A simple Finite State Machine library in Rust. Provide State and Event types (usually enums), then generate a machine with an initial state, give it some transition behaviours and you have your state machine!

Usage

Using the simple coin-operated turnstyle example from the FSM wikipedia entry:

Define your states and events: ```rust // currently states must be cloneable

[derive(Clone)]

enum TurnStyleState { Locked, Unlocked, }

// currently events must be cloneable

[derive(Clone)]

enum TurnStyleEvent { Push, InsertCoin, }

// currently must be convertable to u32 impl Into for TurnStyleState { fn into(self) -> u32 { self as u32 } }

// currently must be convertable to u32 impl Into for TurnStyleEvent { fn into(self) -> u32 { self as u32 } } ```

Create your machine and define your transitions: rust // create the machine initially in the Locked state let mut machine = Machine::new(TurnStyleState::Locked); // create the transition from Locked -> Unlocked upon inserting a coin machine.add_transition( TurnStyleState::Locked, TurnStyleEvent::InsertCoin, TurnStyleState::Unlocked, Box::new(|_| println!("unlocked")) ); // create the transition from Unlocked -> Locked upon pushing the turnstyle machine.add_transition( TurnStyleState::Unlocked, TurnStyleEvent::Push, TurnStyleState::Locked, Box::new(|_| println!("locked")) );

Trigger events as needed and huzzah, off you go: rust // initially we're in the Locked state machine.on_event(TurnStyleEvent::InsertCoin); // now we're Unlocked, ("unlocked" was just printed) machine.on_event(TurnStyleEvent::Push); // now we're Locked again, ("locked" was just printed)

This example is also the test case for the library, although here I've ommitted the test-related details.

To Do

Remove need to Clone inside implementation, I'm sure it's unnecessary
There must be a more elegant way to write both the add transition method and the on event method, perhaps using Option methods?
A better trait than Into (u32) ? Not sure if I can get rid of ANY trait dependancy, but Into currently contributes to the dependancy on Clone, when all I really want is a unique ID for each state/ID (preferably sequential), aka: the enum tag.

Alternatives

Macro based solutions

Other

genfsm