R devel - Apr 2007 - wishlist: additional argument in R_tryEval (Rinternals.h)

Hi,

R_tryEval, exported in Rinternals.h but not part of the API, is
currently defined as:

R_tryEval(SEXP e, SEXP env, int *ErrorOccurred);

I'm trying to embed R in an application (basically yet another GUI),
and this has been very helpful to catch errors. It would be even more
helpful if it also gave access to the visibility flag. I can wrap this
in a call to withVisible, and that works great, but if there is an
error, traceback() contains a bunch of irrelevant levels.

It seems fairly easy to add another argument, similar to
ErrorOccurred, that is set to the visibility flag before returning. Is
this something that could be considered for addition in R-devel? A
possible patch for R/trunk is attached. Mac-GUI/REngine/REngine.m will
also need a patch, but I don't understand the language it's written
in.

-Deepayan
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Hi Deepayan.

 It is not part of the API, but it is used in numerous packages
that would break if such a change were made.
It is an easy change to make, but not necessarily a robust approach
if we keep adding parameters. If we need the room to add more,
using a structure whose fields are modified within the R_tryEval()
would be more flexible for future evolutions.
But then again, that is creeping towards an object and that is
precisely what we need for the evaluator itself...... (More perhaps
in the future.)



 D.

Deepayan Sarkar wrote:
> Hi,
> 
> R_tryEval, exported in Rinternals.h but not part of the API, is
> currently defined as:
> 
> R_tryEval(SEXP e, SEXP env, int *ErrorOccurred);
> 
> I'm trying to embed R in an application (basically yet another GUI),
> and this has been very helpful to catch errors. It would be even more
> helpful if it also gave access to the visibility flag. I can wrap this
> in a call to withVisible, and that works great, but if there is an
> error, traceback() contains a bunch of irrelevant levels.
> 
> It seems fairly easy to add another argument, similar to
> ErrorOccurred, that is set to the visibility flag before returning. Is
> this something that could be considered for addition in R-devel? A
> possible patch for R/trunk is attached. Mac-GUI/REngine/REngine.m will
> also need a patch, but I don't understand the language it's written
> in.
> 
> -Deepayan
> 
> 
> ------------------------------------------------------------------------
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

Even though it isn't officially part of the API it has seen some use
so I'd prefer not to change the interface; instead add

SEXP R_tryEvalWithVis(SEXP e, SEXP env, int *ErrorOccurred, int *visible);

or something along those lines and define R_tryEval internally in
terms of that.

It may be worth thinking a bit more though to see if there is
something else that might be useful at this point.  I vaguely recall
thinking recently about needing something else of this flavor but I
can't seem to remember what it was exactly -- will try to see if I can
recall.

Best,

luke


On Fri, 6 Apr 2007, Deepayan Sarkar wrote:
> Hi,
>
> R_tryEval, exported in Rinternals.h but not part of the API, is
> currently defined as:
>
> R_tryEval(SEXP e, SEXP env, int *ErrorOccurred);
>
> I'm trying to embed R in an application (basically yet another GUI),
> and this has been very helpful to catch errors. It would be even more
> helpful if it also gave access to the visibility flag. I can wrap this
> in a call to withVisible, and that works great, but if there is an
> error, traceback() contains a bunch of irrelevant levels.
>
> It seems fairly easy to add another argument, similar to
> ErrorOccurred, that is set to the visibility flag before returning. Is
> this something that could be considered for addition in R-devel? A
> possible patch for R/trunk is attached. Mac-GUI/REngine/REngine.m will
> also need a patch, but I don't understand the language it's written
> in.
>
> -Deepayan
>
-- 
Luke Tierney
Chair, Statistics and Actuarial Science
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 at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu