[Rd] Pipe operator status, placeholders?

peter dalgaard pd@|gd @end|ng |rom gm@||@com
Tue Apr 19 09:24:32 CEST 2022

You probably want Luke Tierney for the full story, but what I gather from the deliberations (on the private R-core list), there are issues with how non-funcall syntax like lm(....) |> _$coef[2] should work. This, in turn, has to do with wanting to have the placeholder occur only as a toplevel substitution (i.e. "["("$"(_, coef), 2) is a no-go. And the reason for that has to do with the way the pipe works in the absense of placeholder, e.g. the parser gets confused by

> x |> f(g(x=_))
Error in f(x, g(x = "_")) : invalid use of pipe placeholder


> On 17 Apr 2022, at 01:04 , Benjamin Redelings <benjamin.redelings using gmail.com> wrote:
> Hi,
> I see that R 4.2 adds the underscore _ as a placeholder for the new forward pipe operator |> , but only for named arguments. The reason why placeholders for position arguments was NOT added isn't clear to me, so I've been looking for the discussion around the introduction of the placeholder.
> By searching subject lines in the r-devel mailing list archive, I've found
>     https://stat.ethz.ch/pipermail/r-devel/2021-April/080646.html
> https://stat.ethz.ch/pipermail/r-devel/2021-January/080396.html
> https://stat.ethz.ch/pipermail/r-devel/2020-December/080173.html and following messages
> but not much else.
> 1. Am I looking in the wrong place?
> 2. What is the reasoning behind allowing _ as a placeholder only for named arguments?
> take care,
> -BenRI
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Peter Dalgaard, Professor,
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