[Haskell-cafe] how to check thunk

Austin Seipp mad.one at gmail.com
Mon Jul 2 14:13:26 CEST 2012

Hi Rico,

This is certainly a possibility I have not considered. However, I
still think the Right Way Forward is to ultimately deprecate the
current package as quickly as possible and move its outstanding
functionality into GHC. Vacuum is still undeniably useful for older
GHCs, so I would be willing to maintain the current package past that
point. But GHC is quick moving, and considering how Vacuum is so
closely linked to its internals, I think overall this is the right
thing to do to reduce maintenance burden in the long haul (and it
would certainly reduce a lot of code, since a good portion of it
exists in GHC already as I mentioned.)

I'm not completely opposed to other options here, and it's not
entirely my decision either - in particular, it does add more code to
GHC, which GHC HQ has to maintain possibly past my lifetime as a
contributor. So I'm open to being convinced otherwise.

On Mon, Jul 2, 2012 at 6:15 AM, Rico Moorman <rico.moorman at gmail.com> wrote:
> Dear Austin,
> Wouldn't it be a good idea to link the Vacuum version-number to the
> related ghc version number directly as it's functionality is directly
> tied to the ghc version anyway.
> vacuum 7.4 for ghc 7.4; vacuum 7.2 for ghc 7.2 aso.
> Best regards,
> Rico Moorman
> On Mon, Jul 2, 2012 at 12:04 PM, Austin Seipp <mad.one at gmail.com> wrote:
>> Hi,
>> Just a word of note: a while back, I decided to take up maintainership
>> of Vacuum and some associated stuff. In the process of doing this, I
>> realized that the ClosureType code in vacuum may not accurately model
>> reality depending on the GHC version. In particular, the definition of
>> ClosureType in vacuum as currently released on Hackage is woefully out
>> of date with respect to Modern GHC. Matt Morrow it seems originally
>> just copied the definition wholesale when he developed it, but as GHC
>> has evolved, so too has the ClosureType definition. Vacuum has not
>> kept up.
>> I have a github repository[1] containing several cleanups of Vacuum
>> which I'm calling Vacuum 2.0, one of these cleanups being that the
>> ClosureType definition is automatically generated from the GHC
>> definition, and compiled-in accordingly. I have also dropped support
>> for older GHCs (although it could be re-added.)
>> In this case, based on the changes I made I believe it is fairly
>> unlikely that isThunk would turn up being wrong here. The THUNK*
>> definitions seem to have been relatively untouched over GHC's
>> evolution. But for more advanced functionality, it could possibly
>> result in Vacuum as it stands constructing an invalid heap
>> representation based on object misinterpretations.
>> I have been busy with a new job but I am not totally absent, and I
>> think I will take this opportunity to release v2.0 in short order,
>> which is mostly intended as a polish and maintenance release for
>> modern GHCs. In the future I would like to see vacuum deprecated and
>> move all its functionality into GHC - much of the code is deeply
>> intertwined with GHC's runtime representations and in some cases I
>> have seen code in the package that was literally copied verbatim from
>> the GHC sources itself, obviously dating several years. It's hard to
>> assess the validity of much of this code. All of this feels brittle
>> and makes me uneasy, and given the complexity of the package as it
>> stands, will make it extremely difficult to maintain as GHC moves
>> forward.
>> Sorry for the ramble, but I figured it might be relevant if people are
>> going to rely on this functionality.
>> [1] https://github.com/thoughtpolice/vacuum
>> On Mon, Jul 2, 2012 at 2:54 AM, Erik Hesselink <hesselink at gmail.com> wrote:
>>> There is also the 'isevaluated' package (which depends on vacuum, but
>>> seems to do something more involved than your code).
>>> Erik
>>> On Mon, Jul 2, 2012 at 7:40 AM, Chaddaï Fouché <chaddai.fouche at gmail.com> wrote:
>>>> On Mon, Jul 2, 2012 at 5:29 AM, Kazu Yamamoto <kazu at iij.ad.jp> wrote:
>>>>> Hello,
>>>>> Are there any ways to see if a value is a thunk or memorized?
>>>>> I would like to have a function like:
>>>>>   isThunk :: a -> IO Bool
>>>> vacuum allow that and much more though I don't know if it still works
>>>> correctly on GHC 7.4. Anyway your isThunk is
>>>>> isThunk a = fmap GHC.Vacuum.ClosureType.isThunk GHC.Vacuum.closureType
>>>> (Feel free to arrange your imports to make that a bit more readable ;)
>>>> http://hackage.haskell.org/package/vacuum
>>>> --
>>>> Jedaï
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>> --
>> Regards,
>> Austin
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