Samovar

Version 0.1. Subject to change in backwards-incompatible ways.

Samovar is a DSL for world-modeling using predicates rather than explicit objects.

The remainder of this document will probably be trying to explain what I mean by that.

It could be thought of as an "assertion-retraction engine", which itself could be thought of as a very stilted style of Prolog programming plus some syntactic sugar.

Alternately, it could be thought of as assigning preconditions and postconditions, like you would find in a program proof, to actions in a world-model. Instead of proving that the action satisfies the conditions, though, we simply assume it does, and use the conditions to chain actions together in a sensible order.

A Samovar world is an immutable set of rules which operate on a mutable set of facts. Each rule looks like

[A] X [B]

and means "If A holds, then X is a possible action to take, and if you do take it, you must make B hold afterwards."

By "hold" we mean "can unify with the current set of facts."

As an example,

[actor(α),item(β),~holding(α,β)] α picks up the β. [holding(α,β)]

Which can be read "If A is an actor and B is an item and A is not holding B, then one possible action is to say 'A picks up the B' and assert that A is now holding B."

We can add a complementary rule:

[actor(α),item(β),holding(α,β)] α puts down the β. [~holding(α,β)]

And we can package this all into a world-description:

rules
  [actor(α),item(β),~holding(α,β)]  α picks up the β.   [holding(α,β)]
  [actor(α),item(β),holding(α,β)]   α puts down the β.  [~holding(α,β)]
end
situations
  [actor(Ignatz),item(brick)]
end

And an implementation of Samovar can take this world-description and use it to, among other things, generate chains of events like

Ignatz picks up the brick. Ignatz puts down the brick.

Of course, this is a very simple example. A more complex example might have more actors, more items, and more rules (for example, that two actors cannot be holding the same item at the same time.)