New simpleExit() condition (Was: Re: Can example() code stop the example without generating an error?)

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

On 3/14/06, Henrik Bengtsson <hb at maths.lth.se> wrote:

[snip]

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

I just realized that I just might be looking for a way to generate a
user-interrupt signal, e.g. (try pressing Ctrl-C or Ctrl-Break)

  tryCatch(Sys.sleep(10), interrupt=function(intr) print(intr))

A caught "interrupt" object looks like:

 list()
 - attr(*, "class")= chr [1:2] "interrupt" "condition"

So, trying:

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

interrupt <- function(...) {
  invisible(signalCondition(simpleInterrupt(...)))
}

Unfortunately that is not enough; the interrupt seems not to be
signalled. Same holds if you try to "resignal" a caught interrupt,
e.g. (try pressing Ctrl-C or Ctrl-Break *once*):

tryCatch({
  tryCatch({
    print(1)
    Sys.sleep(10)
    print(2)
  }, interrupt=function(intr) {
    cat("User-interrupt signal caught\n")
    signalCondition(intr)
  })
  Sys.sleep(10)
  print(3)
})

gives:

[1] 1
User-interrupt signal caught
<a 10 second sleep>
[1] 3

I was hoping that the *resignaled* user-interrupt signal would break
out of the out outer tryCatch too.

So, I guess, now my question is, is it possible to generate a
low-level user-interrupt signal from source code?  That would be
useful.

Thanks

Henrik