diff --git a/GraphViz.hs b/GraphViz.hs
--- a/GraphViz.hs
+++ b/GraphViz.hs
@@ -1,26 +1,28 @@
-{-# LANGUAGE GeneralizedNewtypeDeriving, OverloadedStrings #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving, OverloadedStrings, FlexibleContexts #-}
 module GraphViz where
 
-import Control.Applicative ((<$>), Applicative(..))
+import Control.Applicative ((<$>), Applicative(..), Alternative(..))
 import Control.Monad
 import Control.Monad.State
 import Control.Monad.Error
 import Control.Concurrent (forkIO)
 import Data.List (intercalate, intersperse, nub)
+import Data.Char (ord)
 
 import qualified Data.Graph.Inductive as Graph
-import Data.HashTable (hashString)
+-- import Data.HashTable (hashString)
 
 import Data.GraphViz (runGraphvizCommand, runGraphvizCanvas', GraphvizCanvas(Xlib), graphElemsToDot, GraphvizOutput(..), toLabel, nonClusteredParams, GraphvizParams(..), GlobalAttributes(GraphAttrs), GraphvizCommand(Dot))
-import Data.GraphViz.Attributes.Colors (Color(X11Color), X11Color(..))
+import Data.GraphViz.Attributes.Colors (Color(X11Color), WeightedColor(..))
+import Data.GraphViz.Attributes.Colors.X11 (X11Color(..))
 import Data.GraphViz.Attributes.HTML
-import Data.GraphViz.Attributes.Complete (Attribute(Ordering,Label,Shape,Color,Width,Regular), Shape(BoxShape), Label(HtmlLabel), HtmlLabel(HtmlText))
+import Data.GraphViz.Attributes.Complete (Attribute(Ordering,Label,Shape,Color,Width,Regular), Shape(BoxShape), Label(HtmlLabel), Order(OutEdges))
 
 import qualified Data.Text.Lazy
 
 import Language.Prolog
 
-htmlStr = HtmlStr . Data.Text.Lazy.pack
+htmlStr = Str . Data.Text.Lazy.pack
 
 -- Graphical output of derivation tree
 resolveTree p q = preview =<< execGraphGenT (resolve_ p q)
@@ -37,7 +39,7 @@
   where
     params = nonClusteredParams { fmtNode = \ (_,l) -> formatNode l
                                 , fmtEdge = \ (_, _, l) -> formatEdge l
-                                , globalAttributes = [GraphAttrs (Ordering "out" : attrs)] -- child nodes are drawn in edge-order
+                                , globalAttributes = [GraphAttrs (Ordering OutEdges : attrs)] -- child nodes are drawn in edge-order
                                 , isDirected = True
                                 }
 
@@ -60,9 +62,9 @@
 labEdges (Gr _ es) = es
 
 
-newtype GraphGenT m a = GraphGenT (StateT Graph m a) deriving (Monad, Functor, MonadFix, MonadPlus, Applicative, MonadError e, MonadState Graph, MonadTrans)
-runGraphGenT  (GraphGenT st) = runStateT  st empty
-execGraphGenT (GraphGenT st) = execStateT st empty
+newtype GraphGenT m a = GraphGenT (StateT Graph m a) deriving (Monad, Functor, MonadFix, MonadPlus, Applicative, MonadError e, MonadState Graph, MonadTrans, Alternative)
+runGraphGenT  (GraphGenT st) = runStateT  st GraphViz.empty
+execGraphGenT (GraphGenT st) = execStateT st GraphViz.empty
 
 
 instance Monad m => MonadGraphGen (GraphGenT m) where
@@ -95,21 +97,21 @@
 
 
 
