diff --git a/mps.cabal b/mps.cabal
--- a/mps.cabal
+++ b/mps.cabal
@@ -1,11 +1,11 @@
 Name:                 mps
-Version:              2010.2.25
+Version:              2010.5.29
 Build-type:           Simple
 Synopsis:             simply oo
 Description:          DSL that allows one to write Haskell from left to right
 License:              BSD3
-Author:               Wang, Jinjing
-Maintainer:           Wang, Jinjing <nfjinjing@gmail.com>
+Author:               Jinjing Wang
+Maintainer:           Jinjing Wang <nfjinjing@gmail.com>
 Build-Depends:        base
 Cabal-version:        >= 1.2
 category:             Development
@@ -15,7 +15,21 @@
 
 library
   ghc-options: -Wall
-  build-depends: base >= 4 && < 5, containers, array, parallel, old-time, time, bytestring >= 0.9, regexpr >= 0.3.4, parsec >= 2, utf8-string >= 0.3.3, directory, old-locale, filepath, template-haskell
+  build-depends:  base >= 4 && < 5
+                , containers
+                , array
+                , parallel
+                , old-time
+                , time
+                , bytestring >= 0.9
+                , regexpr >= 0.3.4
+                , parsec >= 2
+                , utf8-string >= 0.3.3
+                , directory
+                , old-locale
+                , filepath
+                , template-haskell
+                , monoid-owns
   hs-source-dirs: src/
   exposed-modules:  
                     MPS
diff --git a/src/MPS/Env.hs b/src/MPS/Env.hs
--- a/src/MPS/Env.hs
+++ b/src/MPS/Env.hs
@@ -1,7 +1,9 @@
 module MPS.Env (
     module MPS.Light
   , module Prelude
+  , module Data.Monoid.Owns
 ) where
 
 import MPS.Light
-import Prelude hiding ((.), (>), (<), (^), (/), (-))
+import Prelude hiding ((.), (>), (<), (^), (/), (-), (+))
+import Data.Monoid.Owns ((+))