diff --git a/GraphViz.hs b/GraphViz.hs
new file mode 100644
--- /dev/null
+++ b/GraphViz.hs
@@ -0,0 +1,90 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module GraphViz where
+
+import Control.Applicative ((<$>), Applicative(..))
+import Control.Monad
+import Control.Monad.State
+import Control.Monad.Error
+import Data.List (intercalate, intersperse)
+
+import qualified Data.Graph.Inductive as Graph
+import Data.HashTable (hashString)
+
+import Data.GraphViz (preview, runGraphviz, setDirectedness, graphToDot, GraphvizOutput(Png), toLabel, nonClusteredParams, GraphvizParams(..))
+import Data.GraphViz.Attributes.Colors (Color(X11Color), X11Color(..))
+import Data.GraphViz.Attributes.HTML
+
+import qualified Data.Text.Lazy
+
+import Language.Prolog
+
+htmlStr = HtmlStr . Data.Text.Lazy.pack
+
+
+-- Graphical output of derivation tree
+resolveTree p q = preview =<< execGraphGenT (resolve_ p q)
+
+resolveTreeToFile path p q = do
+ graph <- execGraphGenT (resolve_ p q)
+ runGraphviz (setDirectedness graphToDot params graph) Png path
+   where
+    params = nonClusteredParams { fmtNode = \ (_,l) -> [toLabel l]
+                                , fmtEdge = \ (_, _, l) -> [toLabel l]
+                                }
+
+
+type Graph = Graph.Gr HtmlText HtmlText
+
+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 Graph.empty
+execGraphGenT (GraphGenT st) = execStateT st Graph.empty
+
+
+instance Monad m => MonadGraphGen (GraphGenT m) where
+
+   createConnections usf gs branches = do
+      let current = hash (usf, gs)
+      let label = makeNodeLabel usf gs
+      ensureNode current label
+      forM_ branches $ \x@(u',gs') -> do
+         connect current u' gs'
+      when (null branches) $ do
+         modifyLabel current (colorize Red)
+
+   markSolution usf = do
+      let current = hash (usf,[])
+      modifyLabel current (colorize Green)
+
+   markCutBranches stackPrefix = do
+      forM_ stackPrefix $ \(u_,gs_,alts_) -> do
+         forM_ alts_ $ \x -> do
+            let child = hash x
+            modifyLabel child (colorize Gray)
+
+
+ensureNode node label =
+   modify $ \graph ->
+      if Graph.gelem node graph
+         then graph
+         else Graph.insNode (node, label) graph
+
+makeNodeLabel _ [] = [htmlStr "[]"]
+makeNodeLabel _ gs = [htmlStr $ intercalate "," $ map show gs]
+
+makeEdgeLabel [] _ = [HtmlFont [HtmlPointSize 8] [htmlStr "{}"]]
+makeEdgeLabel u  _ = [HtmlFont [HtmlPointSize 8] $ intersperse (HtmlNewline []) [htmlStr $ show v ++ " = " ++ show t | (v,t) <- u]]
+
+modifyLabel node f = do
+   modify $ Graph.gmap $ \cxt@(in_,node',label,out) ->
+      if node == node'
+         then (in_, node', f label, out)
+         else cxt
+
+colorize color label = [HtmlFont [HtmlColor (X11Color color)] label]
+
+connect current u gs = do
+   let new = hash (u, gs)
+   modify $ Graph.insNode (new, makeNodeLabel u gs)
+   modify $ Graph.insEdge (current, new, makeEdgeLabel u gs)
+
+hash = fromEnum . hashString . show
diff --git a/Language/Prolog/GraphViz.hs b/Language/Prolog/GraphViz.hs
new file mode 100644
--- /dev/null
+++ b/Language/Prolog/GraphViz.hs
@@ -0,0 +1,2 @@
+module Language.Prolog.GraphViz (module GraphViz) where
+import GraphViz
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/prolog-graph-lib.cabal b/prolog-graph-lib.cabal
new file mode 100644
--- /dev/null
+++ b/prolog-graph-lib.cabal
@@ -0,0 +1,26 @@
+Name:                prolog-graph-lib
+Version:             0.1
+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:          bartsch@cs.uni-bonn.de
+Homepage:            https://github.com/Erdwolf/prolog
+Category:            Language
+Build-type:          Simple
+Cabal-version:       >=1.6
+
+Source-repository head
+   type: git
+   location: git://github.com/Erdwolf/prolog.git
+
+Library
+  Exposed-Modules: Language.Prolog.GraphViz
+  Other-Modules: GraphViz
+  Build-depends:
+    prolog == 0.1.*,
+    base >=4 && <5,
+    fgl >= 5.4.2.4,
+    mtl >= 2.0.1.0,
+    text >= 0.11.1.5,
+    graphviz >= 2999.12.0.3