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
-pd
> On 17 Apr 2022, at 01:04 , Benjamin Redelings <benjamin.redelings at
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,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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