Empty forall should disable implicit quantification

diff --git a/ghc/compiler/hsSyn/HsTypes.lhs b/ghc/compiler/hsSyn/HsTypes.lhs
index 76076ff..f1343a3 100644 (file)
--- a/ghc/compiler/hsSyn/HsTypes.lhs
+++ b/ghc/compiler/hsSyn/HsTypes.lhs
@@ -177,10 +177,14 @@ mkHsForAllTy exp tvs (L _ []) ty = mk_forall_ty exp tvs ty
 mkHsForAllTy exp tvs ctxt ty = HsForAllTy exp tvs ctxt ty
 
 -- mk_forall_ty makes a pure for-all type (no context)
-mk_forall_ty Explicit [] ty                          = unLoc ty        -- Explicit for-all with no tyvars
-mk_forall_ty exp  tvs  (L _ (HsParTy ty))                    = mk_forall_ty exp tvs ty
+mk_forall_ty exp  tvs  (L _ (HsParTy ty))                  = mk_forall_ty exp tvs ty
 mk_forall_ty exp1 tvs1 (L _ (HsForAllTy exp2 tvs2 ctxt ty)) = mkHsForAllTy (exp1 `plus` exp2) (tvs1 ++ tvs2) ctxt ty
-mk_forall_ty exp  tvs  ty                            = HsForAllTy exp tvs (L noSrcSpan []) ty
+mk_forall_ty exp  tvs  ty                                  = HsForAllTy exp tvs (L noSrcSpan []) ty
+       -- Even if tvs is empty, we still make a HsForAll!
+       -- In the Implicit case, this signals the place to do implicit quantification
+       -- In the Explicit case, it prevents implicit quantification    
+       --      (see the sigtype production in Parser.y.pp)
+       --      so that (forall. ty) isn't implicitly quantified
 
 Implicit `plus` Implicit = Implicit
 exp1     `plus` exp2     = Explicit