More fine refactoring

2 files changed, 276 insertions, 106 deletions

diff --git a/src/directed_graphs.adb b/src/directed_graphs.adb
index 93ad2cb..3914137 100644
--- a/src/directed_graphs.adb
+++ b/src/directed_graphs.adb
@@ -144,8 +144,13 @@ package body Directed_Graphs is
            (Position : in out Cursor;
             Label    : in     Node_Label_Type) is
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         Position.Container.Append_Label (Element (Position), Label);
     end Append_Label;
@@ -204,8 +209,13 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Array is
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         return Position.Container.Children (Element (Position));
     end Children;
@@ -277,6 +287,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Label_Constant_Reference is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Constant_Label_Reference (Element (Position));
     end Constant_Label_Reference;
 
@@ -383,12 +401,8 @@ package body Directed_Graphs is
         if Position.Container = null then
             return False;
         end if;
-        for C in Position.Container.Iterate_Subgraph (Position) loop
-            if Element (C) = Node and Constant_Label_Reference (C) = Label then
-                return True;
-            end if;
-        end loop;
-        return False;
+        return Contains_In_Subgraph (Position, Node) and then
+            Position.Container.Constant_Label_Reference (Node) = Label;
     end Contains_In_Subgraph;
 
     function Contains_In_Subgraph
@@ -398,9 +412,7 @@ package body Directed_Graphs is
     is
         Parent_Check, Child_Check : Boolean := False;
     begin
-        if Position.Container = null or else
-            not Position.Container.Contains (Edge)
-        then
+        if Position.Container = null then
             return False;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
@@ -411,7 +423,7 @@ package body Directed_Graphs is
                 Child_Check := True;
             end if;
             if Parent_Check and Child_Check then
-                return True;
+                return Position.Container.Contains (Edge);
             end if;
         end loop;
         return False;
@@ -425,23 +437,11 @@ package body Directed_Graphs is
     is
         Parent_Check, Child_Check : Boolean := False;
     begin
-        if Position.Container = null or else
-            not Position.Container.Contains (Edge, Label)
-        then
+        if Position.Container = null then
             return False;
         end if;
-        for C in Position.Container.Iterate_Subgraph (Position) loop
-            if Element (C) = Edge.From then
-                Parent_Check := True;
-            end if;
-            if Element (C) = Edge.To then
-                Child_Check := True;
-            end if;
-            if Parent_Check and Child_Check then
-                return True;
-            end if;
-        end loop;
-        return False;
+        return Contains_In_Subgraph (Position, Edge) and then
+            Position.Container.Constant_Label_Reference (Edge) = Label;
     end Contains_In_Subgraph;
 
 
@@ -495,7 +495,9 @@ package body Directed_Graphs is
             return False;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
-            if Position.Container.Node_Labels.Contains (Element (C)) then
+            if Position.Container.Has_Label (Element (C)) and then
+                Position.Container.Constant_Label_Reference (Element (C)) = Label
+            then
                 return True;
             end if;
         end loop;
@@ -522,7 +524,7 @@ package body Directed_Graphs is
             Check := Edge_Label_Maps.Key (E);
             if Inside.Contains (Check.From) and then
                 Inside.Contains (Check.To) and then
-                Edge_Label_Maps.Element (E) = Label
+                Position.Container.Edge_Labels.Constant_Reference (E) = Label
             then
                 return True;
             end if;
@@ -591,9 +593,7 @@ package body Directed_Graphs is
     function Degree
            (Container : in Graph;
             Node      : in Node_Type)
-        return Ada.Containers.Count_Type
-    is
-        use type Ada.Containers.Count_Type;
+        return Ada.Containers.Count_Type is
     begin
         return Container.Indegree (Node) + Container.Outdegree (Node);
     end Degree;
@@ -707,6 +707,9 @@ package body Directed_Graphs is
            (Container : in out Graph;
             Node      : in     Node_Type) is
     begin
+        if Impl.Checks and then not Container.Node_Labels.Contains (Node) then
+            raise Constraint_Error with "Node does not have label";
+        end if;
         Container.Node_Labels.Delete (Node);
     end Delete_Label;
 
