From: "Peña, Botp" <botp@...>
Date: 2004-10-08T14:57:11+09:00
Subject: Re: quality of error messages

Markus [mailto:markus@reality.com] wrote:

> Sent: Friday, October 08, 2004 1:39 PM
> To: ruby-talk@ruby-lang.org
> Subject: Re: quality of error messages
> 
> 
> On Thu, 2004-10-07 at 22:26, "Peña, Botp" wrote:
> > Markus [mailto:markus@reality.com] wrote:
> > 
> > > On Thu, 2004-10-07 at 21:19, Yukihiro Matsumoto wrote:
> > > > Hi,
> > > > 
> > > > In message "Re: quality of error messages"
> > > >     on Fri, 8 Oct 2004 12:58:26 +0900, Jamis Buck
> > > <jgb3@email.byu.edu>
> > > > writes:
> > > > 
> > > > |> We can.  But how we check for missing/broken def/end pairs, 
> > > > |> more
> > > > |> than just syntax error?
> > > > 
> > > > |I believe what is being asked for is more than just a
> > > "syntax error"
> > > > |message. If the error could be more specific, like
> > > "missing 'end' on
> > > > |line x", it would greatly increase the usefulness of the -c 
> > > > |option.
> > > > 
> > > > I know what he wants.  I am not refusing his idea.  The
> > > point is I'm
> > > > not yet sure how to detect missing pairs.
> > > > 
> > > 
> > > 
> > >     ((1+2)+3+4/5
> > > 
> > > There is clearly a ')' missing, but should it be:
> > > 
> > > 
> > >     ((1)+2)+3+4/5  which equals 6.8
> > > 
> > [snip informative text]
> > 
> > 
> > no, we do not have to determine where_ to put the missing 
> ")". We can 
> > be close to the target, but not closer, pls.
> > 
> > as for ((1+2)+3+4/5
> > 
> > the compiler just say that the first "(" has missing ")". 
> That is all. 
> > (1+2) pair is already valid, and therefore consumes the 
> last ")" which 
> > leaves the first "(" missing a partner. Of course, this may not be 
> > what the programmer wants, but hey, the compiler was just 
> helping. Was 
> > it helpful? Many a times, yes..
> > 
> > A "missing partner foo-end on possible foo-begin in line#" 
> message is 
> > a lot better than just plain "syntax error".
> > 
> > Is that fine enough?
> 
>      Sorry, my example over simplified a little.  To save 
> space, I was using an analogy between class/end and '('/')'; 
> and I chose a example that was too simple to really make the point.
> 
>      Consider that each token is on its own line (i.e., that 
> we really are wanting to identify which '(' is missing its 
> ')', not even worrying about where it goes).  Also keep in 
> mind that nested things like '((3))' are valid (and meaningful)*:
> 
>    (((1/2)/((3/4)/5)

(
 (
  (1/2)
   /
  (
   (3/4)
    /
    5
  )


we catch only one (though there are two). And to simplify further, we point
second "(" since it is _inner... But I do not know internal parser. if
parser catches first "(", then it reports first "(". Does not matter w me.

> 
> So, which '(' is missing its ')'?
> 

again, we do _not choose or point where _exactly.

we only say "missing foo-end on possible foo-begin at line#". Compiler
suggest.  The programmer will decide.

> -- Markus

kind regards -botp