I have a PHP code and try to convert to twig with many convertors, but every time code is not working.

Original code:

<?php
$homepage = "/";
$currentpage = $_SERVER['REQUEST_URI'];
echo $_SERVER['REQUEST_URI'];
if ($homepage == $currentpage) { ?>
some html here
<?php }
else { ?>
other html here
<?php } ?>

Converted code:

{% set homepage  "/" %}
{% set currentpage  _SERVER.REQUEST_URI %}
{{ _SERVER.REQUEST_URI }}
{% if  homepage == currentpage %}
some html here
{% else %}
other html here
{% endif %}

I try to change the code many times, every time errors happened. The result:
Fatal error: Uncaught TwigErrorSyntaxError: Unexpected token “string” of value “/” (“end of statement block” expected)