diff -r 9ba88ddc629c -r 4283998fb2be src/lemon/lemon_writer.h
--- a/src/lemon/lemon_writer.h	Thu May 19 11:46:42 2005 +0000
+++ b/src/lemon/lemon_writer.h	Thu May 19 11:49:42 2005 +0000
@@ -243,7 +243,7 @@
 	: idWriter(_idWriter) {}
 
       virtual void write(std::ostream& os, const Item& item) const {
-	return idWriter.writeId(os, item);
+	idWriter.writeId(os, item);
       }
     };
   };
@@ -273,7 +273,7 @@
 
     typedef _Graph Graph;
     typedef _Traits Traits;
-    typedef typename Graph::Node Item;
+    typedef typename Graph::Node Node;
 
     /// \brief Constructor.
     ///
@@ -319,7 +319,7 @@
     NodeSetWriter& writeNodeMap(std::string name, const Map& map, 
 			    const Writer& writer = Writer()) {
       writers.push_back(
-	make_pair(name, new MapWriter<Item, Map, Writer>(map, writer)));
+	make_pair(name, new MapWriter<Node, Map, Writer>(map, writer)));
       return *this;
     }
 
@@ -379,7 +379,7 @@
     /// named map then it will write the map value belongs to the node.
     /// Otherwise if the \c forceId parameter was true it will write
     /// its id in the graph. 
-    void writeId(std::ostream& os, const Item& item) const {
+    void writeId(std::ostream& os, const Node& item) const {
       if (forceIdMap) {
 	os << graph.id(item);
       } else {
@@ -389,10 +389,10 @@
 
   private:
 
-    typedef std::vector<std::pair<std::string, WriterBase<Item>*> > MapWriters;
+    typedef std::vector<std::pair<std::string, WriterBase<Node>*> > MapWriters;
     MapWriters writers;
 
-    WriterBase<Item>* idMap;
+    WriterBase<Node>* idMap;
     bool forceIdMap;
    
     typename SmartConstReference<Graph>::Type graph;   
@@ -430,7 +430,8 @@
 
     typedef _Graph Graph;
     typedef _Traits Traits;
-    typedef typename Graph::Edge Item;
+    typedef typename Graph::Node Node;
+    typedef typename Graph::Edge Edge;
 
     /// \brief Constructor.
     ///
@@ -446,8 +447,7 @@
 		  bool _forceIdMap = true)
       : Parent(_writer), idMap(0), forceIdMap(_forceIdMap),
 	graph(_graph), id(_id),
-	nodeIdWriter(new IdWriter<typename Graph::Node, NodeIdWriter>
-		     (_nodeIdWriter)) {} 
+	nodeIdWriter(new IdWriter<Node, NodeIdWriter>(_nodeIdWriter)) {} 
 
     /// \brief Destructor.
     ///
@@ -481,7 +481,7 @@
     EdgeSetWriter& writeEdgeMap(std::string name, const Map& map, 
 			    const Writer& writer = Writer()) {
       writers.push_back(
-	make_pair(name, new MapWriter<Item, Map, Writer>(map, writer)));
+	make_pair(name, new MapWriter<Edge, Map, Writer>(map, writer)));
       return *this;
     }
 
@@ -546,7 +546,7 @@
     /// named map then it will write the map value belongs to the edge.
     /// Otherwise if the \c forceId parameter was true it will write
     /// its id in the graph. 
-    void writeId(std::ostream& os, const Item& item) const {
+    void writeId(std::ostream& os, const Edge& item) const {
       if (forceIdMap) {
 	os << graph.id(item);
       } else {
@@ -556,16 +556,16 @@
 
   private:
 
-    typedef std::vector<std::pair<std::string, WriterBase<Item>*> > MapWriters;
+    typedef std::vector<std::pair<std::string, WriterBase<Edge>*> > MapWriters;
     MapWriters writers;
 
-    WriterBase<Item>* idMap;
+    WriterBase<Edge>* idMap;
     bool forceIdMap;
    
     typename SmartConstReference<Graph>::Type graph;   
     std::string id;
 
-    std::auto_ptr<IdWriterBase<typename Graph::Node> > nodeIdWriter;
+    std::auto_ptr<IdWriterBase<Node> > nodeIdWriter;
   };
 
   /// \ingroup io_group
@@ -604,7 +604,9 @@
 
     typedef _Graph Graph;
     typedef _Traits Traits;
-    typedef typename Graph::UndirEdge Item;
+    typedef typename Graph::Node Node;
+    typedef typename Graph::Edge Edge;
+    typedef typename Graph::UndirEdge UndirEdge;
 
