sS loadPageAndStore_once(S url) {
  File f = defaultPlaceForStoredWebPage(url);
  if (f.exists()) ret loadTextFile(f);
  S page;
  try {
    page = loadPage(url);
  } catch e {
    print(e);
    page = "ERROR: " + e;
  }
  saveTextFile(f, page);
  saveTextFile(replaceExtension(f, ".url"), url);
  ret page;
}