hcl/lib/h2-scheme.adb

with H2.Ascii;
with H2.Pool;
with System.Address_To_Access_Conversions;

with Ada.Unchecked_Deallocation; -- for h2scm c interface. TOOD: move it to a separate file
with Interfaces.C;


-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXx
with Ada.Characters.Handling;
with Ada.Wide_Characters.Handling;

-- TODO: delete these after debugging
with ada.text_io;
with ada.wide_text_io;
-- TODO: delete above after debugging

-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXx

package body H2.Scheme is

	package body Token is separate;
	package Ch is new Ascii(Object_Character);

	-----------------------------------------------------------------------------
	-- PRIMITIVE DEFINITIONS
	-----------------------------------------------------------------------------

	-- I define these constants to word around the limitation of not being
	-- able to use a string literal when the string type is a generic parameter.
	-- Why doesn't ada include a formal type support for different character
	-- and string types? This limitation is caused because the generic 
	-- type I chosed to use to represent a character type is a discrete type.
	Label_And:      constant Object_String := (Ch.LC_A, Ch.LC_N, Ch.LC_D); -- "and"
	Label_Begin:    constant Object_String := (Ch.LC_B, Ch.LC_E, Ch.LC_G, Ch.LC_I, Ch.LC_N); -- "begin"
	Label_Case:     constant Object_String := (Ch.LC_C, Ch.LC_A, Ch.LC_S, Ch.LC_E); -- "case"
	Label_Cond:     constant Object_String := (Ch.LC_C, Ch.LC_O, Ch.LC_N, Ch.LC_D); -- "cond"
	Label_Define:   constant Object_String := (Ch.LC_D, Ch.LC_E, Ch.LC_F, Ch.LC_I, Ch.LC_N, Ch.LC_E); -- "define"
	Label_If:       constant Object_String := (Ch.LC_I, Ch.LC_F); -- "if"
	Label_Lambda:   constant Object_String := (Ch.LC_L, Ch.LC_A, Ch.LC_M, Ch.LC_B, Ch.LC_D, Ch.LC_A); -- "lambda"
	Label_Let:      constant Object_String := (Ch.LC_L, Ch.LC_E, Ch.LC_T); -- "let"
	Label_Letast:   constant Object_String := (Ch.LC_L, Ch.LC_E, Ch.LC_T, Ch.Asterisk); -- "let*"
	Label_Letrec:   constant Object_String := (Ch.LC_L, Ch.LC_E, Ch.LC_T, Ch.LC_R, Ch.LC_E, Ch.LC_C); -- "letrec"
	Label_Or:       constant Object_String := (Ch.LC_O, Ch.LC_R); -- "or"
	Label_Quote:    constant Object_String := (Ch.LC_Q, Ch.LC_U, Ch.LC_O, Ch.LC_T, Ch.LC_E); -- "quote"
	Label_Set:      constant Object_String := (Ch.LC_S, Ch.LC_E, Ch.LC_T, Ch.Exclamation); -- "set!"

	Label_Car:      constant Object_String := (Ch.LC_C, Ch.LC_A, Ch.LC_R); -- "car"
	Label_Cdr:      constant Object_String := (Ch.LC_C, Ch.LC_D, Ch.LC_R); -- "cdr"
	Label_Setcar:   constant Object_String := (Ch.LC_S, Ch.LC_E, Ch.LC_T, Ch.LC_C, Ch.LC_A, Ch.LC_R); -- "setcar"
	Label_Setcdr:   constant Object_String := (Ch.LC_S, Ch.LC_E, Ch.LC_T, Ch.LC_C, Ch.LC_D, Ch.LC_R); -- "setcar"
	Label_Plus:     constant Object_String := (1 => Ch.Plus_Sign); -- "+"
	Label_Minus:    constant Object_String := (1 => Ch.Minus_Sign); -- "-"
	Label_Multiply: constant Object_String := (1 => Ch.Asterisk); -- "*"
	Label_Divide:   constant Object_String := (1 => Ch.Slash); -- "/"

	-----------------------------------------------------------------------------
	-- EXCEPTIONS
	-----------------------------------------------------------------------------
	Allocation_Error: exception;
	Size_Error: exception;
	Syntax_Error: exception;
	Evaluation_Error: exception;
	Internal_Error: exception;
	IO_Error: exception;
	Stream_End_Error: exception;

	-----------------------------------------------------------------------------
	-- INTERNALLY-USED TYPES
	-----------------------------------------------------------------------------
	type Heap_Element_Pointer is access all Heap_Element;
	for Heap_Element_Pointer'Size use Object_Pointer_Bits; -- ensure that it can be overlayed by an ObjectPointer


	type Thin_Heap_Element_Array is array (1 .. Heap_Size'Last) of Heap_Element;
	type Thin_Heap_Element_Array_Pointer is access all Thin_Heap_Element_Array;
	for Thin_Heap_Element_Array_Pointer'Size use Object_Pointer_Bits;

	subtype Moved_Object_Record is Object_Record (Moved_Object, 0);

	subtype Opcode_Type is Object_Integer range 0 .. 11;
	Opcode_Exit:               constant Opcode_Type := Opcode_Type'(0);
	Opcode_Evaluate_Result:    constant Opcode_Type := Opcode_Type'(1);
	Opcode_Evaluate_Object:    constant Opcode_Type := Opcode_Type'(2);
	Opcode_Evaluate_Group:     constant Opcode_Type := Opcode_Type'(3); -- (begin ...) and closure apply
	Opcode_Evaluate_Procedure: constant Opcode_Type := Opcode_Type'(4);
	Opcode_Apply:              constant Opcode_Type := Opcode_Type'(5);
	Opcode_Read_Object:        constant Opcode_Type := Opcode_Type'(6);
	Opcode_Read_List:          constant Opcode_Type := Opcode_Type'(7);
	Opcode_Read_List_Cdr:      constant Opcode_Type := Opcode_Type'(8);
	Opcode_Read_List_End:      constant Opcode_Type := Opcode_Type'(9);
	Opcode_Close_List:         constant Opcode_Type := Opcode_Type'(10);
	Opcode_Close_Quote:        constant Opcode_Type := Opcode_Type'(11);

	-----------------------------------------------------------------------------
	-- COMMON OBJECTS
	-----------------------------------------------------------------------------
	Cons_Object_Size: constant Pointer_Object_Size := 2;
	Cons_Car_Index: constant Pointer_Object_Size := 1;
	Cons_Cdr_Index: constant Pointer_Object_Size := 2;

	Frame_Object_Size: constant Pointer_Object_Size := 5;
	Frame_Stack_Index: constant Pointer_Object_Size := 1;
	Frame_Opcode_Index: constant Pointer_Object_Size := 2;
	Frame_Operand_Index: constant Pointer_Object_Size := 3;
	Frame_Environment_Index: constant Pointer_Object_Size := 4;
	Frame_Result_Index: constant Pointer_Object_Size := 5;

	Mark_Object_Size: constant Pointer_Object_Size := 1;
	Mark_Context_Index: constant Pointer_Object_Size := 1;

	Procedure_Object_Size: constant Pointer_Object_Size := 1;
	Procedure_Opcode_Index: constant Pointer_Object_Size := 1;

	Closure_Object_Size: constant Pointer_Object_Size := 2;
	Closure_Code_Index: constant Pointer_Object_Size := 1;
	Closure_Environment_Index: constant Pointer_Object_Size := 2;

	procedure Set_New_Location (Object: in Object_Pointer;
	                            Ptr:    in Heap_Element_Pointer);
	procedure Set_New_Location (Object: in Object_Pointer;
	                            Ptr:    in Object_Pointer);
	pragma Inline (Set_New_Location);

	function Get_New_Location (Object: in Object_Pointer) return Object_Pointer;
	pragma Inline (Get_New_Location);

	-----------------------------------------------------------------------------
	-- FOR DEBUGGING. REMVOE THESE LATER
	-----------------------------------------------------------------------------
	procedure Output_Character_Array (Source: in Object_Character_Array) is
		-- for debugging only.
	begin
		for I in Source'Range loop
			--Ada.Text_IO.Put (Source(I));
-- TODO: note this is a hack for quick printing.
			Ada.Text_IO.Put (Standard.Character'Val(Object_Character'Pos(Source(I))));
		end loop;
	end Output_Character_Array;

	-----------------------------------------------------------------------------
	-- POINTER AND DATA CONVERSION
	-----------------------------------------------------------------------------

	function Get_Pointer_Type (Pointer: in Object_Pointer) return Object_Pointer_Type is
		pragma Inline (Get_Pointer_Type);

		Word: Object_Word;
		for Word'Address use Pointer'Address;
	begin 
		return Object_Pointer_Type(Word and Object_Word(Object_Pointer_Type_Mask));
	end Get_Pointer_Type;

	function Is_Pointer (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		return Get_Pointer_Type(Pointer) = Object_Pointer_Type_Pointer;
	end Is_Pointer;

	function Is_Special_Pointer (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		-- though sepcial, these 3 pointers gets true for Is_Pointer.
		return Pointer = Nil_Pointer or else 
		       Pointer = True_Pointer or else
		       Pointer = False_Pointer;
	end Is_Special_Pointer;

	function Is_Normal_Pointer (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		return Is_Pointer(Pointer) and then 
	            not Is_Special_Pointer(Pointer);
	end Is_Normal_Pointer;

	function Is_Integer (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		return Get_Pointer_Type(Pointer) = Object_Pointer_Type_Integer;
	end Is_Integer;

	function Is_Character (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		return Get_Pointer_Type(Pointer) = Object_Pointer_Type_Character;
	end Is_Character;

	function Is_Byte (Pointer: in Object_Pointer) return Standard.Boolean is
	begin
		return Get_Pointer_Type(Pointer) = Object_Pointer_Type_Byte;
	end Is_Byte;

	function Integer_To_Pointer (Int: in Object_Integer) return Object_Pointer is
		Pointer: Object_Pointer;
		Word: Object_Word;
		for Word'Address use Pointer'Address;
	begin
		if Int < 0 then
			-- change the sign of a negative number.
			-- '-Int' may violate the range of Object_Integer
			-- if it is Object_Integer'First. So I add 1 to 'Int'
			-- first to make it fall between Object_Integer'First + 1
			-- .. 0 and typecast it with an extra increment.
			--Word := Object_Word (-(Int + 1)) + 1;

			-- Let me use Object_Signed_Word instead of the trick shown above
			Word := Object_Word (-Object_Signed_Word(Int));

			-- shift the number to the left by 2 and
			-- set the highest bit on by force.
			Word := (Word * (2 ** Object_Pointer_Type_Bits)) or Object_Word(Object_Pointer_Type_Integer) or (2 ** (Word'Size - 1));
		else
			Word := Object_Word (Int);
			-- Shift 'Word' to the left by 2 and set the integer mark.
			Word := (Word * (2 ** Object_Pointer_Type_Bits)) or Object_Word(Object_Pointer_Type_Integer);
		end if;

		--return Object_Label_To_Object_Pointer (Word);
		return Pointer;
	end Integer_To_Pointer;

	function Character_To_Pointer (Char: in Object_Character) return Object_Pointer is
		Pointer: Object_Pointer;
		Word: Object_Word;
		for Word'Address use Pointer'Address;
	begin
		-- Note: Object_Character may get defined to Wide_Wide_Character.
		--   and Wide_Wide_Character'Last is #16#7FFFFFFF#. Such a large value
		--   may get lost when it's shifted left by 2 if Object_Word is 32 bits long
		--   or short. In reality, the last Unicode code point assigned is far
		--   less than #16#7FFFFFFF# as of this writing. So I should not be
		--   worried about it for the time being.
		Word := Object_Character'Pos(Char);
		Word := (Word * (2 ** Object_Pointer_Type_Bits)) or Object_Word(Object_Pointer_Type_Character);
		--return Object_Label_To_Object_Pointer (Word);
		return Pointer;
	end Character_To_Pointer;

	function Byte_To_Pointer (Byte: in Object_Byte) return Object_Pointer is
		Pointer: Object_Pointer;
		Word: Object_Word;
		for Word'Address use Pointer'Address;
	begin
		Word := Object_Word(Byte);
		Word := (Word * (2 ** Object_Pointer_Type_Bits)) or Object_Word(Object_Pointer_Type_Byte);
		return Pointer;
	end Byte_To_Pointer;

	function Pointer_To_Word is new Ada.Unchecked_Conversion (Object_Pointer, Object_Word);
	--function Pointer_To_Word (Pointer: in Object_Pointer) return Object_Word is
	--	Word: Object_Word;
	--	for Word'Address use Pointer'Address;
	--begin
	--	return Word;
	--end Pointer_To_Word;
	pragma Inline (Pointer_To_Word);

	function Pointer_To_Integer (Pointer: in Object_Pointer) return Object_Integer is
		Word: Object_Word := Pointer_To_Word (Pointer);
	begin
		if (Word and (2 ** (Word'Size - 1))) /= 0 then
			-- if the highest bit is set, it's a negative number
			-- originally. strip it off and shift 'Word' to the right by 2.
			return Object_Integer (-Object_Signed_Word (Word and not (2 ** (Word'Size - 1))) / (2 ** Object_Pointer_Type_Bits));
		else
			-- shift Word to the right by Object_Pointer_Type_Bits.
			return Object_Integer (Word / (2 ** Object_Pointer_Type_Bits));
		end if;
	end Pointer_To_Integer;

	function Pointer_To_Character (Pointer: in Object_Pointer) return Object_Character is
		Word: Object_Word := Pointer_To_Word (Pointer);
	begin
		return Object_Character'Val(Word / (2 ** Object_Pointer_Type_Bits));
	end Pointer_To_Character;

	function Pointer_To_Byte (Pointer: in Object_Pointer) return Object_Byte is
		Word: Object_Word := Pointer_To_Word (Pointer);
	begin
		return Object_Byte(Word / (2 ** Object_Pointer_Type_Bits));
	end Pointer_To_Byte;

