Hi Benja, > You can find MaybeT here: > > http://www.haskell.org/haskellwiki/New_monads/MaybeT Thank you, that you spent some time figuring this out. This is exacly what I have expected. (This "print" was debug leftovers). Now I will try to understand how exacly this works. My big thanks to you again, Radek.