X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FInstEnv.lhs;h=15a0c30e770e86a6354a3a7f8e0ad1284272a14d;hb=d9e439063bbd9827df7a6f75471834d8479c3ea3;hp=560c4fc24be1464a8e0c1835138cc92fbd0b0a7b;hpb=940524aec90652b5ef81789c9a453c57c0e42cc9;p=ghc-hetmet.git

diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs
index 560c4fc..15a0c30 100644
--- a/compiler/types/InstEnv.lhs
+++ b/compiler/types/InstEnv.lhs
@@ -7,6 +7,13 @@
 The bits common to TcInstDcls and TcDeriv.
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module InstEnv (
 	DFunId, OverlapFlag(..),
 	Instance(..), pprInstance, pprInstanceHdr, pprInstances, 
@@ -430,10 +437,11 @@ 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