[Rd] Strange behaviour of do.call()

[Duncan Murdoch]

Sorry, it's a silly thinko.  I misspelled the vline argument.  Thanks 
Ivan for the gentle nudge!

Duncan Murdoch

On 19/09/2023 10:44 a.m., Duncan Murdoch wrote:
> The knitr::kable() function does some internal setup, including
> determining the target format, and then calls an internal function using
> 
>     do.call(paste("kable", format, sep = "_"), list(x = x,
>           caption = caption, escape = escape, ...))
> 
> I was interested in setting the `vlign` argument to knitr:::kable_latex,
> using this code:
> 
>     knitr::kable(head(mtcars), format="latex", align = "c", vlign="")
> 
> If I debug knitr::kable, I can see that `vlign = ""` is part of
> list(...).  However, if I debug knitr:::kable_latex, I get weird results:
> 
>     > debug(knitr:::kable_latex)
>     > knitr::kable(head(mtcars), format="latex", align = "c", vlign="")
>     debugging in: kable_latex(x = c("Mazda RX4", "Mazda RX4 Wag", "Datsun
> 710",
>     "Hornet 4 Drive", "Hornet Sportabout", "Valiant", "21.0", "21.0",
>     "22.8", "21.4", "18.7", "18.1", "6", "6", "4", "6", "8", "6",
>     "160", "160", "108", "258", "360", "225", "110", "110", "93",
>     "110", "175", "105", "3.90", "3.90", "3.85", "3.08", "3.15",
>     "2.76", "2.620", "2.875", "2.320", "3.215", "3.440", "3.460",
>     "16.46", "17.02", "18.61", "19.44", "17.02", "20.22", "0", "0",
>     "1", "1", "0", "1", "1", "1", "1", "0", "0", "0", "4", "4", "4",
>     "3", "3", "3", "4", "4", "1", "1", "2", "1"), caption = NULL,
>         escape = TRUE, vlign = "")
> debug: {
> 
>     [rest of function display omitted]
> 
> I see here that vlign = "" is being shown as an argument.  However, when
> I print vlign, sometimes I get "object not found", and somethings I get
> 
>     Browse[2]> vline
>     debug: [1] "|"
> 
> (which is what the default value would be).  In the latter case, I also see
> 
>     Browse[2]> list(...)
>     $vlign
>     [1] ""
> 
> i.e. vlign remains part of the ... list, it wasn't bound to the argument
> named vlign.
> 
> I can't spot anything particularly strange in the way knitr is handling
> this; can anyone else?  My sessionInfo() is below.
> 
> Duncan Murdoch
> 
>   > sessionInfo()
> R version 4.3.1 (2023-06-16)
> Platform: x86_64-apple-darwin20 (64-bit)
> Running under: macOS Monterey 12.6.9
> 
> Matrix products: default
> BLAS:
> /Library/Frameworks/R.framework/Versions/4.3-x86_64/Resources/lib/libRblas.0.dylib
> 
> LAPACK:
> /Library/Frameworks/R.framework/Versions/4.3-x86_64/Resources/lib/libRlapack.dylib;
>    LAPACK version 3.11.0
> 
> locale:
> [1] en_CA.UTF-8/en_CA.UTF-8/en_CA.UTF-8/C/en_CA.UTF-8/en_CA.UTF-8
> 
> time zone: America/Toronto
> tzcode source: internal
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> 
> loaded via a namespace (and not attached):
> [1] compiler_4.3.1 tools_4.3.1    knitr_1.44     xfun_0.40