R devel - Mar 2006 - New simpleExit() condition (Was: Re: Can example() code stop the example without generating an error?)

On 3/14/06, Uwe Ligges <ligges at statistik.uni-dortmund.de>
wrote:
> Henrik Bengtsson wrote:
>
> > Hi,
> >
> > does anyone know if it is possible to write example code (in Rd
> > examples) such that one can stop the example without generating an
> > error?  Example:
> >
> > code A
> > if (cond)
> >   niceStop()
> > code B
>
>
> What about
>
> code A
> if(cond){
>    code B
> }
>
> But maybe I do not get your point.
The purpose is to keep the code clean and I want to avoid nested if
statements.  Further conditions down the stream would make the code
quite ugly.  Pretty much for the same reason you use 'return()' and
'break'.

A nicer and more general solution is to have a subclass "simpleExit"
of "simpleCondition" and make source() catch such signals via
tryCatch(..., simpleExit=function(se) {...}).  Here is a complete
example:

simpleExit <- function(...) {
  cond <- simpleCondition(...)
  class(cond) <- c("simpleExit", class(cond))
  cond
}

exit <- function(...) {
  invisible(signalCondition(simpleExit(...)))
}

evalWithExit <- function(...) {
  tryCatch(..., simpleExit=function(cond) cond)
}

sourceWithExit <- function(...) {
  evalWithExit(source(...))
}


Examples:
>
evalWithExit({cat("Hi\n");exit("Bye!");cat("there\n")});
cat("bye\n")
Hi
<simpleExit: Bye!>
bye

# Compare this...
> code <- 'cat("Hi\n"); exit("Bye!");
cat("there\n")'
> source(textConnection(code))
Hi
there

# ...with this:
> sourceWithExit(textConnection(code))
Hi
<simpleExit: Bye!>

R-core, would this be a useful feature to add to source()?

/Henrik
> Uwe Ligges
>
>
> > I know this sounds weird, but I would like some of my Rd examples to
> > run if and only if another package is available or if a certain large
> > Affymetrix data file is available.  One can put all of the example in
> > a function and return from the function if the package is not
> > available, but then all object assigned are lost. My best/cleanest
> > solution right now is to use break in a dummy for loop. Examples:
> >
> > for (z in 1) {
> >
> > code A
> > if (cond)
> >   break
> > code B
> >
> > }
> >
> > Other suggestions?  The solution must off course pass R CMD check.
> >
> > /Henrik
> >
> > PS. I know example() calls source(), but I'm not sure how R CMD
check
> > does it. DS.
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>

--
Henrik Bengtsson
Mobile: +46 708 909208 (+1h UTC)

I would very much like to see such a feature too.

On 3/14/06, Henrik Bengtsson <hb at maths.lth.se>
wrote:
> On 3/14/06, Uwe Ligges <ligges at statistik.uni-dortmund.de> wrote:
> > Henrik Bengtsson wrote:
> >
> > > Hi,
> > >
> > > does anyone know if it is possible to write example code (in Rd
> > > examples) such that one can stop the example without generating
an
> > > error?  Example:
> > >
> > > code A
> > > if (cond)
> > >   niceStop()
> > > code B
> >
> >
> > What about
> >
> > code A
> > if(cond){
> >    code B
> > }
> >
> > But maybe I do not get your point.
>
> The purpose is to keep the code clean and I want to avoid nested if
> statements.  Further conditions down the stream would make the code
> quite ugly.  Pretty much for the same reason you use 'return()' and
> 'break'.
>
> A nicer and more general solution is to have a subclass
"simpleExit"
> of "simpleCondition" and make source() catch such signals via
> tryCatch(..., simpleExit=function(se) {...}).  Here is a complete
> example:
>
> simpleExit <- function(...) {
>  cond <- simpleCondition(...)
>  class(cond) <- c("simpleExit", class(cond))
>  cond
> }
>
> exit <- function(...) {
>  invisible(signalCondition(simpleExit(...)))
> }
>
> evalWithExit <- function(...) {
>  tryCatch(..., simpleExit=function(cond) cond)
> }
>
> sourceWithExit <- function(...) {
>  evalWithExit(source(...))
> }
>
>
> Examples:
>
> >
evalWithExit({cat("Hi\n");exit("Bye!");cat("there\n")});
cat("bye\n")
> Hi
> <simpleExit: Bye!>
> bye
>
> # Compare this...
> > code <- 'cat("Hi\n"); exit("Bye!");
cat("there\n")'
> > source(textConnection(code))
> Hi
> there
>
> # ...with this:
> > sourceWithExit(textConnection(code))
> Hi
> <simpleExit: Bye!>
>
> R-core, would this be a useful feature to add to source()?
>
> /Henrik
>
> > Uwe Ligges
> >
> >
> > > I know this sounds weird, but I would like some of my Rd examples
to
> > > run if and only if another package is available or if a certain
large
> > > Affymetrix data file is available.  One can put all of the
example in
> > > a function and return from the function if the package is not
> > > available, but then all object assigned are lost. My
best/cleanest
> > > solution right now is to use break in a dummy for loop. Examples:
> > >
> > > for (z in 1) {
> > >
> > > code A
> > > if (cond)
> > >   break
> > > code B
> > >
> > > }
> > >
> > > Other suggestions?  The solution must off course pass R CMD
check.
> > >
> > > /Henrik
> > >
> > > PS. I know example() calls source(), but I'm not sure how R
CMD check
> > > does it. DS.
> > >
> > > ______________________________________________
> > > R-devel at r-project.org mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
> >
>
>
> --
> Henrik Bengtsson
> Mobile: +46 708 909208 (+1h UTC)
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>