diff -r 21aa0195aab9 -r 182da222fceb lemon/lemon_reader.h
--- a/lemon/lemon_reader.h	Mon Jun 13 16:10:36 2005 +0000
+++ b/lemon/lemon_reader.h	Mon Jun 13 17:13:56 2005 +0000
@@ -36,10 +36,33 @@
 #include <lemon/utility.h>
 #include <lemon/bits/item_reader.h>
 
+#include <lemon/concept_check.h>
+#include <lemon/concept/maps.h>
 
 namespace lemon {
 
   namespace _reader_bits {
+
+    template <typename Item>
+    class ItemIdReader {
+    public:
+
+      bool isIdReader() { return true; }
+
+      Item readId(std::istream&, Item) { return Item();}
+      
+      template <class _ItemIdReader>
+      struct Constraints {
+	void constraints() {
+	  bool b = reader.isIdReader();
+	  ignore_unused_variable_warning(b);
+	  Item item = reader.readId(is, Item());
+	}
+	_ItemIdReader& reader;
+	std::istream& is;
+      };
+
+    };
   
     template <typename T>
     bool operator<(T, T) {
@@ -531,6 +554,7 @@
     public:
       typedef _Item Item;
       virtual Item read(std::istream& is) const = 0;
+      virtual bool isIdReader() const = 0;
     };
 
     template <typename _Item, typename _BoxedIdReader>
@@ -547,6 +571,10 @@
       virtual Item read(std::istream& is) const {
 	return boxedIdReader.readId(is, Item());
       }
+
+      virtual bool isIdReader() const {
+	return boxedIdReader.isIdReader();
+      }
     };
 
     class ValueReaderBase {
@@ -817,9 +845,10 @@
 		  const NodeIdReader& _nodeIdReader, 
 		  const std::string& _id = std::string(),
 		  const DefaultSkipper& _skipper = DefaultSkipper()) 
-      : Parent(_reader), graph(_graph), id(_id), skipper(_skipper),
-	nodeIdReader(new IdReader<Node, NodeIdReader>(_nodeIdReader)) {} 
-
+      : Parent(_reader), graph(_graph), id(_id), skipper(_skipper) {
+      checkConcept<_reader_bits::ItemIdReader<Node>, NodeIdReader>();
+      nodeIdReader.reset(new IdReader<Node, NodeIdReader>(_nodeIdReader));
+    }
     /// \brief Destructor.
     ///
     /// Destructor for EdgeSetReader.
@@ -921,6 +950,9 @@
     ///
     /// It reads the content of the section.
     virtual void read(std::istream& is) {
+      if (!nodeIdReader->isIdReader()) {
+	throw DataFormatError("Cannot find nodeset or ID map");
+      }
       std::vector<ReaderBase<Edge>* > index;
       std::string line;
 
@@ -1033,9 +1065,10 @@
 		       const NodeIdReader& _nodeIdReader, 
 		       const std::string& _id = std::string(),
 		       const DefaultSkipper& _skipper = DefaultSkipper()) 
-      : Parent(_reader), graph(_graph), id(_id), skipper(_skipper),
-	nodeIdReader(new IdReader<Node, NodeIdReader>(_nodeIdReader)) {} 
-
+      : Parent(_reader), graph(_graph), id(_id), skipper(_skipper) {
+      checkConcept<_reader_bits::ItemIdReader<Node>, NodeIdReader>();
+      nodeIdReader.reset(new IdReader<Node, NodeIdReader>(_nodeIdReader));
+    }
     /// \brief Destructor.
     ///
     /// Destructor for UndirEdgeSetReader.
@@ -1197,6 +1230,9 @@
     ///
     /// It reads the content of the section.
     virtual void read(std::istream& is) {
+      if (!nodeIdReader->isIdReader()) {
+	throw DataFormatError("Cannot find nodeset or ID map");
+      }
       std::vector<ReaderBase<UndirEdge>* > index;
       std::string line;
 
@@ -1302,8 +1338,10 @@
     template <typename _IdReader>
     NodeReader(LemonReader& _reader, const _IdReader& _idReader, 
 	       const std::string& _id = std::string()) 
-      : Parent(_reader), id(_id), 
-	idReader(new IdReader<typename Graph::Node, _IdReader>(_idReader)) {} 
+      : Parent(_reader), id(_id) {
+      checkConcept<_reader_bits::ItemIdReader<Node>, _IdReader>();
+      idReader.reset(new IdReader<Node, _IdReader>(_idReader));
+    }
 
     /// \brief Destructor.
     ///
@@ -1347,6 +1385,9 @@
     ///
     /// It reads the content of the section.
     virtual void read(std::istream& is) {
+      if (!idReader->isIdReader()) {
+	throw DataFormatError("Cannot find nodeset or ID map");
+      }
       std::string line;
       while (getline(is, line)) {
 	std::istringstream ls(line);
@@ -1394,8 +1435,10 @@
     template <typename _IdReader>
     EdgeReader(LemonReader& _reader, const _IdReader& _idReader, 
 	       const std::string& _id = std::string()) 
-      : Parent(_reader), id(_id), 
-	idReader(new IdReader<typename Graph::Edge, _IdReader>(_idReader)) {} 
+      : Parent(_reader), id(_id) {
+      checkConcept<_reader_bits::ItemIdReader<Edge>, _IdReader>();
+      idReader.reset(new IdReader<Edge, _IdReader>(_idReader));
+    }
 
     /// \brief Destructor.
     ///
@@ -1438,6 +1481,9 @@
     ///
     /// It reads the content of the section.
     virtual void read(std::istream& is) {
+      if (!idReader->isIdReader()) {
+	throw DataFormatError("Cannot find edgeset or ID map");
+      }
       std::string line;
       while (getline(is, line)) {
 	std::istringstream ls(line);
@@ -1487,10 +1533,12 @@
     template <typename _IdReader>
     UndirEdgeReader(LemonReader& _reader, const _IdReader& _idReader, 
 	       const std::string& _id = std::string()) 
-      : Parent(_reader), id(_id), 
-	undirEdgeIdReader(new IdReader<UndirEdge, _IdReader>(_idReader)),
-	edgeIdReader(new IdReader<Edge, _IdReader>(_idReader))
-    {} 
+      : Parent(_reader), id(_id) {
+      checkConcept<_reader_bits::ItemIdReader<UndirEdge>, _IdReader>();
+      checkConcept<_reader_bits::ItemIdReader<Edge>, _IdReader>();
+      undirEdgeIdReader.reset(new IdReader<UndirEdge, _IdReader>(_idReader));
+      egdeIdReader.reset(new IdReader<Edge, _IdReader>(_idReader));
+    }
 
     /// \brief Destructor.
     ///
@@ -1545,6 +1593,12 @@
     ///
     /// It reads the content of the section.
     virtual void read(std::istream& is) {
+      if (!edgeIdReader->isIdReader()) {
+	throw DataFormatError("Cannot find undirected edgeset or ID map");
+      }
+      if (!undirEdgeIdReader->isIdReader()) {
+	throw DataFormatError("Cannot find undirected edgeset or ID map");
+      }
       std::string line;
       while (getline(is, line)) {
 	std::istringstream ls(line);