// Defaults to standard environment (current program directory)
// Subclass for any different environments!
static class LoadEnv {
  S loadStructure(S varName) {
    ret loadTextFile(getProgramFile(varName + ".structure"));
  }

  void saveStructure(S varName, S structure) {
    saveTextFile(getProgramFile(varName + ".structure"), structure);
  }

  void load(O o, S varName) {
    S s = loadStructure(varName);
    if (s != null)
      setOpt(o, varName, unstructure(s));
  }

  void save(O o, S varName) {
    saveStructure(varName, structure(getOpt(o, varName)));
  }
}