[GHC] #11726: Document change in implicit quantification

[GHC]

#11726: Document change in implicit quantification
-------------------------------------+-------------------------------------
           Reporter:  goldfire       |             Owner:
               Type:  task           |            Status:  new
           Priority:  high           |         Milestone:  8.0.1
          Component:  Documentation  |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Simon's big wildcard refactor (1e041b7382b6aa329e4ad9625439f811e0f27232)
 changed the way GHC does implicit quantification. I don't see
 documentation for this, however. (That patch doesn't touch the manual, and
 there are no release notes, at least.)

 This report was prompted by [https://mail.haskell.org/pipermail/haskell-
 cafe/2016-March/123487.html this Haskell-Café post], where Tom Ellis asks
 why we need

 {{{
    -data PackMap a b s t = PackMap (Applicative f => (a -> f b) -> s -> f
 t)
    +data PackMap a b s t = PackMap (forall f. Applicative f => (a -> f b)
 -> s -> f t)
 }}}

 to update for 8.0.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11726>
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