[Rd] Generalised piping into operators

[Michael Milton]

Thanks, this makes sense. Is there a similar precedence reasoning behind
why operator functions (`+` etc) can't be piped into?

On Fri, Apr 21, 2023 at 11:52 PM Duncan Murdoch <murdoch.duncan using gmail.com>
wrote:

> On 21/04/2023 4:35 a.m., Michael Milton wrote:
> > I just checked out R-devel and noticed that the new "pipe extractor"
> > capability coming in 4.3 only works for the 4 extractor operators, but no
> > other standard operators like +, *, %*% etc, meaning that e.g. mtcars |>
> > as.matrix() |> _ + 1 |> colMeans() is a syntax error. In addition, we are
> > still subject to the restriction that the functions on the RHS of a pipe
> > can't have special names, so mtcars |> as.matrix() |> `+`(1) |>
> colMeans() is
> > also a syntax error.
> >
> > Either option would be great, as I find it much cleaner to coordinate a
> > sequence of function calls using pipes rather than nested function calls
> or
> > using temporary variables.
> >
> > May I enquire why both of these expressions are disallowed, and if it
> might
> > be possible to help remove one or both of these restrictions? There is
> some
> > discussion at
> > https://stat.ethz.ch/pipermail/r-devel/2020-December/080210.html but the
> > thread is mostly concerned with other things like the placeholder and
> > whether or not parentheses can be omitted. My naive view is that piping
> > into a special operator function like `+` would be the least ambiguous:
> `+`
> > presumably parses to the same type of token as `colMeans` does, so the
> > function parse tree seems like it would work fine if this was allowed in
> a
> > pipe.
>
> If it were allowed, people would expect expressions like yours to work,
> but as ?Syntax says, your pipe would actually be parsed as something like
>
>    (mtcars |> as.matrix() |> _) + (1 |> colMeans())
>
> because the |> operator has higher precedence than +.
>
> Since parens would be needed somewhere to override this, you may as well
> type
>
>    (as.matrix(mtcars) + 1) |> colMeans()
>
> which is both shorter and arguably clearer than
>
>    mtcars |> as.matrix() |> (_ + 1) |> colMeans()
>
> Duncan Murdoch
>
>
>

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