/bikehorn.ogg", 100, true)
SS13.unregister_signal(datum, signal, callback)

Unregister a signal previously registered using SS13.register_signal. callback should be a datum/callback previously returned by SS13.register_signal. If callback is not specified, ALL signal handlers registered on datum for signal will be unregistered.

SS13.set_timeout(time, func)

Creates a timer which will execute func after time seconds. func should not expect to be passed any arguments, as it will not be passed any. Unlike SS13.wait, SS13.set_timeout does not yield or sleep the current task, making it suitable for use in signal handlers for SS13.register_signal

The following example will output a message to chat after 5 seconds:

SS13.set_timeout(5, function()
	dm.global_proc("to_chat", dm.world, "Hello World!")
SS13.start_loop(time, amount, func)

Creates a timer which will execute func after time seconds. func should not expect to be passed any arguments, as it will not be passed any. Works exactly the same as SS13.set_timeout except it will loop the timer amount times. If amount is set to -1, it will loop indefinitely. Returns a number value, which represents the timer's id. Can be stopped with SS13.end_loop Returns a number, the timer id, which is needed to stop indefinite timers. The following example will output a message to chat every 5 seconds, repeating 10 times:

SS13.start_loop(5, 10, function()
	dm.global_proc("to_chat", dm.world, "Hello World!")

The following example will output a message to chat every 5 seconds, until SS13.end_loop(timerid) is called:

local timerid = SS13.start_loop(5, -1, function()
	dm.global_proc("to_chat", dm.world, "Hello World!")

Prematurely ends a loop that hasn't ended yet, created with SS13.start_loop. Silently fails if there is no started loop with the specified id. The following example will output a message to chat every 5 seconds and delete it after it has repeated 20 times:

local repeated_amount = 0
-- timerid won't be in the looping function's scope if declared before the function is declared.
local timerid
timerid = SS13.start_loop(5, -1, function()
	dm.global_proc("to_chat", dm.world, "Hello World!")
	repeated_amount += 1
	if repeated_amount >= 20 then

Stops all current running loops that haven't ended yet. Useful in case you accidentally left a indefinite loop running without storing the id anywhere.


Stops tracking a datum that was created via SS13.new so that it can be garbage collected and deleted without having to qdel. Should be used for things like callbacks and other such datums where the reference to the variable is no longer needed.

Internal globals

Auxlua defines several registry values for each state. Note that there is no way to access registry values from lua code.


This flag is used to designate that a yielding task should be put in the sleep queue instead of the yield table. Once auxlua determines that a task should sleep, sleep_flag is cleared.


A sequence of threads, each corresponding to a task that has slept. When calling /proc/__lua_awaken, auxlua will dequeue the first thread from the sequence and resume it.


A table of threads, each corresponding to a coroutine that has yielded. When calling /proc/__lua_resume, auxlua will look for a thread at the index specified in the index argument, and resume it with the arguments specified in the arguments argument.


A table of key-value-pairs, where the keys are threads, and the values are tables consisting of the following fields:

  • name: A string containing the name of the task
  • status: A string, either "sleep" or "yield"
  • index: The task's index in sleep_queue or yield_table