1 files changed, 69 insertions, 15 deletions

diff --git a/src/packrat.ads b/src/packrat.ads
index 05a8e6a..d1fc9a0 100644
--- a/src/packrat.ads
+++ b/src/packrat.ads
@@ -191,6 +191,62 @@ package Packrat is
     package Interfaces is
 
 
+        type Node is interface;
+
+
+        function Leaf
+               (New_Item : in Element_Array;
+                Start    : in Positive;
+                Finish   : in Natural)
+            return Node is abstract
+        with Pre'Class =>
+                Finish + 1 >= Start,
+            Post'Class =>
+                Is_Leaf (Leaf'Result);
+
+        function Branch
+               (Label  : in Label_Enum;
+                Start  : in Positive;
+                Finish : in Natural)
+            return Node is abstract
+        with Pre'Class =>
+                Finish + 1 >= Start,
+            Post'Class =>
+                Is_Branch (Branch'Result);
+
+
+        function Is_Leaf
+               (This : in Node)
+            return Boolean is abstract;
+
+        function Is_Branch
+               (This : in Node)
+            return Boolean is abstract;
+
+
+        function Label
+               (This : in Node)
+            return Label_Enum is abstract
+        with Pre'Class =>
+                This.Is_Branch;
+
+        function Elements
+               (This : in Node)
+            return Element_Array is abstract
+        with Pre'Class =>
+                This.Is_Leaf;
+
+        function Start
+               (This : in Node)
+            return Positive is abstract;
+
+        function Finish
+               (This : in Node)
+            return Natural is abstract;
+
+
+
+
         type Cursor is interface;
 
 
@@ -205,12 +261,20 @@ package Packrat is
         with Pre'Class =>
                 not Position.Is_Nothing;
 
+        function Is_Node
+               (Position : in Cursor)
+            return Boolean is abstract
+        with Post'Class =>
+               (if Is_Node'Result then not Position.Is_Nothing);
+
         function Is_Root
                (Position : in Cursor)
             return Boolean is abstract
         with Post'Class =>
                (if Is_Root'Result then
-                Position.Parent.Is_Nothing and Position.Depth = 0);
+                not Position.Is_Nothing and
+                Position.Parent.Is_Nothing and
+                Position.Depth = 0);
 
         function Is_Branch
                (Position : in Cursor)
@@ -224,6 +288,7 @@ package Packrat is
         with Post'Class =>
                (if Is_Leaf'Result then not Position.Is_Nothing);
 
+
         function Label
                (Position : in Cursor)
             return Label_Enum is abstract
@@ -236,7 +301,6 @@ package Packrat is
         with Pre'Class =>
                 Position.Is_Leaf;
 
-
         function Start
                (Position : in Cursor)
             return Positive is abstract
@@ -370,21 +434,11 @@ package Packrat is
                (if Contains'Result then not Position.Is_Nothing);
 
 
-        function Leaf
-               (New_Item : in Element_Array;
-                Start    : in Positive;
-                Finish   : in Natural)
-            return Graph is abstract
-        with Post'Class =>
-                Leaf'Result.Node_Count = 1;
-
-        function Branch
-               (Label  : in Label_Enum;
-                Start  : in Positive;
-                Finish : in Natural)
+        function Singleton
+               (Input : in Node'Class)
             return Graph is abstract
         with Post'Class =>
-                Branch'Result.Node_Count = 1;
+                Singleton'Result.Node_Count = 1;
 
 
         function Is_Empty