// keeps file open
static SS zipFileSnippetToLazyTextMap(S snippetID) {
  final ZipFile zip = new ZipFile(loadLibrary(snippetID));
  O f = func(S name) { loadTextFileFromZipFile(zip, name) };
  ret new LazyValueTreeMap(listFilesInZip(f), f) {
    void cleanMeUp {
      zip.close();
    }
  };
}