@@ -728,6 +731,9 @@ package body Directed_Graphs is
            (Container : in out Graph;
             Edge      : in     Edge_Type) is
     begin
+        if Impl.Checks and then not Container.Edge_Labels.Contains (Edge) then
+            raise Constraint_Error with "Edge does not have label";
+        end if;
         Container.Edge_Labels.Delete (Edge);
     end Delete_Label;
 
@@ -742,7 +748,6 @@ package body Directed_Graphs is
            (Position : in out Cursor)
     is
         Nodes : Node_Vectors.Vector;
-        function V2A is new Vector_To_Array (Node_Type, Node_Array, Node_Vectors);
     begin
         if Impl.Checks and then Position.Container = null then
             raise Constraint_Error with "Graph does not exist";
@@ -750,7 +755,9 @@ package body Directed_Graphs is
         for C in Position.Container.Iterate_Subgraph (Position) loop
             Nodes.Append (Element (C));
         end loop;
-        Position.Container.Delete (V2A (Nodes));
+        for N of Nodes loop
+            Position.Container.Delete (N);
+        end loop;
     end Delete_Subgraph;
 
 
@@ -764,7 +771,6 @@ package body Directed_Graphs is
            (Container : in Graph)
         return Ada.Containers.Count_Type
     is
-        use type Ada.Containers.Count_Type;
         Result : Ada.Containers.Count_Type := 0;
     begin
         for C of Container.Connections loop
@@ -777,11 +783,15 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Ada.Containers.Count_Type
     is
-        use type Ada.Containers.Count_Type;
         Result : Ada.Containers.Count_Type := 0;
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
             Result := Result + Outdegree (Position);
@@ -820,11 +830,16 @@ package body Directed_Graphs is
         Tos : Edge_Vectors.Vector;
         function V2A is new Vector_To_Array (Edge_Type, Edge_Array, Edge_Vectors);
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
-            for E of Outbound (Position) loop
+            for E of Outbound (C) loop
                 Tos.Append (E);
             end loop;
         end loop;
@@ -932,8 +947,13 @@ package body Directed_Graphs is
         Result : Node_Vectors.Vector;
         function V2A is new Vector_To_Array (Node_Type, Node_Array, Node_Vectors);
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
             if Position.Container.Node_Labels.Constant_Reference (Element (C)) = Label then
@@ -951,20 +971,24 @@ package body Directed_Graphs is
         Nodes : Node_Vectors.Vector;
         Result : Edge_Vectors.Vector;
         function V2A is new Vector_To_Array (Edge_Type, Edge_Array, Edge_Vectors);
-        function Keys is new Key_Vector (Edge_Type, Edge_Label_Type, Edge_Label_Maps, Edge_Vectors);
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
             Nodes.Append (Element (C));
         end loop;
-        for E of Keys (Position.Container.Edge_Labels) loop
-            if Nodes.Contains (E.From) and then
-                Nodes.Contains (E.To) and then
+        for E in Position.Container.Edge_Labels.Iterate loop
+            if Nodes.Contains (Edge_Label_Maps.Key (E).From) and then
+                Nodes.Contains (Edge_Label_Maps.Key (E).To) and then
                 Position.Container.Edge_Labels.Constant_Reference (E) = Label
             then
-                Result.Append (E);
+                Result.Append (Edge_Label_Maps.Key (E));
             end if;
         end loop;
         return V2A (Result);
@@ -979,11 +1003,9 @@ package body Directed_Graphs is
 
     function First
            (Container : in Graph)
-        return Cursor
-    is
-        use type Ada.Containers.Count_Type;
+        return Cursor is
     begin
-        if Impl.Checks and then Container.Node_Count = 0 then
+        if Impl.Checks and then Container.Is_Empty then
             raise Constraint_Error with "Graph is empty";
         end if;
         return
@@ -1039,6 +1061,23 @@ package body Directed_Graphs is
            (Parent, Child : in Cursor)
         return Boolean is
     begin
+        if Impl.Checks then
+            if Parent.Container = null then
+                raise Constraint_Error with "Parent Graph does not exist";
+            end if;
+            if Child.Container = null then
+                raise Constraint_Error with "Child Graph does not exist";
+            end if;
+            if Parent.Container /= Child.Container then
+                raise Constraint_Error with "Parent and Child Graph mismatch";
+            end if;
+            if not Parent.Container.Contains (Element (Parent)) then
+                raise Constraint_Error with "Graph does not contain parent node";
+            end if;
+            if not Child.Container.Contains (Element (Child)) then
+                raise Constraint_Error with "Graph does not contain child node";
+            end if;
+        end if;
         return Parent.Container.Has_Edge (Element (Parent), Element (Child));
     end Has_Edge;
 
