microstate::microstate!

macro_rules! microstate (
  (
      $machine:ident { $initial:ident }
      states { $($states:ident),* }

      $($meth:ident {
          $($from:ident => $to:ident)*
      })*
  ) => (
      #[allow(non_snake_case)]
      pub mod $machine {
          #[derive(Clone,PartialEq,Eq,Debug)]
          pub enum State {
              __InvalidState__, // Just be able to match _ further down
              $($states),*
          }
          #[derive(PartialEq,Eq,Debug)]
          pub struct Machine {
              state: State,
          }

          pub fn new() -> Machine {
              Machine::new()
          }

          impl Machine {
              pub fn new() -> Machine {
                  Machine {
                      state: State::$initial
                  }
              }

              pub fn state(&self) -> State {
                  self.state.clone()
              }

              $(pub fn $meth(&mut self) -> Option<State> {
                  match self.state {
                      $( State::$from => { self.state = State::$to; Some(State::$to) } ),*
                          _ => None
                  }
              })*
          }
      }
));

Create a new state machine

It takes a name, the initial value, all possible states and the transitions.

See the main documentation for a proper example.