component GenericStack ( Stack, ElementType );
 type Stack;
      Stack(MaxSize = integer)  -> Stack;
      Empty( Stack )            -> boolean;
      Full ( Stack )            -> boolean;
      Push ( Stack, ElementType)-> nothing;
      Pull ( Stack )            -> ElementType;
begin
      type sequence = term;
      ElementType & sequence => sequence;
      nil = null (sequence);

      head (sequence) -> ElementType;
      head (X & Y) = ElementType:X;

      tail (sequence) -> sequence;
      tail (X & Y) = Y;

      Stack (Size) = Stack:[ list = nil ];
      Empty ( stack ) = (stack.list == nil);
      Full ( stack ) = false;
      Push ( stack, ElementType ) = [ stack.list:= ElementType & stack.list ];
      Pull ( stack ) = [ exception (Empty (stack), "Stack Underflow");
                         Head = head(stack.list); stack.list:=tail(stack.list); Head];
end component GenericStack;