[NTG-context] total pages in external PDF

Dear list, I need to get the number of pages from an external PDF file that I also define with an \env. I think I could get something like this.: \def\Myfilename{\env{filename}} doc = epdf.open(arg[\MyFilename]) total_pages_ = doc:getNumPages() \def\Mypages{total_pages} But mixing both lua and ConTeXt commands the wrong way won’t work. Sorry, but this is all Greek to me. Although I see how it could be done, I cannot write the code for this. Which is the right way to get the code above working? Many thanks for your help, Pablo -- http://www.ousia.tk