diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2014, Thomas Tuegel
+
+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 Thomas Tuegel 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
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+import Distribution.Simple
+main = defaultMain
diff --git a/cached-traversable.cabal b/cached-traversable.cabal
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--- /dev/null
+++ b/cached-traversable.cabal
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+name:                cached-traversable
+version:             0.1.0.0
+synopsis:            Transparent, persistent caching of lazy, traversable structures
+description:
+  cached-traversable provides persistent (on-disk) caching of lazy, traversable
+  structures for any element type which has a Binary instance. Think of it as
+  a poor man's acid-state for deterministic programs.
+license:             BSD3
+license-file:        LICENSE
+author:              Thomas Tuegel
+maintainer:          ttuegel@gmail.com
+copyright:           2014 Thomas Tuegel
+category:            Data
+build-type:          Simple
+cabal-version:       >=1.8
+
+source-repository head
+  type: git
+  location: https://github.com/ttuegel/cached-traversable.git
+
+library
+  exposed-modules:
+    Data.Traversable.Cached
+  build-depends:
+    base >=4.6 && <5,
+    mtl ==2.1.*,
+    binary ==0.5.*,
+    bytestring ==0.10.*,
+    containers ==0.5.*,
+    directory ==1.2.*,
+    filepath ==1.3.*
+  hs-source-dirs: src
diff --git a/src/Data/Traversable/Cached.hs b/src/Data/Traversable/Cached.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Traversable/Cached.hs
@@ -0,0 +1,56 @@
+module Data.Traversable.Cached where
+
+import Control.Applicative
+import Control.Arrow
+import Control.Monad (when)
+import qualified Control.Monad.State.Strict as State
+import Control.Monad.Trans (liftIO)
+import Data.Binary
+import qualified Data.ByteString as BS
+import qualified Data.ByteString.Lazy as LBS
+import Data.Foldable
+import Data.Sequence ((|>))
+import qualified Data.Sequence as Seq
+import Data.Traversable
+import System.Directory (doesFileExist, removeFile, renameFile)
+import System.FilePath ((<.>))
+
+-- | Traverse the given structure, retrieving values from and storing values in
+-- the cache at the given path. Only the element type need be serializable. The
+-- struture must be lazy in the values for this to be effective. This does not
+-- work well for large structures because the entire cache is rewritten every
+-- time a new value is computed. Works best when values are small, but expensive
+-- to compute. Atomicity and consistency are weakly guaranteed by writing the
+-- cache to a new file every time, and renaming the file into place.
+cached :: (Binary a, Traversable t) => FilePath -> t a -> IO (t a)
+cached path dat = do
+    cacheExists <- doesFileExist path
+    cache <- if cacheExists then LBS.readFile path else return LBS.empty
+    newExists <- doesFileExist newPath
+    when newExists $ removeFile newPath
+    as <- State.evalStateT (traverse cached_go dat) (cache, Seq.empty)
+    return as
+  where
+    newPath = path <.> "new"
+
+    appendEncoded = flip (|>) . LBS.toStrict . encode
+
+    flushCache = do
+        (oldCache, newCache) <- State.get
+        -- When there is data yet to be read in oldCache, the cache is not stale
+        -- so there is no reason to write a new one.
+        when (LBS.null oldCache) $ liftIO $ do
+            forM_ newCache (BS.appendFile newPath)
+            renameFile newPath path
+
+    cached_go computed = do
+        decoded <- decodeOrFail . fst <$> State.get
+        case decoded of
+            Left _ -> do
+                State.modify $ const LBS.empty *** appendEncoded computed
+                seq computed flushCache
+                return computed
+            Right (nextCache, _, retrieved) -> do
+                State.modify $ const nextCache *** appendEncoded retrieved
+                seq retrieved flushCache
+                return retrieved