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

[GHC]

#7619: Make worker-wrapper unbox data families
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        Reporter:  akio              |            Owner:  nomeata
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:  type family
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonpj):

 The package inst-env get extended by a kind of side effect when we lad new
 modules. The home-package inst env doesn't. You could combine them into
 one and pass one instead of a pair, but not much would be gained, and
 there'd be some extra computation to build the combined env that might
 only be interrogated once.

 Nothing deep

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7619#comment:7>
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