X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypes%2FGenerics.lhs;fp=ghc%2Fcompiler%2Ftypes%2FGenerics.lhs;h=744b667980e98a0f7a9455329000112ab62efdb6;hb=07c456df1f21bb2291a18ada0e2d749f1ea52c17;hp=d961aa8e4ea8204aa18fda959a06c478d1d47789;hpb=c1f3fad183f553aa46ec9dea33999f387014fded;p=ghc-hetmet.git

diff --git a/ghc/compiler/types/Generics.lhs b/ghc/compiler/types/Generics.lhs
index d961aa8..744b667 100644
--- a/ghc/compiler/types/Generics.lhs
+++ b/ghc/compiler/types/Generics.lhs
@@ -254,8 +254,12 @@ mkTyConGenInfo tycon [from_name, to_name]
        | dc <- datacons ]
   = Nothing
 
+  | null datacons	-- There are no constructors; 
+  = Nothing		-- there are no values of this type
+
   | otherwise
-  = Just (EP { fromEP = mkVanillaGlobal from_name from_ty from_id_info,
+  = ASSERT( not (null datacons) )	-- mk_sum_stuff loops if no datacons
+    Just (EP { fromEP = mkVanillaGlobal from_name from_ty from_id_info,
 	       toEP   = mkVanillaGlobal to_name   to_ty   to_id_info })
   where
     maybe_datacons = tyConDataCons_maybe tycon