22.4 Browser() commands

As well as allowing you to run regular R code, browser() provides a few special commands. You can use them by either typing short text commands, or by clicking a button in the RStudio toolbar

• Next, n: executes the next step in the function. If you have a variable named n, you’ll need print(n) to display its value.

• Step into, or s: works like next, but if the next step is a function, it will step into that function so you can explore it interactively.

• Finish, or f: finishes execution of the current loop or function.

• Continue, c: leaves interactive debugging and continues regular execution of the function. This is useful if you’ve fixed the bad state and want to check that the function proceeds correctly.

• Stop, Q: stops debugging, terminates the function, and returns to the global workspace. Use this once you’ve figured out where the problem is, and you’re ready to fix it and reload the code.

There are two other slightly less useful commands that aren’t available in the toolbar:

• Enter: repeats the previous command. I find this too easy to activate accidentally, so I turn it off using options(browserNLdisabled = TRUE).

• where: prints stack trace of active calls (the interactive equivalent of traceback).