Shared via Rust Playground

playground.rs

struct Vm {
    pc: usize,
}

impl Vm {
    fn new() -> Vm {
        Vm { pc: 0 }
    }

    fn execute<F>(&mut self, mut probe: F)
        where F: FnMut(&mut Vm)
    {
        loop {
            probe(self);
        }
    }
}

struct Beeper {
    beeping: bool
}

impl Beeper {
  fn new() -> Beeper {
    Beeper { beeping: false }
  }
  
  fn toggle(&mut self) {
    self.beeping != self.beeping;
  }
}

fn main() {
    let mut vm = Vm::new();
    let mut beeper = Beeper::new();
    
    vm.execute(|x: &mut Vm| {
        println!("{}", x.pc);
        
        beeper.toggle();
    });
    
    beeper.toggle();
}