diff --git a/Debug/Diff.hs b/Debug/Diff.hs
new file mode 100644
--- /dev/null
+++ b/Debug/Diff.hs
@@ -0,0 +1,6 @@
+-- | Display a colorized diff between two Haskell values.
+module Debug.Diff
+    ( diff
+    ) where
+
+import Debug.Diff.Config
diff --git a/Debug/Diff/Config.hs b/Debug/Diff/Config.hs
new file mode 100644
--- /dev/null
+++ b/Debug/Diff/Config.hs
@@ -0,0 +1,54 @@
+-- | Display the difference between two Haskell values,
+-- with control over the diff parameters.
+module Debug.Diff.Config
+    ( Config(..)
+    , defConfig
+    , diffWith
+    , diff
+    ) where
+
+import Text.Groom
+import Text.Printf
+import System.IO
+import System.IO.Temp
+import System.Process
+import System.Exit
+
+-- | Configuration of the diff command
+data Config = Config
+    { context :: Maybe Int  -- ^ Lines of context, for a unified diff.
+    , command :: String     -- ^ Diff command; @colordiff@ by default.
+    , args    :: [String]   -- ^ Extra arguments to the diff command.
+    } deriving (Eq, Ord, Read, Show)
+
+-- | A default configuration.
+defConfig :: Config
+defConfig = Config
+    { context = Just 3
+    , command = "colordiff"
+    , args    = [] }
+
+-- | Display the difference between two Haskell values,
+-- with control over the diff parameters.
+diffWith :: (Show a, Show b) => Config -> a -> b -> IO ()
+diffWith cfg x y =
+    withSystemTempFile "ddiff_x" $ \px hx ->
+    withSystemTempFile "ddiff_y" $ \py hy -> do
+        hPutStrLn hx (groom x)
+        hClose hx
+        hPutStrLn hy (groom y)
+        hClose hy
+        let ctxArg n = ["-U", show n]
+            allArgs = args cfg ++ maybe [] ctxArg (context cfg) ++ [px, py]
+        (_, _, _, hdl) <- createProcess (proc (command cfg) allArgs)
+        ec <- waitForProcess hdl
+        case ec of
+            ExitFailure n | n > 1 ->
+                hPrintf stderr
+                    "debug-diff: command %s with args %s exited with code %d\n"
+                    (show (command cfg)) (show allArgs) n
+            _ -> return ()
+
+-- | Display a colorized diff between two Haskell values.
+diff :: (Show a, Show b) => a -> b -> IO ()
+diff = diffWith defConfig
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,26 @@
+Copyright (c) Keegan McAllister 2011
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+1. Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+2. 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.
+3. Neither the name of the author nor the names of his 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 AUTHORS 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
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,4 @@
+#! /usr/bin/runhaskell
+
+import Distribution.Simple
+main = defaultMain
diff --git a/debug-diff.cabal b/debug-diff.cabal
new file mode 100644
--- /dev/null
+++ b/debug-diff.cabal
@@ -0,0 +1,29 @@
+name:                debug-diff
+version:             0.1
+license:             BSD3
+license-file:        LICENSE
+synopsis:            Display a colorized diff between two Haskell values
+category:            Debug
+author:              Keegan McAllister <mcallister.keegan@gmail.com>
+maintainer:          Keegan McAllister <mcallister.keegan@gmail.com>
+build-type:          Simple
+cabal-version:       >=1.2
+description:
+  @Debug.Diff@ is a quick tool for comparing two Haskell values, as
+  when diagnosing a test failure.  It pretty-prints the values
+  (using the @groom@ library) and passes them to an external @diff@
+  command (@colordiff@ by default), which writes the diff to standard
+  output.
+  .
+  @Debug.Diff.Config@ provides more control over the diff parameters.
+
+library
+  exposed-modules:
+      Debug.Diff
+    , Debug.Diff.Config
+  ghc-options:      -Wall
+  build-depends:
+      base      >= 3 && < 5
+    , groom     >= 0.1
+    , temporary >= 1.1
+    , process   >= 1.0