-- TODO: move away these utilities routines
	--function To_Thin_String_Pointer (Source: in Object_Pointer) return Thin_String_Pointer is
	--	type Character_Pointer is access all Object_Character;
	--	Ptr: Thin_String_Pointer;
		
	--	X: Character_Pointer;
	--	for X'Address use Ptr'Address;
	--	pragma Import (Ada, X);
	--begin
		-- this method requires Object_Character_Array to have aliased Object_Character.
		-- So i've commented out this function and turn to a different method below.
	--	X := Source.Character_Slot(Source.Character_Slot'First)'Access; 
	--	return Ptr;
	--end To_Thin_String_Pointer;	

	--function To_Thin_String_Pointer (Source: in Object_Pointer) return Thin_String_Pointer is
	--	function To_Thin_Pointer is new Ada.Unchecked_Conversion (System.Address, Thin_String_Pointer);
	--begin
	--	return To_Thin_Pointer(Source.Character_Slot'Address);
	--end To_Thin_String_Pointer;	

	function To_Thin_String_Pointer (Source: in Object_Pointer) return Thin_String_Pointer is
		X: aliased Thin_String;
		for X'Address use Source.Character_Slot'Address;
	begin
		return X'Unchecked_Access;
	end To_Thin_String_Pointer;	

	procedure Put_String (TS: in Thin_String_Pointer);
	pragma Import (C, Put_String, "puts");

	-- TODO: delete this procedure 
	procedure Print_Object_Pointer (Msg: in Standard.String; Source: in Object_Pointer) is
		W: Object_Word;
		for W'Address use Source'Address;

		Ptr_Type: Object_Pointer_Type;
	begin
		Ptr_Type := Get_Pointer_Type(Source);
		if Ptr_Type = Object_Pointer_Type_Character then
			Ada.Text_IO.Put_Line (Msg & Object_Character'Image(Pointer_To_Character(Source)));
		elsif Ptr_Type = Object_Pointer_Type_Integer then
			Ada.Text_IO.Put_Line (Msg & Object_Integer'Image(Pointer_To_Integer(Source)));
		elsif Is_Special_Pointer (Source) then
			Ada.Text_IO.Put_Line (Msg & " at " & Object_Word'Image(W));
		elsif Source.Kind = Character_Object then
			Ada.Text_IO.Put (Msg & " at " & Object_Word'Image(W) & 
			                   " at " & Object_Kind'Image(Source.Kind) & 
			                   " size " & Object_Size'Image(Source.Size) & " - ");
			if Source.Kind = Moved_Object then
				Output_Character_Array (Get_New_Location(Source).Character_Slot);
			else
				Output_Character_Array (Source.Character_Slot);
			end if;
		else
			Ada.Text_IO.Put_Line (Msg & " at " & Object_Word'Image(W) & " at " & Object_Kind'Image(Source.Kind));
		end if;
	end Print_Object_Pointer;

	function String_To_Integer_Pointer (Source: in Object_String) return Object_Pointer is
		V: Object_Integer := 0;
		Negative: Standard.Boolean := False;
		First: Object_String_Size;
	begin
		-- TODO: BIGNUM, RANGE CHECK, ETC
		pragma Assert (Source'Length > 0);

		First := Source'First;
		if Source(First) = Ch.Minus_Sign then
			First := First + 1;
			Negative := Standard.True;
		elsif Source(First) = Ch.Plus_Sign then
			First := First + 1;
		end if;
		for I in First .. Source'Last loop
			V := V * 10 + Object_Character'Pos(Source(I)) - Object_Character'Pos(Ch.Zero);
		end loop;	

		if Negative then	
			V := -V;
		end if;

		return Integer_To_Pointer(V);
	end String_To_Integer_Pointer;

	-----------------------------------------------------------------------------
	-- MEMORY MANAGEMENT
	-----------------------------------------------------------------------------
-- (define x ())
-- (define x #())
-- (define x $())
-- (define x #( 
--              (#a . 10)  ; a is a synbol
--              (b . 20)   ; b is a variable. resolve b at the eval-time and use it.
--              ("c" . 30) ; "c" is a string
--            )
-- )
-- (clone x y) -- deep copy
-- (define y x) -- reference assignment
-- (set! x.a 20) -- syntaic sugar
-- (set! (get x #a) 20)
-- (define x (make-hash))


	-- I wanted to reuse the Size field to store the pointer to
	-- the new location. GCC-GNAT 3.2.3 suffered from various constraint
	-- check errors. So i gave up on this procedure.
	--------------------------------------------------------------------
	--procedure Set_New_Location (Object: in Object_Pointer; Ptr: in Heap_Element_Pointer) is
		--New_Addr: Heap_Element_Pointer;
		--for New_Addr'Address use Object.Size'Address;
		--pragma Import (Ada, New_Addr); 
	--begin
		--New_Addr := Ptr;
	--end Set_New_Location;
	--function Get_New_Location (Object: in Object_Pointer) return Object_Pointer is
		--New_Ptr: Object_Pointer;
		--for New_Ptr'Address use Object.Size'Address;
		--pragma Import (Ada, New_Ptr); 
	--begin
		--return New_Ptr;
	--end;

	-- Instead, I created a new object kind that indicates a moved object.	
	-- The original object is replaced by this special object. this special 
	-- object takes up the smallest space that a valid object can take. So
	-- it is safe to overlay it on any normal objects.
	procedure Set_New_Location (Object: in Object_Pointer; Ptr: in Heap_Element_Pointer) is
		Moved_Object: Moved_Object_Record;
		for Moved_Object'Address use Object.all'Address;
		-- pramga Import must not be specified here as I'm counting
		-- on the default initialization of Moved_Object to overwrite
		-- the Kind discriminant in particular.
		--pragma Import (Ada, Moved_Object); -- this must not be used.
		function To_Object_Pointer is new Ada.Unchecked_Conversion (Heap_Element_Pointer, Object_Pointer);
	begin
		Moved_Object.New_Pointer := To_Object_Pointer (Ptr);
	end Set_New_Location;

	procedure Set_New_Location (Object: in Object_Pointer; Ptr: in Object_Pointer) is
		Moved_Object: Moved_Object_Record;
		for Moved_Object'Address use Object.all'Address;
		--pragma Import (Ada, Moved_Object); -- this must not be used.
	begin
		Moved_Object.New_Pointer := Ptr;
	end Set_New_Location;

	function Get_New_Location (Object: in Object_Pointer) return Object_Pointer is
	begin
		return Object.New_Pointer;
	end Get_New_Location;

	function Allocate_Bytes_In_Heap (Heap:       access Heap_Record; 
	                                 Heap_Bytes: in     Heap_Size) return Heap_Element_Pointer is
		Avail: Heap_Size;
		Result: Heap_Element_Pointer;
		Real_Bytes: Heap_Size := Heap_Bytes;
	begin
		if Real_Bytes < Moved_Object_Record'Max_Size_In_Storage_Elements then
			-- Guarantee the minimum object size to be greater than or 
			-- equal to the size of a moved object for GC to work.
			Real_Bytes := Moved_Object_Record'Max_Size_In_Storage_Elements;	
		end if;

		Avail := Heap.Size - Heap.Bound;
		if Real_Bytes > Avail then
			return null;
		end if;
		
		Result := Heap.Space(Heap.Bound + 1)'Unchecked_Access;
		Heap.Bound := Heap.Bound + Real_Bytes;
		return Result;
	end Allocate_Bytes_In_Heap;

	procedure Copy_Object (Source: in     Object_Pointer;
	                       Target: in out Heap_Element_Pointer) is
		pragma Inline (Copy_Object);
		subtype Target_Object_Record is Object_Record (Source.Kind, Source.Size);
		type Target_Object_Pointer is access all Target_Object_Record;

		Target_Object: Target_Object_Pointer;
		for Target_Object'Address use Target'Address;
		pragma Import (Ada, Target_Object); 
	begin
		-- This procedure should work. but gnat 4.3.2 on whiite(ppc32,wii)
		-- produced erroneous code when it was called from Move_One_Object().
		-- Target_Object_Record'Size, Target_Object.all'Size, and
		-- Target_Object_Record'Max_Size_In_Stroage_Elements were not
		-- always correct. For example, for a character object containing
		-- the string "lambda", Target_Object.all'Size returned 72 while
		-- it's supposed to be 96. Use Copy_Object_With_Size() below instead.
		Target_Object.all := Source.all;
		pragma Assert (Source.all'Size = Target_Object.all'Size);
	end Copy_Object;

	procedure Copy_Object_With_Size (Source: in     Object_Pointer;
	                                 Target: in out Heap_Element_Pointer;
	                                 Bytes:  in     Heap_Size) is
		pragma Inline (Copy_Object_With_Size);
		-- This procedure uses a more crude type for copying objects.
		-- It's the result of an effort to work around some compiler
		-- issues mentioned above.
		Tgt: Thin_Heap_Element_Array_Pointer;
		for Tgt'Address use Target'Address;
		pragma Import (Ada, Tgt);

		Src: Thin_Heap_Element_Array_Pointer;
		for Src'Address use Source'Address;
		pragma Import (Ada, Src);
	begin
		Tgt(1..Bytes) := Src(1..Bytes);
	end Copy_Object_With_Size;

	procedure Collect_Garbage (Interp: in out Interpreter_Record) is

		Last_Pos: Heap_Size;
		New_Heap: Heap_Number;

		--function To_Object_Pointer is new Ada.Unchecked_Conversion (Heap_Element_Pointer, Object_Pointer);

		function Move_One_Object (Object: in Object_Pointer) return Object_Pointer is
		begin
			if Is_Special_Pointer (Object)  then
Print_Object_Pointer ("Moving special ...", Object);
				return Object;
			end if;

			if Object.Kind = Moved_Object then
Print_Object_Pointer ("Moving NOT ...", Object);
				-- the object has moved to the new heap.
				-- the size field has been updated to the new object
				-- in the 'else' block below. i can simply return it
				-- without further migration.
				return Get_New_Location (Object);
			else
Print_Object_Pointer ("Moving REALLY ...", Object);
				declare
					Bytes: Heap_Size;

					-- This variable holds the allocation result
					Ptr: Heap_Element_Pointer;

					-- Create an overlay for type conversion
					New_Object: Object_Pointer;
					for New_Object'Address use Ptr'Address;
					pragma Import (Ada, New_Object); 
				begin

					-- Target_Object_Record'Max_Size_In_Storage_Elements gave 
					-- some erroneous values when compiled with GNAT 4.3.2 on 
					-- WII(ppc) Debian.
					--Bytes := Target_Object_Record'Max_Size_In_Storage_Elements;
					Bytes := Object.all'Size / System.Storage_Unit;

					-- Allocate space in the new heap
					Ptr := Allocate_Bytes_In_Heap (
						Heap => Interp.Heap(New_Heap),
						Heap_Bytes => Bytes
					);

					-- Allocation here must not fail because
					-- I'm allocating the new space in a new heap for
					-- moving an existing object in the current heap.
					-- It must not fail, assuming the new heap is as large
					-- as the old heap, and garbage collection doesn't
					-- allocate more objects than in the old heap.
					pragma Assert (Ptr /= null);

					-- Copy the payload to the new object
					--Copy_Object (Object, Ptr); -- not reliable with some compilers
					Copy_Object_With_Size (Object, Ptr, Bytes); -- use this instead
					pragma Assert (Object.all'Size = New_Object.all'Size);
					pragma Assert (Bytes = New_Object.all'Size / System.Storage_Unit);

					-- Let the size field of the old object point to the
					-- new object allocated in the new heap. It is returned
					-- in the 'if' block at the beginning of this function
					-- if the object is marked with FLAG_MOVED;
					Set_New_Location (Object, Ptr);

Ada.Text_IO.Put_Line (Object_Word'Image(Pointer_To_Word(Object)) & Object_Word'Image(Pointer_To_Word(New_Object)));
Ada.Text_IO.Put_Line ("  Flags....after " & Object_Kind'Image(Object.Kind) & " New Size " & Object_Size'Image(Object.Size) & " New Loc: " & Object_Word'Image(Pointer_To_Word(Object.New_Pointer)));
					-- Return the new object
					return New_Object;
				end;
			end if;
		end Move_One_Object;

		function Scan_New_Heap (Start_Position: in Heap_Size) return Heap_Size is
			Ptr: Heap_Element_Pointer;

			Position: Heap_Size;
		begin
			Position := Start_Position;

--Text_IO.Put_Line ("Start Scanning New Heap from " & Heap_Size'Image (Start_Position) & " Bound: " & Heap_Size'Image (Interp.Heap(New_Heap).Bound));
			while Position <= Interp.Heap(New_Heap).Bound loop

--Text_IO.Put_Line (">>> Scanning New Heap from " & Heap_Size'Image (Position) & " Bound: " & Heap_Size'Image (Interp.Heap(New_Heap).Bound));
				Ptr := Interp.Heap(New_Heap).Space(Position)'Unchecked_Access;

				declare
					Object: Object_Pointer;
					for Object'Address use Ptr'Address;
					pragma Import (Ada, Object); -- not really needed

					--subtype Target_Object_Record is Object_Record (Object.Kind, Object.Size);
					Bytes: Heap_Size;

				begin
					--Bytes := Target_Object_Record'Max_Size_In_Storage_Elements;
					Bytes := Object.all'Size / System.Storage_Unit;
				
--Text_IO.Put_Line (">>> Scanning Obj " & Object_Kind'Image (Object.Kind) & " size " & Object_Size'Image(Object.Size) & " at " & Object_Word'Image(Pointer_To_Word(Object)) & " Bytes " & Heap_Size'Image(Bytes));

					if Object.Kind = Pointer_Object then
						for i in Object.Pointer_Slot'Range loop
							if Is_Pointer (Object.Pointer_Slot(i)) then
								Object.Pointer_Slot(i) := Move_One_Object (Object.Pointer_Slot(i));
							end if;
						end loop;
					end if;

					Position := Position + Bytes;
				end;

			end loop;

			return Position;
		end Scan_New_Heap;

		procedure Compact_Symbol_Table is
			Pred: Object_Pointer;
			Cons: Object_Pointer;
		begin
-- TODO: Change code here if the symbol table structure is changed to a hash table.

