The "Stack" class implementation

#define Stack_Class_Source
#include <stack.ih>

SOM_Scope boolean  SOMLINK full(Stack somSelf, Environment *ev)
{
    StackData *somThis = StackGetData(somSelf);
    StackMethodDebug("Stack","full");

    /* Return TRUE if stack is full. */
    return (_stackTop == stackSize);
}

SOM_Scope boolean  SOMLINK empty(Stack somSelf, Environment *ev)
{
    StackData *somThis = StackGetData(somSelf);
    StackMethodDebug("Stack","empty");

    /* Return TRUE if stack is empty.*/
    return (_stackTop == 0);
}

SOM_Scope long  SOMLINK top(Stack somSelf, Environment *ev)
{
    StackData *somThis = StackGetData(somSelf);
    StackMethodDebug("Stack","top");

    if (_stackTop > 0)
    {
       /* Return top element in stack without removing it from
        * the stack.
        */
       return (_stackValues[_stackTop-1]);
    }
    else
    {
       somSetException(ev, USER_EXCEPTION,
                       ex_STACK_UNDERFLOW, NULL);
       return (-1L);
    }
}

SOM_Scope long  SOMLINK pop(Stack somSelf, Environment *ev)
{
    StackData *somThis = StackGetData(somSelf);
    StackMethodDebug("Stack","pop");

    if (_stackTop > 0)
    {
       /* Return top element in stack and remove it from the
        * stack.
        */
       _stackTop--;
       return (_stackValues[_stackTop]);
    }
    else
    {
       somSetException(ev, USER_EXCEPTION,
                       ex_STACK_UNDERFLOW, NULL);
       return (-1L);
    }
}

SOM_Scope void  SOMLINK push(Stack somSelf,
                             Environment *ev, long el)
{
    StackData *somThis = StackGetData(somSelf);
    StackMethodDebug("Stack","push");

    if (_stackTop < stackSize)
    {
      /* Add element to top of the stack. */
      _stackValues[_stackTop] = el;
      _stackTop++;
    }
    else
    {
       somSetException(ev, USER_EXCEPTION,
                       ex_STACK_OVERFLOW, NULL);
    }
}

SOM_Scope void  SOMLINK somDefaultInit(Stack somSelf,
                                       somInitCtrl* ctrl)
{
    StackData *somThis;
    somInitCtrl globalCtrl;
    somBooleanVector myMask;
    StackMethodDebug("Stack","somDefaultInit");
    Stack_BeginInitializer_somDefaultInit;

    Stack_Init_SOMObject_somDefaultInit(somSelf, ctrl);

    /* stackTop is index into stackValues for next pushed
     * stack element.
     * stackValues[0..(stackSize-1)] holds stack elements.
     */
    _stackTop = 0;
}