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.

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