[R-pkg-devel] modification of warning messages

[Hadley Wickham]

Try warningcall(R_NilValue, "message")

Hadley

On Wednesday, June 22, 2016, Aaron King <kingaa at umich.edu> wrote:

> I am in the midst of trying to improve error and warning messages in a
> complex package.  I find myself wanting to modify R's default behavior when
> printing warnings.  Specifically, it frequently happens for me that the
> call that is printed with the warning message is not informative.  When the
> warning arises in R code, I have the ability to suppress the printing of
> the call by setting 'call.=FALSE'.  However, when the warning arises in C
> code (via the 'warning()' function), I have no such option.
>
> 'tryCatch' and 'withCallingHandlers' are of no use (or at least, if they
> are, I haven't figured out how).
>
> Consider the following simple example:
>
> Contents of file 'example.c':
> --------------------------------------------------
> #include <R.h>
>
> void example (int *x) {
>   if (*x>0)
>     error("ouch");
>   else if (*x<0) {
>     warning("duck!");
>     *x = 22;
>   } else {
>     *x = 11;
>   }
> }
> --------------------------------------------------
>
> Compile and load the C code:
> --------------------------------------------------
> system2(R.home("bin/R"),args=c("CMD","SHLIB","example.c"))
> dyn.load(paste0("example",.Platform$dynlib.ext))
> --------------------------------------------------
>
> The function 'f' calls 'example' as defined above.  On an error, it
> modifies the error message using 'tryCatch'.
> --------------------------------------------------
> f <- function (x) {
>     y <- tryCatch(
>         .C("example",x=as.integer(x))$x,
>         error = function (e) {
>             stop("in f: ",conditionMessage(e),call.=FALSE)
>         }
>     )
>     y
> }
> --------------------------------------------------
>
> Get an error:
>
> > f(1)
> Error: in f: ouch!
>
> Get a warning:
>
> > f(-1)
> [1] 22
> Warning message:
> In doTryCatch(return(expr), name, parentenv, handler) : duck!
>
> It's the fact that 'doTryCatch(return(expr), name, parentenv, handler)' is
> meaningless to the user that bothers me.  How can I modify the warning?
>
> Thanks in advance for any insight.
>
> --
> Professor Aaron A. King
> Ecology & Evolutionary Biology
> Mathematics
> Center for the Study of Complex Systems
> University of Michigan
> GPG Public Key: 0x15780975
>
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>
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>


-- 
http://hadley.nz

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