@@ -1076,6 +1115,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Boolean is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Has_Label (Element (Position));
     end Has_Label;
 
@@ -1107,6 +1154,23 @@ package body Directed_Graphs is
            (Parent, Child : in Cursor)
         return Boolean is
     begin
+        if Impl.Checks then
+            if Parent.Container = null then
+                raise Constraint_Error with "Parent Graph does not exist";
+            end if;
+            if Child.Container = null then
+                raise Constraint_Error with "Child Graph does not exist";
+            end if;
+            if Parent.Container /= Child.Container then
+                raise Constraint_Error with "Parent and Child Graph mismatch";
+            end if;
+            if not Parent.Container.Contains (Element (Parent)) then
+                raise Constraint_Error with "Graph does not contain parent node";
+            end if;
+            if not Child.Container.Contains (Element (Child)) then
+                raise Constraint_Error with "Graph does not contain child node";
+            end if;
+        end if;
         return Parent.Container.Has_Labeled_Edge (Element (Parent), Element (Child));
     end Has_Labeled_Edge;
 
@@ -1130,6 +1194,23 @@ package body Directed_Graphs is
            (Left, Right : in Cursor)
         return Boolean is
     begin
+        if Impl.Checks then
+            if Left.Container = null then
+                raise Constraint_Error with "Left operand Graph does not exist";
+            end if;
+            if Right.Container = null then
+                raise Constraint_Error with "Right operand Graph does not exist";
+            end if;
+            if Left.Container /= Right.Container then
+                raise Constraint_Error with "Left and right operand Graph mismatch";
+            end if;
+            if not Left.Container.Contains (Element (Left)) then
+                raise Constraint_Error with "Graph does not contain left operand node";
+            end if;
+            if not Right.Container.Contains (Element (Right)) then
+                raise Constraint_Error with "Graph does not contain right operand node";
+            end if;
+        end if;
         return Left.Container.Has_Neighbor (Element (Left), Element (Right));
     end Has_Neighbor;
 
@@ -1165,6 +1246,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Edge_Array is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Inbound (Element (Position));
     end Inbound;
 
@@ -1180,7 +1269,6 @@ package body Directed_Graphs is
             Node      : in Node_Type)
         return Ada.Containers.Count_Type
     is
-        use type Ada.Containers.Count_Type;
         Lock : Impl.With_Lock (Container.Tamper_Info'Unrestricted_Access);
         Count : Ada.Containers.Count_Type := 0;
     begin
@@ -1198,6 +1286,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Ada.Containers.Count_Type is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Indegree (Element (Position));
     end Indegree;
 
@@ -1309,7 +1405,7 @@ package body Directed_Graphs is
     function Iterate_Subgraph
            (Container : in Graph;
             Position  : in Cursor)
-        return Graph_Iterator_Interfaces.Forward_Iterator'Class
+        return Graph_Iterator_Interfaces.Reversible_Iterator'Class
     is
         Root_Node, Current_Node : Node_Type;
         Path_Up   : Node_Vectors.Vector;
@@ -1338,6 +1434,7 @@ package body Directed_Graphs is
                 end if;
             end loop Select_Next;
         end loop Depth_First;
+        Node_Sort.Sort (Visited);
         return It : Subgraph_Iterator do
             It.Container := Container'Unrestricted_Access;
             It.Nodes := Visited;
@@ -1388,6 +1485,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Label_Type is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Label (Element (Position));
     end Label;
 
@@ -1442,6 +1547,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Label_Reference is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Label_Reference (Element (Position));
     end Label_Reference;
 
