[antlr-interest] error handling

[Bryan Ewbank]

I use a different approach, because catching exceptions outside the
parser means your customer only get the first syntax error each time. 
I'd prefer to give them as many as possible...

I tell antlr to disable exceptions for most productions, then enable
exceptions for a few key production recovery points (statement,
expression, and a few others), then have my own reportError() method
that keeps a running count of errors seen:

   MyParser extends Parser;
   options {  defaultErrorHandler=false; }
   ...
   expression
   options {defaultErrorHandler=true;}
   :
      expr    { ## = #( #[EXPR,"EXPR"], ## ); }
   ;


The top level routine in my parser returns true/false based on the
number of errors:

     parseme
     returns [bool r = true]
     :
         realParseProduction
         { if (nerr > 0) r = false; }
     ;