DebuggingInRmd

broken.Rmd

We set up knitr so it doesn't catch errors, then set
`options(error=recover)` to set up R's debug-on-error machinery.

We have to do one additional thing, before the options call though: 
trace the recover function with`sink(NULL)` to turn off the output 
capturing so the R console is useful when the debugging framework 
dumps us back into it. This has to happen before the options call
because that call grabs the `recover` object and stores it somewhere
so setting a trace on recover after the call won't affect the cached
version that gets called upon an error.

All of these steps (in this order) can happen in the R session rather 
than the Rmd document, and generally should.

```{r init}
knitr::opts_chunk$set(error=FALSE)
trace(recover, quote(sink(NULL)))
options(error=recover)
```

Now we define a function and then break it. Our function will appear
near the bottom of the list of frames in the debugger, we can pretty
much ignore anything above it unless we are hunting a bug in knitr.

```{r brokestuff}
awesomefun = function(i) {
	   stopifnot(is(i, "integer"))
	   i
}

awesomefun("whaaaat")
```