How can knitr know whether the R code evaluation has error?

Question

The knitr would always evaluate the R code before formatting the output, so just wondering how can I know whether the R code evaluation has error. Thanks

**knitr** uses the **evaluate** package to run each chunk, catching and handling any warnings and errors. [Here](https://stackoverflow.com/a/14613363/980833) is an old answer of mine that might help you to see how it does so. — Josh O'Brien, Jan 17 '18 at 01:34

score 1 · Answer 1 · answered Jan 17 '18 at 03:29

Basically it boils down to three lines of code in the evaluate package. The key is withCallingHandlers(), which can be used to capture errors, messages, and warnings, etc. A minimal example:

withCallingHandlers(1 + 'a', error = function(e) {
  cat('An error occurred! The error object is:\n')
  str(e)
})

If you don't want the error to halt R, you can wrap the code in try().

How can knitr know whether the R code evaluation has error?

1 Answers1