[GHC] #7619: Make worker-wrapper unbox data families

[GHC]

#7619: Make worker-wrapper unbox data families
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    Reporter:  akio              |       Owner:                  
        Type:  feature request   |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  Compiler          |     Version:  7.7             
    Keywords:  type family       |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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Changes (by simonpj):

  * difficulty:  => Unknown


Comment:

 Yes absolutely.  The trick here is that

  * To get from `(Foo Int)` to the underlying data type involves generating
 a coercion.
  * So if `foo` wants to unbox its argument, the worker/wrapper code must
 include coercions.
  * Where do those coercions come from?  You need the type-family instance
 environment, and even then it's a bit dodgy to be looking them up in the
 optimiser.
  * Or maybe we can gather them from the code itself during analysis, and
 keep them in the demand signature.

 Same thing happens in CPR I think

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7619#comment:1>
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