     /// \brief Constructor.
     ///
@@ -620,8 +622,7 @@
 		       bool _forceIdMap = true)
       : Parent(_writer), idMap(0), forceIdMap(_forceIdMap),
 	graph(_graph), id(_id),
-	nodeIdWriter(new IdWriter<typename Graph::Node, NodeIdWriter>
-		     (_nodeIdWriter)) {} 
+	nodeIdWriter(new IdWriter<Node, NodeIdWriter>(_nodeIdWriter)) {} 
 
     /// \brief Destructor.
     ///
@@ -655,7 +656,7 @@
     UndirEdgeSetWriter& writeUndirEdgeMap(std::string name, const Map& map, 
 					  const Writer& writer = Writer()) {
       writers.push_back(
-	make_pair(name, new MapWriter<Item, Map, Writer>(map, writer)));
+	make_pair(name, new MapWriter<UndirEdge, Map, Writer>(map, writer)));
       return *this;
     }
 
@@ -742,7 +743,27 @@
     /// an "id" named map then it will write the map value belongs to the 
     /// undirected edge. Otherwise if the \c forceId parameter was true it 
     /// will write its id in the graph. 
-    void writeId(std::ostream& os, const Item& item) const {
+    void writeId(std::ostream& os, const UndirEdge& item) const {
+      if (forceIdMap) {
+	os << graph.id(item);
+      } else {
+	idMap->write(os, item);
+      }
+    } 
+
+    /// \brief Write the id of the given edge.
+    ///
+    /// It writes the id of the given edge. If there was written 
+    /// an "id" named map then it will write the map value belongs to the 
+    /// edge. Otherwise if the \c forceId parameter was true it 
+    /// will write its id in the graph. If the edge is forward map
+    /// then its prefix character is \c '+' elsewhere \c '-'.
+    void writeId(std::ostream& os, const Edge& item) const {
+      if (graph.forward(item)) {
+	os << "+ ";
+      } else {
+	os << "- ";
+      }
       if (forceIdMap) {
 	os << graph.id(item);
       } else {
@@ -752,16 +773,17 @@
 
   private:
 
-    typedef std::vector<std::pair<std::string, WriterBase<Item>*> > MapWriters;
+    typedef std::vector<std::pair<std::string, 
+				  WriterBase<UndirEdge>*> > MapWriters;
     MapWriters writers;
 
-    WriterBase<Item>* idMap;
+    WriterBase<UndirEdge>* idMap;
     bool forceIdMap;
    
     typename SmartConstReference<Graph>::Type graph;   
     std::string id;
 
-    std::auto_ptr<IdWriterBase<typename Graph::Node> > nodeIdWriter;
+    std::auto_ptr<IdWriterBase<Node> > nodeIdWriter;
   };
 
   /// \ingroup io_group
@@ -778,7 +800,7 @@
   class NodeWriter : public CommonSectionWriterBase {
     typedef CommonSectionWriterBase Parent;
     typedef _Graph Graph;
-    typedef typename Graph::Node Item;
+    typedef typename Graph::Node Node;
   public:
     
     /// \brief Constructor.
@@ -806,7 +828,7 @@
     /// \brief Add a node writer command for the NodeWriter.
     ///
     /// Add a node writer command for the NodeWriter.
-    void writeNode(const std::string& name, const Item& item) {
+    void writeNode(const std::string& name, const Node& item) {
       writers.push_back(make_pair(name, &item));
     }
 
@@ -835,9 +857,9 @@
 
     std::string id;
 
-    typedef std::vector<std::pair<std::string, const Item*> > ItemWriters;
-    ItemWriters writers;
-    std::auto_ptr<IdWriterBase<Item> > idWriter;
+    typedef std::vector<std::pair<std::string, const Node*> > NodeWriters;
+    NodeWriters writers;
+    std::auto_ptr<IdWriterBase<Node> > idWriter;
   };
 
   /// \ingroup io_group
@@ -854,7 +876,7 @@
   class EdgeWriter : public CommonSectionWriterBase {
     typedef CommonSectionWriterBase Parent;
     typedef _Graph Graph;
-    typedef typename Graph::Edge Item;
+    typedef typename Graph::Edge Edge;
   public:
     
