diff --git a/flat-mcmc.cabal b/flat-mcmc.cabal
--- a/flat-mcmc.cabal
+++ b/flat-mcmc.cabal
@@ -1,5 +1,5 @@
 name:                flat-mcmc
-version:             1.1.1
+version:             1.2.1
 synopsis:            Painless general-purpose sampling.
 homepage:            http://jtobin.github.com/flat-mcmc
 license:             MIT
@@ -53,14 +53,16 @@
   exposed-modules:  Numeric.MCMC.Flat
   build-depends:
       base             >  4     && < 6
+    , formatting       >= 6     && < 7
     , mcmc-types       >= 1.0.1 && < 2
     , monad-par        >= 0.3.4.7 && < 1
     , monad-par-extras >= 0.3.3 && < 1
     , mwc-probability  >= 1.0.1 && < 2
     , pipes            >  4     && < 5
     , primitive
+    , text
     , transformers
-    , vector
+    , vector           >= 0.10  && < 1
 
 Test-suite rosenbrock
   type:                exitcode-stdio-1.0
diff --git a/lib/Numeric/MCMC/Flat.hs b/lib/Numeric/MCMC/Flat.hs
--- a/lib/Numeric/MCMC/Flat.hs
+++ b/lib/Numeric/MCMC/Flat.hs
@@ -1,4 +1,5 @@
 {-# OPTIONS_GHC -fno-warn-type-defaults #-}
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RecordWildCards #-}
 
 -- |
@@ -42,10 +43,15 @@
 import Control.Monad.Par.Combinator (parMap)
 import Control.Monad.Primitive (PrimMonad, PrimState, RealWorld)
 import Control.Monad.Trans.State.Strict (get, put, execStateT)
+import Data.Monoid
 import Data.Sampling.Types as Sampling.Types hiding (Chain(..))
+import qualified Data.Text as T
+import qualified Data.Text.IO as T (putStrLn)
 import Data.Vector (Vector)
 import qualified Data.Vector as V
 import qualified Data.Vector.Unboxed as U
+import Formatting ((%))
+import qualified Formatting as F
 import Pipes (Producer, lift, yield, runEffect, (>->))
 import qualified Pipes.Prelude as Pipes
 import System.Random.MWC.Probability as MWC
@@ -55,15 +61,27 @@
   , chainPosition :: !Ensemble
   }
 
-instance Show Chain where
-  show Chain {..} =
-      init
-    . filter (`notElem` "[]")
-    . unlines
-    . V.toList
-    . V.map show
-    $ chainPosition
+-- | Render a Chain as a text value.
+render :: Chain -> T.Text
+render Chain {..} = renderEnsemble chainPosition
+{-# INLINE render #-}
 
+renderParticle :: Particle -> T.Text
+renderParticle =
+      T.drop 1
+    . U.foldl' glue mempty
+  where
+    glue = F.sformat (F.stext % "," % F.float)
+{-# INLINE renderParticle #-}
+
+renderEnsemble :: Ensemble -> T.Text
+renderEnsemble =
+      T.drop 1
+    . V.foldl' glue mempty
+  where
+    glue a b = a <> "\n" <> renderParticle b
+{-# INLINE renderEnsemble #-}
+
 type Particle = U.Vector Double
 
 type Ensemble = Vector Particle
@@ -71,15 +89,19 @@
 symmetric :: PrimMonad m => Prob m Double
 symmetric = fmap transform uniform where
   transform z = 0.5 * (z + 1) ^ (2 :: Int)
+{-# INLINE symmetric #-}
 
 stretch :: Particle -> Particle -> Double -> Particle
-stretch p0 p1 z = U.zipWith (+) (U.map (* z) p0) (U.map (* (1 - z)) p1)
+stretch p0 p1 z = U.zipWith str p0 p1 where
+  str x y = z * x + (1 - z) * y
+{-# INLINE stretch #-}
 
 acceptProb :: Target Particle -> Particle -> Particle -> Double -> Double
 acceptProb target particle proposal z =
     lTarget target proposal
   - lTarget target particle
   + log z * (fromIntegral (U.length particle) - 1)
+{-# INLINE acceptProb #-}
 
 move :: Target Particle -> Particle -> Particle -> Double -> Double -> Particle
 move target p0 p1 z zc =
@@ -88,6 +110,7 @@
   in  if   zc <= min 1 (exp pAccept)
       then proposal
       else p0
+{-# INLINE move #-}
 
 execute
   :: PrimMonad m
@@ -112,7 +135,8 @@
       result = runPar $
         parMapChunk granularity worker (zip3 [1..n] zs zcs)
 
-  return $ V.fromList result
+  return $! V.fromList result
+{-# INLINE execute #-}
 
 -- | The 'flat' transition operator for driving a Markov chain over a space
 --   of ensembles.
@@ -123,12 +147,13 @@
   Chain {..} <- get
   let size = V.length chainPosition
       n    = truncate (fromIntegral size / 2)
-      e0   = V.slice 0 n chainPosition
-      e1   = V.slice n n chainPosition
+      e0   = V.unsafeSlice 0 n chainPosition
+      e1   = V.unsafeSlice n n chainPosition
   result0 <- lift (execute chainTarget e0 e1 n)
   result1 <- lift (execute chainTarget e1 result0 n)
   let ensemble = V.concat [result0, result1]
   put (Chain chainTarget ensemble)
+{-# INLINE flat #-}
 
 chain :: PrimMonad m => Chain -> Gen (PrimState m) -> Producer Chain m ()
 chain = loop where
@@ -136,6 +161,7 @@
     next <- lift (MWC.sample (execStateT flat state) prng)
     yield next
     loop next prng
+{-# INLINE chain #-}
 
 -- | Trace 'n' iterations of a Markov chain and stream them to stdout.
 --
@@ -169,9 +195,10 @@
 mcmc n chainPosition target gen = runEffect $
         chain Chain {..} gen
     >-> Pipes.take n
-    >-> Pipes.mapM_ print
+    >-> Pipes.mapM_ (T.putStrLn . render)
   where
     chainTarget = Target target Nothing
+{-# INLINE mcmc #-}
 
 -- A parallel map with the specified granularity.
 parMapChunk :: NFData b => Int -> (a -> b) -> [a] -> Par [b]
@@ -180,4 +207,5 @@
   chunk m ys =
     let (as, bs) = splitAt m ys
     in  as : chunk m bs
+{-# INLINE parMapChunk #-}