1 files changed, 11 insertions, 4 deletions
diff --git a/compiler/utils/UniqFM.lhs b/compiler/utils/UniqFM.lhs
index a13a17c412..d8e08f599a 100644
--- a/compiler/utils/UniqFM.lhs
+++ b/compiler/utils/UniqFM.lhs
@@ -20,9 +20,9 @@ and ``addToUFM\_C'' and ``Data.IntMap.insertWith'' differ in the order
 of arguments of combining function.
 
 \begin{code}
-{-# LANGUAGE DeriveTraversable, GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE DeriveTraversable, DeriveDataTypeable, GeneralizedNewtypeDeriving #-}
+{-# OPTIONS_GHC -Wall #-}
 
-{-# OPTIONS -Wall #-}
 module UniqFM (
         -- * Unique-keyed mappings
         UniqFM,       -- abstract type
@@ -60,9 +60,10 @@ module UniqFM (
         eltsUFM, keysUFM, splitUFM,
         ufmToSet_Directly,
         ufmToList,
-        joinUFM
+        joinUFM, pprUniqFM
     ) where
 
+import FastString
 import Unique           ( Uniquable(..), Unique, getKey )
 import Outputable
 
@@ -319,5 +320,11 @@ joinUFM eltJoin l (OldFact old) (NewFact new) = foldUFM_Directly add (NoChange,
 
 \begin{code}
 instance Outputable a => Outputable (UniqFM a) where
-    ppr ufm = ppr (ufmToList ufm)
+    ppr ufm = pprUniqFM ppr ufm
+
+pprUniqFM :: (a -> SDoc) -> UniqFM a -> SDoc
+pprUniqFM ppr_elt ufm
+  = brackets $ fsep $ punctuate comma $
+    [ ppr uq <+> ptext (sLit ":->") <+> ppr_elt elt
+    | (uq, elt) <- ufmToList ufm ]
 \end{code}