From 07c456df1f21bb2291a18ada0e2d749f1ea52c17 Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Wed, 10 Apr 2002 13:09:39 +0000
Subject: [PATCH] [project @ 2002-04-10 13:09:39 by simonmar] (from Simon P.J)
 Make generics work with zero-constructor datatypes.

---
 ghc/compiler/types/Generics.lhs |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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
-- 
1.7.10.4