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

[GHC]

#13735: RankNTypes don't work with PatternSynonyms
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by Iceland_jack:

@@ -18,1 +18,1 @@
- {{{
+ {{{#!hs

New description:

 {{{#!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:

 {{{#!hs
 -- $ 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)
 }}}

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13735#comment:2>
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