So I've studied the Zend implementation in depth as part of my phd, and I'm the author of a lot of the implementation, and all of the optimizations and static analysis in phc. So I know quite a bit about this, and looked through the implementation.

First thing is that it's clearly a very clean and high quality implementation. It's clear the author knows a substantial amount of both the implementation of the Zend engine and its semantics. This is clear from the replication of zvals, and things like separation.

However I think that it's missing most of the copy on write, reference and separation semantics. These are pretty complex so that's not unexpected. And example here is the function implementation that copies the parameter list - that's almost certainly not right. I don't see reference counts or separation in assignment either.

That said, I didn't look fully so I could be wrong.

I would recommend the author use the test suites from phc, Zend, and hiphop - that would help highlight a lot of the weird corner cases (example copying an array that had referenced in it!)

Anyway, very cool (especially impressive for 6 hours!) and I hope you go on with this :)

(Comment via phone, excuse typos)