[R-pkg-devel] Call internal R functions in C

[Cai Li]

 *Dear Duncan, Thank you very much for your helpful advice! In addition,
could you kindly help answer my follow-up questions below? *

*Instead of passing the private R package environment to C, is there a way
to alter the namespace so that files in the "R" directory of the package
can be read by the C code but not exported to users? There are specialized
export and import functions in the "roxygen2" package that can be used to
alter the namespace, and I'm wondering whether altering the namespace would
work as well
(https://cran.r-project.org/web/packages/roxygen2/vignettes/namespace.html
<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcran.r-project.org%2Fweb%2Fpackages%2Froxygen2%2Fvignettes%2Fnamespace.html&data=04%7C01%7Ccai.li%40yale.edu%7Cfef92ea6326d4803577808d909969553%7Cdd8cbebb21394df8b4114e3e87abeb5c%7C0%7C0%7C637551364617695111%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=PKtQPhcpncRWSzSY5FrYR2Pcbn6LaYDDX0GhEgVtLtA%3D&reserved=0>).*

*However, if passing the private R package environment to C is the
only/best way for the R functions to be read by C without getting exported,
could you kindly offer additional advice for how to do this? I can pass an
"environment" object from R to C within an SEXP object in C. However, I'm
not sure how to pass the "environment" object between C functions. For
instance, in the following function, could I declare a "char" object and
save the "environment" object as a "char" within the C code?*












*void maketree_diff(int n,               int nc,               double *y,
            double **data,               int *types,               int
*ncat,               int *treat,               struct node *tree,
    int nmin2,               int maxdepth,               int method)*

On Mon, Apr 26, 2021 at 5:30 AM Duncan Murdoch <murdoch.duncan using gmail.com>
wrote:

> On 25/04/2021 10:30 p.m., Cai Li wrote:
> > Thanks Duncan! I was advised not to export those functions in the
> > namespace and keep them as internals. In terms of this, could you advise
> > what specific changes should I make to the C code so that I can evaluate
> > them in a suitable environment? I tried something like
> > "PROTECT(func_R=lang2(install("Package:::R_function"), func_data))," but
> > it did not work. Sorry this may be too naive and thanks again.
>
> That line creates the expression to evaluate, it doesn't evaluate it.
> You need to call eval() (the C function) on the result.  Here's some
> code from rgl that does something similar:
>
> R code to initialize:
>
> rgl.init <- function(initValue = 0, onlyNULL = FALSE, debug =
> getOption("rgl.debug", FALSE))
>    .Call( rgl_init,
>      initValue, onlyNULL, environment(rgl.init), debug )
>
> The important thing here is "environment(rgl.init)", which is the
> private environment within the package.
>
> Then in C code, save that environment:
>
>    rglNamespace = in_namespace;
>
> and use it later:
>
>    result = eval(PROTECT(lang2(PROTECT(install("rglFonts")),
>
> PROTECT(ScalarString(mkChar(family))))), rglNamespace);
>
> Duncan Murdoch
>
> >
> > Cai
> >
> > On Sun, Apr 25, 2021 at 8:46 PM Duncan Murdoch <murdoch.duncan using gmail.com
> > <mailto:murdoch.duncan using gmail.com>> wrote:
> >
> >     On 25/04/2021 7:23 p.m., Cai Li wrote:
> >      > Hello All,
> >      >
> >      > I'm developing a package with C code. My question may be naive: I
> >     have
> >      > several internal R functions that need to be called by C, but I
> >     cannot get
> >      > it to work or find a solution. It can work if I export those
> internal
> >      > functions in namespace, but it fails if I just want to keep them
> as
> >      > internal functions without exporting them. I guess I need some
> >     flags to
> >      > indicate the "internal" R internal functions? Could you please
> >     share your
> >      > thoughts on how to fix this? Much appreciated in advance!
> >      >
> >      > //   set up call to R function "R_function"
> >      >      SEXP func_R;
> >      >      PROTECT(func_R=lang2(install("R_function"), func_data));
> >      >
> >
> >     It all depends on the environment where you evaluate that expression,
> >     just as it would if it was R code.  You can't see internal package
> >     functions from the global environment, you need to evaluate them in
> the
> >     package namespace environment.
> >
> >     Duncan Murdoch
> >
>
>

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