Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/catseye/samovar

Model worlds using propositions and run simulations in them
https://github.com/catseye/samovar

dsl experimental-language hoare-logic production-system production-systems proposition simulation-engine story-generation

Last synced: about 1 month ago
JSON representation

Model worlds using propositions and run simulations in them

Awesome Lists containing this project

README 

        
Samovar

=======



Version 0.6 | _Entry_ [@ catseye.tc](https://catseye.tc/node/Samovar)

| _See also:_ [The League of Extraordinarily Dull Gentlemen](https://git.catseye.tc/NaNoGenMo-Entries-2018/blob/master/league/README.md)

∘ [The Swallows](https://git.catseye.tc/The-Swallows/)



- - - -



**Samovar** is a domain-specific language (DSL) for modelling a world using

propositions (facts), and possible events that can occur based on those facts,

changing them.



Here is a short example of a Samovar description:



    scenario IgnatzWithBrick {

      

        [actor(?A),item(?I),~holding(?A,?I)]  ?A picks up the ?I.   [holding(?A,?I)]

        [actor(?A),item(?I),holding(?A,?I)]   ?A puts down the ?I.  [~holding(?A,?I)]

    

        actor(Ignatz).

        item(brick).

    

        goal [].

    }



And an implementation of Samovar could take this scenario and use it to,

among other things, generate textual descriptions of chains of events like



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



Of course, this is a very simple example.  (It doesn't even prevent two

actors from picking up the same item at the same time!)  For more complex

examples, and a fuller description of the language, see

[doc/Samovar.md](doc/Samovar.md), which also serves as a test suite.



### Implementation



The reference implementation of Samovar, `samovar`, is written in Python.

It can run under either Python 2.7 or Python 3.x (tested with 3.5 or higher.)



### Discussion



This looks like logic programming but the internals are actually much simpler,

and what it's doing is not logical inference.



The internals are far simpler than an inference engine or a theorem

prover: there are no logical rules in the database, only propositions, so

they can be selected by simple pattern-matching rather than full unification.



I originally described it as an "assertion-retraction engine", which could

be thought of as a highly stylized form of Prolog programming.  Alternately,

it could be thought of as assigning preconditions and postconditions, like

in [Hoare logic][], to actions in a world-model.  Instead of constructing a

proof, though, we simply chain actions together, by selecting any next one

whose preconditions hold, and altering the world so that its postconditions hold.



In (I think) autumn 2019, I came across the concept of a [production system][],

and I realized that is basically what Samovar implements.  Researching it

further, I discovered [CLIPS][], a production system built in 1985,

and I realized that Samovar is not essentially different from an

inefficiently-implemented, stripped-down version of CLIPS.



The main innovation in Samovar is the ability to "narrate" the choices the

production system makes, with human-readable text.



This isn't too surprising, since my goal with Samovar was to make an expressive

language, a syntax in which the author could write a story generator without

the undue effort of switching context between prose and code.  Picking logical

propositions for the "code" and placing them before and after each fragment of

prose was a reasonably "ergonomic" choice, and happens to coincide with the

structure of a production system.



[Hoare logic]: https://en.wikipedia.org/wiki/Hoare_logic

[production system]: https://en.wikipedia.org/wiki/Production_system_(computer_science)

[CLIPS]: https://en.wikipedia.org/wiki/CLIPS



### TODO



*   Maybe allow variables to be notated so that they can bind reflexively,

    e.g. `?*A looks at ?*B` can bind both variables to Alice.

*   Make `?_` work such that you can say `¬holding(?_, club)` to mean

    "if no one is holding the club".