A custom knitr engine for blockquotes

Here’s how easy it is to create a knitr language engine:

# create a custom language block that blockquotes its contents
knitr::knit_engines$set("blockquote" = function(options) {
  if (isFALSE(options$echo)) return()
  
  output <- paste0("> ", options$code, collapse = "\n")
  
  if (!is.null(options$source_url)) {
    output <- sprintf("%s\n[[source]](%s)", output, options$source_url)
  }
  
  output
})

Writing a chunk like:

```{blockquote}
#| source_url: https://tjmahr.com
Look at this **markdown**!
  
Here is a nested blockquote:
  
  > Cool!

Yes.
```

Will yield the following output:

Look at this markdown!

Here is a nested blockquote:

Cool!

Yes. [source]

I wanted to make this a hook function but couldn’t figure it out.