[antlr-interest] Re: second lexical pass
idontwantanidwith2000init
idontwantanidwith2000init at yahoo.com
Sun Apr 11 11:43:29 PDT 2004
I've ment multiple values of course :)
That's what I wanted to do, Terr, more or less. :)
I'm sad though. With lex I could handle it without a second parser.
But it seems a better aproch then putting it all together in one
parser.
Let me explain why:
'"'YYYY-MM-DD hh:mm:ss'"' is a STRING.
and there isn't a simple way to express this relationship.
Maybe it's an idea for improving the lexer.
What do you think?
--- In antlr-interest at yahoogroups.com, Terence Parr <parrt at c...>
wrote:
>
> On Apr 11, 2004, at 6:25 AM, idontwantanidwith2000init wrote:
>
> > Is there an elegant way to do a second lexical path instead of
> > writing two lexers?
> >
> > For instance:
> > STRING_LITERAL:
> > '"' (~('\r'|'n'|'\\') | '\\' .) '"' ;
> >
> > now STRING_LITERAL will colide with any special string you'd
like to
> > match, for instance:
> > DATE_TIME : '"'YYYY-MM-DD hh:mm:ss'"'
> >
> > I've managed to merge it with:
> > '"'(LETTER)*'"'
> > '"'(LETTER)*'.'(LETTER)*'"'
> > '"'(LETTER)*'-'(LETTER)*'"'
> > Which was a diffucult task but doable.
> >
> >
> > I thought about it and merging these rules is possible, but it
will
> > take me days to write it and we haven't talked about validation.
> > (It is a good to write down my thoughts I'm starting to convince
> > myself that it is a good idea)
> >
> > What do you think is a proper solution?
>
> My first thought is that you have a two-level grammatical issue
here.
> First you have to match a string and then determine if it
satisfies a
> "nested structure" which is the date/time stuff. You can't really
use
> another rule in the same lexer object as it will consume the
input.
> Perhaps a compromise. Make a new lexer rule that will match
DATE_TIME
> as you've done and make it protected. Then, make a *new* instance
of
> your lexer. Set it up with a copy of the text matched inside the
> string and then directly call DATE_TIME with a try/catch around it
to
> catch failure. Gotta love LL based lexers :)
>
> Ter
> --
> Professor Comp. Sci., University of San Francisco
> Creator, ANTLR Parser Generator, http://www.antlr.org
> Cofounder, http://www.jguru.com
> Cofounder, http://www.knowspam.net enjoy email again!
> Cofounder, http://www.peerscope.com pure link sharing
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