[Rd] capturing multiple warnings in tryCatch()

[Henrik Bengtsson]

Simon's suggestion with withCallingHandlers() is the correct way.
Also, note that if you use tryCatch() to catch warnings, you're
*interrupting* the evaluation of the expression of interest, e.g.

> res <- tryCatch({ message("hey"); warning("boom"); message("there"); 42 }, warning = function(w) { message("Warning caught: ", conditionMessage(w)); 3.14 })
hey
Warning caught: boom
> res
[1] 3.14

Note how it never completes your expression.

/Henrik

On Thu, Dec 2, 2021 at 1:14 PM Simon Urbanek
<simon.urbanek using r-project.org> wrote:
>
>
> Adapted from demo(error.catching):
>
> > W=list()
> > withCallingHandlers(foo(), warning=function(w) { W <<- c(W, list(w)); invokeRestart("muffleWarning") })
> > str(W)
> List of 2
>  $ :List of 2
>   ..$ message: chr "warning 1"
>   ..$ call   : language foo()
>   ..- attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>  $ :List of 2
>   ..$ message: chr "warning 2"
>   ..$ call   : language foo()
>   ..- attr(*, "class")= chr [1:3] "simpleWarning" "warning" "condition"
>
> Cheers,
> Simon
>
>
> > On Dec 3, 2021, at 10:02 AM, Fox, John <jfox using mcmaster.ca> wrote:
> >
> > Dear R-devel list members,
> >
> > Is it possible to capture more than one warning message using tryCatch()? The answer may be in ?conditions, but, if it is, I can't locate it.
> >
> > For example, in the following only the first warning message is captured and reported:
> >
> >> foo <- function(){
> > +   warning("warning 1")
> > +   warning("warning 2")
> > + }
> >
> >> foo()
> > Warning messages:
> > 1: In foo() : warning 1
> > 2: In foo() : warning 2
> >
> >> bar <- function(){
> > +   tryCatch(foo(), warning=function(w) print(w))
> > + }
> >
> >> bar()
> > <simpleWarning in foo(): warning 1>
> >
> > Is there a way to capture "warning 2" as well?
> >
> > Any help would be appreciated.
> >
> > John
> >
> > --
> > John Fox, Professor Emeritus
> > McMaster University
> > Hamilton, Ontario, Canada
> > Web: http://socserv.mcmaster.ca/jfox/
> >
> >
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
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