arser calls the application's callback routine to get the function's ID number. The application must assign each function a word-sized ID which is greater than or equal to the constant FUNCTION_ID_FIRST_EXTERNAL_FUNCTION_BASE. This constant is defined as 0x8000.</P>
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When the Evaluator needs to evaluate a function, it checks to see if the function is external or internal. If the function is internal, it looks up the functions address and calls it. If the function is external, it calls the application's c