    -- | Simple graphviz output.
    module Data.Graph.Inductive.Graphviz(
        Orient(..),
        graphviz, graphviz'
    ) where

    import Data.Graph.Inductive.Graph

    data Orient = Portrait | Landscape deriving (Eq, Show)

    o2s :: Orient -> String
    o2s Portrait = "\trotate = \"0\"\n"
    o2s Landscape = "\trotate = \"90\"\n"

    -- | Formats a graph for use in graphviz.
    graphviz :: (Graph g, Show a, Show b) =>    g a b   -- ^ The graph to format
    					 -> String  -- ^ The title of the graph
    					 -> (Double, Double)	-- ^ The size
    								-- of the page
    					 -> (Int, Int)	-- ^ The width and
    							-- height of the page
    							-- grid
    					 -> Orient  -- ^ The orientation of
    						    -- the graph.
    					 -> String

    i2d :: Int -> Double
    i2d = fromInteger . toInteger

    graphviz g t (w, h) p@(pw', ph') o =
        let n = labNodes g
    	e = labEdges g
    	ns = concatMap sn n
    	es = concatMap se e
    	sz w' h' = if o == Portrait then show w'++","++show h' else show h'++","++show w'
    	ps = show w++","++show h
    	(pw, ph) = if o == Portrait then p else (ph', pw')
    	--gs = show ((w*(i2d pw))-m)++","++show ((h*(i2d ph))-m)
    	gs = sz (w*(i2d pw)) (h*(i2d ph))
        in "digraph "++t++" {\n"
    	    ++"\tmargin = \"0\"\n"
    	    ++"\tpage = \""++ps++"\"\n"
    	    ++"\tsize = \""++gs++"\"\n"
    	    ++o2s o
    	    ++"\tratio = \"fill\"\n"
    	    ++ns
    	    ++es
    	++"}"
        where sn (n, a) | sa == ""	= ""
    		    | otherwise	= '\t':(show n ++ sa ++ "\n")
    	    where sa = sl a
    	  se (n1, n2, b) = '\t':(show n1 ++ " -> " ++ show n2 ++ sl b ++ "\n")

    -- | Format a graph for graphviz with reasonable defaults: title of \"fgl\",
    -- 8.5x11 pages, one page, landscape orientation
    graphviz' :: (Graph g, Show a, Show b) => g a b -> String
    graphviz' g = graphviz g "fgl" (8.5,11.0) (1,1) Landscape

    sq :: String -> String
    sq ('"':s) | last s == '"'  = init s
    	   | otherwise	    = s
    sq ('\'':s) | last s == '\''	= init s
    	    | otherwise		= s
    sq s = s

    sl :: (Show a) => a -> String
    sl a =
        let l = sq (show a)
        in if (l /= "()") then (" [label = \""++l++"\"]") else ""