@@ -1495,6 +1608,14 @@ package body Directed_Graphs is
             Children :    out Node_Array;
             Label    :    out Node_Label_Type) is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         Position.Container.Labeled_Context (Element (Position), Parents, Children, Label);
     end Labeled_Context;
 
@@ -1588,6 +1709,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Array is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Neighbors (Element (Position));
     end Neighbors;
 
@@ -1625,6 +1754,9 @@ package body Directed_Graphs is
     is
         Cursor_Copy : Cursor := Position;
     begin
+        if Impl.Checks and then Object.Container /= Position.Container then
+            raise Constraint_Error with "Iterator and Cursor refer to different Graphs";
+        end if;
         Next (Cursor_Copy);
         return Cursor_Copy;
     end Next;
@@ -1637,6 +1769,9 @@ package body Directed_Graphs is
         use type Node_Maps.Cursor;
         Result : Cursor := Position;
     begin
+        if Impl.Checks and then Object.Container /= Position.Container then
+            raise Constraint_Error with "Iterator and Cursor refer to different Graphs";
+        end if;
         if Position.Container = null or Position.Place = Node_Maps.No_Element then
             return No_Element;
         end if;
@@ -1673,18 +1808,22 @@ package body Directed_Graphs is
 
     function Node_Count
            (Position : in Cursor)
-        return Ada.Containers.Count_Type
-    is
-        use type Ada.Containers.Count_Type;
-        Result : Ada.Containers.Count_Type := 0;
+        return Ada.Containers.Count_Type is
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
-        for N in Position.Container.Iterate_Subgraph (Position) loop
-            Result := Result + 1;
-        end loop;
-        return Result;
+        declare
+            It : Graph_Iterator_Interfaces.Reversible_Iterator'Class :=
+                Position.Container.Iterate_Subgraph (Position);
+        begin
+            return Subgraph_Iterator (It).Nodes.Length;
+        end;
     end Node_Count;
 
 
@@ -1738,8 +1877,13 @@ package body Directed_Graphs is
         Result : Node_Vectors.Vector;
         function V2A is new Vector_To_Array (Node_Type, Node_Array, Node_Vectors);
     begin
-        if Impl.Checks and then Position.Container = null then
-            raise Constraint_Error with "Graph does not exist";
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
         end if;
         for C in Position.Container.Iterate_Subgraph (Position) loop
             Result.Append (Element (C));
@@ -1780,6 +1924,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Edge_Array is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Outbound (Element (Position));
     end Outbound;
 
@@ -1806,6 +1958,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Ada.Containers.Count_Type is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Outdegree (Element (Position));
     end Outdegree;
 
@@ -1840,6 +2000,14 @@ package body Directed_Graphs is
            (Position : in Cursor)
         return Node_Array is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         return Position.Container.Parents (Element (Position));
     end Parents;
 
@@ -1877,6 +2045,9 @@ package body Directed_Graphs is
     is
         Cursor_Copy : Cursor := Position;
     begin
+        if Impl.Checks and then Object.Container /= Position.Container then
+            raise Constraint_Error with "Iterator and Cursor refer to different Graphs";
+        end if;
         Previous (Cursor_Copy);
         return Cursor_Copy;
     end Previous;
@@ -1889,6 +2060,9 @@ package body Directed_Graphs is
         use type Node_Maps.Cursor;
         Result : Cursor := Position;
     begin
+        if Impl.Checks and then Object.Container /= Position.Container then
+            raise Constraint_Error with "Iterator and Cursor refer to different Graphs";
+        end if;
         if Position.Container = null or Position.Place = Node_Maps.No_Element then
             return No_Element;
         end if;
@@ -1973,6 +2147,9 @@ package body Directed_Graphs is
             Node      : in     Node_Type;
             Label     : in     Node_Label_Type) is
     begin
+        if Impl.Checks and then not Container.Contains (Node) then
+            raise Constraint_Error with "Graph does not contain node";
+        end if;
         Container.Node_Labels.Replace (Node, Label);
     end Replace_Label;
 
