I was thinking a little about a Python/Perl VM merge. One problem I imagine would be difficult to reconcile is the subtle difference in semantics of various basic types. Consider the various bits of Python's (proposed) number system that Perl might not have (or want): rationals, automatic promotion from machine ints to longs, complex numbers. These may not work well with Perl's semantics. What about exceptions? Do Python and Perl have similar notions of what exceptional conditions exist?
Actually, this may not be as big a deal as I thought before. The PVM doesn't have a lot of knowledge about types built into its instruction set. It knows a bit about classes, lists, dicts, but not e.g. about ints and strings. The opcodes are mostly very abstract: BINARY_ADD etc. --Guido van Rossum (home page: http://www.python.org/~guido/)