state machine syntax

gistfile1.rs

pub enum State {
  A,
  B(u8),
  C(u8),
  D
  Error
}
  
enum Output {
  X(u8),
  Y,
  Z,
  Default
};

pub fn parse(arg:u8) -> (State, Output);

machine!(MyMachine(State) {
  {
    initial: State::A,
    error:   State::Error  // Sink state, if the transition is not valid
  }

  event [tr1] {
    State::A    => State::B(0),
    State::B(i) => State::C(i+1)
  }

  event [tr2(arg1:u8) -> Option<u8> : None] { // the value after ':' is the default return value
    State::A    => { (State::B(0),   Some(42))  } ,
    State::B(i) => { (State::C(i+1), Some(i+1)) }
  }

  event [tr3(arg1:u8) -> Output : Output::Default] {
    State::A    => { parse(arg1)     },
    State::B(i) => { parse(arg1 + i) }
   }
});

let mut m = Machine { state: State::A };
m.tr1(); // returns a Option<()>. None if the current state does not accept this transition
m.tr2(42);