sanitize function for DirectedGraph

1 files changed, 12 insertions, 3 deletions

diff --git a/src/Hakyll/Core/DirectedGraph.hs b/src/Hakyll/Core/DirectedGraph.hs
index bf52277..66905f7 100644
--- a/src/Hakyll/Core/DirectedGraph.hs
+++ b/src/Hakyll/Core/DirectedGraph.hs
@@ -8,6 +8,7 @@ module Hakyll.Core.DirectedGraph
     , neighbours
     , reverse
     , reachableNodes
+    , sanitize
     ) where
 
 import Prelude hiding (reverse)
@@ -59,9 +60,17 @@ reachableNodes set graph = reachable (setNeighbours set) set
   where
     reachable next visited
         | S.null next = visited
-        | otherwise = reachable (sanitize neighbours') (next `S.union` visited)
+        | otherwise = reachable (sanitize' neighbours') (next `S.union` visited)
       where
-        sanitize = S.filter (`S.notMember` visited)
-        neighbours' = setNeighbours (sanitize next)
+        sanitize' = S.filter (`S.notMember` visited)
+        neighbours' = setNeighbours (sanitize' next)
 
     setNeighbours = S.unions . map (flip neighbours graph) . S.toList
+    
+-- | Remove all dangling pointers, i.e. references to notes that do 
+-- not actually exist in the graph.
+--
+sanitize :: Ord a => DirectedGraph a -> DirectedGraph a
+sanitize (DirectedGraph graph) = DirectedGraph $ M.map sanitize' $ graph
+  where
+    sanitize' (Node t n) = Node t $ S.filter (`M.member` graph) n