I'm new here, but some of the London PerlMongers know me.
To cut to the point, I started writing a book about implementing other languages in Perl. Then the publisher went quiet. So I continued anyway. Then I got despondant, and what I have so far is here.
It's really Section 1 of 3, "Interpreters", the other two sections would be "Parsing" and "Compilation".
It's unfinished, insofar as the OO extension code is done but I'm not happy with it yet, and the continuation passing interpreter is conceptual only (trampoline implementation probably).
I'm not sure if I'll finish it, but it seems such a waste to throw it all away so feel free to read, comment etc.