From: "Mauricio Fernández" <batsman.geo@...>
Date: 2004-01-23T22:58:22+09:00
Subject: Re: BibTeX parser

On Fri, Jan 23, 2004 at 06:27:45AM +0900, Daniel Carrera wrote:
> On Fri, Jan 23, 2004 at 06:08:37AM +0900, Mauricio Fern�ndez wrote:
> 
> > Looks like you're doing the parser by hand...
> 
> Yes, because I am a parser-newbie and I don't know better.
> 
> > wouldn't it be easier with, say, racc?  As for the lexer [snip]
> 
> What's racc?  Do you have a link?

http://i.loveruby.net/en/racc.html
It's a parser generator similar to YACC (kind of de facto standard) for
Ruby.

> What's a lexer?

Normally parsing is made in 2 steps. In the typical example of an
arithmetic expression
  1 + 2
the lexer would break the input into _tokens_ (syntactic atoms)
  type       value (semantic info)
  NUMBER     1
  OPPLUS
  NUMBER     2
which would be passed to the parser, that would recognize the expression
according to a number of rules (productions).

> Where can I learn how to make good parsers?  I'd really like to do this 
> right.

There's a billion books on this, essentially any on compiler
construction. Reading such a thing would probably be overkill, and you
can probably get by if you read the tutorial included in bison's .info
documentation (bison is the GNU parser generator, compatible with yacc;
if you understand how to use it you can make use of racc similarly).

> 
> > mmm I guess Coco/Rb could be a good option too, since you also get a
> > lexer, and LL(1) should be enough for this.
> 
> Links for Coco/Rb?

http://raa.ruby-lang.org/list.rhtml?name=coco-rb

You could also try Seattle.rb's pure-Ruby port of Coco/R 
 http://www.zenspider.com/ZSS/Products/CocoR/index.html

> 
> Thanks for all the help!  I just *knew* I was doing something wrong.
> Thanks for pointing me the right direction.
> 
> I will do a google search for "lexer", "grammar" and the other things you 
> mentioned and I didn't understand.  But if you have good links for me I'd 
> love to get them.

You can start here
http://www.gnu.org/software/bison/manual/html_node/Language-and-Grammar.html#Language%20and%20Grammar
and then proceed to the examples... Even though they're in C, they
should be very helpful if you use racc later.


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