[GHC] #6069: Rank 2 Polymorphism Compile Error

[GHC]

#6069: Rank 2 Polymorphism Compile Error
--------------------------+-------------------------------------------------
 Reporter:  clinton       |          Owner:                
     Type:  bug           |         Status:  new           
 Priority:  normal        |      Component:  Compiler      
  Version:  7.4.1         |       Keywords:                
       Os:  Windows       |   Architecture:  x86_64 (amd64)
  Failure:  None/Unknown  |       Testcase:                
Blockedby:                |       Blocking:                
  Related:                |  
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 Not sure if this is a bug, perhaps this should be a feature request.

 Given the following code:


 {{{
 {-# LANGUAGE Rank2Types #-}

 import Control.Monad.ST
 import Data.STRef

 fourty_two :: forall s. ST s Int
 fourty_two = do
   x <- newSTRef (42::Int)
   readSTRef x

 main = (print . runST) fourty_two -- (1)
 main = (print . runST) $ fourty_two -- (2)
 main = ((print . runST) $) fourty_two -- (3)
 }}}


 (1) and (3) compile successfully, but (2) does not. I'm not sure why this
 is the case.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6069>
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