			Pred := Nil_Pointer;
			Cons := Interp.Symbol_Table;
			while Cons /= Nil_Pointer loop
				pragma Assert (Cons.Tag = Cons_Object);	

				declare
					Car: Object_Pointer renames Cons.Pointer_Slot(Cons_Car_Index);
					Cdr: Object_Pointer renames Cons.Pointer_Slot(Cons_Cdr_Index);
				begin
					pragma Assert (Car.Kind = Moved_Object or else Car.Tag = Symbol_Object);

					if Car.Kind /= Moved_Object and then
					   (Car.Flags and Syntax_Object) = 0 then
						-- A non-syntax symbol has not been moved. 
						-- Unlink the cons cell from the symbol table.

--Text_IO.Put_Line ("COMPACT_SYMBOL_TABLE Unlinking " & Character_Array_To_String (Car.Character_Slot));
						if Pred = Nil_Pointer then
							Interp.Symbol_Table := Cdr;
						else
							Pred.Pointer_Slot(Cons_Cdr_Index) := Cdr;
						end if;
					end if;
					
					Cons := Cdr;	
				end;
			end loop;
		end Compact_Symbol_Table;

	begin
		-- As the Heap_Number type is a modular type that can 
		-- represent 0 and 1, incrementing it gives the next value.
		New_Heap := Interp.Current_Heap + 1;

		-- Migrate objects in the root table
Print_Object_Pointer ("Root_Table ...", Interp.Root_Table);
		Interp.Root_Table := Move_One_Object (Interp.Root_Table);
		Interp.Mark := Move_One_Object (Interp.Mark);

		-- Scane the heap
		Last_Pos := Scan_New_Heap (Interp.Heap(New_Heap).Space'First);

		-- Traverse the symbol table for unreferenced symbols.
		-- If the symbol has not moved to the new heap, the symbol
		-- is not referenced by any other objects than the symbol 
		-- table itself 
Ada.Text_IO.Put_Line (">>> [COMPACTING SYMBOL TABLE]");
		Compact_Symbol_Table;

Print_Object_Pointer (">>> [MOVING SYMBOL TABLE]", Interp.Symbol_Table);
		-- Migrate the symbol table itself
		Interp.Symbol_Table := Move_One_Object (Interp.Symbol_Table);

Ada.Text_IO.Put_Line (">>> [SCANNING HEAP AGAIN AFTER SYMBOL TABLE MIGRATION]");
		-- Scan the new heap again from the end position of
		-- the previous scan to move referenced objects by 
		-- the symbol table. 
		Last_Pos := Scan_New_Heap (Last_Pos);

		-- Swap the current heap and the new heap
		Interp.Heap(Interp.Current_Heap).Bound := 0;
		Interp.Current_Heap := New_Heap;
Ada.Text_IO.Put_Line (">>> [GC DONE]");
	end Collect_Garbage;

	function Allocate_Bytes (Interp: access Interpreter_Record;
	                         Bytes:  in     Heap_Size) return Heap_Element_Pointer is

		-- I use this temporary variable not to change Result
		-- if Allocation_Error should be raised.
		Tmp: Heap_Element_Pointer;
	begin
		pragma Assert (Bytes > 0);

		Tmp := Allocate_Bytes_In_Heap (Interp.Heap(Interp.Current_Heap), Bytes);
		if Tmp = null and then (Interp.Trait.Trait_Bits and No_Garbage_Collection) = 0 then
			Collect_Garbage (Interp.all);
			Tmp := Allocate_Bytes_In_Heap (Interp.Heap(Interp.Current_Heap), Bytes);
			if Tmp = null then
				raise Allocation_Error;
			end if;
		end if;

		return Tmp;
	end Allocate_Bytes;

	function Allocate_Pointer_Object (Interp:  access Interpreter_Record;
	                                  Size:    in     Pointer_Object_Size;
	                                  Initial: in     Object_Pointer) return Object_Pointer is

		subtype Pointer_Object_Record is Object_Record (Pointer_Object, Size);
		type Pointer_Object_Pointer is access all Pointer_Object_Record;

		Ptr: Heap_Element_Pointer;
		Obj_Ptr: Pointer_Object_Pointer;
		for Obj_Ptr'Address use Ptr'Address;
		pragma Import (Ada, Obj_Ptr);
		Result: Object_Pointer;
		for Result'Address use Ptr'Address;
		pragma Import (Ada, Result);
	begin
		Ptr := Allocate_Bytes (
			Interp,
			Heap_Size'(Pointer_Object_Record'Max_Size_In_Storage_Elements)
		);

		Obj_Ptr.all := (
			Kind => Pointer_Object,
			Size => Size,
			Flags => 0,
			Scode => 0,
			Tag => Unknown_Object,
			Pointer_Slot => (others => Initial)
		);

		return Result;
	end Allocate_Pointer_Object;

	function Allocate_Character_Object (Interp: access Interpreter_Record;
	                                    Size:   in     Character_Object_Size) return Object_Pointer is

		subtype Character_Object_Record is Object_Record (Character_Object, Size);
		type Character_Object_Pointer is access all Character_Object_Record;

		Ptr: Heap_Element_Pointer;
		Obj_Ptr: Character_Object_Pointer;
		for Obj_Ptr'Address use Ptr'Address;
		pragma Import (Ada, Obj_Ptr);
		Result: Object_Pointer;
		for Result'Address use Ptr'Address;
		pragma Import (Ada, Result);
	begin
		Ptr := Allocate_Bytes (
			Interp.Self,
			Heap_Size'(Character_Object_Record'Max_Size_In_Storage_Elements)
		);

		Obj_Ptr.all := (
			Kind => Character_Object,
			Size => Size,
			Flags => 0,
			Scode => 0,
			Tag => Unknown_Object,
			Character_Slot => (others => Ch.NUL),
			Character_Terminator => Ch.NUL
		);

		return Result;
	end Allocate_Character_Object;

	function Allocate_Character_Object (Interp: access Interpreter_Record;
	                                    Source: in     Object_String) return Object_Pointer is
		Result: Object_Pointer;
	begin
		if Source'Length > Character_Object_Size'Last then
			raise Size_Error;
		end if;
		
		Result := Allocate_Character_Object (Interp, Character_Object_Size'(Source'Length));
		Result.Character_Slot := Source;
		return Result;
	end Allocate_Character_Object;

	function Allocate_Byte_Object (Interp: access Interpreter_Record;
	                               Size:   in     Byte_Object_Size) return Object_Pointer is

		subtype Byte_Object_Record is Object_Record (Byte_Object, Size);
		type Byte_Object_Pointer is access all Byte_Object_Record;

		Ptr: Heap_Element_Pointer;
		Obj_Ptr: Byte_Object_Pointer;
		for Obj_Ptr'Address use Ptr'Address;
		pragma Import (Ada, Obj_Ptr);
		Result: Object_Pointer;
		for Result'Address use Ptr'Address;
		pragma Import (Ada, Result);
	begin
		Ptr := Allocate_Bytes (Interp.Self, Heap_Size'(Byte_Object_Record'Max_Size_In_Storage_Elements));
		Obj_Ptr.all := (
			Kind => Byte_Object,
			Size => Size,
			Flags => 0,
			Scode => 0,
			Tag => Unknown_Object,
			Byte_Slot => (others => 0)
		);
		return Result;
	end Allocate_Byte_Object;

	function Verify_Pointer (Source: in Object_Pointer) return Object_Pointer is
		pragma Inline (Verify_Pointer);
	begin
		if not Is_Normal_Pointer(Source) or else
		   Source.Kind /= Moved_Object then
			return Source;
		end if;	

		return Get_New_Location(Source);
	end Verify_Pointer;
	-----------------------------------------------------------------------------

	function Make_Cons (Interp:  access Interpreter_Record;
	                    Car:     in     Object_Pointer;
	                    Cdr:     in     Object_Pointer) return Object_Pointer is
		Cons: Object_Pointer;
	begin
		Cons := Allocate_Pointer_Object (Interp, Cons_Object_Size, Nil_Pointer);
		Cons.Pointer_Slot(Cons_Car_Index) := Verify_Pointer(Car); -- TODO: is this really a good idea? resise this...
		Cons.Pointer_Slot(Cons_Cdr_Index) := Verify_Pointer(Cdr); --       If so, use Verify_pointer after Allocate_XXX
		Cons.Tag := Cons_Object;
		return Cons;
	end Make_Cons;

	function Is_Cons (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Cons);
	begin
		return Is_Normal_Pointer(Source) and then 
		       Source.Tag = Cons_Object;
	end Is_Cons;

	function Get_Car (Source: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Car);
		pragma Assert (Is_Cons(Source));
	begin
		return Source.Pointer_Slot(Cons_Car_Index);
	end Get_Car;

	procedure Set_Car (Source: in out Object_Pointer;
	                   Value:  in     Object_Pointer) is
		pragma Inline (Set_Car);
		pragma Assert (Is_Cons(Source));
	begin
		Source.Pointer_Slot(Cons_Car_Index) := Value;
	end Set_Car;

	function Get_Cdr (Source: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Cdr);
		pragma Assert (Is_Cons(Source));
	begin
		return Source.Pointer_Slot(Cons_Cdr_Index);
	end Get_Cdr;

	procedure Set_Cdr (Source: in out Object_Pointer;
	                   Value:  in     Object_Pointer) is
		pragma Inline (Set_Cdr);
		pragma Assert (Is_Cons(Source));
	begin
		Source.Pointer_Slot(Cons_Cdr_Index) := Value;
	end Set_Cdr;


	function Reverse_Cons (Source:   in Object_Pointer; 
	                       Last_Cdr: in Object_Pointer := Nil_Pointer) return Object_Pointer is
		pragma Assert (Is_Cons(Source));

		-- Note: The non-nil cdr in the last cons cell gets lost.
		--       e.g.) Reversing (1 2 3 . 4) results in (3 2 1)
		Ptr: Object_Pointer;
		Next: Object_Pointer;
		Prev: Object_Pointer;
	begin
		--Prev := Nil_Pointer;
		Prev := Last_Cdr;
		Ptr := Source;
		loop
			Next := Get_Cdr(Ptr);
			Set_Cdr (Ptr, Prev);
			Prev := Ptr;
			if Is_Cons(Next) then
				Ptr := Next;
			else
				exit;
			end if;
		end loop;

		return Ptr;
	end Reverse_Cons;
	-----------------------------------------------------------------------------

	function Make_String (Interp: access  Interpreter_Record;
	                      Source: in      Object_String) return Object_Pointer is
		Result: Object_Pointer;
	begin
Ada.Text_IO.Put_Line ("Make_String...");
		Result := Allocate_Character_Object (Interp, Source);
		Result.Tag := String_Object;
--Print_Object_Pointer ("Make_String Result - " & Source, Result);
		return Result;
	end Make_String;

	function Is_Symbol (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Symbol);
	begin
		return Is_Normal_Pointer (Source) and then 
		       Source.Tag = Symbol_Object;
	end Is_Symbol;

	function Make_Symbol (Interp: access Interpreter_Record;
	                      Source: in     Object_String) return Object_Pointer is
		Ptr: Object_Pointer;
	begin
		-- TODO: the current linked list implementation isn't efficient.
		--       change the symbol table to a hashable table.

		-- Find an existing symbol in the symbol table.	
		Ptr := Interp.Symbol_Table;
		while Ptr /= Nil_Pointer loop
			pragma Assert (Is_Cons(Ptr));

			declare
				Car: Object_Pointer renames Ptr.Pointer_Slot(Cons_Car_Index);
				Cdr: Object_Pointer renames Ptr.Pointer_Slot(Cons_Cdr_Index);
			begin
--Text_IO.Put_Line (Car.Kind'Img & Car.Tag'Img & Object_Word'Image(Pointer_To_Word(Car)));
				pragma Assert (Car.Tag = Symbol_Object);

	 			--if Match_Character_Object(Car, Source) then
				if Car.Character_Slot = Source then
					return Car;
--Print_Object_Pointer ("Make_Symbol Result (Existing) - " & Source, Car);
				end if;

				Ptr := Cdr;	
			end;
		end loop;

--Text_IO.Put_Line ("Creating a symbol .. " & Source);
		-- Create a symbol object
		Ptr := Allocate_Character_Object (Interp, Source);
		Ptr.Tag := Symbol_Object;

-- TODO: ensure that Result is not reclaimed by GC.

