[GHC] #7015: Add support for 'static'

[GHC]

#7015: Add support for 'static'
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              Reporter:  edsko       |            Owner:
                  Type:  feature     |           Status:  patch
  request                            |        Milestone:  7.10.1
              Priority:  normal      |          Version:  7.4.2
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D119   |
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Comment (by facundo.dominguez):

 Forbidding polymorphic types in the static form makes it less obvious
 defining a combinator like the following:
 {{{
 staticCompose :: Static (b -> c) -> Static (a -> b) -> Static (a -> c)
 staticCompose sf sg = staticLabel (static (.)) `staticApply` sf
 `staticApply` sg
 }}}
 This is actually defined in the version of distributed-static in hackage:
 {{{
 composeStatic :: (Typeable a, Typeable b, Typeable c) => Static ((b -> c)
 -> (a -> b) -> a -> c)
 composeStatic = staticLabel "$compose"

 staticCompose :: (Typeable a, Typeable b, Typeable c)
               => Static (b -> c) -> Static (a -> b) -> Static (a -> c)
 staticCompose g f = composeStatic `staticApply` g `staticApply` f
 }}}
 It doesn't mean that we can't live with the restriction, but we will have
 to figure out the impact upwards before committing, I guess.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7015#comment:28>
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