ptnet-core 0.1.2

Core types and traits for modeling and simulating Place/Transition nets.
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/*!
This module provides an extension to allow for guarded transitions.

In some cases it is desirable to model conditions that will enable/disable a transition beyond the required set of input
tokens. To accomplish this we add a guard function \\(G\\) to our net definition.

$$\tag{Guarded Net} N = \left\langle P,T,A,G \right\rangle$$

This function maps the set of transitions and a *particular marking* to a truth value.

$$\tag{Guard Function} G: T \times M_n \mapsto  \left \mathbb{B}$$

This function is called from within the existing enable check as follows.

$$\tag{Guarded enabled} enabled\left(t \in T, M_n \right) = \forall p \in {}^{\bullet}t: min(A(p,t)) \land G(t, M_n)$$

*/

use crate::net::Transition;
use crate::sim::{Marking, Tokens};

// ------------------------------------------------------------------------------------------------
// Public Types
// ------------------------------------------------------------------------------------------------

///
/// This trait determines whether a particular transition has an associated guard, and can evaluate
/// such a guard.
///
/// Note that calling evaluate when no guard is present **should** be free, and return
/// `false`.
///
pub trait GuardedTransition: Transition {
    type Tokens: Tokens;
    type Marking: Marking<Tokens = Self::Tokens>;

    ///
    /// Returns `true` if this transition has an associated guard function, else `false`.
    ///
    fn is_guarded(&self) -> bool;

    ///
    /// Return the result of evaluating the associated guard function. A value of `true` allows
    /// the transition to enable, `false` will disable it.
    ///
    fn evaluate_guard(&self, current: &Self::Marking) -> bool;
}