[project @ 2005-02-07 12:21:29 by simonmar]

After no response on libraries@haskell.org... John Meacham's
Data.Graph patch, which returns an extra component from
graphFromEdges.  The old version of graphFromEdges is available as
graphFromEdges'.

diff --git a/Data/Graph.hs b/Data/Graph.hs
index 4205964..2edf495 100644 (file)
--- a/Data/Graph.hs
+++ b/Data/Graph.hs
@@ -28,7 +28,7 @@ module Data.Graph(
 
        -- ** Building graphs
 
-       graphFromEdges, buildG, transposeG,
+       graphFromEdges, graphFromEdges', buildG, transposeG,
        -- reverseE,
 
        -- ** Graph properties
@@ -121,7 +121,7 @@ stronglyConnCompR [] = []  -- added to avoid creating empty array in graphFromEd
 stronglyConnCompR edges0
   = map decode forest
   where
-    (graph, vertex_fn) = graphFromEdges edges0
+    (graph, vertex_fn,_) = graphFromEdges edges0
     forest            = scc graph
     decode (Node v []) | mentions_itself v = CyclicSCC [vertex_fn v]
                       | otherwise         = AcyclicSCC (vertex_fn v)
@@ -179,6 +179,16 @@ outdegree  = mapT numEdges
 indegree :: Graph -> Table Int
 indegree  = outdegree . transposeG
 
+-- | Identical to 'graphFromEdges', except that the return value
+-- does not include the function which maps keys to vertices.  This
+-- version of 'graphFromEdges' is for backwards compatibility.
+graphFromEdges'
+       :: Ord key
+       => [(node, key, [key])]
+       -> (Graph, Vertex -> (node, key, [key]))
+graphFromEdges' x = (a,b) where
+    (a,b,_) = graphFromEdges x
+
 -- | Build a graph from a list of nodes uniquely identified by keys,
 -- with a list of keys of nodes this node should have edges to.
 -- The out-list may contain keys that don't correspond to
@@ -186,9 +196,9 @@ indegree  = outdegree . transposeG
 graphFromEdges
        :: Ord key
        => [(node, key, [key])]
-       -> (Graph, Vertex -> (node, key, [key]))
+       -> (Graph, Vertex -> (node, key, [key]), key -> Maybe Vertex)
 graphFromEdges edges0
-  = (graph, \v -> vertex_map ! v)
+  = (graph, \v -> vertex_map ! v, key_vertex)
   where
     max_v                  = length edges0 - 1
     bounds0         = (0,max_v) :: (Vertex, Vertex)