[GHC] #11032: Missing result type handling for State# s in foreign import prim.

[GHC]

#11032: Missing result type handling for State# s in foreign import prim.
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        Reporter:  ekmett            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (FFI)    |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 I see in `TcType` this comment:
 {{{
 Note [Marshalling VoidRep]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 We don't treat State# (whose PrimRep is VoidRep) as marshalable.
 In turn that means you can't write
         foreign import foo :: Int -> State# RealWorld

 Reason: the back end falls over with panic "primRepHint:VoidRep";
         and there is no compelling reason to permit it
 }}}
 I don't think there is any fundamental reason not to allow this.  Would
 someone like to free it up?  It'd mean looking at that `ptrRepHint` stuff.
 Thanks!

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11032#comment:2>
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