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[REBOL] Re: Does REBOL cons?

From: volker:nitsch:gma:il at: 16-Mar-2006 0:06

Blocks are areas, not lists. On 3/15/06, Jeff Massung <massung-gmail.com> wrote:
> Okay, so, I've been trying something out, comparing REBOL to Lisp. The > functions in REBOL make it appear as though the lists (series!) in REBOL are > just your average conses (first, next, associations, etc). Because of this > and constant data optimizations, etc, this function in REBOL makes sense: > > foo: func [/local a] [ > a: [a b c] > append a [d] > ] > > >> foo > == [a b c d] > > >> foo > == [a b c d d] > > This makes sense, at least, until after the second call. The above function > would be akin to the following Lisp code, which does *almost* the same > thing: > > (defun foo () > (let ((a '(a b c))) > (nconc a '(d)))) > > The main difference being that the second call to (foo) will result in an > infinite list, because '(d) is scoped data, just like '(a b c), and the > second call will cons '(d) with itself, giving us '(a b c d d d d d ...). > > In REBOL, everything seems to match up, except that [d] doesn't cons with > itself. Now, IMO, this is good, desired behavior (not generating an infinite > list). However, what this implies "under-the-hood" is that REBOL doesn't use > traditional consing for lists, but does something else instead. > > I was wondering if anyone could shed a little light on this. If REBOL does > use consing, then why don't I end up with an infinite, self-referencing > list? If it doesn't using consing, what does it use (not that it matters, > I'm just curious)? This is actually a little exciting to me, because if it > isn't using your typical consing, then that means REBOL's associated lists > could potentially be a lot faster than Lisp's (which, of course, have O(n) > access times). > > Jeff M. > > -- > massung-gmail.com > > -- > To unsubscribe from the list, just send an email to > lists at rebol.com with unsubscribe as the subject. >
-- -Volker Any problem in computer science can be solved with another layer of indirection. But that usually will create another problem. David Wheeler