-- Make it GC-aweare. Protect Ptr
		-- Link the symbol to the symbol table. 
		Interp.Symbol_Table := Make_Cons (Interp.Self, Ptr, Interp.Symbol_Table);
		return Ptr;
	end Make_Symbol;

	-----------------------------------------------------------------------------

	function Make_Array (Interp: access Interpreter_Record;
	                     Size:   in     Pointer_Object_Size) return Object_Pointer is
		Arr: Object_Pointer;
	begin
		Arr := Allocate_Pointer_Object (Interp, Size, Nil_Pointer);
		Arr.Tag := Array_Object;
		return Arr;
	end Make_Array;

	function Is_Array (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Array);
	begin
		return Is_Normal_Pointer(Source) and then 
		       Source.Tag = Array_Object;
	end Is_Array;

	-----------------------------------------------------------------------------

	--
	-- Environment is a cons cell whose slots represents:
	--   Car: Point to the first key/value pair.
	--   Cdr: Point to Parent environment
	-- 
	-- A key/value pair is held in an array object consisting of 3 slots.
	--   #1: Key
	--   #2: Value
	--   #3: Link to the next key/value array.
	--
	-- Interp.Environment     Interp.Root_Environment
     --   |                      |
	--   |                      V
	--   |     +----+----+    +----+----+
	--   +---> | |  |   ----> | |  | Nil|
	--         +-|--+-----    +-|--+-----
	--           |              |
	--           |              +--> another list
	--           V
	--         +----+----+----+   +----+----+----+   +----+----+----+   +----+----+----+
	--   list: | |  | |  |  ----> | |  | |  | -----> | |  | |  | -----> | |  | |  | Nil|
	--         +-|--+-|-------+   +-|--+-|-------+   +-|--+-|-------+   +-|--+-|-------+
	--           |    |             |    |             |    |             |    |
	--           V    V             V    V             V    V             V    V
	--          Key  Value          Key  Value        Key  Value         Key  Value
	--
	-- Upon initialization, Interp.Environment is equal to Interp.Root_Environment.
	-- CDR(Interp.Root_Environment) is Nil_Pointer.
	--
	-- TODO: Change environment implementation to a hash table or something similar

	function Make_Environment (Interp: access Interpreter_Record;
	                           Parent: in     Object_Pointer) return Object_Pointer is
		pragma Inline (Make_Environment);
	begin
		return Make_Cons(Interp, Nil_Pointer, Parent);
	end Make_Environment;

	function Find_In_Environment_List (Interp: access Interpreter_Record;
	                                   List:   in     Object_Pointer;
	                                   Key:    in     Object_Pointer) return Object_Pointer is
		Arr: Object_Pointer;
	begin
		Arr := List;
		while Arr /= Nil_Pointer loop
			pragma Assert (Is_Array(Arr));
			pragma Assert (Arr.Size = 3);
			
			if Arr.Pointer_Slot(1) = Key then
				return Arr;
			end if;

			Arr := Arr.Pointer_Slot(3);
		end loop;	

		return null; -- not found. note that it's not Nil_Pointer.
	end Find_In_Environment_List;

	procedure Set_Environment (Interp: in out Interpreter_Record;
	                           Key:    in     Object_Pointer;
	                           Value:  in     Object_Pointer) is
		Arr: Object_Pointer;
	begin
		pragma Assert (Is_Symbol(Key));

		Arr := Find_In_Environment_List(Interp.Self, Get_Car(Interp.Environment), Key);
		if Arr = null then
			-- Add a new key/value pair
			-- TODO: make it GC-aware - protect Key and Value
			Arr := Make_Array(Interp.Self, 3);
			Arr.Pointer_Slot(1) := Key;
			Arr.Pointer_Slot(2) := Value;

			-- Chain the pair to the head of the list
			Arr.Pointer_Slot(3) := Get_Car(Interp.Environment);	
			Set_Car (Interp.Environment, Arr);
		else
			-- overwrite an existing pair
			Arr.Pointer_Slot(2) := Value;
		end if;
	end Set_Environment;

	function Get_Environment (Interp: access Interpreter_Record;
	                          Key:    in     Object_Pointer) return Object_Pointer is
		Envir: Object_Pointer;
		Arr: Object_Pointer;
	begin
		Envir := Interp.Environment;	
		while Envir /= Nil_Pointer loop
			pragma Assert (Is_Cons(Envir));
			Arr := Find_In_Environment_List(Interp, Get_Car(Envir), Key);
			if Arr /= Nil_Pointer then
				return Arr.Pointer_Slot(2);
			end if;

			-- Move on to the parent environment
			Envir := Get_Cdr(Envir);
		end loop;
		return null; -- not found
	end Get_Environment;

	procedure Push_Environment (Interp: in out Interpreter_Record) is
		pragma Inline (Push_Environment);
		pragma Assert (Is_Cons(Interp.Environment));
	begin
		Interp.Environment := Make_Environment (Interp.Self, Interp.Environment);
	end Push_Environment;

	procedure Pop_Environment (Interp: in out Interpreter_Record) is
		pragma Inline (Pop_Environment);
		pragma Assert (Is_Cons(Interp.Environment));
	begin
		Interp.Environment := Get_Cdr(Interp.Environment);
	end Pop_Environment;
	                     
		
	-----------------------------------------------------------------------------

	function Make_Syntax (Interp: access Interpreter_Record;
	                      Opcode: in     Syntax_Code;
	                      Name:   in     Object_String) return Object_Pointer is
		Result: Object_Pointer;
	begin
		Result := Make_Symbol (Interp, Name);
		Result.Flags := Result.Flags or Syntax_Object;
		Result.Scode := Opcode;
--Ada.Text_IO.Put ("Creating Syntax Symbol ");
--Put_String (To_Thin_String_Pointer (Result));
		return Result;
	end Make_Syntax;

	function Is_Syntax (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Syntax);
	begin
		return Is_Symbol(Source) and then (Source.Flags and Syntax_Object) /= 0;
	end Is_Syntax;

	function Make_Procedure (Interp: access Interpreter_Record;
	                         Opcode: in     Procedure_Code;
	                         Name:   in     Object_String) return Object_Pointer is
		-- this procedure is for internal use only
		Symbol: Object_Pointer;
		Proc:   Object_Pointer;
	begin
-- TODO: make temporaries GC-aware
		-- Make a symbol for the procedure
		Symbol := Make_Symbol (Interp, Name);

		-- Make the actual procedure object
		Proc := Allocate_Pointer_Object (Interp, Procedure_Object_Size, Nil_Pointer);
		Proc.Tag := Procedure_Object;
		Proc.Pointer_Slot(Procedure_Opcode_Index) := Integer_To_Pointer(Opcode);

		-- Link it to the top environement
		pragma Assert (Interp.Environment = Interp.Root_Environment); 
		pragma Assert (Get_Environment (Interp.Self, Symbol) = null);
		Set_Environment (Interp.all, Symbol, Proc);

		return Proc;
	end Make_Procedure;

	function Is_Procedure (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Procedure);
	begin
		return Is_Normal_Pointer(Source) and then 
		       Source.Tag = Procedure_Object;
	end Is_Procedure;

	function Get_Procedure_Opcode (Proc: in Object_Pointer) return Procedure_Code is
		pragma Inline (Get_Procedure_Opcode);
		pragma Assert (Is_Procedure(Proc));
		pragma Assert (Proc.Size = Procedure_Object_Size);
	begin
		return Pointer_To_Integer(Proc.Pointer_Slot(Procedure_Opcode_Index));
	end Get_Procedure_Opcode;
	
	-----------------------------------------------------------------------------

	function Make_Frame (Interp:  access Interpreter_Record;
	                     Stack:   in     Object_Pointer; -- current stack pointer
	                     Opcode:  in     Object_Pointer;
	                     Operand: in     Object_Pointer;
	                     Envir:   in     Object_Pointer) return Object_Pointer is
		Frame: Object_Pointer;
	begin
-- TODO: create a Frame in a special memory rather than in Heap Memory.
--       Since it's used for stack, it can be made special.
		Frame := Allocate_Pointer_Object (Interp, Frame_Object_Size, Nil_Pointer);
		Frame.Tag := Frame_Object;
		Frame.Pointer_Slot(Frame_Stack_Index) := Stack;
		Frame.Pointer_Slot(Frame_Opcode_Index) := Opcode;
		Frame.Pointer_Slot(Frame_Operand_Index) := Operand;
		Frame.Pointer_Slot(Frame_Environment_Index) := Envir;
--Print_Object_Pointer ("Make_Frame Result - ", Result);

		return Frame;
	end Make_Frame;

	function Is_Frame (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Frame);
	begin
		return Is_Normal_Pointer(Source) and then 
		       Source.Tag = Frame_Object;
	end Is_Frame;

	function Get_Frame_Result (Frame: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Frame_Result);
		pragma Assert (Is_Frame(Frame));
	begin
		return Frame.Pointer_Slot(Frame_Result_Index);
	end Get_Frame_Result;

	--procedure Set_Frame_Result (Frame: in out Object_Pointer;
	--                            Value: in     Object_Pointer) is
	--	pragma Inline (Set_Frame_Result);
	--	pragma Assert (Is_Frame(Frame));
	--begin
	--	Frame.Pointer_Slot(Frame_Result_Index) := Value;
	--end Set_Frame_Result;

	procedure Chain_Frame_Result (Interp: in out Interpreter_Record;
	                              Frame:  in out Object_Pointer;
	                              Value:  in     Object_Pointer) is
		pragma Inline (Chain_Frame_Result);
		pragma Assert (Is_Frame(Frame));

		Ret_Head: Object_Pointer renames Frame.Pointer_Slot(Frame_Result_Index);
	begin
-- TODO: make it GC-aware

		-- Add a new cons cell to the front
		Ret_Head :=  Make_Cons (Interp.Self, Value, Ret_Head);
	end Chain_Frame_Result;

	procedure Clear_Frame_Result (Frame: in out Object_Pointer) is
	begin
		Frame.Pointer_Slot(Frame_Result_Index) := Nil_Pointer;
	end Clear_Frame_Result;

	function Get_Frame_Environment (Frame: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Frame_Environment);
		pragma Assert (Is_Frame(Frame));
	begin
		return Frame.Pointer_Slot(Frame_Environment_Index);
	end Get_Frame_Environment;

	function Get_Frame_Opcode (Frame: in Object_Pointer) return Opcode_Type is
		pragma Inline (Get_Frame_Opcode);
		pragma Assert (Is_Frame(Frame));
	begin
		return Pointer_To_Integer(Frame.Pointer_Slot(Frame_Opcode_Index));
	end Get_Frame_Opcode;

	procedure Set_Frame_Opcode (Frame:  in Object_Pointer; 
	                            OpcodE: in Opcode_Type) is
		pragma Inline (Set_Frame_Opcode);
		pragma Assert (Is_Frame(Frame));
	begin
		Frame.Pointer_Slot(Frame_Opcode_Index) := Integer_To_Pointer(Opcode);
	end Set_Frame_Opcode;

	function Get_Frame_Operand (Frame: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Frame_Operand);
		pragma Assert (Is_Frame(Frame));
	begin
		return Frame.Pointer_Slot(Frame_Operand_Index);
	end Get_Frame_Operand;

	procedure Set_Frame_Operand (Frame: in out Object_Pointer;
	                             Value: in     Object_Pointer) is
		pragma Inline (Set_Frame_Operand);
		pragma Assert (Is_Frame(Frame));
	begin
		Frame.Pointer_Slot(Frame_Operand_Index) := Value;
	end Set_Frame_Operand;

	-----------------------------------------------------------------------------

	function Make_Mark (Interp:  access Interpreter_Record;
	                    Context: in     Object_Integer) return Object_Pointer is
		Mark: Object_Pointer;
	begin
		Mark := Allocate_Pointer_Object (Interp, Mark_Object_Size, Nil_Pointer);
		Mark.Pointer_Slot(Mark_Context_Index) := Integer_To_Pointer(Context);
		Mark.Tag := Mark_Object;
		return Mark;
	end Make_Mark;

	-----------------------------------------------------------------------------

	function Make_Closure (Interp: access Interpreter_Record;
	                       Code:   in     Object_Pointer;
	                       Envir:  in     Object_Pointer) return Object_Pointer is
		Closure: Object_Pointer;
	begin
		Closure := Allocate_Pointer_Object (Interp, Closure_Object_Size, Nil_Pointer);
		Closure.Tag := Closure_Object;
		Closure.Pointer_Slot(Closure_Code_Index) := Code;
		Closure.Pointer_Slot(Closure_Environment_Index) := Envir;
		return Closure;
	end Make_Closure;

	function Is_Closure (Source: in Object_Pointer) return Standard.Boolean is
		pragma Inline (Is_Closure);
	begin
		return Is_Normal_Pointer(Source) and then 
		       Source.Tag = Closure_Object;
	end Is_Closure;

	function Get_Closure_Code (Closure: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Closure_Code);
		pragma Assert (Is_Closure(Closure));
	begin
		return Closure.Pointer_Slot(Closure_Code_Index);
	end Get_Closure_Code;

	function Get_Closure_Environment (Closure: in Object_Pointer) return Object_Pointer is
		pragma Inline (Get_Closure_Environment);
		pragma Assert (Is_Closure(Closure));
	begin
		return Closure.Pointer_Slot(Closure_Environment_Index);
	end Get_Closure_Environment;

	-----------------------------------------------------------------------------
	procedure Deinitialize_Heap (Interp: in out Interpreter_Record) is
	begin
		for I in Interp.Heap'Range loop
			if Interp.Heap(I) /= null then
				declare
					subtype Target_Heap_Record is Heap_Record (Interp.Heap(I).Size);
					type Target_Heap_Pointer is access all Target_Heap_Record;
					package Pool is new H2.Pool (Target_Heap_Record, Target_Heap_Pointer, Interp.Storage_Pool);

					Heap: Target_Heap_Pointer;
					for Heap'Address use Interp.Heap(I)'Address;
					pragma Import (Ada, Heap); 
				begin
					Pool.Deallocate (Heap);
				end;
			end if;
		end loop;
	end Deinitialize_Heap;

	procedure Close_Stream (Stream: in out Stream_Pointer) is
	begin
		Close (Stream.all);
		Stream := null;
	exception
		when others =>
			Stream := null; -- ignore exception
	end Close_Stream;

	procedure Start_Named_Input_Stream (Interp: in out Interpreter_Record;
	                                    Name:   in     Constant_Object_String_Pointer) is
		package IO_Pool is new H2.Pool (IO_Record, IO_Pointer, Interp.Storage_Pool);

		IO: IO_Pointer := null;
		Stream: Stream_Pointer := null;
	begin
		begin
			IO := IO_Pool.Allocate;
			Interp.Stream.Allocate (Interp, Name, Stream);
		exception
			when others =>	
				if IO /= null then
					if Stream /= null then
						Interp.Stream.Deallocate (Interp, Stream);
					end if;
					IO_Pool.Deallocate (IO);
				end if;
				raise;
		end;

