Flow\Parser::parseConcatExpression PHP Method

    protected function parseConcatExpression()
    {
        $line = $this->stream->getCurrentToken()->getLine();
        $left = $this->parseJoinExpression();
        while ($this->stream->consume(Token::OPERATOR, '~')) {
            $right = $this->parseJoinExpression();
            $left = new Expression\ConcatExpression($left, $right, $line);
            $line = $this->stream->getCurrentToken()->getLine();
        }
        return $left;
    }