From: simonmar <unknown>
Date: Wed, 10 Apr 2002 13:09:39 +0000 (+0000)
Subject: [project @ 2002-04-10 13:09:39 by simonmar]
X-Git-Tag: Approx_11550_changesets_converted~2163
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=07c456df1f21bb2291a18ada0e2d749f1ea52c17;p=ghc-hetmet.git

[project @ 2002-04-10 13:09:39 by simonmar]
(from Simon P.J) Make generics work with zero-constructor datatypes.
---

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