[Haskell-cafe] Cleaning up stable names?

Peter Verswyvelen bugfact at gmail.com
Tue Sep 1 14:57:50 EDT 2009

Yes that is possible too. But it feels "obvious" to first lookup by
stable name. I had no idea stable names were so volatile. They should
be called unstable names then :-)

In .NET it is possible to assign an identifier to an object, and that
identifier will always be the same for the same object, no matter
where to garbage collectors moves the object in memory. For Haskell,
at first sight it would feel natural to have something like that too.

On Tue, Sep 1, 2009 at 8:31 PM, Luke Palmer<lrpalmer at gmail.com> wrote:
> Have you considered computing a hash of the scene graph description
> (compositionally)?  This gives you all the same advantages, including
> re-using shared subparts of the graph (which would be unlikely to stay
> around for very long as stable names).
> Luke
> On Tue, Sep 1, 2009 at 11:02 AM, Peter Verswyvelen<bugfact at gmail.com> wrote:
>> I was planning to use them for caching OpenGL display lists and render
>> targets. These are generated from a pure scene graph description, and
>> if the same description is handed over to the render engine, it would
>> just reuse the previously cached OpenGL object.  I can of course just
>> embedding and IORef inside the pure structures, that would also work I
>> guess
>> On Tue, Sep 1, 2009 at 6:09 PM, Job Vranish<jvranish at gmail.com> wrote:
>>> Well usually, when I've used stable names, I've just used them to check if
>>> things are the same, and then thrown them away. So no chance for a space
>>> leak. It's usually unsafe to keep stable names around for very long as they
>>> can lose their ability to tell if two things are the same (if this surprises
>>> you, you should carefully reread
>>> http://haskell.org/ghc/docs/latest/html/libraries/base/System-Mem-StableName.html#v%3AmakeStableName
>>> ).
>>> Out of curiosity, how are you planning on using them?
>>> - Job
>>> On Tue, Sep 1, 2009 at 3:40 AM, Peter Verswyvelen <bugfact at gmail.com> wrote:
>>>> but without that function, stable names are not that useful I guess? they
>>>> would cause a space leak?
>>>> On Mon, Aug 31, 2009 at 10:59 PM, Job Vranish <jvranish at gmail.com> wrote:
>>>>> I also would like a isStableNameTargetAlive function.
>>>>> Though if you had such a function then you probably _could_ make a
>>>>> deRefStableName function, which, since there isn't one, probably means that
>>>>> such a function would be hard to make.
>>>>> - Job
>>>>> On Sun, Aug 30, 2009 at 4:54 PM, Peter Verswyvelen <bugfact at gmail.com>
>>>>> wrote:
>>>>>> >From the documentation, I don't think I grasp how stable names work.
>>>>>> From the docs:
>>>>>> "There is no deRefStableName operation. You can't get back from a stable
>>>>>> name to the original Haskell object. The reason for this is that the
>>>>>> existence of a stable name for an object does not guarantee the existence of
>>>>>> the object itself; it can still be garbage collected."
>>>>>> From this I can conclude that stable names behave a bit like weak
>>>>>> pointers.
>>>>>> However, suppose I have a hash table of these stable names. How can I
>>>>>> remove the redundant stable names from the table? I mean removing stable
>>>>>> names that refer to an object that is garbage collected? I don't see any
>>>>>> function for checking that (e.g. isStableNameTargetAlive or something)
>>>>>> Thanks,
>>>>>> Peter
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