[REBOL] Re: On mutability and sameness
From: agem:crosswinds at: 7-Jun-2001 18:57
Hello Joel
>>>>>>>>>>>>>>>>>> Ursprüngliche Nachricht <<<<<<<<<<<<<<<<<<
Am 07.06.01, 14:23:11, schrieb Joel Neely <[joel--neely--fedex--com]> zum
Thema [REBOL] Re: On mutability and sameness:
> Hello, Volker,
> Volker Nitsch wrote:
> >
> > Am 07.06.01, 00:07:53, schrieb "Larry Palmiter"
> > <[larry--ecotope--com]> zum
> > Thema [REBOL] Re: On mutability and sameness:
> >
> > > Hi Joel
> >
> > > > But it is equally inaccurate to assume that they are
> > > > fixed-size
> > > > scalar values, isn't it?
> > > >
> > > > >> foo: 9.8.7.6.5.4.3.2.1.0
> > > > == 9.8.7.6.5.4.3.2.1.0
> > > > >> repeat i 10 [print foo/:i]
> >
> > > >> foo: 1.2.3.4.5.6.7.8.9.10.11
> > > ** Syntax Error: Invalid tuple -- 1.2.3.4.5.6.7.8.9.10.11
> >
> You're right. Experiments confirm that ten is the maximum
> number of elements in a tuple.
> > > The "scalar" types could be tagged pointers (references)
> > > as suggested by Volker. A few bits in the pointer could
> > > designate the type and whether the value is contained
> > > within the pointer. As you probably know this is a common
> > > way of implementing "scalar" types in Scheme.
> ...
> >
> > Ok, correction: max slot size 10 byte. Not much different
> > to ~8 (around 8). ;-)
> > i was speculationg a usual floating point number needs 8 byte,
> > a pair! 2* 4-byte integer, so 8 sounded good.
> >
> > Well, with 16 bytes there is space for
> > 1 native pointer/handle(4 bytes)
> > + 10 bytes data
> > + 2 byte something.
> > some kind of type-description + tuple-length?
> > i think this would be most simple to implement
> >
> Yes. This was what I referred to earlier as a "self-relative
> descriptor". That technique has been around since the late
> 60's. A data value is represented by a descriptor, which
> contains type information and a "pointer" to the data.
> To save space and time, however, data which can fit into the
> "pointer" portion of the descriptor are placed there. There
> are some variations on this theme. The decision as to where
> to allocate the data storage may be determined solely by the
> data type (e.g., integer). In this case, such data values
> are not "sharable". OTOH, the decision may be deferred, in
> which case there is a need for a separate bit in the
> descriptor -- the "self-relative" bit -- that indicates whether
> the data is inside the descriptor or simply referenced by the
> descriptor. In this case, even "small" data values may be
> shared.
> The behavior we've been exploring is consistent with the idea
> that REBOL uses a type-dependent descriptor, and implements
> the refinements on DATE! values as special-purpose mutations
> on the self-relative value.
ah! thanks for another part for my lexicon :-)
it's nice to have a more »sound« definition than my
»hm, this piece is here and that's there«
which makes my talking somtimes hard ;-)
Thanks.
> -jn-
Volker
