catch (Throwable t) { rethrow(t);
catch (RuntimeException t) { rethrow(t, RuntimeException.class);
  public Value execute(Env env)    throws Throwable  {    try {      if (_init != null)        _init.eval(env);      while (_test == null || _test.evalBoolean(env)) {        env.checkTimeout();        Value value = _block.execute(env);        if (value == null || value instanceof ContinueValue) {        }        else if (value instanceof BreakValue)          return null;        else          return value;        if (_incr != null)          _incr.eval(env);      }    }    catch (Throwable t) {      rethrow(t);    }    return null;  }