MODULE Stacks; (** AUTHOR ""; PURPOSE ""; *)

IMPORT
	Out := KernelLog;

TYPE	
	Object = OBJECT
	END Object;
	
	Stack* = OBJECT
	VAR
		top-,capacity-: LONGINT;
		pool: POINTER TO ARRAY OF Object;
		
		PROCEDURE & InitStack*(capacity: LONGINT);
		BEGIN
			SELF.capacity := capacity;
			SELF.top := -1;
			NEW(SELF.pool,capacity)
		END InitStack;
		
		PROCEDURE Push*(a:Object);
		BEGIN
			INC(SELF.top);
			ASSERT(SELF.top < SELF.capacity,100);
			SELF.pool[SELF.top] := a
		END Push;
		
		PROCEDURE Pop*(): Object;
		VAR
			r: Object;
		BEGIN
			ASSERT(SELF.top >= 0);
			r := SELF.pool[SELF.top];
			DEC(SELF.top);RETURN r
		END Pop;
		
		PROCEDURE Top*(): Object;
		BEGIN
			ASSERT(SELF.top >= 0);
			RETURN SELF.pool[SELF.top]
		END Top;
		
		PROCEDURE IsEmpty*(): BOOLEAN;
		BEGIN
			RETURN SELF.top < 0
		END IsEmpty;
		
	END Stack;
	
	BoxedInt = OBJECT
	(Object)
	VAR
		val-: LONGINT;

	PROCEDURE & InitBoxedInt*(CONST val: LONGINT);
	BEGIN	
		SELF.val := val
	END InitBoxedInt;

	END BoxedInt;

	PROCEDURE Test*;
	VAR
		s: Stack;
		bi: BoxedInt;
		obj: Object;
	BEGIN
		NEW(s,10); (* A new stack of ten objects *)
		NEW(bi,100);s.Push(bi);
		NEW(bi,102);s.Push(bi);		
		NEW(bi,104);s.Push(bi);
		Out.Ln;
		Out.String("Capacity:> ");Out.Int(s.capacity,0);Out.Ln;
		Out.String("Size:> ");Out.Int(s.top + 1,0);Out.Ln;
		obj := s.Pop(); obj := s.Pop();
		WITH obj: BoxedInt DO
			Out.String("obj:> ");Out.Int(obj.val,0);Out.Ln
		ELSE
			Out.String("Unknown object...");Out.Ln;
		END (* with *)
	END Test;
END Stacks.