[GHC] #3384: Add HsSyn prettyprinter tests

[GHC]

#3384: Add HsSyn prettyprinter tests
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        Reporter:  igloo             |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Test Suite        |              Version:
      Resolution:                    |             Keywords:
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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Comment (by alanz):

 The current AST does not allow faithful reproduction of a context with
 extra parens around it.  So

 {{{#!hs
 foo :: (Show a) => a -> String
 }}}
 and
 {{{#!hs
 foo :: ((Show a)) => a -> String
 }}}

 produce the same AST fragment.  `ghc-exactprint` works around this by
 using the API Annotations.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3384#comment:10>
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