@Override
 public StorageResults fetch(Expression userQuery) {
   Expression expression = userQuery.normalize();
   Matcher matcher = expression.accept(new MatcherCreator());
   List<DataRecord> matchRecords = new LinkedList<DataRecord>();
   for (DataRecord dataRecord : storage) {
     if (matcher.match(dataRecord)) {
       matchRecords.add(dataRecord);
     }
   }
   List<DataRecord> filteredRecords = expression.accept(new Filter(matchRecords));
   return new InMemoryStorageResults(filteredRecords);
 }
 @Override
 public void visit(ExpressionList el) {
   for (Iterator iter = el.getExpressions().iterator(); iter.hasNext(); ) {
     Expression expression = (Expression) iter.next();
     expression.accept(this);
   }
 }
  /** Model check a property. */
  public Result check(Expression expr) throws PrismException {
    Modules2PTA m2pta;
    Result res;
    String resultString;
    long timer;

    // Starting model checking
    timer = System.currentTimeMillis();

    // Check for system...endsystem - not supported yet
    if (modulesFile.getSystemDefn() != null) {
      throw new PrismException(
          "The system...endsystem construct is not supported yet (try the digital clocks engine instead)");
    }

    // Translate ModulesFile object into a PTA object
    mainLog.println("\nBuilding PTA...");
    m2pta = new Modules2PTA(prism, modulesFile);
    pta = m2pta.translate();
    mainLog.println("\nPTA: " + pta.infoString());

    // Check for references to clocks - not allowed (yet)
    // (do this before modifications below for better error reporting)
    expr.accept(
        new ASTTraverseModify() {
          public Object visit(ExpressionVar e) throws PrismLangException {
            if (e.getType() instanceof TypeClock) {
              throw new PrismLangException(
                  "Properties cannot contain references to clocks (try the digital clocks engine instead)",
                  e);
            } else {
              return e;
            }
          }
        });

    // Take a copy of property, since will modify
    expr = expr.deepCopy();
    // Remove property refs ands labels from property
    expr = (Expression) expr.expandPropRefsAndLabels(propertiesFile, labelList);
    // Evaluate constants in property (easier to do now)
    expr = (Expression) expr.replaceConstants(constantValues);
    // Also simplify expression to optimise model checking
    expr = (Expression) expr.simplify();

    // Do model checking
    res = checkExpression(expr);

    // Model checking complete
    timer = System.currentTimeMillis() - timer;
    mainLog.println("\nModel checking completed in " + (timer / 1000.0) + " secs.");

    // Print result to log
    resultString = "Result";
    if (!("Result".equals(expr.getResultName())))
      resultString += " (" + expr.getResultName().toLowerCase() + ")";
    resultString += ": " + res;
    mainLog.print("\n" + resultString + "\n");

    // Return result
    return res;
  }