[Rd] New pipe operator

[Hugh Parsonage]

I'm surprised by the aversion to

mtcars |> nrow

over

mtcars |> nrow()

and I think the decision to disallow the former should be
reconsidered.  The pipe operator is only going to be used when the rhs
is a function, so there is no ambiguity with omitting the parentheses.
If it's disallowed, it becomes inconsistent with other treatments like
sapply(mtcars, typeof) where sapply(mtcars, typeof()) would just be
noise.  I'm not sure why this decision was taken

If the only issue is with the double (and triple) colon operator, then
ideally `mtcars |> base::head` should resolve to `base::head(mtcars)`
-- in other words, demote the precedence of |>

Obviously (looking at the R-Syntax branch) this decision was
considered, put into place, then dropped, but I can't see why
precisely.

Best,


Hugh.







On Sat, 5 Dec 2020 at 04:07, Deepayan Sarkar <deepayan.sarkar using gmail.com> wrote:
>
> On Fri, Dec 4, 2020 at 7:35 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
> >
> > On 04/12/2020 8:13 a.m., Hiroaki Yutani wrote:
> > >>   Error: function '::' not supported in RHS call of a pipe
> > >
> > > To me, this error looks much more friendly than magrittr's error.
> > > Some of them got too used to specify functions without (). This
> > > is OK until they use `::`, but when they need to use it, it takes
> > > hours to figure out why
> > >
> > > mtcars %>% base::head
> > > #> Error in .::base : unused argument (head)
> > >
> > > won't work but
> > >
> > > mtcars %>% head
> > >
> > > works. I think this is a too harsh lesson for ordinary R users to
> > > learn `::` is a function. I've been wanting for magrittr to drop the
> > > support for a function name without () to avoid this confusion,
> > > so I would very much welcome the new pipe operator's behavior.
> > > Thank you all the developers who implemented this!
> >
> > I agree, it's an improvement on the corresponding magrittr error.
> >
> > I think the semantics of not evaluating the RHS, but treating the pipe
> > as purely syntactical is a good decision.
> >
> > I'm not sure I like the recommended way to pipe into a particular argument:
> >
> >    mtcars |> subset(cyl == 4) |> \(d) lm(mpg ~ disp, data = d)
> >
> > or
> >
> >    mtcars |> subset(cyl == 4) |> function(d) lm(mpg ~ disp, data = d)
> >
> > both of which are equivalent to
> >
> >    mtcars |> subset(cyl == 4) |> (function(d) lm(mpg ~ disp, data = d))()
> >
> > It's tempting to suggest it should allow something like
> >
> >    mtcars |> subset(cyl == 4) |> lm(mpg ~ disp, data = .)
>
> Which is really not that far off from
>
> mtcars |> subset(cyl == 4) |> \(.) lm(mpg ~ disp, data = .)
>
> once you get used to it.
>
> One consequence of the implementation is that it's not clear how
> multiple occurrences of the placeholder would be interpreted. With
> magrittr,
>
> sort(runif(10)) %>% ecdf(.)(.)
> ## [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
>
> This is probably what you would expect, if you expect it to work at all, and not
>
> ecdf(sort(runif(10)))(sort(runif(10)))
>
> There would be no such ambiguity with anonymous functions
>
> sort(runif(10)) |> \(.) ecdf(.)(.)
>
> -Deepayan
>
> > which would be expanded to something equivalent to the other versions:
> > but that makes it quite a bit more complicated.  (Maybe _ or \. should
> > be used instead of ., since those are not legal variable names.)
> >
> > I don't think there should be an attempt to copy magrittr's special
> > casing of how . is used in determining whether to also include the
> > previous value as first argument.
> >
> > Duncan Murdoch
> >
> >
> > >
> > > Best,
> > > Hiroaki Yutani
> > >
> > > 2020年12月4日(金) 20:51 Duncan Murdoch <murdoch.duncan using gmail.com>:
> > >>
> > >> Just saw this on the R-devel news:
> > >>
> > >>
> > >> R now provides a simple native pipe syntax ‘|>’ as well as a shorthand
> > >> notation for creating functions, e.g. ‘\(x) x + 1’ is parsed as
> > >> ‘function(x) x + 1’. The pipe implementation as a syntax transformation
> > >> was motivated by suggestions from Jim Hester and Lionel Henry. These
> > >> features are experimental and may change prior to release.
> > >>
> > >>
> > >> This is a good addition; by using "|>" instead of "%>%" there should be
> > >> a chance to get operator precedence right.  That said, the ?Syntax help
> > >> topic hasn't been updated, so I'm not sure where it fits in.
> > >>
> > >> There are some choices that take a little getting used to:
> > >>
> > >>   > mtcars |> head
> > >> Error: The pipe operator requires a function call or an anonymous
> > >> function expression as RHS
> > >>
> > >> (I need to say mtcars |> head() instead.)  This sometimes leads to error
> > >> messages that are somewhat confusing:
> > >>
> > >>   > mtcars |> magrittr::debug_pipe |> head
> > >> Error: function '::' not supported in RHS call of a pipe
> > >>
> > >> but
> > >>
> > >> mtcars |> magrittr::debug_pipe() |> head()
> > >>
> > >> works.
> > >>
> > >> Overall, I think this is a great addition, though it's going to be
> > >> disruptive for a while.
> > >>
> > >> Duncan Murdoch
> > >>
> > >> ______________________________________________
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> > >
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