diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2013, Adam C. Foltzer
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Adam C. Foltzer nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/persistent-refs.cabal b/persistent-refs.cabal
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--- /dev/null
+++ b/persistent-refs.cabal
@@ -0,0 +1,36 @@
+name:                persistent-refs
+version:             0.1
+license:             BSD3
+license-file:        LICENSE
+author:              Adam C. Foltzer
+maintainer:          acfoltzer@gmail.com
+homepage:            https://github.com/acfoltzer/persistent-refs
+bug-reports:         https://github.com/acfoltzer/persistent-refs/issues
+category:            Data
+build-type:          Simple
+cabal-version:       >=1.8
+synopsis:            
+    Haskell references backed by an IntMap for persistence and reversibility.
+description:
+    This library provides support for a persistent version of the
+    'Control.Monad.ST.ST' monad. Internally, references are backed by a
+    'Data.IntMap.IntMap', rather than being mutable variables on the
+    heap. This decreases performance, but can be useful in certain
+    settings, particularly those involving backtracking.
+
+source-repository head
+  type:     git
+  location: git://github.com/acfoltzer/persistent-refs.git
+
+library
+  build-depends:     base         >= 4.0 && < 5,
+                     containers   >= 0.4 && < 0.6,
+                     lens         >= 3.7 && < 3.9,
+                     mtl          >= 2.1 && < 2.2,
+                     ref-fd       >= 0.3 && < 0.4,
+                     transformers >= 0.3 && < 0.4
+  exposed-modules:   Control.Monad.ST.Persistent,
+                     Data.STRef.Persistent
+  other-modules:     Control.Monad.ST.Persistent.Internal
+  hs-source-dirs:    src
+  ghc-options:       -Wall
diff --git a/src/Control/Monad/ST/Persistent.hs b/src/Control/Monad/ST/Persistent.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/ST/Persistent.hs
@@ -0,0 +1,26 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Control.Monad.ST.Persistent
+-- Copyright   :  (c) Adam C. Foltzer 2013
+-- License     :  BSD3
+--
+-- Maintainer  :  acfoltzer@gmail.com
+-- Stability   :  experimental
+-- Portability :  non-portable (requires rank-2 types for runST)
+--
+-- This library provides support for a persistent version of the
+-- 'Control.Monad.ST.ST' monad. Internally, references are backed by a
+-- 'Data.IntMap.IntMap', rather than being mutable variables on the
+-- heap. This decreases performance, but can be useful in certain
+-- settings, particularly those involving backtracking.
+--
+-----------------------------------------------------------------------------
+
+module Control.Monad.ST.Persistent (
+    -- * The Persistent 'ST' Monad
+    ST
+  , runST
+  ) where
+
+import Control.Monad.ST.Persistent.Internal
+
diff --git a/src/Control/Monad/ST/Persistent/Internal.hs b/src/Control/Monad/ST/Persistent/Internal.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/ST/Persistent/Internal.hs
@@ -0,0 +1,49 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE Rank2Types #-}
+{-# LANGUAGE TemplateHaskell #-}
+
+{-# OPTIONS_GHC -ddump-splices #-}
+module Control.Monad.ST.Persistent.Internal where
+
+import Control.Applicative (Applicative)
+import Control.Lens
+import Control.Monad.State.Strict
+import Data.IntMap
+import GHC.Base
+
+data Heap = Heap { _heap :: IntMap Any, _next :: Int }
+-- makeLenses ''Heap
+
+-- manually using splices because TH before 7.6 can't handle Any
+heap :: Lens' Heap (IntMap Any)
+heap _f_a1T2 (Heap __heap'_a1T3 __next_a1T5)
+  = ((\ __heap_a1T4 -> Heap __heap_a1T4 __next_a1T5)
+     `fmap` (_f_a1T2 __heap'_a1T3))
+{-# INLINE heap #-}
+next :: Lens' Heap Int
+next _f_a1T6 (Heap __heap_a1T7 __next'_a1T8)
+  = ((\ __next_a1T9 -> Heap __heap_a1T7 __next_a1T9)
+     `fmap` (_f_a1T6 __next'_a1T8))
+{-# INLINE next #-}
+
+emptyHeap :: Heap
+emptyHeap = Heap { _heap = empty, _next = minBound }
+
+-- | A persistent version of the 'Control.Monad.ST.ST' monad.
+newtype ST s a = ST (State Heap a)
+    deriving (Functor, Applicative, Monad)
+
+-- | Run a computation that uses persistent references, and return a
+-- pure value. The rank-2 type offers similar guarantees to
+-- 'Control.Monad.ST.runST'.
+runST :: (forall s. ST s a) -> a
+runST (ST c) = evalState c emptyHeap
+
+-- I'm not sure whether the semantics of this transformer actually
+-- make any sense, so I'm not exporting this for now...
+
+newtype STT s m a = STT (StateT Heap m a)
+    deriving (Functor, Applicative, Monad, MonadIO)
+
+runSTT :: Monad m => (forall s. STT s m a) -> m a
+runSTT (STT c) = evalStateT c emptyHeap
diff --git a/src/Data/STRef/Persistent.hs b/src/Data/STRef/Persistent.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/STRef/Persistent.hs
@@ -0,0 +1,60 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.STRef.Persistent
+-- Copyright   :  (c) Adam C. Foltzer 2013
+-- License     :  BSD3
+--
+-- Maintainer  :  acfoltzer@gmail.com
+-- Stability   :  experimental
+-- Portability :  non-portable (requires rank-2 types for runST)
+--
+-- Mutable references in the persistent
+-- 'Control.Monad.ST.Persistent.ST' monad.
+--
+-----------------------------------------------------------------------------
+
+module Data.STRef.Persistent (
+    -- * 'STRef's
+    STRef
+    -- * 'MonadRef' Operations
+  , MonadRef(..)
+  , modifyRef'
+  ) where
+
+import Control.Lens
+import Control.Monad.Ref
+import Control.Monad.ST.Persistent.Internal
+import Data.IntMap as IntMap
+import Data.Maybe
+import Unsafe.Coerce
+
+newtype STRef s a = STRef Int
+
+newSTRef :: a -> ST s (STRef s a)
+newSTRef x = ST $ do 
+    i <- next <<%= (+1)
+    heap %= insert i (unsafeCoerce x)
+    return (STRef i)
+
+readSTRef :: STRef s a -> ST s a
+readSTRef (STRef i) = 
+    ST $ uses heap (unsafeCoerce . fromJust . IntMap.lookup i)
+
+writeSTRef :: STRef s a -> a -> ST s ()
+writeSTRef (STRef i) x = 
+    ST $ heap %= insert i (unsafeCoerce x)
+
+instance MonadRef (STRef s) (ST s) where
+    newRef   = newSTRef
+    readRef  = readSTRef
+    writeRef = writeSTRef
+
+modifyRef' :: MonadRef r m => r a -> (a -> a) -> m ()
+modifyRef' r f = do
+    x <- readRef r
+    let x' = f x
+    x' `seq` writeRef r x'