From: Brian Candler <B.Candler@...>
Date: 2004-10-08T18:19:50+09:00
Subject: Re: quality of error messages

On Fri, Oct 08, 2004 at 02:26:26PM +0900, "Pe?a, Botp" wrote:
> > 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..

I think in most cases not. For the most common missing 'end' error, the
compiler detects it at the end of the file, and the line it thinks it pairs
with is the first line of the file. Hence it localises the error to
somewhere between the first line and last line of the file, which is not
very helpful :-)

Concrete example:

class A
  def m1
  end
  def m2
    if true
      puts "hello"
  end
  def m3
  end
end
class B
  def m1
  end
  def m2
  end
  def m3
  end
end
class C
end

is parsed as:

class A
  def m1
  end
  def m2
    if true
      puts "hello"
    end
    def m3
    end
  end
  class B
    def m1
    end
    def m2
    end
    def m3
    end
  end
  class C
  end

Since class definitions can occur within other classes (very useful), and
'def' can occur within another 'def' (not so useful for me), that's how it
gets parsed.

Regards,

Brian.