Flow\Parser::parseUnaryExpression PHP Method

    protected function parseUnaryExpression()
    {
        if ($this->stream->test(Token::OPERATOR, array('-', '+'))) {
            switch ($this->stream->getCurrentToken()->getValue()) {
                case '-':
                    return $this->parseNegExpression();
                case '+':
                    return $this->parsePosExpression();
            }
        }
        return $this->parsePrimaryExpression();
    }