From: Roger Hale <[EMAIL PROTECTED]>
Date: Thu, 07 Apr 2005 04:23:41 -0400
Leopold Toetsch wrote:
> Roger Hale <[EMAIL PROTECTED]> wrote:
>
>>Leopold Toetsch wrote:
>>
>>>As @ARGS (or @IN_ARGS, @OUT_ARGS) is being stored in the context, and
>>>that context is defacto the continuation, yes - a tail-call would
>>>inherit this information.
>
>>But as each tail-call supplies a new @ARGS, how can this be the case?
>
> We would have two parts in the context: @IN_ARGS, @OUT_ARGS. The
> C<tailcall> opcode can preserve that part with the return context.
It seems to me that both @IN_ARGS and @OUT_ARGS get used for other
things (the tail-calls' arguments) in a chain of tail-calls.
The definition of a tail call is that it returns its callee's results
back to its caller unmodified. So if @OUT_ARGS is used for other
things, then it's not a tail call.
Consider this chain:
A calls B(@OUT_ARGS 1)[continuation: A*] in context c
B(@IN_ARGS 1)[c10n: A*] calls C(@OUT_ARGS 2)[c10n: A*]
C(@IN_ARGS 2)[c10n: A*] wants to know context c, as it's getting
ready to return something. Neither @IN_ARGS (the arguments C
received from B) nor @OUT_ARGS (the arguments of any call C may make)
has this information . . .
I don't think this is a real situation. If B passes C the continuation
it got from A, then the call to C is indeed a tail call [1], and cannot
have different @OUT_ARGS from the call to B, because B never regains
control when C returns. Your notation in that case has to be:
B(@IN_ARGS 1)[c10n: A*] calls C(@OUT_ARGS 1)[c10n: A*]
Or do you mean something different from a tail call? If so, could you
please express it in a programming language?
. . . but the continuation (I propose) does; and this continues to be
good for whoever wants to know: the return object holds the return
context.
No?
regards,
Roger
I believe so, but I think this is what Leo meant by "... that context is
defacto the continuation." There doesn't need to be a separate "return
object" because it would be one-to-one with the continuation.
-- Bob Rogers
http://rgrjr.dyndns.org/
[1] If not implemented via "tailcall", it would use an additional stack
frame, but the semantics would otherwise be identical.
