debugging - Stop an R program without error

Question

Is there any way to stop an R program without error?

For example I have a big source, defining several functions and after it there are some calls to the functions. It happens that I edit some function, and want the function definitions to be updated in R environment, but they are not actually called.

I defined a variable justUpdate and when it is TRUE want to stop the program just after function definitions.

ReadInput <- function(...) ...
Analyze <- function(...) ...
WriteOutput <- function(...) ...

if (justUpdate)
    stop()
# main body
x <- ReadInput()
y <- Analyze(x)
WriteOutput(y)

I have called stop() function, but the problem is that it prints an error message.

ctrl+c is another option, but I want to stop the source in specific line.

The problem with q() or quit() is that it terminates R session, but I would like to have the R session still open.

As @JoshuaUlrich proposed browser() can be another option, but still not perfect, because the source terminates in a new environment (i.e. the R prompt will change to Browser[1]> rather than >). Still we can press Q to quit it, but I am looking for the straightforward way.

Another option is to use if (! justUpdate) { main body } but it's clearing the problem, not solving it.

Is there any better option?

Answer 1

I found a rather neat solution here. The trick is to turn off all error messages just before calling stop(). The function on.exit() is used to make sure that error messages are turned on again afterwards. The function looks like this:

stop_quietly <- function() {
  opt <- options(show.error.messages = FALSE)
  on.exit(options(opt))
  stop()
}

The first line turns off error messages and stores the old setting to the variable opt. After this line, any error that occurs will not output a message and therfore, also stop() will not cause any message to be printed.

According to the R help,

on.exit records the expression given as its argument as needing to be executed when the current function exits.

The current function is stop_quietly() and it exits when stop() is called. So the last thing that the program does is call options(opt) which will set show.error.messages to the value it had, before stop_quietly() was called (presumably, but not necessarily, TRUE).