Dan~
On Tue, 16 Nov 2004 15:25:24 -0500, Dan Sugalski <[EMAIL PROTECTED]> wrote: > At 3:12 PM -0500 11/16/04, Matt Fowles wrote: > > > >Dan~ > > > >On Tue, 16 Nov 2004 13:41:25 -0500, Dan Sugalski <[EMAIL PROTECTED]> wrote: > >> At 10:32 AM -0800 11/16/04, Jeff Clites wrote: > >> >The continuation preserves the frame (the mapping from logical > >> >variables to their values), but not the values of those variables at > >> >the time the continuation was created. > >> > >> This is one of the fundamental properties of continuations, but it > >> does throw people. And it's why register contents have to be thrown > >> away when a continuation is invoked, since the registers have values, > >> and continuations don't preserve values. > > > >I think right here we have the crux of my failure to understand. I > >was/am under the impression that the continuation will restore the > >register frame to exactly as it was when the continuation was taken. > >Thus those registers which are values (I,N) will continue to have the > >value they had when the continuation was taken, while those registers > >which are pointers/references (S, P) will still point to the same > >place, but that data may have changed. Is this correct? > > No. The registers are just about the only thing that *isn't* restored. > > Continuations put the environment back. This includes things like the > lexical pad stack, the namespace stack, the stack itself, any > security credentials... basically everything that describes the > environment. *Data*, on the other hand, is *not* restored. Data stays > as it is. > > Registers are a special case of data, and they're just declared crud > by fiat, since otherwise things get nasty and unpredictable. Then I am not sure what you mean by "The return continuation PMC type, used to create return continuations used for call/return style programming, guarantees that registers 16-31 will be set such that the contents of those registers are identical to the content of the registers when the return continuation was I<created>." I read that as saying that registers will be restored by continuations. If that is not what it is intended to mean, could you clarify for me. Thanks, Matt -- "Computer Science is merely the post-Turing Decline of Formal Systems Theory." -???
