// MetaTransformer that understands Transformable and List
static MetaTransformer metaTransformer_transformableAndList() {
  ret new MetaTransformer(new MetaTransformer.StructureHandler() {
    public O transform(O o, IF1 recurse) {
      if (o cast Transformable)
        ret o.transformUsing(recurse);
      if (o cast L)
        ret map_ping(recurse, o);
      null;
    }
    
    public void visit(O o, IVF1 recurse) {
      if (o cast Visitable)
        o.visitUsing(recurse);
      else if (o cast L)
        for ping (O x : o)
          recurse.get(x);
    }
  });
}