@@ -1980,6 +2157,14 @@ package body Directed_Graphs is
            (Position : in out Cursor;
             Label    : in     Node_Label_Type) is
     begin
+        if Impl.Checks then
+            if Position.Container = null then
+                raise Constraint_Error with "Graph does not exist";
+            end if;
+            if not Has_Element (Position) then
+                raise Constraint_Error with "Cursor points to nothing";
+            end if;
+        end if;
         Position.Container.Replace_Label (Element (Position), Label);
     end Replace_Label;
 
@@ -1988,6 +2173,9 @@ package body Directed_Graphs is
             Edge      : in     Edge_Type;
             Label     : in     Edge_Label_Type) is
     begin
+        if Impl.Checks and then not Container.Contains (Edge) then
+            raise Constraint_Error with "Graph does not contain edge";
+        end if;
         Container.Edge_Labels.Replace (Edge, Label);
     end Replace_Label;
 
@@ -2136,40 +2324,19 @@ package body Directed_Graphs is
             Count     : in Positive := 1)
         return Node_Array
     is
-        function Keys is new Key_Vector (Node_Type, Node_Vectors.Vector, Node_Maps, Node_Vectors);
-        Nodes : Node_Array (1 .. Count);
-        Used : Node_Vectors.Vector := Keys (Container.Connections);
-        Next_Node : Node_Type := Node_Type'First;
-        Vector_Index : Positive := 1;
-        Result_Index : Positive := 1;
-    begin
-        Node_Sort.Sort (Used);
-        while Result_Index <= Nodes'Last loop
-            if Vector_Index > Used.Last_Index or else
-                Next_Node < Used (Vector_Index)
-            then
-                Nodes (Result_Index) := Next_Node;
-                if Impl.Checks and then
-                    (Next_Node = Node_Type'Last and Result_Index < Nodes'Last)
-                then
-                    raise Constraint_Error with "Not enough unused nodes";
-                else
-                    Next_Node := Node_Type'Succ (Next_Node);
-                    Result_Index := Result_Index + 1;
-                end if;
-            elsif Next_Node > Used (Vector_Index) then
-                Vector_Index := Vector_Index + 1;
-            else  --  Next_Node = Used (Vector_Index)
-                if Impl.Checks and then
-                    Next_Node = Node_Type'Last
-                then
-                    raise Constraint_Error with "Not enough unused nodes";
-                else
-                    Next_Node := Node_Type'Succ (Next_Node);
-                end if;
+        function V2A is new Vector_To_Array (Node_Type, Node_Array, Node_Vectors);
+        Nodes : Node_Vectors.Vector;
+    begin
+        for N in Node_Type'First .. Node_Type'Last loop
+            if not Container.Contains (N) then
+                Nodes.Append (N);
+            end if;
+            if Integer (Nodes.Length) = Count then
+                return V2A (Nodes);
             end if;
         end loop;
-        return Nodes;
+        raise Constraint_Error with "Not enough unused nodes";
+        return V2A (Nodes);
     end Unused_Nodes;
 
 
diff --git a/src/directed_graphs.ads b/src/directed_graphs.ads
index 7039d76..c4d48f7 100644
--- a/src/directed_graphs.ads
+++ b/src/directed_graphs.ads
@@ -560,14 +560,18 @@ package Directed_Graphs is
 
 
 
+    --  Iterates through all Nodes in the Graph in order of Node_Type.
     function Iterate
            (Container : in Graph)
         return Graph_Iterator_Interfaces.Reversible_Iterator'Class;
 
+    --  Iterates through all reachable Nodes in the subgraph in order
+    --  of Node_Type. Note that this is NOT the same as the order of
+    --  either breadth first or depth first search.
     function Iterate_Subgraph
            (Container : in Graph;
             Position  : in Cursor)
-        return Graph_Iterator_Interfaces.Forward_Iterator'Class;
+        return Graph_Iterator_Interfaces.Reversible_Iterator'Class;
 
     function First
            (Container : in Graph)
@@ -627,9 +631,8 @@ private
        (Index_Type   => Positive,
         Element_Type => Node_Type);
 
-    function "="
-           (Left, Right : in Node_Vectors.Vector)
-        return Boolean renames Node_Vectors."=";
+    use type Node_Vectors.Vector;
+    use type Ada.Containers.Count_Type;
 
     package Node_Sort is new Node_Vectors.Generic_Sorting;