fibers and ranges: what's wrong here?

[zeljkog via Digitalmars-d-learn]

import std.stdio, core.thread;

struct Tree{
    int val;
    Tree[] tree;
}

struct TreeRange{
  Tree curtree;
  bool empty;
  Fiber worker;

  this(Tree t){
    worker = new Fiber(&fiberFunc);
    curtree = t;
    popFront();
  }
  void fiberFunc(){
    Tree t = curtree;
    Fiber.yield();
    foreach(child; t.tree){
      curtree = child;
      fiberFunc();
    }
  }
  int front(){ return curtree.val; };
  void popFront() {
    worker.call();
    empty = worker.state == Fiber.State.TERM;
  }
}

void main() {
  auto tt = Tree(5, [Tree(7,[Tree(11), Tree(4)]), Tree(10)]);
  auto tr1 = TreeRange(tt);
  foreach(v; tr1){
    writef("%2d, ", v);
  }
  writeln();
  for(auto r = TreeRange(tt); !r.empty; r.popFront())
    writef("%2d, ", r.front);
  writeln();
}

output:
 5,  5,  5,  5,  5,
 5,  7, 11,  4, 10,

Is it supposed to work?