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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:36.0pt">
That's explained in the paper. A StableName# is a pointer to a stable name object in the heap that *contains* an index into the stable name table. Basically, the garbage collector needs to know whether a stable name is alive or not, so it can work out when
to clear it from the table.<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Very good. But could it be explained in a Note too? The paper is from a long time ago, contains lots of surrounding explanation, and might well be out of date (even if it in fact is not out of date).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">So the entry in the table /also/ points to the same, heap-allocated StableName#? Doesn’t that keep it alive? Or is this akin to the treatment of weak pointers? (Which is part of the same paper.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Do we anywhere keep a pointer to the object that this is a stable name of?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> David Feuer <david.feuer@gmail.com>
<br>
<b>Sent:</b> 21 August 2018 09:25<br>
<b>To:</b> Simon Peyton Jones <simonpj@microsoft.com><br>
<b>Cc:</b> David Feuer <david@well-typed.com>; ghc-devs <ghc-devs@haskell.org>; marlowsd@gmail.com<br>
<b>Subject:</b> Re: Stable name equality<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<o:p> </o:p></p>
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On Tue, Aug 21, 2018, 3:39 AM Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<br>
Actually I'm confused. Currently we have<br>
<br>
data StableName a = StableName (StableName# a)<br>
<br>
I believe (but there is no documentation to state) that the (StableName# a) <br>
* Has kind (TYPE UnliftedRep)<br>
* Is the index of the entry in the Stable Name Table<br>
<br>
But if it's the index, why isn't it an IntRep? UnliftedRep is for pointers?<o:p></o:p></p>
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<o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
That's explained in the paper. A StableName# is a pointer to a stable name object in the heap that *contains* an index into the stable name table. Basically, the garbage collector needs to know whether a stable name is alive or not, so it can work out when
to clear it from the table.<o:p></o:p></p>
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<o:p> </o:p></p>
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<br>
Moreover eqStableName# :: StableName# a -> StableName# b -> Bool<br>
is directly implemented in the code generator (StgCmmPrim) by an equality<br>
comparison.<br>
<br>
If these things are correct, it would be great to write them down in a Note.<br>
<br>
And if they are right, I'm now lost about what you question is. Equality is<br>
/already/ implemented by direct equality comparison, no?<o:p></o:p></p>
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<o:p> </o:p></p>
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It's currently implemented by an equality test on the indices stored in the stable name objects, rather than the pointers to those objects, if I'm not very much mistaken.<o:p></o:p></p>
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