sclass LazyVar<A> implements IVar<A>, ISetter<A> {
  *() {}
  *(A *v) {}
  *(IF0<A> *f) {}
  
  IF0<A> f;
  
  // will keep var around after the fact (we could change this by counting how many threads are waiting)
  Var<OKOrError<A>> calculating;
  A v;
  
  public A get() {
    bool meCalc;
    
    synchronized {
      meCalc = calculating = null;
      if (meCalc)
        calculating = new Var;
    }
    
    if (meCalc) {
      OKOrError<B> b = okOrError(() -> f!);
      calculating.set(b);
      synchronized { ret v = b!; }
    } else {
      try {
        waitUntilNotNull(calculating);
        ret a;
      }
    }
  }
  public synchronized bool has() { ret v != null; }
  public synchronized void clear() { v = null; }
  
  toString { ret str(this.get()); }

  !include #1023196
}