[GHC] #13498: More storable instances?

[GHC]

#13498: More storable instances?
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        Reporter:  wyager            |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries/base    |              Version:  8.0.1
      Resolution:                    |             Keywords:  Storable,
                                     |  Foreign, Ptr
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 wyager):

 > the encoding would be quite arbitrary

 How is this an argument against adding the encodings? If they function
 correctly, why does it matter that they aren't "fixed" in some sense?

 > Why are the tags 8 bit wide, and why are the tag values 0 and 1?

 Because it makes sense and works. Why, for a {{{Ratio}}}, is the numerator
 stored before the denominator? Presumably for the same reason. The choice
 of representation doesn't really matter a whole lot; the point of this
 feature request isn't to bikeshed over the exact implementation, but to
 establish if there's some fundamental stumbling block with this approach.

 > then there is the issue of alignment

 I *think* my `lcm` trick solves this for sum types. For product types,
 there are some obvious approaches.

 > If you need serialization, you can use `Data.Binary`.

 Besides `Data.Binary` being vastly slower than `Storable`, the primary use
 case here is `Data.Vector.Storable`  and `Data.Array.Storable`. You can't
 write an `Unbox` instance for `Maybe a`, but you can (as I've done here)
 write a `Storable` instance.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13498#comment:2>
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