[GHC] #8822: Allow -- ^ Haddock syntax on record constructors

[GHC]

#8822: Allow -- ^ Haddock syntax on record constructors
-------------------------------------+-------------------------------------
       Reporter:  Fuuzetsu           |             Owner:
           Type:  feature request    |            Status:  new
       Priority:  normal             |         Milestone:
      Component:  Compiler (Parser)  |           Version:  7.9
       Keywords:                     |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple   |   Type of failure:  None/Unknown
     Difficulty:  Unknown            |         Test Case:
     Blocked By:                     |          Blocking:
Related Tickets:                     |
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 Original ticket is on Haddock Trac
 [http://trac.haskell.org/haddock/ticket/144 here] which I'm opening here
 as it requires lexer/parser changes.

 The idea is that given something like

 {{{
 -- | A tree with labeled internal nodes
 data Tree =
     Empty                -- ^ Leaf
   | Branch               -- ^ Internal node
     { label :: a         -- ^ Node label
     , subtrees :: [Tree] -- ^ List of subtrees
     }
 }}}

 we'd like it to parse as the user would expect instead of failing. We're
 currently forced to do something like

 {{{
 -- | A tree with labeled internal nodes
 data Tree =
     Empty                -- ^ Leaf
   | -- | Internal node
     Branch
     { label :: a         -- ^ Node label
     , subtrees :: [Tree] -- ^ List of subtrees
     }
 }}}

 which is quite ugly. I can't think of a reason why the first form wouldn't
 be allowed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8822>
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