foo.php

<?php

function parseTemplate($template, array $variables = [], array &$throwBacks = array())
{
    $scope = function() use ($variables, $template, &$throwBacks)
    {
        extract($variables);
        ob_start();
        $throwBacks = include sprintf('%s/static/%s', __DIR__, $template);

        if ( ! is_array($throwBacks) )
        {
            $throwBacks = (array) $throwBacks;
        }

        $content = ob_get_clean();
        return $content;
    };

    return $scope();
}

navigation.html -> get_defined_vars()

array(3) {
  ["variables"]=>
  array(0) {
  }
  ["template"]=>
  string(21) "pages/newsletter.html"
  ["throwBacks"]=>
  &array(0) {
  }
}