[GHC] #11028: Refactor ConDecl

[GHC]

#11028: Refactor ConDecl
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           Reporter:  simonpj        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The `ConDecl` type in `HsDecls` is an uneasy compromise.  For the most
 part, `HsSyn` directly reflects the syntax written by the programmer; and
 that gives just the right "pegs" on which to hang Alan's
 [wiki:ApiAnnotations API annotations].  But `ConDecl` doesn't properly
 reflect the syntax of Haskell-98 and GADT-style data type declarations.

 To be concrete, here's a draft new data type
 {{{
 data ConDecl name
   | ConDeclGADT
       { con_names   :: [Located name]
       , con_type    :: LHsSigType name  -- The type after the ‘::’
       , con_doc     :: Maybe LHsDocString
       , con_old_rec :: Bool }

   | ConDeclH98
       { con_name    :: Located name

       , con_implict  :: HsImplicitBndrs ()
         -- ^ Implicit binders, added by renamer

       , con_qvars     :: Maybe [LHsTyVarBndr name]
         --  User-written foralls (if any)

       , con_cxt       :: Maybe (LHsContext name)
         -- ^ User-written context (if any)

       , con_details   :: HsConDeclDetails name
           -- ^ Arguments

       , con_doc       :: Maybe LHsDocString
           -- ^ A possible Haddock comment.
       } deriving (Typeable)
 }}}
 Note that
  * For GADTs, just keep a type.  That's what the user writes.  (NB:
 `HsType` can represent records on the LHS of an arrow: `{ x:Int,y:Bool }
 -> T`

  * `con_qvars` and `con_cxt` are both `Maybe` because they are both
 optional (the `forall` and the context of an existential data type)

  * The `con_old_rec` is a warning thing for GADTs (see current source
 code)

 This ticket is just to track the thought and invite feedback.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11028>
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