Hi,
I would like to bring up and old suggestion
[http://tolstoy.newcastle.edu.au/R/devel/06/03/4512.html] of adding an
exit condition, so that for instance it is possible to silently exit
from scripts and Rd examples similar to return() for functions, e.g.
\examples{
require("foo") || exit("Example will not run without the 'foo' package.")
...
}
I know this can be solved by a simple if {require("foo")} { }
statement, but the above is to avoid such nested code, especially in
example code, cf. return() and break.
Here are the details to get this working:
1. Define a new condition class similar to simpleWarning() and simpleError():
simpleExit <- function(...) {
cond <- simpleCondition(...)
class(cond) <- c("simpleExit", class(cond)) cond
}
2. Setup a method to generate such a condition similar to warning() and stop():
exit <- function(...) {
invisible(signalCondition(simpleExit(...))) }
}
3. That is the basic framework. We can then use tryCatch() to catch
and return upon a simpleExit as follows:
evalWithExit <- function(...) {
tryCatch(..., simpleExit=function(cond) cond) }
}
Then it is matter of flavor if one wants to update source() with an
argument 'allowExits=FALSE' or have a standalone function:
sourceWithExit <- function(...) {
evalWithExit(source(...))
}
5. The code example() needs to be updated accordingly, i.e. replacing
source() with sourceWithExit().
6. src/scripts/check.in needs to updated so that the examples are
sourced detecting simpleExit:s.
Steps 1-4 can be added without side effects. It is Step 5 & 6 that
needs extra care. I am happy to contribute the above if it would be
accepted.
Best,
Henrik
PS. As I queried on in my follow up of the March 2006 thread, if there
is a way to signal user-interrupts programatically, all of the above
is not necessary. DS.
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