The idea of an interactive education tool is a basic of coding, and web programming. And like you mention different implementations will have differing strengths and weaknesses. For me a Perl implementation would be a natural conclusion.

Perhaps what I was getting at is more the idea of interactive documentation. perlhack and the concurrent documentation already describe the various versions and how to get hacking.

At the stage I am at in my own development I am looking to explore deeper issues such as different programming paradigms. When I was suggesting a project based tutorial on the Version update from Perl 4 to Perl 5, I was more properly thinking about something that took into consideration the paradigm differences.

But I was also considering something with a bit more advanced concepts involved. Debugging as a self-exploratory educational tool is best likened to the idea of freeclimbing, everything is wonderful untill you slip that one time. And using examples of Major version updates is like starting out fifty feet up a grade E.

My suggestion refined, would be to produce examples of minor version updates that involve a guided debugging solution for specific updates. Maybe something that followed an internal function through several minor/major updates also.

A common theme throughout many implementations is that Perl isn't actually doing x or actually doing y. But this has been mostly with things such as objects, regular expressions, exceptions and so on. Though it seems more and more to me that nothing Perl does is what it appears to be doing. This itself does seem like a fundamental property of Perl. So something that clues the user in to this aspect further could also be useful.

After all a Perl scalar exhibits duality, perhaps Perl versions are also a kind of duality, but of Perl itself.