diff --git a/LevMar/Chart.hs b/LevMar/Chart.hs
--- a/LevMar/Chart.hs
+++ b/LevMar/Chart.hs
@@ -9,15 +9,16 @@
     , Graphics.Rendering.Chart.PlotValue
     ) where
 
-import Data.Accessor                ((^=), (.>))
-import Data.Colour                  (withOpacity, opaque)
-import Data.Colour.Names            (red, blue)
+import Control.Monad                ( fmap )
+import Data.Accessor                ( (^=), (.>) )
+import Data.Colour                  ( withOpacity, opaque )
+import Data.Colour.Names            ( red, blue )
 import Graphics.Rendering.Chart
-import Graphics.Rendering.Chart.Gtk (renderableToWindow)
+import Graphics.Rendering.Chart.Gtk ( renderableToWindow )
 import LevMar.Fitting
-import NFunction                    (($*))
-import Text.Printf                  (printf)
-import System.IO                    (FilePath)
+import NFunction                    ( ($*) )
+import Text.Printf                  ( printf )
+import System.IO                    ( FilePath )
 
 data FileType = PDF  -- ^Portable Document Format
               | PNG  -- ^Portable Network Graphics
@@ -28,7 +29,7 @@
 -- |Apply the Levenbarg-Marquardt algorithm and plot the results in a
 -- window.
 levmarChart :: forall n k r a.
-               ( Nat n, ComposeN n
+               ( Nat n
                , Nat k
                , PlotValue r, LevMarable r
                , PlotValue a, Fractional a
@@ -60,7 +61,7 @@
 -- |Apply the Levenbarg-Marquardt algorithm and plot the results in a
 -- file.
 levmarChartFile :: forall n k r a.
-               ( Nat n, ComposeN n
+               ( Nat n
                , Nat k
                , PlotValue r, LevMarable r
                , PlotValue a, Fractional a
@@ -131,13 +132,13 @@
               -> (SizedList n r, Info r, CovarMatrix n r)
               -> Renderable ()
 renderResults model samples (params, info, _) = toRenderable r
-    where xs = map fst samples
+    where xs = fmap fst samples
 
           r :: Layout1 a r
           r = layout1_title ^= title
-            $ layout1_plots ^= map (Left) [samplePts, fitted]
-            $ layout1_left_axis   .> laxis_title ^= "x-axis"
-            $ layout1_bottom_axis .> laxis_title ^= "y-axis"
+            $ layout1_plots ^= fmap Left [samplePts, fitted]
+            $ layout1_left_axis   .> laxis_title ^= "y-axis"
+            $ layout1_bottom_axis .> laxis_title ^= "x-axis"
             $ defaultLayout1
 
           title :: String
@@ -158,13 +159,13 @@
                     $ defaultPlotPoints
 
           fitted = toPlot
-                 $ plot_lines_values ^= [zip fittedXs $ map (model $* params) fittedXs]
+                 $ plot_lines_values ^= [zip fittedXs $ fmap (model $* params) fittedXs]
                  $ plot_lines_style .> line_color ^= (red `withOpacity` 0.5)
                  $ defaultPlotLines
 
           fittedXs :: [a]
           fittedXs | null xs   = []
-                   | otherwise = [ minX + (fromIntegral i / fromIntegral lenXs) * (abs $ maxX - minX)
+                   | otherwise = [ minX + (fromIntegral i / fromIntegral lenXs) * abs (maxX - minX)
                                  | i <- [0 .. lenXs]
                                  ]
               where minX   = minimum xs
diff --git a/example.hs b/example.hs
--- a/example.hs
+++ b/example.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+
 module Main where
 
 import Control.Monad  (sequence_)
@@ -21,39 +23,40 @@
 -------------------------------------------------------------------------------
 -- Model functions
 
-constant  :: Num r => Model N1 r r
-linear    :: Num r => Model N2 r r
-quadratic :: Num r => Model N3 r r
-cubic     :: Num r => Model N4 r r
+constant  :: Num r => SimpleModel N1 r
+linear    :: Num r => SimpleModel N2 r
+quadratic :: Num r => SimpleModel N3 r
+cubic     :: Num r => SimpleModel N4 r
 
 constant        a _ = a
 linear        b a x = b * x     + constant      a x
 quadratic   c b a x = c * x*x   + linear      b a x
 cubic     d c b a x = d * x*x*x + quadratic c b a x
 
-trig  :: Floating r => Model N2 r r
+trig  :: Floating r => SimpleModel N2 r
 trig a b x = a * cos x + b * sin x
 
 -------------------------------------------------------------------------------
 -- Jacobians
 
-constantJacob  :: Num r => Jacobian N1 r r
-linearJacob    :: Num r => Jacobian N2 r r
-quadraticJacob :: Num r => Jacobian N3 r r
-cubicJacob     :: Num r => Jacobian N4 r r
+constantJacob  :: Num r => SimpleJacobian N1 r
+linearJacob    :: Num r => SimpleJacobian N2 r
+quadraticJacob :: Num r => SimpleJacobian N3 r
+cubicJacob     :: Num r => SimpleJacobian N4 r
 
 constantJacob        _ _ = 1     ::: Nil
 linearJacob        _ a x = x     ::: constantJacob      a x
 quadraticJacob   _ b a x = x*x   ::: linearJacob      b a x
 cubicJacob     _ c b a x = x*x*x ::: quadraticJacob c b a x
 
-trigJacob :: Floating r => Jacobian N2 r r
+trigJacob :: Floating r => SimpleJacobian N2 r
 trigJacob _ _ x = cos x ::: sin x ::: Nil
 
 -------------------------------------------------------------------------------
 -- Test utility function
 
-testChart :: ( ComposeN n
+testChart :: forall n r a.
+             ( Nat n
              , PlotValue r, Fractional r, LevMarable r, Random r
              , PlotValue a, Fractional a
              )
@@ -63,7 +66,8 @@
           -> [a]
           -> r
           -> IO ()
-testChart f j ps xs noise = levmarChart f j
+testChart f j ps xs noise = levmarChart f
+                                        j
                                         initPs
                                         samples'
                                         1000
@@ -75,7 +79,7 @@
                            >> return ()
     where
       ns         = take (length xs) $ randoms $ mkStdGen rndGenSeed
-      initPs     = (SL.replicate (SL.length ps) 0)
+      initPs     = SL.replicate 0 :: SizedList n r
       samples    = zip xs $ map (f $* ps) xs
       samples'   = zipWith (\(x, y) n -> (x, y + (n - 0.5) * 2 * noise)) samples ns
       rndGenSeed = 123456
diff --git a/levmar-chart.cabal b/levmar-chart.cabal
--- a/levmar-chart.cabal
+++ b/levmar-chart.cabal
@@ -1,5 +1,5 @@
 name:          levmar-chart
-version:       0.1
+version:       0.2
 cabal-version: >= 1.6
 build-type:    Simple
 stability:     experimental
@@ -28,7 +28,7 @@
                , Chart         == 0.11.*
                , colour        == 2.3.*
                , data-accessor == 0.2.*
-               , levmar        == 0.1.*
+               , levmar        == 0.2.*
   exposed-modules: LevMar.Chart
   ghc-options: -Wall -O2
 
@@ -37,7 +37,7 @@
                , Chart         == 0.11.*
                , colour        == 2.3.*
                , data-accessor == 0.2.*
-               , levmar        == 0.1.*
+               , levmar        == 0.2.*
                , random        == 1.0.*
   other-modules: LevMar.Chart
   ghc-options: -Wall -O2