[antlr-interest] Ambiguous grammar or Antlr?

[Loring Craymer]

Don't believe everything you read--excessive optimism is the developer's friend, and Ter was in the full throes of developing ANTLR when he wrote TDAR.  Refactoring is a normal (and usually critical) part of grammar development; Jim was offering good advice.

--Loring


----- Original Message ----
> From: Gary R. Van Sickle <g.r.vansickle at att.net>
> To: antlr-interest at antlr.org
> Sent: Thursday, July 2, 2009 10:47:30 PM
> Subject: Re: [antlr-interest] Ambiguous grammar or Antlr?
> 
> Jim Idle wrote:
> 
> [snip] 
> > Even with backtracking, you still need to know something 
> > about LL(k) and parsing etc, and switching on backtrack mode 
> > will hide all your problems. It also means, as you have found 
> > out, that in the event of a syntax error, you cannot 
> > determine much  about the location of your error.
> > 
> > Basically, you will need to left factor at least some parts 
> > of your grammar. In this case, if you have something like:
> > 
> > | ID
> > | ID '(' expr ')'
> > | ID something else
> > 
> > and (probably more complicated than that is your issue), then 
> > look to do:
> > 
> > | ID (  '(' expr
> >          | something
> >       )?
> > 
> > and so on.
> 
> But isn't the whole point of LL(*) to eliminate the need to do exactly this
> sort of left-factoring?  Section 11.3 of Ter's book gives essentially the
> former as an example of why LL(*) makes it so you don't have to do a manual
> refactoring such as the latter.  In fact, that section makes the argument
> that one should *not* do the left-factoring manually, if for no other reason
> than to maintain the readability of the grammar.
> 
> -- 
> Gary R. Van Sickle
> 
> 
> 
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