[GHC] #14587: Unidirectional pattern signatures do not need to be invariant w.r.t. higher-rank polymorphism

[GHC]

#14587: Unidirectional pattern signatures do not need to be invariant w.r.t.
higher-rank polymorphism
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           Reporter:  goldfire       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           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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 Best explained by example:

 {{{#!hs
 data T = MkT (forall a. a -> a)

 pattern PT :: (Int -> Int) -> T
 pattern PT x <- MkT x
 }}}

 This looks perfectly reasonable to me. And the hand-written matcher is
 also accepted. Note that a similar bidirectional pattern synonym should
 indeed be rejected.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14587>
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