// collects into l until max is reached or target element is found
static <A> Collector<A> limitedSearchCollector(final Collection<A> l, final int max, final A target) {
  ret new Collector<A>() {
    bool found;
    
    bool full() {
      ret found || l(l) >= max;
    }
    
    void add(A a) {
      if (!full()) l.add(a);
      if (eq(a, target)) found = true;
    }
    
    bool contains(A a) {
      ret l.contains(a);
    }
  };
}