Once upon a time, BOBHYTAPb, Shmumer, others and yours truly thought
that a short-term LARP-like online game
could be interesting. (Nothing came of it, of course.) One of the
problems sited at the time was that computer games were lacking in
modeling of reality in general (duh!). In particular, the thought
went, the problem is with OOP itself. So YODL was conceived. (Did I
mention that nothing came out of it?) Shortly thereafter I discovered
articles… A while later, I found notes about YODL
which I reproduce here in their incoherent entirety without any hopes
that anyone cares
, using this LJ as my personal repository of
stuff to refer to, maybe…

interface to other language/objects/functions?

1. Interceptable actions

The most limiting feature of this scheme is the finality of all
actions. In MUDs, one active object can intercept another object’s
action and veto it. Here, once an action is initiated it is performed
(see the caveat below). Other object can only react to it later
on. Example: in a MUD, you can place a closed chest and a guardian
over it. If you try to open the chest, the guardian stops you – have
to kill him first. In this scheme, if you are close enough to the
chest to open it – you open it, guardian or not.

2. Environment as a priviledged interceptor

Broadcasting messages to those that are interested and are eligible
cf 1?

3. yodl abstract

YODL is a mark-up language used to rapidly create new game worlds by placing objects in them.
Objects can be existing, taken from the library, as well as newly created (with the YODL as well!)
on the basis of other objects. YODL supports inheritance, with every object inheriting its properties
at least from some ideal object(s) (instances of which cannot be created) , or from other functional
objects. As is standard for such inheritances, properties can be overriden, added, erased.

An object can be created by inheriting from two objects – thus compound objects (e..g, a rifle with
laser targeting can be created out of stock rifle and stock laser pointer).

As much as it seems like a use of standard OO (object-oriented) approach, YODL presents important
innovation over traditional OO approach:

We strive to make the worlds we create believable. To do that, ideally,the user must be able to do
with a given object what he can do to it in the real world. That is impossible under standard OO paradigm.

In the OO paradigm, the designer must specify the behavior that each object is capable of. If a certain behaviour is not specified, the object cannot perform it. This is a great disadvantage. It is impossible to think of all the things it is possible to do with, for example, a cup. What if a user would like to try to hammer nails with it?

YODL provides for that and other behavior by NOT providing specifically for a behavior in an
object. Instead, YODL allows designers to specify a set of actions generally available (hitting, throwing,
heating up an object~) Then the object acted upon executes that action upon itself, and the action,
based on the object’s properties, decides on the consequences. For example, consider a metal cup and
ceramic one. The designer did not specify if either cup can be hit. However, an action of being hit
is in the system, and if a cup is hit, based on its properties, the action will decide if the cup breaks
(ceramic) or bends (metal).

In contrast to OO, this can be termed AO – action-oriented paradigm.
This is a misnomer, however, since YODL does not give preference to
actions (verbs) in favor of objects (nouns). Not getting into
linguistic debates, if we need both to better describe our world,
we will have both.

Other concepts introduced in YODL are related. To go into details, we need to
provide full YODL specification, which we can’t right now. Of interest immediately, however,
are also the following concepts.

  • Action inheritance – to ease the work of designers, actions can be inherited just as objects can be.
  • Faces – actions that can be inflicted upon the object can be
    calculated automatically, some being discarded (e.g., if an action of
    -Y´break¡ cannot possibly be inflicted upon an object, it is

Remaining actions represent a ´face¡ of an object. This is useful to the user, who can then be presented with a list of actions he can do upon the object, as a menu. More importantly, however, this can provide differentiating ´cognitive portraits¡ of user’s characters, forcing the character to see an object in some way. For example, a character that has never heard of a gun will be able to ´press the trigger¡ but not to ´shoot¡ the gun – and definitely not to load it.

Context-aware programming, in that respect like AOP.

An ACTOR is a performer of actions. An OBJECT is something the actions are performed on.


An INTERFACE REQUIRES PROPERTY REFERENCES. When implementing the INTERFACE, the OBJECT must PROVIDE those to the INTERFACE. If the PROPERTY is not set by the OBJECT, it may be deemed UNKNOWN. The INTERFACE must specifically allow a PROPERTY to have an unknown state.

Properties have a state of Unknown. If an Object’s Interface Requires a PR for the Object, and the state of the Property is currently Unknown, the Object never returns that interface as a member of the Face. (or what of optional)

A subset of a collection of INTERFACES that an OBJECT implements is a FACE of the OBJECT. An OBJECT thus has many FACES. (-L~~~~~~~~?) (set of methods???)

When the ACTOR interacts with the OBJECT, the ACTOR constructs an INSTANCE of his PERCEPTION INTERFACE (parameterized both by LOCAL_ENVIRONMEN) and passes it to the OBJECT. Based on the received INSTANCE of the PERCEPTION interface, the OBJECT returns to the Actor a Face, that is, a subset of its collection of Interfaces. What the Actor sees then is a particular Face of the Object, parameterized by the current Actor’s Perception and the current state of Local_Environment.

(Addendum: The Object doesn’t choose shit. It just passes the PERCEPTION to the Intertfaces, and they decide which Subinterfaces make up the face).


A Role is a collection of Interfaces (CF. Role theory – GG2001).

Multiple Inheritance Resolution: User Intervention. If an Actor invokes a Method appearing in more than one Interface, the Actor is asked to specify which Interface he had in mind. Or, the desiner provides a default order?

Deconstruction Interface:

BASIC Interface

A tool for script creation — just record the proceedings

Environment Triggers — implicit, e.g., an air balloon’s trigger on local pressure.

PROPERTIES — not just numbers, but instead objects with access methods!

Properties implying interfaces requiring them? — Properties only imply Passive; ACTIVE require knowledge and must be explicitly declared.

Every Interface comes of two Complementary types — Active and Passive. Pasive interface contains handlers for the Active interface.

The Actor passes the collection of his Active interfaces to the Object (with the Perception module). The Object returns a Collection of the Actors subinterfaces, corresponding to what the Object can handle given the current state of Environment and of the Actor. This could inolve Fallback on some of the active interfaces of the actor to their ancestors, as best as the object can handle for that particular interface.

Environment and Actor are special cases of Objects. The also provide Faces to the Actor. Actor’s Face includes Inventory, for example.

Case Study: Actor contains Active “Run” and Passive “Run”. P-RUN changes actors coordinates.

Waht goes into Environment? Walls treated as Objects? Is Environment any different from a specialized collection of Objects we don’t want to ttreat as Objects? Philosophically?

A Face includes all the Representation stuff — graphics, audio, smells, whatever. In fact, these should depend upon the Actor’s Perception and not on ly on the state of the Object.

PH: An Interface can be separated into Effect and Implementation.

Flying is an effect. Winged Flying, Propeller Flying, Jet Flying – implementations of that effect. This mimics Templates — but not completely.

Properties imply Passive intefaces — Passive Interfaces are written using fixed property names. Ergo, Interface designers must communicate heavily.

 Keyword unknown 
 Actions {
 Hit (subject object) where 
 Object has , is
 Subject has 
 Actor me {
 Knows hit 
 class chair implements matter {
 state = solid;
 // weight not here - automatically unknown
 class Neanderthal knows wood {
 class Bird knows wood 
 interface matter{
 property state : {solid, liquid, gas};
 optional property weight;
 interface wood implements matter {
 property hardness : 3;
 class blade implements iron {
 property edge: .1; 
 cut (matter m) {
 if (m.state=solid) {
 if ()~ 
 Neanderthal N; 
 Bird b; 
 Wood w;
 Knife k;

Some random links jotted in these notes:

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