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

[haskell-directory.git] / Data / Set.hs

diff --git a/Data/Set.hs b/Data/Set.hs
index 2029faa..9300127 100644 (file)
--- a/Data/Set.hs
+++ b/Data/Set.hs
@@ -113,6 +113,7 @@ module Data.Set  (
 
 import Prelude hiding (filter,foldr,null,map)
 import qualified Data.List as List
+import Data.Monoid (Monoid(..))
 import Data.Typeable
 
 {-
@@ -146,6 +147,11 @@ data Set a    = Tip
 
 type Size     = Int
 
+instance Ord a => Monoid (Set a) where
+    mempty  = empty
+    mappend = union
+    mconcat = unions
+
 #if __GLASGOW_HASKELL__
 
 {--------------------------------------------------------------------