While you are fiddling with stopifnot(), please consider changing the form
of the error thrown so that it includes the caller's call. The change
would be from something like
stop( <<the message>> )
to
stop(simpleError( <<the message>>, sys.call(-1)))
For the following code
f <- function(x, y) {
stopifnot(x > y)
x - y
}
g <- function(x, y, z) {
c(f(x, y), f(y, z))
}
g(6,3,4)
you would see
Error in f(y, z) : x > y is not TRUE
instead of the less informative
Error: x > y is not TRUE
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, May 19, 2017 at 5:31 AM, Martin Maechler <[email protected]
> wrote:
> >>>>> Suharto Anggono Suharto Anggono via R-devel <[email protected]>
> >>>>> on Thu, 18 May 2017 16:27:09 +0000 writes:
>
> >> From an example in
>
> >> http://www.uni-muenster.de/ZIV.BennoSueselbeck/s-html/
> helpfiles/nargs.html
> >> , number of arguments in '...' can be obtained by
>
> > (function(...)nargs())(...) .
>
> neat and good. Though really is not exactly "well readable".
>
> In the mean time, there is ...length() in R-devel [somewhat
> experimentally]
>
> > I now realize that sys.call() doesn't expand '...' when
> > the function is called with '...'. It just returns the call as is.
> yes.
> > If 'stopifnot' uses sys.call() instead of
> > match.call() , the following example behaves improperly:
>
> > g <- function(...) stopifnot(...)
> > g(TRUE, FALSE)
>
> Indeed. Very improperly (it does not stop).
>
> However, calling stopifnot() with a '...' passed from above is
> not a very good idea anyway, because stopifnot has to assume it
> is called with explicit expressions.
> Hence we have
>
> > g <- function(...) stopifnot(...) ; g(1 == 1, 3 < 1)
> Error: ..2 is not TRUE
>
> {and to "fix" this, e.g., with an extra optional argument} would
> lead to more complications which I really think we do not want}.
>
> But the example does show we should keep match.call().
> Martin
>
> > --------------------------------------------
> > On Thu, 18/5/17, Martin Maechler
> > <[email protected]> wrote:
>
> > Subject: Re: [Rd] stopifnot() does not stop at first
> > non-TRUE argument
>
> > Cc: [email protected] Date: Thursday, 18 May, 2017,
> > 3:03 PM
>
> >>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at
> r-project.org>
> >>>>> on Tue, 16 May 2017 16:37:45 +0000 writes:
>
> >> switch(i, ...) extracts 'i'-th argument in '...'. It is
> >> like eval(as.name(paste0("..", i))) .
>
> > Yes, that's neat.
>
> > It is only almost the same: in the case of illegal 'i' the
> > switch() version returns invisible(NULL)
>
> > whereas the version we'd want should signal an error,
> > typically the same error message as
>
> >> t2 <- function(...) ..2 t2(1)
> > Error in t2(1) (from #1) : the ... list does not contain
> > 2 elements
> >>
>
>
> >> Just mentioning other things: - For 'n', n <- nargs() can
> >> be used.
>
> > I know .. [in this case, where '...' is the only formal
> > argument of the function]
>
> >> - sys.call() can be used in place of match.call() .
>
> > Hmm... in many cases, yes.... notably, as we do *not* want
> > the argument names here, I think you are right.
>
> > ______________________________________________
> > [email protected] mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> [email protected] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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