I may be mistaken, but the expression
(test%fun_ptr(n,x)) is unikely to succeed: you ask first to evaluate the function being pointed to by fun_ptr and then get the size of the result. So far so good, but fun_ptr is not pointing to anything, unless I am overlooking something in the code.
Thank you for your quick reply! I need to investigate a bit further first, I just stupidly copied the example):(
I don't know how to delete the post so I made it empty... Sorry for taking your time!