		--IO.Stream := Stream;
		--IO.Pos := IO.Data'First - 1;
		--IO.Last := IO.Data'First - 1;
		--IO.Flags := 0;
		--IO.Next := Interp.Input;
		--Interp.Input := IO;

		IO.all := IO_Record'(
			Stream => Stream,
			Data => (others => Object_Character'First),
			Pos | Last => IO.Data'First - 1,
			Flags => 0,
			Next => Interp.Input,
			Iochar => IO_Character_Record'(End_Character, Object_Character'First)
		);
		Interp.Input := IO;
	end Start_Named_Input_Stream;

	procedure Stop_Named_Input_Stream (Interp: in out Interpreter_Record) is
		package IO_Pool is new H2.Pool (IO_Record, IO_Pointer, Interp.Storage_Pool);
		IO: IO_Pointer;
	begin
		pragma Assert (Interp.Input /= Interp.Base_Input'Unchecked_Access);
		IO := Interp.Input;
		Interp.Input := IO.Next;

		pragma Assert (IO.Stream /= null);
		Close_Stream (IO.Stream);
		Interp.Stream.Deallocate (Interp, IO.Stream);
		IO_Pool.Deallocate (IO);
	end Stop_Named_Input_Stream;

	-----------------------------------------------------------------------------

	procedure Open (Interp:            in out Interpreter_Record;
	                Initial_Heap_Size: in     Heap_Size;
	                Storage_Pool:      in     Storage_Pool_Pointer := null) is

		procedure Initialize_Heap (Size: Heap_Size) is
			subtype Target_Heap_Record is Heap_Record (Size);
			type Target_Heap_Pointer is access all Target_Heap_Record;
			package Pool is new H2.Pool (Target_Heap_Record, Target_Heap_Pointer, Interp.Storage_Pool);
		begin
			for I in Interp.Heap'Range loop
				Interp.Heap(I) := null; -- just in case
			end loop;

			for I in Interp.Heap'Range loop
				declare
					Heap: Target_Heap_Pointer;
					for Heap'Address use Interp.Heap(I)'Address;
					pragma Import (Ada, Heap); 
				begin
					Heap := Pool.Allocate;
				end;
			end loop;

		exception
			when others =>
				Deinitialize_Heap (Interp);
				raise;
		end Initialize_Heap;

		procedure Make_Syntax_Objects is
			Dummy: Object_Pointer;
		begin
			Dummy := Make_Syntax (Interp.Self, And_Syntax,    Label_And); -- "and"
			Dummy := Make_Syntax (Interp.Self, Begin_Syntax,  Label_Begin); -- "begin"
			Dummy := Make_Syntax (Interp.Self, Case_Syntax,   Label_Case); -- "case"
			Dummy := Make_Syntax (Interp.Self, Cond_Syntax,   Label_Cond); -- "cond"
			Dummy := Make_Syntax (Interp.Self, Define_Syntax, Label_Define); -- "define"
			Dummy := Make_Syntax (Interp.Self, If_Syntax,     Label_If); -- "if"
			Dummy := Make_Syntax (Interp.Self, Lambda_Syntax, Label_Lambda); -- "lamba"
			Dummy := Make_Syntax (Interp.Self, Let_Syntax,    Label_Let); -- "let"
			Dummy := Make_Syntax (Interp.Self, Letast_Syntax, Label_Letast); -- "let*"
			Dummy := Make_Syntax (Interp.Self, Letrec_Syntax, Label_Letrec); -- "letrc"
			Dummy := Make_Syntax (Interp.Self, Or_Syntax,     Label_Or); -- "or"
			Dummy := Make_Syntax (Interp.Self, Quote_Syntax,  Label_Quote); -- "quote"
			Dummy := Make_Syntax (Interp.Self, Set_Syntax,    Label_Set); -- "set!"
		end Make_Syntax_Objects;

		procedure Make_Procedure_Objects is
			Dummy: Object_Pointer;
		begin
			Dummy := Make_Procedure (Interp.Self, Car_Procedure,      Label_Car); -- "car"
			Dummy := Make_Procedure (Interp.Self, Cdr_Procedure,      Label_Cdr); -- "cdr"
			Dummy := Make_Procedure (Interp.Self, Setcar_Procedure,   Label_Setcar); -- "setcar"
			Dummy := Make_Procedure (Interp.Self, Setcdr_Procedure,   Label_Setcdr); -- "setcdr"
			Dummy := Make_Procedure (Interp.Self, Add_Procedure,      Label_Plus); -- "+"
			Dummy := Make_Procedure (Interp.Self, Subtract_Procedure, Label_Minus); -- "-"
			Dummy := Make_Procedure (Interp.Self, Multiply_Procedure, Label_Multiply); -- "*"
			Dummy := Make_Procedure (Interp.Self, Divide_Procedure,   Label_Divide); -- "/"
		end Make_Procedure_Objects;
	begin
		declare
			Aliased_Interp: aliased Interpreter_Record;
			for Aliased_Interp'Address use Interp'Address;
			pragma Import (Ada, Aliased_Interp);
		begin
			-- Store a pointer to the interpreter record itself.
			-- I use this pointer to call functions that accept the "access"
			-- type to work around the ada95 limitation of no "in out" as
			-- a function parameter. Accoring to Ada95 RM (6.2), both a 
			-- non-private limited record type and a private type whose
			-- full type is a by-reference type are by-rereference types.
			-- So i assume that it's safe to create this aliased overlay 
			-- to deceive the compiler. If Interpreter_Record is a tagged
			-- limited record type, this overlay is not needed since the
			-- type is considered aliased. Having this overlay, however,
			-- should be safe for both "tagged" and "non-tagged".
			-- Note: Making it a tagged limit record caused gnat 3.4.6 to
			--       crash with an internal bug report.
			--Interp.Self := Interp'Unchecked_Access; -- if tagged limited
			Interp.Self := Aliased_Interp'Unchecked_Access;
		end;

		Interp.Storage_Pool := Storage_Pool;
		Interp.Root_Table := Nil_Pointer;
		Interp.Symbol_Table := Nil_Pointer;

		Interp.Base_Input.Stream := null;
		Interp.Input := Interp.Base_Input'Unchecked_Access;
		Interp.Token := (End_Token, (null, 0, 0));

-- TODO: disallow garbage collecion during initialization.
Ada.Text_IO.Put_Line ("1111111111");
		Initialize_Heap (Initial_Heap_Size);
		Interp.Mark := Make_Mark (Interp.Self, 0); -- to indicate the end of cons evluation
		Interp.Root_Environment := Make_Environment (Interp.Self, Nil_Pointer);
		Interp.Environment := Interp.Root_Environment;
Ada.Text_IO.Put_Line ("11111111111111111111111111111111111111");
		Make_Syntax_Objects;
Ada.Text_IO.Put_Line ("2222222222222222222222222");
		Make_Procedure_Objects;
Ada.Text_IO.Put_Line ("99999");

Ada.Text_IO.Put_Line (IO_Character_Record'Size'Img);
Ada.Text_IO.Put_Line (IO_Character_Record'Max_Size_In_Storage_Elements'Img);
	exception
		when others =>
			Deinitialize_Heap (Interp);
	end Open;

	procedure Close (Interp: in out Interpreter_Record) is
	begin
		-- Destroy all unstacked named input streams 
		while Interp.Input /= Interp.Base_Input'Unchecked_Access loop
			Stop_Named_Input_Stream (Interp);
		end loop;

		if Interp.Base_Input.Stream /= null then
			-- Close the main input stream.
			Close_Stream (Interp.Base_Input.Stream);
		end if;

		Deinitialize_Heap (Interp);
		Token.Purge (Interp);
	end Close;

	function Get_Storage_Pool (Interp: in Interpreter_Record) return Storage_Pool_Pointer is
	begin
		return Interp.Storage_Pool;	
	end Get_Storage_Pool;

	procedure Set_Option (Interp: in out Interpreter_Record;
	                      Option: in     Option_Record) is
	begin
		case Option.Kind  is
			when Trait_Option =>
				Interp.Trait := Option;
			when Stream_Option =>
				Interp.Stream := Option;
		end case;
	end Set_Option;

	procedure Get_Option (Interp: in out Interpreter_Record;
	                      Option: in out Option_Record) is
	begin
		case Option.Kind  is
			when Trait_Option =>
				Option := Interp.Trait;
			when Stream_Option =>
				Option := Interp.Stream;
		end case;
	end Get_Option;

	procedure Set_Input_Stream  (Interp: in out Interpreter_Record;
	                             Stream: in out Stream_Record'Class) is
	begin
		--Open (Stream, Interp);		
		Open (Stream);

		-- if Open raised an exception, it wouldn't reach here.
		-- so the existing stream still remains intact.
		if Interp.Base_Input.Stream /= null then
			Close_Stream (Interp.Base_Input.Stream);
		end if;

		Interp.Base_Input := IO_Record'(
			Stream => Stream'Unchecked_Access,
			Data => (others => Object_Character'First),
			Pos | Last => Interp.Base_Input.Data'First - 1,
			Flags => 0,
			Next => null,
			Iochar => IO_Character_Record'(End_Character, Object_Character'First)
		);
	end Set_Input_Stream;

	--procedure Set_Output_Stream (Interp: in out Interpreter_Record;
	--                             Stream: in out Stream_Record'Class) is
	--begin
	--	
	--end Set_Output_Stream;

	procedure Print (Interp: in out Interpreter_Record; 
	                 Source: in     Object_Pointer) is

		procedure Print_Atom (Atom: in Object_Pointer) is
			Ptr_Type: Object_Pointer_Type;

			procedure Print_Pointee is
				W: Object_Word;
				for W'Address use Atom'Address;
			begin
				case W is
				when Nil_Word =>
					Ada.Text_IO.Put ("()");

				when True_Word =>
					Ada.Text_IO.Put ("#t");

				when False_Word =>
					Ada.Text_IO.Put ("#f");

				when others => 
					case Atom.Tag is
						when Cons_Object =>
							-- Cons_Object must not reach here.
							raise Internal_Error;

						when Symbol_Object =>
							Output_Character_Array (Atom.Character_Slot);

						when String_Object =>
							Ada.Text_IO.Put ("""");	
							Output_Character_Array (Atom.Character_Slot);
							Ada.Text_IO.Put ("""");	
	
						when Closure_Object =>
							Ada.Text_IO.Put ("#Closure");
	
						when Continuation_Object =>
							Ada.Text_IO.Put ("#Continuation");
	
						when Procedure_Object =>
							Ada.Text_IO.Put ("#Procedure");
	
						when Array_Object =>
							Ada.Text_IO.Put ("#Array");

						when Others =>
							if Atom.Kind = Character_Object then
								Output_Character_Array (Atom.Character_Slot);
							else
								Ada.Text_IO.Put ("#NOIMPL#");
							end if;
						end case;
				end case;
			end Print_Pointee;

			procedure Print_Integer is
				 X: constant Object_Integer := Pointer_To_Integer (Atom);
			begin
				Ada.Text_IO.Put (Object_Integer'Image(X));
			end Print_Integer;

			procedure Print_Character is
				 X: constant Object_Character := Pointer_To_Character (Atom);
			begin
				Ada.Text_IO.Put (Object_Character'Image(X));
			end Print_Character;

			procedure Print_Byte is
				 X: constant Object_Byte := Pointer_To_Byte (Atom);
			begin
				Ada.Text_IO.Put (Object_Byte'Image(X));
			end Print_Byte;

		begin
			Ptr_Type := Get_Pointer_Type(Atom);
			case Ptr_Type is
			when Object_Pointer_Type_Pointer =>
				Print_Pointee;

			when Object_Pointer_Type_Integer =>
				Print_Integer;

			when Object_Pointer_Type_Character =>
				Print_Character;

			when Object_Pointer_Type_Byte =>
				Print_Byte;
			end case;
		end Print_Atom;

		procedure Print_Object (Obj: in Object_Pointer) is
			Cons: Object_Pointer;
			Car: Object_Pointer;
			Cdr: Object_Pointer;

		begin
			if Is_Cons (Obj) then
				Cons := Obj;
				Ada.Text_IO.Put ("(");

				loop
					Car := Get_Car(Cons);

					if Is_Cons (Car) then
						Print_Object (Car);
					else
						Print_Atom (Car);
					end if;

					Cdr := Get_Cdr(Cons);
					if Is_Cons (Cdr) then
						Ada.Text_IO.Put (" ");
						Cons := Cdr;
						exit when Cons = Nil_Pointer;
					else
						if Cdr /= Nil_Pointer then
							Ada.Text_IO.Put (" . ");
							Print_Atom (Cdr);
						end if;
						exit;
					end if;
				end loop;

				Ada.Text_IO.Put (")");
			else
				Print_Atom (Obj);
			end if;
		end Print_Object;


		Stack: Object_Pointer; -- TODO: make it into the interpreter_Record so that GC can workd
		Opcode: Object_Integer;
		Operand: Object_Pointer;

	begin
		-- TODO: Let Make_Frame use a dedicated stack space that's apart from the heap.
		--       This way, the stack frame doesn't have to be managed by GC.

-- TODO: use a interp.Stack.
-- TODO: use Push_Frame
		Stack := Make_Frame (Interp.Self, Nil_Pointer, Integer_To_Pointer(0), Nil_Pointer, Nil_Pointer);  -- just for get_frame_environment...

