[racket] Understanding GC when working with streams

Ever? Or for the purpose discussed earlier?
 On Sep 9, 2013 7:17 AM, "Matthias Felleisen" <matthias at ccs.neu.edu> wrote:

>
> I wonder whether you really want lazy streams. -- Matthias
>
>
>
> On Sep 9, 2013, at 10:19 AM, Lawrence Woodman wrote:
>
> > On 09/09/13 07:19, Stephen Chang wrote:
> >> Konrad's exactly right. Your filtered-nums blows up because you named
> >> the stream and then traversed the entire thing. In general, if you
> >> hang onto the head of the stream while traversing then the GC can't
> >> collect anything because since you have a pointer to the head, every
> >> element of the stream is still reachable.
> >>
> >> Compare to a common traversal pattern like:
> >>
> >>     (let loop ([s <some stream>]) ... (loop (stream-rest s)))
> >>
> >> where the head is dropped on each loop iteration.
> >>
> >> Other comments:
> >> - (stream-length (gen-filtered-nums)) is fine because there's no
> >> pointer to the head, so the GC collects as you traverse.
> >>
> >> - in-range is fine because it's constant space and not a
> >> cons-cell-based stream. It's more like a generator.
> >>
> >> - the for/sum is actually collecting while traversing, just more
> >> slowly. I'm not exactly sure why, I may look into it. On my machine,
> >> it got up to 500mb or so but it finished.
> >
> > Thanks, and to Konrad too.  You're mention of in-range being more
> > like a generator, actually makes me wonder whether a generator would
> > be a better choice for processing large data sets, from databases and
> > csv files, sequentially.  What do you think?
> >
> >
> > Lorry
> >
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