jetasap / smlang-rs

A State Machine Language DSL procedual macro for Rust

smlang: A no_std State Machine Language DSL in Rust

A state machine language DSL based on the syntax of Boost-SML.

Aim

The aim of this DSL is to facilitate the use of state machines, as they quite fast can become overly complicated to write and get an overview of.

Transition DSL

The DSL is defined as follows:

statemachine!{
    *SrcState1 + Event1 [ guard1 ] / action1 = DstState2, // * denotes starting state
    SrcState2 + Event2 [ guard2 ] / action2 = DstState1,
    // ...
}

Where guard and action are optional and can be left out. A guard is a function which returns true if the state transition should happen, and false if the transition should not happen, while action are functions that are run during the transition which are guaranteed to finish before entering the new state.

This implies that any state machine must be written as a list of transitions.

State machine context

The state machine needs a context to be defined. The StateMachineContext is generated from the statemachine! proc-macro and is what implements guards and actions, and data that is available in all states within the state machine and persists between state transitions:

statemachine!{
    State1 + Event1 = State2,
    // ...
}

pub struct Context;

impl StateMachineContext for Context {}

fn main() {
    let mut sm = StateMachine::new(Context);

    // ...
}

See example examples/context.rs for a usage example.

State data

Any stat may have some data associated with it (except the starting state), which means that this data is only exists while in this state.

pub struct MyStateData(pub u32);

statemachine!{
    State1(MyStateData) + Event1 = State2,
    // ...
}

See example examples/state_with_data.rs for a usage example.

Event data

Data may be passed along with an event into the guard and action:

pub struct MyEventData(pub u32);

statemachine!{
    State1 + Event1(MyEventData) [guard] = State2,
    // ...
}

Event data may also have associated lifetimes which the statemachine! macro will pick up and add the Events structure. This means the following will also work:

pub struct MyEventData<'a>(pub &'a u32);

statemachine!{
    State1 + Event1(MyEventData<'a>) [guard1] = State2,
    State1 + Event2(&'a [u8]) [guard2] = State3,
    // ...
}

See example examples/event_with_data.rs for a usage example.

Guard and Action syntax

See example examples/guard_action_syntax.rs for a usage-example.

State Machine Examples

Here are some examples of state machines converted from UML to the State Machine Language DSL. Runnable versions of each example is available in the examples folder.

Linear state machine

DSL implementation:

statemachine!{
    *State1 + Event1 = State2,
    State2 + Event2 = State3,
}

This example is available in ex1.rs.

Looping state machine

DSL implementation:

statemachine!{
    *State1 + Event1 = State2,
    State2 + Event2 = State3,
    State3 + Event3 = State2,
}

This example is available in ex2.rs.

Using guards and actions

DSL implementation:

statemachine!{
    *State1 + Event1 [guard] / action = State2,
}

This example is available in ex3.rs.

Contributors

List of contributors in alphabetical order:

• Emil Fresk (@korken89)

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License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.