pub enum Workload<T> {
  Done(T),
  More(Box<dyn FnOnce() -> Workload<T>>)
}

impl<T> Workload<T> {

  pub fn done(t: T) -> Workload<T> {
    Workload::Done(t)
  }

  pub fn more<K: FnOnce() -> Workload<T>>(k: K) -> Self {
    Workload::More(Box::new(k))
  }

  pub fn bind<U, K: FnOnce(&mut T) -> Workload<U>>(&mut self, next: K) -> Workload<U> {
    match self {
      Workload::Done(val) => next(val),
      Workload::More(fun) => fun().bind(next)
    }
  }
}