[GHC] #13735: RankNTypes don't work with PatternSynonyms

[GHC]

#13735: RankNTypes don't work with PatternSynonyms
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 data PLambda a = Var a | Int Int | Bool Bool | If (PLambda a) (PLambda a)
 (PLambda a)
   | Add (PLambda a) (PLambda a) | Mult (PLambda a) (PLambda a)
   | Eq  (PLambda a) (PLambda a) | Lam (a -> PLambda a)
   | App (PLambda a) (PLambda a)

 newtype Lam = L { un :: forall a. PLambda a }
 }}}

 {{{#!hs
 llam :: (forall a. a -> PLambda a) -> Lam
 llam f = L (Lam f)
 }}}

 works fine, but does not with pattern synonyms:

 {{{
 -- $ ghci -ignore-dot-ghci tirr.hs
 -- GHCi, version 8.2.0.20170507: http://www.haskell.org/ghc/  :? for help
 -- [1 of 1] Compiling Main             ( tirr.hs, interpreted )
 --
 -- tirr.hs:20:25: error:
 --     • Couldn't match expected type ‘forall a. a -> PLambda a’
 --                   with actual type ‘a0 -> PLambda a0’
 --     • In the declaration for pattern synonym ‘LLam’
 --     • Relevant bindings include
 --         a :: a0 -> PLambda a0 (bound at tirr.hs:20:25)
 --    |
 -- 20 | pattern LLam a = L (Lam a)
 --    |                         ^
 -- Failed, modules loaded: none.
 -- Prelude>

 pattern LLam :: (forall a. a -> PLambda a) -> Lam
 pattern LLam a = L (Lam a)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13735>
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