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

[Serguei Sokol]

Le 26/01/2024 à 10:31, Serguei Sokol a écrit :
> Le 25/01/2024 à 19:04, Berwin A Turlach a écrit :
>> 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")
>> }
>>
> By nitpicking a little bit, this test won't work for v5.0 as minor "0" 
> is less then "1". There are a more canonical ways to test the version 
> and send a message (or a 'warning()'):
>
> if (getVersion() >= "4.1") {
Oops, it won't work for v10.0. Better would be:

if (utils::compareVersion(getVersion(), "4.1.0") >= 0) {

Best,
Serguei.

> cat(eval(parse(text="1:3 |> sum()")), "\n")
> } else {
>    message("You have to upgrade to R >= 4.1.0 to run this example")
> }
>
> Best,
> Serguei.