Go forward to Rpcalc Error.
Go backward to Rpcalc Lexer.
Go up to RPN Calc.

The Controlling Function
------------------------

   In keeping with the spirit of this example, the controlling function
is kept to the bare minimum.  The only requirement is that it call
`yyparse' to start the process of parsing.

     main ()
     {
       yyparse ();
     }