Skip Montanaro wrote:
Guido> The PVM doesn't have a lot of knowledge about types built into Guido> its instruction set.... The opcodes are mostly very abstract: Guido> BINARY_ADD etc.
Yeah, but the runtime behind the virtual machine knows a hell of a lot about the types. A stream of opcodes doesn't mean anything without the semantics of the functions the interpreter loop calls to do its work. I thought the aim of Eric's Parrot idea was that Perl and Python might be able to share a virtual machine. If both can generate something like today's BINARY_ADD opcode, the underlying types of both Python and Perl better have the same semantics.
I don't think that needs to be true _in toto_. In other words, some opcodes can be used by both languages, some can be language-specific. The implementation of the VM for a given opcode can be shared per language, or even just partially shared. BINARY_ADD can do the same thing in most languages for 'native' types, and defer to per-language codepaths for objects, for example. One problem with a hybrid approach might be that optimizations become really hard to do if you can't assume much about the semantics, or if you can only assume the union of the various semantics. But the idea is intriguing anyway =). --david