The book I would like to read (or maybe someday write) is "Perl/Magic Programming". There's a limited audience for the subject matter, so I'll probably never see it, but I like the opportunity to dream.
I work with Meditech, a very proprietary hospital system that is programmed in a language called "Magic". (Are any of you Monks familiar with it?) It's a difficult system to interface with, but it is possible to do some scripting into it using Visual Basic and some windows dlls.
One of my goals is to write a Perl scripting interface into Magic. I suspect that if VB can communicate with Meditech then Perl should be able to as well. And I suspect Perl could do it with less code and less overhead. But since the book hasn't been written yet, I guess I'll have to figure out how to get it done and write the book myself.
