[Rd] SET_TYPEOF no longer allowed, how should I call R from within C?

[Matthew Fidler]

Thank yiou

On Tue, Jun 25, 2024, 3:57 PM Duncan Murdoch <murdoch.duncan using gmail.com>
wrote:

> On 2024-06-25 5:25 a.m., Matthew Fidler wrote:
> > Hi,
> >
> > I have adapted code to run R from within C from the writing R extensions
> > here
> >
> >
> https://colinfay.me/writing-r-extensions/system-and-foreign-language-interfaces.html
>
> That was written in 2017.  You should use the one that came with R, or
> even better, the one that comes with the development version of R.
>
> Duncan Murdoch
>
> >
> > As a more comprehensive example of constructing an R call in C code and
> > evaluating, consider the following fragment of printAttributes in
> > src/main/print.c.
> >
> >      /* Need to construct a call to
> >
> >         print(CAR(a), digits=digits)
> >
> >         based on the R_print structure, then eval(call, env).
> >
> >         See do_docall for the template for this sort of thing.
> >
> >      */
> >
> >      SEXP s, t;
> >
> >      t = s = PROTECT(allocList(3));
> >
> >      SET_TYPEOF(s, LANGSXP);
> >
> >      SETCAR(t, install("print")); t = CDR(t);
> >
> >      SETCAR(t, CAR(a)); t = CDR(t);
> >
> >      SETCAR(t, ScalarInteger(digits));
> >
> >      SET_TAG(t, install("digits"));
> >
> >      eval(s, env);
> >
> >      UNPROTECT(1);
> >
> > At this point CAR(a) is the R object to be printed, the current
> attribute.
> > There are three steps: the call is constructed as a pairlist of length 3,
> > the list is filled in, and the expression represented by the pairlist is
> > evaluated.
> >
> > A pairlist is quite distinct from a generic vector list, the only
> > user-visible form of list in R. A pairlist is a linked list (with CDR(t)
> > computing the next entry), with items (accessed by CAR(t)) and names or
> > tags (set by SET_TAG). In this call there are to be three items, a symbol
> > (pointing to the function to be called) and two argument values, the
> first
> > unnamed and the second named. Setting the type to LANGSXP makes this a
> call
> > which can be evaluated.
> >
> >
> >
> > New checks  tells me that this is no longer allowed since it was not part
> > of the public api any longer.
> >
> >
> > So, how does one call R from C then?
> >
> > Also should the writing R extensions be updated with the new approved
> > approach?
> >
> >
> > Thanks in advance.
> >
> > Matt
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>

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