		Opcode := 1;
		Operand := Source;

		loop
			case Opcode is
			when 1 =>
				if Is_Cons(Operand) then
					-- push cdr
					Stack := Make_Frame (Interp.Self, Stack, Integer_To_Pointer(2), Get_Cdr(Operand), Nil_Pointer); -- push cdr
					Ada.Text_IO.Put ("(");
					Operand := Get_Car(Operand);
					Opcode := 1;
				else
					Print_Atom (Operand);
					if Stack = Nil_Pointer then 
						Opcode := 0; -- stack empty. arrange to exit
						Operand := True_Pointer; -- return value
					else
						Opcode := Pointer_To_Integer(Stack.Pointer_Slot(Frame_Opcode_Index));
						Operand := Stack.Pointer_Slot(Frame_Operand_Index);
						Stack := Stack.Pointer_Slot(Frame_Stack_Index); -- pop
					end if;
				end if;

			when 2 =>

				if Is_Cons(Operand) then
					-- push cdr
					Stack := Make_Frame (Interp.Self, Stack, Integer_To_Pointer(2), Get_Cdr(Operand), Nil_Pointer); -- push
					Ada.Text_IO.Put (" ");
					Operand := Get_Car(Operand); -- car
					Opcode := 1;
				else
					if Operand /= Nil_Pointer then
						-- cdr of the last cons cell is not null.
						Ada.Text_IO.Put (" . ");
						Print_Atom (Operand);
					end if;
					Ada.Text_IO.Put (")");

					if Stack = Nil_Pointer then
						Opcode := 0; -- stack empty. arrange to exit
					else
						Opcode := Pointer_To_Integer(Stack.Pointer_Slot(Frame_Opcode_Index));
						Operand := Stack.Pointer_Slot(Frame_Operand_Index);
						Stack := Stack.Pointer_Slot(Frame_Stack_Index); -- pop 
					end if;
				end if;

			when others =>
				exit;
			end case;
		end loop;

		--Print_Object (Source);
		Ada.Text_IO.New_Line;
	end Print;

	function Pointer_To_Opcode (Pointer: in Object_Pointer) return Opcode_Type is
		pragma Inline (Pointer_To_Opcode);
	begin	
		return Pointer_To_Integer(Pointer);
	end Pointer_To_Opcode;

	function Opcode_To_Pointer (Opcode: in Opcode_Type) return Object_Pointer is
		pragma Inline (Opcode_To_Pointer);
	begin	
		return Integer_To_Pointer(Opcode);
	end Opcode_To_Pointer;

	procedure Push_Frame (Interp:  in out Interpreter_Record;
	                      Opcode:  in     Opcode_Type; 
	                      Operand: in     Object_Pointer) is
		pragma Inline (Push_Frame);
	begin
		Interp.Stack := Make_Frame (Interp.Self, Interp.Stack, Opcode_To_Pointer(Opcode), Operand, Interp.Environment);
	end Push_Frame;

	--procedure Pop_Frame (Interp.Stack: out Object_Pointer;
	--                     Opcode:  out Opcode_Type;
	--                     Operand: out Object_Pointer) is
	--	pragma Inline (Pop_Frame);
	--begin
	--	pragma Assert (Interp.Stack /= Nil_Pointer);
	--	Opcode := Pointer_To_Opcode(Interp.Stack.Pointer_Slot(Frame_Opcode_Index));
	--	Operand := Interp.Stack.Pointer_Slot(Frame_Operand_Index);
	--	Interp.Stack := Interp.Stack.Pointer_Slot(Frame_Stack_Index); -- pop 
	--end Pop_Frame;

	procedure Pop_Frame (Interp: in out Interpreter_Record) is
		pragma Inline (Pop_Frame);
	begin
		pragma Assert (Interp.Stack /= Nil_Pointer);
		Interp.Environment := Interp.Stack.Pointer_Slot(Frame_Environment_Index); -- restore environment
		Interp.Stack := Interp.Stack.Pointer_Slot(Frame_Stack_Index); -- pop 
	end Pop_Frame;

	procedure Execute (Interp: in out Interpreter_Record) is

		LC: IO_Character_Record renames Interp.Input.Iochar;

		procedure Evaluate_Result is
			pragma Inline (Evaluate_Result);
		begin
			-- The result from the previous frame is stored in the current frame.
			-- This procedure takes the result and switch it to an operand and clears it.
			-- It is used to evaluate the result of Read_Object in principle.
			-- It takes only the head(car) element of the result chain. 
			-- Calling this function to evaluate the result of any arbitrary frame 
			-- other than 'Read_Object' is not recommended.
			Set_Frame_Operand (Interp.Stack, Get_Car(Get_Frame_Result(Interp.Stack)));
			Clear_Frame_Result (Interp.Stack);
			Set_Frame_Opcode (Interp.Stack, Opcode_Evaluate_Object);
		end Evaluate_Result;

		procedure Evaluate_Group is
			pragma Inline (Evaluate_Group);

			Operand: Object_Pointer;
			Car: Object_Pointer;
			Cdr: Object_Pointer;
		begin
			Operand := Get_Frame_Operand(Interp.Stack);
			pragma Assert (Is_Normal_Pointer(Operand));

			case Operand.Tag is
				when Cons_Object =>
					Car := Get_Car(Operand);
					Cdr := Get_Cdr(Operand);

					if Is_Cons(Cdr) then
						-- Let the current frame remember the next expression list
						Set_Frame_Operand (Interp.Stack, Cdr);
					else
						if Cdr /= Nil_Pointer then
							-- The last CDR is not Nil.
							Ada.Text_IO.Put_Line ("$$$$..................FUCKING CDR. FOR GROUP....................$$$$");
							-- raise Syntax_Error;
						end if;

						-- Change the operand to a mark object so that the call to this 
						-- procedure after the evaluation of the last car goes to the 
						-- Mark_Object case.
						Set_Frame_Operand (Interp.Stack, Interp.Mark); 
					end if;

					-- Clear the return value from the previous expression.
					Clear_Frame_Result (Interp.Stack);

					-- Arrange to evaluate the current expression
					Push_Frame (Interp, Opcode_Evaluate_Object, Car);

				when Mark_Object =>
					Operand := Get_Frame_Result (Interp.Stack);
					Pop_Frame (Interp); -- Done

					-- There must be only 1 return value chained in the Group frame.
					pragma Assert (Get_Cdr(Operand) = Nil_Pointer);

					-- Transfer the only return value to the upper chain
					Chain_Frame_Result (Interp, Interp.Stack, Get_Car(Operand));

				when others =>
					raise Internal_Error;
			end case;
		end Evaluate_Group;

		procedure Evaluate_Object is
			pragma Inline (Evaluate_Object);

			Operand: Object_Pointer;
			Car: Object_Pointer;
			Cdr: Object_Pointer;
		begin
		<<Start_Over>>
			Operand := Get_Frame_Operand(Interp.Stack);

			if not Is_Normal_Pointer(Operand) then
				-- integer, character, specal pointers
				-- TODO: some normal pointers may point to literal objects. e.g.) bignum
				goto Literal;
			end if;
		
			case Operand.Tag is
				when Symbol_Object => -- Is_Symbol(Operand)
					-- TODO: find it in the Environment hierarchy.. not in the current environemnt.
					Car := Get_Environment (Interp.Self, Operand);
					if Car = null then
						-- unbound
						Ada.Text_IO.Put_Line ("Unbound symbol....");
						Print (Interp, Operand);		
						raise Evaluation_Error;
					else
						-- symbol found in the environment
						Operand := Car; 
						goto Literal;  -- In fact, this is not a literal, but can be handled in the same way
					end if;

				when Cons_Object => -- Is_Cons(Operand)
					Car := Get_Car(Operand);
					Cdr := Get_Cdr(Operand);
					if Is_Syntax(Car) then
						-- special syntax symbol. normal evaluate rule doesn't 
						-- apply for special syntax objects.

						case Car.Scode is
							when Begin_Syntax =>

								Operand := Cdr; -- Skip "begin"

								if not Is_Cons(Operand) then
									-- e.g) (begin)
									--      (begin . 10)
									Ada.Text_IO.Put_LINE ("FUCKNING CDR FOR BEGIN");
									raise Syntax_Error;
									--Pop_Frame (Interp);  -- Done

								else
									Set_Frame_Opcode (Interp.Stack, Opcode_Evaluate_Group);
									Set_Frame_Operand (Interp.Stack, Operand);

									if (Interp.Trait.Trait_Bits and No_Optimization) = 0 then
										-- I call Evaluate_Group for optimization here.
										Evaluate_Group; -- for optimization only. not really needed.
										-- I can jump to Start_Over because Evaluate_Group called 
										-- above pushes an Opcode_Evaluate_Object frame.
										pragma Assert (Get_Frame_Opcode(Interp.Stack) = Opcode_Evaluate_Object);
										goto Start_Over; -- for optimization only. not really needed.
									end if;
								end if;

							when Define_Syntax =>
								-- (define x 10) 
								-- (define (add x y) (+ x y)) -> (define add (lambda (x y) (+ x y)))
								Operand := Cdr; -- Skip "define"

								if not Is_Cons(Operand) then
									-- e.g) (define)
									--      (define . 10)
									Ada.Text_IO.Put_LINE ("FUCKNING CDR FOR DEFINE");
									raise Syntax_Error;
								elsif Get_Cdr(Operand) /= Nil_Pointer then
									-- TODO: IMPLEMENT OTHER CHECK
									null;
								end if;
					
								--Pop_Frame (Interp);	 -- Done
								--Chain_Frame_Result (Interp, Interp.Stack,  Get_Car(Operand));
								-- TODO: IMPLEMENT DEFINE.

							when Lambda_Syntax =>
								-- (lambda (x y) (+ x y));
								Operand := Cdr; -- Skip "lambda"
								if not Is_Cons(Operand) then
									-- e.g) (lambda)
									--      (lambda . 10)
									Ada.Text_IO.Put_LINE ("FUCKNING CDR FOR BEGIN");
									raise Syntax_Error;
									--Pop_Frame (Interp);  -- Done
								else
									if not Is_Cons(Get_Car(Operand)) then
										Ada.Text_IO.Put_Line ("INVALID PARRAMETER LIST");
										raise Syntax_Error;
										--Pop_Frame (Interp);  -- Done
									end if;

--Print (Interp, Get_Cdr(Operand));
									if not Is_Cons(Get_Cdr(Operand)) then
										Ada.Text_IO.Put_Line ("NO BODY");
										raise Syntax_Error;
										--Pop_Frame (Interp);  -- Done
									end if;

									declare
										Closure: Object_Pointer;
									begin
										Closure := Make_Closure (Interp.Self, Operand, Interp.Environment);
										Pop_Frame (Interp);  -- Done
										Chain_Frame_Result (Interp, Interp.Stack, Closure);
									end;
								end if;

							when Quote_Syntax =>
								Operand := Cdr; -- Skip "quote"
								if not Is_Cons(Operand) then
									-- e.g) (quote)
									--      (quote . 10)
									Ada.Text_IO.Put_LINE ("FUCKNING CDR FOR QUOTE");
									raise Syntax_Error;
								elsif Get_Cdr(Operand) /= Nil_Pointer then
									Ada.Text_IO.Put_LINE ("WRONG NUMBER OF ARGUMENTS FOR QUOTE");
									raise Syntax_Error;
								end if;
								Pop_Frame (Interp);	 -- Done
								Chain_Frame_Result (Interp, Interp.Stack,  Get_Car(Operand));

							when others =>
								Ada.Text_IO.Put_Line ("Unknown syntax");	
								--Set_Frame_Opcode (Interp.Stack, Opcode_Evaluate_Syntax);  -- Switch to syntax evaluation
								raise Internal_Error;
						end case;
					else
						if (Interp.Trait.Trait_Bits and No_Optimization) = 0 then
							while not Is_Normal_Pointer(Car) loop
								-- This while block is for optimization only. It's not really needed.
								-- If I know that the next object to evaluate is a literal object,
								-- I can simply reverse-chain it to the return field of the current 
								-- frame without pushing another frame dedicated for it.
	
								-- TODO: some normal pointers may point to a literal object. e.g.) bignum
								Chain_Frame_Result (Interp, Interp.Stack, Car);
								if Is_Cons(Cdr) then
									Operand := Cdr;
									Car := Get_Car(Operand);
									Cdr := Get_Cdr(Operand);
								else
									-- last cons 
									Operand := Reverse_Cons(Get_Frame_Result(Interp.Stack));
									Clear_Frame_Result (Interp.Stack);
									Set_Frame_Opcode (Interp.Stack, Opcode_Apply); 
									Set_Frame_Operand (Interp.Stack, Operand);
									return;
								end if;
							end loop;
						end if;

						if Is_Cons(Cdr) then
							-- Not the last cons cell yet
							Set_Frame_Operand (Interp.Stack, Cdr); -- change the operand for the next call 
						else
							-- Reached the last cons cell
							if Cdr /= Nil_Pointer then
								-- The last CDR is not Nil.
								Ada.Text_IO.Put_Line ("$$$$..................FUCKING CDR.....................$$$$");
								-- raise Syntax_Error;
							end if;

							-- Change the operand to a mark object so that the call to this 
							-- procedure after the evaluation of the last car goes to the 
							-- Mark_Object case.
							Set_Frame_Operand (Interp.Stack, Interp.Mark); 
						end if;

						-- Arrange to evaluate the car object
						if (Interp.Trait.Trait_Bits and No_Optimization) = 0 then
							Push_Frame (Interp, Opcode_Evaluate_Object, Car);
							goto Start_Over; -- for optimization only. not really needed.
						end if;
					end if;

				when Mark_Object =>
					-- TODO: you can use the mark context to differentiate context

					-- Get the evaluation result stored in the current stack frame by
					-- various sub-Opcode_Evaluate_Object frames. the return value 
					-- chain must be reversed Chain_Frame_Result reverse-chains values.
					Operand := Reverse_Cons(Get_Frame_Result(Interp.Stack));

