Not to hijack the OP's thread, but a follow-up question: what speed-up can realistically be expected? I 've seen Koichi's slides and they look impressive but if I am not mistaken the optimizations looked to be concerned with basic math operations and so on. what about function calls / blocks / object instantiations / hash and array implementation / .... ? Is YARV going to muscle those around as well, or not really? if so (or if not), what performance improvements would be within reach? thanks, stijn