X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcTyClsDecls.lhs;h=89afedfda8ea757cf3f95eadc40de2bea19bac76;hb=19b44dcc5e5b9f92735fa99aa45dfaa94777177c;hp=3880f1f956e7b7bd9bbaf037679fc4d87b816891;hpb=0ed91c9c2e3e252af15b6dd69e3f682aebaad118;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcTyClsDecls.lhs b/compiler/typecheck/TcTyClsDecls.lhs
index 3880f1f..89afedf 100644
--- a/compiler/typecheck/TcTyClsDecls.lhs
+++ b/compiler/typecheck/TcTyClsDecls.lhs
@@ -1054,6 +1054,9 @@ checkValidDataCon tc con
     addErrCtxt (dataConCtxt con)		$ 
     do	{ checkTc (dataConTyCon con == tc) (badDataConTyCon con)
 	; checkValidType ctxt (dataConUserType con)
+	; checkValidMonoType (dataConOrigResTy con)
+		-- Disallow MkT :: T (forall a. a->a)
+		-- Reason: it's really the argument of an equality constraint
 	; ifM (isNewTyCon tc) (checkNewDataCon con)
     }
   where
@@ -1214,7 +1217,7 @@ badGadtDecl tc_name
 
 badExistential con_name
   = hang (ptext SLIT("Data constructor") <+> quotes (ppr con_name) <+>
-		ptext SLIT("has existential type variables, or a context, or both"))
+		ptext SLIT("has existential type variables, or a context"))
        2 (parens $ ptext SLIT("Use -XExistentialQuantification or -XGADTs to allow this"))
 
 badStupidTheta tc_name