[R-pkg-devel] Native pipe in package examples

[Berwin A Turlach]

On Thu, 25 Jan 2024 09:44:26 -0800
Henrik Bengtsson <henrik.bengtsson using gmail.com> wrote:

> On Thu, Jan 25, 2024 at 9:23 AM Berwin A Turlach
> <berwin.turlach using gmail.com> wrote:
> >
> > G'day Duncon,

Uups, apologies for the misspelling of your name Duncan.  Fingers were
too fast. :)

[...]
> > But you could always code your example (not tested :-) ) along lines
> > similar to:
> >
> > if( with(version, all(as.numeric(c(major, minor)) >= c(4, 1))) ){
> >   ## code that uses native pipe
> > }else{
> >   cat("You have to upgrade to R >= 4.1.0 to run this example\n")
> > }  
> 
> That will unfortunately not work in this case, because |> is part of
> the new *syntax* that was introduced in R 4.1.0.  Older versions of R
> simply doesn't understand how to *parse* those two symbols next to
> each other, e.g.
> 
> {R 4.1.0}> parse(text = "1:3 |> sum()")
> expression(1:3 |> sum())
> 
> {R 4.0.5}> parse(text = "1:3 |> sum()")
> Error in parse(text = "1:3 |> sum()") : <text>:1:6: unexpected '>'
> 1: 1:3 |>
>          ^
> 
> In order for R to execute some code, it needs to be able to parse it
> first. Only then, it can execute it.  So, here, we're not even getting
> past the parsing phase.

Well, not withstanding 'fortune(181)', you could code it as:

if( with(version, all(as.numeric(c(major, minor)) >= c(4, 1))) ){
   cat(eval(parse(text="1:3 |> sum()")), "\n")
}else{
  cat("You have to upgrade to R >= 4.1.0 to run this example\n")
}  


Admittedly, it would be easier to say "Depends: R (>= 4.1.0)" in the
DESCRIPTION file. :)

Cheers,

	Berwin