I had not seen the de Renstroem ... So the function is even not working as I was expecting.

frazap:   WRT the use of Test::More for posing questions (to PerlMonks or to yourself during development!), see also neilwatson's article How to ask better questions using Test::More and sample data. Of course, the essential question you're asking yourself during development is "Does this code work the way I think it works?"