[R] [External] Re: Parser For Line Number Tracing

[Duncan Murdoch]

Sorry, I'm not seeing the first problem now: 
options(show.error.locations = TRUE) works fine.  Not sure what I did 
wrong before.

I'm still seeing `traceback()` failing to report the attempt to call 
nofunction().  I suppose this is because a context is never set up for 
the failed call.  Perhaps findFun3 could set up a fake context so that 
traceback() adds one more entry?

Duncan Murdoch


On 2025-01-19 3:39 p.m., Duncan Murdoch wrote:
> Thanks for pointing out the options.  Using
> 
>      options(show.error.locations = TRUE)
> 
> works on Ivo's example, but it doesn't show a location if the error
> happens in a function that doesn't have srcrefs, because the known
> location isn't on the top of the stack.
> 
> Perhaps TRUE (and maybe "top"?) should look back through the stack until
> it finds a known location, and report that, or another option (e.g.
> "highest"?) could be added to do that.
> 
> And still I think traceback() should show the top call in Ivo's example.
> 
> Duncan
> 
> 
> On 2025-01-19 11:46 a.m., luke-tierney using uiowa.edu wrote:
>> On Sun, 19 Jan 2025, Ivo Welch wrote:
>>
>>> Hi Duncan — Wonderful.  Thank you.  Bug or no bug, I think it would be
>>> a huge improvement for user-friendliness if R printed the last line by
>>> default *every time* a script dies.  Most computer languages do so.
>>>
>>> Should I file it as a request for improvement to the R code
>>> development team?  Maybe R can be improved at a very low cost to the
>>> development team and a very high benefit to newbies.
>>
>> No. There are already many ways to influence the way the default error
>> handler prints information about errors, mstly via options(). In
>> particular you may want to look at entries in ?options for
>>
>> show.error.locations
>> showErrorCalls
>> showWarningCalls
>>
>> and adjust your options settings accordingly.
>>
>> Best,
>>
>> luke
>>
>>>
>>> Regards,
>>>
>>> /ivo
>>>
>>> On Sun, Jan 19, 2025 at 2:39 AM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>>>>
>>>> On 2025-01-18 8:27 p.m., Ivo Welch wrote:
>>>>> I am afraid my errors are worse!  (so are my postings.  I should have
>>>>> given an example.)
>>>>>
>>>>> ```
>>>>> x <- 1
>>>>> y <- 2
>>>>> nofunction("something stupid I am doing!")
>>>>> z <- 4
>>>>> ```
>>>>>
>>>>> and
>>>>>
>>>>> ```
>>>>>> source("where-is-my-water.R")
>>>>> Error in nofunction("something stupid I am doing!") :
>>>>>      could not find function "nofunction"
>>>>> ```
>>>>>
>>>>> and no traceback is available.
>>>>
>>>> Okay, I see.  In that case traceback() doesn't report the line, but it
>>>> still is known internally.  You can see it using the following function:
>>>>
>>>> showKnownLocations <- function() {
>>>>      calls <- sys.calls()
>>>>      srcrefs <- sapply(calls, function(v) if (!is.null(srcref <- attr(v,
>>>>
>>>> "srcref"))) {
>>>>        srcfile <- attr(srcref, "srcfile")
>>>>        paste0(basename(srcfile$filename), "#", srcref[1L])
>>>>      } else ".")
>>>>      cat("Current call stack locations:\n")
>>>>      cat(srcrefs, sep = " ")
>>>>      cat("\n")
>>>> }
>>>>
>>>> I haven't done much testing on this, but I think it can be called
>>>> explicitly from any location if you want to know how you got there, or
>>>> you can set it as the error handler using
>>>>
>>>>      options(error = showKnownLocations)
>>>>
>>>> For example, try this script:
>>>>
>>>>      options(error = showKnownLocations)
>>>>      f <- function() showKnownLocations()
>>>>      x <- 1
>>>>      f()
>>>>      y <- 2
>>>>      nofunction("something stupid I am doing!")
>>>>      z <- 4
>>>>
>>>> I see this output from source("test.R"):
>>>>
>>>>     > source("test.R")
>>>>      Current call stack locations:
>>>>      . . . . test.R#4 test.R#2
>>>>      Error in nofunction("something stupid I am doing!") :
>>>>        could not find function "nofunction"
>>>>      Current call stack locations:
>>>>      . . . . test.R#6
>>>>
>>>> The first report is from the explicit call in f() on line 2 that was
>>>> invoked on line 4, and the second report happens during error handling.
>>>>
>>>> I supppose the fact that traceback() isn't showing you the line 6
>>>> location could be considered a bug.
>>>>
>>>> Duncan Murdoch
>>>>
>>>>
>>>
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>>
>