     /// \brief Constructor.
@@ -881,7 +903,7 @@
     /// \brief Add an edge writer command for the EdgeWriter.
     ///
     /// Add an edge writer command for the EdgeWriter.
-    void writeEdge(const std::string& name, const Item& item) {
+    void writeEdge(const std::string& name, const Edge& item) {
       writers.push_back(make_pair(name, &item));
     }
 
@@ -910,10 +932,10 @@
 
     std::string id;
 
-    typedef std::vector<std::pair<std::string, const Item*> > ItemWriters;
-    ItemWriters writers;
+    typedef std::vector<std::pair<std::string, const Edge*> > EdgeWriters;
+    EdgeWriters writers;
 
-    std::auto_ptr<IdWriterBase<Item> > idWriter;
+    std::auto_ptr<IdWriterBase<Edge> > idWriter;
   };
 
   /// \ingroup io_group
@@ -930,7 +952,9 @@
   class UndirEdgeWriter : public CommonSectionWriterBase {
     typedef CommonSectionWriterBase Parent;
     typedef _Graph Graph;
-    typedef typename Graph::UndirEdge Item;
+    typedef typename Graph::Node Node;
+    typedef typename Graph::Edge Edge;
+    typedef typename Graph::UndirEdge UndirEdge;
   public:
     
     /// \brief Constructor.
@@ -943,8 +967,8 @@
     UndirEdgeWriter(LemonWriter& _writer, const _IdWriter& _idWriter, 
 	       const std::string& _id = std::string()) 
       : Parent(_writer), id(_id), 
-	idWriter(new IdWriter<typename Graph::UndirEdge, _IdWriter>
-		 (_idWriter)) {} 
+	undirEdgeIdWriter(new IdWriter<UndirEdge, _IdWriter>(_idWriter)),
+	edgeIdWriter(new IdWriter<Edge, _IdWriter>(_idWriter)) {}
 
     /// \brief Destructor.
     ///
@@ -956,11 +980,18 @@
 
   public:
 
+    /// \brief Add an edge writer command for the UndirEdgeWriter.
+    ///
+    /// Add an edge writer command for the UndirEdgeWriter.
+    void writeEdge(const std::string& name, const Edge& item) {
+      edgeWriters.push_back(make_pair(name, &item));
+    }
+
     /// \brief Add an undirected edge writer command for the UndirEdgeWriter.
     ///
-    /// Add an edge writer command for the UndirEdgeWriter.
-    void writeUndirEdge(const std::string& name, const Item& item) {
-      writers.push_back(make_pair(name, &item));
+    /// Add an undirected edge writer command for the UndirEdgeWriter.
+    void writeUndirEdge(const std::string& name, const UndirEdge& item) {
+      undirEdgeWriters.push_back(make_pair(name, &item));
     }
 
   protected:
@@ -970,16 +1001,21 @@
     /// It gives back true when the header line start with \c \@undiredges,
     /// and the header line's id and the writer's id are the same.
     virtual std::string header() {
-      return "@edges " + id;
+      return "@undiredges " + id;
     }
 
     /// \brief  Writer function of the section.
     ///
     /// Write the content of the section.
     virtual void write(std::ostream& os) {
-      for (int i = 0; i < (int)writers.size(); ++i) {
-	os << writers[i].first << ' ';
-	idWriter->write(os, *(writers[i].second));
+      for (int i = 0; i < (int)undirEdgeWriters.size(); ++i) {
+	os << undirEdgeWriters[i].first << ' ';
+	undirEdgeIdWriter->write(os, *(undirEdgeWriters[i].second));
+	os << std::endl;
+      }
+      for (int i = 0; i < (int)edgeWriters.size(); ++i) {
+	os << edgeWriters[i].first << ' ';
+	edgeIdWriter->write(os, *(edgeWriters[i].second));
 	os << std::endl;
       }
     }
@@ -988,10 +1024,15 @@
 
     std::string id;
 
-    typedef std::vector<std::pair<std::string, const Item*> > ItemWriters;
-    ItemWriters writers;
+    typedef std::vector<std::pair<std::string, 
+				  const UndirEdge*> > UndirEdgeWriters;
+    UndirEdgeWriters undirEdgeWriters;
+    std::auto_ptr<IdWriterBase<UndirEdge> > undirEdgeIdWriter;
 
-    std::auto_ptr<IdWriterBase<Item> > idWriter;
+    typedef std::vector<std::pair<std::string, const Edge*> > EdgeWriters;
+    EdgeWriters edgeWriters;
+    std::auto_ptr<IdWriterBase<Edge> > edgeIdWriter;
+
   };
 
   /// \ingroup io_group