(* this program simulates the tower of hanoi problem. DO TO THE LIMITATIONS *)
(* IMPOSED BY THE RISC MACHINE, THE RECURSIVE DEAPTH OF THE SOLUTION IS     *)
(* IS LIMITED.								    *)

MODULE HANOI;

CONST
	mindisk = 1;
	maxdisk = 26;
	terminate = -1;

TYPE
	towertype = RECORD
			tower : ARRAY [ mindisk .. maxdisk] OF CHAR;
			top : INTEGER;
		    END; (* RECORD *)

VAR
	source,dest,aux : towertype;
	disk : INTEGER;
	counter : INTEGER;




			(* INITIALIZE *)

PROCEDURE initialize();
BEGIN (* initialize *)
	source.top := mindisk - 1;
	dest.top   := mindisk - 1;
	aux.top    := mindisk - 1;
END initialize;




			(* SETSOURCE *)

PROCEDURE setsource(): INTEGER;
VAR
	num : INTEGER;
	disk : INTEGER;
BEGIN (* setsource *)
	READ(num);
	IF ( num > terminate ) THEN
	  FOR disk := ORD('A') TO ORD("A") + num - 1 DO
		INC(source.top);
		source.tower[ source.top ] := CHR(disk);
	  END; (* FOR *)
	END; (* IF *)
	RETURN(num);
END setsource;




			(* MOVE *)

PROCEDURE move( VAR source,dest : towertype );
BEGIN (* move *)
	INC(dest.top);
	dest.tower[ dest.top ] := source.tower[ source.top ];
	DEC(source.top);
END move;



			(* PRINT *)

PROCEDURE print();
VAR
	index : INTEGER;
BEGIN (* print *)
	WRITE("source       -> ");
	FOR index := mindisk TO source.top DO
		WRITE(source.tower[index]);
		WRITE(" ");
	END; (* FOR *)
	WRITELN;
	WRITE("auxiliary    -> ");
	FOR index := mindisk TO aux.top DO
		WRITE(aux.tower[index]);
		WRITE(" ");
	END; (* FOR *)
	WRITELN;
	WRITE("destination  -> ");
	FOR index := mindisk TO dest.top DO
		WRITE(dest.tower[index]);
		WRITE(" ");
	END; (* FOR *)
	WRITELN;
	WRITELN;
END print;


			(* TOWERS *)

PROCEDURE TOWERS( disk : INTEGER; VAR source,dest,aux : towertype );
BEGIN (* TOWERS *)
	IF disk = 1 THEN
		move(source,dest);
		print();
	ELSE
		TOWERS( disk - 1, source, aux, dest);
		move(source,dest);
	 	print();
		TOWERS( disk - 1, aux, dest, source);
	END; (* IF *)
END TOWERS;


BEGIN (* HANOI *)
	counter := 0;
	REPEAT
		initialize();
		disk := setsource();
		IF (disk > terminate)
		  THEN
		    INC(counter);
		    WRITELN;
		    WRITE("   TOWERS OF HANOI TRACE : test number -> ");
		    WRITE(counter);
		    WRITELN;
		    print();
		    TOWERS( disk, source, dest, aux);
		END;
	UNTIL (disk <= terminate);
END HANOI.