// MetaTransformer that understands Collection (will convert to List) and Map
static MetaTransformer metaTransformer_collectionAndMap() {
  ret new MetaTransformer(new MetaTransformer.StructureHandler() {
    public O transform(O o, IF1 recurse) {
      if (o cast Cl)
        ret map_ping(recurse, o);
      if (o cast Map)
        ret mapKeysAndValues(recurse, o);
      null;
    }
    
    public void visit(O o, IVF1 recurse) {
      if (o cast Cl)
        for ping (O x : o)
          recurse.get(x);
      else if (o cast Map)
        for ping (O x, O y : (Map<O>) o) {
          recurse.get(x);
          recurse.get(y);
        }
    }
  });
}