Error Recovery in Yacc

Hello,


    I am trying to use lex and yacc to write a parser, but I am running
into some problems with the error recovery. I have searched through the
O'Reilly book, but I can't seem to find the answer to my problem.


    Basically, my problem is when the parser comes across a token it
doesn't expect. For example, if I have the rules:


command_sequence:
                                | command_sequence command
                                ;


command: subject verb object
              ;


subject: (The list of possible subjects.)


verb: (List of verbs)


object: (List of objects)


    When I run my parser on a file, if it is looking for a subject and
it comes across something else (like a verb), the parser doesn't
recognize any more rules (even if there are valid commands after the
error) until it completes on a rule which started before the error.


    I would like to store the offensive token and put the parser into a
state where it can continue happily, but unfortunately, I can't find
any resources which discuss this. Does anyone know how to achieve
this, or is there a better way to recover from this error? I suppose
I could use the brute force method of adding tons of rules to handle
the offensive tokens, but if possible, I would like to use a more
elegant solution.


  - Vicki


Vicki Tardif ----------------------------------- voice: (617) 577-9800
net.Genesis fax: (617) 577-9850
56 Rogers St vke@netgen.com
Cambridge, MA 02142 --------------------------- http://www.netgen.com/
[Yacc error recovery is a losing battle if you want to do much more than
resync at a punctuation mark. -John]
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