}

// Returns a handler that stores every seen task and an ancillary function to retrieve those
func collecting() (handler, func() tasks) {
	var seen = make(map[*task]struct{})
	return func(t *task) action {
			seen[t] = struct{}{}
			for _, dep := range t.depends {
				seen[dep] = struct{}{}
			}
			return action{}
		}, func() tasks {
			seq := make(tasks, 0, len(seen))
			for k, _ := range seen {
				seq = append(seq, k)
			}
			sort.Stable(seq)
			return seq
		}
}