// Should only have one per Concepts because of add logs

concept PersistentLister implements ILister {

  new HashMap<S, L> lists;

  new HashMap<S, Map> treeMaps;

  new HashMap<S, Map> hashMaps;

  new HashMap<S, Set> treeSets;

  new HashMap<S, IVar> vars;

  transient bool nonSaving;

  public L getList(S name) {

    ret getList(name, ll());

  }

  public synchronized L getList(S name, L defaultList) {

    L l = lists.get(name);

    if (l == null) {

      lists.put(name, l = listInConcept(this, cloneList(defaultList)));

      change();

    }

    ret l;

  }

  public synchronized IVar getVar(S name, O defaultValue) {

    IVar v = vars.get(name);

    if (v == null) {

      vars.put(name, v = varInConcept(this, new Var));

      change();

    }

    if (!v.has() && defaultValue != null)

      v.set(defaultValue);

    ret v;

  }

  public synchronized Map getTreeMap(S name) {

    Map m = treeMaps.get(name);

    if (m == null) {

      treeMaps.put(name, m = mapInConcept(this, new TreeMap));

      change();

    }

    if (getOpt_raw(m, 'm) == null)

     fail("map not sane: " + className(m) + " " + struct(m));

    ret m;

  }

  public synchronized Map getHashMap(S name) {

    Map m = hashMaps.get(name);

    if (m == null) {

      hashMaps.put(name, m = mapInConcept(this, new HashMap));

      change();

    }

    applyPersistentMapLogFile(_concepts.programID, name, m, !nonSaving);

    if (getOpt_raw(m, 'm) == null)

     fail("map not sane: " + className(m) + " " + struct(m));

    ret m;

  }

  public synchronized Set getTreeSet(S name) {

    Set m = treeSets.get(name);

    if (m == null) {

      treeSets.put(name, m = setInConcept(this, new TreeSet));

      change();

    }

    ret m;

  }  

}