1 files changed, 85 insertions, 0 deletions
diff --git a/src/packrat.ads b/src/packrat.ads
index 36410d5..628923f 100644
--- a/src/packrat.ads
+++ b/src/packrat.ads
@@ -1,8 +1,93 @@
 
 
+with
+
+    Ada.Strings.Unbounded;
+
+
 package Packrat is
 
 
+    Parse_Error : exception;
+
+
+
+
+    package Errors is
+
+
+        subtype Error_Message is String
+            with Dynamic_Predicate => Valid_Message (Error_Message);
+
+        type Error_Info is record
+            Symbol   : Ada.Strings.Unbounded.Unbounded_String;
+            Position : Natural;
+        end record;
+
+        type Error_Info_Array is array (Positive range <>) of Error_Info;
+
+
+        --  Note: No consideration is given to ordering of Error_Info items
+        --        encoded into an Error_Message string.
+
+        --  Note: Using "&" to join two Valid Error_Messages together
+        --        will result in an Error_Message that is also Valid,
+        --        but for best results Join should be used instead to
+        --        prevent duplication of Error_Info in the message.
+
+
+        function Valid_Identifier
+               (Check : in String)
+            return Boolean;
+
+        function Valid_Identifier
+               (Check : in Ada.Strings.Unbounded.Unbounded_String)
+            return Boolean;
+
+        function Valid_Identifier_Array
+               (Check : in Error_Info_Array)
+            return Boolean;
+
+        function Valid_Message
+               (Check : in String)
+            return Boolean;
+
+
+        function Join
+               (Left, Right : in Error_Message)
+            return Error_Message;
+
+
+        function Encode
+               (Name : in String;
+                Pos  : in Natural)
+            return Error_Message
+            with Pre => Valid_Identifier (Name);
+
+        function Encode
+               (Name : in Ada.Strings.Unbounded.Unbounded_String;
+                Pos  : in Natural)
+            return Error_Message
+            with Pre => Valid_Identifier (Name);
+
+        function Encode
+               (Info : in Error_Info)
+            return Error_Message
+            with Pre => Valid_Identifier (Info.Symbol);
+
+        function Encode_Array
+               (Info : in Error_Info_Array)
+            return Error_Message
+            with Pre => Valid_Identifier_Array (Info);
+
+        function Decode
+               (Msg : in Error_Message)
+            return Error_Info_Array;
+
+
+    end Errors;
+
+
 private