private static void AssertExpression(AlgebraicExpressions expression, string expected)
 {
     var visitor = new ToTextVisitor();
     expression.Accpet(visitor);
     string actual = visitor.GetResult();
     Assert.AreEqual(expected, actual);
 }
 private static void AssertExpression(AlgebraicExpressions expression, int expected)
 {
     var visitor = new ToValueVisitor();
     expression.Accpet(visitor);
     int actual = visitor.GetResult();
     Assert.AreEqual(expected, actual);
 }