[erlang-questions] Better error messages would be helpful

[David Mercer]

Richard A. O'Keefe wrote:

> > On May 17, 2013, at 9:40 AM, David Mercer <dmercer@REDACTED> wrote:
> >
> >> Richard A. O'Keefe wrote:
> >>
> >>> Part of the problem is precisely the fact that the parser is
> written
> >>> in Yecc.
> >>
> >> Back in the day, I'd have known the answer to this, but I figure
> some
> >> of you are more knowledgeable than I ever was: What parsing
> >> technology besides hand-rolled would produce better error messages?
> ANTLR?
> >> Parsec?  PEG?
> >
> >
> > Menhir
> >
> > http://gallium.inria.fr/~fpottier/menhir/
> 
> Menhir is definitely interesting, and if I had experienced anything
> other than extreme frustration with Godi, I would have liked to try it.
> But judging from section 8 of the Menhir manual, a Menhir-built parser
> would be no better than a Yecc-built one here.
> It might even be worse: the manual says that the current lookahead
> token is *replaced* by an ERROR token as part of recovery, and in the
> example we are discussing, the token in question is ")" and it is
> correct, and should be retained.  What is more, the Menhir manual is
> quite explicit that error detection may be deferred.
> 
> What the user needs in cases like this is the information that an
> earlier token (fun) caused the parser to be looking for a particular
> token (end) but it encountered a closer (right paren) before finding
> it.  Something basically top-down should have an easier time of it.

Is there a grammar language/parsing technology that you could use for this, or would it all pretty much be hand-roll-your-own?