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

[Duncan Murdoch]

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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>