Generalised piping into operators

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