private void GetUnaryExpression()
        {
            var token = _lexer.LookAheadToken();

            if (token.Type == Token.EType.UNARYMINUS)
            {
                _lexer.Advance();
            }

            GetAtomicValue();

            if (token.Type == Token.EType.UNARYMINUS)
            {
                _compilerEnvironment.AddInstruction(new UnaryMinusInstruction());
            }
        }