Refactor ConDeclwip/T11028-2

Summary:
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 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 }

  | ConDeclH98
      { con_name    :: Located name

      , con_qvars     :: Maybe (LHsQTyVars name)
        -- User-written forall (if any), and its implicit
        -- kind variables
        -- Non-Nothing needs -XExistentialQuantification

      , 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

    For ConDeclGADT the type variables of the data type do not scope
    over the con_type; whereas for ConDeclH98 they do scope over con_cxt
    and con_details.

Test Plan: ./validate

Reviewers: simonpj, austin, goldfire, bgamari

Subscribers: goldfire, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D1558

GHC Trac Issues: #11028

1 files changed, 5 insertions, 7 deletions

diff --git a/compiler/parser/Parser.y b/compiler/parser/Parser.y
index fb5c8dbd45..bbde989293 100644
--- a/compiler/parser/Parser.y
+++ b/compiler/parser/Parser.y
@@ -1895,10 +1895,9 @@ gadt_constr_with_doc
 gadt_constr :: { LConDecl RdrName }
     -- see Note [Difference in parsing GADT and data constructors]
     -- Returns a list because of:   C,D :: ty
-        : con_list '::' ctype
-                {% do { let { (anns,gadtDecl) = mkGadtDecl (unLoc $1) $3 }
-                      ; ams (sLL $1 $> gadtDecl)
-                            (mu AnnDcolon $2:anns) } }
+        : con_list '::' sigtype
+                {% ams (sLL $1 $> (mkGadtDecl (unLoc $1) (mkLHsSigType $3)))
+                       [mu AnnDcolon $2] }
 
 {- Note [Difference in parsing GADT and data constructors]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1925,13 +1924,13 @@ constrs1 :: { Located [LConDecl RdrName] }
 constr :: { LConDecl RdrName }
         : maybe_docnext forall context '=>' constr_stuff maybe_docprev
                 {% ams (let (con,details) = unLoc $5 in
-                  addConDoc (L (comb4 $2 $3 $4 $5) (mkSimpleConDecl con
+                  addConDoc (L (comb4 $2 $3 $4 $5) (mkConDeclH98 con
                                                    (snd $ unLoc $2) $3 details))
                             ($1 `mplus` $6))
                         (mu AnnDarrow $4:(fst $ unLoc $2)) }
         | maybe_docnext forall constr_stuff maybe_docprev
                 {% ams ( let (con,details) = unLoc $3 in
-                  addConDoc (L (comb2 $2 $3) (mkSimpleConDecl con
+                  addConDoc (L (comb2 $2 $3) (mkConDeclH98 con
                                            (snd $ unLoc $2) (noLoc []) details))
                             ($1 `mplus` $4))
                        (fst $ unLoc $2) }
@@ -2671,7 +2670,6 @@ stmtlist :: { Located ([AddAnn],[LStmt RdrName (LHsExpr RdrName)]) }
 -- here, because we need too much lookahead if we see do { e ; }
 -- So we use BodyStmts throughout, and switch the last one over
 -- in ParseUtils.checkDo instead
--- AZ: TODO check that we can retrieve multiple semis.
 
 stmts :: { Located ([AddAnn],[LStmt RdrName (LHsExpr RdrName)]) }
         : stmts ';' stmt  {% if null (snd $ unLoc $1)