-formatNode :: NodeLabel -> [Attribute]
+formatNode :: NodeLabel -> [Data.GraphViz.Attributes.Complete.Attribute]
 formatNode ((_,(_,u',[])), _, WasNotCut) = -- Success
   Shape BoxShape :
   case filterOriginal u' of
     [] -> [ toLabel ("" :: String)
-          , Width 0.2
+          , Data.GraphViz.Attributes.Complete.Width 0.2
           , Regular True
-          , Color [X11Color Green]
+          , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Green) Nothing)]
           ]
     uf -> [ toLabel $ colorize Green $ htmlUnifier uf
-          , Color [X11Color Green]
+          , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Green) Nothing)]
           ]
 formatNode ((_,(_,_,gs')), [], WasNotCut) = -- Failure
     [ toLabel $ colorize Red [htmlGoals gs'] 
-    , Color [X11Color Red]
+    , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Red) Nothing)]
     ]
 formatNode ((_,(_,_,gs')), _, WasNotCut) =
     [ toLabel [htmlGoals gs'] ]
@@ -117,34 +119,34 @@
   Shape BoxShape :
   case filterOriginal u' of
     [] -> [ toLabel ("" :: String)
-          , Width 0.2
+          , Data.GraphViz.Attributes.Complete.Width 0.2
           , Regular True
-          , Color [X11Color Gray]
+          , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Gray) Nothing)]
           ]
     uf -> [ toLabel $ colorize Gray $ htmlUnifier uf
-          , Color [X11Color Gray]
+          , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Gray) Nothing)]
           ]
 formatNode ((_,(_,_,gs')), _, WasCut) = -- Cut
     [ toLabel $ colorize Gray [htmlGoals gs']
-    , Color [X11Color Gray]
+    , Data.GraphViz.Attributes.Complete.Color [(WC (X11Color Gray) Nothing)]
     ]
 
 
-formatEdge :: EdgeLabel -> [Attribute]
+formatEdge :: EdgeLabel -> [Data.GraphViz.Attributes.Complete.Attribute]
 formatEdge ((_,u ,_),_)  =
-    [ toLabel [HtmlFont [HtmlPointSize 8] $ htmlUnifier $ simplify u] ]
+    [ toLabel [Font [PointSize 8] $ htmlUnifier $ simplify u] ]
 
 simplify = ([] +++)
 
 htmlGoals = htmlStr . intercalate "," . map show
 
 htmlUnifier [] = [htmlStr " "]
-htmlUnifier u  = intersperse (HtmlNewline []) [ htmlStr $ show v ++ " = " ++ show t | (v,t) <- u ]
+htmlUnifier u  = intersperse (Newline []) [ htmlStr $ show v ++ " = " ++ show t | (v,t) <- u ]
 
 modifyLabel node f =
    modify $ relabelNode f node
 
-colorize color label = [HtmlFont [HtmlColor (X11Color color)] label]
+colorize color label = [Font [Data.GraphViz.Attributes.HTML.Color (X11Color color)] label]
 
 hash :: Path -> Int
 -- TODO This is a complicated way to hash a list of integers.
@@ -152,3 +154,6 @@
 hash = fromEnum . hashString . show
 
 filterOriginal = filter $ \(VariableName n _, _) -> n == 0
+
+hashString = fromIntegral . foldr f 0
+  where f c m = ord c + (m * 128) `rem` 1500007
diff --git a/prolog-graph-lib.cabal b/prolog-graph-lib.cabal
--- a/prolog-graph-lib.cabal
+++ b/prolog-graph-lib.cabal
@@ -1,11 +1,10 @@
 Name:                prolog-graph-lib
-Version:             0.2.0.1
+Version:             0.2.1
 Synopsis:            Generating images of resolution trees for Prolog queries.
 Description:         This is the library part (See <http://hackage.haskell.org/package/prolog-graph> for the command line tool).
 License:             PublicDomain
 Author:              Matthias Bartsch
-Maintainer:          none
-Homepage:            https://github.com/Erdwolf/prolog
+Maintainer:          Marcel Fourné (haskell@marcelfourne.de)
 Category:            Language
 Build-type:          Simple
 Cabal-version:       >=1.6
@@ -20,3 +19,7 @@
     mtl >= 2.0.1.0,
     text >= 0.11.1.5,
     graphviz >= 2999.12.0.3
+
+source-repository head
+  type: git
+  location: https://github.com/mfourne/prolog-graph-lib