Elisa

component Stacks ( Stack, Element );
  type Stack;
       Stack( MaxSize = integer) -> Stack;
       Empty( Stack ) -> boolean;
       Full ( Stack ) -> boolean;
       Push ( Stack, Element) -> nothing;
       Pull ( Stack ) -> Element;
begin
       Stack( MaxSize ) =
          Stack:[MaxSize; index:=0; area = array( Element, MaxSize)];  

       Empty( stack ) = (stack.index <= 0);

       Full ( stack ) = (stack.index >= stack.MaxSize);

       Push ( stack, element ) = 
                [ exception(Full(stack), "Stack Overflow");
                  stack.index:=stack.index + 1; 
                  stack.area[stack.index]:=element ];

       Pull ( stack ) = 
                [ exception(Empty(stack), "Stack Underflow");
                  stack.index:=stack.index - 1; 
                  stack.area[stack.index + 1] ];

  end component Stacks;