					-- Refresh the current stack frame to Opcode_Apply.
					-- This should be faster than Popping the current frame and pushing
					-- a new frame.
					--   Envir := Get_Frame_Environment(Interp.Stack);
					--   Pop_Frame (Interp); -- done
					--   Push_Frame (Interp, Opcode_Apply, Operand, Envir); 
					Clear_Frame_Result (Interp.Stack);
					Set_Frame_Opcode (Interp.Stack, Opcode_Apply); 
					Set_Frame_Operand (Interp.Stack, Operand);

				when others =>
					-- normal literal object
					goto Literal;
			end case;
			return;

		<<Literal>>
			Pop_Frame (Interp); -- done
Ada.Text_IO.Put ("Return => ");
Print (Interp, Operand);
			Chain_Frame_Result (Interp, Interp.Stack, Operand);
		end Evaluate_Object;

		procedure Evaluate_Procedure is
			pragma Inline (Evaluate_Procedure);
		begin
			null;
		end Evaluate_Procedure;

		procedure Apply is
			pragma Inline (Apply);

			Operand: Object_Pointer;
			Func: Object_Pointer;
			Args: Object_Pointer;

			procedure Apply_Car_Procedure is
			begin
				Pop_Frame (Interp); -- Done with the current frame
				Chain_Frame_Result (Interp, Interp.Stack, Get_Car(Args));
			end Apply_Car_Procedure;

			procedure Apply_Cdr_Procedure is
			begin
				Pop_Frame (Interp); -- Done with the current frame
				Chain_Frame_Result (Interp, Interp.Stack, Get_Cdr(Args));
			end Apply_Cdr_Procedure;

			procedure Apply_Add_Procedure is
				Ptr: Object_Pointer := Args;
				Num: Object_Integer := 0; -- TODO: support BIGNUM
				Car: Object_Pointer;
			begin
				while Ptr /= Nil_Pointer loop
					-- TODO: check if car is an integer or bignum or something else.
					--       if something else, error
					Car := Get_Car(Ptr);
					if not Is_Integer(Car) then
Ada.Text_IO.Put ("NOT INTEGER FOR ADD"); Print (Interp, Car);
						raise Evaluation_Error;
					end if;
					Num := Num + Pointer_To_Integer(Car);
					Ptr := Get_Cdr(Ptr);
				end loop;

				Pop_Frame (Interp); -- Done with the current frame
				Chain_Frame_Result (Interp, Interp.Stack, Integer_To_Pointer(Num));
			end Apply_Add_Procedure;

			procedure Apply_Subtract_Procedure is
				Ptr: Object_Pointer := Args;
				Num: Object_Integer := 0; -- TODO: support BIGNUM
				Car: Object_Pointer;
			begin
				if Ptr /= Nil_Pointer then
					Car := Get_Car(Ptr);
					if not Is_Integer(Car) then
						raise Evaluation_Error;
					end if;
					Num := Pointer_To_Integer(Car);

					while Ptr /= Nil_Pointer loop
						-- TODO: check if car is an integer or bignum or something else.
						--       if something else, error
						Car := Get_Car(Ptr);
						if not Is_Integer(Car) then
							raise Evaluation_Error;
						end if;
						Num := Num - Pointer_To_Integer(Car);
						Ptr := Get_Cdr(Ptr);
					end loop;
				end if;

				Pop_Frame (Interp); --  Done with the current frame
				Chain_Frame_Result (Interp, Interp.Stack, Integer_To_Pointer(Num));
			end Apply_Subtract_Procedure;

			procedure Apply_Closure is
				Fbody: Object_Pointer;
				Param: Object_Pointer;
				Arg: Object_Pointer;
			begin
				-- For a closure created of "(lambda (x y) (+ x y) (* x y))"
				-- Get_Closure_Code(Func) returns "((x y) (+ x y) (* x y))"

				-- Push a new environmen for the closure
				Interp.Environment := Make_Environment (Interp.Self, Get_Closure_Environment(Func));
-- TODO: GC. Func may be invalid if GC has been invoked.

				Fbody := Get_Closure_Code(Func);
				pragma Assert (Is_Cons(Fbody)); -- the reader must ensure this.

				Param := Get_Car(Fbody); -- Parameter list
				--Arg := Get_Car(Args); -- Actual argument list
				Arg := Args; -- Actual argument list

				Fbody := Get_Cdr (Fbody); -- Real function body
				pragma Assert (Is_Cons(Fbody)); -- the reader must ensure this as wel..

				while Is_Cons(Param) loop

					if not Is_Cons(Arg) then
Print (Interp, Arg);
						Ada.Text_IO.Put_Line (">>>> Too few arguments <<<<");	
						raise Evaluation_Error;
					end if;

					-- Insert the key/value pair into the environment
					Set_Environment (Interp, Get_Car(Param), Get_Car(Arg));

					Param := Get_Cdr(Param);
					Arg := Get_Cdr(Arg);
				end loop;

				-- Perform cosmetic checks for the parameter list
				if Param /= Nil_Pointer then
					Ada.Text_IO.Put_Line (">>> GARBAGE IN PARAMETER LIST <<<");
					raise Syntax_Error;
				end if;

				-- Perform cosmetic checks for the argument list
				if Is_Cons(Arg) then
						Ada.Text_IO.Put_Line (">>>> Two many arguments <<<<");	
						raise Evaluation_Error;
				elsif Arg /= Nil_Pointer then	
					Ada.Text_IO.Put_Line (">>> GARBAGE IN ARGUMENT LIST <<<");
					raise Syntax_Error;
				end if;
					
-- TODO: GC. the environment construction can cause GC. so Fbody here may be invalid.
-- TODO: is it correct to keep the environement  in the frame?
				Set_Frame_Opcode (Interp.Stack, Opcode_Evaluate_Group);
				Set_Frame_Operand (Interp.Stack, Fbody);
				Clear_Frame_Result (Interp.Stack);
			end Apply_Closure;

		begin
			Operand := Get_Frame_Operand(Interp.Stack);
			pragma Assert (Is_Cons(Operand));

Print (Interp, Operand);
			Func := Get_Car(Operand);
			if not Is_Normal_Pointer(Func) then
				Ada.Text_IO.Put_Line ("INVALID FUNCTION TYPE");
				raise Evaluation_Error;
			end if;
	
			Args := Get_Cdr(Operand);

			-- No GC must be performed here.
			-- Otherwise, Operand, Func, Args get invalidated
			-- since GC doesn't update local variables.

			case Func.Tag is
				when Procedure_Object => 
					case Get_Procedure_Opcode(Func) is
						when Car_Procedure =>
							Apply_Car_Procedure;
						when Cdr_Procedure =>
							Apply_Cdr_Procedure;

						when Add_Procedure =>
							Apply_Add_Procedure;
						when Subtract_Procedure =>
							Apply_Subtract_Procedure;

						when others =>
							raise Internal_Error;
					end case;	

				when Closure_Object =>
					Apply_Closure;

				when Continuation_Object =>
					null;

				when others =>
					Ada.Text_IO.Put_Line ("INVALID FUNCTION TYPE");
					raise Internal_Error;

			end case;
		end Apply;

		procedure Fetch_Character is
		begin
		-- TODO: calculate Interp.Input.Row, Interp.Input.Column
			if Interp.Input.Pos >= Interp.Input.Last then
				if Interp.Input.Flags /= 0 then
					-- An error has occurred or EOF has been reached previously.
					-- Note calling this procedure after EOF results in an error.
					Interp.Input.Iochar := (Error_Character, Object_Character'First);
					--return;
					raise IO_Error;
				end if;

				Interp.Input.Pos := Interp.Input.Data'First - 1;
				begin
					Read (Interp.Input.Stream.all, Interp.Input.Data, Interp.Input.Last);
				exception
					when others =>
						-- The callee can raise an exception upon errors.
						-- If an exception is raised, data read into the buffer 
						-- is also ignored.
						Interp.Input.Flags := Interp.Input.Flags and IO_Error_Occurred;
						Interp.Input.Iochar := (Error_Character, Object_Character'First);
						--return;
						raise IO_Error;
				end;
				if Interp.Input.Last < Interp.Input.Data'First then	
					-- The callee must read 0 bytes on EOF 
					Interp.Input.Flags := Interp.Input.Flags and IO_End_Reached;
					Interp.Input.Iochar := (End_Character, Object_Character'First);
					return;
				end if;
			end if;
			Interp.Input.Pos := Interp.Input.Pos + 1;
			Interp.Input.Iochar := (Normal_Character, Interp.Input.Data(Interp.Input.Pos));
		end Fetch_Character;

		function Is_White_Space (X: in Object_Character) return Standard.Boolean is
		begin
			return X = Ch.Space or else X = Ch.HT or else X = Ch.VT or else 
			       X = Ch.CR or else X = Ch.LF or else X = Ch.FF;
		end Is_White_Space;

		function Is_Identifier_Stopper (X: in Object_Character) return  Standard.Boolean is
		begin
			return X = Ch.Left_Parenthesis or else X = Ch.Right_Parenthesis or else
			       X = Ch.Apostrophe or else LC.Value = Ch.Quotation or else
			       X = Ch.Number_Sign or else LC.Value = Ch.Semicolon or else 
		            Is_White_Space(X);
		end Is_Identifier_Stopper;

		procedure Skip_Spaces_And_Comments is
		begin
			loop
				exit when LC.Kind /= Normal_Character;

				-- Normal character
				if Is_White_Space(LC.Value) then
					Fetch_Character;
				elsif LC.Value = Ch.Semicolon then
					-- Comment.
					loop
						Fetch_Character;

						exit when LC.Kind = End_Character; -- EOF before LF

						if LC.Kind = Normal_Character and then 
						   LC.Value = Object_Character'Val(Standard.Character'Pos(Standard.ASCII.LF)) then
							Fetch_Character; -- Read the next character after LF
							exit;
						end if;
					end loop;
				else
					exit;
				end if;
			end loop;
		end Skip_Spaces_And_Comments;

		procedure Fetch_Token is
			Tmp: Object_String(1..10); -- large enough???
		begin
			if not Interp.LC_Unfetched then
				Fetch_Character;
			else
				-- Reuse the last character unfetched
				Interp.LC_Unfetched := Standard.False;
			end if;
			Skip_Spaces_And_Comments;
			if LC.Kind /= Normal_Character then
				Token.Set (Interp, End_Token);
				return;
			end if;

			-- TODO: Pass Token Location when calling Token.Set

			-- Use Ch.Pos.XXX values instead of Ch.XXX values as gnat complained that 
			-- Ch.XXX values are not static. For this reason, "case LC.Value is ..."
			-- changed to use Object_Character'Pos(LC.Value).
			case Object_Character'Pos(LC.Value) is

				when Ch.Pos.Left_Parenthesis =>
					Token.Set (Interp, Left_Parenthesis_Token, LC.Value);

				when Ch.Pos.Right_Parenthesis =>
					Token.Set (Interp, Right_Parenthesis_Token, LC.Value);

				when Ch.Pos.Period =>
					Token.Set (Interp, Period_Token, LC.Value);

				when Ch.Pos.Apostrophe =>
					Token.Set (Interp, Single_Quote_Token, LC.Value);

				when Ch.Pos.Quotation =>
					Fetch_Character;
					Token.Set (Interp, String_Token);
					loop
						if LC.Kind /= Normal_Character then
							-- String ended prematurely.
							-- TODO: Set Error code, Error Number.... Error location
							raise Syntax_Error;		
						end if;
	
						if LC.Value = Ch.Backslash then
							Fetch_Character;
							if LC.Kind /= Normal_Character then
								-- String ended prematurely.
								-- TODO: Set Error code, Error Number.... Error location
								raise Syntax_Error;		
							end if;
							-- TODO: escape letters??? \n \r \\ etc....
							Token.Append_Character (Interp, LC.Value);
						elsif LC.Value = Ch.Quotation then
							exit;
						else
							Token.Append_Character (Interp, LC.Value);
							Fetch_Character;
						end if;
					end loop;

				when Ch.Pos.Number_Sign =>
					Fetch_Character;
					-- TODO: t, false, etc

				when Ch.Pos.Zero .. Ch.Pos.Nine =>
					-- TODO; negative number, floating-point number, bignum, hexdecimal, etc
					Token.Set (Interp, Integer_Token);
					loop
						Token.Append_Character (Interp, LC.Value);
						Fetch_Character;
						if LC.Kind /= Normal_Character or else
						   LC.Value not in Ch.Zero .. Ch.Nine  then
							-- Unfetch the last character
							Interp.LC_Unfetched := Standard.True;
							exit;
						end if;
					end loop;

				when Ch.Pos.Plus_Sign | Ch.Pos.Minus_Sign =>

					Tmp(1) := LC.Value;
	
					Fetch_Character;
					if LC.Kind = Normal_Character and then
					   LC.Value in Ch.Zero .. Ch.Nine then
						Token.Set (Interp, Integer_Token, Tmp(1..1));
						loop
							Token.Append_Character (Interp, LC.Value);
							Fetch_Character;
							if LC.Kind /= Normal_Character or else
							   LC.Value not in Ch.Zero .. Ch.Nine  then
								-- Unfetch the last character
								Interp.LC_Unfetched := Standard.True;
								exit;
							end if;
						end loop;
					else
						Token.Set (Interp, Identifier_Token, Tmp(1..1));
						loop
					-- TODO: more characters
							if LC.Kind /= Normal_Character or else
							   Is_Identifier_Stopper(LC.Value) then
								-- Unfetch the last character
								Interp.LC_Unfetched := Standard.True;
								exit;
							end if;
	
							Token.Append_Character (Interp, LC.Value);
							Fetch_Character;
						end loop;
					end if;

				when others =>
					Token.Set (Interp, Identifier_Token);
					loop
						Token.Append_Character (Interp, LC.Value);
						Fetch_Character;
						--exit when not Is_Ident_Char(C.Value);
					-- TODO: more characters
						if LC.Kind /= Normal_Character or else
						   Is_Identifier_Stopper(LC.Value) then
							-- Unfetch the last character
							Interp.LC_Unfetched := Standard.True;
							exit;
						end if;
					end loop;
			end case;
			
--Ada.Text_IO.Put (">>>>>>>>>>>>>>>>>>>>>>> Token: " & Interp.Token.Value.Ptr(1..Interp.Token.Value.Last));
		end Fetch_Token;

		procedure Read_List is
			pragma Inline (Read_List);
			V: Object_Pointer;
		begin
			-- This procedure reads each token in a list.
			-- If the list contains no period, this procedure reads up to the 
			-- closing right paranthesis; If a period is contained, it transfers
			-- the control over to Read_List_Cdr.
			
