new Monad<List>() { // List :: * -> * (kind checks)
  public <A> List<A> pure(A a) {
    return List.single(a);
  }

  public <A, B> List<B> bind(Transformer<A, List<B>> t, List<A> a) {
    List<B> r = List.empty();
    for(e : a) r.addAll(t.transform(e));        
    return r;
  }          
};