[project @ 2005-10-25 09:29:16 by ross]

[ghc-base.git] / Data / Map.hs

diff --git a/Data/Map.hs b/Data/Map.hs
index 37a9695..cafb0a1 100644 (file)
--- a/Data/Map.hs
+++ b/Data/Map.hs
@@ -150,6 +150,7 @@ module Data.Map  (
 import Prelude hiding (lookup,map,filter,foldr,foldl,null)
 import qualified Data.Set as Set
 import qualified Data.List as List
+import Data.Monoid (Monoid(..))
 import Data.Typeable
 
 {-
@@ -189,6 +190,11 @@ data Map k a  = Tip
 
 type Size     = Int
 
+instance (Ord k) => Monoid (Map k v) where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
 #if __GLASGOW_HASKELL__
 
 {--------------------------------------------------------------------