Probably a simple PHP string solution – help?

Hey guys,

<?php previous_post_link('%link', 'Previous in category', TRUE); ?> (http://codex.wordpress.org/Template_Tags/previous_post_link)

This is what I want to do:
<?php previous_post_link('%link', 'Previous in' . single_cat_title(), TRUE); ?>

Are functions/variables allowed as parameters?

Thanks,