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+-- | Dump a directed graph in dot format. Used for debugging purposes
+--
+module Hakyll.Core.DirectedGraph.Dot
+ ( toDot
+ , writeDot
+ ) where
+
+import Hakyll.Core.DirectedGraph
+import qualified Data.Set as S
+
+-- | Convert a directed graph into dot format for debugging purposes
+--
+toDot :: Ord a
+ => (a -> String) -- ^ Convert nodes to dot names
+ -> DirectedGraph a -- ^ Graph to dump
+ -> String -- ^ Resulting string
+toDot showTag graph = unlines $ concat
+ [ return "digraph dependencies {"
+ , concatMap showNode (S.toList $ nodes graph)
+ , return "}"
+ ]
+ where
+ showNode node = map (showEdge node) $ S.toList $ neighbours node graph
+ showEdge x y = " \"" ++ showTag x ++ "\" -> \"" ++ showTag y ++ "\";"
+
+-- | Write out the @.dot@ file to a given file path. See 'toDot' for more
+-- information.
+--
+writeDot :: Ord a => FilePath -> (a -> String) -> DirectedGraph a -> IO ()
+writeDot path showTag = writeFile path . toDot showTag