debugr is a package designed to support debugging in R. It mainly provides the dwatch() function which prints a debug output to the console or to a file. A debug output can consist of a static text message, the values of one or more objects (potentially transformed by applying some functions) or the value of one or multiple (more complex) R expressions.

Whether or not a debug message is displayed can be made dependent on the evaluation of a criterion phrased as an R expression. Generally, debug messages are only shown if the debug mode is activated. The debug mode is activated and deactivated with debugr_switchOn() and debugr_switchOff(), respectively, which change the logical debugr.active value in the global options. Since debug messages are only displayed in debug mode, the dwatch() function calls can even remain in the original code as they remain silent and won't have any effect until the debug mode is switched on again.

This is a basic example which shows you how to use dwatch(). It prints out the value of the z object every time z exceeds the threshold of 40,000.

library(debugr)

myfunction <- function(x) {
  justastring <- "Not much information here"
  z <- 1

  for(i in 1:x) {
    # This call can remain in your code; it is only activated when the debug mode is switched on
    dwatch(crit = "z > 40000", objs = c("z"))
    z <- z * i
  }
  invisible(z)
}

# Turn debug mode on
debugr_switchOn()

# Call function for debugging
myfunction(10)