[Rd] [External] Calling applyClosure from a package?

[iuke-tier@ey m@iii@g oii uiow@@edu]

On Sun, 14 Apr 2024, Matthew Kay wrote:

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>
> Hi,
>
> Short version of my question: Rf_applyClosure was marked
> attribute_hidden in Oct 2023, and I am curious why and if there is an
> alternative interface to it planned.

applyClosure has never been part of the API and was/is not intended
for use by packages. Keeping things like this internal is essential to
give us flexibility to make needed improvements to the basic engine.
Moving this out of the installed headers and marking it as not to be
exported merely clarifies that it is internal.

> Long version:
>
> I have been toying with building a package that makes it easier to do
> non-standard evaluation directly using promises, rather than wrapping
> these in a custom type (like e.g. rlang does). The advantage of this
> approach is that it should be fully compatible with functions that use
> the standard R functions for NSE and inspecting function context, like
> substitute(), match.call(), or parent.frame(). And indeed, it works!
> -- in R 4.3, that is. The prototype version of the package is here:
> https://github.com/mjskay/uneval  (the relevant function to my
> question is probably do_invoke, in R/invoke.R).
>
> While testing on R-devel, I noticed that Rf_applyClosure(), which used
> to be exported, is now marked with attribute_hidden. I traced the
> change to this commit in Oct 2023:
> https://github.com/r-devel/r-svn/commit/57dbe8ad471c8a34314ee74362ad479db03c033a
>
> However, the commit message did not give me clarity on the reason for
> the change, and I have not been able to find mention of this change in
> R-devel, R-package-devel, or the R bug tracker.
> So, I am curious why this function is no longer exported and if there
> is an alternative function planned to take its place.
>
> Neither Rf_eval nor do.call can do what I need to fully support
> rlang-style NSE using base R. The problem is that I need to be able to
> manually set up the list of promises provided as arguments to the
> function.
>
> I fully understand that the answer to my question might be "don't do
> that" ;).

That would be my advice: Don't do that. The API does not provide an
interface for working with promises; in fact the existence of promises
is not guaranteed in the future. Some packages have unfortunately made
use of some internal functions related to promises. For the ones on
CRAN we will work with the maintainers to find alternate
approaches. This may mean adding some functions to the API for dealing
with some lazy-evaluation-related features at a higher level.

Best,

luke

> But I will humbly suggest that it would be really nice to be
> able to do NSE that can capture expressions with heterogeneous
> environments and pass these to functions in a way that is compatible
> with existing R functions that do NSE. The basic tools to do it are
> there in R 4.3, I think...
>
> Thanks for the help!
>
> ---Matt
>
> --
> Matthew Kay
> Associate Professor
> Computer Science & Communication Studies
> Northwestern University
> matthew.kay using u.northwestern.edu
> http://www.mjskay.com/
>
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>

-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu/