X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FInstEnv.lhs;h=7aaea5cff768bd204751589e519f104acf5174fa;hb=474b582b68ea9289f3da4355da816164138604b0;hp=560c4fc24be1464a8e0c1835138cc92fbd0b0a7b;hpb=940524aec90652b5ef81789c9a453c57c0e42cc9;p=ghc-hetmet.git

diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs
index 560c4fc..7aaea5c 100644
--- a/compiler/types/InstEnv.lhs
+++ b/compiler/types/InstEnv.lhs
@@ -430,10 +430,11 @@ lookupInstEnv (pkg_ie, home_ie) cls tys
     (pkg_matches,  pkg_unifs)  = lookup pkg_ie  
     all_matches = home_matches ++ pkg_matches
     all_unifs   = home_unifs   ++ pkg_unifs
-    pruned_matches 
-	| null all_unifs = foldr insert_overlapping [] all_matches
-	| otherwise	 = all_matches	-- Non-empty unifs is always an error situation,
-					-- so don't attempt to pune the matches
+    pruned_matches = foldr insert_overlapping [] all_matches
+	-- Even if the unifs is non-empty (an error situation)
+	-- we still prune the matches, so that the error message isn't
+	-- misleading (complaining of multiple matches when some should be
+	-- overlapped away)
 
     --------------
     lookup env = case lookupUFM env cls of