sclass AI_ExecuteSimpleForWhere implements Steppable {
  ForWhere fw;
  DeepZipTools tools;
  S functionName;
  Iterator elements;
  
  swappable void addLogicRule(BasicLogicRule rule) {}
  swappable Iterable elementsForFunction(S functionName) { null; }
  
  public bool step() {
    if (elements == null) {
      Pair p = forWhereParseSimpleFunctionCall(fw, tools);
      if (p == null) true;
      functionName = (S) p.a;
      elements = iterator(elementsForFunction(functionName));
    }
    
    if (!elements.hasNext()) true;
    addLogicRule((BasicLogicRule) tools.replaceVars(fw.body, litmap(var, elements.next())));
  }
}