From: "Luke A. Kanies" <luke@...>
Date: 2003-12-12T05:54:12+09:00
Subject: Re: problems with racc: $end token

On Fri, 12 Dec 2003, Jim Freeze wrote:

> On Friday, 12 December 2003 at  3:55:31 +0900, Luke A. Kanies wrote:
>
> Hi Luke
>
> I took your code and repeated the $end problem.
> I removed the problem by putting an optional return
> after your define { } block.

Um, wow, thank you!

I ended up finally figuring out how to turn on debugging in racc (yep, a
hack: I had to use -E and then edit the parser.rb file manually, setting
@yydebug = true), and this enabled me to figure out, that, well, my
grammer didn't do anything like I expected.

So, I ended up basically rewriting the grammar itself.  In doing so, I was
finally able to avoid the $end error.  In other words, it was definitely a
grammar problem, and I probably would have caught it much sooner if I had
figured out earlier how to turn debugging on.  The silly thing is, I know
there's an API for turning it on, but I haven't been able to extract it
yet.

The problem here is that I have used perl's Parse::Yapp, which behaves
quite differently in many ways, and most especially in how it deals with
syntax errors.  It is totally my fault, because I was unconsciously
expecting racc to behave a certain way, and when it didn't I got very
confused.  With the advent of debugging, I figured it out relatively
quickly.

As a side note, the grammar rules must set the value of 'return'.  For
some reason, racc does not use explicit mechanisms for returning data;
instead you have to set the value of 'return' and it returns that for you.
This also caused a bunch of problems for me.

To summarize:

There is debugging in racc, and using racc -E to embed the parser and then
manually setting @yydebug = true can turn it on.  I'm sure there's a
better way.

Also, you must set 'return' manually, although it can be any type of
variable.

Thanks for all your help, Jim.

Luke

-- 
Today I dialed a wrong number...The other person said, "Hello?" and
I said, "Hello, could I speak to Joey?"...
They said, "Uh...I don't think so...he's only 2 months old."
I said, "I'll wait."  -- Steven Wright