in reply to Perl modules and the GPL
As far as I understand it, the GPL only governs distribution. As the GPL is implemented via copyright and the concept of a "derived work", and use of an API is not a "derived work", the interpreter gap that Perl creates insulates your code while using a GPLed library. Any XS wrapper (statically) linking to a GPLed library gets infected by the GPL, but that's where the infection ends. If you want to play it really safe, you can write a second implementation to the same API, like Term::ReadLine::Perl is for Term::ReadLine.