On Sun, Jun 12, 2005 at 09:41:05PM -0700, Bill Coffman wrote: > Continuations can be taken from within any sub, and possibly even > when appending to a list, if you're using lazy list eval.
Oh no ... it's even worse than you think. Almost *any* opcode that operates on a PMC can trigger a continuation. And I only need two words to prove it: "Tied variables." Ouch ouch ouch. Sounds to me like register allocation is effectively dead, and all that's left is register renumbering. The only exception (ahem) I can think of is if we start supporting, and compilers start emitting, continuation resets (i.e. protected areas that guarantee that continuations won't propagate out; kind of like the effect of C< eval BLOCK > on Perl's die). But even then, it might not be worth the effort just to get a little tiny bit of reuse out of an effectively infinite register set. > There are also some issue about changing variables through continuations, > like you can only change PMC integers, which point to some fixed location, > containing the int, i.e. you can only use references. These parts make less > sense to me, but the issue is basically, some registers are restored, and > some are kept safe? Well, that issue hasn't been quite resolved either. I think that's been answered: We don't have to save & restore anything, because it's all automatically saved by virtue of being in memory as the state of a *virtual* machine. -- Chip Salzenberg <[EMAIL PROTECTED]>
