diff --git a/Statistics/Function.hs b/Statistics/Function.hs
--- a/Statistics/Function.hs
+++ b/Statistics/Function.hs
@@ -15,6 +15,7 @@
       minMax
     , sort
     , partialSort
+    , indices
     -- * Array setup
     , createU
     , createIO
@@ -39,6 +40,11 @@
             -> UArr e
 partialSort k = apply (\a -> I.partialSort a k)
 {-# INLINE partialSort #-}
+
+-- | Return the indices of an array.
+indices :: (UA a) => UArr a -> UArr Int
+indices a = enumFromToU 0 (lengthU a - 1)
+{-# INLINE indices #-}
 
 data MM = MM {-# UNPACK #-} !Double {-# UNPACK #-} !Double
 
diff --git a/Statistics/RandomVariate.hs b/Statistics/RandomVariate.hs
--- a/Statistics/RandomVariate.hs
+++ b/Statistics/RandomVariate.hs
@@ -1,4 +1,5 @@
-{-# LANGUAGE BangPatterns, CPP, MagicHash, Rank2Types, ScopedTypeVariables #-}
+{-# LANGUAGE BangPatterns, CPP, DeriveDataTypeable, MagicHash, Rank2Types,
+    ScopedTypeVariables #-}
 -- |
 -- Module    : Statistics.RandomVariate
 -- Copyright : (c) 2009 Bryan O'Sullivan
@@ -44,6 +45,7 @@
 import Data.Int (Int8, Int16, Int32, Int64)
 import Data.Ratio ((%), numerator)
 import Data.Time.Clock.POSIX (getPOSIXTime)
+import Data.Typeable (Typeable)
 import Data.Word (Word, Word8, Word16, Word32, Word64)
 import Foreign.Marshal.Alloc (allocaBytes)
 import Foreign.Marshal.Array (peekArray)
@@ -241,7 +243,7 @@
                                
 -- | An immutable snapshot of the state of a 'Gen'.
 newtype Seed = Seed (UArr Word32)
-    deriving (Eq, Read, Show)
+    deriving (Eq, Read, Show, Typeable)
 
 -- | Save the state of a 'Gen', for later use by 'restore'.
 save :: Gen s -> ST s Seed
diff --git a/Statistics/Resampling.hs b/Statistics/Resampling.hs
--- a/Statistics/Resampling.hs
+++ b/Statistics/Resampling.hs
@@ -20,7 +20,7 @@
 import Control.Monad.ST (ST)
 import Data.Array.Vector
 import Data.Array.Vector.Algorithms.Intro (sort)
-import Statistics.Function (createU)
+import Statistics.Function (createU, indices)
 import Statistics.RandomVariate (Gen, uniform)
 import Statistics.Types (Estimator, Sample)
 
@@ -53,7 +53,7 @@
 -- | Compute a statistical estimate repeatedly over a sample, each
 -- time omitting a successive element.
 jackknife :: Estimator -> Sample -> UArr Double
-jackknife est sample = mapU f . enumFromToU 0 . subtract 1 . lengthU $ sample
+jackknife est sample = mapU f . indices $ sample
     where f i = est (dropAt i sample)
 {-# INLINE jackknife #-}
 
diff --git a/statistics.cabal b/statistics.cabal
--- a/statistics.cabal
+++ b/statistics.cabal
@@ -1,5 +1,5 @@
 name:           statistics
-version:        0.3.3
+version:        0.3.4
 synopsis:       A library of statistical types, data, and functions
 description:
   This library provides a number of common functions and types useful