I have seen the Make DLL option in serveral programs, like C++ and Visual Basic; if I make a little program like a calculator in VB, is it so that I can then exprot that as a DLL and call a Calculator from GM? Or is it only allowed to include code (and no interface)?
I could try to find this out myself, maybe, but it's easier to ask here :D

DLLs include only code. It has no interface!

I see. So it's just a function making use of what the current interface has.

Thanks.