			Fetch_Token;
		
			case Interp.Token.Kind is
				when End_Token =>
Ada.Text_IO.Put_Line ("ERROR: PREMATURE LIST END");
					raise Syntax_Error;

				when Left_Parenthesis_Token =>
					Push_Frame (Interp, Opcode_Read_List, Nil_Pointer);

				when Right_Parenthesis_Token =>
					V := Get_Frame_Result(Interp.Stack);
					if V /= Nil_Pointer then
						V := Reverse_Cons(V); -- TODO: GC
					end if;
					Pop_Frame (Interp); 
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when Period_Token =>
					V := Get_Frame_Result(Interp.Stack);
					if V = Nil_Pointer then
						-- . immediately after (
						raise Syntax_Error;
					else
						Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_Cdr);
					end if;

				when Single_Quote_Token =>
					Push_Frame (Interp, Opcode_Close_Quote, Nil_Pointer);
					Push_Frame (Interp, Opcode_Read_Object, Nil_Pointer);

				when Integer_Token =>
					-- TODO: bignum
					V := String_To_Integer_Pointer(Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when String_Token =>
					V := Make_String (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when Identifier_Token =>	
					V := Make_Symbol (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when others =>
					-- TODO: set various error info
					raise Syntax_Error;
			end case;
		end Read_List;

		procedure Read_List_Cdr is
			pragma Inline (Read_List_Cdr);
			V: Object_Pointer;
		begin
			-- This procedure reads the first token after a period has been read.
			-- It transfers the control over to Read_List_End once it has read 
			-- and processed the token. It chains the value made of the token  
			-- to the front of the frame's return value list expecting Read_List_End
			-- to handle the head item specially.
			Fetch_Token;
		
			case Interp.Token.Kind is
				when End_Token =>
Ada.Text_IO.Put_Line ("ERROR: PREMATURE LIST END");
					raise Syntax_Error;

				when Left_Parenthesis_Token =>
					Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_End);
					Push_Frame (Interp, Opcode_Read_List, Nil_Pointer);

				when Single_Quote_Token =>
Ada.Text_IO.Put_Line ("ERROR: CDR QUOT LIST END");
					Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_End);
					Push_Frame (Interp, Opcode_Close_Quote, Nil_Pointer);
					Push_Frame (Interp, Opcode_Read_Object, Nil_Pointer);

				when Integer_Token =>
					-- TODO: bignum
					V := String_To_Integer_Pointer(Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_End);
					Chain_Frame_Result (Interp, Interp.Stack, V);
			
				when String_Token =>
					V := Make_String (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_End);
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when Identifier_Token =>	
					V := Make_Symbol (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Set_Frame_Opcode (Interp.Stack, Opcode_Read_List_End);
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when others =>
					-- TODO: set various error info
					raise Syntax_Error;
			end case;

		end Read_List_Cdr;

		procedure Read_List_End is
			pragma Inline (Read_List_End);
			V: Object_Pointer;
		begin
			Fetch_Token;

			case Interp.Token.Kind is
				when Right_Parenthesis_Token =>
					V := Get_Frame_Result(Interp.Stack);
					pragma Assert (V /= Nil_Pointer);
					-- The first item in the chain is actually Cdr of the last cell.
					V := Reverse_Cons(Get_Cdr(V), Get_Car(V)); -- TODO: GC
					Pop_Frame (Interp); 
					Chain_Frame_Result (Interp, Interp.Stack, V);
				when others =>
					raise Syntax_Error;
			end case;
		end Read_List_End;

		procedure Close_List is
			pragma Inline (Close_List);
			V: Object_Pointer;
		begin
			V := Get_Frame_Result(Interp.Stack);
			pragma Assert (Get_Cdr(V) = Nil_Pointer);
			Pop_Frame (Interp); -- Done with the current frame
			Chain_Frame_Result (Interp, Interp.Stack, Get_Car(V));
		end Close_List;

		procedure Close_Quote is
			pragma Inline (Close_Quote);
			V: Object_Pointer;
		begin
-- TODO: use Interp.Quote_Syntax instead of Make_Symbol("quote")
			Chain_Frame_Result (Interp, Interp.Stack, Make_Symbol(Interp.Self, Label_Quote));
			V := Get_Frame_Result(Interp.Stack);
			Pop_Frame (Interp); -- Done with the current frame
			Chain_Frame_Result (Interp, Interp.Stack, V);
		end Close_Quote;

		procedure Read_Object is
			pragma Inline (Read_Object);
			V: Object_Pointer;
		begin
			Fetch_Token;

			case Interp.Token.Kind is
				when End_Token =>
Ada.Text_IO.Put_Line ("INFO: NO MORE TOKEN ");
					raise Stream_End_Error;

				when Left_Parenthesis_Token =>
					Set_Frame_Opcode (Interp.Stack, Opcode_Close_List);
					Push_Frame (Interp, Opcode_Read_List, Nil_Pointer);

				when Single_Quote_Token =>
					Set_Frame_Opcode (Interp.Stack, Opcode_Close_Quote);
					Push_Frame (Interp, Opcode_Read_Object, Nil_Pointer);

				when Integer_Token =>
					-- TODO: bignum
					V := String_To_Integer_Pointer(Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					Pop_Frame (Interp); -- Done with the current frame
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when String_Token =>
					V := Make_String (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Pop_Frame (Interp); -- Done with the current frame
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when Identifier_Token =>	
					V := Make_Symbol (Interp.Self, Interp.Token.Value.Ptr.all(1..Interp.Token.Value.Last));
					-- TODO: make V gc-aware
					Pop_Frame (Interp); -- Done with the current frame
					Chain_Frame_Result (Interp, Interp.Stack, V);

				when others =>
					-- TODO: set various error info
					raise Syntax_Error;
			end case;
		end Read_Object;

	begin
		
		-- Stack frames looks like this upon initialization
		-- 
		--               | Opcode                 | Operand    | Result
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | Source     | Nil
		--     bottom    | Opcode_Exit            | Nil        | Nil
		--
		-- For a source (+ 1 2), it should look like this.
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | Source       | Nil
		--     bottom    | Opcode_Exit            | Nil          | Nil
		-- 
		-- The operand changes to the cdr of the source.
		-- The symbol '+' is pushed to the stack with Opcode_Evaluate_Object.
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | +            | Nil
		--               | Opcode_Evaluate_Object | (1 2)        | Nil
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- After the evaluation of the symbol, the pushed frame is removed
		-- and the result is set to the return field.
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | (1 2)        | (#Proc+)
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- The same action is taken to evaluate the literal 1.
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | 1            | Nil
		--               | Opcode_Evaluate_Object | (2)          | (#Proc+)
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- The result of the valuation is reverse-chained to the return field. 
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | (2)          | (1 #Proc+)
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- The same action is taken to evaluate the literal 2.
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | 2            | Nil
		--               | Opcode_Evaluate_Object | Mark         | (1 #Proc+)
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- The result of the valuation is reverse-chained to the return field. 
		--     -----------------------------------------------------------------
		--     top       | Opcode_Evaluate_Object | Mark         | (2 1 #Proc+)
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- Once evluation of each cons cell is complete, switch the top frame
		-- to 'Apply' reversing the result field into the operand field and
		-- nullifying the result field afterwards.
		--     -----------------------------------------------------------------
		--     top       | Apply                  | (#Proc+ 1 2) | Nil
		--     bottom    | Opcode_Exit            | Nil          | Nil
		--
		-- The apply operation produces the final result and sets it to the 
		-- parent frame while removing the apply frame.
		--     -----------------------------------------------------------------
		--     top/bottom| Opcode_Exit            | Nil          | (3)
		
		-- The caller must push some frames before calling this procedure
		pragma Assert (Interp.Stack /= Nil_Pointer);

		loop
			case Get_Frame_Opcode(Interp.Stack) is
				when Opcode_Exit =>
					exit;

				when Opcode_Evaluate_Result =>
					Evaluate_Result;

				when Opcode_Evaluate_Object =>
					Evaluate_Object;

				when Opcode_Evaluate_Group =>
					Evaluate_Group;
					
				when Opcode_Evaluate_Procedure =>
					Evaluate_Procedure;

				when Opcode_Apply =>
					Apply;

				when Opcode_Read_Object =>
					Read_Object;

				when Opcode_Read_List =>
					Read_List;

				when Opcode_Read_List_Cdr =>
					Read_List_Cdr;

				when Opcode_Read_List_End =>
					Read_List_End;

				when Opcode_Close_List =>
					Close_List;

				when Opcode_Close_Quote =>
					Close_Quote;

			end case;
		end loop;

		-- the stack must be empty when the loop is terminated
		--pragma Assert (Interp.Stack = Nil_Pointer);

	exception
		when Stream_End_Error =>
			raise;

		when others =>
			Ada.Text_IO.Put_Line ("EXCEPTION OCCURRED");
			-- TODO: restore stack frame???
			-- TODO: restore envirronemtn frame???
			raise;
	end Execute;

	procedure Evaluate (Interp: in out Interpreter_Record;
	                    Source: in     Object_Pointer;
	                    Result: out    Object_Pointer) is
	begin
		
		pragma Assert (Interp.Stack = Nil_Pointer);
		Interp.Stack := Nil_Pointer;

		-- Push a pseudo-frame to terminate the evaluation loop
		Push_Frame (Interp, Opcode_Exit, Nil_Pointer);

		-- Push the actual frame for evaluation
		Push_Frame (Interp, Opcode_Evaluate_Object, Source);

		Execute (Interp);

		pragma Assert (Get_Frame_Opcode(Interp.Stack) = Opcode_Exit);

		Result := Get_Frame_Result (Interp.Stack);
		-- There must be only 1 value chained to the top-level frame
		-- once evaluation is over.
		pragma Assert (Get_Cdr(Result) = Nil_Pointer);
		-- Get the only value chained 
		Result := Get_Car(Result);
		Pop_Frame (Interp);

		pragma Assert (Interp.Stack = Nil_Pointer);

	end Evaluate;

	procedure Run_Loop (Interp: in out Interpreter_Record;
	                    Result: out    Object_Pointer) is
		-- standard read-eval-print loop
	begin
		Result := Nil_Pointer;

		loop
			pragma Assert (Interp.Stack = Nil_Pointer);
			Interp.Stack := Nil_Pointer;

			Push_Frame (Interp, Opcode_Exit, Nil_Pointer);
			--Push_Frame (Interp, Opcode_Print_Result, Nil_Pointer);
			Push_Frame (Interp, Opcode_Evaluate_Result, Nil_Pointer);
			Push_Frame (Interp, Opcode_Read_Object, Nil_Pointer);

			Execute (Interp);

			pragma Assert (Get_Frame_Opcode(Interp.Stack) = Opcode_Exit);

			-- TODO: this result must be kept at some where that GC dowsn't sweep.
			Result := Get_Frame_Result (Interp.Stack); 
			pragma Assert (Get_Cdr(Result) = Nil_Pointer);
			Result := Get_Car(Result);
			Pop_Frame (Interp);

Ada.Text_IO.Put ("REsULT>>>>>");
Print (Interp, Result);
			pragma Assert (Interp.Stack = Nil_Pointer);
Ada.Text_IO.Put_Line (">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LOOP ITERATION XXXXXX CHECKPOINT"); 
		end loop;

	exception
		when Stream_End_Error =>
			-- this is not a real error. this indicates the end of input stream.
			Ada.Text_IO.Put_LINE ("=== BYE ===");

		when others =>
			Ada.TEXT_IO.PUT_LINE ("ERROR ERROR ERROR");
			raise;
	end Run_Loop;
	
	-----------------------------------------------------------------------------
--
--	function h2scm_open return Interpreter_Pointer;
--	pragma Export (C, h2scm_open, "h2scm_open");
--
--	procedure h2scm_close (Interp: in out Interpreter_Pointer);
--	pragma Export (C, h2scm_close, "h2scm_close");
--
--	function h2scm_evaluate (Interp: access Interpreter_Record;
--	                         Source: in     Object_Pointer) return Interfaces.C.int;
--	pragma Export (C, h2scm_evaluate, "h2scm_evaluate");
--
--	procedure h2scm_dealloc is new 
--		Ada.Unchecked_Deallocation (Interpreter_Record, Interpreter_Pointer);
--
--	function h2scm_open return Interpreter_Pointer is
--		Interp: Interpreter_Pointer;	
--	begin
--		begin
--			Interp := new Interpreter_Record;
--		exception
--			when others =>
--				return null;
--		end;
--
--		begin
--			Open (Interp.all, 1_000_000, null);
--		exception
--			when others =>
--				h2scm_dealloc (Interp);
--				return null;
--		end;
--
--		return Interp;
--	end h2scm_open;
--
--	procedure h2scm_close (Interp: in out Interpreter_Pointer) is
--	begin
--Text_IO.Put_Line ("h2scm_close");
--		Close (Interp.all);	
--		h2scm_dealloc (Interp);
--	end h2scm_close;
--
--	function h2scm_evaluate (Interp: access Interpreter_Record;
--	                         Source: in     Object_Pointer) return Interfaces.C.int is
--	begin
--		return Interfaces.C.int(Interp.Heap(Interp.Current_Heap).Size);
--	end h2scm_evaluate;
	
end H2.Scheme;