dumb: make yacc tolerate "extra" stuff in a file

tdeckard@vitalimages.com
22 Aug 1999 14:45:04 -0400

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dumb: make yacc tolerate "extra" stuff in a file tdeckard@vitalimages.com (1999-08-22)
Re: dumb: make yacc tolerate "extra" stuff in a file scinar@my-deja.com (1999-08-27)
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From: tdeckard@vitalimages.com
Newsgroups: comp.compilers
Date: 22 Aug 1999 14:45:04 -0400
Organization: Compilers Central
Keywords: yacc, comment

Dumb question:


How do I convince yacc to overlook elements in the file for which
it lacks patterns? My file to be parsed contains


fred
{
        lots of stuff
}
barney
{
        lots of stuff
}


flinstone.yacc:
...
%%
my_file :
          barneyToken '{' myfilestuff '}' { }
          ;
...


I'd like to ignore everything but barney, or at least ignore the
stuff in fred { }?
I've tried patterns of the form


my_file :
      | fredToken '{' ... '}' {}
      | barneyToken '{' ... '}' {}
      ;


Thanks!
Todd
[You don't, yacc insists on matching everything it sees. I'd do a lexical
hack, e.g. instead of the invalid ... put something like this:


  | fredToken '{' { munchmode(); } '}' { /* whatever*/ }


where munchmode() tells the lexer to skip everything up to the close brace.
This is easy to do in flex with start states. Don't forget to count
matching braces, flex can't do that for you. -John]


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