A code generator for finite state machines with the following features:

• An entry api to transition the state machine.
• Illegal states and transitions are unrepresentable.
• States can contain data.
• Custom #[derive(..)] support.
• #![no_std] support.
• Inline SVG diagrams of the state machine in docs.

// define the machine.
// you can also use the DOT language if you prefer.
fsmentry::dsl! {
    /// This is a state machine for a traffic light
    // Documentation on nodes and states will appear in the generated code
    pub TrafficLight {
        Red; // this is a state
        Green: String; // this state has data inside it.

        /// Cars speed up
        // this documentation is shared among all the edges
        Red -> RedAmber -> Green;
        //     ^ states are implicitly created

        /// Cars slow down
        Green -> Amber -"make sure you stop!"-> Red;
        //             ^ this documentation is for this edge only
    }
}

use traffic_light::{TrafficLight, Entry};

// instantiate the machine
let mut machine = TrafficLight::new(traffic_light::State::Red);
loop {
    match machine.entry() {
        Entry::Red(it) => it.red_amber(), // transition the state machine
        // when you transition to a state with data,
        // you must provide the data
        Entry::RedAmber(it) => it.green(String::from("this is some data")),
        Entry::Green(mut it) => {
            // you can inspect or mutate the data in a state...
            let data: &String = it.get();
            let data: &mut String = it.get_mut();
            // ...and you get it back when you transition out of a state
            let data: String = it.amber();
        },
        Entry::Amber(it) => break,
    }
}

Features

• macros (default): Include the [dot] and [dsl] macros.
• svg (default): The macros will shell out to dot, if available, and generate a diagram of the state machine for documentation.
• std (default): Includes the [FSMGenerator], for custom codegen tools.
• cli: This does not affect the library, but if you

  cargo install fsmentry --features=cli
  

  You will get an fsmentry binary that you can use to generate code.

Here are more details about the generated code.

fsmentry::dsl! {
    #[derive(Clone, Debug, derive_quickcheck_arbitrary::Arbitrary)]
    pub MyStateMachine { .. }
}
use my_state_machine::{MyStateMachine, State, Entry};
// ^ A module with matching publicity is generated for the state machine.
//   The `#[derive(..)]`s apply to the `State` and the `MyStateMachine` items.

let mut machine = MyStateMachine::arbitrary(g);

// you can also inspect and mutate the state yourself.
let state: &State = machine.state();
let state: &mut State = machine.state_mut();

match machine.entry() {
    // states with no transitions and no data are empty entries
    Entry::DeadEnd => {},
    // states with no transitions give you the data
    Entry::DeadEndWithData(data) => {
        let _: &mut String = data;
    },
    Entry::WithTransitions(handle) => {
        // otherwise, you get a struct which allows you to transition the machine.
        // (It will have getters for data as appropriate).
        handle.dead_end();
    }
    // ...
}