2   The Eval Stack
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     Internally, Clipper is organized as a stack based machine.  It uses
     an area of memory called the Eval Stack to contain operands,
     function parameters, and intermediate results.  The Eval Stack is
     simply a contiguous group of VALUEs that are accessed as a stack.
     Its use is analogous to the way the processor stack is used by C
     programs.

     For example, in a Clipper function call, parameters are placed
     (pushed) onto the Eval Stack before the function is executed.  The
     function operates on the top-most items in the Eval Stack and
     produces a result.  After the function completes, the parameter
     values are removed (popped) from the Eval Stack and replaced with
     the function result.