[GHC] #11526: unsafeLookupStaticPtr should not live in IO

[GHC]

#11526: unsafeLookupStaticPtr should not live in IO
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        Reporter:  edsko             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Core Libraries    |              Version:  8.0.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by edsko):

 > Hmm. I'm deeply suspicious of `StaticKey` . It plays no role in our plan
 of record StaticPointers. If we don't have `StaticKey` the whole issue
 doesn't arise.

 `StaticKey` is a low-level implementation detail. I have just added
 support for static pointers to the existing `distributed-static` package,
 based on the support for static pointers that exists in ghc today. The
 higher level API that `distributed-static` exposes is simply that `Static
 a` has a `Binary` instance (for `Typeable a`). But this is precisely where
 the problem is: if looking up a static pointer is not pure, then we cannot
 give a `Binary` instance.

 Facundo's objection is that in fact looking up a static pointer ''isn't''
 pure. If that is true, then `unsafeLookupStaticPtr` should indeed live in
 IO, but then not having `StaticKey` is not going to solve the problem,
 it's just going to move it: whatever shape the decoder of `Static` takes
 (`Binary` instance, separate function, ...) will have to deal with it.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11526#comment:6>
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