pub fn handle(ctx, state, sender, message) {
    let state = match state { () => 0, state => state };
    if message.op == "inc" {
        let new_state = state + 1;
        ctx.info(`New State: ${new_state}`);
        ctx.send(ctx.this, #{op: "inc"});
        new_state
    } else {
        panic("unknown counter operation")
    }
}