[GHC] #9628: Add Annotations to the AST to simplify source to source conversions

[GHC]

#9628: Add Annotations to the AST to simplify source to source conversions
-------------------------------------+-------------------------------------
              Reporter:  alanz       |            Owner:  alanz
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:  D297        |
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Comment (by alanz):

 The multiple annotation approach seems promising, first stab results in

 Annotation types

 {{{
 #!haskell
 data AnnModule = AnnModule SrcSpan
             deriving (Eq,Data,Typeable,Show)

 data AnnWhere = AnnWhere SrcSpan
             deriving (Eq,Data,Typeable,Show)

 -- Should this be AnnBraces? The tokens are ITocurly / ITccurly
 data AnnCurlies = AnnCurlies (SrcSpan,SrcSpan)
             deriving (Eq,Data,Typeable,Show)

 data AnnSemi = AnnSemi SrcSpan
             deriving (Eq,Data,Typeable,Show)

 data AnnComma = AnnComma SrcSpan
             deriving (Eq,Data,Typeable,Show)

 -- | Pragma declaration, e.g. '{-# SOURCE' '#-}'
 data AnnPragma = AnnPragma (SrcSpan,SrcSpan)
             deriving (Eq,Data,Typeable,Show)

 }}}

 Helper functions in parser

 {{{
 #!haskell
 -- | Given a list of @Maybe annotation@, add the @Just@ ones to the
 -- given location
 ams :: Located a -> [Maybe (SrcSpan -> P ())] -> P (Located a)
 ams a@(L l _) bs = (mapM_ (\a -> a l) $ catMaybes bs) >> return a

 mj :: (Outputable a,Typeable a,Show a,Eq a)
    => (SrcSpan -> a) -> Located e -> Maybe (SrcSpan -> P ())
 mj c l = Just (\s -> addAnnotation s (c (gl $l)))

 mm :: (Outputable a,Typeable a,Show a,Eq a)
    => (SrcSpan -> a) -> Maybe SrcSpan -> Maybe (SrcSpan -> P ())
 mm c Nothing = Nothing
 mm c (Just l) = Just (\s -> addAnnotation s (c l))

 mm2 :: (Outputable a,Typeable a,Show a,Eq a)
     => ((SrcSpan,SrcSpan) -> a) -> Maybe (SrcSpan,SrcSpan)
     -> Maybe (SrcSpan -> P ())
 mm2 c Nothing = Nothing
 mm2 c (Just (l1,l2)) = Just (\s -> addAnnotation s (c (l1,l2)))

 }}}

 Example rule in parser

 {{{
 module  :: { Located (HsModule RdrName) }
         : maybedocheader 'module' modid maybemodwarning maybeexports
 'where' body
                 {% fileSrcSpan >>= \ loc ->
                    ams (L loc (HsModule (Just $3) $5 (fst $ snd $7) (snd $
 snd $7) $4 $1
                       ) )
                      [mj AnnModule $3, mj AnnWhere $6
                      ,mm2 AnnCurlies (fst $ fst $7),mm AnnSemi (snd $ fst
 $7)] }

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9628#comment:23>
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