.  Parsing continues until <tt>done_parsing()</tt>
is called (this is done automatically, for example, when the parser
accepts).  It then returns a <tt>Symbol</tt> with the <tt>value</tt>
instance variable containing the RESULT of the start production, or
<tt>null</tt>, if there is no value.<p>

In addition to the normal parser, the runtime system also provides a debugging
version of the parser.  This operates in exactly the same way as the normal
parser, but prints debugging messages (by calling 
<tt>publi