static S testStructureFunction(O input) {
  ret testStructureFunction(input, true);
}

static S testStructureFunction(O input, bool compare) {
  S s;
  time {
    s = structure(input);
  }
  print("struct", shorten(s, 500));
  O o;
  print("unstructuring " + l(s) + " chars");
  time {
    o = unstructure(s);
  }
  S x = structure(o);
  assertEquals(s, x);
  if (compare)
    assertEqualsVerbose(input, o);
  ret x;
}