[R] Line numbers in error messages

[Tony Plate]

Please ignore this message -- it was an old one that I meant to delete, not 
send, because I found that in R, information about the expression and 
function of each frame didn't seemed to be stored in dumps, which makes 
this of thing difficult to do (at least I couldn't find this information in 
a sample dump.)

-- Tony Plate

>I agree it's not completely straightforward, but given the current 
>function, the current expression, and a list of which expressions have 
>already been executed (presumably from the execution engine), one should 
>be able to deduce a line number in many cases.
>
>-- Tony Plate
>
>At Monday 06:32 PM 4/12/2004, Thomas Lumley wrote:
>>On Mon, 12 Apr 2004, Tony Plate wrote:
>>
>> > Isn't source file information often recorded in the "source" attribute on
>> > functions (or calls)?  Could either the execution engine or the debugger
>> > refer to that information?  (Though, in the debugger it might be 
>> impossible
>> > to uniquely identify expressions that appear multiple times in the 
>> function
>> > code.)  If line info was printed out only when source was saved in the
>> > "source" attribute, this could still be useful.
>>
>>Yes, but it's still not that straightforward.  The "source" attribute is
>>just text. The execution engine doesn't know where it is in the text, and
>>there's no guarantee that, for example, deparse() on an expression will
>>return a substring of the original text.  And that's before things get
>>really complicated.
>>
>>Consider:
>> > lm(y~x)
>>Error in eval(expr, envir, enclos) : Object "y" not found
>> > traceback()
>>7: eval(expr, envir, enclos)
>>6: eval(predvars, data, env)
>>5: model.frame.default(formula = y ~ x, drop.unused.levels = TRUE)
>>4: model.frame(formula = y ~ x, drop.unused.levels = TRUE)
>>3: eval(expr, envir, enclos)
>>2: eval(mf, parent.frame())
>>1: lm(y ~ x)
>>
>>The majority of these expressions (lines 3, 4, 5 and 7) do not appear
>>anywhere in any of the functions being called.
>>
>>Now, it might well be possible to produce something that would give
>>source line numbers where they were available, with a few false negatives.
>>This would be an interesting project, but it isn't trivial.
>>
>>         -thomas
>>
>>
>>
>> > -- Tony Plate
>> >
>> >
>> > At Monday 05:41 PM 4/12/2004, Duncan Murdoch wrote:
>> > >On Mon, 12 Apr 2004 15:20:58 -0700, you wrote:
>> > >
>> > > >Hi Patrick,
>> > > >
>> > > >>It's very simple using a browser() line in your function somewhere you
>> > > >>know your code's OK, then run line by line.
>> > > >>
>> > > >The problem is that sometimes you have code of a few hundred lines, to
>> > > >which you have added a strange little line that craps out because of
>> > > >some silly mistake that would be apparent if you knew which line to 
>> look
>> > > >at.  However....  you don't want to start inserting browser statements
>> > > >inside the code, hoping to get close, you just want to know what line
>> > > >caused the issue.
>> > >
>> > >This is something that's on my wish list too, but it would require
>> > >fairly low-level changes.  Right now the parser doesn't record source
>> > >file information on a line, so there's no way an error message could
>> > >report it.
>> > >
>> > >It's not absolutely obvious how to do it, either:  code can come from
>> > >files, from saved images, from stuff you typed at the console prompt,
>> > >from a connection, as the result of evaluating an expression, etc.
>> > >It's a lot more complicated to do this in an interpreted language like
>> > >R than in a compiled language.
>> > >
>> > >Duncan Murdoch
>> > >
>> > >______________________________________________
>> > >R-help at stat.math.ethz.ch mailing list
>> > >https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>> > >PLEASE do read the posting guide! 
>> http://www.R-project.org/posting-guide.html
>> >
>> > ______________________________________________
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>>
>>Thomas Lumley                   Assoc. Professor, Biostatistics
>>tlumley at u.washington.edu        University of Washington, Seattle