diff --git a/HSet.cabal b/HSet.cabal
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--- /dev/null
+++ b/HSet.cabal
@@ -0,0 +1,25 @@
+Name:                   HSet
+Version:                0.0.0
+Author:                 Athan Clark <athan.clark@gmail.com>
+Maintainer:             Athan Clark <athan.clark@gmail.com>
+License:                BSD3
+License-File:           LICENSE
+Synopsis:               Faux heterogeneous sets
+Cabal-Version:          >= 1.10
+Build-Type:             Simple
+Category:               Data
+
+Library
+  Default-Language:     Haskell2010
+  HS-Source-Dirs:       src
+  GHC-Options:          -Wall
+  Exposed-Modules:      Data.HSet.Mutable
+  Other-Modules:        Data.HSet.Types
+  Build-Depends:        base >= 4.8 && < 5
+                      , containers
+                      , hashtables
+                      , hashable
+
+Source-Repository head
+  Type:                 git
+  Location:             https://github.com/athanclark/HSet
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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+Copyright (c) 2016, Athan Clark
+
+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 Athan Clark 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/src/Data/HSet/Mutable.hs b/src/Data/HSet/Mutable.hs
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--- /dev/null
+++ b/src/Data/HSet/Mutable.hs
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+module Data.HSet.Mutable
+  ( HKey
+  , HSet
+  , new
+  , insert
+  , lookup
+  , delete
+  ) where
+
+import Data.HSet.Types
+
+import Prelude hiding (lookup, length)
+import Data.Maybe (fromMaybe)
+
+import Data.Typeable.Internal (Fingerprint, TypeRep (TypeRep))
+import Data.Dynamic
+
+import           Data.HashTable.ST.Basic (HashTable)
+import qualified Data.HashTable.ST.Basic as HT
+import Control.Monad.ST
+
+
+
+data HSet s = HSet
+  { hSetValues :: {-# UNPACK #-} !(HashTable s HKey' Dynamic)
+  , hSetCount  :: {-# UNPACK #-} !(HashTable s Fingerprint Int)
+  }
+
+
+new :: ST s (HSet s)
+new = HSet <$> HT.new <*> HT.new
+
+
+insert :: ( Typeable a
+          ) => a -> HSet s -> ST s (HKey a)
+insert x (HSet xs count) = do
+  let (TypeRep f _ _ _) = typeOf x
+  c <- fromMaybe 0 <$> HT.lookup count f
+  HT.insert count f (c+1)
+  let k = HKey' f c
+  HT.insert xs k (toDyn x)
+  pure (HKey k)
+
+
+lookup :: ( Typeable a
+          ) => HKey a -> HSet s -> ST s (Maybe a)
+lookup (HKey k) (HSet xs _) = (>>= fromDynamic) <$> HT.lookup xs k
+
+
+delete :: HKey a -> HSet s -> ST s ()
+delete (HKey k@(HKey' f _)) (HSet xs count) = do
+  HT.delete count f
+  HT.delete xs k
diff --git a/src/Data/HSet/Types.hs b/src/Data/HSet/Types.hs
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--- /dev/null
+++ b/src/Data/HSet/Types.hs
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+{-# LANGUAGE
+    DeriveGeneric
+  #-}
+
+module Data.HSet.Types where
+
+import Data.Typeable.Internal (Fingerprint (..))
+
+import GHC.Generics
+import Data.Hashable
+
+
+
+data HKey' = HKey'
+  { getTypeIndex :: {-# UNPACK #-} !Fingerprint
+  , getTypeCount :: {-# UNPACK #-} !Int
+  } deriving (Eq, Generic)
+
+instance Hashable Fingerprint where
+  hashWithSalt s (Fingerprint x y) =
+    s `hashWithSalt` x `hashWithSalt` y
+
+instance Hashable HKey'
+
+newtype HKey a = HKey
+  { getHKey :: HKey'
+  } deriving (Eq)