petnat 0.0.1

A Petri net plugin for Bevy Engine. 🍾

About

petnat will equip you with Petri nets to use in your Bevy projects. It's a powerful way to model states, processes, resources, and more.

This is a very experimental project, and actual Bevy integration is unavailable yet. Feedback and thoughts are welcome!

Rough idea

1. Model something using places and transitions.
2. Define a PetriNet<NetId> resource.
3. Add a Token<NetId> component to an entity.
4. Mark places with the Token according to the context.
5. Transitions will be scheduled or triggered with Events (needs experimenting).
6. Implement game logic based on the current marking of the Token.
7. Hopefully add static analysis on the net somehow via Rust's type system?

Example

Here is an example of how Petri nets are defined and used.

// impl NetId
enum Choice {}

// impl Place<Choice>
enum P0 {}
enum P1 {}
enum P2 {}
enum P3 {}

// impl Trans<Choice>
enum T0 {}
enum T1 {}

/// Two transitions sharing a preset place (P1).
/// When one of them fires, the other ceases to be enabled.
/// 
/// ## Before (asterisks denote the current marking):
/// 
/// (P0)* --> |T0| -\
/// (P1)* -<         >-> (P3)
/// (P2)* --> |T1| -/
/// 
/// ## After T0 fires:
/// 
/// (P0)  --> |T0| -\
/// (P1)  -<         >-> (P3)*
/// (P2)* --> |T1| -/
fn choice() -> PetriNet<Choice> {
    PetriNet::empty()
        .add_place::<P0>()
        .add_place::<P1>()
        .add_place::<P2>()
        .add_place::<P3>()
        .add_trans::<
            T0, 
            ((P0, W1), (P1, W1)),
            (P3, W1) // W1, W2, W3, ... – arc weights
        >()
        .add_trans::<
            T1, 
            ((P1, W1), (P2, W1)), 
            (P3, W1)
        >()
}

fn test_choice() {
    let net = choice();
    let mut token = net.spawn_token();
    token.mark::<P0>(1);
    token.mark::<P1>(1);
    token.mark::<P2>(1);
    assert!(net.is_enabled::<T0>(&token));
    assert!(net.is_enabled::<T1>(&token));
    assert!(net.fire::<T0>(&mut token).is_some());
    assert!(!net.is_enabled::<T1>(&token));
}