Simple state machine pattern in Rust (https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f66b41f93d7a9a2ef704d4aa5b5b0a44)

statemachine.rs

#[derive(Debug, PartialEq)]
pub enum State {
    Intro,
    StartScreen,
    PlayGame,
    Paused,
    Faulted,
}

#[derive(Debug, Clone, Copy)]
pub enum Event {
    IntroFinished,
    GameStartRequested,
    PauseRequested,
    UnpauseRequested,
}

pub struct GameplayStateMachine {
    state: State,
}

impl GameplayStateMachine {
    pub fn new() -> Self {
        GameplayStateMachine {
            state: State::Intro,
        }
    }

    pub fn handle_events(&mut self, events: Vec<Event>) {
        for event in events.iter() {
            self.handle_event(&event);
        }
    }

    pub fn handle_event(&mut self, event: &Event) {
        self.state = match (&self.state, event) {
            (State::Intro, Event::IntroFinished) => {
                println!("Introducing the game!");
                State::StartScreen
            }
            (State::StartScreen, Event::GameStartRequested) => {
                println!("Starting the game!");
                State::PlayGame
            }
            (State::PlayGame, Event::PauseRequested) => {
                println!("Paused.");
                State::Paused
            }
            (State::Paused, Event::UnpauseRequested) => {
                println!("Unpaused");
                State::PlayGame
            }
            _ => {
                println!("Faulted!");
                State::Faulted
            }
        };
    }
}

fn main() {
 let mut machine = GameplayStateMachine::new();

    let events = vec![
        Event::IntroFinished,
        Event::GameStartRequested,
        Event::PauseRequested,
        Event::UnpauseRequested,
        Event::PauseRequested,
        Event::UnpauseRequested,
    ];

    for event in events.iter() {
      machine.handle_event(&event);
    }
}