Fix Trac #3013: multiple constructors in a GADT decl

Makes GADT syntax consistent by allowing multiple constructors
to be given a single signature
   data T wehre
       A, B :: T
       C :: Int -> t

diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index f9976b4..7465adb 100644 (file)
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -1150,9 +1150,9 @@ gadt_constrlist :: { Located [LConDecl RdrName] }
        |     vocurly    gadt_constrs close     { $2 }
 
 gadt_constrs :: { Located [LConDecl RdrName] }
-        : gadt_constrs ';' gadt_constr  { LL ($3 : unLoc $1) }
+        : gadt_constrs ';' gadt_constr  { sL (comb2 $1 (head $3)) ($3 ++ unLoc $1) }
         | gadt_constrs ';'             { $1 }
-        | gadt_constr                   { L1 [$1] } 
+        | gadt_constr                   { sL (getLoc (head $1)) $1 } 
 
 -- We allow the following forms:
 --     C :: Eq a => a -> T a
@@ -1160,15 +1160,15 @@ gadt_constrs :: { Located [LConDecl RdrName] }
 --     D { x,y :: a } :: T a
 --     forall a. Eq a => D { x,y :: a } :: T a
 
-gadt_constr :: { LConDecl RdrName }
-        : con '::' sigtype
-              { LL (mkGadtDecl $1 $3) } 
+gadt_constr :: { [LConDecl RdrName] }
+        : con_list '::' sigtype
+                { map (sL (comb2 $1 $3)) (mkGadtDecl (unLoc $1) $3) } 
         -- Syntax: Maybe merge the record stuff with the single-case above?
         --         (to kill the mostly harmless reduce/reduce error)
         -- XXX revisit audreyt
        | constr_stuff_record '::' sigtype
                { let (con,details) = unLoc $1 in 
-                 LL (ConDecl con Implicit [] (noLoc []) details (ResTyGADT $3) Nothing) }
+                 [LL (ConDecl con Implicit [] (noLoc []) details (ResTyGADT $3) Nothing)] }
 {-
        | forall context '=>' constr_stuff_record '::' sigtype
                { let (con,details) = unLoc $4 in 
@@ -1728,6 +1728,10 @@ con      :: { Located RdrName }
        | '(' consym ')'        { LL (unLoc $2) }
        | sysdcon               { L1 $ nameRdrName (dataConName (unLoc $1)) }
 
+con_list :: { Located [Located RdrName] }
+con_list : con                  { L1 [$1] }
+         | con ',' con_list     { LL ($1 : unLoc $3) }
+
 sysdcon        :: { Located DataCon }  -- Wired in data constructors
        : '(' ')'               { LL unitDataCon }
        | '(' commas ')'        { LL $ tupleCon Boxed $2 }

diff --git a/compiler/parser/RdrHsSyn.lhs b/compiler/parser/RdrHsSyn.lhs
index 187d64d..3ca1b29 100644 (file)
--- a/compiler/parser/RdrHsSyn.lhs
+++ b/compiler/parser/RdrHsSyn.lhs
@@ -28,7 +28,7 @@ module RdrHsSyn (
                              -- -> (FastString, RdrName, RdrNameHsType)
                              -- -> P RdrNameHsDecl
        mkExtName,           -- RdrName -> CLabelString
-       mkGadtDecl,          -- Located RdrName -> LHsType RdrName -> ConDecl RdrName
+       mkGadtDecl,          -- [Located RdrName] -> LHsType RdrName -> ConDecl RdrName
                              
        -- Bunch of functions in the parser monad for 
        -- checking and constructing values
@@ -813,11 +813,19 @@ checkValSig (L l (HsVar v)) ty
 checkValSig (L l _)         _
   = parseError l "Invalid type signature"
 
-mkGadtDecl :: Located RdrName
+mkGadtDecl :: [Located RdrName]
            -> LHsType RdrName -- assuming HsType
-           -> ConDecl RdrName
-mkGadtDecl name (L _ (HsForAllTy _ qvars cxt ty)) = mk_gadt_con name qvars cxt ty
-mkGadtDecl name ty                               = mk_gadt_con name [] (noLoc []) ty
+           -> [ConDecl RdrName]
+-- We allow C,D :: ty
+-- and expand it as if it had been 
+--    C :: ty; D :: ty
+-- (Just like type signatures in general.)
+mkGadtDecl names ty
+  = [mk_gadt_con name qvars cxt tau | name <- names]
+  where
+    (qvars,cxt,tau) = case ty of
+                       L _ (HsForAllTy _ qvars cxt tau) -> (qvars, cxt,      tau)
+                       _                                -> ([],    noLoc [], ty)
 
 mk_gadt_con :: Located RdrName
             -> [LHsTyVarBndr RdrName]

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 3120601..d23da18 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -2353,6 +2353,16 @@ otherwise is a <emphasis>generalised</emphasis> data type (<xref linkend="gadt"/
 </para></listitem>
 
 <listitem><para>
+As with other type signatures, you can give a single signature for several data constructors.
+In this example we give a single signature for <literal>T1</literal> and <literal>T2</literal>:
+<programlisting>
+  data T a where
+    T1,T2 :: a -> T a
+    T3 :: T a
+</programlisting>
+</para></listitem>
+
+<listitem><para>
 The type signature of
 each constructor is independent, and is implicitly universally quantified as usual. 
 Different constructors may have different universally-quantified type variables